TECHNICAL FIELD

The invention relates to the combinatorial approach to the discovery and development of new alloys. More particularly, it relates to methods and systems that rely on high energy electron beams for rapid synthesis of combinatorial alloy libraries.

BACKGROUND

Combinatorial methods can greatly accelerate the discovery and development of materials whose properties cannot be readily predicted from their composition and processing history. By screening libraries of samples of such materials spanning defined ranges of composition and processing conditions, materials with desirable properties can be identified from among a large number of possible combinations. Combinatorial methods have seen widespread use in the pharmaceutical and chemical industries. Successful application of the combinatorial approach relies on rapid synthesis of sample libraries and rapid screening for desirable properties. Whenever libraries can be formed as two-dimensional arrays— for example, films with varying compositions deposited on different areas of a substrate or different mixtures of chemicals disposed in a planar array of microscopic wells— synthesis and screening are amenable to automation and can be further accelerated.

Applying combinatorial methods to the discovery and development of structural alloys is particularly challenging because, for the majority of alloy systems, samples must be synthesized at extremely high temperatures and under clean conditions. Further, l sample volumes must be homogeneous over relatively large volumes, in order to exhibit bulk-like properties and facilitate rapid screening of mechanical properties.

Known approaches to combinatorial alloy development have started with specimens assembled to contain interfaces between alloy components. In one set of experiments, a feed rod comprising sections of Al and Co separated by a gradually inclined interface was subjected to the well-known zone melting process to form a Co-AI alloy with continuously varying composition along the length of the rod. See M.Th. Cohen-Adad et al. , New Combinatorial Approach in Material Science, 22(4) J. Phas. Equilib. & Diff. 379-85 (2001); Melting Zone Technique as a Tool for a Combinatorial Approach in Material Science, 289 (1-2) J. Alloys and Compounds 185-196 (1999). Structure and composition of the Co-AI alloy rod were investigated using optical and electron microscopy and electron microprobe analysis ("EPMA"), and mechanical properties using microhardness. Samples prepared by this technique are necessarily one- dimensional. In other work, pieces of the alloy constituents were assembled and held at high temperature to generate interfacial diffusion zones containing different alloy compositions. See J.C. Zhao et al., Evaluation of Phase Relations in the Nb-Cr-AI System at 1000C Using a Diffusion-Multiple Approach, 25(2) J. Phas. Equilib. & Diff. 152-9 (2004). The so-called diffusion multiple approach is limited to combinations of elements that diffuse relatively rapidly. (Nevertheless, a typical heating cycle can last thousands of hours.) Because the technique produces rapidly varying composition profiles occupying relatively small volumes, particularly at the triple points where pairs of interfaces meet, compositional and structural analysis must be performed using techniques with high spatial resolution, such as electron probe microanalysis ("EPMA") and electron backscatter diffraction ("EBSD"), and alloy properties must be measured using a technique with correspondingly high spatial resolution. High energy electron beams are used as localized and highly controllable heat sources under clean conditions in a range of metallurgical processes, from welding to vapor deposition to refining. Compared with laser heat sources, high energy electron beams generally transfer a much higher fraction of the incident energy into a given volume and the energy deposition profile does not vary radically with surface condition. A concentrated high energy electron beam can rapidly deliver enough energy to melt or vaporize material adjacent to the surface of an alloy specimen, with the precise volume melted or vaporized depending on the energy deposition profile within the specimen— as determined by the beam energy and the beam current, size, shape and dwell time, which collectively determine the electron density variation across the beam, usually referred to as beam profile, and the energy absorption coefficients of the materials comprising the specimen— and the response of the materials comprising the specimen to the energy introduced— as determined by their thermodynamic and other relevant properties. For example, in electron beam welding, a highly concentrated beam can prevent molten material from closing the weld, allowing the formation of significantly deeper welds than the penetration depth of the electron beam (typically, from a few to a few tens of microns). In vapor deposition, a beam scanned across part of the surface of a cooled block of material can create a melt pool that acts as a stable vapor source. A rapidly scanned electron beam can also texture the surfaces of metals by melting multiple locations of the surface and redistributing the molten material to form macroscopic features such as pillars or holes. US Pat. No. 7,667, 158, Buxton et al., Surfi-Sculpt™-Revolutionary surface processing with an electron beam, ASM International, ISEC Congress, St. Paul, MN, Aug. 1-3, 2005.

Efforts have been made to apply electron beam melting to combinatorial alloy development in samples containing interfaces between two metals. J. Frafjord, Combinatorial Design of Nickel-Chromium Alloys by Physical Vapor Deposition and Electron Beam Welding, M.S., Univ. Tenn. (Dec. 2004). In a series of experiments, Cr or Ni films having a maximum thickness of a few microns and a wedge-shaped profile were deposited onto Ni or Cr substrates and treated in a commercial electron beam welding system. Trenches of material extending through the films into the substrate were melted by sweeping the electron beam in a straight line along a direction of maximum thickness gradient, with the aim of producing alloy compositions ranging from pure Ni to pure Cr in a single specimen. The structure and composition of the electron-beam melted trenches were investigated using optical microscopy and energy dispersive x-ray spectroscopy ("EDS"), and their mechanical properties— hardness and elastic modulus— measured by nano-indentation. However, when compared to other combinatorial approaches used by the same group— namely, multilayer and co- deposited films with laterally varying compositions— the electron beam method produced specimens with greatly truncated composition ranges. Pharr et al., Development of Combinatorial Methods for Alloy Design and Optimization, Final Report, section 4.4 ORNL/TM-2005/133 (June 2006); A. Rar et al., PVD Synthesis and High-Throughput Property Characterization of Ni-Fe-Cr Alloy Libraries, 16 Measur. Sci. and Technol. 46-53, 52 (2005). The diminished composition ranges were related to redistribution of material within the trench, while scatter in mechanical data was attributed to a combination of surface roughness and the presence of multiple phases. Overall, the electron beam samples showed non-uniform microstructures with voids and near-surface inhomogeneity.

The present invention overcomes the above and other limitations of the prior art by employing a maneuverable high energy electron beam to rapidly synthesize libraries of alloy samples having well-defined bulk-like compositions that are amenable to rapid screening. SUMMARY OF THE INVENTION

In one embodiment, a method is provided for generating a combinatorial alloy library comprising the following steps: furnishing a solid specimen comprising spatially varying concentrations of at least two elements adjacent to a specimen surface; addressing at least a portion of the specimen surface with a high energy electron beam to melt specimen material encompassed within a plurality of volumes abutting the specimen surface, each volume comprising average concentrations of the at least two elements, and the plurality of volumes comprising diverse average concentrations of the at least two elements; forming from the molten material a multiplicity of discrete and substantially homogeneous molten zones comprising diverse concentrations of the at least two elements; and, cooling the multiplicity of discrete molten zones to form a multiplicity of discrete and substantially homogenous alloy sample regions comprising diverse concentrations of the at least two elements.

In various embodiments, the multiplicity of alloy sample regions may consist of more than ten, fifty or one hundred regions. In various other embodiments, each region may have a volume of greater than 100, 1 ,000 or 5,000 mm ³ .

In one embodiment, the specimen may comprise a base section comprised of a first element and a layer comprised of a second element overlying at least a portion of a surface of the base section, and at least some of the plurality of volumes may encompass portions of the layer and underlying base section. In such an embodiment, the specimen may further comprise a second layer comprised of a third element overlying at least a portion of a surface of the first layer, and at least some of the plurality of volumes may encompass portions of the second and first layers and the underlying base section. In another embodiment, the specimen may comprise a first base section comprised of a first element abutting a second base section comprised of a second element, the interface between the first and second sections intersecting the specimen surface, and at least some of the plurality of volumes may encompass portions of the interface adjacent to the specimen surface. In such an embodiment the specimen may further comprise a layer comprised of a third element disposed at the interface between the first and second sections, and at least some of the plurality of volumes may encompass portions of the layer comprised of a third element.

In yet another embodiment, the specimen may comprise a base section comprised of a first element and a plurality of islands comprised of diverse concentrations of a second element overlying a surface of the base section, and at least some of the plurality of volumes may encompass portions of at least one island and the underlying base section. In such an embodiment, the islands may be formed according to the following steps: disposing above the surface of the base section a laminar member having upper and lower surfaces; addressing at least a portion of the upper surface of the laminar member with a high energy electron beam to melt member material encompassed within a plurality of member volumes, each member volume abutting the lower and upper surfaces of the member and encompassing different amounts of at least one element, the plurality of member volumes encompassing diverse amounts of the at least one element; and translating molten material derived from the plurality of member volumes onto the surface of the base section to form the plurality of islands.

In other embodiments, at least a fraction of the plurality of volumes may consist of two or more contiguous sub-volumes, the contours of the sub-volumes being adapted to encompass portions of the specimen having enhanced concentrations of the one or more elements. In other embodiments, in the step of forming a multiplicity of substantially homogeneous and discrete molten zones, each of at least a fraction of the multiplicity of molten zones may be formed from material encompassed within a single corresponding volume. In such other embodiments, the each of at least a fraction of the multiplicity of molten zones may be confined at least partially within the single corresponding volume.

In other embodiments, a fraction of the plurality of volumes may comprise main volumes and satellite volumes, each main volume being associated with one or more satellite volumes, and, in the step of forming a multiplicity of substantially homogeneous and discrete molten zones, each of at least a fraction of the multiplicity of molten zones may be formed from material encompassed within a single corresponding main volume and its associated one or more satellite volumes, the material from the one or more satellite volumes being translated with an electron beam to aggregate with the material from the single corresponding main volume. In such other embodiments, the each of at least a fraction of the multiplicity of molten zones may be confined at least partially within the single corresponding main volume.

In other embodiments, at least one of the plurality of volumes may intersect a lower surface of the specimen, at least one mould or region of a retaining surface being disposed below the lower specimen surface, and material derived from the at least one of the plurality of volumes may be translated onto the at least one region of a retaining surface or into the at least one mould to form at least one of the plurality of molten zones.

In other embodiments, before or during the step of cooling the multiplicity of discrete molten zones, at least a fraction of the multiplicity of molten zones may be addressed with an electron beam scanning protocol to maintain or increase the homogeneity of the least a fraction of the multiplicity of molten zones.

In other embodiments, the step of cooling the multiplicity of discrete molten zones may include addressing at least a fraction of the multiplicity of molten zones with the electron beam to induce diverse cooling rates among the multiplicity of molten zones.

In other embodiments, the step of cooling the multiplicity of discrete molten zones to form a multiplicity of alloy sample regions may include a step of addressing at least a fraction of the multiplicity of alloy regions with the electron beam to induce diverse cooling rates among the multiplicity of alloy regions.

In other embodiments, the step of cooling the multiplicity of discrete molten zones to form a multiplicity of alloy sample regions may be followed by addressing the surfaces of one or more of the multiplicity of alloy sample regions with the high energy electron beam to remelt and smooth the surfaces.

Other embodiments may further comprise the step of addressing one or more of the alloy sample regions with an electron beam or other probe to characterize alloy region structure or composition, or may further comprise the step of addressing one or more of the alloy sample regions with a probe to characterize alloy region mechanical properties.

In yet other embodiments, a system for performing any of the above methods may be provided comprising: a work chamber housing a specimen mounting stage; an electron beam column coupled to the work chamber and configured to direct an electron beam towards a specimen in the specimen mounting stage, the electron beam column comprising beam focusing and deflection systems; and a pumping system for evacuating the work chamber and beam column. In other embodiments, the system may further comprise a specimen imaging system using the electron beam, and the electron beam voltage may be operable between 10 and 60 kV and the beam current between 0 and 66 mA.

In other embodiments, the beam deflection system may allow a beam exiting the column and aligned with its optical axis to be deflected by up to 3 degrees at a scanning frequency of between 0.1 and 10,000 Hz, and/or the electron beam spot size up to around 0.5 mm at a distance of between around 50 and 250 mm below the base of the column.

In other embodiments, the specimen mounting stage may be configured to deliver controlled lateral movement of the specimen with respect to the electron beam.

In other embodiments, the electron beam column and specimen stage may be coupled to a programmable logic controller.

In yet other embodiments, an alloy library obtainable by any of the above methods may be provided. BRIEF DESCRI PTION OF THE FIGURES

Figure 1 shows an embodiment with a layered specimen and regular-shaped volumes.

Figure 2 shows an embodiment with a layered specimen geometry using irregular- shaped volumes.

Figure 3 shows an embodiment with a layered specimen geometry using main and subsidiary volumes.

Figure 4 shows an embodiment with a specimen geometry comprising an exposed interface.

Figure 5(a)-(c) show an embodiment with a specimen geometry comprising islands. Various features of the invention are described herein with reference to the figures, the written description and claims. These features may be combined with or interchanged in any permutation other than one in which the features are mutually exclusive. Comprising is used to mean including but not limited to the listed features. DETAILED DESCRIPTION

A suitable specimen, having a surface that is sufficiently large to accommodate formation of a multiplicity of discrete molten zones and discrete sample alloy regions, may be furnished in a variety of different shapes and sizes. The specimen surface may also be sufficiently flat to allow the multiplicity of discrete molten zones and discrete alloy regions to be formed as a two-dimensional array, rendering the specimen more easily addressable by the electron beam during synthesis and by electron beam-based and other probes of structure and composition or properties during screening. Examples of suitable specimen shapes include a parallel-sided plate having a rectangular cross section. For example, a plate having a surface with an area of 10,000 to 20,000 mm ² may contain a library of 10, 50, 100 or more discrete alloy sample regions, each sample alloy region volume ranging anywhere from 100, 1 ,000, 5,000 or more mm ³ , depending on the intended use or type of analysis to be performed. Though reference is made in the following to examples of specimens having an overall plate-like shape, it should be understood that suitable specimens may be furnished in a variety of different shapes.

Specimens having suitable spatially varying concentrations of at least two elements adjacent to a sample surface may be furnished in a variety of geometries, including a body (plate-shaped or other) comprised of one element having a surface coated with one or more layers comprised of one or more other elements (as shown, for example, in Figures 1 to 3); a body (plate-shaped or other) comprising multiple sections comprised of different elements with interfaces between sections intersecting a specimen surface (for example, Figure 4); or a body (plate-shaped or other) comprised of one element having islands comprising another element disposed across a specimen surface (for example, Figure 5). Though these geometries are separately described, they may be combined in the same specimen. Other suitable specimen geometries may also be employed, alone or in combination with the layer, exposed interface and island geometries.

A spatially varying concentration is disposed adjacent to a specimen surface if concentrations of the at least two elements either abut the surface, or lie close enough to the surface to allow volumes of the specimen encompassing the concentrations to be melted by addressing portions of the surface with a high energy electron beam. In melting the material encompassed within a given volume, some vaporization of solid material and evaporation of liquid material may inevitably occur. In any event, by controlling the energy deposition profile of the beam within the specimen— as determined by the beam energy and profile, taking account of the energy absorption coefficients of the materials comprising the specimen— a significant fraction of the material encompassed within a given volume may be melted and retained in the molten state at the specimen surface. The molten material may also be at least partially confined within the volume. Each volume encompassing melted material may be separated from the remainder of the plurality of volumes by unmelted portions of the specimen or there may be contact between adjacent volumes, possibly at the surface openings. If the volume is extended to a sufficient depth within a sufficiently shallow region of the specimen, the volume may extend from upper to lower specimen surfaces. Though the variation of the concentrations of the two or more elements may not be uniform within a given volume— for example, a volume encompassing a portion of a layer and specimen body (Figures 1 to 3), a portion of an interface (Figure 4), a portion of an island and specimen body (Figure 5)— each volume may nevertheless comprise an average concentration of the at least two elements. A volume comprising average concentrations of the at least two elements may be melted to form a substantially homogeneous molten zone comprising the same average concentrations, absent preferential loss or accumulation of the one or more elements or other elements comprising the volume or molten zone. A plurality of volumes, comprising diverse average concentrations of the at least two elements adjacent to the specimen surface, may be melted by addressing portions of the surface with the electron beam to form a multiplicity of homogeneous molten zones comprising diverse average compositions of the at least two elements.

The electron beam may address different portions of the specimen surface, which may be disposed in an array, leading to the formation, from a plurality of volumes, of a multiplicity of molten zones and alloy regions also disposed in an array. Different portions of the specimen surface (or molten zones or alloy regions) may be addressed by scanning the beam between different surface portions (or molten zones or alloy regions) while the specimen remains more or less fixed. Alternatively, different portions of the specimen surface (or molten zones or alloy regions) may be addressed by translating the specimen while the beam remains more or less fixed. Different portions of the specimen surface (or molten zones or alloy regions) with a given specimen may be addressed by a combination of specimen translation and beam scanning. Addressing a given portion of the surface to melt material encompassed within a given volume and form a molten zone, in order to generate a required beam profile and energy deposition profile within the specimen, may also involve scanning of the beam in a defined pattern across that portion of the specimen surface or molten zone. A typical scanning profile, in view of the response characteristics of typical beam deflection systems, may involve a circular beam path executed at a frequency between 0.1 and 100 Hz.

Once formed, a molten zone may be maintained in a homogenous state, or further homogenized, if necessary, before cooling to form a substantially homogenous alloy region, by the further stirring action of the electron beam. A typical scan for homogenization may involve a circular beam path executed at a frequency between 0.1 and 1000 Hz. A substantially homogeneous molten zone or alloy region may be inhomogeneous at its surface and interfaces.

For sufficiently well-separated volumes, a single substantially homogeneous molten zone may be formed from material derived from a single volume and may be partially confined within that volume. Such a molten zone may be cooled to form a substantially homogeneous sample alloy region also partially confined within that volume. In other embodiments, as discussed below, the molten material obtained from more than one volume may be combined by moving material with the electron beam to form a single substantially homogeneous molten zone and substantially homogeneous alloy region, Such a molten zone or alloy region may be confined within one of the volumes. In other embodiments, the volume may extend from the upper specimen surface to a lower specimen surface.

Molten material derived from a volume extending from upper to lower specimen surfaces may be cast into a suitable mould or allowed to fall onto a region of a suitable retaining surface disposed underneath the specimen by, for example, permitting the molten material to flow out of the volume under the force of gravity. A multiplicity of molten zones, and a multiplicity of alloy regions, may be formed on a multiplicity of regions of the retaining surface, or in a multiplicity of moulds. As for a library of alloy regions formed on an upper specimen surface, the molten zones may be further homogenized, the cooling rate of the molten zones and alloy regions may be varied, and the alloy regions may be disposed in an array to facilitate screening.

Figures 1 , 2 and 3 show examples of a specimen having a surface layer, comprising a base plate 1 composed of a first element, having on its upper surface a sheet 2 composed of a second element, having on its upper surface a coating 3 composed of a third element. Different inventive embodiments— a volume; a volume consisting of two or more sub-volumes; a molten zone comprising material derived from main and subsidiary volumes— will be described using this illustrative specimen geometry. In these and all other embodiments, including those shown in Figures 4 and 5, "element" will generally be used to refer to a metal. These three embodiments may be combined in the same specimen, or used with other specimen geometries, including the exposed interface and island geometries described below.

In the schematic cross section of Figure 1 , electron beams 11 and 12 are shown as having melted material encompassed and volumes bounded by the original specimen surface and surfaces 13 and 14, which define, if projected onto the plane of the specimen surface, approximately circular cross sections that decrease in diameter with increasing depth away from the upper specimen surface 9. The exact contour of each volume will depend on the energy deposition profile, specimen geometry and composition. Electron beams shown schematically as 11 and 12 may be stationary beams or may be locations of the same beam that is rapidly scanned between the two locations. Beams 11 and 12 may also be beam profiles established by applying a scanning protocol to broaden or otherwise alter the energy deposition profile of the electron beam. (If the beam or beam profile is not substantially circularly symmetric when projected onto the plane defined by upper specimen surface 9, or if the specimen composition is not substantially circularly symmetric, the cross sections of the volumes from which material is melted may no longer be circularly symmetric.) Notwithstanding the relatively small separation between molten zones shown in Figure 1 , the material comprising the molten zones, represented by melt pools 15 and 16, may be derived substantially from volumes bounded by surfaces 13 and 14, respectively. Further, though the surfaces 17 and 18 of melt pools 15 and 16 are shown in Figure 1 (and in Figures 2 and 3) as being flat and parallel to the specimen surface 9, a range of processes may dynamically alter the overall shape and surface profile of the molten zone, as discussed below. In any event, the total penetration depth of beams 11 and 12 into the base plate composed of a first element may be increased or decreased, for example, by increasing or decreasing one or both of beam power density and dwell time, leading to differences in the size and average composition of volumes bounded by surfaces 13 and 14, and thus differences in the composition of melt pools 15 and 16 with respect to the first, second and third elements. As illustrated, melt pools 15 and 16, since they originate from volumes bounded by surfaces 13 and 14, will contain more or less equal quantities of the second and third elements, but a greater quantity and proportion of the first element would be present in pool 16.

For the specimen geometry illustrated in Figure 1 , one or more electron beams may be scanned across the specimen surface to address a plurality of volumes to form a multiplicity of molten zones spanning a range of penetration depths and different compositions. Accordingly, molten zones 15 and 16 may be understood as illustrating only part of a larger range of beam penetration depths and melt zone compositions, or may represent the end points of a range. The beam may also be scanned across the regions of the surface adjacent to a molten zone, in order to increase the total volume of material entering the molten zone by sweeping material from adjacent surface volumes into the molten zone, as shown in Figure 3 and discussed below. Once a multiplicity of molten zones spanning a range of concentrations of the first, second and third elements, such as molten zones 15 and 16, has been formed, the multiplicity of zones may be cooled to form a multiplicity of alloy regions having correspondingly diverse concentrations of the first, second and third elements. The cooling of each molten zone may be done rapidly— for example, by simply removing the electron beam— or may be performed more gradually— for example, by slowly reducing the dwell time or power density of the beam addressing that molten zone. Taking into account the proximity of other molten zones, and the energy being delivered by the electron beam to those zones, the cooling rate of a given molten zone may be adapted to minimize segregation, in homogeneities and surface imperfections that may be introduced during the cooling phase. Similarly, in order to prevent sudden thermal stresses, which may lead to surface cracking, for example, an alloy region may also be cooled gradually by slowly decreasing the amount of heat delivered by the electron beam. Composition and cooling conditions, and thus processing histories, may be varied between molten and alloy regions formed within a single specimen of the type shown in Figure 1. In the schematic cross-section shown in Figure 2, the plate-like specimen is again shown as comprising a base plate 1 composed of a first element, having on its upper surface a sheet 2 composed of a second element, having on its upper surface a coating 3 composed of a third element. However, electron beam profiles 21 and 22 are now shown as melting volumes bounded by surfaces 23 and 24 having cross sections with diameters that vary according to whether the volume intersects portions of the specimen composed of first, second and third elements. As for the embodiment described with reference to Figure 1 , beam profiles may be single beams or multiple beams that may be scanned within or between volumes to create an appropriate energy deposition profile sufficient to melt a given volume or sub-volume. In the schematic of Figure 2, beams 21 -1 and 22-1 represent the beam profile used to create the greatest depth and smallest lateral diameter portions of volumes bounded by surfaces 23 and 24, shown schematically as sub-volumes bounded in part by surfaces 23-1 and 24-1 extending into the base plate composed of first element. (The contour of the entire surface bounding a particular sub-volume will depend on the order in which the sub-volumes are formed. If, for example, sub-volume bounded by surface 23-1 were formed first, the remainder of surface 23-1 , not shown in the figure, would have a regular shape, similar to surfaces 13 and 14.) Beams 21 -2 and 22-2 represent the beam profile used to create the intermediate depth and intermediate diameter portions of volumes bounded by surfaces 23 and 24, shown schematically as sub-volumes bounded by surfaces 23-2 and 24-2 extending laterally into the sheet composed of second element. Finally, beams 21 -3 and 22-3 represent the beam profile used to create the smallest depth and greatest diameter portions of volumes bounded by surfaces 23 and 24, shown schematically as sub-volumes bounded by surfaces 23-3 and 24-3 extending laterally into the coating composed of third element. As shown in the schematic, melt pool 26 created from the volume bounded by surface 24 contains larger quantities and higher proportions of the second and third elements with respect to the first element than are contained in melt pool 26 created from the volume bounded by surface 24.

The quantities and proportions of the first, second and third elements encompassed by volume bounded by surface 23 may be controlled by varying electron beam profiles 21 - 1 , 21 -2 and 21 -3 to change the diameters and depths of sub-volumes bounded by surfaces 23-1 , 23-2 and 23-3. Thus, the quantities and proportions of the first, second and third elements entering melt pool 25 from the volume bounded by surface 23 may be controlled by varying electron beam profiles 21 -1 , 21 -2 and 21 -3. Similarly, the quantities and proportions of the first, second and third elements entering melt pool 26 from volume bounded by surface 24 may be controlled by varying electron beam profiles 22-1 , 22-2 and 22-3. According to the schematic in Figure 2, melt pool 26 would have greater quantities and higher proportions of the second and third elements with respect to the first element than melt pool 25. In general, the quantities and proportions of the first, second and third elements entering a given molten zone from a given volume may be controlled by varying the diameters and depths of the sub- volume that substantially encompass the region of the specimen associated with a given metal The size of each sub-volume may be adjusted to a given total volume that remains substantially unchanged for a number of discrete volumes, while the relative composition of one or more metals varies between those discrete volumes.

Though, in the schematic in Figure 2, melt pool surfaces 27 and 28 are shown as flat, a dynamic non-flat surface profile may be expected, for at least the reasons discussed below. Further for a given irregular-shaped volume, such as volumes bounded by surfaces 23 or 24, the melt sub-volumes, bounded by surfaces 23-1 , 23-2 and 23-3 or 24-1 , 24-2 and 24-3, may be produced simultaneously or in a given order, so long as melt pools 25 and 26 are appropriately homogeneous and may be cooled to create sufficiently uniform alloy regions. In any event, by identifying a multiplicity of irregular shaped volumes, such as volumes bounded by surfaces 23 or 24, and by melting or vaporizing the material encompassed by the plurality of volumes, a multiplicity of molten zones having a range of composition of the first, second and third elements may be created, which, if appropriately homogenized and cooled, may create a multiplicity of sample alloy regions spanning a range of alloy compositions of the first, second and third elements, disposed within the same specimen. As noted for Figure 1 , by varying, for example, the cooling rate of the molten zones and alloy sample regions, alloy sample regions having a variety of processing histories may also be formed in the same specimen. In the schematic shown in Figure 3, the plate-like specimen again comprises a base plate 1 composed of a first element, having on its upper surface a sheet 2 composed of a second element, having on its upper surface a coating 3 composed of a third element. However, only a single molten zone or melt pool 35 is shown extending via a main volume bounded by surface 33 through the third, second and first elements. Molten zone 35 is shown here produced by beam profile 31 and, more particularly, by main beam 31 -1. As already discussed with respect to Figures 1 and 2, main beam 31 - 1 may represent the position of a stationary beam or a beam profile created by rapidly scanning one or more beams within the molten zone 35 or between a multiplicity of molten zones. Further, the schematic representation of a flat melt pool surface in Figure 3 is not meant to imply that the surface of the melt pool is necessarily flat, since the melt pool surface may display a dynamic and non-flat profile, as a result of the factors already discussed for Figures 1 and 2.

In Figure 3, secondary beams 31 -2 are shown impinging on the upper specimen surface 9 away from melt zone 35 and acting to displace waves 3-2 and 3-3 of coating third element towards the main melt pool 35. By repeating a series of inward radial sweeping movements of secondary beams 31 -2 and 31 -3, as shown by the arrows, satellite volumes bounded by surfaces 33-2 and 33-3 of coating 3 may be displaced and waves 3-2 and 3-3 of third element transported into melt pool 35. The satellite volumes bounded by surfaces 33-2 and 33-3 may be formed, and waves 3-2 and 3-3 of third element transported, before or during or after the formation of melt pool 35. By selectively directing different controlled amounts of material from coating 3 into a multiplicity of molten zones, the proportion of the third element comprising coating 3 within those melt zones may be varied.

In Figure 3, the volume bounded by surface 33 is shown as having a regular profile, as for Figure 1. Material may also be introduced into melt zones that are created with different depths and shapes, as for volumes bounded by surface 13 and 14 shown in Figure 1 , or into melt zones formed from sub-volumes, as for volumes bounded by surface 23 and 24 shown in Figure 2.

Though, in Figures 1 to 3, the molten zone surfaces are shown as flat and parallel to the original specimen surface 9, occupying exactly the same volume as the solid material, molten zones may be expected to deviate from this idealized behavior as a result of factors such as volume changes upon melting, solid vaporization and melt evaporation, convection within the melt pool, melt interaction with the electron beam, and melt surface tension.

In the surface layer geometry, as illustrated by Figures 1 , 2 and 3, the spatially varying concentration may consist of one or more layers each composed of different elements, or mixtures of elements, disposed on the surface of a plate, and the plate may itself be composed of a mixture of elements. The layer of multilayers may cover the entire surface of the underlying plate, an entire large surface or only part or parts of a large surface, and may be of uniform or variable thickness. The layers or multilayers may be formed by one or more different techniques, such as vacuum evaporation, sputtering, electrochemical deposition, electron beam melting of a powder spray, or any other suitable coating processes. Alternatively, layers or multilayers may be formed as auxiliary plates, sheets or foils disposed on or above, or joined to, the surface of the underlying plate. Combinations of deposited layers, coatings, auxiliary plates, sheets, foils, powders, etc., may be used in the same specimen. In general, the means used to form the layers or multilayers is unimportant, so long as the furnished specimen has the desired spatially varying concentration of alloy components abutting a specimen surface, sufficient structural integrity and does not present unacceptable levels of contaminants. In a second specimen geometry, the spatially varying concentrations adjacent to a specimen surface may be in the form of one or more exposed interfaces intersecting the specimen surface. The specimen geometry may be as simple as a plate or block divided into two sections by an interface disposed approximately orthogonal to the large surface of the combined plate, each section being composed of a different element. In other embodiments, the specimen surface may be intersected by more than one interface and be divided into more than two different sections, each comprising two or more different elements. A layer comprising of a third element may be introduced at the interface between sections composed of first and second elements. Each section may be composed of more than one element and pairs of interfaces may be disposed sufficiently close together to allow a single molten zone formed on the specimen surface to intersect two interfaces at the same time.

A specimen geometry comprising a plate or block divided into section 41 , composed of a first element, and section 42, composed of a second element, is shown schematically in Figure 4. The interface 43 between sections 41 and 42 is shown as intersecting specimen surface 49. The interface 43 may have a layer of a higher concentration of third element. As for the specimen geometry with surface layers or multilayers discussed above with respect to Figure 1 , 2 and 3, assuming the exposed interfaces are sufficiently contaminant-free, precise and uniform, the means of formation of the specimen shown in Figure 4 is, in general, not important. Molten zone 45-1 formed by beam profile 47-1 from a volume bounded by surface 44-1 and molten melt zone 45-2 formed by beam 47-2 from a volume bounded by surface 44-2 are shown. For convenience, the upper surfaces of molten zones 45-1 and 45-2 are not labeled separately and are, moreover, shown as flat and parallel with specimen surface 49, though this may not be accurate, for the reasons already discussed with respect to the layer specimen geometry shown in Figures 1 , 2 and 3. In view of different displacements relative to interface 43, molten zone 45-1 will comprise a higher concentration of the first element than the second element, and molten zone 45-2 will have a higher concentration of the second element than the first element. A number of equal-shaped volumes, comprising a range of concentrations between those of molten zones 45-1 and 45-2, may be formed by displacing the volumes along the interface, as indicated by the parallel dashed lines. In another embodiment, volumes may be melted comprised of sub-volumes extending preferentially into a layer of third element at interface 43, or into regions 41 and 42, comprising the first and second elements. A third specimen geometry, a base plate composed of one element with islands composed of a second element, is shown in Figures 5a, b and c. Figures 5a and 5b show one means of forming the islands. However, as for the other specimen geometries, the means of forming spatially varying concentrations of one or more elements adjacent a specimen surface is unimportant, so long as the specimen is sufficiently free of contamination.

In Figures 5(a) and 5(b), a laminar member 52, composed of a second element and having an upper surface 52-1 and lower surface 52-2, is shown disposed above upper surface 51 -1 of base plate 51 , which is composed of a first element. The surfaces of the laminar member need not be uniformly parallel, so long as a portion of the upper surface 52-2 of laminar member 52 may be addressed with electron beam or beam profile 54 (as discussed above with respect to Figures 1 to 4) to melt material encompassed within a volume bounded by the upper 52-1 and lower 52-2 surfaces of the laminar member 52 to form molten zone 55. In Figure 5(b), molten zone 55. has been translated onto upper surface 51 -1 of base plate 51 , to form island 57 of melted material, leaving opening 53 in laminar member 52 corresponding the boundary of the volume melted to form molten zone 55. The translation of molten zone 55 may done by simply allowing the molten zone to fall onto surface 51 -1 , or by inducing contact between molten zone and the base plate surface . Once located on upper surface 51 -1 , and once electron beam or beam profile 54 has been removed, molten zone 55 may solidify rapidly to form island 57. By addressing various portions of the upper surface 52-1 of member 52 with the high energy electron beam, different volumes of the second element may be melted and translated onto upper surface 51 -1 to create a plurality of islands. Where the member is composed of a single element, variations in melted volume, and therefore island size, may be used to vary the quantity of the second element introduced onto the surface of the base plate. However, the member may be comprised of more than one element and its composition may vary laterally, allowing islands of differing compositions to be introduced onto the surface of the base plate. In any event, once the islands are formed, and once the member has been removed, the islands distributed across the surface of the base plate may be addressed by a high energy electron beam or beam profile to melt material encompassed within a plurality of volumes encompassing different islands, and thus form a multiplicity of discrete and substantially homogeneous molten zones comprising diverse concentrations of the two elements, as shown in Figure 5(c), where electron beam or beam profile 56 is shown to have produced molten zone 59 from base and island material. Molten zones of diverse compositions may also be produced from islands of equal size and uniform composition, by melting material from different sized volumes. The melting of volumes may also be performed using sub-volumes, and material may also be moved from satellite volumes into main volumes as discussed for the embodiments above. The multiplicity of molten zones may be cooled to form a multiplicity of discrete and substantially homogeneous alloy regions comprising diverse compositions of the two elements. The laminar member may be comprised of a third element, and the concentration of second and third elements may vary laterally across the laminar member, allowing its composition to be varied between molten zones and alloy regions. The base region may also comprise elements in addition to the first element of the example shown in Figure 5.

In Figures 1 to 4, the surfaces bounding the volumes of melted material are shown as intersecting the upper specimen surface (shown as 9 in Figures 1 to 3 and 49 in Figure 4) and extending some finite distance into the base plate (Figures 1 to 3) or plate (Figure 4). Though the lower specimen surfaces are not indicated in Figures 1 to 4, with a suitable specimen geometry and suitable electron beam conditions, the volumes may be extended as far as a lower specimen surface, as for the laminar member 52 shown in Figures 5(a) and (b). Where a volume extends between upper and lower specimen surfaces, a molten material derived from such a volume may be translated onto a region of a suitable retaining surface or cast into a suitable mould, where the molten zone may be further homogenized and cooled to form a discrete and substantially homogeneous alloy region. In similar fashion to base plate 51 , shown disposed below laminar member 52 in Figures 5(a) and 5(b) to receive molten zone 55, the suitable retaining surface or mould may be disposed below the specimen to receive molten zones formed from suitably thin regions of specimens with geometries of the types shown in Figures 1 to 4 (and indeed of the island type shown in Figure 5(c)). A multiplicity of discrete and suitably homogeneous molten zones formed on regions of a suitable retaining surface or in suitable moulds may be disposed in an array to facilitate screening, once the molten zones are cooled to form a multiplicity of discrete and substantially homogeneous alloy regions. As for the laminar member 52 shown in Figure 5, the specimen may be displaced relative to the retaining surface or mould to allow an electron beam to address the molten zones, to vary homogenization and cooling rates, and alloy regions, to vary cooling rates. By addressing with a high energy electron beam at least a portion of a surface of a specimen comprising one or more of the above geometries, or any other suitable geometry, a plurality of volumes of specimen material abutting the surface may be melted to form a multiplicity of discrete and substantially homogenous molten zones having diverse compositions, which may be cooled to form a multiplicity of discrete alloy regions having a range of composition and processing histories. Molten zones may be maintained in a substantially homogenous state, or further homogenized, by action of the electron beam. For example, a high frequency electron beam scanning protocol (up to, for example, around 10,000 Hz) may be executed across the surface of a molten zone, including during the cooling phase when the alloy regions are formed. Once alloy regions are formed, their surfaces may be glazed, by remelting and solidification, to smooth or flatten their surfaces, to facilitate alloy region screening.

Well-spaced and sufficiently large alloy regions formed on a library plate, preferably as a regular array, are suited to rapid screening using a broad variety of characterization techniques. As noted above, the library plate supporting the multiplicity of alloy regions may simply comprise all or part of the original specimen, may comprise all or part of a retaining surface supporting a multiplicity of alloy regions formed from material derived from the specimen, or may support a multiplicity of alloy regions formed in moulds from material derived from the specimen. The library plate may be adapted to furnish alloy regions in a regular array to facilitate screening. The screening may include the rapid extraction of structural and compositional information using electron-based techniques, such as EBSD and EDS performed in a scanning electron microscope, or x-ray based techniques, such as diffraction and fluorescence. Mechanical properties may be rapidly measured using techniques such as indentation. The screening may be performed in the electron beam melting system or the library plate may be removed and screened elsewhere. An electron beam system suitable for performing the combinatorial approaches using the specimen geometries outlined above may comprise a work chamber housing a specimen mounting stage, an electron beam column coupled to the work chamber and configured to direct an electron beam towards a specimen in the specimen mounting stage, the electron beam column comprising beam focusing and deflection system, and a pumping system for evacuating the work chamber and beam column. The specimen may be in the form of a plate. The system may comprise a specimen imaging system or systems, allowing the specimen to be viewed either before, during and after it is addressed by the high energy electron beam. The imaging system may be optical or may use the scanned high energy electron beam, preferably operating in a lower power mode, with an appropriate detector for imaging purposes.

A typical electron beam source may be operable between 10 and 60 kV at a beam current between 0 and 66 mA, and may deliver a beam at the specimen with a spot size of up to about 0.5 mm, where spot size is defined according to normal practice in electron beam welding.

The beam may be focused onto a specimen, usually located anywhere between 50 and 250 mm from the base of the beam column, may exit the column at an angle of plus or minus three degrees from the optical axis of the beam column and may be scanned between these extremes at a scanning frequency of between 0.1 and 10,000 Hz. The specimen mounting stage within the work chamber may allow controlled lateral movement of the specimen with respect to the electron beam. For example, the beam may be deflected to execute a circular path on a stationary specimen, or the specimen may be translated to execute a circular path underneath the beam. The movement of the specimen stage with respect to the beam, and of the beam with respect to the stage, may be controlled using a programmable logic controller ("PLC"). Other functions of the electron beam specimen, loading, unloading, pumping, etc., may also be controlled using a PLC.

The electron beam system may be coupled to electron beam-based and other structural, chemical and physical property probes useful for screening the alloy sample library.