Method of additively manufacturing a structure on a pre ^¬ existing component out of the powder bed

The present invention relates to a method of additive manu ^¬ facturing of the structure on a pre-existing, preferable single crystalline, component out of the powder bed. The method may relate to a repair or refurbishment method for gas tur- bine components, such as burners or blades. Further, an ac ^¬ cording apparatus comprising a radiation source, capable of generating a beam pattern, is presented.

Preferably, the component denotes a component applied in a turbo machine, e.g. in the flow path hardware of a gas tur ^¬ bine. The component is preferably made of a superalloy and/or nickel-based alloy, particularly a precipitation, solution or age-hardened alloy. Additive manufacturing techniques comprise e.g. powder bed methods, such as selective laser melting (SLM) or selective laser sintering (SLS) or electron beam melting (EBM) .

A method of selective laser melting is described in EP 2 601 006 Bl, for example.

Additive manufacturing (AM) methods have proven to be useful and advantageous in the fabrication of prototypes or complex and filigree components, such as lightweight design or cool- ing components comprising mazelike internal structures. Fur ^¬ ther, additive manufacture stands out for its short chain of process steps, as a manufacturing step can be carried out di ^¬ rectly based on corresponding CAD/CAM and/or construction data .

The term "additive" in the context of manufacturing shall particularly denote a layer-wise, generative and/or bottom-up manufacturing process. The additive manufacturing as described herein may be or relate to rapid prototyping.

Powder bed manufacturing methods such as selective laser melting or selective laser sintering are relatively well known methods for manufacturing parts or components from powder material, for instance. Conventional apparatuses or set ^¬ ups for such methods usually comprise a manufacturing or build platform on which the component is built layer-by-layer after the feeding of a layer of base material which may then be melted, e.g. by the energy of a laser beam and subsequent ^¬ ly solidified. The layer thickness is e.g. determined by a wiper that moves, e.g. automatically, over the powder bed and removes excess material. Typical layer thicknesses amount to 20 ym or 40 ym. During the manufacture, said laser beam scans over the surface and melts the powder on selected areas which may be predetermined by a CAD-file according to the geometry of the component to be manufactured. In gas turbine technology, particularly in the manufacture of components from the corresponding flow path hardware, there is the stringent demand to provide the components with excel ^¬ lent mechanical and thermal properties in order to enable the components to endure the harsh turbine environment. Particu- larly, the required creep and rupture resistivity of the com ^¬ ponents may almost only be complied with when awarding the components with a single crystalline structure. In case of turbine blades, which are conventionally refurbished by means of laser cladding or laser metal deposition, the refurbished structure has usually a poorer structural quality as compared to the cast root or base. Even though it may be possible, at least to a certain extent, to make the refurbished structure adopt crystallinity of the base in the LMD process, it is not yet achieved to provide for such a pseudomorphic or epitaxial "growth" of the refurbished structure in case of powder bed based process, such as SLM or EBM. Particularly, melt pool dynamics are important when it is intended to provide a re- furbished structure with the same (single) crystalline prop ^¬ erties as an underlying and pre-existing substrate structure.

It is, thus, an object of the present invention to provide means which allow an improvement of material phase and crys ^¬ talline texture of a refurbished and/or manufactured struc ^¬ ture on top of the pre-existing substrate in powder bed re ^¬ lated additive processes. The mentioned object is achieved by the subject-matters of the independent claims. Advantageous embodiments are subject- matter of the dependent claims.

An aspect of the present invention relates to a method of ad ^¬ ditive manufacturing of said structure on a pre-existing component. In case of a repair or hybrid-manufacturing method, the pre-existing component together with the coated or refurbished structure may then represent the refurbished part or article .

The method comprises disposing the pre-existing component in a bed of a powdery base material and levelling the component, such that a manufacturing plane of the component can be re- coated with the base material. Therefore, a manufacturing plane is preferably approached to the surface of the powder bed, or vice versa. This has expediently to be carried out in a very accurate manner, as recoated powder layer thicknesses amount to as little as 50 ym or less. The method further comprises alternatingly recoating and irradiating the manufacturing plane with an energy beam in order to additively build up the structure, wherein the irradi ^¬ ation is carried out in that the (coated) manufacturing plane is scanned by the beam in a non-continuous way. In other words, the irradiation may be carried out in an interrupted way, i.e. interrupted by way of time and/or space. The irradiation is further carried out in that - for the irradiation according to a second vector for the structure - the beam or beam spot on the powder bed is either only guided parallel with respect to a previous first vector or the irra- diation process is paused after the irradiation of the first vector for a time span between e.g. 1/10 of a second to 2 se ^¬ conds until the irradiation is continued with the second vec ^¬ tor. The term "vector" as used herein shall describe a stripe or trajectory of the beam spot on the powder bed according to which base material is firstly melted and subsequently solid ^¬ ified. A vector may, thus, be a "stripe" or section according to which an area of the powder bed has to be exposed with the energy beam for solidification. It has to be noted that any area to be solidified has to be exposed with the energy beam according to specific vector pattern, as the desired area cannot be exposed as a whole.

By the given means, a favourable phase change from liquid to solid may be achieved which allows for a deposited structure to be textured according to the same crystallinity as the pre-existing component. In case of single crystalline, colum ^¬ nar crystalline or directionally solidified component, the structure may also be awarded with the same favourable crys ^¬ talline mechanical properties as the component. This is achieved in that the scan vector or irradiation direction is preferably chosen such that the melt pool always moves in "forward" direction and is not "turning back" into a previously heated area or zone affected by heat of the previous vector. Thus, the favourable crystalline texture of the structure is maintained or prevails and is not destroyed, as would be the case when the beam is "meandered back". The pre ^¬ sent invention addresses the need to increase process effi ^¬ ciency for industrialization of AM-manufacture . Particularly, the idea offers advantages for the manufacture of hybrid- parts.

In an embodiment - for the irradiation according to the second vector for the structure - the beam is not guided in a direction anti-parallel to the first vector, but only in a direction parallel to the first vector.

In an embodiment, the beam is scanned over the manufacturing plane in a lined or row-type, and preferably not in a mean ^¬ der-like fashion. In other words, the vector geometry for the manufacturing process is chosen such that the irradiation is carried out according to the way of reading a book, i.e.

linewise scanning, e.g. from the left to right, or vice ver- sa .

In an embodiment the pre-existing component is a, preferably single, crystalline or directionally solidified structure. In an embodiment, irradiation parameters are chosen such that the structure is established in a single crystalline texture as well.

In an embodiment, irradiation parameters are chosen such that the structure is established in a columnar crystalline tex ^¬ ture .

In an embodiment, irradiation parameters are chosen such that the structure is established in a dendritic crystalline tex- ture .

These embodiments, particularly the single crystalline embod ^¬ iment of the pre-existing component as well as the structure, allow to award the structure and thus, the readily refur- bished article with favourable material properties, e.g.

properties which allow for highest (thermal) creep resistivi ^¬ ty and rupture strength in an application of the article, e.g. the turbine blade during its intended operation. Even when the structure is provided with a dendritic and/or somewhat polycrystalline texture on the single crystalline component, the inventive advantage can at least partly be ex ^¬ ploited . According to the presented method, the structure may be ki- netically forced to "grow" or be established according to the same "crystallinity" as the component. This may be the case, as manufacturing parameters may be chosen such that a seeded, epitaxial, or pseudomorphic growth of the structure is facil ^¬ itated .

The term "pseudomorphic" shall mean, that the structure adopts crystallinity of the underlying component at least up to a certain thickness.

In an embodiment, the method is a selective laser melting method .

In an embodiment, the method is a selective laser sintering method .

In an embodiment, the method is an electron beam melting method.

In an embodiment, the method is a repair process, wherein the structure is a refurbished or refurbishment structure. A further aspect of the present invention relates to an appa ^¬ ratus for the additive manufacture of the structure from a powder bed comprising a substrate or support and a radiation source capable of generating a beam pattern (energy beam) . The apparatus is further configured such that a manufacturing plane of the substrate can selectively be irradiated or ex ^¬ posed to with at least one energy beam in order to additively build up the structure on the substrate, wherein the sub ^¬ strate is displaceable, e.g. horizontally or laterally dis- placeable, with respect to the beam pattern only by mechani- cal means such as a gantry system. This advantageously allows for expensive optical scanners for the beam movement during the process to be dispensed with. In an embodiment, the radiation source is configured to gen ^¬ erate a row-type beam pattern of a plurality of energy beams.

In an embodiment, the apparatus is set up to displace the structure in a direction transverse to the row direction. Ac ^¬ cording to this embodiment, the apparatus may be provided with a bar or brush of laser spots which can be mechanically replaced with respect to the support or the substrate by me ^¬ chanical means. Thus, a cost-efficient "low-tech" approach may be provided for the apparatus, i.e. without the use of sophisticated optical measures, wherein at the same time the inventive advantages of the method may be realized.

Advantages relating to the described method and/or the de- scribed structure may as well pertain to the apparatus and vice versa.

Further features, expediencies and advantageous refinements become apparent from the following description of the exem- plary embodiment in connection with the Figures.

Figure 1 shows a schematic perspective view of an additive manufacturing process of the prior art. Figure 2 shows a schematic perspective view of an additive manufacture of a structure on top of a pre-existing component out of the powder bed according to the present invention.

Figure 3 shows a schematic perspective view of an apparatus according to the present invention.

Figure 4 shows a schematic flow chart of method steps of the present invention. Like elements, elements of the same kind and identically act ^¬ ing elements may be provided with the same reference numerals in the Figures. Figure 1 shows an article or a part 10. The part 10 is actu ^¬ ally being manufactured additively out of the powder bed 3 in that said powder is solidified by an energy beam 4. The ener ^¬ gy beam 4 may be a laser beam. The energy beam 4 is prefera- bly generated by a radiation source 21. By means of the scan ^¬ ner 11 or according optics, the energy beam may, e.g. be moved over the powder bed 3 in a meander-like fashion, as shown and indicated by the arrow in Figure 1. The presented method as shown in Figure 1 describes a conven ^¬ tional way of irradiating a powder bed. Each line, section or part of the trajectory of the beam 4 over the powder bed may be described by vectors which define or compose said meander. After a single layer of base material 3 has been solidified, a base or a support, carrying the part 10 is usually lowered by a distance corresponding to the layer thickness.

According to this conventional approach, e.g. after having guided the energy beam 4 in the first horizontal line, the energy beam is only marginally guided downwards, in order to "meander back" towards the beginning or in a direction anti- parallel to the first vector. Thereby, parts of the first ir ^¬ radiated lines, or vector (s) become again exposed to the heat of the energy beam 4, i.e. for a second time in a short time span. Thus, a melt pool (not explicitly indicated in Figure

1; cf. numeral MP in Figure 2) is moved again towards regions which have recently been melted. This provides adverse struc ^¬ tural defects or poor crystallinity for the structure to be established, as the structure may be remelted (again) after it has once been solidified. This particularly prevents the structure from being established according to the same crystallinity as an underlying layer, for example.

Figure 2 illustrates the situation comparable to the one as shown in Figure 1 wherein, however, a structure 1 which has newly to be manufactured, on top of the pre-existing compo ^¬ nent 2, is established out of the powder bed 3 according to the inventive method. The component 2 and the structure 1 may then, when completely be manufactured, represent a refur ^¬ bished article 10.

After the pre-existing component 2 having been disposed or arranged in the powder bed 3 (cf. step a) in Figure 4), the component 2, or as the case may be a manufacturing plane MP thereof, has to be leveled (cf. step b) in Figure 4) such that the manufacturing plane of the component can be recoated with the base material 3 and/or irradiated with the energy beam 4 (cf . step c) in Figure 4) .

According to the present invention, the irradiation is carried out in that the different vectors for the structure 1 are scanned by the laser beam 4 in a non-continuous and/or row-type fashion, e.g. according to the way of reading the lines of the book from left to right or vice versa.

In the present embodiment, the energy beam 4 is preferably guided from left to right over the powder bed 3, as indicated by the arrows or vectors in Figure 2. The top line, stripe or trajectory represents vector VI.

A subsequent vector according to which the base material 3 is to be irradiated or scanned afterwards is denoted with vector V2. In contrast to Figure 1, after having scanned the first line or vector VI, irradiation is interrupted and the laser beam 4 is preferably moved to the left side of the part in order to scan vector V2 in the same manner as vector VI .

Therefore, the pre-existing component 2 or support carrying the same may be moved, e.g. to the left. Alternatively, an energy source 21 may be moved, e.g. to the right.

In an alternative embodiment, e.g. vector V2 may be scanned from right to left, i.e. anti-parallel with respect to vector VI. However, in this case, the irradiation has to be timely paused for a time span of e.g. a tenth of a second to 2 se ^¬ conds, such that heat, provided from the energy beam to the powder bed may already have been dissipated until the energy beam 4 and therewith a melt pool MP, which may extend over various vectors, is moved again through already solidified regions . Thus, the non-continuous, i.e. timely paused scan/irradiation direction of vectors provides as well for the inventive ad ^¬ vantages, i.e. the establishment of the structure with a crystalline texture as the one of the pre-existing component. Figure 3 shows an apparatus 20 according to the present in ^¬ vention. The apparatus 20 comprises a gantry system or radia ^¬ tion source 21. The radiation source 21 comprises a plurality of laser emitters and/or laser beams 4. The radiation source 21 is capable of providing a row-type beam pattern 22. The radiation source 21 may be or comprise a laser bar. Reference numeral 21 may be a gantry.

The apparatus 20 further comprises a support or substrate 5. The substrate 5 is preferably horizontally displaceable with respect to the beam pattern 22, viz. in a direction orthogonal to the row direction of the beam pattern 22. This is indicated by the arrow shown below in Figure 3.

It is further indicated in Figure 3 that - for the manufac- turing of the structure 1 or for refurbishing of part 10 along with the inventive advantages, the whole row of energy beams may be moved simultaneously and relatively to the sup ^¬ port (either by movement of the support relative to the radi ^¬ ation source 21 or vice versa) .

Thereby, expensive optics or scanners for moving the energy beam, as is usual in SLM process, may be dispensed.

The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which particularly includes every combination of any features which are stated in the claims, even if this feature or this combination of features is not explicitly stated in the claims or in the examples.