Powder material

The present invention refers to a powder material for addi tive manufacturing providing an improved microstructure and shape of a product. Furthermore, the present invention refers to a method of additive manufacturing utilizing such powder material in the step of manufacturing a product or repairing a product. Additionally, the present invention refers to a use of such powder material for additive manufacturing. Fur thermore, the present invention refers to a product manufac tured or repaired utilizing such powder material or method.

Additive manufacturing is a very flexible method of manufac turing, wherein a product is manufactured by adding material on an existing part or right from the scratch. In recent years the possibilities significantly improved and this new method of manufacturing products has been introduced into in dustrial applications. Especially, the possibility to build up structures utilizing geometries not possible using conven tional methods of manufacturing significantly increases the benefit provided herewith. Methods like 3D printing, for ex ample, utilize a metal or metal composition powder being melted layer by layer to manufacture a complex 3D structure. Despite the high flexibility provided with such method, cer tain requirements are still to be considered. Especially for applications demanding a high accuracy was noted that, for example, minor deviations occur despite optimized operating conditions. As the requirements for such manufacturing meth ods constantly increase, preventing such deviations provides a significant challenge to be solved. For example, preventing deviations of the shape of the product resulting in post pro cessing steps. For example, preventing cavities enclosed in the product influencing the integrity and stability.

These problems are solved by the products and methods as dis closed hereafter and in the claims. Further beneficial embod- iments are disclosed in the dependent claims and the further description. These benefits can be used to adapt the corre sponding solution to specific needs or to solve further prob lems.

According to one aspect the present invention refers to a powder material for additive manufacturing comprising, pref erably consisting of, particles, at most 25 weight percent (wt.-%), preferred at most 22 wt.-%, more preferred at most 13 wt.-%, even more preferred at most 9 wt.-%, of the parti cles provide a particle size differing more than 20% from the D ₅₀ based on the value of the D ₅₀ . In specific embodiments it is even preferred that the particle size of the aforemen tioned upper limit of the particles that are less than 17%, more preferred less than 15% from the D ₅₀ . The term "D _x " as used herein like Di ₀ , D ₅₀ or D ₁₀₀ refers to the particle size at which X wt.-% of the particles provide at most this parti cle size determined utilizing volume average particle size distribution. For example, a D ₅₀ of 30mpi characterizes that 50 wt.-% of the particles provide a particle size of 30mpior less determined utilizing volume average particle size dis tribution. The determination of the D ₅₀ is, for example, re alized using laser granulometry utilizing a particle size measurement device of the company Quantachrome (device: Cilas 1064). The measurement is performed according to the manufac turer specifications. For this purpose, 1.5g of the powder material is dispersed in 100ml ethanol, treated for 300 sec onds in an ultrasonic bath (device: Sonorex IK 52, company Bandelin) and then placed in the sample preparation cell of the measuring device using a Pasteur pipette and measured several times. The resulting average values are formed from the individual measurement results. The evaluation of the scattered light signals is carried out according to the Fraunhofer method.

Surprisingly it was noted, that corresponding powder materi als provide the significantly improved reliability with re gard to the structures manufactured utilizing additive manu- facturing. It is assumed that such more homogeneous powder provides a more consistent powder structure when applied as powder bed or even when sprayed onto the surface to be treat ed resulting in an improved process. Typically, it should be expected that such minor deviations of the particle size should make little difference. Also, current processes achieve high-quality results with commonly available materi als. It also seems that many other effects resulting in, for example, deviations from the predefined operating conditions are far greater than the effect of corresponding powder mate rials. Resulting deviations of the final product are current ly corrected by some post processing steps if they are not acceptable to current products. However, newly developed and optimized processing methods significantly decrease such oth er effects resulting in such deviations originating from the powder material becoming dominant. Therefore, it was surpris ingly noted that optimized manufacturing processes like in the 3D printing area, especially when utilizing a powder bed to be melted layer-wise, are suffering from such former low- level problem becoming significant for future applications.

According to a further aspect the present invention refers to a method of additive manufacturing containing the step of manufacturing the product from an inventive powder material or repairing a product utilizing an inventive powder materi al. Especially, it was noted that 3D printing significantly benefits from utilizing such inventive powder material. For example, 3D printing processes utilizing a powder bed to man ufacture structures layer-wise by melting layers of powder material provide a significantly more homogeneous and relia ble process utilizing the inventive powder material.

According to a further aspect the present invention refers to a use of an inventive powder material for additive manufac turing, more preferred 3D-printing.

According to a further aspect the present invention refers to a product manufactured from an inventive powder material or according to an inventive method or repaired utilizing an in ventive powder material or an inventive method.

To simplify understanding of the present invention it is re ferred to the detailed description hereafter and the figures attached as well as their description. Herein, the figures are to be understood being not limiting the scope of the pre sent invention, but disclosing preferred embodiments explain ing the invention further.

Fig. 1 shows a schematic cross-section through a theoreti cal powder layer of the inventive powder material;

Fig. 2 shows a schematic cross-section through a theoreti cal powder layer of a conventional powder material depicting smaller particles included;

Fig. 3 shows a schematic cross-section through a theoreti cal powder layer of a conventional powder material depicting a bigger particle included.

According to one aspect, the present invention refers to a supported product as specified above.

Additive manufacturing methods are well established despite being relatively new. Especially additive manufacturing meth ods like 3D printing became topic for industrial applications in the past years and show a big potential to complement or replace existing conventional methods of manufacturing. The additive manufacturing methods are characterized by that a material is applied without some limiting element like some casting mold to build up the product. Examples of especially useful additive manufacturing methods are selective laser melting, electron beam melting and binder jetting. Such meth ods like, for example, binder jetting build up a product uti lizing a powder material containing a binder, wherein the binder typically is removed in a later step to provide the final product. Very useful for the current application are 3D printing additive manufacturing methods like selective laser melting and electron beam melting building up the product from a powder bed, wherein the powder is melted layer by lay er. By repeating this melting process for each layer of the product the 3-dimensional product is provided.

It was noted that typical embodiments utilize a powder mate rial containing a particle size providing a D50 selected from a specific range. According to further embodiments it is pre ferred that the D50 is selected from the range from 14pm to 53pm, more preferred from 16pm to 51pm, even more preferred from 24pm to 45pm. It was noted that the benefits with regard to the processability of the powder is increased for such particle sizes.

For typical applications like 3D printing processes it was noted that the powder material can be beneficially selected from a certain range. According to further embodiments it is preferred that at least 80 wt.-%, more preferred at least 90 wt.-%, even more preferred at least 95 wt.-%, of the pow der material provides a particle size selected from the range from 12pm to 55pm, more preferred from 15pm to 50pm, even more preferred from 18pm to 46pm. For example, this allows to utilize existing powder material feeding devices including recoaters used to provide a homogeneously distributed powder layer.

Additionally, it was noted that it is typically beneficial to define an upper limit of the particle size. According to fur ther embodiments it is preferred that the powder material provides a particle size of at most 60pm, more preferred at most 57pm, even more preferred at most 52pm. Although, the inventive effects are also observed for bigger particles it was noted that the effect is weaker compared to smaller par ticles. Surprisingly, it was noted that such absolute upper limit of the particle sizes is beneficially combined with the ranges of the particle sizes as specified above. Although, this absolute limit is near the upper limit of the ranges specifying only certain amount of the particles the overall benefit significantly improves when removing the possibility that single very large particles may be included.

To provide products for highly advanced technical fields like the field of continuous flow engines like gas turbines or steam turbines, especially gas turbines, a number of additive manufacturing methods have been well established in the art. Examples are selective laser melting (SLM) or electron beam melting (EBM). Herein, the aforementioned manufacturing meth ods are especially beneficially utilized to provide metallic components of such technical fields. According to further em bodiments it is preferred that the powder material consists of at least 90 wt.-%, more preferred at least 95 wt.-%, even more preferred at least 98 wt.-%, of a metal or a metal al loy. Typically, it is preferred that such metal or metal al loy provides a high temperature resistance. Such metals or metal alloys allow to utilize the inventive powder materials, for example, for the hot path components of continuous flow engines. For example, such metal or metal alloy can be se lected from titanium and nickel superalloys. Especially use ful materials in this context are nickel superalloys. Corre sponding manufacturing methods utilizing such powder material allow to easily realize complex components specifically opti mized to provide improved characteristics. For example, the possibility to provide a highly specific and reliable cooling channel layout inside a component of a continuous flow engine is very beneficial. Surprisingly, it was noted that a signif icant benefit can already be obtained for additive manufac turing processes already utilized in industrial processes. A further significant improvement is expected for optimized processes and conditions not yet implemented on an industrial scale. Nonmetallic components contained in the powder materi al can be, for example, nonmetallic coatings of the particles or binder as utilized for binder jetting.

A further material to be beneficially utilized according to the present invention is a mixture of a ceramic material and a binder material. According to further embodiments it is preferred that the powder material consists of at least 90 wt.-%, more preferred at least 95 weight %, even more pre ferred at least 98 wt.-%, of a combination of a ceramic mate rial and binder. It was noted that such material provides an improved applicability. To provide the inventive powder mate rial it can be necessary in this context to bind the binder material to the surface of the ceramic material as the binder material tends to provide a wider size distribution possible resulting in a segregation depending on the handling. Sur prisingly, it was noted that adapting corresponding powder materials accordingly improves the feeding process and pro cessability as well as stability and reliability of the re sulting structure to fulfill the predefined geometric re quirements. Additional components being no ceramic material or binder can be, for example, metal particle or polymeric materials. For example, it can also be preferred to include materials optimizing the flow properties of the powder mate rial.

According to further embodiments it is preferred that the powder material consists of at least 80 wt.-%, more preferred at least 90 wt.-%, even more preferred at least 95 wt.-%, of a ceramic material. For specific applications like heat shields as utilized in continuous flow engines like gas tur bines, the inventive powder material essentially consisting of ceramic materials provides a significantly improved pro cessability compared to ceramic powder materials not ful filling the requirements of the invention. Especially, the possibility to avoid additional post processing steps that might result in cracks of some ceramic product is highly ben eficial. Additional components besides the ceramic material can be, for example, a binder or a component as mentioned above.

Furthermore, it was noted that establishing the predefined connection of the upper limit and lower limit excluding fin est particles can furthermore be utilized to provide an im- proved effect. According to further embodiments it is pre ^¬ ferred that the powder material provides a Dioo, a Dio and a difference D, wherein the difference D = Dioo - Dio,wherein D is at most 21% of the Diocw more preferred at most 17% of the Diocw even more preferred at most 14%, of the Dioo· Surprising ^¬ ly, it was noted that including such further requirement in ^¬ creases the effect of the powder material while some complex step to remove the finest particles can be neglected. Remov ^¬ ing just finest particles on the other hand was surprisingly less beneficial than expected. Thus, such distribution can easily be realized reducing the cost of providing such powder material while improving its effect.

For certain applications like, for example, selective laser melting or electron beam melting utilizing a powder bed to be melted layer-wise it is typically beneficial to decrease the overall deviation from the mean size. According to further embodiments it is preferred that powder material provides a particle size distribution L being at most 1.9, more pre ^¬ ferred at most 1.5, even more preferred at most 1.2, wherein L is calculated according to formula (I)

L = (Dgo-Dio)/D ₅₀ (I)·

Furthermore, it was noted that for typical embodiments like utilizing nickel superalloys it was even preferred to further narrow down the particle size distribution factor L. Accord ing to further embodiments it is preferred that the particle sizes distribution factor L is at most 0.8, more preferred at most 0.5, even more preferred at most 0.4. It was noted that corresponding powder materials, for example, provide an im proved processability utilizing conventional recoaters.

However, it was further noted that for certain embodiments it was less beneficial to decrease such overall deviation from the mean size below a certain degree. According to further embodiments it is preferred that the powder material provides a particle size distribution factor L being at least 0.08, more preferred at least 0.12, even more preferred at least 0.14, wherein L is calculated according to formula (I)

L - (D ₉₀ -D ₁₀ )/D ₅₀ (I).

Surprisingly, it was noted that the improvements obtained in relation to the effort required to provide such powder mate rial renders certain powder materials less attractive for utilization .

According to further embodiments it is preferred that the powder material provides a particle size distribution fac tor L being selected from the range from 0.08 to 1.9, more preferred from the range from 0.12 to 1.2, even more pre ferred from the range from 0.14 to 0.8, wherein L is calculated according to formula (I)

L - (D ₉₀ -D ₁₀ )/D ₅₀ (I).

For generic powder materials it is typically beneficial to provide an upper limit of bigger particles taking into ac count the mean size of these particles. According to further embodiments it is preferred that at most 5 wt.-%, more pre ferred at most 3 wt.-%, even more preferred at most 2 wt.-%, of the particles provide a particle size being at least 20% higher than the D ₅₀ based on the value of the D ₅₀ . According to specific embodiments it is even preferred that the parti cle size of the aforementioned upper limit of the particles is at least 17%, more preferred at least 15%, from the D ₅₀ . While it was noted that the transport process inside a powder feeding device can surprisingly be positively influenced by an increased amount of bigger particles such relatively de creased amount of bigger particles is surprisingly beneficial for additive manufacturing processes like those manufacturing structures out of a powder bed by layer-wise melting powder bed layers. For certain embodiments to guarantee highest pre cision for such additive manufacturing methods it can even be preferred to reduce the amount of such particles to less than 0.5 wt.-% or even 0 wt.-%.

While the technical teaching as disclosed herein can be ap plied to a broad variety of particles it was noted that it is especially pronounced for spherical particles. According to further embodiments it is preferred that at least 95 wt.-%, even more preferred at least 98 wt.-%, of the particles are essentially spherical. The term "essential spherical" as used herein refers to a shape of the particles, wherein the parti cles provide a surface, a center point and a surface dis tance, wherein the surface distance represents the distance from the center point to the surface, wherein the particle provides a biggest surface distance and a smallest surface distance, wherein the center point is selected to provide the smallest difference between the biggest surface distance and the smallest surface distance, wherein the particle provides a distance from the center point to each point of the surface being less than 10%, more preferred less than 5%, even more preferred less than 3%, differing from the average value of the surface distance, wherein the average value of the sur face distance is the mean value of the highest and lowest surface distance.

According to a further aspect the present invention refers to a method of additive manufacturing, preferably 3D-printing, containing the step of manufacturing a product or repairing a product utilizing an inventive powder material.

Furthermore, it was noted that certain additive manufacturing methods benefit more strongly from the inventive powder mate rials. According to further embodiments it is preferred that the additive manufacturing method utilizes a powder bed of the powder material, wherein the method contains the step of selective melting a part of the powder bed to manufacture or repair the product. Examples of additive manufacturing meth ods that above average benefit from utilizing the inventive powder material are selective laser melting and electron beam melting.

According to a further aspect the present invention refers to a use of an inventive powder material for additive manufac turing, more preferred 3D-printing.

Typically, the inventive powder material is especially bene ficially utilized to manufacture or repair a product. Accord ing to further embodiments it is preferred that a product is manufactured or repaired, more preferred manufactured.

According to a further aspect the present invention refers to a product manufactured from an inventive powder material or according to an inventive method or repaired utilizing an in ventive powder material or repaired according to an inventive method.

For example, the inventive powder material can be beneficial ly utilized to provide a green body to be fused together in a further process step. According to further embodiments it is preferred that the product consists of a multitude of parti cles held together by a binder. This allows to provide a sol id component with flexible geometry by applying a sintering process on said product. Surprisingly, it was noted that de spite effects like sintering shrinkage resulting in a minor change of the form during such post processing step it became possible utilizing the inventive powder material to provide a high accuracy of the shape. In this context, it appears that more reliable predictions of, for example, the sintering shrinkage are possible.

The present invention was only described in further detail for explanatory purposes. However, the invention is not to be understood being limited to these embodiments as they repre sent embodiments providing benefits to solve specific prob lems or fulfilling specific needs. The scope of the protec- tion should be understood to be only limited by the claims attached.

Figure 1 shows a schematic cross-section through a theoreti cal powder layer 2 of an inventive powder material. The pow der layer 2 is located on a surface 3 utilized as base to support the product to be manufactured. Alternatively, the surface 3 could be a part of the product to be repaired. In such case the damaged part is, for example, cut off or grind ed. The additive manufacturing process is utilized to build up a comparable or an improved version of the removed part.

The powder material consisting of a metal alloy provides a very homogeneous size of the particles 1, wherein the parti cles 1 shown provide essentially the same size and a spheri cal shape. Based on the small deviations of the particle size it is possible to provide a very structured layer of the par ticles with very little spaces between them.

As it can be seen in the figure that topmost layer is slight ly displaced resulting in bigger spaces between the middle and the topmost layer. Surprisingly, it was observed that such regular and predictable spaces appearing can be far more easily compensated in case possible cavities might result therefrom. Based on sensors or other indicators it is possi ble to detect such larger scale deviations. In such case, the operating conditions can be adapted to ensure the homogeneous structure of the resulting product.

Utilizing such powder material, for example, in an 3D print ing process like selective laser melting or electron beam melting is especially beneficial. Herein, such layers of the powder material are applied onto a surface and selectively melted to create a 3D object.

Figure 2 shows a schematic cross-section through a theoreti cal powder layer 2 of a conventional powder material depict ing smaller particles 4 included. Contrary to the powder ma- terial of figure 1 a greater number of smaller particles 4' influence the arrangement of the powder particles 1' in the depicted cross-section. The more chaotic arrangement of the particles results in bigger and smaller spaces between the particles possibly leading to cavities. Based on the unpre dictable nature of such arrangement and the singular appear ance of such cavities statistically distributed it is far more complicated to detect such deviations in highly opti mized manufacturing processes and, for example, provide a counter action ensuring a homogeneous structure.

Figure 3 shows a schematic cross-section through a theoreti cal powder layer 2' of a conventional powder material depict ing a bigger particle 5' included. It is assumed that a com parable effect to this depicted theoretical case is occurring in case of even a small number of significantly bigger parti cles 5'. Herein, the spherical particles 1' providing a very homogenous size are not able to provide a high density of the powder layer 2' at certain locations resulting in significant spaces between them. This can result in bigger cavities in cluded in the product reducing its quality or even rendering it unusable. The bigger spaces compared to the smaller parti cles as shown in figure 2 should indicate the observation that a smaller number of big particles apparently disturb the structure of the powder layer 2' more than a comparable amount of smaller particles.

While the theoretical figures as shown in figures 1 to 3 are simplifying the real subject matter to provide an easy under standable explanation it has been noted that the effect seems to be greater than just to be expected from such explanation. It is assumed that additional effects are present currently not identified resulting in the complete improvement observed for the embodiments as described in the description.

The present invention was only described in further detail for explanatory purposes. However, the invention is not to be understood being limited to these embodiments as they repre- sent embodiments providing additional benefits to solve spe cific problems or fulfilling specific needs. The scope of the protection should be understood to be only limited by the claims attached.