WO2016058644A1

WO2016058644A1 - Method of manufacturing bulk metallic glass components

Info

Publication number: WO2016058644A1
Application number: PCT/EP2014/072214
Authority: WO
Inventors: David John JARVIS; Wayne Eric Voice; David John BROWNE; Philip John MEAGHER
Original assignee: European Space Agency
Priority date: 2014-10-16
Filing date: 2014-10-16
Publication date: 2016-04-21

Abstract

The present invention relates to a method of manufacturing a bulk metallic glass component 9. The method comprises providing a template 1, embedding the template 1 in a thermosetting polymer 3 and curing this polymer. The template 1 may e.g. be made by 3D-printing of a plastic material. The template 1 is removed from the cured thermosetting polymer 3 to obtain a mould 4 containing a mould cavity 5. A bulk metallic glass feedstock 7 is heated into the super-cooled liquid temperature region and pressed through an inlet in the mould 4 to plastically flow into and fill the mould cavity 5. After this hot-pressing step, the mould 4 and the bulk metallic glass are cooled, and the thermosetting polymer mould 4 is removed to reveal the thus formed bulk metallic glass component9.A component 9 comprising a coating 11 can be made by, as a part of the process, applying this coating 11 either to the template 1 before embedding or to the mould cavity 5.

Description

METHOD OF MANUFACTURING BULK METALLIC GLASS COMPONENTS

FIELD OF THE INVENTION The present invention relates to a method of manufacturing a bulk metallic g lass component, and in particular a method by which components with complex three- dimensional shape can be made.

BACKGROUND OF THE INVENTION

Miniaturization is a key trend within a number of technological areas includ ing e.g . space applications. Therefore it will be required to be able to produce reliable miniature metallic parts for functional and structural parts. There are only very few techniques available for producing metallic components on a small length scale, and it is very d ifficult to do this with high levels of shape complexity. One option is micro-machining but this is possible only for simple shapes and for certain materials. Another option is micro-casting under high pressure, but this process is d ifficult to control since the high temperatures needed can result in undesired chemical reactions and nucleation within the microstructure. For casting of thin-walled features, often filling of the mould is incomplete - a defect known as misrun . Other disadvantages of micro-casting are that liq uid-to-solid shrinkage often creates porosity and lowers the dimensional stability. Furthermore, there are limitations to both the surface finish and the precision of surface patterning or machining that can be achieved with micro-casting of conventional alloys; this is due to their polycrystalline nature and resultant grain boundary effects.

An alternative has emerged in recent years, which is known as thermoplastic forming of bulk metallic g lasses, BMGs. These special amorphous alloys have no solid ification shrinkage and can be formed plastically within a particular

temperature range, called the super-cooled reg ion, in which the material is a super-cooled liq uid, i .e. a highly viscous liquid and hence thermoplastic.

Recent studies on BMG-forming involves squeezing the alloy in the super-cooled state into a silicon mould that has been etched using lithographic techniques. However, since lithography only allows etching in a vertical direction, the shapes made so far have been rather flat and 2-dimensional. This is acceptable for certain applications, but for other applications more complex 3-dimensional metal micro-parts are necessary.

Hence, an improved method of manufacturing a bulk metallic glass component would be advantageous.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a method of manufacturing a bulk metallic glass (BMG) component by which method small parts can be made with higher levels of shape complexity than with known methods.

It is another object of the invention to provide a method by which BMG

components can be manufactured with high precision with respect to dimensions and surface roughness.

It is an object of some embodiments of the invention to provide a method by which 3-dimensional shapes of BMG components can be made. It is another object of some embodiments of the invention to provide a method by which BMG components comprising one or more at least partly embedded additional elements can be made in one manufacturing process.

It is a further object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a method of manufacturing a BMG component that solves the above mentioned problems of the prior art.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a method of manufacturing a bulk metallic glass component, the method comprising : - providing a template,

- embedding the template in a thermosetting polymer and curing this

polymer,

- removing the template from the cured thermosetting polymer to obtain a mould containing a mould cavity having an inlet extending to an outer surface of the mould,

- heating a bulk metallic glass feedstock into the super-cooled liquid

temperature region,

- pressing the heated bulk metallic glass feedstock through the inlet to

plastically flow into and fill the mould cavity,

- cooling the mould and the bulk metallic glass, and

- removing the thermosetting polymer mould to reveal the thus formed bulk metallic glass component. The shape of the template and the arrangement thereof in relation to the thermosetting polymer into which it is embedded, is so that the mould obtained therefrom has an inlet forming a passage for the bulk metallic glass feedstock, the inlet extending from the mould cavity to the outer surface of the mould. The embedding of the template in the thermosetting polymer is e.g. done by placing the template in a container into which the thermosetting polymer is poured and kept until it has cured. Alternatively, the template can be immersed into un-cured thermosetting polymer contained in a container. The thermosetting polymer material used for the manufacturing may e.g. be an epoxy or a composite of epoxy and Al-powder, but any polymer material that can withstand the temperatures and pressures applied are intended to be covered by the scope of the present invention. The removal of the mould to reveal the bulk metallic glass component can e.g. be done mechanically, such as by cutting and milling . Alternatively or in combination therewith chemical treatment can be used e.g. to soften the thermosetting polymer to ease the removal. It may furthermore be possible to deliberately incorporate weak lines, such as ridges in the surface, into the mould so that it is easier to break into smaller pieces, manually or mechanically. In presently preferred embodiments of the invention, the template may be made from plastic material. However, it can be made by any suitable material which can be removed again in order to form the mould cavity. It can e.g. also be a metal having a low melting point so that it can be removed by heating. The material for the template must be chosen so that it is ensured that the shape and dimensions of the template - and thereby the resulting mould cavity - are not influenced to any detrimental extent by the handling and the embedding. The template may be provided by 3D-printing. This is a commercially available technique by which complex three-dimensional shapes can be made with high precision in respect of both dimensions and surface roughness. The possibility of having complex three-dimensional geometries gives a much larger design freedom compared to what has been possible with known 2D lithographic methods.

In some embodiments of the invention a coating may be applied to the template before embedding in the thermosetting polymer so that the coating becomes a coating of the mould cavity when the template is removed. This coating will then become an outer coating of the manufactured component.

In alternative embodiments, a coating may be applied to the surface of the mould cavity before pressing the heated bulk metallic glass feedstock into the mould cavity. This alternative may be advantageous e.g. for combinations of materials that could include a risk of damaging the coating during removal of the template.

For both ways of obtaining a coating, the coating can e.g. be a metal coating, such as a coating applied by electroless nickel, copper, silver or gold or platinum plating. The methods involving application of a coating can e.g . be used to obtain a component with a coating having a higher surface hardness or electrical properties different from those of the bulk metallic glass itself. It can also be used to ensure a good corrosion resistance. Examples of possible material combinations are a Ce-based BMG coated in platinum for catalytic applications, or coated in silver for biomedical applications. A possible advantage of the application of coatings is that the template may now have an electrically conductive surface, enabling further build-up of a thicker surface coating via conventional electroplating . In the limit, as the coating layers are thickened in such a way they develop strength and may become regarded as the mould itself. Also, the polymer template may be impregnated with carbon black, to yield inherent conductivity which may also enable direct electroplating.

The template may be removed from the mould cavity by dissolving or melting the material from which the template is made. As one among many possible materials can be mentioned that if the template is made from e.g . PVA it can be dissolved in water. Another possible solvent is acetone which can be used for e.g. dissolution of polystyrene. A material useful for a template to be removed after melting, is e.g. a thermoplastic material having a melting temperature low enough to not cause any damage to the surrounding thermosetting polymer.

The bulk metallic glass for use with a method according to the present invention may be selected from the following groups of BMG materials: ETM/Ln-LTM/BM- Al/Ga; ETM/Ln-LTM/BM-Metalloid; AI/Ga-LTM/BM-Metalloid; IIA-ETM/Ln-LTM/BM; LTM/BM-Metalloid; ETM/Ln-LTM/BM; IIA-LTM/BM-Metalloid, where IIA is Alkaline Metal, EMT is Early Transmission Metal (IIIA-VIIA), Ln is Lanthanide Metal, LTM is Late Transition Metal (VII-VIIB), BM is IIIB-IVB Metal (In, Sn, Ti, Pb).

The outer dimensions of the bulk metallic glass component being manufactured in accordance with the present invention may be in the order of micro-meters, mm, or cm. The surface roughness of the bulk metallic glass component being manufactured may be in the order of nano- to micro-meters. The possible dimensions as well as the surface roughness are mainly dependent on the manufacturing technique used to provide the template, such as the capabilities and precision of a 3D-printer in the embodiment described above.

In some embodiments of the invention, one or more templates may be provided and embedded in the thermosetting polymer, the one or more templates being designed and arranged so that the resulting mould cavity has a shape that enables multi-parts of bulk metallic glass components being manufactured concurrently in one mould. Such multi-parts can be intended to be used as such or be distributed to an end-user for later separation . In embod iments where the multi-parts are to be separated into individual parts, they are typically

interconnected by connectors resulting from interconnecting channels between separate mould cavities.

A method as described above may further comprise the step of arranging an additional element in the mould cavity before pressing the heated bulk metallic glass feedstock into the mould cavity thereby at least partly embedding the additional element in the bulk metallic glass. Such an additional element may e.g . be a d iamond or other metal object, such as a screw or bolt, and the resulting component comprising the additional element can e.g . be used for drill bits, or embedded technology.

In a second aspect the invention relates to a bulk metallic glass component manufactured as described above.

In a third aspect the invention relates to the use of a bulk metallic glass

component manufactured as described above for one of the following applications : latch, spring, sensor, resonator, gyroscope, MEM, impeller or biomed ical device.

The first, second and third aspect of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embod iments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

The method of manufacturing a bulk metallic glass component according to the invention will now be described in more detail with regard to the accompanying fig ures. The fig ures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Figure 1 shows schematically and in cross-sectional view the overall steps in the manufacturing method . Figure 2 shows schematically and in cross-sectional view how a coating can be applied to the template resulting in a coating on the outer surface of the component being manufactured .

Figure 3 shows schematically and in cross-sectional view a mould with a bolt protruding into the mould cavity.

Figure 4 shows schematically and in cross-sectional view the manufacturing of multi-part components.

Figure 5 shows an example of a component manufactured by a method according to the present invention . DETAILED DESCRIPTION OF AN EMBODIMENT

The overall steps in a method of manufacturing a bulk metallic glass component according to the present invention are shown schematically and in cross-sectional view in fig ure 1. Figure l .a shows an example of a template 1 comprising an inlet part 2 which is to form the inlet into the mould cavity. Figure l . b shows how the template 1 is embedded in a thermosetting polymer 3 typically contained in an outer mould or container (not shown) in which it is kept during curing of the thermosetting polymer 3. The template 1 is then removed from the cured thermosetting polymer 3 to obtain a mould 4 containing a mould cavity 5 having an inlet 6 extend ing to an outer surface of the mould 4; this is shown in fig ure I .e. Figure l .d shows the step of heating a bulk metallic g lass feedstock 7 into the super-cooled liq uid temperature region, typically by use of a hot-press. Fig ure l .e shows the step of pressing the heated bulk metallic glass feedstock 7 throug h the inlet 6 to plastically flow into and fill the mould cavity 5. These two latter steps are typically done by use of hot-pressing which is a process that in itself will be well known to the person skilled in the art. The process may comprise heating of the mould 4 itself in order to improve the flowability of the BMG inside the mould . The mould 4 and the bulk metallic glass are cooled where after the thermosetting polymer 3 mould is removed to reveal the thus formed bulk metallic g lass component 9 as shown in figure l .f. The inlet part 10 will typically be removed e.g. by cutting and/or machining.

In order to avoid air being trapped inside the mould cavity 5 during the hot- pressing, small microscopic vent channels (not shown) can be made in the mould 4. Such vent channels can e.g. be made by drilling small holes, such as in the order of 0.5 mm in diameter, or by embedding thin wires, made from e.g.

aluminium or copper, in the mould which thin wires are subsequently pulled out again to form the vent channels. Furthermore, the vent channels and easily be incorporated as protrusions of the template, leaving a through-passage to the exterior of the part, when the template is dissolved . Alternatively or in

combination therewith, the process can be done under vacuum which may have the further advantage that undesired oxidation can be avoided . The process parameters used will be dependent on the actual materials being manufactured. The temperature to which the bulk metallic glass feedstock is heated will typically be in the order of 100-700°C, such as in the order of 400- 600°C for the Zr-based BMGs and in the order of 500-700°C for the Fe-based BMGs. The pressure used to press the heated bulk metallic glass feedstock into the mould cavity will typically be in the order of 5-250 MPa depending on the features of the part being manufactured, the operating temperature, and the heating method. Which parameters to use for a given application can be determined e.g . by experimentation or computer simulations or a combination thereof.

In some embodiments of the invention, the template 1 is made from plastic material which has been made into the desired shape by 3D-printing. However, other ways of providing the template 1 are also covered by the present invention; some of these have been described above.

For some applications it will be advantageous to manufacture the component to comprise a coating on at least a part of the outer surface. This can e.g. be done as shown schematically in figure 2. Such a coating could e.g. be applied to make a component having a surface layer with high corrosion resistance, biocompatibility, increased hardness, low friction, improved electrical conductivity etc. Figure 2. a shows the template 1 having a coating 11 applied to the outer surface. The thickness of the coating 11 shown in the figure is exaggerated compared to a real thickness which would typically be in the order of 1-100 microns; this

exaggeration of the thickness is for illustrative purposes only. In principle any relevant coating thickness can be used within the scope of the present invention. Figure 2.b shows the template 1 with the coating 11 embedded in the

thermosetting polymer 3, and figure 2.c shows the resulting mould 4 after removal of the template 1. As shown, the initial coating 11 of the template 1 becomes a coating 11 of the mould cavity 5 when the template 1 is removed. The following steps of pressing bulk metallic glass feedstock 7 into the mould cavity 5 are as in figure 1. Figure 2.d shows the resulting component 9 having the coating 11 on the whole of the outer surface. It may also be relevant for some

components 9 to cover only a part of the outer surface. An alternative to the method shown in figure 2 would be to apply the coating 11 to the surface of the mould cavity 5 after removal of the template 1 and before pressing the heated bulk metallic glass feedstock 7 into the mould cavity 5. This would resemble figure 2.c and the following steps would be as described above and resulting in the component 9 as shown in figure 2.d. Which of the two alternative methods of applying a coating 11 that is most appropriate would depend on e.g. the material combinations and the geometries. The purpose of having a coating 11 on the inner surface of the mould cavity 5 could also be to lower the frictional forces acting on the metallic glass feedstock 7 during filling of the mould cavity 5. It can also be used to prevent adhesion of the mould material to the sample, to improve heat transfer (faster cooling of samples, less risk of crystallisation), or to reduce the risk of damaging fine sections of the part while removing the mould material mechanically (arrests crack propagation).

The removal of the template 1 from the mould cavity 5 can e.g. be done by dissolving or melting the plastic material from which the template 5 is made as described above.

A method as described above can be used for the manufacturing of a large number of components. Some examples are sensors, resonators, gyroscopes, MEMs, or impellers. These are examples of components that can take advantage of the combination of complex shapes and high dimensional tolerances which is obtainable with methods according to the present invention. They may also take advantage of the possibility of having an outer coating providing e.g. high corrosion resistance, electrical conductivity or high surface roughness.

Some typical outer dimensions of the bulk metallic glass component being manufactured are in the order of micro-meters, mm, or cm. For high precision components, the surface roughness may be in the order of nano- to micro-meters. In some embodiments of the invention an additional element is embedded into the bulk metallic glass component. This can be obtained by arranging an additional element in the mould cavity before pressing the heated bulk metallic glass feedstock into the mould cavity thereby at least partly embedding the additional element in the bulk metallic glass. Figure 3 shows schematically and in cross-sectional view a mould 4 with a bolt 12 sticking into the mould cavity 5. As the BMG alloy feedstock 7 is then squeezed into the mould cavity 5, it envelopes and forms around the bolt 12. Thus, the bolt 12 is now embedded as part of the resulting BMG component 9 in a multi-material manner. Examples of applications for such an embodiment are sensors and MEMs. This bolt 12 is an example of an additional element which is embedded into the bulk metallic glass component 9.

A possible embodiment of the invention is to use the method for manufacturing multi-parts of bulk metallic glass components concurrently in one mould. This can be done by arranging and embedding one or more templates 1 in the

thermosetting polymer 3, the one or more templates 1 being designed and arranged so that the resulting mould cavity 5 has a shape that enables multi-parts to be manufactured. An example is shown schematically in figure 4 showing schematically the manufacturing of a multi-part having six cross-shaped parts. Figure 5 shows an example of a component 9 which has been made by a method as described above. The BMG composition is: Ce57.5% Cu22.5% AI10% Fel0%. The processing temperature used for the hot-pressing was 150°C. At this temperature, the viscosity of this BMG is of the order of 1 x 10^6 Pa-s, and the time until crystallisation is about 600s. The pressure to achieve mould filling is about 125 MPa. Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention . Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. Method of manufacturing a bulk metallic glass component (9), the method comprising :

- providing a template (1),

- embedding the template (1) in a thermosetting polymer (3) and curing this polymer,

- removing the template (1) from the cured thermosetting polymer (3) to obtain a mould (4) containing a mould cavity (5) having an inlet (6) extending to an outer surface of the mould (4),

- heating a bulk metallic glass feedstock (7) into the super-cooled liquid temperature region,

- pressing the heated bulk metallic glass feedstock (7) through the inlet (6) to plastically flow into and fill the mould cavity (5),

- cooling the mould (4) and the bulk metallic glass, and

- removing the thermosetting polymer mould (4) to reveal the thus formed bulk metallic glass component (9).

2. Method according to claim 1, wherein the template (1) is made from plastic material.

3. Method according to claim 1 or 2, wherein the template (1) is provided by 3D- printing.

4. Method according to any of the preceding claims, wherein a coating (11) is applied to the template (1) before embedding in the thermosetting polymer (3) so that the coating (11) becomes a coating (11) of the mould cavity (5) when the template (1) is removed.

5. Method according to any of claims 1 to 3, wherein a coating (11) is applied to the surface of the mould cavity (5) before pressing the heated bulk metallic glass feedstock (7) into the mould cavity (5).

6. Method according to any of the preceding claims, wherein the template (1) is removed from the mould cavity (5) by dissolving or melting the plastic material from which the template (1) is made.

7. Method according to any of the preceding claims, wherein the bulk metallic glass is selected from the following groups of BMG materials: ETM/Ln-LTM/BM- Al/Ga; ETM/Ln-LTM/BM-Metalloid; AI/Ga-LTM/BM-Metalloid; IIA-ETM/Ln-LTM/BM; LTM/BM-Metalloid; ETM/Ln-LTM/BM; IIA-LTM/BM-Metalloid, where IIA is Alkaline Metal, EMT is Early Transmission Metal (IIIA-VIIA), Ln is Lanthanide Metal, LTM is Late Transition Metal (VII-VIIB), BM is IIIB-IVB Metal (In, Sn, Ti, Pb).

8. Method according to any of the preceding claims, wherein the outer dimensions of the bulk metallic glass component (9) being manufactured are in the order of micro-meters, mm, or cm.

9. Method according to any of the preceding claims, wherein the surface roughness of the bulk metallic glass component (9) being manufactured is in the order of nano- to micro-meters.

10. Method according to any of the preceding claims, wherein one or more templates (1) are provided and embedded in the thermosetting polymer (3), the one or more templates (1) being designed and arranged so that the resulting mould cavity (5) has a shape that enables multi-parts of bulk metallic glass components (9) being manufactured concurrently in one mould (4).

11. Method according to any of the preceding claims further comprising the step of arranging an additional element (12) in the mould cavity (5) before pressing the heated bulk metallic glass feedstock (7) into the mould cavity (5) thereby at least partly embedding the additional element (12) in the bulk metallic glass.

12. A bulk metallic glass component (9) manufactured by any of the preceding claims.

13. Use of a bulk metallic glass component (9) manufactured by any of the preceding claims for one of the following applications: latch, spring, sensor, resonator, gyroscope, MEM, impeller or biomedical device.