Field of Invention

The field of the invention relates to a method for preparing a magnesium composite material. The field of the invention further relates to a magnesium composite material obtainable from the method according to the present invention.

Background

A light metal material providing a relatively high strength, such as tensile strength or bending strength, may be based on using aluminum and titanium composite structures. Light metal composite structures may be constructed by conventional forging or casting methods, by extrusion using powder metallurgy methods, by powder metallurgy methods such as powder bed methods, and laser or electron beam methods.

Many light metals are based on an aluminum alloy, which comprises one or more additional alloy components, such as silicon (Si), scandium (Sc), copper (Cu), magnesium (Mg), nickel (Ni), iron (Fe), vanadium (V), titanium (Ti), zirconium (Zr), ytterbium (Y), manganese (Mn), hafnium (HI), niobium (Nb), tantalum (Ta) or mixtures thereof. Other light metals may be based on a titanium alloy, which comprises one or more additional alloy components selected from the group consisting of aluminum (Al), vanadium (V) or mixtures thereof.

However, the known light metal aluminum alloys and the titanium alloys have inadequate strength values. Therefore, a desire exists to provide a composite material which would have improved strength properties in comparison with traditional light metal materials.

Moreover, a desire exists to provide a method for preparing the composite material which would have improved strength properties in comparison with traditional light metal materials.

Summary

According to a first aspect of the invention there is provided a method for preparing a magnesium composite material, the method comprising the steps of:

a. Providing:

i. a graphene platelets powder;

ii. a nano titanium powder (N);

iii. a magnesium silicide powder; and

iv. another titanium powder (M, L); b. Mixing the components i. and ii., preferably under inert atmospheric conditions, to obtain a graphene titanium conglomerate;

c. Mixing the graphene titanium conglomerate with the components iii. and iv.;

d. Processing the mixture of step c. under inert atmospheric conditions by:

i. Heating the mixture up to a target temperature (Tt), wherein the target temperature (Tt) is in the range of 780 - 1050 °C, while applying a pressure (Pi) to the mixture in the range of 0 - 10 MPa;

ii. Keeping the mixture at the target temperature (Tt) while applying a target pressure (Pt) to the mixture in the range of 50 - 200 MPa in order to form the magnesium composite material; and

iii. Letting the temperature decrease to room temperature.

According to another aspect of the invention there is provided a magnesium composite material obtainable from the method according to the present invention, wherein the magnesium composite material has a density in the range 2.0 - 2.3 kg/m3, preferably 2.1 - 2.2 kg/m3.

In an exemplary embodiment, the nano titanium powder ii. has a particle size in the range 1 nm - 500 nm, preferably in the range 10 nm - 50 nm.

In an exemplary embodiment, the step of providing said other titanium powder iv. comprises the steps of providing a first titanium powder part (M) having a mean particle size in the range 1 - 10 pm and providing a second titanium powder part (L) having a mean particle size in the range 10 - 50 pm.

In an exemplary embodiment, a ratio between the mean particle size of the first titanium powder part (M) and the mean particle size of the second titanium powder part (L) is between 1 : 1 and 1 : 6, preferably between 1 : 2 and 1 : 4, more preferably about 1 : 3.

In an exemplary embodiment, a ratio between a mean particle size of the magnesium silicide powder (iii.) and a mean particle size of the first titanium powder part (M) provided in step a. and mixed in step c. is between 10 : 1 and 16 : 1, preferably between 12 : 1 and 14 : 1, more preferably about 13 : 1.

In an exemplary embodiment, the graphene platelets powder (i.) has a mean value of a longest particle dimension in the range 1 - 10 pm, preferably 1 - 5 pm. In an exemplary embodiment, a ratio between a mean particle size of the magnesium silicide powder (iii.) and a mean value of a longest particle dimension of the graphene platelets powder (i.) provided in step a. and mixed in step c. is between 20 : 1 and 32 : 1, preferably between 24 : 1 and 28 : 1 , more preferably about 26 : 1.

In an exemplary embodiment, the graphene platelets comprise a graphene laminate structure having a stack of graphene layers of between 10 and 30 sheets.

In an exemplary embodiment, in step a the amount of the magnesium silicide powder (iii.) is 60.0 - 99.5 vol. %, preferably 67.8 - 99.0 vol. %, based on the total volume of the components i. - iv.

In an exemplary embodiment, in step a the amount of the graphene platelets powder (i.) is 0.5 - 20.0 vol. %, preferably 1.0 - 16.1 vol. %, based on the total volume of the components i. - iv.

In an exemplary embodiment, in step a the amount of the titanium powder (iv.) is 8.0 - 35.0 vol.

%, preferably 16.2 - 32.4 vol. %, based on the total volume of the components i. - iv.

In an exemplary embodiment, in step b the volume ratio of the graphene platelet pow'der i. to the nano titanium powder (N) ii. is 60 to 99 vol. % based on the total volume of the graphene platelet powder i. and the nano titanium powder (N) ii..

In an exemplary embodiment, in step d. and/or in step b. the inert atmospheric conditions are provided by using a protective gas comprising at least one of Argon and SF6.

In an exemplary embodiment, step dii. is performed during a time in the range of 10 - 120 minutes.

In an exemplary embodiment, step dii. is performed using a spark plasma sintering process.

In another aspect of the invention, a method is provided for preparing a magnesium composite material, the method comprising the steps of:

a. Providing:

i. a graphene platelets powder;

ii. a nano titanium powder (N);

iii. a magnesium silicide powder; and

iv. another titanium powder (L); b. Mixing the components i. and ii., preferably under inert atmospheric conditions, to obtain a graphene titanium conglomerate;

c. Mixing the graphene titanium conglomerate with the other titanium powder iv.;

d. Processing the mixture of step c. using an additive manufacturing process, wherein a three- dimensional titanium-graphene structure is formed by applying a laser beam to the mixture, wherein the three-dimensional titanium-graphene structure has pores; and

e. Processing the titanium-graphene structure under inert atmospheric conditions (in the essential absence of oxygen), comprising the steps of:

i. Heating the titanium-graphene structure to a target temperature (Tc) 1000 - 1500 °C; and ii. Melting the magnesium silicide i. and applying the molten magnesium silicide to the titanium-graphene structure at the target temperature to fill the pores of the titanium-graphene structure; and

iii. Letting the temperature decrease to room temperature.

According to another aspect of the invention there is provided a magnesium composite material obtainable from the method according to the present invention, w'herein the magnesium composite material has a density in the range 2.0 - 2.3 kg/ni3, preferably 2.1 - 2.2 kg/ni3.

In an exemplary embodiment, the three-dimensional titanium-graphene structure is made in step d. by at least one of a selective laser melting or a selective laser sintering induced by the laser beam.

In an exemplary embodiment, in step eii. the magnesium silicide is casted into pores of the three- dimensional titanium-graphene structure.

In an exemplary embodiment, step d. comprises layerwdse forming the three-dimensional titanium- graphene structure, wherein each layer is formed by stepwise forming a layer of the mixture and locally applying a laser beam to the layer to induce a selective laser melting of the layer.

In an exemplary embodiment, step d. comprises forming the titanium-graphene structure having 60.0 - 99 vol. % porosity, preferably having 83.8 - 98.4 vol. % porosity.

In an exemplary embodiment, the pores formed in step d. have a pore dimension in the range of 100 microns to 1200 microns, preferably in the range of 128 microns to 1024 microns .

In an exemplary embodiment, the pores formed in step d. have a cross section shape being at least one of a hexagonal, circular and cubical. In an exemplary embodiment, the magnesium composite material provided in step a. comprises graphene platelets having a mean longest dimension of on average 1 - 10 pm, preferably 1 - 5 pm.

In an exemplary embodiment, the graphene platelets comprise a graphene laminate structure having a stack of graphene layers of between 10 and 30 sheets.

In an exemplary embodiment, in step a the amount of the magnesium silicide powder (iii.) is 60.0 - 99.5 vol. %, preferably 67.8 - 99.0 vol. %, based on the total volume of the components i. - iv.

In an exemplary embodiment, in step c. the inert atmospheric conditions are provided by using a protective gas comprising at least one of Argon and SF6.

In another aspect of the invention a magnesium composite material obtainable from a method according to the invention, wherein the magnesium composite material has a density in the range 2.0 - 2.3 kg/m3, preferably 2.1 - 2.2 kg/m3.

In an exemplary embodiment, the magnesium composite material comprises graphene platelets having a mean longest dimension of 1 - 10 pm, preferably 1 - 5 pm.

In an exemplary embodiment, the magnesium composite material comprises a plurality of graphene domains, each graphene domain containing graphene platelets and titanium, preferably the graphene domain consisting essentially of graphene platelets and titanium., wherein preferably the graphene domain has a domain size of at least 1 pm.

In another aspect of the invention, a method is provided for preparing a graphene titanium conglomerate as intermediate for a magnesium composite material, the method comprising the steps of:

a. Providing:

i. a graphene platelets powder;

ii. a nano titanium powder (N);

b. Mixing the components i. and ii. under inert atmospheric conditions to obtain a graphene titanium conglomerate.

The graphene titanium conglomerate is an intermediate, which can be used to form a magnesium composite material based on the graphene titanium conglomerate. In an exemplary embodiment, the nano titanium powder ii. has a particle size in the range 1 nm - 500 nm, preferably in the range 10 nm - 50 nm.

In an exemplary embodiment, the graphene platelets powder (i.) has a mean value of a longest particle dimension in the range 1 - 10 pm, preferably 1 - 5 pm.

In an exemplary embodiment, the graphene platelets comprise a graphene laminate structure having a stack of graphene layers of between 10 and 30 sheets.

In an exemplary embodiment, in step b the volume ratio of the graphene platelet powder i. to the nano titanium powder (N) ii. is 60 to 99 vol. % based on the total volume of the graphene platelet powder i. and the nano titanium powder (N) ii..

The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates schematically a flow diagram of an embodiment of a method for preparing a magnesium composite material;

FIG. 2 illustrates schematically a stacking of components after step S30 of the embodiment of the method according to the flow' diagram of FIG. 1 ;

FIG. 3 illustrates schematically a flow diagram of another embodiment of a method for preparing a magnesium composite material;

FIG. 4 illustrates schematically a cross section of a three-dimensional titanium-graphene structure obtained in step SI 30 of the embodiment of the method according to the flow diagram of FIG. 3; and

FIG. 5 illustrates schematically a perspective view' of a three-dimensional titanium-graphene structure obtained in step SI 30 of the embodiment of the method according to the flow diagram of FIG. 3.

Description of embodiments

Raw Materials Magnesium Silicide (Mg ₂ Si) powder (MGS)

Purity > 99.7%

Particle size: 3- 10 mm

Density: 1.99 g/cm ³

Titanium Powder type (TV)

Purity > 99.8%

Size: 10 - 50 nm

Density: 4.5 g/cm’

Titanium powder type (M)

Purity > 99.8%

Size: 2 - 10 mhi

Density: 4.5 g/cm ³

Spherical powder

Titanium powder type (L)

Purity > 99.8%

Size: 10 - 50 pm

Density: 4.5 g/cm ³

Spherical powder

Graphene Nano Platelets ( GNP1 ) powder

Thickness: 5 - 10 nm

Density: 2.0 - 2.2 g/cm’

Surface area: 300-500 m ² /g

Length: 1 - 5 pm

Measuring methods

A particle size of a powder can be determined with known measurement techniques for determining a particle size. For a particle having a size in a nanometer range, the particle size of the primary particles can be determined by using a TEM technique.

For a particle having a size in a micrometer range, the particle size of primary particles can be determined by using a known laser diffraction technique. The laser diffraction technique may be used to determine a Particle Size Distribution D50, which is also known as median diameter or medium value of particle size distribution; it is the value of the particle diameter at 50% in the cumulative distribution.

Length of graphene platelet particles. A length of graphene platelet particles can be determined using SEM techniques. A length of graphene platelet particles is typically a longest dimension of the graphene platelet particles.

Density can be determined using known techniques for powders.

The volume % of a powder in a mixture can be determined based on a weight % of the powder and the predetermined or known density of the powder.

Porosity of a structure can be determined using known techniques to determine the porosity (expressed in volume %) of a porous structure, such as direct techniques using known densities, optical techniques, or immersion techniques to absorb an amount of fluid into the pores.

Pore size of pores in a structure can be determined by making a cross section of the structure and using SEM or optical microscopic techniques to determine the pore size.

FIG. 1 illustrates schematically a flow diagram of an embodiment of a method for preparing a magnesium composite material.

In step S 10 Mg ₂ Si powder (MGS) is ball-milled under Ar atmosphere using zirconia balls at a weight ratio of between 10:1 to 15: 1 and a ball-milling speed of 200-300 rpm for a predetermined time to reduce a particle size of the Mg ₂ Si powder to a desired particle size. The desired particle size Mg ₂ Si powder is in the range 0.1 mm - 1.0 mm. The predetermined time lies in the range 1-5 hr. After the step S10, the particle size of the Mg ₂ Si powder is in the range 0.1 mm - 1.0 mm.

In step S20 a Graphene Nano platelet powder (GNPl) is ball-milled with titanium Nano powder (N) using a planetary ball mill (zirconia balls) in ethanol and under Ar atmosphere at a ball-milling speed of 300 - 700 rpm for 2- 12 h. The volume ratio of the Graphene Nano platelet powder was 60 to 99 vol. % based on the total volume of the Graphene Nano platelet powder and the titanium Nano powder (N). The ball-to-powder weight ratio is between 10 : 1 to 15 : 1. The mixture is then dried in an oven at 120 °C under Ar atmosphere to obtain a graphene titanium conglomerate (TDG) wherein the graphene is decorated with the titanium. In step S30 a composite powder mixture is formed by mixing 0.5 - 20.0 vol. %, preferably 1.6 - 16.2 vol. % of graphene titanium conglomerate (TDG) with 60.0 - 99.5 vol. %, preferably 67.6 - 99.0 vol. %, of the Mg ₂ Si powder obtained in step S 10, and 8.0- 35.0 vol. %, preferably 16.2 - 32.4 vol. % of titanium powder type ((L) +type (M)) of which 40 to 65 vol.% is Type (L) and of which 35 to 60 to vol.% is Type (M). The mixing is carried out in a rotary mixer for 2-24 h.

A preferred powder particle size ratio of Mg ₂ Si powder to titanium powder type (L) and type (M) is 13/3/1. A preferred powder particle size ratio of titanium type (M) powder to graphene titanium conglomerate (TDG) powder is 2/1.

Possible powder particle ratios to produce a functional composite are not limited to what is mentioned above.

Step S10 is optional.In case the Mg ₂ Si powder already is provided in the desired particle size (0.1 mm - 1.0 mm), step S30 may be carried out using said Mg ₂ Si powder without performing step S10.

FIG. 2 illustrates schematically a stacking of components in the powder mixture after the mixing step S30 of the embodiment of the method according to the flow diagram of FIG. 1. The components in the mixture are Mg ₂ Si particles 10, titanium particles 20 and graphene platelet particles 30. Preferably, the graphene platelet particles 30 are the graphene titanium conglomerate (TDG) particles obtained in step S20. The titanium particles 20 are interposed to Mg ₂ Si particles 10. The graphene titanium conglomerate (TDG) particles 30 are arranged adjacent to the titanium particles 20.

In step S40 the composite pow'der mixture of step S30 is heated under protective gas (90 % Argon + 10 % SF6), and a pre-pressure in the range of 0-10 MPa up to a target temperature in the range of 780-1050 °C.

In step S50, when the mixture reaches the target temperature at the end of step S40, the compaction load increases from 0-10 MPa to a pressure in the range 50-200 MPa and the mixture will be kept at that condition for 10-120 minutes to obtain a consolidated composite.

In step S60 the composite will be slowly cooled down (furnace cooled) to room temperature.

The obtained magnesium composite material, which is obtained by the method of FIG. 1 has a density in the range 2.0 - 2.3 kg/m3, preferably 2.1 - 2.2 kg/m3.

Additionally, obtained the magnesium composite material comprises graphene platelets, which are on average 1 - 10 pm long, preferably 1 - 5 pm long. Additionally, the magnesium composite material comprises a plurality of graphene domains, each graphene domain containing graphene platelets and titanium, wherein the graphene domain consists essentially of graphene platelets and titanium, i.e. more than 90 vol% of the graphene domains is based on the graphene platelets and titanium. The graphene domains may have a domain size of at least 1 pm.

In particular, the graphene platelets in the magnesium composite material are predominantly encapsulated in a titanium phase.

FIG. 3 illustrates schematically a flow diagram of another embodiment of a method for preparing a magnesium composite material.

In step S120 a Graphene Nano platelet powder (GNP1) is bail-milled with titanium Nano powder (N) using a planetary ball mill (zirconia balls) in ethanol and under Ar atmosphere at a ball-milling speed of 300 - 700 rpm for 2- 12 h. The volume ratio of the Graphene Nano platelet powder was 60 to 99 vol. % based on the total volume of the Graphene Nano platelet powder and the titanium Nano powder (N). The ball-to-powder weight ratio is between 10 : 1 to 15 : 1. The mixture is then dried in an oven at 120 °C under Ar atmosphere to obtain a graphene titanium conglomerate (TDG) wherein the graphene is decorated with the titanium.

In step S 130 a composite powder mixture is formed by mixing 0.5 - 20.0 vol. %, preferably 1.6 - 16.2 vol. % of graphene titanium conglomerate (TDG) with titanium powder type (L) in a rotary mixer for 2-24 h.

In step S 130 the prepared mixture of step S30 of Ti type (L) + TDG is 3D printed using selective laser melting process or a selective sintering process to form a three-dimensional titanium- graphene structure. A selective laser melting (SLM) process is a known process, which uses a laser beam to locally melt the powder mixture. A selective laser sintering (SLS) process is a known process, which uses a laser beam to locally sinter the powder mixture.

Step S130 comprises layerwise forming the three-dimensional titanium-graphene structure, wherein each layer is formed by stepwise forming a layer of the mixture and locally applying a laser beam to the layer to induce a selective laser melting of the layer.

The titanium-graphene structure formed in step S30 has pores having a sponge-like structure, i.e. the pores are in fluid communication to one another. The titanium-graphene structure has a 60 - 99 % porosity. The pore sizes are in the range from 100 microns to 1000 microns. The pore structure can take various forms, including but not limited to hexagonal, circular or cubical. FIG. 4 illustrates schematically a cross section of a three-dimensional titanium-graphene structure obtained in step S I 30 of the embodiment of the method according to the flow diagram of FIG. 3. In FIG. 4 a three-dimensional titanium-graphene structure 110 is shown, which has pores having a cubical cross section.

In step S 140 Subsequently, the 3D printed titanium-graphene structure (Ti-GNP mesh) is placed in a crucible and heated to 1100-1200 °C under protective gas (90% Argon +10% SF6.

In step SI 50 where molten Mg ₂ Si (MGS) is casted into the titanium-graphene structure (Ti-GNP mesh) to fill the pores of the titanium-graphene structure (Ti-GNP mesh). In FIG. 4 also the three- dimensional titanium-graphene structure 110b is shown, which has been processed in step S150, wherein the pores are filed with Mg ₂ Si 120.

In step S 160 the furnace is cooled to room temperature.

The obtained magnesium composite material, which is obtained by the method of FIG. 3 has a density in the range 2.0 - 2.3 kg/m3, preferably 2.1 - 2.2 kg/m3.

Additionally, obtained the magnesium composite material comprises graphene platelets, which are on average 1 - 10 pm long, preferably 1 - 5 pm long.

Additionally, the magnesium composite material comprises a plurality of graphene domains, each graphene domain containing graphene platelets and titanium, wherein the graphene domain consists essentially of graphene platelets and titanium, i.e. more than 90 vol% of the graphene domains is based on the graphene platelets and titanium. The graphene domains may have a domain size of at least 1 pm.

In particular, the graphene platelets in the magnesium composite material are predominantly encapsulated in a titanium phase.

FIG. 5 illustrates schematically a flow diagram of an embodiment of a method for preparing a graphene titanium conglomerate (TDG). The graphene titanium conglomerate (TDG) is prepared according to step S20 of the method shown in FIG. I or according to step SI 20 of the method shown in FIG.3.

In the method the Graphene Nano platelet powder (GNP1) 210 is ball-milled with titanium Nano powder (N) 220 using a planetary ball mill (zirconia balls) in ethanol and under Ar atmosphere at a ball-milling speed of 300 - 700 rpm for 2- 12 h. The volume ratio of the Graphene Nano platelet powder was 60 to 99 vol. % based on the total volume of the Graphene Nano platelet powder and the titanium Nano powder (N). The ball-to-powder weight ratio is between 10 : 1 to 15 : 1. The mixture is then dried in an oven at 120 °C under Ar atmosphere to obtain a graphene titanium conglomerate (TDG) 230 wherein the graphene is decorated with the titanium. It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative units or modules embodying the principles of the invention.

Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.