Structure with enamelled coating and method of forming same

Abstract

The present disclosure provides structures with enamelled coatings and methods of forming the same. In particular, methods of forming an enamelled coating on a structure made of a metal matrix composite (MMC) are provided. In some embodiments, the method includes providing a structure formed from an MMC, the MMC having a given coefficient of thermal expansion (CTE). An enamel mixture is formed to include a glass material and a pigment material, and the materials are selected to produce a mixture having a substantially similar CTE. The surface of the MMC structure is coated with an enamel mixture, and then the structure is heated to melt the enamel mixture. After the heat treatment, the heated coated MMC structure is cooled, thereby obtaining a glass enameling coating having a color corresponding to the selected pigment.

Description

Technical Field

[0001] The present disclosure relates to structures having enameled coatings and methods of forming the same. Background Art

[0002] Many types of electronic devices are portable, "handheld" mobile devices. In order to protect the electronic, communication and display components of such devices, the device's housing (e.g., chassis, case, housing, etc.) should be designed to be strong and resilient, as well as thin and light.

[0003] Designing an attractive and durable, yet thin and light enclosure often results in a compromise such that one or more desired characteristics do not achieve the expected performance. Thus, there is a need for an enclosure design that combines durability in a thin, light, and aesthetically pleasing package.

[0004] The presently disclosed subject matter is directed to avoiding the disadvantages of the above-mentioned problems. Summary of the invention

[0005] According to the present disclosure, a method for forming an enameled coating on a structure made of a metal matrix composite (MMC) is provided. In some instances, the method includes providing a structure formed by an MMC having a given coefficient of thermal expansion (CTE). An enamel mixture is formed to include a glass frit material and a pigment material, and the material is selected to produce a mixture having a substantially similar CTE. The surface of the MMC structure is coated with the enamel mixture, and then the structure is heated to melt and bond the enamel mixture. After the heat treatment, the heated coated MMC structure is cooled to obtain a glass enameled coating having a color corresponding to the selected pigment.

[0006] The needs of conventional methods are addressed by the methods and apparatus of the present invention, which relate to MMC structures (eg, housings for electronic devices), and more particularly to components of MMC structures coated with glass enameling coatings.

[0007] These and other features of the present disclosure will become more fully apparent from the following description and appended claims, as set forth hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to further clarify the above and other features of the present disclosure, a more particular description of the subject matter will be presented by reference to specific embodiments thereof, which are shown in the accompanying drawings. It should be understood that these drawings depict only some embodiments of the subject matter and therefore should not be considered to limit the scope thereof.

[0009] Figure 1 A table listing material options for an electronic device housing application according to aspects of the present disclosure is shown.

[0010] FIG. 2A to FIG. 2E An exemplary anodized substrate according to the present disclosure is shown.

[0011] Figure 3A An exemplary glass enameling technique applied to an MMC substrate according to aspects of the present disclosure is shown.

[0012] Figure 3B An exemplary MMC substrate with a glass enameling coating according to aspects of the present disclosure is shown, wherein there is a CTE mismatch between the MMC and the glass enameling coating.

[0013] Figure 4A A table of exemplary enamel mixture compositions for glass enameling MMC substrates according to aspects of the present disclosure is provided.

[0014] Figure 4B and Figure 4C An embodiment of an MMC housing having an enameled coating according to aspects of the present disclosure is shown.

[0015] Figure 5A An MMC substrate having an exposed surface according to aspects of the present disclosure is shown, and Figure 5B Shown after application of the enamel mixture and heat treatment Figure 5A MMC substrate.

[0016] Figure 6 is a flow chart representing an exemplary method 100 for enamel coating an MMC according to aspects of the present disclosure.

[0017] These figures are not necessarily drawn to scale. Where appropriate, similar or identical reference numerals are used to refer to similar or identical components. DETAILED DESCRIPTION

[0018] A method for forming an enameling coating on a structure made of a metal matrix composite (MMC) is provided.

[0019] Go to Figure 1, a table listing various material options for electronic enclosure applications is shown. As shown, light grey boxes represent favorable values, black boxes represent less favorable values, and medium grey boxes represent intermediate values. The material options considered include stainless steel, aluminum, magnesium, titanium, Al / SiC-55p MMC, and Al / Al2O3-50p MMC. The material properties considered are the material's mass (g / cc), stiffness, ductility, strength, hardness (relative to other materials), CTE, thermal conductivity, and cost (relative to other materials).

[0020] It may be desirable to use MMC in consumer devices, for example, to limit the bendability of the frame (e.g., increase rigidity) while remaining light and thin. A measure of the stiffness of a material is provided by Young's modulus, which is expressed in Pascals (Pa) or Newtons / m 2 (In higher magnitudes, defined as Gigapascals - GPa or kilonewtons / mm 2 ) measurement. For the purposes of this disclosure, a Young's modulus of the order of 125 GPa provides a sufficiently rigid structural framework for device structures. Some exemplary materials considered meet or exceed this standard, such as Al / SiC-55p MMC. Al / SiC MMC exhibits a density similar to aluminum, but with increased stiffness. Many different processes can be used to form Al / SiC materials, such as, but not limited to, die-casting, extrusion, forging, thixoforming, power metallurgy, etc.

[0021] In some cases, a structural element (e.g., a frame) can be used to protect the electrical contents of a consumer electronic device from mechanical damage (e.g., from bending, impact, etc.). Steel is an option for such a structural frame because it exhibits high stiffness. However, steel also has a high density, which results in high component quality. Aluminum is also an attractive material, having a significantly lower density than steel. However, aluminum exhibits low relative stiffness, which can result in bending. For example, bending electronic components can result in catastrophic damage, making preventing bending a primary goal of the structure.

[0022] In addition to the need for lightweight, durable structures, various consumer electronic devices, and particularly military equipment, benefit from structures that provide the desired stiffness / strength for a variety of environmental factors, but are lighter in weight than structures made from steel or other high-strength materials.

[0023] For similar chassis applications, titanium has attractive properties, however titanium has a high relative cost. Stainless steel has a high quality, which may be less attractive for small portable devices. Aluminum and magnesium both exhibit low stiffness values. Thus, MMCs offer a favorable combination of physical properties while being easily customized for specific applications.

[0024] In some embodiments, results of the disclosed techniques and applications are shown using Al / SiC. As shown, Al / SiC has a relatively low mass, providing a desired light frame. The stiffness is relatively high, the thermal conductivity is also relatively high, and the CTE is relatively low. Despite the challenges in relative ductility and strength, Al / SiC remains an attractive candidate material for such devices.

[0025] like Figure 1 As shown in , Al2O3 materials are cheaper than Al, which may reduce the blending cost of MMC. SiC particles are more expensive than Al, which may increase the mixing cost of MMC. However, these favorable properties can make these materials a good choice for some applications.

[0026] As used herein, metal matrix composite (MMC) is a material with at least two components-one is metal and the other is ceramic or organic compound (and / or different types of metals). MMC is made by dispersing reinforcement into a metal matrix. In some exemplary MMCs, carbon fiber is used as a reinforcement used with an aluminum matrix, producing a composite material showing low density and high strength. In another embodiment, MMC is made of aluminum (Al) impregnated with ceramic particles such as silicon carbide to form Al / SiC MMC. In certain embodiments, aluminum oxide can be used to form Al / Al2O MMC. Depending on the metal (matrix) type, reinforcement chemistry, reinforcement shape (e.g., particles, fibers, whiskers, etc.) and the ratio between the two components, a series of useful properties can be designed. Advantageously, the performance / characteristics of MMC can be customized for desired density, stiffness, ductility (elongation), strength, machinability and / or thermal behavior.

[0027] A variety of different MMCs can be used with the disclosed technology, and the scope of the present disclosure is not limited to any particular material or class of materials. The metal matrix can be reinforced with any acceptable type of carbon fiber, ceramic fiber, or ceramic, where the selected reinforcement type (and percentage) will result in an MMC with specific properties in terms of stiffness and strength.

[0028] In the disclosed embodiments, the MMC is described in terms of a material content that includes a first metallic material (e.g., aluminum, steel, titanium, magnesium alloy) and a second reinforcing material (e.g., SiC, Al2O4 and / or B4C) present in a second amount (e.g., up to about 55%).

[0029] For consumer applications such as portable electronic devices (e.g., mobile phones, tablets, etc.), it is desirable to obtain MMC parts in a variety of colors. Anodizing technology is relatively inexpensive and can provide a variety of color finishes for aluminum, magnesium or titanium materials. However, when used on MMC, anodizing produces a dull, matte and unattractive surface finish. Turning now to the drawings, FIG. 2A to FIG. 2E Some of the challenges of manufacturing anodized structures are shown. FIG. 2A to FIG. 2E Images representing substrates (e.g., housings) of various compositions utilizing anodization are shown. However, each figure shows a discontinuity in the application of anodization. The figures represent aluminum substrate 6061A1; and MMC substrates Al / SiC-55p, Al / Al2O3-50p, Al / Al2O3-30p, and Al / Al2O3-25p, respectively.

[0030] In one embodiment, anodizing a housing made of substantially pure Al produces a smooth red surface (e.g., Figure 2A However, each MMC substrate develops a matte (e.g., rough, damaged) finish. In some embodiments, the anodized layer grows at locations on the surface that substantially expose Al, but not at locations with other particle types. For example, Figure 2B The Al / SiC embodiments do not maintain color (eg, turn gray), and the MMC substrates containing Al / Al2O3 do accept color, but the color is less vivid as the enhancement concentration increases (which may be desirable for durability and coating fidelity).

[0031] A challenge in enameling MMC is that the coefficient of thermal expansion (CTE) of the coating material (e.g., glass) should substantially match the CTE of the MMC substrate material. If there is a significant difference between the CTE of the coating material and the MMC substrate material, the coating tends to separate from the MMC substrate during cooling from the thermal treatment due to the different shrinkage of the materials. In order to better match the CTE between the materials, two or more components (provided as melts) can be batched together to produce an enamel mixture or slurry having a CTE equal to or substantially similar to the CTE of the MMC substrate material.

[0032] Advantageously, the disclosed method can produce structures having one or more colors while having the mechanical and thermal advantages of MMC structures. In some cases, glass enameling can provide enhanced coloring and coating effects compared to other techniques (e.g., anodizing). For consumer applications such as electronic mobile devices, the ability to color structural parts with a wide range of colors may be attractive to manufacturers and consumers.

[0033] In order to provide many desired properties on MMC substrates, glass enameling can be applied to consumer products such as phone chassis. Chassis for mobile phones are currently made of aluminum (Al), however, MMC provides the opportunity to produce lighter, thinner and stronger chassis. The challenge for this application of MMC is that even though Al can be easily anodized to produce products of many colors, anodization is not effective for MMC.

[0034] As explained above, MMC housings exhibit a combination of desirable properties for personal device frames, including low mass (similar to aluminum) and high stiffness (similar to steel). However, MMCs with aluminum as the primary component and reinforced with SiC or Al2O3 content present challenges in maintaining consistent and attractive coatings. Although some exemplary MMC housings are shown and described as single rectangles, various other geometric shapes and / or topologies for MMC structural elements can be used for applications seeking to increase the rigidity and / or strength of the structure (e.g., useful for industrial or military applications).

[0035] Figure 3A 2 shows an exemplary glass enameling technique disclosed herein for use on an MMC substrate. Figure 3A As shown, an enamel mixture / paste 12 of glass powder is applied to the surface of the MMC substrate 10A. The slurry 12 includes a mixture of one or more frits (e.g., pigment frit 14 and glass frit 16). As shown, the MMC substrate 10A is coated with the slurry 12 and heated by a heat treatment 18 to melt the frit, producing a glass coating 20 on the MMC substrate 10B. Although Figure 3A Two material types are shown in the embodiment of FIG, but three, four, five, six, seven, eight, nine, ten or more material types may be included in the slurry (eg, as a melt).

[0036] In some embodiments, the slurry 12 can be designed to produce a transparent or translucent coating after firing (e.g., heat treatment 18). In this way, the slurry 12 can include a glass frit 16 or a combination of glass materials so that the resulting glass coating 20 is substantially transparent while providing a protective layer on the MMC substrate 10B. However, if desired, a pigment frit 14 can be added to the slurry 12 to produce a colored coating. In one embodiment, a certain amount of red pigment (e.g., about 10wt% of the slurry) is added to the mixture as a pigment frit 14 to produce a red glass coating 20.

[0037] In some embodiments, two or more different non-pigmented glass frits 16 are used (e.g., to form a glass material). An advantage of using two or more different glass frits is that glass frits having different CTE values ​​can be selected that collectively approximate the desired CTE and firing temperature for use with a selected substrate. For example, some frits may be sold along with a description of their CTE and firing temperature (with a label in the table below). Figure 4A ). However, each melt may have a different chemical composition to achieve these properties. Therefore, combining melts with different properties can produce the desired effect, including the incorporation of the pigments disclosed herein.

[0038] However, as explained herein, combining pigments with glass enameling materials can result in cracked and delaminated coatings if the CTE between the enameling material and the MMC substrate is not matched. Figure 3B As shown in the example of , the color may be unevenly distributed on the surface of the MMC frame, thereby showing crack lines and poorly bonded coatings.

[0039] As disclosed herein, if the material used in the enamel mixture has a CTE that does not substantially match the CTE of the MMC substrate, delamination may occur during cooling. As provided, the CTE of the melt mixture can be customized by mixing one or more melts together, or even using different melts with different CTEs.

[0040] During the enameling process, the coated MMC is fired at a specific temperature designed to melt the melt, thereby allowing the coating material to adhere to the MMC substrate. The temperature is selected to be lower than the solidus temperature of the MMC substrate material (e.g., alloy) to avoid melting the MMC.

[0041] In an exemplary MMC substrate formed from a SiC-reinforced Al alloy, the high Si content in the alloy sets the solidus temperature at about 577° C., which may be lower than the solidus temperature of a typical Al alloy. Therefore, the melt must be selected to produce an enamel mixture having a firing temperature lower than the solidus temperature of the SiC-reinforced Al alloy.

[0042] As disclosed herein, a coating can be applied to one or more surfaces of a structure treated with the MMC enameling technique by the following steps: 1) applying an enamel mixture or slurry (e.g., containing glass frit and pigment) to the surface of the structure, and 2) heat treating (e.g., firing) the structure in a furnace.

[0043] Figure 4A A table of exemplary enamel mixture compositions disclosed herein for glass enameling MMC substrates is provided. As shown, the MMC substrate is provided with a SiC / Al content of approximately 55%. The MMC substrate has a CTE of approximately 11 and a maximum temperature of approximately 577°C.

[0044] The enamel mixture is composed of melt A and melt B at concentrations of about 33% and 67%, respectively. Melt A corresponds to a CTE of about 9.3 and a firing temperature of about 500°C, while melt B corresponds to a CTE of about 12.5 and a firing temperature of about 560°C. When combined in the enamel mixture in the percentages shown, the resulting CTE is about 11.4 and the firing temperature is about 540°C.

[0045] As explained herein, there is a significant similarity between the CTE of the substrate and the melt mixture. For example, the melt mixture CTE is within a threshold difference (less than 5%, but can be less than 1%, 10%, 15%, 20% or any other amount to achieve the desired result). In addition, the firing temperature of the melt mixture is lower than the maximum temperature of the MMC substrate.

[0046] Figure 4B and Figure 4C 2 shows an embodiment of an MMC housing 30A and 30B with an enameled coating disclosed herein. Each of the MMC housings is an aluminum alloy with a SiC component. As shown, Figure 4B The MMC housing 30A has an upper portion 32A and a lower portion 34A, the upper portion 32A being treated with a glass enamel mixture having 10% pigment, and the lower portion 34A being free of pigment. Figure 4C The MMC housing 30B has an upper portion 32B and a lower portion 34B, the upper portion 32B being treated with a glass enamel mixture having 10% pigment, and the lower portion 34B being free of pigment.

[0047] Figure 4B and Figure 4CThe difference in the finishes between the MMC shells 30A is derived from the heat treatment time. As provided, the MMC shell 30A is treated in a specific treatment environment (e.g., ambient air) for a relatively short amount of time (e.g., 5 minutes). The MMC shell 30B is treated in a similar treatment environment for a relatively long amount of time (e.g., 20 minutes). The relatively dark appearance of the upper portion 32B of the MMC shell 30B shows a darker color relative to the upper portion 32A of the MMC shell 30A. This is a result of the extended heat treatment time of the MMC shell 30B, which allows more time for the molten enamel mixture to produce a richer color.

[0048] Figure 5A An MMC substrate with an exposed surface is shown. Figure 5B The MMC substrate after applying an enamel mixture (e.g., including glass frit and pigment frit) and heat treating on the MMC substrate is shown. As shown, a substantially consistent glass coating is obtained, showing a rich and durable color. In particular, the constituent materials of the enamel mixture are selected so that the CTE of the frit combination is substantially matched to the CTE of the MMC substrate. Therefore, compared with other technologies, the veneer glass coating is less likely to delaminate during the cooling process.

[0049] Figure 5A and Figure 5B The MMC substrate shown in can be used in consumer applications such as mobile electronic devices. The ability to color device housing parts with a wide range of colors is an attractive prospect for manufacturers and consumers. The disclosed technology and coating can be used in consumer applications where the aesthetics of the parts are important features.

[0050] Furthermore, in some embodiments, the glass enameling applied to the MMC housing provides a wear and / or corrosion resistant coating in addition to providing color.

[0051] Figure 6 1 is a flow chart representing an exemplary method 100 for enamel coating MMC according to the present disclosure. In box 102, an MMC (e.g., AlSiC-55p) is selected. In box 104, the CTE of the selected MMC is determined. In box 106, a coating material for the enamel mixture is selected. For example, the type of material (e.g., glass, pigment, etc.) is selected. In the absence of a pigment frit, a separate glass frit produces a transparent or translucent coating after heat treatment. However, a colored coating can be achieved by adding a pigment frit to the enamel mixture. In addition, the coating material (and the enamel mixture) is selected to ensure that the firing temperature is lower than the solidus temperature of the MMC to avoid damaging the MMC substrate.

[0052] At block 108, the amount of each of the coating materials is determined. For example, the CTE of the enamel mixture should be within a threshold range of the CTE of the selected MMC. Thus, the amount of coating materials (e.g., two or more provided as multiple frits) is determined to produce a suitable CTE. At block 110, the enamel mixture (which may include the coating materials in a medium (e.g., water)) is applied to one or more surfaces of the MMC.

[0053] In box 112, the coated MMC is subjected to a heat treatment to melt the enamel mixture. For example, the temperature, treatment duration and / or treatment environment conditions can be determined to achieve the desired result. As disclosed herein, the coated MMC can be heated in an ambient air environment at a temperature of up to 600°C for 5 to 20 minutes or longer. For example, some enameled coatings benefit from a longer heating time to ensure that the glass frit is completely or almost completely melted, resulting in better coloring. In box 114, the coated MMC is cooled, thereby providing a durable colored coating for the underlying material.

[0054] In some embodiments, the coated MMC is subjected to one or more additional surface treatments to enhance the protective or aesthetic properties of the finish product.

[0055] In a disclosed embodiment, a method for forming an enameled coating on a structure made of a metal matrix composite (MMC) is provided, the method comprising providing a structure formed of MMC; forming an enamel mixture having one or more glass materials and zero or more pigment materials; coating the enamel mixture on a surface of the MMC structure; heating the coated MMC structure to melt the enamel mixture; and cooling the heated coated MMC structure to obtain a glass enameled coating.

[0056] In some embodiments, the MMC of the MMC structure comprises a first CTE. In some embodiments, the glass material comprises a second CTE. The pigment material comprises a third CTE.

[0057] In an embodiment, the method further comprises selecting a ratio of glass material to pigment material to obtain an enamel mixture having a first CTE. In an embodiment, the method further comprises selecting the MMC from Al / SiC or Al / Al2O3.

[0058] In some embodiments, forming the enamel mixture includes mixing a glass frit of a glass material and a pigment frit of a pigment material with a liquid medium.

[0059] In some disclosed embodiments, a method for forming an enameled coating on a structure made of a metal matrix composite (MMC) is provided, the method comprising providing a structure formed of an MMC structure having an MMC, the MMC having a first coefficient of thermal expansion (CTE); forming an enamel mixture having a second CTE similar to the first CTE; coating the enamel mixture on a surface of the MMC structure; heating the coated MMC structure to melt the enamel mixture; and cooling the heated coated MMC structure to obtain a glass enameled coating.

[0060] In some embodiments, the value of the second CTE is within 10% of the value of the first CTE. In an embodiment, the enamel mixture includes a glass material having a third CTE and a pigment material having a fourth CTE, and the second CTE is different from the third CTE and the fourth CTE. In an embodiment, the enamel mixture includes approximately two-thirds glass material and one-third pigment material.

[0061] In some embodiments, the heating is performed in a furnace at a temperature greater than 500° C. In an embodiment, the method further comprises selecting the MMC from Al / SiC or Al / Al 2 O 3 .

[0062] In some disclosed embodiments, a structure with an enameled coating is provided. The structure includes a structural frame formed by an MMC containing metal and ceramic or an organic compound; and an enameled coating on the surface of the MMC, the enameled coating comprising a coating material and a pigment material.

[0063] In some embodiments, the coating material is a glass or ceramic material, and the pigment material is a colored dye. In an embodiment, the MMC has a first CTE and the enameled coating has a CTE substantially similar to the first CTE.

[0064] In some embodiments, the MMC includes Al / SiC or Al / Al2O3.

[0065] In an embodiment, the Young's modulus value of the MMC is greater than 125 GPa.

[0066] Without limitation, the following is a list of specific advantages and features of the present disclosure.

[0067] In the drawings, similar features are indicated by the same reference numerals throughout.

[0068] The above description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concept conceived by the applicant. It should be understood that, with the beneficial effects of the present disclosure, the features described above according to any embodiment or aspect of the disclosed subject matter can be used alone or in combination with any other described features in any other embodiment or aspect of the disclosed subject matter.

Claims

1. A method for forming an enameling coating on a structure made of a metal matrix composite (MMC), the method comprising: providing a structure formed from the MMC; forming an enamel mixture having one or more glass materials and zero or more pigment materials; coating the enamel mixture on the surface of the MMC structure; heating the coated MMC structure to melt the enamel mixture; as well as The heated coated MMC structure is cooled to obtain a glass enameled coating.

2. The method of claim 1, further comprising selecting an MMC of the MMC structure having a first coefficient of thermal expansion (CTE). 3 . The method of claim 2 , further comprising selecting a first glass material having a second CTE. The method of claim 3 , further comprising selecting a second glass material having a third CTE.

5. The method of claim 1, further comprising selecting a ratio of the glass material and the pigment material to provide the enamel mixture with a first CTE.

6. The method of claim 1, further comprising selecting the MMC from Al / SiC or Al / Al2O3.

7. The method according to claim 1, wherein: Forming the enamel mixture includes mixing a glass frit of the glass material and a pigment frit of the pigment material with a liquid medium.

8. A method of forming an enameling coating on a structure made of a metal matrix composite (MMC), the method comprising: providing a structure formed of an MMC structure having an MMC having a first coefficient of thermal expansion (CTE); forming an enamel mixture having a second CTE similar to the first CTE; coating the enamel mixture on the surface of the MMC structure; heating the coated MMC structure to melt the enamel mixture; as well as The heated coated MMC structure is cooled to obtain a glass enameled coating.

9. The method according to claim 8, wherein: The value of the second CTE is within 10% of the value of the first CTE.

10. The method according to claim 8, wherein: The enamel mixture includes a glass material having a third CTE and a pigment material having a fourth CTE, the second CTE being different from the third CTE and the fourth CTE.

11. The method according to claim 10, wherein: The enamel mixture includes approximately two thirds of one frit material and one third of another frit material.

12. The method according to claim 8, wherein: The heating is performed in a furnace at a temperature greater than 500°C.

13. The method of claim 8, further comprising selecting the MMC from Al / SiC or Al / Al2O3.

14. A structure having an enameled coating, comprising: A structural framework formed of a metal matrix composite (MMC) comprising a metal and a ceramic or organic compound; as well as The enameled coating on the surface of MMC comprises a coating material and a pigment material.

15. The structure according to claim 14, wherein: The structure is a housing for an electronic consumer device.

16. The structure according to claim 15, wherein: The coating material is a glass or ceramic material and the pigment material is a colored dye.

17. The structure of claim 15, wherein: The MMC has a first coefficient of thermal expansion (CTE), and the enameled coating has a CTE substantially similar to the first CTE.

18. The structure of claim 15, wherein: The MMC includes one or more of aluminum or aluminum alloys.

19. The structure of claim 18, wherein: The MMC includes Al / SiC or Al / Al2O3.

20. The structure of claim 15, wherein: The Young's modulus value of the MMC is greater than 125 GPa.

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