Mixing material rotating system and manufacturing method

Abstract

Rotary systems including multiple interconnected rotating elements such as gears or traction rollers are provided, and more particularly, rotary systems in which the interconnected rotating elements are configured to have a longer operational life. The rotary systems can be planetary rotary systems including a central sun element, an outer or ring element, and two or more planetary elements interconnected between the sun element and the outer or ring element. The rotating elements within the system can be formed of materials that interact to allow for extended operational life and / or operation in extreme environments or without lubrication. The multiple elements can be formed of hybrid materials having different hardness and modulus properties, including steel and bulk metallic glasses.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Provisional Application No. 63 / 582,933, filed September 15, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This disclosure describes a rotating system, and more particularly, a gear, a gearbox, and a traction drive that include a hybrid rotating component, the hybrid rotating component being a combination of a crystalline metal component and a bulk metallic glass rotating component. Background Technology

[0004] Rotating systems (such as gearboxes and traction drives) are mechanisms commonly used to transfer energy from an input to an output. They typically utilize a set of interconnected rotating elements, such as gears or rollers. In many cases, these systems operate to change input / output speeds (e.g., rotational speed) and / or torque. Rotating systems can also be used to change the direction of energy transfer. One type of gearbox and traction drive is a planetary system, which consists of three parts: a sun element, several planetary elements, and outer or ring elements. The system operates on the principle of having a central element around which the other elements rotate. The central element, located at the center of the planetary system, is called the "sun element." In most cases, it is the input element. The outer elements consist of two or more outer elements or "planetary elements." The outer ring elements surround the planetary elements and hold the entire system together. The planetary elements are connected to each other via planetary carriers. The planetary system is connected to an output shaft. The planetary elements contact the outer ring elements and the sun element, thereby generating rotation. A gap is set when the carriers hold the planetary elements in their basic form. Summary of the Invention

[0005] Embodiments of this disclosure relate to rotating systems, and more particularly to gears, gearboxes, and traction drive devices comprising hybrid rotating components, said hybrid rotating components comprising a combination of crystalline metal components and bulk metallic glass rotating components.

[0006] Many embodiments of this disclosure may relate to gears and gearboxes, and more particularly, to gears and gearboxes comprising hybrid components, said hybrid components comprising a combination of crystalline metallic components and bulk metallic glass components.

[0007] Various embodiments may also relate to traction drive devices and traction drive device components, and more particularly, to traction drive devices and components comprising a combination of crystalline metal rotating components and bulk metal glass rotating components.

[0008] Many embodiments of this disclosure relate to an apparatus comprising: a solar element made of a first material having a first modulus; a plurality of planetary elements made of a second material having a second modulus; and a ring element; wherein the solar element and the ring element are coaxial with an axis, and each of the plurality of planetary elements is disposed between the solar element and the ring element; wherein the solar element and each of the plurality of planetary elements engage at a first interface and transmit motion therebetween, and each of the plurality of planetary elements and the ring element engage at a second interface; and wherein at least one of the first material and the second material is a bulk metallic glass, and the first modulus and the second modulus are not equal.

[0009] In some embodiments, the solar element wears out at a rate proportional to the number of planetary elements.

[0010] In some embodiments, the first and second materials are selected such that the first and second moduli are proportional to the rate, such that the wear of the solar element and each of the planetary elements is approximately symmetrical.

[0011] In some embodiments, the second material has a lower modulus than the first material, and the device is further configured to minimize contact stress at the first interface.

[0012] In some embodiments, the solar element and the plurality of planetary elements are configured as gears having a plurality of gear teeth, and the device is further configured to balance the wear of the plurality of gear teeth.

[0013] In some embodiments, the hardness and modulus of the solar element are higher than those of each of the plurality of planetary elements.

[0014] In some embodiments, the device further includes an annular element, wherein the first rotating element is configured to rotate about an axis, and the annular element is coaxially disposed with the first rotating element, and the second rotating element is disposed between the first rotating element and the annular element.

[0015] In some embodiments, at least one of the first material or the second material is a steel alloy.

[0016] In some embodiments, the device is configured to operate at a temperature higher than a set temperature.

[0017] In some embodiments, at least one of the plurality of planetary elements and the solar element further includes a third material at the contact surface.

[0018] In some embodiments, the third material is an oxide or a ceramic.

[0019] Many embodiments of this disclosure relate to an apparatus comprising: a first rotating element made of a first material and having a first surface rotating at a first speed; and a second rotating element made of a second material and having a second surface rotating at a second speed; wherein the first surface and the second surface are made of different materials and are joined at a mixed material interface to transmit motion; wherein the first rotating element rotates in a first cycle period, the second rotating element rotates in a second cycle period, and the first cycle period is different from the second cycle period; and wherein at least one of the first material and the second material is a bulk metallic glass.

[0020] In some embodiments, the first speed and the second speed are different.

[0021] In some embodiments, the first rotating element and the second rotating element are configured as gears.

[0022] In some embodiments, the first material and the second material are different.

[0023] In some embodiments, the first material and the second material are selected for desired properties, which are selected from the group consisting of service life, operating environment, hardness, or modulus.

[0024] In some embodiments, the first cycle period is longer than the second cycle period, and the first material is selected for a modulus higher than that of the second material.

[0025] In some embodiments, the modulus is selected for low contact stress at the interface of the hybrid materials.

[0026] In some embodiments, the device is configured as a traction drive.

[0027] In some embodiments, the first rotating element wears at a first wear rate, the second rotating element wears at a second wear rate, and the first wear rate and the second wear rate are not equal.

[0028] In some embodiments, the modulus of the first material is selected to be proportional to the first wear rate, and the modulus of the second material is selected to be proportional to the second wear rate.

[0029] In some embodiments, the device is configured such that the wear of the first rotating element and the second rotating element is approximately symmetrical.

[0030] In some embodiments, the first surface and the second surface are configured to engage without lubrication.

[0031] In some embodiments, the first surface comprises a third material that is harder than the first material.

[0032] In some embodiments, the third material is an oxide or a ceramic.

[0033] In some embodiments, the oxide is formed by heating the first rotating element to approximately the glass transition temperature of the first material.

[0034] Various embodiments of this disclosure relate to a method of manufacturing an apparatus, the method comprising: selecting a first rotating element made of a first material having a first modulus; selecting a second rotating element made of a second material having a second modulus; wherein the first material and the second material are different, and at least one of the first material and the second material is a bulk metallic glass; arranging the first rotating element and the second rotating element to engage at an interface such that rotation of the first rotating element transmits motion to the second rotating element; and wherein the first rotating element wears at a first rate, the second rotating element wears at a second rate, and the wear of the first rotating element and the second rotating element is approximately symmetrical.

[0035] In some embodiments, the method further includes heating the first rotating element to the glass transition temperature of the first material, thereby forming a third material on the surface of the first rotating element.

[0036] In some embodiments, the method further includes selecting an annular element and arranging the annular element such that the annular element engages with the second rotating element, and the second rotating element is disposed between the first rotating element and the annular element.

[0037] In some embodiments, the first material or the second material is a steel alloy.

[0038] In some embodiments, the second material has a lower modulus than the first material, and the first and second rotating elements are arranged to minimize contact stress.

[0039] Further embodiments and features are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon review of the specification or may be learned by practice of the disclosed subject matter. The nature and advantages of this disclosure can be further understood by reference to the remainder of the specification and the accompanying drawings, which form part of this disclosure. Attached Figure Description

[0040] These and other features and advantages of the invention will be better understood when considered in conjunction with the accompanying data and drawings, and by referring to the following detailed description, in which:

[0041] Figure 1 provides a schematic diagram of a planetary gearbox according to the prior art.

[0042] Figures 2A and 2B provide schematic diagrams of planetary gearboxes according to the prior art.

[0043] Figure 3 Data are provided on the results of life tests conducted at room temperature on conventional steel gearboxes and gearboxes made of bulk metallic glass (BMG) materials and steel / BMG hybrid materials, according to embodiments of the present disclosure.

[0044] Figures 4A to 4F provide images of embodiments of the sun gear and planetary gears after testing in an experiment designed to generate... Figure 3 The data summarized in the article.

[0045] Figure 5 Data are provided on the results of life tests conducted at low temperatures on conventional steel gearboxes and gearboxes made of BMG material and steel / BMG hybrid materials, according to embodiments of the present disclosure.

[0046] Figures 6A to 6D provide images of embodiments of the sun gear and planetary gears after testing in an experiment designed to generate... Figure 5 The data summarized in the article.

[0047] Figures 7A to 7D provide schematic diagrams of various gear elements according to the prior art.

[0048] Figure 8 provides a schematic diagram of a non-realistic traction drive device according to the prior art.

[0049] Figure 9 provides a schematic diagram of a planetary traction drive device according to the prior art.

[0050] Figure 10 A disassembled gearbox is depicted according to some embodiments of the present disclosure.

[0051] Figure 11 The performance of BMG alloy planetary gears at room temperature is described according to some embodiments of the present disclosure.

[0052] Figure 12 The performance of BMG alloy planetary gears according to some embodiments of the present disclosure at low temperature is described.

[0053] Figure 13 The present disclosure describes the contact stresses experienced by COTS steel sun gear material and various planetary gear materials according to some embodiments. Detailed Implementation

[0054] The embodiments of the invention described herein are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Rather, these embodiments were chosen to enable those skilled in the art to practice the invention. All structural and functional equivalents of the elements of the disclosed embodiments, known to those skilled in the art, are expressly incorporated herein by reference and are intended to be covered by the claims of the invention. Furthermore, no element, component, or method step in this disclosure is intended to be offered to the public, whether or not such element, component, or method step is expressly recited in the claims.

[0055] Many embodiments of this disclosure relate to mechanical systems in which multiple rotating elements engage to contact each other in order to transmit rotational motion between them, and more particularly to rotating systems in which at least one element is placed under greater stress during operation. Various embodiments relate to systems in which the rotating elements are gears, such as gearboxes comprising multiple interlocking gears, and more particularly to gearboxes and gears configured to have a longer service life. In many embodiments, the gearbox is a planetary gear type, comprising a central sun gear, an outer or ring gear, and two or more planetary gears interlocked between the sun gear and the outer or ring gear. In other embodiments, the gears can be bevel gears, worm gears, and helical gears. Embodiments can include any pair of gears that rotate against each other, where the wear strain of one gear in the pair is greater than that of the other. Embodiments can also relate to non-gear rotating systems, such as traction drives.

[0056] Regardless of the specific nature of the rotating elements, the embodiments all include rotating systems in which the wear of the rotating elements is unequal. Therefore, embodiments implement a mixture of materials in the rotating elements to balance the wear of the elements. Various embodiments include gears formed from materials selected to allow for extended service life and / or operation in extreme environments or without lubrication. In many such embodiments, multiple categories of gears are formed from materials with different hardness and modulus properties. Various embodiments implement lower modulus materials (e.g., bulk metallic glass (BMG)) in the rotating elements: the rotating element has fewer cycles and a lower wear rate compared to the mating elements. In some exemplary hybrid planetary gearbox embodiments, the planetary gears may be formed from a lower hardness / lower modulus material, and the sun gear may be formed from a higher hardness / higher modulus material. In some such hybrid embodiments, the material with higher hardness / higher modulus can be steel, while the material with lower hardness / lower modulus can be BMG. In other embodiments, it should be understood that hybrid embodiments can comprise bulk metallic glass with different hardness / modulus, provided that the rotating element (multiple rotating elements) undergoing the highest number of cycles has a higher modulus, thereby reducing the contact stress between the high-cycle rotating element (multiple rotating elements) and other low-cycle rotating elements (multiple rotating elements). The embodiments also relate to methods of manufacturing such gearboxes.

[0057] The precision gear industry typically focuses on the mass production of steel gears. Within the broader industry, several sub-sectors specialize in precision gears, including robotics, medical devices, automotive, food service, drones / unmanned aerial vehicles, and aerospace. Precision gear manufacturing can be both time-consuming and expensive, with some top-tier, high-demand products experiencing long lead times. Several key drivers exist across these market segments. In the automotive market, the driver is the need for cost reduction; in the aerospace market, it's the need for customized, lightweight solutions. In the commercial aerospace, medical robotics, food service, and food manufacturing markets, performance requirements exist, such as the need to operate under cryogenic and unlubricated conditions.

[0058] While there is interest in unlubricated gearboxes that can operate in extreme environments, conventional steel gears suffer severe wear under unlubricated conditions. Furthermore, although current steel manufacturing methods for steel gears (machining, heat treatment, shot peening, superfinishing, electropolishing, and hard coatings (DLC, nitriding)) allow for extremely high power density transmission gears, the manufacturing and delivery cycles are very long, and some gear system applications do not require high power density. In many applications using existing steel gear technologies, the long delivery cycles actually add unnecessary weight and system complexity to the space platform. The Young's modulus of steel (approximately 200 GPa) and Poisson's ratio (approximately 0.30) result in high contact stresses on the gear tooth surfaces, necessitating wet lubrication so that the steel gear tooth surfaces can roll and slide against each other without scuffing and wear. At low temperatures, typical wet gear lubricants become extremely viscous and unsuitable for use as circulating lubricants (the most common wet lubricants in the aerospace and space industries are based on perfluorinated oils and greases and are rated for temperatures no lower than -70°C; they are also sensitive to contact pressure and decompose on steel surfaces). This necessitates heating the entire gearbox in a space environment, increasing system complexity, weight, and significant power consumption. An alternative to wet lubricants is the use of sputtered MoS2 as a dry lubricant; however, dry lubricants are also sensitive to contact stress and can be completely scraped off the gear teeth after only a fraction of the gear's typical lifespan.

[0059] Focusing on specific examples of space applications, operating in conditions on planetary bodies such as comets, asteroids, Mars, the Moon, and icy moons requires technologies that can operate over a wide temperature range (including cryogenic temperatures), have low density to reduce spacecraft mass, require lower power by eliminating the need for heating, and can operate in vacuum or abrasive conditions. Typical gearboxes used in planetary robotics applications are steel gearboxes that are heated to prevent the liquid lubricant from solidifying. For example, the Mars rovers Perseverance and Curiosity both used wet-lubricated steel gearboxes in their drive motors, which required significant heat to maintain the lubricant at the appropriate operating temperature. Smaller gearboxes (such as the one powering the Ingenuity helicopter) are typically heated using motors but require daily solar charging to operate. In future planetary missions, such as those to asteroids or icy moons, robotic systems will be limited by mass and power, driving the need for non-steel actuators that can operate without lubricants. However, in these conventional gearboxes, when the lubricant is removed, the gearbox fails completely after fewer than a few thousand output cycles, even with torque less than half of its rated torque under lubricated conditions on Earth. Therefore, this disclosure aims to eliminate this undesirable weight, system complexity, and low cycle life by finding gear materials that can provide precise motion under extreme conditions, such as in cryogenic vacuum or without lubrication.

[0060] Embodiments of this disclosure relate to hybrid gearboxes with improved wear characteristics. In various embodiments, such gearboxes are capable of operating under extreme conditions, such as in unlubricated and low-temperature operations. Many embodiments relate to planetary gearboxes comprising a central sun gear that rotates about a central axis and is interlocked with one or more planetary gears, the planetary gears being disposed between the sun gear and annular or outer gears. An exemplary planetary gearbox is shown in Figure 1. Although two planetary gears are shown in Figure 1, it should be understood that any number of planetary gears can be used in such a gearbox, for example, three or four planetary gears as shown in Figures 2A and 2B. Embodiments utilize combinations of materials to provide gearboxes with improved service life under extreme conditions, such as extreme temperatures, pressures, and unlubricated applications. Embodiments of this disclosure consider optimal gear geometry, wear surfaces, wear mechanisms, selection of suitable materials for pins and bearings, and center distance to mitigate thermal expansion mismatch. The embodiments of this disclosure utilize combinations of materials with different hardness / modulus properties to significantly improve the service life and conditions of gearboxes, specifically, combinations of different steels, combinations of different BMGs, and combinations of steel and BMGs.

[0061] Figure 3Data on unlubricated life tests are provided for conventional all-steel gearboxes, gearboxes made of BMG gears manufactured according to embodiments of the invention, and hybrid gearboxes made of a combination of steel and BMG. Planetary gearbox tests are performed under conditions of 25°C, 225 RPM, and loads of 1 Nm, 1.5 Nm, and 2 Nm, according to the procedures given in exemplary embodiments. In such embodiments, it should be understood that the number of wear interactions experienced by the sun gear per revolution is several times that of any single planetary gear. More specifically, in the tests, data are provided for conventional gearboxes made of all-steel interlocking gears, gearboxes made of BMG gears (e.g., Cu) according to embodiments of the invention, and gearboxes made of BMG gears (e.g., Cu). 43 Zr 43 The test was conducted on a gearbox formed of Al7Be7, and a hybrid gearbox comprising both steel gear elements and BMG gear elements (e.g., BMG based on copper, nickel, titanium, zirconium, etc.) according to embodiments of the present invention.

[0062] Figures 4A through 4F illustrate the state of the planetary and sun gears of one embodiment of each tested gearbox configuration after testing. As shown in Figures 4A and 4B, post-test gear wear inspections revealed that conventional COTS gearboxes, comprising steel planetary and sun gears, resulted in rapid and complete failure of the sun gear under all torques, leading to complete gearbox failure. In contrast, as shown in Figures 4C and 4D, gearboxes comprising all-BMG planetary and sun gears (e.g., copper-based) according to embodiments of the invention significantly extend gearbox life (e.g., by a factor of 5) under all torques. While this improvement is significant compared to the operating life of unlubricated conventional steel gearboxes, the hybrid gearbox embodiment (e.g., copper-based BMG planetary gears paired with a steel sun gear) exhibits an unprecedented improvement. In fact, as shown, the hybrid gearbox according to the embodiments has twice the operating life of the all-BMG gearbox (again under all torques) and delivers a gearbox comparable to fully lubricated gearboxes used in extreme conditions in space applications (e.g., cryogenics, vacuum, temperature fluctuations, etc.). Specifically, space applications typically require 10,000 to 100,000 output revolutions. Results show that at a torque of 2 Nm (the continuous rated torque of a COTS steel gearbox under normal Earth lubrication conditions), the conventional unlubricated steel gearbox has a lifespan of approximately 30 minutes, providing only 1,705 output revolutions; the all-BMG gearbox according to the embodiment has a lifespan of 2.6 hours, providing 8,863 output revolutions; and the hybrid gearbox has a lifespan of 8.7 hours, providing 29,659 output revolutions. Furthermore, the wear shown in Figures 4E and 4F is uniformly distributed between the sun gear and planetary gears; this overall wear pattern is distinctly different from the wear patterns seen in the COTS steel configuration of Figures 4A and 4B, or the pair of BMG configurations of Figures 4C and 4D.

[0063] These harsh, unlubricated tests were chosen to explore the performance limits of bare, unlubricated materials and to identify failure modes. Although these tests deliberately employ unlubricated conditions, they still provide insight into the failure scenarios of cryogenic lubricants currently developed for spaceflight conditions. Common cryogenic lubricants exist in the form of dry film solid lubricants (e.g., MoS2, WS2) and specially formulated chemical oil lubricants (e.g., perfluoropolyethers, polyalkylcyclopentanes). Dry film solid lubricants have a limited lifespan because the coating wears down with repeated cycles. Furthermore, the lifespan of dry film lubricants is highly sensitive to applied contact stress, as higher contact stress removes more film and shortens the effective service life. Specially formulated wet lubricants are also prone to failure due to vacuum evaporation under high contact stress. Therefore, testing under high contact stress in unlubricated conditions allows us to understand the challenging conditions even for specially lubricated systems under the harsh conditions of cryogenic temperatures and vacuum.

[0064] The planetary gearbox was further tested according to the process given in the exemplary embodiment at an input speed of -50°C and 225 rpm to compare the low-temperature performance of the COTS steel gearbox and the copper-based BMG hybrid gearbox. Figure 5 This demonstrates that when operating at -50°C, the lifespan of the COTS steel gearbox is significantly shorter than that of the copper-based BMG hybrid gearbox. Figures 6A to 6D show the state of the sun gear and planetary gears after the -50°C test. The same wear trend as in Figures 4A to 4F is again observed in Figures 6A to 6D, where the sun gear of the COTS steel gearbox suffers catastrophic failure, while the progressive and mutual wear of the copper-based BMG hybrid gearbox extends its service life. This unique combination of low stiffness, good hardness, and good wear resistance of this exemplary BMG material enables this very slow wear interaction.

[0065] These results demonstrate that, according to embodiments of the invention, by changing the material of the interlocking gears, gearboxes capable of operating under extreme conditions (e.g., under unlubricated conditions) and with improved lifespan can be formed. More specifically, the tests described in this disclosure show that gearboxes fail due to wear conditions between gears and demonstrate that by managing the wear characteristics of the interlocking gears throughout the gearbox, operational life and use under extreme conditions can be improved. For example, tests show that conventional all-steel gearboxes fail primarily due to jamming caused by severe wear. In short, once the steel of the interlocking gears begins to wear and produces steel chips (Figures 4A and 4B provide typical wear images for steel gearboxes), these steel wear chips cause gearbox jamming and lead to catastrophic failure. In the closed, tightly tolerant environment of an operating gearbox, chips accumulate, and if they cannot be quickly ground into powder, the gear teeth jam and exceed their strength, resulting in complete gear tooth breakage. In contrast, the BMG gearbox according to embodiments of the invention exhibits improved lifespan, at least in part due to the absence of this jamming phenomenon. The combination of properties provided by BMG (e.g., low modulus, high strength, high wear resistance, low density, no strain hardening or ductile plasticity) means that when the material wears (Figures 4C and 4D provide typical wear images for a full BMG gearbox), it does not generate debris that would jam the gearbox like steel. Therefore, although wear will occur, the gearbox will not experience premature catastrophic failure due to wear.

[0066] Some of these observations can be explained by the contact stresses of gear interactions. For example, the contact stresses are lowest in embodiments using all-BMG gears (due to a low modulus of approximately 100 GPa), while they are highest in all-steel configurations (due to a high modulus of approximately 200 GPa). Thus, it can be seen that the higher contact stresses of steel gears lead to the most catastrophic failures. However, gearbox embodiments cannot be optimized solely by referencing contact stresses. For example, according to hybrid gearboxes, the contact stresses when steel gears are interlocked with BMG gears fall between those of all-steel gearboxes and all-BMG gearboxes, yet, as previously mentioned, hybrid gearboxes exhibit the lowest wear rates. Furthermore, the wear exhibited by the gears in hybrid gearboxes (e.g., symmetrical fillet wear of both planetary and sun gears) differs from the asymmetric wear exhibited in conventional steel gearboxes (Figures 4E and 4F provide typical wear images of hybrid gearboxes). (Figure 4 provides a comparison of the wear patterns of planetary gears for all three gearbox types.) Although symmetrical wear is shown as significantly extending life in this embodiment, it should be understood that the embodiment can still be considered for rotating systems with asymmetrical wear, provided that the mutual damage caused by the rotating pairs is minimized.

[0067] The gearbox according to embodiments uses a material for the interlocking gears such that the contact stress on the interlocking gears is kept lower than that experienced by a steel gearbox, and the modulus between the sun gear and planetary gears is balanced to provide an approximately symmetrical overall gear wear pattern. As previously mentioned, because the center gear or sun gear engages multiple planetary gears, its wear dominates the wear within the gearbox; therefore, reducing the wear of the center gear or sun gear according to embodiments helps to improve the overall service life of the gearbox. In many embodiments, the planetary gears are formed of a material with a lower modulus and therefore lower contact stress to minimize damage to the sun gear with each interaction; however, the specific levels of hardness and modulus will depend on the characteristics of the sun gear. In most BMGs, toughness decreases with increasing hardness, but then harder steels can be used, potentially increasing the overall service life of the gearbox. In short, the gearbox according to embodiments is configured by balancing the wear imposed on each gear element by the gear elements it meshes with. Therefore, in many embodiments, the selected material combination results in the material forming the center gear or sun gear having a higher hardness / modulus than the material of the surrounding planetary gears. In various embodiments of the hybrid gearbox, a sun gear, formed of steel or BMG material with high hardness / modulus, is paired with one or more planetary gears, and the planetary gears are formed of BMG material with low modulus and high hardness. In various embodiments, a steel sun gear is combined with copper-based BMG planetary gears.

[0068] Although specific combinations of gear materials for BMG gearboxes and hybrid gearboxes according to embodiments of the present invention have been discussed above, it should be understood that many different combinations of materials can be used according to such embodiments. According to many embodiments, the combination of materials is selected by determining the wear rate of a given material combination under a given pair of contact stresses, and by selecting a material combination that satisfies the following conditions: its contact stress is lower than that of a conventional steel gearbox pair, and the wear rates between the various interlocking gears are approximately symmetrical under the proposed operating conditions, or where the mutual damage caused by the mating rotating element pairs is minimized. An exemplary BMG may comprise a composition based on copper, nickel, iron, titanium, and zirconium. The selection of a specific alloy will depend on the proposed application. Those skilled in the art will be able to determine the selection of a specific alloy for a particular application based on available alloy data. For example, the ZrCuNiBe alloy (Vitreloy 1b) has excellent glass-forming ability (GFA) and can be cast into all-glass parts with a thickness exceeding 20 cm. The TiZrCuBe alloy is known for its low density, comparable to crystalline β-titanium alloys. CuZrAlBe is a well-known copper-based BMG, which is more brittle than other BMGs, but exhibits excellent wear resistance in gear-to-gear tests.43 Zr 43 Al7Be7 can be used in many geochemical applications because replacing zirconium with copper exhibits superior wear performance in air. In contrast, when wear tests are conducted in a vacuum, copper-rich alloys show only a slight improvement in wear performance, while zirconium-rich alloys show a significant improvement.

[0069] While the foregoing discussion focuses on the composition used to form the gear body, many embodiments may also include surface treatments or coatings to improve the lifespan of gear components. In conventional gearboxes, lubrication is used to prevent wear, and if problems persist even with lubrication, shot peening or hard coatings can be used to delay the onset of wear as much as possible. Typically, such coatings or treatments are not used in unlubricated scenarios because the coatings are very thin and the damage is so severe that the coating is almost immediately worn away. However, the use of BMG in gearboxes according to embodiments of the invention offers other possibilities. Although BMG has integral properties, its wear performance varies by orders of magnitude in different alloy systems due to chemical effects. An important finding is that copper-zirconium-based (copper-based) BMG exhibits significantly improved wear performance, indicating that the formation of the ceramic oxide layer controls this performance. Forming zirconium oxide of varying thicknesses on a copper-based amorphous metal results in tribological properties that are more than an order of magnitude better than those of conventional gear steel. Therefore, many embodiments include hard layers (e.g., oxide and ceramic surfaces) on the gear components of the gearbox. In various embodiments, a coating can be formed by placing the BMG gear in a furnace (near the glass transition temperature (Tg) of BMG) to grow a thin oxide film. Any suitable coating chemistry system (e.g., copper oxide and zirconium oxide systems) can be used. The oxide can be formed on any gear element, including, for example, oxidizing the BMG planetary gear and setting it together with a steel sun gear, or oxidizing the BMG sun gear and setting it together with an unoxidized BMG planetary gear.

[0070] While the foregoing discussion focuses on gearboxes incorporating planetary gears, it should be understood that this is merely a single use case of embodiments of this disclosure. Any rotating gear system comprising at least two rotating elements experiencing different cycle rates can include the aforementioned hybrid material components. Examples of other gear systems that use the aforementioned higher hardness / modulus material for high-cycle rotating elements and the aforementioned lower hardness / modulus material for low-cycle elements include, but are not limited to: worm gear systems (Figure 7A), bevel gear systems (Figure 7B), and helical gear systems (Figure 7C). In some embodiments of the invention, a helical gear system can be arranged in the planetary gearbox arrangement described above (Figure 7D), but regardless of the specific arrangement of the gear components, embodiments of such rotating systems (where at least one pair of gears rotates together and transmits motion between them, and where the elements of the gear pair cycle at different rates) can include hybrid material components as described herein, thereby improving the overall lifespan of the gear system. In particular, for those rotating systems where lubricants are unsuitable or unavailable, the systems and methods described in the embodiments of the invention can increase lifespan in the absence of lubrication or under extreme conditions.

[0071] The foregoing sections have described a rotating system incorporating gears; however, the hybrid material methods and systems described above can also be included in other types of rotating systems in which at least two rotating elements engage to transmit motion between them, and where at least one rotating element circulates at a higher rate. An exemplary system is a traction drive.

[0072] A traction drive is a mechanical power transmission system used to transmit motion and power between two rotating shafts. They are common in a wide range of applications, from vehicles to industrial machinery. The main principle of a traction drive is to transmit torque using the friction between contact surfaces. Traction drives do not rely on gears or belts, but rather on the gripping and frictional forces between contact surfaces to transmit power.

[0073] As shown in Figure 8, a traction drive typically consists of two components: a drive wheel and a driven wheel. These wheels are in contact with each other, and torque is transmitted through friction between their surfaces. The rotation of the drive wheel generates a force between the surfaces, causing the driven wheel to rotate. The amount of torque transmitted depends on the coefficient of friction between the surfaces, the normal force pressing them together, and other factors. Traditional traction drive technology uses traction fluid to transmit torque while preventing severe wear. The traction coefficient determines the traction force and therefore the torque that can be transmitted for a given normal force. The traction fluid is subjected to high pressure to increase its viscosity so that force can be transmitted more efficiently through friction. These traction fluids have a traction coefficient of approximately 0.1, and therefore can transmit approximately 10% of the applied normal force.

[0074] Traction drives offer numerous advantages. They can be highly efficient due to the direct transmission of torque without the need for intermediate components like gears, thus reducing energy loss. Compared to traditional gear systems, traction drives provide smoother torque delivery, reducing vibration and noise. They can also be more compact and lightweight than some traditional mechanical transmission systems. The absence of gears or belts means fewer components that may wear out and require maintenance. However, using traction drives also presents challenges. They have a limited torque capacity and may not be suitable for applications requiring extremely high torque transmission. Using a traction fluid with a traction coefficient of 0.1 limits force transmission efficiency; for example, typically only 10% of the normal force can be transmitted. In some cases, slippage can occur between contact surfaces, potentially leading to decreased efficiency or inaccurate speed control. Over time, contact surfaces may wear due to friction, requiring regular maintenance, especially for high-cycle components.

[0075] It should be understood that although the hybrid embodiments involve any traction drive in which two rotating rollers engage with each other and have different cycle rates, as shown in Figure 9, the traction drive can take the form of a planetary traction system, which operates similarly to the planetary gearboxes discussed earlier. In this example, the drive system has a sun roller, planetary rollers (in the exemplary system shown in the figure, four planetary rollers are positioned around the sun roller), and an annular element (which is fixed). These parts are preloaded by an interference fit, i.e., the annular element is slightly smaller, so that when the planetary rollers and sun roller are squeezed into place, the planetary rollers and sun roller flex, and compressive loads are generated at the contact surfaces. This load allows the system to transmit torque without slippage. As in a planetary gearbox, the planetary rollers and sun roller experience two main failure modes: rolling contact fatigue and rolling bending fatigue.

[0076] In short, like other rotating systems discussed in this article, conventional traction drives suffer from wear and require appropriate material selection and normal force control to ensure efficient operation and maximize component life. Furthermore, like many gear systems, particularly planetary gearboxes, conventional traction drives require lubrication to operate. However, the traction fluid reduces force transmission, and the system suffers wear, limiting the lifespan of the drive components.

[0077] By using hybrid materials on the roller components, the traction drive formed according to embodiments of the present invention has a longer lifespan and better ability to operate under extreme conditions and in the absence of traction fluid. As previously discussed with respect to planetary gearboxes, because the center roller or sun roller engages multiple planetary rollers, its wear dominates the wear within the traction drive. Therefore, reducing wear on the center roller or sun roller according to embodiments of the present invention helps to improve the overall service life of the drive system. In many embodiments, the planetary rollers are formed of materials with lower modulus and therefore lower contact stress to minimize damage to the sun roller with each interaction; however, the specific levels of hardness and modulus will depend on the characteristics of the sun roller. In most BMGs, toughness decreases with increasing hardness, but harder steels can be used, potentially increasing the overall service life of the drive. In short, the traction drive according to embodiments of the present invention (like a planetary gearbox) is configured by balancing and / or reducing the wear imposed on each roller element by the roller elements it mats with. Therefore, in many embodiments, the combination of materials is selected such that the material forming the center roller or sun roller has a higher hardness / modulus than the material of the surrounding planetary rollers. In various embodiments of the hybrid traction drive, a sun roller formed of steel or BMG material with high hardness / modulus is paired with one or more planetary rollers, and the planetary rollers are formed of BMG material with low modulus and high hardness. In various embodiments, a steel sun roller is combined with a copper-based BMG planetary roller.

[0078] Although the implementation of the hybrid traction drive system is similar to that described with respect to planetary gearboxes, it offers additional advantages not applicable to gearboxes. First, the ability to operate without lubrication is crucial, as lubrication reduces the system's ability to transmit torque between components (as described above). Furthermore, the traction rollers are designed to flex when subjected to strain within the traction drive system; the low modulus of the BMG material in the hybrid system embodiment not only reduces contact stress but also allows for greater flexural deformation of the rollers in the contact block area. This greater flexural deformation translates to a larger contact block area, thus effectively increasing the traction force exerted on the drive unit compared to the harder, less ductile materials used in conventional traction drive systems.

[0079] Exemplary embodiments

[0080] To test the wear and life characteristics of the gearbox according to an embodiment of the present invention, the following procedure is used.

[0081] ● Disassemble and clean the commercial off-the-shelf gearbox to remove any lubricant.

[0082] ● Replace the standard lubricated bearings with bearings suitable for unlubricated use.

[0083] ● Assemble the gearbox (for these tests, use a single-stage gearbox with four planetary gears driven by one sun gear).

[0084] ● The gearbox assembly consists of conventional steel gears, BMG gears (e.g., copper-based alloys), or a combination of steel gears and BMG gears (in all cases, the outer ring gear housing remains unchanged).

[0085] ● Install the gearbox in the test bench and balance the gearbox and test bench to the required test temperature.

[0086] ● Complete 7,000 input cycles of torque-free break-in and bring the gearbox to a stop.

[0087] ● The output load is applied to the gearbox by the brake, and then the input motor is run in a constant direction and at a constant input motor speed, and the constant output load is maintained until failure.

[0088] ●The system is considered to have reached a failure state when any of the following conditions are met:

[0089] ○ The motor cannot provide the torque required to rotate the gearbox, which manifests as an alarm in the motor control program and a complete stop at both the input and output ends.

[0090] ○ The gearbox can no longer transmit torque to the output. This manifests as the input rotating freely, but the output torque drops to zero, and the output shaft stops rotating completely.

[0091] To form BMG gears, while net-shape injection molding can be used for mass production, cylindrical gears, bevel gears, or worm gears can be rapidly produced from high-quality BMG raw materials using a subtractive process. In such an embodiment, alloying, melting, and pouring up to 300 grams of titanium-based, zirconium-based, or copper-based BMG into a precision-machined mold are performed using a tilting casting arc melt to form the raw material. This raw material is an ultra-high purity BMG material (typically with an oxygen content below 200 ppm and a carbon content below 100 ppm) to ensure the highest material performance, thereby ensuring optimal performance of the manufactured BMG gears. Gear elements are formed from cylindrical preforms used to manufacture large planetary gears and gearbox housings for small planetary gearboxes. In one example, the cylindrical raw material may have a diameter exceeding 1.5 inches and be made from copper-based BMG optimized for low-wear gears. These cylinders are then cut to length and subsequently precision-machined into gears, or machined into housings with internal gears via wire electrical discharge machining (EDM). Although copper-based BMG raw materials have been described above, it should be understood that many different alloys can be formed: zirconium-based alloys with excellent glass-forming ability (GFA), titanium-based alloys with densities comparable to β-titanium alloys, and copper-zirconium-based alloys that have proven to have good wear resistance. While not discussed, BMG composites can also be used, which greatly expands the range of BMG options for various applications.

[0092] To ensure that BMG gear components meet the required tolerances, CMM inspection equipment, including the Liebherr WGT280 and Zeiss O-Inspect, can be used. These devices are capable of measuring gears with an accuracy of 1 micrometer, ranging from a minimum of 2 mm to a maximum of 10 cm. The inspection equipment ensures that the BMG gears are machined to the correct tolerances, enabling the assembled planetary gearbox to operate efficiently in its assembled state. For the tests presented in this paper, the gears meet the tolerance specifications of ISO 1328-1:2013 quality classes Q3 to Q5. Achieving high quality classes reduces stress concentration and helps prevent premature failure of the BMG material, significantly extending its lifespan. Therefore, BMG gears can be tested under optimal operating conditions, and the relationship between gearbox life and pitch speed, contact stress, and temperature can be properly determined. Furthermore, the improvement of BMG gears compared to existing technologies in unlubricated, low-temperature operation can be measured.

[0093] Gearbox life testing was conducted using a 22 mm single-stage gearbox with a reduction ratio of 4.4 and a module of 0.4, following the aforementioned test procedure. The single-stage gearbox comprises four planetary gears fixed to an output bracket, each operating on a zirconia pin sliding bearing. The output bracket has an output bearing press-fitted into the ring gear housing. The output bracket is axially constrained to the ring gear by an external press-fit ring. Figure 10 The disassembled gearbox is shown.

[0094] Six different gear pairs were tested to investigate their wear, life, and failure modes. These tests were conducted to develop a gearbox that can provide improved performance and life in a cryogenic vacuum environment under contact stresses resulting from conventional lubrication failure. The gearbox configurations tested included:

[0095] ● Steel ring gears, steel sun gears, steel planetary gears (COTS steel gearboxes)

[0096] ● Steel ring gears, steel sun gears, copper-based BMG planetary gears (copper-based BMG hybrid gearboxes)

[0097] ● Steel ring gears, steel sun gears, zirconium-based BMG planetary gears (zirconium-based BMG hybrid gearboxes)

[0098] ● Steel ring gears, steel sun gears, titanium-based BMG planetary gears (titanium-based BMG hybrid gearboxes)

[0099] ● Steel ring gears, steel sun gears, zirconium-based beryllium-free BMG planetary gears (zirconium-based beryllium-free BMG hybrid gearboxes)

[0100] ● Steel ring gears, copper-based BMG sun gears, copper-based BMG planetary gears (copper-based BMG gearboxes)

[0101] The configurations of the COTS steel gearbox, the copper-based BMG hybrid gearbox, and the copper-based BMG gearbox were tested at 25°C under constant direction, constant input speed of 225 rpm, and torques of 1 Nm, 1.5 Nm, and 2 Nm, according to the exemplary procedure described above. Figure 3 The results are shown in Figure 4, which illustrates the wear after the test. It can be seen that the copper-based BMG hybrid gearbox has the longest lifespan, followed by the copper-based BMG gearbox, while the COTS steel gearbox has the worst performance. The cumulative damage to the sun gear results in the shorter lifespan of both the COTS steel gearbox and the copper-based BMG gearbox.

[0102] Further testing was conducted at -50°C in a liquid nitrogen-cooled heat treatment chamber. The gearboxes tested were configured as a COTS steel gearbox and a copper-based BMG hybrid gearbox. Testing was performed according to the exemplary procedure described above under conditions of constant direction, constant speed of 225 rpm, and torques of 1 Nm and 2 Nm. Figure 5 The lifespan results are shown in Figure 6, which illustrates the wear condition after the test.

[0103] The failure mechanism for all COTS steel gearbox tests was characterized as follows: severe tooth surface wear damage accumulated on the sun gear, eventually generating sufficiently large wear debris, leading to catastrophic failure of the sun gear teeth. For all tests, the planetary gears accumulated a certain amount of tooth surface damage but still rotated freely around their carrier pins. If the generated steel wear debris was small enough not to cause gearbox jamming, the test could proceed; however, if any large debris was generated, it would enter the gear mesh and cause significant damage, subjecting the steel sun gear teeth to overload stress. The plasticity and work hardening of the steel wear debris increased the likelihood of damage caused by any generated wear debris. The copper-based BMG hybrid gearbox again exhibited the distributed interwear seen in the 25°C test, resulting in a significantly increased lifespan compared to the COTS steel gearbox.

[0104] Following the exemplary procedure detailed above, further testing was conducted on the hybrid BMG planetary gear configurations. The four gearbox configurations tested were a copper-based BMG hybrid, a zirconium-based BMG hybrid, a titanium-based BMG hybrid, and a zirconium-based beryllium-free hybrid gearbox configuration. These four configurations were tested at temperatures of 25°C and -50°C, with constant output loads of 0.5 Nm, 1 Nm, and 2 Nm. Tests with loads of 1 Nm and 2 Nm were run at a constant speed of 225 RPM, and tests with a load of 0.5 Nm were run at a constant speed of 1000 RPM. Figure 11 Life results of four hybrid BMG planetary gearbox configurations at 25°C are depicted. Figure 12 The lifespan results of four hybrid BMG planetary gearbox configurations are depicted at -50°C. At both room temperature and cryogenic temperatures, the copper-based BMG hybrid planetary gearbox configuration maintained the longest operating time under the test criteria. At both room temperature and cryogenic temperatures, the all-BMG planetary gearbox configuration maintained a longer operating time under the test criteria than the equivalent COTS steel gearbox configuration.

[0105] Under test conditions of 25°C and -50°C, the copper-based BMG planetary gear outperformed all other BMG planetary gears tested for torques of 0.5 Nm, 1 Nm, and 2 Nm. The greatest difference occurred at the highest torque of 2 Nm.

[0106] To demonstrate how lower stiffness materials reduce contact stress in an exemplary embodiment of the gearbox, contact stresses for the sun gear-planet gear meshing interaction and the planet gear-ring gear meshing interaction were calculated using gear calculation software (KISSsoft) for various embodiments of the planetary gear material. These stresses were calculated using steel sun gears and steel ring gears with detailed gear dimensions, tolerance data, specified steel material properties, and bulk metallic glass material properties.

[0107] The contact stress is calculated from the input torque, which is calculated from the output torque assuming a gearbox efficiency of 84%. Figure 13 This paper demonstrates the contact stresses of sun-planetary gear meshing in steel planetary gears, copper-based BMG planetary gears, zirconium-based BMG planetary gears, titanium-based BMG planetary gears, and zirconium-based beryllium-free planetary gears. The contact stresses are normalized to the maximum stress at 2 Nm for steel planetary gears. It is clearly visible that the lower Young's modulus and higher Poisson's ratio of these exemplary BMG materials have an effect on reducing the contact stresses of the sun-planetary gear interaction. Steel has a Young's modulus of approximately 200 GPA and a Poisson's ratio of 0.3, while the exemplary BMG materials have a Young's modulus of approximately 90-100 GPA and a Poisson's ratio of 0.35 to 0.37. By replacing the steel planetary gears with exemplary bulk metal-glass planetary gears with lower stiffness and higher Poisson's ratio, the contact stress between the steel sun gear and the BMG planetary gears is reduced by approximately 20% under a load of 0.15 Nm and by approximately 30-35% under a load greater than 0.5 Nm, compared to the contact stress between the steel sun gear and the steel planetary gears.

[0108] The stress in planetary-ring gear meshing is approximately 30% lower than that in sun-planet gear meshing, and the ring gear teeth exhibit the fewest total number of meshing interactions. Under any test conditions, the ring gear tooth surfaces showed almost no damage. Therefore, we focus on the higher stress and damage that occurs in sun-planet gear interactions. Gearbox performance is not solely determined by contact stress. Resistance to sliding wear, alloy strength, toughness, and hardness all influence overall performance, and data indicate that BMG materials, with their low stiffness, high Poisson's ratio, good toughness, and good resistance to sliding wear, demonstrate excellent performance in both unlubricated and lubricated planetary gearbox systems experiencing lubrication failure.

[0109] Principle of Equivalence

[0110] The description of this invention is provided for illustrative and descriptive purposes only. It is not intended to be exhaustive or to limit the invention to the precise forms described; many modifications and variations are possible in accordance with the teachings above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application. The description will enable others skilled in the art to best utilize and practice the invention in various embodiments and with various modifications suitable for a particular purpose. The scope of the invention is defined by the following claims.

[0111] As used herein, unless the context clearly indicates otherwise, the singular terms “a” and “the” may include plural indicators. Unless explicitly stated otherwise, references to objects in the singular are not intended to mean “one and only one” but rather “one or more”.

[0112] As used in this article, the term "group" refers to a collection of one or more objects. Thus, for example, a group of objects can contain a single object or multiple objects.

[0113] As used herein, the terms “approximately” and “about” are used to describe and indicate small variations. When used with an event or situation, these terms can refer to instances where the event or situation occurred precisely or instances where the event or situation was very close to occurring. When used with a numerical value, these terms can refer to a range of variation of that value less than or equal to ±10%, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, “approximately” alignment can refer to a range of angular variation less than or equal to ±10°, such as less than or equal to ±5°, less than or equal to ±4°, less than or equal to ±3°, less than or equal to ±2°, less than or equal to ±1°, less than or equal to ±0.5°, less than or equal to ±0.1°, or less than or equal to ±0.05°.

[0114] In addition, quantities, ratios, and other numerical values ​​may sometimes be presented in range format throughout this document. It should be understood that such range format is used for convenience and brevity, and should be flexibly interpreted to include not only the values ​​explicitly specified as range limits, but also all individual values ​​or subranges covered within that range, as if each value and subrange were explicitly specified. For example, a ratio in the range of approximately 1 to approximately 200 should be understood to include both the explicitly listed limits of approximately 1 and approximately 200, as well as individual ratios such as approximately 2, approximately 3, and approximately 4, and subranges such as approximately 10 to approximately 50, approximately 20 to approximately 100, etc.

Claims

1. An apparatus comprising: A solar element, said solar element being made of a first material having a first modulus; Multiple planetary elements, wherein the multiple planetary elements are made of a second material having a second modulus; as well as Ring element; The solar element and the annular element are coaxial with an axis, and each of the plurality of planetary elements is disposed between the solar element and the annular element; Wherein, each of the solar element and the plurality of planetary elements engages at a first interface and transmits motion between them, and each of the plurality of planetary elements and the ring element engages at a second interface; and Wherein, at least one of the first material and the second material is a bulk metallic glass, and the first modulus and the second modulus are not equal.

2. The apparatus according to claim 1, wherein, The solar element wears out at a rate proportional to the number of planetary elements.

3. The apparatus according to claim 2, wherein, The first and second materials are selected such that the first and second moduli are proportional to the rate, such that the wear of each of the planetary elements and the solar element is approximately symmetrical.

4. The apparatus according to claim 3, wherein, The second material has a lower modulus than the first material, and the device is also configured to minimize the contact stress at the first interface.

5. The apparatus according to claim 3, wherein, The solar element and the plurality of planetary elements are configured as gears with a plurality of gear teeth, and the device is further configured to balance wear on the plurality of gear teeth.

6. The apparatus according to claim 1, wherein, The solar element has a higher hardness and modulus than each of the plurality of planetary elements.

7. The apparatus of claim 6, further comprising an annular element, wherein the first rotating element is configured to rotate about an axis, and the annular element is coaxially disposed with respect to the first rotating element, and the second rotating element is disposed between the first rotating element and the annular element.

8. The apparatus according to claim 1, wherein, At least one of the first material or the second material is a steel alloy.

9. The apparatus according to claim 1, wherein, The device is configured to operate at a temperature higher than a set temperature.

10. The apparatus according to claim 1, wherein, At least one of the plurality of planetary elements and the solar element further includes a third material at the contact surface.

11. The apparatus according to claim 10, wherein, The third material is an oxide or a ceramic.

12. An apparatus comprising: A first rotating element, the first rotating element being made of a first material and having a first surface rotating at a first speed; as well as The second rotating element is made of a second material and has a second surface that rotates at a second speed; The first surface and the second surface are made of different materials and are joined at the interface of the mixed materials to transmit motion; Wherein, the first rotating element rotates with a first cycle period, the second rotating element rotates with a second cycle period, and the first cycle period is different from the second cycle period; and Wherein, at least one of the first material and the second material is a bulk metallic glass.

13. The apparatus according to claim 12, wherein, The first speed and the second speed are different.

14. The apparatus according to claim 12, wherein, The first rotating element and the second rotating element are configured as gears.

15. The apparatus according to claim 12, wherein, The first material and the second material are different.

16. The apparatus according to claim 12, wherein, The first material and the second material are selected for desired properties, which are selected from the group consisting of service life, operating environment, hardness or modulus.

17. The apparatus according to claim 16, wherein, The first cycle period is longer than the second cycle period, and the first material is selected for a modulus higher than that of the second material.

18. The apparatus according to claim 17, wherein, The modulus is selected for low contact stress at the interface of the hybrid material.

19. The apparatus according to claim 17, wherein, The device is configured as a traction drive.

20. The apparatus according to claim 16, wherein, The first rotating element wears at a first wear rate, the second rotating element wears at a second wear rate, and the first wear rate and the second wear rate are not equal.

21. The apparatus according to claim 20, wherein, The modulus of the first material is selected to be proportional to the first wear rate, and the modulus of the second material is selected to be proportional to the second wear rate.

22. The apparatus according to claim 21, wherein, The device is configured such that the wear of the first rotating element and the second rotating element is approximately symmetrical.

23. The apparatus according to claim 12, wherein, The first surface and the second surface are configured to engage without lubrication.

24. The apparatus according to claim 12, wherein, The first surface comprises a third material that is harder than the first material.

25. The apparatus according to claim 24, wherein, The third material is an oxide or a ceramic.

26. The apparatus according to claim 25, wherein, The oxide is formed by heating the first rotating element to approximately the glass transition temperature of the first material.

27. A method of manufacturing an apparatus, comprising: Select a first rotating element made of a first material having a first modulus; Select a second rotating element made of a second material having a second modulus; Wherein, the first material and the second material are different, and at least one of the first material and the second material is a bulk metallic glass; The first rotating element and the second rotating element are arranged to engage at an interface such that rotation of the first rotating element transmits motion to the second rotating element; and The first rotating element wears at a first rate, the second rotating element wears at a second rate, and the wear of the first rotating element and the second rotating element is approximately symmetrical.

28. The method of claim 27, further comprising heating the first rotating element to the glass transition temperature of the first material, thereby forming a third material on the surface of the first rotating element.

29. The method of claim 27, further comprising selecting an annular element and arranging the annular element such that the annular element engages with the second rotating element, and the second rotating element is disposed between the first rotating element and the annular element.

30. The method according to claim 27, wherein, The first material or the second material is a steel alloy.

31. The method according to claim 27, wherein, The second material has a lower modulus than the first material, and the first and second rotating elements are arranged to minimize contact stress.

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