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SUSTech breaks the "short board" of titanium alloys that are not wear-resistant

Posted by: Zhou HanPing 2021-12-22 Comments Off on SUSTech breaks the "short board" of titanium alloys that are not wear-resistant

Sliding wear is one of the important factors affecting the service life of metal components. Therefore, the design and development of new high-strength, super wear-resistant alloy materials is essential to ensure the reliability, durability and efficiency of engineering components that are used in harsh operating conditions. 

Recently, the research group of Assistant Professor Ren Fuzeng of the Department of Materials Science and Engineering of Southern University of Science and Technology proposed a new strategy to achieve ultra-high wear resistance by adjusting the alloy interface structure and chemical composition.

Sliding wear is one of the important factors affecting the service life of metal components. At a lower service temperature, the wear resistance of metal components mainly depends on the hardness of the material and the evolution of the microstructure of the material’s subsurface during the friction process; while in the high temperature service environment, the surface of the material is not only sheared by frictional contact Stress and compressive stress, and are prone to thermal softening and high-temperature oxidation, which greatly affect the wear performance of the material. The complex force-heat effect in the high-temperature friction environment puts forward more stringent requirements for the high-temperature stability design of the metal grain structure.

The use of titanium alloy has a history of several decades since its industrial production in the late 1950s. It has obtained a series of excellent characteristics such as low density, high specific strength, corrosion resistance and good biocompatibility. Rapid development. It has shown strong vitality in a short period of time and has become an indispensable material in the fields of aerospace, ships, medical equipment, petrochemicals, and military energy.

However, an unavoidable problem faced by titanium alloy products is its poor friction and wear performance. When it is rubbed against alumina, its wear rate is 10-2-10-3 mm3/N·m, which greatly limits It is widely used in harsh environments. For example, in the biomedical field, low wear resistance can cause titanium alloy implants to loosen, and wear particles around the prosthesis can cause inflammation, which is one of the main reasons for the failure of prosthesis replacement surgery and reoperation.

With the continuous expansion of titanium alloy applications, there are more and more problems related to the friction and wear properties of titanium alloys. Therefore, improving the wear resistance of titanium alloys is particularly important for the service durability of titanium alloys.

Innovation: Improve the wear resistance of alloys by adjusting the interface structure and chemical properties

Ren Fuzeng’s research group proposed the strategy of nanocrystalline grain structure, grain boundary atom segregation and introduction of high-density coherent nano-precipitated phases to achieve ultra-high wear resistance of the alloy at room temperature and high temperature.

Based on a large number of alloy phase diagrams and thermodynamic calculations, the research team selected TiMoNb alloy with equal atomic ratio as the model system, and designed the composition and preparation process from the classic strengthening mechanism. The main strengthening ideas include the following aspects: 1. It is solid solution strengthening: the three elements of Ti, Mo and Nb have great solid solubility among each other. Among them, Mo-Nb is completely solid solution, and no intermetallic compound is formed between the three elements, ensuring solid solution strengthening The second is the coherent interface: the three elements have very close atomic radii (rTi = 1.46Å, rMo = 1.36Å, rNb = 1.43Å) and all have a body-centered cubic (bcc) structure, which helps to coherent The formation of the interface; the third is precipitation strengthening: the binary phase diagram of Ti-Mo and Ti-Nb shows that a small amount of Ti will be precipitated from the bcc matrix at about 850°C, which brings the possibility of precipitation strengthening; the fourth is fine-grained Strengthening: Through mechanical alloying and spark plasma rapid sintering (SPS), it is expected to prepare ultra-fine crystal/nanocrystalline matrix, and finally obtain the effect of fine-grain strengthening; Fifth, the three alloying elements of Ti, Mo and Nb are common in The traditional high-temperature alloy system is a prerequisite for the alloy to be used in high-temperature environments. The research group successfully prepared a bulk TiMoNb alloy with a density of greater than 99% and a hardness of up to 650 HV by optimizing the high-energy ball milling and SPS process.

Microstructure analysis shows that the alloy consists of two phases, including a B1 matrix phase with an average grain size (d) of 188 nm and a dispersed Ti-rich B2 precipitated phase (d = 79 nm; 7 vol.%), B1 and The two phases of B2 are coherent interface. With the aid of three-dimensional atom probe (3D APT) technology, Ti atoms were found to segregate at the B1/B2 interface with a thickness of about 3nm, which fully shows that the strengthening mechanism designed at the beginning of the experiment is reflected in the alloy. Using alumina ball as the friction pair (hardness-1500 HV), the wear resistance test results of TiMoNb alloy show that at room temperature, the wear rate of TiMoNb alloy and alumina is in the same order of magnitude, (10-4 (mm3/ N·m); At 600℃, the wear rate of TiMoNb alloy is as low as 3.15×10-6mm3/N·m, which shows that the alloy has super high wear resistance and greatly breaks through the wear resistance of traditional titanium alloys. Based on the in-depth characterization and analysis of the composition and structure of the wear scar surface and subsurface, the research team further revealed the origin of fatigue cracks and clarified its wear mechanism in room temperature and high temperature environments.

Ren Fuzeng introduced that the research results provide new ideas for the design of new high-strength wear-resistant alloys that are used in extreme environments, and will help to develop the application of multi-principal alloys in the field of wear resistance. , Wear-resistant, thermally stable alloys have a certain significance, and explore potential research directions for expanding the application of interfacial phase engineering in the field of multi-principal element high-entropy alloys. The TiMoNb alloy developed in this research can be used in high-temperature wear-resistant materials, and its high strength, good biocompatibility, and corrosion resistance make it widely used in the fields of dentistry, orthopedics and other medical implant materials. .

This research was funded by the Shenzhen Basic Research Discipline Layout Project, Guangdong Innovation and Entrepreneurship Team and other projects, as well as the technical support of the imaging platform (Pimi Center) of the Analysis and Testing Center of Southern University of Science and Technology.

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