The research team of Ren Fuzeng, assistant professor in the Department of Materials Science and Engineering, Southern University of Science and Technology, proposed a new strategy to achieve equal room temperature and high temperature ultra-high temperature control through the nanostructure of the grain structure, the segregation of the grain boundary atoms and the introduction of high-density coherent nanoprecipitation. High wear resistance. Related research results were published in Acta Materialia, a top journal in the field of metal materials.
Sliding wear is one of the important factors affecting the service life of metal components. Therefore, the design and development of new high-strength, ultra-wear-resistant alloy materials is essential to ensure the reliability, durability and efficiency of engineering components serving in harsh working conditions. At lower service temperatures, the wear resistance of metal components mainly depends on the hardness of the material and the microstructure evolution of the subsurface of the material during friction; in high-temperature service environments, the material surface is not only subject to shear caused by frictional contact Stress and compressive stress, and are prone to thermal softening and high temperature oxidation, which greatly affects the wear performance of the material. The complex force-heat effect in the high temperature friction environment puts more stringent requirements on the high temperature stability design of the metal grain structure.
Titanium alloys have the advantages of high strength, corrosion resistance, high temperature resistance, and good biocompatibility, and are widely used in biomedicine such as bone, dentistry, and automotive and aerospace industries. However, the traditional titanium alloy has a shortcoming that cannot be ignored: poor wear resistance (when worn against alumina, the wear rate is 10-2–10-3 mm3 / N · m), which greatly limits its harsh environment Widely used in. For example, in the field of biomedicine, low wear resistance can lead to loosening of titanium alloy implants, and the wear particles around the prosthesis can cause inflammation, which is one of the main reasons for the failure of prosthetic replacement surgery and reoperation. Therefore, improving the wear resistance of titanium alloys is particularly important for the durability of titanium alloys in service.
Based on this, Ren Fuzeng’s group proposed the ultra-high wear resistance of the alloy at room temperature and high temperature through the strategy of nano-grain structure, segregation of grain boundary atoms and the introduction of high-density coherent nano-precipitated phases. On the basis of extensive screening of alloy phase diagrams and thermodynamic calculations, the researchers of the research group selected the TiMoNb alloy of 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:
• One is solid solution strengthening: the three elements Ti, Mo and Nb have a great solid solubility with each other. Among them, Mo-Nb is completely solid solution, and no intermetallic compounds are formed between the three elements, which guarantees solid solution. The effect of solution strengthening; • The second is the coherent interface: the three elements have very close atomic radii (rTi = 1.46, rMo = 1.36, rNb = 1.43) and are all body-centered cubic (bcc) structures, which contribute 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 precipitate out of the bcc matrix around 850 ° C, which brings the possibility of precipitation strengthening; • The fourth is Fine-grain strengthening: through mechanical alloying and rapid discharge plasma sintering (SPS) to prepare ultra-fine crystal / nanocrystalline matrix, and finally obtain the effect of fine-grain strengthening; • Fifth, Ti, Mo, Nb three alloys Elements are common in traditional high-temperature alloy systems and are a prerequisite for the alloy to serve in high-temperature environments.
The research group successfully prepared a bulk TiMoNb alloy with a density greater than 99% and a hardness of up to 650 HV by optimizing high-energy ball milling and SPS processes.
Microstructure analysis showed that the alloy consisted of two phases, including a B1 matrix phase with an average grain size (d) of 188 nm and a dispersed Ti B2-rich precipitate phase (d = 79 nm; 7 vol.%), B1 and The two phases of B2 are coherent interfaces. With the help of 3D APT technology, Ti atoms were found to be segregated 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 the alumina ball as the friction pair (hardness ~ 1500 HV), the wear resistance test results of the TiMoNb alloy show that: at room temperature, the wear rate of the TiMoNb alloy and alumina is on 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, showing that the alloy has ultra-high wear resistance, which greatly breaks through the wear resistance of traditional titanium alloy. 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 serving in extreme environments, which will help to explore the application of multi-primary alloys in the field of wear resistance and high strength designed for harsh environments. , Wear-resistant, thermally stable alloys have a certain significance, and dig the potential research direction for expanding the application of interface phase engineering in the field of multi-primary high-entropy alloys. The TiMoNb alloy developed in this study can be used in high-temperature wear-resistant materials. Its high strength, good biocompatibility, and corrosion resistance make it widely used in dental implants, orthopedics, and other medical implant materials. .