Preparation And Tribological Properties Of Plasma Mo Alloyed Layers On TLM Titanium Alloy Surface

The new β-type titanium alloys possess high strength-to-weight ratio,excellent corrosion resistance and good machining performance of the common titanium alloys. More importantly, their elastic modulus is more close to the bone tissue. Therefore, these titanium alloys are becoming promising biomedical implant materials in recent years. However, the titanium alloys show low surface hardness and poor load-bearing capacity, and often suffer from adhesion during the sliding process and the accumulation of metal wear debris may cause inflammation, resulting in final implant failures. Surface modification technique has been one of effective ways to improve the wear resistance. Based on some theories and research achievements of predecessors, Mo modified layers on TLM substrate were prepared by double glow plasma surface alloying technique in this paper, in order to achieve the purpose of improving the friction and wear properties. Some basic characteristics, such as surface morphology, composition distribution, surface micro-hardness and wettability of the Mo modified layers obtained at three temperatures(900 ℃, 950 ℃ and 1000 ℃) were analyzed. The tribological properties of TLM substrate and alloyed samples after sliding against A12O3 ceramic balls were discussed in different loads(5 N, 8 N) anddifferent friction environments(air, simulated human body fluids and simulated artificial saliva). The main research results are as follows:(1) Mo modified layers can be successfully fabricated on TLM titanium alloy surfaces using double glow plasma alloying technique. After Mo alloying,the surfaces of TLM samples show higher roughness, with rugged pyramid shape. Mo element of surface modified layers has a gradient distribution along depth direction. The modified layers mainly contain Mo phase and have good surface wettability. With the increase of alloying temperature, Mo modified layer becomes thicker. The surface microhardness of alloyed samples at different treated temperature has a significant increase than TLM substrate, and exhibits load-dependent manner.(2) Mo alloyed samples are more antifriction and hard-wearing than TLM substrate, with lower friction coefficient and specific wear rate in the same friction condition. In air and simulated human body fluids, the wear resistance of alloyed samples increases with the increase of alloying temperature. While the samples treated at 900 ℃ and 950 ℃ exhibit better wear resistance than the ones treated at 1000 ℃ when the sliding tests are carried in simulated artificial saliva.(3) When the load changes,the wear volume of TLM substrate changes largely than that of Mo alloyed samples, indicating that the load has a greater influence on the wear resistance of substrate and a lower influence on that of Mo alloyed samples.(4) The sliding processes of two simulated solutions show lower and morestable friction coefficient than that of air environment due to the lubrication of solutions. Besides, the debris generated during sliding process can be washed away in time by the solutions, decreasing the abrasive and adhesion wear. The TLM samples show excellent friction and wear performance during these two simulated solutions within the combined effect of lubrication and washing.