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Research on Double Glow Plasma Tungsten-molybdenizing of TC4 Titanium Alloy and Friction Wear Properties

Author: JiangLi
Tutor: LuoXinZuo
School: Nanjing University of Aeronautics and Astronautics
Course: Materials Processing Engineering
Keywords: TC4 alloy double glow plasma W-Mo alloying wear resistance corrosion resistance high-temperature oxidation resistance
CLC: TG174.44
Type: Master's thesis
Year: 2009
Downloads: 57
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Abstract


Titanium alloys are widely applied to aerospace, rocket, missile, chemistry, energy sources and light industry due to their high specific strength, low density and high hot strength. However, low hardness, poor wear resistance and severe adhesive wear restrain the further application. Surface modification is a feasible solution to those problems, and it has become a research focus in materials science and technology. Currently, various surface technologies are employed to improve surface properties of titanium alloys, majority of them are coating technologies. But coatings always have the low bonding strength which often leads to spalling damage, especially under fatigue loadings. It was proposed in this dissertation to fabricate W-Mo diffusion layer on titanium alloy to improve friction and wear properties by double glow plasma surface alloying process. The alloy elements in the diffusion layer are gradient distribution, and good metallurgical bonding can be obtained between the modified layer and titanium alloys base.W-Mo alloying layer has been prepared on TC4 substrate with double glow plasma alloying technology. The effects of processing parameters on modified layer was investigated and the optimized parameters were obtained as follows: processing temperature 860℃, holding time 4h, discharge pressure 60Pa, source voltage 820~870V, cathode voltage 250~350V, distance between source and cathode 16mm. XRD and EDS results show that the as-fabricated modified layer is mainly composed of MoTi, TixW1-x, Mo and W phases, with the gradient distribution of alloy elements from the surface to substrate. The bonding strength was measured by using the automatic scratch tester, and the result exhibited the good adhesion strength between the modified layer and the substrate.The friction and wear properties of the as-prepared modified layer were investigated at room and elevated temperature systematically. The surface microhardness was measured by nano-indentation and microhardness test respectively, and it is found that the hardness is improved obviously after W-Mo alloying. The friction-wear performance of both W-Mo alloying layer and substrate was studied by ball-on-disc wear test under different conditions, such as different friction pair material, different speed and loading, different temperature and so on. The results indicate that antifriction effect of W-Mo modified layer is not obviously improved with GCr15 mate material, while opposite with Si3N4 one. The wear resistance of W-Mo modified layer can be improved with whatever friction pair material. The friction coefficient has decreasing tendency with the increasing of loading and rotating speed. The wear resistance of W-Mo+C modified layers is also enhanced, though its antifriction is not obviously increased. The wear test under elevated temperature proves that the friction coefficient of W-Mo modified layer is more stable than that of TC4 substrate, and the W-Mo modified layer possesses high wear resistance under high temperature.Corrosion resistance and high temperature oxidation resistance properties of W-Mo alloying layer are measured respectively. The corrosion resistance of W-Mo alloying layer is also the same with the substrate, while the high temperature oxidation resistance is better.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology > Metal complex layer of protection
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