Research On High Temperature Friction And Wear Properties Of TD3 Alloy And Its Plasma Nitriding

Ti₃Al based alloy(TD3)is an ideal lightweight high temperature structural material for aerospace vehicles due to its low density,high specific strength and low coefficient of expansion.However,its poor wear resistance limits its application.The surface of TD3 was nitrided by cathode assisted plasma nitriding.The morphology and phase structure of the nitrided layer were analyzed by metallographic microscope,scanning electron microscope with energy dispersive spectrum and X-ray diffraction respectively.The effects of different temperatures on the friction and wear properties of TD3 substrate and the nitrided TD3 were studied;At 400?and 600?,the friction and wear properties were investigated at different speeds and loads.The wear scar morphology was observed by metallographic microscope,scanning electron microscope and energy dispersive spectrometer.The relative weight loss of TD3 and the nitrided TD3 was measured by electronic analytical balance to obtain the wear rate.Under 950?×4h×200Pa plasma nitrided process parameters,A nitrided layer with a thickness of about 8?m was formed on the surface of TD3 alloy.The main phases of nitrided layer are TN,Ti₂N and Ti₂Al N.The surface hardness of the nitrided layer can reach 1100Hv,which is about three times that of TD3 substrate(about 360HV).The results of high temperature friction and wear experiments showed that the friction coefficient and wear rate of TD3 would increase and then decrease,and the degree of abrasive wear and oxidation increase with raising the temperature.The increase of load or speed resulted in the increase of the friction coefficient and wear rate.At 600?,under higher load and linear velocity the friction coefficient and wear rate increase,the friction composite layer was formed on the surface of wear scar,which would reduce the friction coefficient and wear amount.After nitriding,the friction coefficient and wear rate of TD3 can be effectively reduced,and the fluctuation range of friction coefficient became smaller.Before the nitriding layer was worn through,the wear scar morphology was mainly caused by plastic deformation.With the increase of temperature,the plastic deformation became serious and begins to exfoliate.Under the same conditions,the oxygen content in the wear scar of the nitridied sample was lower than that of TD3 substrate.After the nitriedng layer was worn through,because the subsurface layer was the transition layer,the friction coefficient of the nitrided layer was still slightly lower than that of TD3 substrate,and the furrow appeared in the wear scar.The wear mechanism is abrasive wear,and the wear is intensified and the wear rate is increased...