Microstructure And Wear Resistance Of The Modified Layer Formed On TiAl Based Alloy

Ti-Al intermetallic compounds have specialties of low density,high melting point,high specific strength and so on,so that regarded as new ideal structural materials for elevated temperature applications in aeronautics and astronautics. However, there are also some disadvantages in the wear resistance of Ti-Al intermetallic compounds that have restricted their actual uses. There are many friction couples in aeronautics,astronautics,missileries and so on, which demand satisfactory performances of resisting to wears and frictions. As the need for high temperature structural materials is so urgent in aeronautics and astronautics especially for defence purposes, improving the wear resistance of Ti-Al intermetallic compounds has become a key problem.In the paper, the typical alloyed layer was obtained by double glow plasma alloying niobium and following plasma carburization on the TiAl based alloy after optimizing technics parameters. The microstructure,composition and phase structure of the surface modified layers will be analyzed by means of OM,GDS,XRD,SEM,EDS and TEM respectively,and the hardness was also tested.The evaluation of wear behaviors and mechanism were studied through ball-on-disc dry rubbing under room temperature and 600℃. The experimental results show that:(1) The better modified layers can be acquired under specifically technological parameters, the modified layer had strong combine force because of metallurgically bonding to the TiAl substrate without spalling; (2) After alloying niobium on TiAl based alloy, AlNb₂ ,β-AlNbTi₂ and so on were formed on the alloyed layer; After compound alloying NbC on TiAl based alloy, NbC and Nb₂C both high hardness phases were formed on the alloyed layer, (3)The process of the plasma carburization after the plasma niobizing can greatly accelerate plasma carburization;(4)Both plasma alloying Nb and compound alloying Nb+C on TiAl based alloy can improve greatly wear resistance.Because of the different wear mechanism under room temperature and high temperature,the wear resistance of compound alloying NbC was better than the substate and plasma alloying Nb under room temperature,but the wear resistance of plasma alloying Nb was better than compound alloying NbC under high temperature.