An Experimental Study On The Mechanical Properties, Tribological Behavior And Ternary Phase Diagram Of Ti-Si Alloys With Different Alloying Elements

Microstructure of Ti-Si alloys is observed. The results showed that the size and shape of the eutectic cells were better than the hypereutectic alloy and hypoeutectic alloy. The silicide separated out from cast Ti-Si alloys was analyzed by X-ray diffraction. Experimental results indicate that the microstructure of the cast Ti-Si eutectic alloy is composed ofα-Ti and Ti₅Si₃.The microstructures, mechanical properties, fracture mechanisms and Vicker's hardness of Ti-Si eutectic alloy with different alloying elements which are Al element and rear earths (RE) La and Gd, were studied. The results showed that RE elements can transform the size of the colonies evidently fine, and Si atoms in Ti₅Si₃ phase were partially substituted by RE atoms which resulted in the formation of new silicide Ti₅(Si,RE)₃ phases. Al element changes the microstructure from large eutectic cells that consist of layered tablet phases Ti₅Si₃ andα-Ti to near-equiaxed or rod-like Ti₅Si₃ particle reinforced continuousα-Ti (Al, Si) solid solutions. The compressive ductility and strength of Ti-Si eutectic alloys with little RE (0.025 at. %) at room temperature were improved. Vicker's hardness of Ti-Si eutectic alloys with La were also improved. The strength and hardness of Ti-Si-Al alloys were increased. However, the compressive ductility was reduced.The effect of Al element alloying on the tribological behavior of Ti-Si eutectic alloys have been studied. The experimental results show that the microstructural change greatly improves the ductility and reduces brittle fracture of massive superficial materials during wear process. Microplough and local delamination are the main wear mechanisms of Al-added Ti-Si alloys. Therefore, the wear resistance and friction stability are simultaneously improved.The phase relationships in the La-Ti-Sn ternary system at 200℃have been investigated mainly by means of X-ray powder diffraction (XRD) with the aid of scanning electron microscope (SEM), optical microscopy (OM) and differential thermal analysis (DTA). The isothermal section consists of 13 single phase regions, 23 binary phase regions and 11 ternary phase regions. A binary compound Ti₂Sn₃ is confirmed. Therefore, there are 10 binary compounds exist in the system in all, which are La₅Sn₃, La₅Sn₄, LaSn, La₃Sn₅, and LaSn₃, Ti₃Sn, Ti₂Sn, Ti₅Sn₃, Ti₆Sn₅ and Ti₂Sn₃. No ternary compound is found in the work.