An Experimental Study On Microalloying And Elevated Temperature Wear Behavior, And Ternary Phase Diagram Of Ti-Si Alloys

The microstructures of Ti-Si alloys is observed.The microstructures, mechanical properties,elevated temperature wear and phase equilibria of Ti-Si alloys with different alloying elements were studied.The influence of Ce and Zr microalloying on the structure of Ti-11at.%Si alloys has been investigated. Moreover,the effect of 16 at.%Al on the structure,mechanical property and elevated temperature wear mechanisms of Ti-Si eutectic alloy was studied.The phase relationship has also been investigated in the Ti-Si-Sn ternary system at 200℃.Experimental results indicate that Ce elements can refine the colonies evidently and Si atoms in Ti₅Si₃ phase were partially substituted by Ce atoms which resulted in the formation of new silicide Ti₅(Si,Ce)₃ phases.8 at.%Zr element greatly modifies the microstructure by forming tiny intermetallic compound(Ti,Zr)₂Si instead of rod-like Ti₅Si₃ particle.The microstructural characteristics and elevated temperature wear behavior of a Ti-11Si-16Al alloy(TSA)have been investigated,compared with the as-cast Al-free Ti-Si eutectic alloy(TS).Experimental results show that addition of 16 at.%Al greatly modifies the microstructure by forming near-equiaxed Ti₅Si₃,rod-like Ti₃Al and rosette-like eutectic cells distributing on a continuousα-Ti(Al,Si)solid solution phase.Therefore,mechanical properties such as Vickers' hardness,elastic modulus and strength are significantly improved.In situ hot pressing and sintering of the hybrid oxide particles form a compact-and-hard glaze layer on the worn surface of the alloy.It has protective effects on the TSA specimen by relieving oxygen diffusion,alleviating rubbing of the counterpart and providing solid lubricant effect by the hybrid oxide particles.This effectively improves the elevated temperature wear resistance and friction stability.The phase relationships in the Ti-Si-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 14 single phase regions,26 binary phase regions and 13 ternary phase regions.No ternary compound is found in the work.The solid solubility of single phases was determined by the disappearing-phase method of the X-ray diffraction analysis. The maximum solid solubility of Sn in Ti and Si in Ti₅Sn₃ is about 8 at.%and 15 at.%respectively.The solid solubility rang of Ti₃Sn is 13-25 at.%.Sn.A new ternary compound A(New phase)was found.