Study Of Electrospark Deposition And Deposited Hardening Technology For ZTA15 Alloy

ZTA15 titanium alloy is a structural material with high specific strength, but itshardness is very low and its wear-resistance is poor, so the casting often lose efficacyand be destroyed for surface wear and tear. For enhancing the surface hardness ofZTA15 casting, this article strengthens the surface of ZTA15 titanium alloy usingelectrospark deposition and surface overlay welding technology.It can obtain a deposited layer which is about 10μm～100μm thick on the surfaceof titanium using graphite,YG11,Ni45,Stellite6 and chrome carbide electrodes. Thedeposited layer which is made by electrode and matrix under pulse discharge processhas carbide or intermetallics. The hardness of the deposited layer increases 1～5 timescomparing with matrix. The hardness of the deposited layer which is made bygraphite electrode is highest, it is up to 2000HV0.05.The thickness of the deposited layer on titanium is affected by capacitance andtime. The thickness of the deposited layer made by YG11 and Chrome carbideelectrodes increases first and decreases then with capacitance is increasing, and thepeak value presents at the capacitance is 720μF. But the thickness of the depositedlayer made by graphite,Ni45 and Stellite6 electrodes always increases with theincrease of capacitance, but the trend is slow up. The thickness of the deposited layermade by metal electrode is increasing first and decreasing then with the increase oftime, and the peak value is present at the time is about 1.3min.Under the optimizationprocess, the thickness of the deposited layer on titanium is 100μm, so it fit to workunder the situation where is not requiring retreatment or has a low wear.Develop a new deposited titanium alloy with high hardness by alloying process.Its cast hardness is HRC38.5, but after welding metallurgy its hardness is up toHRC45.8.It can obtain a deposited layer which is 3mm thick by TIG on ZTA15 alloy. There are no cracks, wholes in the fusion area.The sectional hardness of deposited layer is graded distribution. The hardness ofdeposited layer is up to 420HV0.2. The tensile-strength which is 1080MPa of thedeposited layer alloy is higher than ZTA15 matrix's 985MPa, and the strength of theheat-affected zone is same as matrix. The bond strength between deposited layer andmatrix is higher than matrix. The shear strength of the deposited layer is up to776MPa, which is higher than that of matrix. The ballistic work of the deposited layerand HAZ is 20J and 30J. The fracture mechanism of the deposited sample ismicrovoid coalescence fracture. D1 alloy is applying on the surface hardening ofvalve's seal contact face. Obtaining a surface hardening layer with high quality, andimprove the life of valve.