Effect of Hydrogen Free Carburized Layer on Mechanical Properties of TC4 Titanium Alloy

Abstract

The surface hardness of TC4 titanium alloy increased by 2.84 times after carburizing. After 1, 2, 3 h treatment, the tensile strength and the non proportional elongation strength of the samples with or without diffusion layer (heat treatment) are equivalent to those of the original sample. The elongation at the end of the 3 kinds of heat treatment (i.e., non - permeable layer) is better than that of the original sample, and the elongation at post fracture and the shrinkage rate of the cross section have a great decrease. With the extension of time, the elongation and the shrinkage of the section decreased. The pretreated TC21 titanium alloy specimens were carburized in a vacuum carburizing furnace. The phase structure, microstructure, hardness and wear resistance of the carburized layer were analyzed by X ray diffraction (XRD), scanning electron microscope (SEM), micro Vivtorinox (HV) hardness tester and friction and wear tester. After hydrogen carburizing, the TC4 titanium alloy changed from the original adhesive wear to the hard friction, and the scratch surface was smooth, which significantly improved the wear resistance of the titanium alloy. The titanium gear with hydrogen free carburizing has been successfully applied in practice. In the process of fracture, the outer surface layer is continuously exfoliated and the outer surface is filled with circular crack. The crack is gradually increasing from the root to the middle, the root is small crack, and the more the crack is wider to the middle crack. As time goes on, cracks are mainly concentrated near the fracture surface, and the root of the specimen is less.