Interstitial Hardening of the Surface of Titanium Alloys by Vacuum Heat Treatment

We have determined the kinetic parameters of interaction of VT1-0, VT5, OT4-1, and VT16 alloys with a rarefied gaseous medium. We have established the interrelation between the parameters of chemical heat treatment (T, tau, and p), the interstitial hardening of surface layers of the metal, and its phase and structural state. The conditions of saturation (T, tau, and p) being equal, hardened layers differing in the microhardness and thickness of the layer (H and l) are formed on titanium alloys of different structural classes. Single-phase VT1-0 and VT5 alpha-titanium alloys as well as OT4-1 pseudo-alpha-alloy are the most sensitive to the conditions of gas saturation: the hardness and its gradient in the hardened layer grow significantly. As the beta-phase content increases (VT16), changes in the parameters of chemical heat treatment affect less the hardness of the surface layer, but the depth of the hardened zone grows with temperature T and time tau.