Kinetics carburization of titanium alloys during thermal diffusion saturation from gaseous medium

Abstract

The purpose of the study is to establish the patterns of high-temperature interaction of titanium alloys with carbon-containing gaseous media. Methodology. Investigated samples of industrial titanium alloys a- (VT5-1 and PT-7M), pseudo-(OT4-1), (a + b) – (VT14 and VT19) classes. After fabrication, the samples were annealed in vacuum according to the mode: T = 800 °C,
τ = 5 h, P = 0.05 MPa, Imin = 0,1 mPa × dm³× s^-1. The saturating medium was a gas mixture of argon and propane. The volume content of propane was 16.7%. Titanium alloys were saturated at temperatures T = 750°C, 800°C and 850°C for 1 hour, 3 hours and 5 hours. Results. Bottom analysis of gravimetric data obtained by discrete gravimetry showed that in the argon-propane mixture with pressure P = 0.106 Pa at various temperatures (T = 750, 800 and 850 °C for 1, 3 and 5 hours). The mass of samples of the VT1-0 alloy increases linearly. The carbon saturation kinetics of the VT5-1 alloy has significant deviations from linearity and the actual weight gain after 5 hours of exposure is almost 2 times less than for the VT1-0 alloy. The interaction of titanium alloys VT14 and VT19 with a carbon-containing gaseous medium at a residual pressure of P = 0.106 Pa is characterized by a monotonic increase in the mass of the samples beyond the temperatures and duration under study. Originality. It has been established that the interaction at high temperatures (T = 750 ... 850 °C) of titanium alloys with a rarefied carbon-containing gas medium (Ar + 16.7 % C₃H₈) at a pressure of P = 0.106 Pa leads to an increase in the mass of the samples, approaching linear, indicating a controlling stage of interaction − reactions at the gas – metal interface. Practical value. High temperature interaction of titanium alloys with a carbon-containing gaseous medium is accompanied by deviation of parameters of the crystal lattice of the hardened layers. Carburization seems to influence physical-chemical properties of the near-surface layer of metal.