Kinetics of thermodiffusion of TZ20 titanium alloy gas-nitride within temperature of 500 °C–650 °C

Surface nitriding is an effective method for improving surface hardness, wear resistant, corrosion resistance etc. surface properties and ensuring effective, safe, and long-term applications of alloys. This work investigated the kinetics of thermodiffusion of gas nitriding and practical nitriding of TZ20 titanium alloy within 500 °C–650 °C. Differential scanning calorimeter was also used to explore nitriding behavior and its activation energy E. Results showed that nitriding on TZ20 alloy within the temperature range of 500 °C–650 °C followed the parabolic law, and E value approximated 186 kJ/mol. Phase analysis revealed that nitride products changed gradually from Ti2N to Ti3N2−x + Ti4N3−x as nitriding temperature increased from 500 °C to 650 °C. The relationship between weight gain and thickness of nitride layer indicated that weight will increase 0.118 mg/cm2 for each additional millimeter in thickness. Furthermore, surface hardness of TZ20 alloy before and after nitriding treatment was investigated. Surface hardness of specimen after nitriding at 650 °C for 1 h dramatically increased from approximately 400 HV to 870 HV. The findings will not only promote practical applications of new Ti–Zr–Al–V series alloys but also supplement the surface alloying theory. © 2017 Elsevier B.V.