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 degrees C-650 degrees 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 degrees C-650 degrees 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 degrees C-650 degrees C. The relationship between weight gain and thickness of nitride layer indicated that weight will increase 0.118 mg/cm(2) 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 degrees 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. (C) 2017 Elsevier B.V. All rights reserved.