Novel precursor of nitrogen for the synthesis of TiC0.7N0.3 through vacuum oven-induced combustion

Abstract

TiC0.7N0.3 is widely used as a cutting tool and an abrasion-resistant material for operations requiring high wear resistance and strength. In this study, we attempted to solve one of the main issues in TiC0.7N0.3; synthesis at high temperature (>1000 °C). The use of NH4NO3 powder was put forward for the first time as a precursor to supply N2 gas for synthesizing TiC0.7N0.3 nanopowders at a low temperature of 180 °C. Ti, C, and NH4NO3 served as feedstocks. Raw materials were mixed at different milling times (1, 5, 10, 15, and 20 h) at 300 rpm in Ar gas to avoid oxidation. XRD results revealed that no new peaks of TiC0.7N0.3 appeared after milling. Prior to vacuum synthesis at 180 °C, the as-milled powders were dried at 50 °C for 1 h and shaped into cylindrical pellets under a pressure of 150 MPa. The TiC0.7N0.3 peaks were distinctively present at 5–20 h except for samples milled at 1 h. Notably, activation energy decreased from 256.9 kJ/mol to 76.68 kJ/mol with prolonged milling time from 1 h to 20 h. This decrease was due to the decreased activation energy with prolonged milling time. The reaction between C and NH4NO3 was found to be exothermic, which favored the release of N2. With increased temperature caused by the exothermic reaction, the melted Ti particles reacted simultaneously with the released N2 gas, whereas the remaining C synthesized TiC0.7N0.3.