Thermal stability of nanostructured NiCrC coating prepared by HVAF spraying of cryomilled powders

Thermal stability of nanostructured NiCrC coating prepared by high velocity air-fuel (HVAF) spraying of cryomilled feedstock powders was investigated. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were utilized for characteristic analysis. Recrystallization and normal grain growth occur when isothermal treatment is performed at 923 K (0.55 TM) for up to 100 h, and the average grain size increases from initial 41 nm for as-deposited state to around 100 nm for nearly equilibrium state. Isochronal treatment at 823 K and 1023 K was also conducted for comparison. Accordingly, for 0.49 to 0.61 T/TM, the time exponent n deduced from D1/n - D01/n = kt increases from 0.15 to 0.30. The observed high thermal stability is attributed primarily to a Zener pinning mechanism arising from the fine Cr2O3 dispersions and the solute drag effect as well.