Nozzle geometry influences gas dynamics, such as gas density, velocity and temperature, making sprayed particle behavior one of the most important parameters in cold spray process. Gas flow at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour (convergent –divergent and convergent-divergent-barrel), entrance geometry of convergent–divergent nozzle and powder injection position at nozzle on the cold spray process. The process changes inside the nozzle were observed through numerical simulation studies and the results were used to find a correlation with coating properties. A copper and titanium powder was used in the experiments. Working gas (is nitrogen) pressure and temperature at nozzle-intake were 3MPa and 623K, respectively. In addition, the change in the nozzle contour and the change in the entrance convergent section length of the gun nozzle were found to have a slight effect on the coating microstructure. Powder injection position was also found to influence deposition efficiency and coating properties. Deposition efficiency of both copper and titanium increase with increasing the length of the convergent section of the nozzle.

This paper describes a new technique for measuring junction temperature with high accuracy in accelerated operational tests (junction temperature ≥200°C) based on the measurements of temperature dependence of gate-leakage current on a GaAs FET (gate-leakage method). The gate-leakage current on the GaAs FET is monitored in the accelerated operational tests. Then, junction temperature and thermal resistance are calculated from the temperature dependence of the gate-leakage current, especially from the temperature dependence in high temperature region. We have measured the junction temperature and the thermal resistance using this method in accelerated operational tests, and have confirmed that the junction temperature can be estimated within a range of ten degrees. The results by this method have been compared with data of simulation, and the validity has been confirmed.