FUNDAMENTAL-STUDY ON REACTION PLASMA SPRA YING BY MEANS OF RF THERMALPLASMA

The RF thermal plasma nitriding process of a Ti alloy was fundamentall y investigated. Based on the results obtained in the nitriding process , reaction plasma spraying was carried out to fabricate the nitride co ating. The results obtained are summarized as follows: 1) As a result of RF thermal plasma nitriding of the Ti alloy, the TiN surface layer, followed by the TiN, Ti2N and Ti mixed layers in the order of depth d irection, was observed on the surface region of the alloy substrate. 2 ) A linear relationship was recognized in the relation between the thi ckness of the nitride layer and the square root of treatment time. The rfore, the thermal plasma process seemed to be a diffusion dominating process. From the comparison of the nitride layer thickness under the same conditions of substrate temperature, the effect of hydrogen addit ion on nitrogen was investigated. 3) The diffusion rate of nitrogen in the Ti alloy substrate: Rd was estimated from the experimental result s obtained, and the plasma spraying of Ti powder was conducted under t he deposition rate of less than Rd. Consequently, the possibility of t he reaction plasma spraying was found in the present study.