グラファイト上に成膜した金属溶射皮膜の密着強度評価

抄録

Graphite is a candidate material for heat sink, because it has extremely high thermal conductivity, and low density. On the other hand, graphite has low solderability. Therefore, it is required to improve solderability by means of a copper bond layer on the graphite surface. The conventional coating methods as represented by CVD and PVD need high vacuum environment and those deposition rates are very low. In this work, we discuss the applicability of Low-Temperature Plasma Spray (LTPS) for thin coating production onto the graphite surface. LTPS is a kind of plasma spray technique, it has high deposition rate, 10 μm/s in an atmospheric environment. The LTPS copper coating, however, does not have highly adhesion strength. However, LTPS titanium coating shows enough adhesion strength on the graphite substrates. Therefore, insertion of Ti bond layer for improvement of adhesion strength between copper coating and graphite is considered. In this study, in order to optimize coating conditions, we make some specimens in different conditions and measure particle temperature and particle velocity and flame temperature. As a result of measurements, Ti particle temperature was over 2800°C between 20 and 60mm from spray nozzle, and particle velocity was 60~100m/s. Experimental results indicate that as spray distance decrease, porosity size in a coating is smaller.