Abstract
A basic study was carried out on the reaction products on the surface of titanium castings obtained with molds lined with high purity oxide pellets(e.g., SiO2, Al2O3, MgO, and YSZ).In a preliminary study, high purity titanium plates(99.99%)were heat treated to examine the relationship between color changes and the reaction products on their surface.The following results were obtained using a TF-PSPC(Thin Film Position Sensitive Proportional Counter)at an angle of the two-degree incidence and EPMA(Electron Probe X-ray Micro Analyzer)of the surface of these materials.When high purity titanium plates were treated by heat in the atmosphere, rutile was generated as the primary product on their surface, and the rutile production increased rapidly above 900℃.The products responsible for coloring by casting at less than 600℃ could not be identified by TF-PSPC under the conditions of this study.In the surface layer of the titanium castings produced by the actual casting process, the depth of penetration of major elements of various high purity oxide pellets with which the molds were lined decreased in the order of quartz>alumina>magnesia and zirconia, and that of TITAVEST-PS was the greatest next only to quartz.The depth of penetration of Si into the surface of titanium castings depended on the silicon concentration on the cast surface at a casting temperature of 900℃, but it was dependent on the casting temperature at a fixed silicon concentration.The structure of the hardened layer on the surface of titanium castings into which Si had penetrated differed with the casting temperature.
