한국주조공학회

The main purpose of this study is to investigate the effects of process parameter on alpha-case formation of Ti and TiAl castings. The previous studies showed that the molten titanium is excessively reactive to the refractory oxide mold, resulting in alpha-case of the titanium castings regardless of composition of titanium alloys. However, the behavior of the alpha-case formation of TiAl alloy is not consistent with conventional titanium alloy. In order to investigate the alpha-case formation of Ti and TiAl castings with pro- cess parameter, especially the associated factors of investment mold such as mold material, binder and mold preheating tempera- ture. An attempt has been made to characterize the alpha-case of titanium castings by using optical microscope, EDS, XRD, EMPA and hardness profiles. The formation of the alpha-case on the surface of pure titanium during investment casting was rather by that of solid solution with metallic element from mold material. The required mold strength was obtained with CaZrO3 because of the possibility of using water soluble binder. However, the separation phenomenon between facing and back-up mold materials should be considered. The interfacial reaction of TiAl alloy showed different behavior from that of pure titanium and A1203 was best mold materials. The effect of binder as well as mold material on the formation ofalpha-case was significant.

Ti, TiAl alloys, alpha~case, investment mold, CaZrO3, A1203, binder