Improved Leachability of CaO Modified Y2O3 Ceramic Cores for Investment Casting of Titanium Alloys

Abstract

Y₂O₃ ceramic cores are ideal adapters for titanium alloy casting owing to the excellent high-temperature chemical inertness. However, they are difficult to be chemically de-coring, which seriously limits their application in castings with complex internal cavity. In order to benefit the leaching behavior as well as the chemically compatible with titanium alloys, a new class of Y₂O₃-based cores modified by CaO was investigated in this work. The effects of CaO content on the microstructure, mechanical properties, chemical leachability, and interfacial reaction with TC4 alloy along with the internal cavity roughness were investigated. When the content of CaO was 4 wt.%, the porosity is 32.64%, and the room temperature strength was maintained at 19.89 MPa, which were close to the performance of ceramic cores with pure Y₂O₃. Citric acid solution was determined to be the ideal leaching solution, which was capable of dissolving Y₂O₃-CaO ceramic cores without affecting the quality and composition of titanium alloy. Compared to pure Y₂O₃ ceramic cores, the leaching behavior was significantly improved by 4 wt.% of CaO and the leaching time was reduced from 90 h to 6.5 h. It was further demonstrated that it has superior high-temperature chemical compatibility in liquid titanium alloys, and this work provides a new guidance for improved leachability of Y₂O₃ ceramic core for investment casting of titanium alloys.