Si 및 C이 첨가된 일방향응고된 TiAl-Nb 합금의 파괴인성

Abstract

The microstructure and mechanical properties of directional solidified Ti-47Al-3Nb, Ti-47Al-3Nb-0.2Si- 0.1C, Ti-47Al-3Nb-0.3Si-0.2C alloys were investigated. It was found that the lamellar thickness of Si and C doped alloys was fine and uniform, and little or no precipitates were found. Room temperature yield stress increased rapidly with increasing Si and C contents due to fine lamellar distribution and solid solution hardening. However, fracture toughness of type I specimens of the alloys decreased slightly with increasing Si and C contents. It was considered that a2 volume fraction decreased with increasing Si and C contents so that the delamination-type separation was decreased which contributes the high resistance of crack propagation for type I specimens. Furthermore, fracture toughness of Ti-47Al-3Nb-0.2Si-0.1C alloy specimens with type I orientation, polycrystalline form, and with type III orientation increased in order of type III, polycrystal and type I. These results are discussed and the ability to obtain a respectable combination of strength and toughness through Si and C addition to a TiAl-Nb alloy produced by directional solidification is demonstrated.