진공 브레이징을 통해 제조한 TiAl/HI-TEMP 820/SCM440H 재료의공정 온도에 따른 미세조직 및 기계적 특성 평가

Abstract

The TiAl alloy is attracting attention as a lightweight and heat-resistant material, because of itshigh specific strength, excellent high-temperature formability, and fatigue strength. However, its applicationsare limited by its high unit price and low room temperature ductility. To overcome this issue, dissimilarlybonded materials have been extensively employed. This involves joining a brittle metal to a low-cost metalthat possesses excellent plasticity, using various dissimilar bonding techniques. In this study, TiAl/HI-TEMP820/SCM440H materials were fabricated using a vacuum brazing process under different temperatureconditions. After the brazing process, the microstructure of the interfacial area revealed seven distinct layersresulting from chemical reactions between the base metals and the filler metal. These reaction layersconsisted of a Ni solid solution, intermetallic compounds (Ti3Al, TiNi2Al, Ti2Ni, FeNi), and borides (CrB, TiB2,FeB). To analyze the effect of brazing temperature on the relationship between the microstructure andmechanical properties at the interface of TiAl/HI-TEMP 820/SCM440H materials, conventional uniaxial testsand nanoindentation tests were performed. The measured nanohardness exhibited a significantly largedistribution for each reaction layer, with the highest hardness values observed in the intermetallic compoundsand borides layers. Additionally, room temperature tensile tests confirmed that fractures initiated in the highhardnessand brittle intermetallic compounds and borides layers.