다이어프램 밸브용 극박 Co계 및 Ni계 합금 소재들의 미세조직 및 인장 특성

초록

The microstructure and room temperature tensile properties of ultra-thin sheet superalloys (Co based Elgiloy and Ni based Hastelloy C22) were investigated. Elgiloy exhibited FCC and HCP phases and Hastelloy C22 showed an FCC structure with observed twin boundaries. Both alloys exhibited deformation bands inside the grains during tensile deformation. Elgiloy showed intermediate tensile properties between as-rolled and heat-treated states, whereas Hastelloy C22 exhibited higher tensile and yield strengths than conventional materials. Fracture surface analysis of Elgiloy revealed shallow dimples and striated fracture patterns along weak interfaces between FCC and band-shaped HCP phases, indicative of crack propagation. In contrast, Hastelloy C22 showed brittle fracture characteristics, such as river patterns concentrated at the center and cleavage features near the edges. Elgiloy exhibited strain hardening from TRIP effects during tensile deformation, showed higher tensile strength after yielding than Hastelloy C22. The 60° shear fracture angle is Elgiloy was caused by high strain concentration and microcracks at FCC/HCP interfaces. Hastelloy C22 displayed higher yield strength due to deformation twins and increased dislocation density. Fracture initiation in Hastelloy C22 occurred at twin boundary cross-sections, and its higher atomic bond energy and twin-induced strengthening resulted in a higher elastic modulus compared to Elgiloy.

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