cocrfenimo05 高熵合金600-1000℃时效硬化与微结构研究 - yoke.pdf

CoCrFeNiMo0.5 高熵合金600-1000℃時效硬化與微結構研究 Age hardening and microstructure of CoCrFeNiMo0.5 high entropy alloy 許銘化* 張良奕 李哲甫 孫道中 M. H. Shiu* L. Y. Jang C. F. Lee T. T. Shun 逢甲大學材料科學及工程學系 摘要 CoCrFeNiMo0.5 合金鑄材為樹枝狀結構，硬度為HV319 ，基地相dendrite 為A1 Type FCC 固溶體，次要相interdendrite 為富Cr-Mo 的σ 相 。合金鑄材經600-1000 ℃時效處 理 144 小時之硬度變化顯示初期硬化效果隨溫度提高而增加，在700℃有最佳的時效硬 化效果，硬度值達HV518 ，硬度增加量HV 199(上升率62%) ，700℃之後時效硬化效果 隨著溫度提高而降低，但皆沒有軟化的現象發生。微結構觀察顯示合金700℃最佳的時 效硬化效果歸因於大量blocky type 富Cr-Mo 的σ 相在interdendrite 周圍析出，使合金硬 度大幅提升；合金經800- 1000℃時效處理後則觀察到interdendrite 逐漸轉變成富Mo-Cr 的μ 相，且富Cr-Mo 的σ 析出相亦開始粗化與轉變成顆粒狀富Mo-Cr 的μ 相，故硬化 效果低於700℃。 關鍵詞：高熵合金、時效硬化、微結構、析出相 Abstract The as-cast CoCrFeNiMo0.5 alloy exhibits a dendritic structure and hardness is HV319. The primary phase of dendrite is A1 Type FCC solid solution, and secondary phase of interdendrite is (Cr,Mo)-rich σ phase. Alloy after 144 hr aging at 600- 1000℃, the variation of hardness shows that hardening effect increases with increasing temperature in the beginning. The optimal age hardening occurs at 700℃ and the hardness reaches HV518 (HV199 or 62% increase). When ageing temperature above 700℃, the hardening effect decreases with further increase in temperature. However, no softening occurs even after 1000℃ aging. The microstructure shows the optimal age hardening at 700℃is due to heavy blocky precipitates of (Cr,Mo)-rich σ phase around the interdrite. Alloy after 800-1000℃ aging treatment, the interdrite gradually transfers to (Mo,Cr)-rich μphase, and the precipitates of (Cr,Mo)-rich σ phase coarsen and transfer to particle type of (Mo,Cr)-rich μphase in the meantime. This explains the less hardening effect with aging temperature above 700℃. Key words: high entropy alloys, age hardening, microstructure, precipitate 前言 數百年以來，合金系統開發的範疇均集中在單一主元素，其原子百分比皆大於