低溫輥軋與後續退火對CoCrNi中熵合金微觀結構與機械性質的影響

The effect of cryo rolling and annealing on microstructure and mechanical properties of CoCrNi medium entropy alloy

鄭黛婷(Tulustia Japanesa)

指導教授 ： 楊哲人

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101398

摘要

本文使用低溫輥軋與後續退火研究其對於CoCrNi 中熵合金微結構與機械性質的影響。觀察微結構可發現低溫輥軋導入高差排密度、剪切帶以及大量變形雙晶，這些低溫變形組織使材料之最大抗拉強度約1500 MPa、破裂應變約2%。後續700°C退火使冷輥試片產生部分再結晶結構、800°C 退火產生完全再結晶結構，增加退火溫度或退火時間皆使材料之強度下降，但同時可提升伸長量。600°C退火熱處理中可觀察到退火誘導異常硬化(annealing-induced abnormal hardening)現象，材料之強度與硬度與退火前相比提升約25%，與更高退火溫度相比，在相同退火時間下，更可提升約50%。和室溫冷輥軋相比，低溫輥軋可導入更多應變能，有效提升再結晶速率，且無論是部分再結晶或是完全再結晶組織，皆可證實低溫輥軋具有更佳的晶粒細化效果。

關鍵字

CoCrNi ； 中熵合金 ； 低溫輥軋 ； 退火 ； 變形雙晶 ； 部分再結晶 ； 完全再結晶

並列摘要

Cryo rolling and subsequent annealing were introduced to CoCrNi medium entropy alloy to study its effect on microstructure and mechanical properties. Cryo rolling was observed to raise high-density dislocation, shear bands, and profuse deformation twin. The combination of the deformed structure yielded the ultimate tensile strength of ~1500 MPa and strain-to-failure around 2%. Subsequent annealing on cryo rolled specimen introduced partially recrystallized microstructure at annealing at 700°C and fully recrystallized at 800°C, with increasing annealing time and temperature decreased the strength but simultaneously improved the elongation. Abnormal hardening induced by annealing was observed after at 600°C, which increased the ultimate tensile strength (UTS) and hardness up to 25% compared to the condition which did not anneal and up to 50% compared to the condition annealed at higher temperature for the same annealing time. In addition, cryo rolling was shown to induce more strain during the rolling than cold rolling and provided a faster recrystallization rate. Grain refinement effects were also verified in both partial and fully recrystallized microstructure in the cryo rolling specimen.

並列關鍵字

CoCrNi ； medium entropy alloy ； cryo rolling ； annealing ； deformation twin ； partially recrystallization ； fully recrystallization

參考文獻

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