元素及氧化鈦對鈷鉻鎳中熵合金微結構與機械性質的影響

Effects of titanium and titanium dioxide additions on the microstructures and mechanical properties of CoCrNi

張瑋哲(Wei-Che Chang)

指導教授 ： 薛承輝

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202201981

摘要

本研究中(CoCrNi)100-xTix與(CoCrNi)100-x(TiO2)x中熵合金是由高真空電弧融煉爐所製備再經過均質化、熱軋以及退火來調質，在Ti系列中，在Ti-1.0和Ti-2.0中中熵合金的基材還是保持FCC結構，然而在Ti-3.0和Ti-4.0有生成HCP相的Ti(Ni, Co)3 析出物。在CoCrNi中添加Ti不只會因為較大的原子半徑造成晶格扭曲，同時也會帶來晶粒細化的效果，Ti含量的增加以及HCP相析出物的生成造成機械性質的提升，極限抗拉強度以及硬度的上升從866 MPa以及212 HV分別上升到1490 MPa以及409 HV，但同時也造成延性的下降，從77%下降到26%。在TiO2系列中，中熵合金保持著FCC結構，而且TiO2奈米顆粒均勻的分布，電子背散射衍射的結果顯露出了晶粒大小會隨著TiO2的添加而下降，TiO2的添加會帶來良好的機械性質例如極限抗拉強度、延性以及硬度，從TiO2-0的866 MPa、77%和212 HV分別到TiO2-0.4的1130 MPa、65%和248 HV，機械性質的結果展現了極限抗拉強度以及降伏強度大量的上升而同時只損失一點的延性，而其主要歸因於氧化物散佈強化以及晶粒細化所造成的強度以及硬化的上升。

關鍵字

中熵合金 ； 氧化物散佈強化 ； 機械性質 ； 微結構 ； 二氧化鈦添加 ； 鈦添加

並列摘要

In this study, a series of (CoCrNi)100-xTix and (CoCrNi)100-x(TiO2)x medium entropy alloys (MEAs) was fabricated, respectively, by high vacuum arc melting followed by homogenization, hot-rolling and annealing. In Ti series, the alloys remained a single-phase FCC solid solution for x=0, 1.0 and 2.0 and the Ti(Ni, Co)3 precipitates of HCP phase formed for x=3.0 and 4.0. The presence of Ti, which had the larger atomic radius than the other constituent elements, in the solid solution enhanced the lattice distortion and resulted in grain refinement. The addition of Ti led to the enhanced mechanical properties with the ultimate tensile strength and Vickers hardness increased from 866 MPa and 212 HV at x=0 to 1490 MPa and 409 HV, respectively, at x=4.0. However, the corresponding fracture elongation decreased from 77% to 26%. The strengthening mechanisms were mainly attributed to solid solution strengthening, grain refinement and precipitation strengthening. In TiO2 series, the MEAs were mainly composed of FCC matrix, in which TiO2 nanoparticles were uniformly distributed. Electron backscattered diffraction results revealed that the grain size decreased with the TiO2 addition. The addition of TiO2 led to good mechanical properties with the UTS, elongation and hardness of 866 MPa, 77% and 212 HV at x=0 to ~1130 MPa, ~65% and 248 HV, respectively, at x=0.4. The results demonstrated that both the yield strength and ultimate tensile strength were enhanced significantly with little loss in ductility.

並列關鍵字

medium entropy alloys ； oxide dispersion strengthening ； mechanical properties ； microstructure ； TiO2 nanoparticle addition ； Ti addition

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