烧结方式对CoCrNi中熵合金组织及力学性能的影响

Effect of Sintering Methods on Microstructure and Mechanical Properties of CoCrNi Medium Entropy Alloy

采用机械合金化法(MA)球磨制备CoCrNi中熵合金原料粉末,结合放电等离子烧结(SPS)或高真空烧结制取CoCrNi中熵合金,研究了球磨时间以及退火对CoCrNi中熵合金原料粉末微观形貌、颗粒尺寸及相结构的影响规律,对不同烧结方式制备的合金块体进行微观结构及力学性能研究。结果表明:随着球磨时间的延长,各单质粉末颗粒尺寸不断减小并逐渐融合,在球磨25 h后,原料粉末主要为fcc固溶体结构,还有少量的bcc相;在后续烧结过程中,少量bcc相发生相转变,组织中只有fcc相结构;退火烧结样品的弹性模量为6.57 GPa,是真空烧结的1.55倍,屈服强度为279.28 MPa,与真空烧结后样品的屈服强度相当,退火烧结的延伸率为35.97%,明显大于直接真空烧结;SPS烧结的块体合金表现出高达793.72MPa的屈服强度和61.08%的塑性应变,且维氏硬度(HV)达到3910.2MPa,与其它2种烧结方法相比,SPS在实现高熵合金(HEAs)快速低温烧结方面更具潜力。

CoCrNi medium entropy alloy raw material powder was prepared by mechanical alloying ball milling, in combination with spark plasma sintering or high vacuum sintering to prepare CoCrNi medium entropy alloy. The effects of milling time and annealing on the morphology, particle size and phase structure of CoCrNi medium entropy alloy powder were studied. The microstructure and mech anical properties of the alloy blocks prepared by different sintering methods were stud ied. The results show that with the extension of milling time, the particle size of each elemental powder decreases and gradually merges. After milling for 25 h, the raw powder is ma inly fcc solid solution structure, with a small amount of bcc phase. In the subsequent sintering process, a small amount of bcc phase changes, and only fcc phase structure exists in the structure. The elastic modulus of the annealed sample is 6.57 GPa, which is 1.55 times of t hat of the vacuum sintered sample. The yield strength of the annealed sample is 279.28 MPa, which is equivalent to that of the vacuum sintered sample. The elongation of the annealed sample is 35.97%, which is significantly higher than that of the direct vacuum sintere d sample. The SPS sintered bulk alloy has a yield strength of 793.72 MPa, a plastic strain of 61.08%, and a Vickers hardness of 39 10.2 MPa. Compared with the other two sintering methods, SPS has more potential in realizing rapid low temperature sintering of HEAs.