冷轧变形量对热处理后CoCrFeMnNi高熵合金退火孪晶及力学性能的影响

The Influence of Cold-Rolling and Heat Treatment to the Annealing Twins and Mechanical Property in the CoCrFeMnNi High-Entropy Alloy

摘要:

经冷变形与热处理后的CoCrFeMnNi高熵合金性能会受到在退火过程中产生退火孪晶的影响，而孪晶形貌与种类的变化与冷变形量和热处理条件相关。探究了高温短时热处理下，冷变形量对退火孪晶及力学性能的影响。采用真空中频感应熔炼炉制备了FCC单相CoCrFeMnNi高熵合金，样品经均匀化退火后使用两辊轧机沿同一方向进行多次冷轧，得到不同变形量的样品。样品在900 ℃条件下退火1 h，采用金相显微镜、X射线衍射与透射电子显微镜对样品的微观组织形貌进行表征以观察样品中退火孪晶的变化，在室温下对样品进行了静态单轴拉伸试验，研究了不同变形量对于退火孪晶的影响以及退火前后力学性能的变化。结果表明，退火孪晶的种类和数量会随变形量变化：变形量30%的样品内部晶粒尺寸大，退火孪晶的种类和数量最少；变形量80%的样品晶粒尺寸与30%的样品相近，但退火孪晶数量、种类多；变形量50%的样品晶粒尺寸最小，退火孪晶数量与种类中等。未经热处理的样品其抗拉强度与变形程度呈正相关，抗拉强度最高可达到1 333.44 MPa，经900 ℃×1 h退火处理后，其抗拉强度与变形程度呈负相关，抗拉强度最高为585.81 MPa。结果表明，CoCrFeMnNi高熵合金在高温短时间的热处理条件下具有良好的相稳定性，轧制和退火后均为FCC单相结构，没有析出相产生。冷变形后的样品在热处理后样品内部发生了再结晶，晶粒的尺寸大小与退火孪晶的数量和种类以及样品的力学性能会随着变形量的不同产生变化。同时，合金内部产生的小尺寸退火孪晶起到了存储位错的作用。

Abstract:

The properties of CoCrFeMnNi high entropy would be affected by annealing twins which formed during the anneal， and the microstructure and types of twins were influenced by the cold deformation degree and heat treatment. This research was designed to study the influences of deformation degree to the twins. FCC single phase CoCrFeMnNi high entropy alloy was prepared by vacuum medium frequency induction melting furnace. The samples in different deformation were obtained by cold-rolling after homogenizing annealing， then the samples were annealed at 900 ℃ for 1 h. The microstructure characterization of annealing twins in the samples was obtained by optical microscope， X-ray diffraction and transmission electron microscope， and the static uniaxial tensile test at room temperature. The effects of deformation on annealing twins and the changes of mechanical properties before and after annealing were studied. The results show that the 30% deformation sample gets large grain size with a small number and variety of annealing twins. The grain size of 80% deformation sample is similar to the sample with 30% deformation， but the number and type of annealing twins are maximum. The 50% deformation sample shows the smallest grain size with medium quantity and variety of annealing twins. The tensile strength， getting from the tensile test， of the samples without heat treatment was positively correlated with the deformation degree and the highest tensile strength was 1 333.44 MPa， while the tensile strength was negatively correlated with the deformation degree after annealing at 900 ℃×1 h and the highest tensile strength was 585.81 MPa. The result shows that the CoCrFeMnNi high entropy alloy shows satisfying phase stability. The FCC structure was invariable during the cold-rolling and anneal without precipitated phase. The cold deformed samples appeared recrystallization after anneal， which causes the change of grain size， the quantity and variety of annealing twins and the mechanical property. At the same time， the ability of storage dislocation in alloy gets stronger due to the small-sized annealing twins.