Residual stress estimation in crystalline phases of high-entropy alloys of the AlxCoCrFeNi system

Abstract

Introduction. All plastically deformed alloys are characterized by crystal defects that increase the internal energy of the system. These defects also result in residual stresses that have a complex effect on the material properties. Macrostresses are often the most critical and can lead to warpage, reduced corrosion resistance, and changes in material strength characteristics. The purpose of this work is to assess the residual stresses of the primitive cubic phase of high entropy alloys Al0.6CoCrFeNi and AlCoCrFeNi. Research methods. The crystal structure of the alloys is studied using the method of X-ray diffraction analysis. Experiments on X-ray diffraction analysis were carried out at the Siberian Center for Synchrotron and Terahertz Radiation on a VEPP-4 (Novosibirsk, INF SB RAS, 5-A line «X-ray microscopy and tomography»). Studies using synchrotron radiation were carried out in the transmission mode. The evaluation of the residual macrostresses of the crystalline phases of the alloys was based on the analysis of the change in the shape of the diffraction rings with a change in the azimuth angle (). Materials. The objects of research are ingots of high-entropy alloys Al0.6CoCrFeNi and AlCoCrFeNi. The ingots were obtained from pure metals by argon arc melting with cooling on a copper plate. To conduct further studies, cylindrical samples are cut from the ingots, which were subjected to plastic deformation according to the uniaxial compression scheme. Results and discussion. The obtained results indicate that the Al0.6CoCrFeNi alloy is characterized by higher macrostresses than the AlCoCrFeNi alloy. The residual deformation of the B2 phase lattice of AlCoCrFeNi alloy along the direction [100] is 2.5% at an external load of 2,500 MPa. The distortion value of the lattice of this phase for the alloy Al0.6CoCrFeNi is equal to 5.5% under similar external conditions. In addition, the plastic deformation of the Al0.6CoCrFeNi HEA did not lead to its destruction. This allows concluding that the increased ductility of this alloy is associated not only with the presence of a phase with a FCC lattice, but also with an increased compliance of the phase with a primitive lattice.