Effect Of Deep Cryogenic Treatment On Microstructure And Properties Of Al_xCrFe₂Ni₂ High Entropy Alloy

Since the concept of high-entropy alloy was put forward,its simple phase structure and excellent performance have become a hot topic of research by domestic and foreign scholars.The research of new materials is usually compared with that of traditional alloys,so alloying,ceramic phase addition,extrusion,rolling and heat treatment,which are often used in traditional alloys,have also become the research direction of high-entropy alloys.However,the high price of alloying elements selected by most high-entropy alloy systems has limited their application prospects,and as a branch of heat treatment,the effect of deep cryogenic treatment on high-entropy alloy,which is widely used in traditional alloy research,has not been studied.In this paper,AlCrFeNi high-entropy alloy with relatively low cost was selected as the research object,and Al_xCrFe₂Ni₂ high-entropy alloy with different Al contents was designed to obtain a group of Al_xCrFe₂Ni₂ high-entropy alloy with the best comprehensive performance,which was cryogenized at different time?4,8,12,24,48 h?.The effects of deep cryogenic treatment on the microstructure and properties of Al_xCrFe₂Ni₂ high entropy alloy were studied by means of scanning electron microscopy?SEM?,X-ray diffraction?XRD?,hardness tester,electronic universal testing machine and friction and wear testing machine.The results show that the crystal structure of Al_xCrFe₂Ni₂ high-entropy alloy changes with the increase of Al content?x=0.2?1.6?:Single FCC phase?x?0.6?,FCC phase+BCC phase ?0.8?x?1.0?,single BCC phase?x?1.2?;With the increase of Al content,the amd structure appeared in the alloy structure,which gradually increased,and finally completely changed to amd structure;The element distribution in the alloy changed from uniformly distributed?x<0.6?to Al,Ni enriched in BCC phase,Fe and Cr enriched in FCC phase?0.6<x<1.2?,and finally became uniformly distributed again?x?1.2?.When the x value increased from 0.2 to 1.6,the vickers hardness of Al_xCrFe₂Ni₂ high-entropy alloy increased from 105 HV to 465 HV and reached a maximum value of 342.85%at x=1.6.The yield strength increased from 139 MPa to 1288 MPa, and the alloy broke when x?1.2 was compressed at room temperature.The maximum value increased by 826.62%when x=1.6.After deep cryogenic treatment,the crystal structure of AlCrFe₂Ni₂ high-entropy alloy remained unchanged and remained BCC+FCC phase,but the orientation of BCC phase and B2phase in the alloy changed.After deep cryogenic treatment,the long stripe FCC phase in the alloy structure broke,became shorter and more disordered.During deep cryogenic treatment,the disordered BCC phase and B2 phase were transformed into each other;After treatment,the distribution of elements in the microstructure of the alloy did not change obviously.Al and Ni were still enriched in BCC phase,while Fe and Cr were enriched in FCC phase.With the increase of deep cryogenic treatment time,there was no obvious brittle transition.The vickers hardness,yield strength and wear resistance of the AlCrFe₂Ni₂ alloy increased first and then decreased.The optimal comprehensive mechanical properties were obtained at the deep cryogenic treatment time of 4 h,the vickers hardness of 338 HV was 11.6%higher than that of the cast alloy,the yield strength of 920 MPa was 22.7%higher than that of the cast alloy,and the average friction coefficient was 0.643.