Preparation And Properties Of AlCoCrFeNiCuCNTs (x) High Entropy Alloy By Powder Metallurg

High-entropy alloys have been in the focus of research topic due to their unique alloy design concepts and excellent comprehensive properties.Among them,the AlCoCrFeNiCusix-element system high-entropy alloy is one of the earliest studied systems in the field of alloys,which has a simple FCC+BCC dual-phase structure,high strength,and good corrosion resistance,but poor plasticity performance and mechanical properties need to be further improved.Currently,the research on CNTs as a reinforcing phase to strengthen AlCoCrFeNiCuhigh-entropy alloys is not completely clear in China,and there are still some uncertain factors affecting the microstructure and properties.Therefore,further research and exploration are needed.In this paper,AlCoCrFeNiCuCNTs(x)(x=0.2wt.%、0.5wt.%、0.8wt.%、1.0wt.%、1.2wt.%)high entropy alloy was prepared by powder metallurgy method,and the relationship between microstructure and properties was studied.The microstructure of AlCoCrFeNiCuCNTs(x)high entropy alloy powder and bulk was analyzed by means of SEM,EDS,XRD,Raman spectroscopy and metallographic microscope.The physical and chemical properties of high entropy alloy were characterized by density,microhardness,compression mechanical properties,electrochemical corrosion and nitric acid corrosion resistance,and the relationship and difference between CNTs and Ni-CNTs on the microstructure and properties of high entropy alloy were studied.It is found that the ball milling speed and milling time are of great significance to the distribution uniformity and CNTs dispersion of high entropy alloy powder.The high entropy alloy powder prepared by 300r/min ball milling for 10 h has relatively uniform particle distribution and uniform particle size.CNTs adheres to the surface of alloy particles in the form of a single root and the agglomeration is not obvious.The study of AlCoCrFeNiCuCNTs(x)high entropy alloy powder with different mass fraction of CNTs shows that the phase structure of AlCoCrFeNiCuCNTs(x)high entropy alloy powder is similar to that of high entropy alloy without CNTs.After mechanical ball milling,there is still a diffraction peak of elemental elements,and the alloy powder has not been fully alloyed.The solid solution high entropy alloy bulk was obtained by vacuum hot pressing sintering at 1200 °C.Because the nickel plating layer of Ni-CNTs can promote the interface bonding between alloy and CNTs to some extent,its dispersion in alloy powder is obviously better than that of CNTs.The R value of Al Co Cr Fe Ni Cu(Ni-CNTs(x))alloy powder is higher than that of Al Co Cr Fe Ni Cu(Ni-CNTs(x))high entropy alloy powder,indicating that Ni-CNTs is easier to alloy with other metals.The study of AlCoCrFeNiCuCNTs(x)high entropy alloy with different CNTs content shows that with the increase of CNTs content,a large number of CNTs aggregates appear in the high entropy alloy,in which the contents of carbide and hard phase are increasing.When the CNTs content is less than or equal to 0.5wt.%,CNTs has good dispersion in high entropy alloy,which can inhibit the growth of alloy particles and refine grains.For the high entropy alloy with the addition of CNTs,the phase structure of the high entropy alloy changes with the change of CNTs content.When the mass fraction are 1.0% and 1.2%,the main phase changes from FCC to BCC.For Al Co Cr Fe Ni Cu(Ni-CNTs(x))high entropy alloy,FCC is still the main phase with the change of Ni-CNTs content.Due to the increase of CNTs agglomeration and the amount of carbides,the density of AlCoCrFeNiCuCNTs(x)high entropy alloy is lower than that of high entropy alloy without CNTs.Because of the existence of hard phase,the density of Ni-CNTs high entropy alloy increases at first and then decreases gradually.The study on the mechanical properties of high entropy alloy blocks shows that the hardness of the alloy increases at first and then decreases with the increase of CNTs content.At the Ni-CNTs content 0.5wt.%,the hardness of Ni-CNTs high entropy alloy reaches 570.98 HV,which is nearly 25% higher than that of high entropy alloy without CNTs.CNTs significantly improves the strength of high-entropy alloy,and the compressive strength is about 15% higher than that of high-entropy alloy without CNTs.At the same time,when the content is 0.5wt.%,the plasticity of high-entropy alloy is 36.81%,which is nearly 15% higher than that of high-entropy alloy without CNTs.For the addition of CNTs high entropy alloy,cleavage fracture and ductile fracture occur simultaneously during compression,while the fracture mode of adding Ni-CNTs high entropy alloy is mainly ductile fracture.The electrochemical corrosion of high entropy alloy shows that the corrosion resistance of high entropy alloy increased at first and then decreased with the increase of CNTs content.When the content of Ni-CNTs is 0.8wt.%,the high entropy alloy has the best electrochemical corrosion performance,and the corrosion voltage reaches-167 m V.The study of nitric acid corrosion resistance shows that the nitric acid corrosion resistance of the alloy increases at first and then decreases with the increase of CNTs content.When the Ni-CNTs content is 0.5wt.%,the nitric acid corrosion resistance of high entropy alloy is the best.The corrosion morphologies of high entropy alloys are affected by both pitting corrosion and surface corrosion.