| Metal materials are important for industry,and how to improve the strength of metal structural materials has always been the focus of researchers High-entropy alloys(HEAs)break the limitation of traditional metals single principal element.The designability and adjustability of the components of HEAs are conducive to the formation of a special micro-structure structure,thereby obtaining ultra-high strength.The appearance and development of HEAs s have greatly expanded the field of metal materials and become one of the hot spots in the research of new metal structural materials in recent years However,the comprehensive mechanical properties of HEAs need further improvementIn this paper,the most popular AlFeNiCoCr high-entropy alloy is studied as a research object.AlFeNiCoCrB_x high-entropy alloy powders were synthesized using a high-energy ball mill.The as-synthesized powders were then dandified by spark plasma sintering(SPS)technique.The effect of B content on structure and mechanical properties of the AlFeNiCoCr high-entropy alloy was systematically studied.Furthermore,the effects of sintering process parameters(ball milling time,holding time and heat treatment temperature)on the structure of the AlFeNiCoCrB high-entropy alloy were discussed.The main conclusions can be drawn as follows:(1)For the as-milled AlFeNiCoCrB_x high-entropy alloy powders,when x=0 and 0.5,the main phases are FCC and BCC;when x=1,the only phase can be detected is BCC.With B content increased from 0 to 1,the diffraction peak of the as-milled powders gradually shifted to the right,which indicates lattice distortion induced by the B doping.For the as-sintered AlFeNiCoCrB_x high-entropy alloy samples,Al-based phase appeared with no obvious differences of BCC and FCC phases.In addition,a boride phase is observed The microscopic morphology of the block presents a network structure enriched with B,Fe and Cr elements.The thickness of the boride-rich area increased with the increase of B content.The hardness of AlFeNiCoCrB_x high-entropy alloy bulk samples increased with B content.When x=1,the hardness of the alloy is about 2 times of the B-free alloy.However,the AlFeNiCoCrB is brittle.With the addition of rare earth element Y to the AlFeNiCoCrB high-entropy alloy,the network structure in the alloy disappears and the continuity between the substrates is improved.Fracture toughness increases by about 40%with only 8%hardness lose(2)The composition of the Al-Fe-Ni-Co-Cr-B mixed powders with different ball milling time was studied.It was found that during the mechanical alloying process,the lower the melting point of each component,the earlier the alloying process is completed.After 60 hours of ball milling,the alloying process was completed,with the powder grain refinement of about 36%,and the lattice strain of 0.703%.When the alloying fails to complete,the components in the synthesized spherical-like powder are not evenly distributed,with Al,Co,Ni→Fe→Cr from outside to inside.In the AlFeNiCoCrB high-entropy alloy bulk samples sintered from powders synthesized at different ball milling time,the boride content increases with the ball milling time,and the hardness also increases(3)When the heat treatment temperature of the AlFeNiCoCrB_x(x=0,1)powders exceeds 700℃,boride phase appears in the powder.As the heat treatment temperature increases,the boride content increases,indicates that the formation of boride is related to the temperature.No obvious changes can be found for phase composition of the B-free powders with the change of heat treatment temperature;In addition,the solid solution phase of the BCC structure gradually changes into the solid solution phase of the FCC structure(4)In AlFeNiCoCrB_x(x=0,0.5 and 1)high-entropy alloys,when x=0 and 1,the phase composition remains unchanged with the change of the holding time;when x=0.5,the phase composition of the as-sintered samples changed.For AlFeNiCoCrB bulk sample,no obvious change can be found with different heat treatment holding times. |
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