High-entropy alloys(HEAs),with a new alloying concept,could possess many unique mechanical and functional properties.The current work investigated whether one such alloy offers potential for bearing surfaces under dry conditions.The dry,reciprocating sliding wear characteristics of AlCoCrFeNiTi0.5alloy were investigated under various applied loads and sliding speeds.Transmission electron microscopy(TEM) and scanning electron microscopy(SEM) were utilized to characterize internal structure and wear surfaces of the alloy,respectively.It is found that the AlCoCrFeNiTi0.5alloy preserves better wear resistance than Fe77Ni23solid solution alloy,Ti-46Al-2Cr-2Nb intermetallic alloy,or a wear-resistant steel AISI52100,especially under higher loads.The wear rate increases slowly with the applied loads increasing and keeps steady under different sliding speeds.The wear mechanisms are abrasive wear,adhesive wear and oxidative wear.The nano-sized Fe-Cr solid solution and Al-NiTi rich intermetallic phase precipitated in the dendritic regions and the formation of oxidation play important roles in the good wear resistances of this high-entropy alloy.
Yuan YuJun WangJin-Shan LiHong-Chao KouSi-Zhe NiuSheng-Yu ZhuJun YangWei-Min Liu
Refractory high-entropy alloys present attractive mechanical properties,i.e.,high yield strength and fracture toughness,making them potential candidates for structural applications.Understandings of atomic and electronic interactions are important to reveal the origins for the formation of high-entropy alloys and their structure−dominated mechanical properties,thus enabling the development of a predictive approach for rapidly designing advanced materials.Here,we report the atomic and electronic basis for the valence−electron-concentration-categorized principles and the observed serration behavior in high-entropy alloys and highentropy metallic glass,including MoNbTaW,MoNbVW,MoTaVW,HfNbTiZr,and Vitreloy-1 MG(Zr_(41)Ti_(14)Cu_(12.5)Ni_(10)Be_(22.5)).We find that the yield strengths of high-entropy alloys and high-entropy metallic glass are a power-law function of the electron-work function,which is dominated by local atomic arrangements.Further,a reliance on the bonding-charge density provides a groundbreaking insight into the nature of loosely bonded spots in materials.The presence of strongly bonded clusters and weakly bonded glue atoms imply a serrated deformation of high-entropy alloys,resulting in intermittent avalanches of defects movement.
William Yi WangShun Li ShangYi WangFengbo HanKristopher A.DarlingYidong WuXie XieOleg N.SenkovJinshan LiXi Dong HuiKarin A.DahmenPeter K.LiawLaszlo J.KecskesZi-Kui Liu
The effect of heat treatment on microstructure and tensile properties of as-cast Al_(0.5)CoCrFeNi high-entropy alloy was investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM) equipped with energy-dispersive spectroscopy(EDS), and tensile tests.The results show that heat treatment strongly affects the microstructure, particularly the morphology of bcc phases,and improves tensile properties. Microstructure analysis reveals that rod-shaped and elliptoid phases appear in the matrix after heat treatment at 1150 ℃. Besides, under850 ℃ heat-treated condition, ultimate tensile strength increases by about 60% without sacrificing much plasticity,which can be attributed to the content of bcc phases and fine precipitates dispersed in the dendrites. For other heattreated conditions, tensile ductility increases by at least30%, especially 60% for heat treatment at 450 ℃, and strength also improves. Fracture analysis indicates that the fracture mode of heat treatment at 850 ℃ is a mixture of quasi-cleavage and ductile fracture, while the other heattreated conditions show the mode of ductile fracture.
The tribological properties of AlCoCrFeNi and AlCoCrFeNiTi_(0.5) high entropy alloys under gear oil and multiply alkylated cyclopentanes(MACs)lubrication condition have been studied.The equiaxed crystal structure of AlCoCrFeNi alloy is obtained after heat-treatment.The AlCoCrFeNiTi_(0.5) alloy keeps dendrite structure.Under the gear oil with good lubrication action,AlCoCrFeNiTi_(0.5) alloy preserves better tribological properties than AlCoCrFeNi alloy.The delamination and crack behaviors tend to occur in the grain boundary of AlCoCrFeNi alloy and along the interdendrite region of AlCoCrFeNiTi_(0.5) alloy.Under the MACs with relatively poor lubrication action,the applied load slightly influences the wear behavior of AlCoCrFeNi alloy,but seriously impacts the wear mechanism of AlCoCrFeNiTi_(0.5) alloy.Compared with AlCoCrFeNi alloy,AlCoCrFeNiTi_(0.5) alloy keeps better wear-resistance at low applied load of 100 N,but preserves less wearresistance at high applied load of 200 N.
Yuan YuJun WangJinshan LiJun YangHongchao KouWeimin Liu
