Study On Microstructures And Properties Of CrFeNiTi_x Quaternary Component Alloys

High entropy alloy?HEA?is defined as a new class of alloy with high configurational entropy in regular liquid state,which which breaks through the design of traditional alloys.Due to the presence of four effects,HEAs present unique structure and novel properties such as excellent mechanical property,strong oxidation resistance and thermal property,as well as exceptional electrical property,bringing about people's attention and good prospect of application.By referring to some strengthening mechanism of traditional alloys,such as solid solution strengthening,precipitation strengthening etc,CrFeNiTi_x multi component alloys with Ti addition were prepared through arc melting based on Cr-Fe-Ni equimolar-ratio alloy.In this work,the microstructure and properties of CrFeNiTi_x quaternary alloys were studied to improve the theory of phase formation of HEAs with at least four equiatomic or near-equiatomic elements.At the same time,it could provide a reference to enhance the properties of HEAs.All conclusions could be drawn as follows.As-cast CrFeNiTi_x alloys consisted of the principal face-centered cubic?FCC?CrFeNi solid solution and body-centered cubic?BCC?[Fe,Cr]solid solution,with an amount of Ni₃Ti hexagonal close-packed?HCP?intermetallic.Meanwhile,a small amount of Ni_2.67Ti_1.33 high-temperature phase appeared because of the casting process.The alloys exhibited the typical dendrite,when x<0.4,FCC and BCC phases existed in the dendrites,rich-?Ni,Ti?phase existed in the inter-dendrites,and grain growth of CrFeNiTi_0.3 alloy appeared.When x?0.4,BCC phase was precipitated from dendrites,forming zone of phase transition from FCC to BCC phase.In addition,a large number of uniform and circular rich?Ni,Ti?nano-precipitated phases were found in the dendrites of CrFeNiTi_0.4.4 alloy.After annealing,the main change was the gradual disappearance of Ni_2.67Ti_1.33 phase.The main structure of the alloy was dendrites and granular structure,and the component segregation was weakened.Meanwhile,the round?Ni,Ti?nanoparticles matured and grew into needle-rod structure.The hardness of CrFeNiTi_x alloys was increased with the addition of Ti content,reaching a maximum of 718.2HV.After heat treatment,the hardness of the alloys was increased obviously.Additionally,the compressive strength of as-cast CrFeNiTi_x alloys increased with the increase of Ti content,up to 2475.41MPa.Under the influence of precipitation strengthening and solid solution strengthening,the compressive strength and plastic deformation of the annealed alloys decreased obviously.From the fracture morphology analysis,it can be seen that CrFeNiTi_x alloys were dominated by brittle cleavage fracture and intergranular fracture,which is attributed to excessive precipitation of?Ni,Ti?phase that makes the alloys'plasticity worse.In the meantime,electrothermal and magnetic properties of CrFeNiTi_x alloy at room temperature were investigated and the related factors affecting the results show that the resistivity of CrFeNiTi_x alloys increases with increasing Ti content.As a whole,coercive force of CrFeNITi_x alloys were on the rise with the addition of Ti content.Also,the saturation magnetization,remanent magnetization,etc presented maximum,then decreased with the increasing Ti content.In the meantime,various magnetic properties of alloys after annealing had a certain degree of decline.In Addition,oxidation behavior of CrFeNiTi_x?x=0.2,0.4,0.6?alloys at 900°C and electrochemical corrosion of CrFeNiTi_x alloys in NaCl and H₂SO₄ solutions were investigated.The result showed that the Ti content increased from 0.2 to 0.6,the oxide index was increased from 2 to 3.The products of oxidation were mainly Cr₂O₃ and TiO₂,including outer TiO₂,the middle and single Cr₂O₃ layer,the inner and discontinuous TiO₂ layer.The thickness of oxide layer increases with the increase of Ti content.What's more,the corrosion resistance of CrFeNiTi_x alloys in NaCl solution and H₂SO₄ solutions decreased with the increase of Ti content,mainly including oxygen consumption corrosion and hydrogen evolution corrosion.