Study On The Composition Design And Properties Of High Entropy Alloys Based On Chromite

With the rapid development of economy,China’s total demand for chromite is increasing day by day.However,the total amount of chromite resources in China is particularly deficient.The characteristics of"scattered","low"and"small"make it particularly important to make full use of the limited chromite resources.In order to solve the problems of high emission,high energy consumption and low comprehensive utilization rate in the beneficiation and smelting of chromite resources.It provides theoretical and technical guidance for the rapid application of ferrochrome ore powder in the field of equipment manufacturing and mineral processing application in China.At the same time,improve the reliability and stability of mining equipment,and help coal enterprises to green mining,sustainable development,efficiency and consumption reduction.Based on the study of the intrinsic state parameters and first-principles calculation of CrFeNiAlSi alloy system,this paper uses chromite powder,laser sintering and laser cladding technology to directly and rapidly synthesize high entropy alloy matrix composites.The composition CrFeNiAlSi of the five-element high entropy alloy matrix composite prepared based on chromite powder was optimized and explored.The elements B,Co and Ti were added and their contents were adjusted to adjust the phase content and promote the composition of the in-situ precipitated phase,which provided a design idea for further using chromite powder to prepare high entropy alloy and its composite materials,and at the same time,high-performance multiphase high entropy alloy for mining equipment and key components was developed.The study results show that the:To clarify the influence of Cr,Fe and other elements on the whole alloy,so as to provide a more scientific range of composition ratio selection for the rapid preparation of HEAs from chromite.According to the solid solution formation rule,six parameters of CrFeNiAlSi series high entropy alloy have been calculated.At equimolar ratios of Cr_1.6-2.0,Fe_1.6-2.0,Ni_1.6-2.0,Al_<1.0and Si_0.2for other elements,the alloy tends to form the structural BCC;at other ratios,the alloy tends to form the coexistence of the structural BCC and the intermetallic compound of Si.The lattice constant,density and elastic properties of the alloy have been calculated by using the first principle and virtual lattice approximation method to construct the BCC structure model.The Cr_0.6,Fe_0.2,Fe_0.4,Fe_0.6,Fe_1.2,Ni_0.6,Ni_0.8,Ni_2.0,Al_1.2,Si_0.4alloys show more obvious elastic isotropic characteristics.HEAC have been successfully prepared by laser sintering and laser cladding with chromite ore powder as doping component.The hardness and wear resistance of CrFeNiAlSi HEAC and Cr Fe Ni Al_0.5Si HEAC coatings have been improved after adding a certain amount of chromite ore powder.The laser sintered CrFeNiAlSi HEAC was composed of BCC phase.After doping chromite powder,they were composed of BCC phase,FCC phase,Cr₅Si₃phase and chromite phase.When the content of chromite ore powder is 6%,the microhardness value of the alloy is the largest,909 HV,and the wear amount per unit area of the alloy is the smallest,50.4 mg·cm^-2.The laser cladding Cr Fe Ni Al_0.5Si HEAC coating is a single BCC phase.When the equivalent atomic ratio of chromite ore powder is greater than 5.0%,the diffraction peak of FCC phase and Al₂O₃appears.The equivalent atomic ratio of chromite ore powder is from 0%to 15%,the hardness of the coating have increased from 643.5 HV to838.1 HV,the hardness have increased by 1.3 times,the wear amount per unit area have reduced by 30.7%,and the wear rate have reduced from 20.2mg·cm^-2to 14.0 mg·cm^-2.The phase of CrFeNiAlSi HEA obtained by laser sintering,laser cladding and vacuum melting was simple,the laser cladding alloy was a single BCC phase,and the other were BCC phase and FCC phase.The maximum hardness of laser cladding alloy was 875.1 HV,and the best wear resistance was 8.96mg·cm^-2.The vacuum melting dual phase CrFeNiAlSi alloy have been annealed at 600℃,800℃and 1000℃.The three temperature-annealed alloys were still in duplex.At three annealing temperatures,800℃annealing had the smallest element segregation and the most uniform element distribution.The alloy annealed at 800℃was passivated in 3.5wt%Na Cl solution,and the V_corrwas 0.016 mm/a,and the corrosion resistance was the best.B,Co and Ti elements can make CrFeNiAlSi HEAs form multiphase structure.B_xseries HEAs were composed of BCC phase,（Cr,Fe）₃Si phase and（Cr,Fe）B compound.Co_xHEAs all contain BCC phase and Cr₃Si phase.When the Co content increases to 1.2,a weak Ni Co Cr diffraction peak appeared.Ti_xHEAs consisted of BCC phase,Cr₃Si phase and Laves phase.The three kinds of hexabasic alloys all had dendritic morphology.The intergranular phase of gold is rich in Si,and the intragranular phase is Al Ni.B segregation and Cr form needle like second phase in B_xseries alloys;The intergranular and intragranular content of cobalt element in Co_xHEA is close to the nominal composition,and there is no segregation.The Ti element in Ti_xseries HEAs is enriched and presents a lamellar Laves phase.The content of B,Co and Ti of CrFeNiAlSi HEA have the best value on the hardness,wear resistance,corrosion resistance and high-temperature oxidation resistance.Ti_0.6HEA obtained the best comprehensive properties.The HEA has a maximum microhardness of 1415HV,a minimum wear per unit area of 0.72 mg·cm^-2,and a minimum annual corrosion rate of0.011 mm/a.When the HEA is oxidized at 800℃for 100h at constant temperature,B,Co and Ti elements can improve the high-temperature oxidation resistance of the alloy.The oxidation weight gain of B_0.1HEA was 2.85 mg·cm^-2,and that of B_0.7HEA decreased to 1.74 mg·cm^-2.With the extension of oxidation time,the oxidation weight gain of Co_xsystem and Ti_xsystem HEAs increased slowly in a parabolic trend.After 100 hours,the oxidation weight gain of Co_1.2and Ti_1.2HEA were 0.700 mg·cm^-2and 0.605 mg·cm^-2.The paper has 92 graphs,41 tables,and 191 references.