| At present,agricultural machinery equipment is included in China's key development areas,and the performance of key components of agricultural machinery in China is still far behind the international advanced level.The development of new agricultural machinery materials is extremely important for the development of agricultural machinery equipment.Medium entropy alloy is a new metal material proposed on the basis of high entropy alloy,which shows the characteristics of high strength plasticity due to the particularity of the structure,and has become a new research hotspot in the field of metal materials,and has broad application prospects in the key components of agricultural machinery.In this paper,Cr Co Ni medium entropy alloy was formed by selective laser melting(SLM)technology.The effects of different laser power on the microstructure and properties of Cr Co Ni medium entropy alloy formed by SLM were studied in order to determine the optimal forming power.The effects of post-treatment on microstructure and mechanical properties of entropy alloy in Cr Co Ni prepared by SLM were studied by deep cryogenic treatment and annealing post-treatment.Specific research results are as follows:The effects of laser power(225 W,250 W,275 W,300 W and 325 W)on the microstructure and mechanical properties of Cr Co Ni medium entropy alloy formed by SLM were studied.It was found that the phase structure of Cr Co Ni medium entropy alloy formed by different laser power is a single face centered cubic(FCC)solid solution.With the increase of laser power,the compactness and mechanical properties of the alloy increased and then decreased.Compared with other powers,the Cr Co Ni medium entropy alloy prepared by 275 W has the highest hardness(the hardness of cross-section and longitudinal section is about351 HV and 345 HV),the lowest wear amount(the wear amount of cross-section and longitudinal section is about 160 mg and 161 mg),the highest yield strength and tensile strength(695.40 ± 9.42 MPa and 959.37 ± 16.07 MPa respectively),and the elongation at break is 27.10 ± 2.39%.The effects of different time(4 h,12 h,24 h)cryogenic treatment on the microstructure and mechanical properties of Cr Co Ni medium entropy alloy formed by 275 W laser power were studied.It was found that the alloy is still a single FCC phase,but the internal defects of the alloy decreased and then increased with the cryogenic time.After cryogenic treatment,the grain size of Cr Co Ni medium entropy alloy formed by SLM was refined and the mechanical properties were improved.The hardness of the cross-section and longitudinal section of the alloy after cryogenic treatment for 12 h were increased by 7.5% and 4.9% respectively compared with that before cryogenic treatment,the wear amount of the cross-section and longitudinal section is reduced by 10.6% and 12.4% respectively compared with that before cryogenic treatment,the yield strength of the alloy after cryogenic treatment for 12 h was reduced by 8.2%,the tensile strength was increased by 0.3%,and the elongation at break is increased by 41.3%,The plasticity of the alloy was improved most significantly after cryogenic treatment for 12 h.The alloy can maintain high strength and good plasticity at the same time.The effects of annealing treatment at different time and temperature on the microstructure and mechanical properties of Cr Co Ni medium entropy alloy formed by 275 W laser power were studied.It was found that the phase structure of the alloy did not change to a single FCC phase,but the melt path gradually disappeared with the increase of annealing temperature and time.When the annealing temperature was 700?,the alloy grain was refined and the alloy properties were improved.The hardness of the cross section of the alloy annealed at 700? for 12 h and the longitudinal section of the alloy annealed at 700? for 8 h were the highest,which were increased by 7.5% and 9% respectively compared with that before annealing.The wear of the cross section of the alloy annealed at 700? for 12 h and the wear of the longitudinal section of Cr Co Ni medium entropy alloy formed by laser melting at 800 ? and post-treatment were the least,Compared with that before annealing,it decreased by 12.5% and 6.2% respectively.In the tensile test,the appropriate annealing time and temperature could effectively improve the strength and plasticity of the alloy.The plasticity of the alloy was the most obvious when annealed at 600? for 12 h,reaching 35.32± 7.37%,which was 30.3% higher than that before annealing,but the strength was slightly lower than that before annealing.The tensile strength was the most obvious when annealed at800? for 3 h,which was 2.9% higher than that before annealing.In addition,the plasticity was not reduced while maintaining high strength,compared with the alloy before annealing. |
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