时效热处理对增材制造FeCoNi中熵合金微观组织与力学性能的影响

Effect of Aging Heat Treatment on Microstructure and Mechanical Properties of FeCoNi Medium Entropy Alloys Fabricated by Additive Manufacturing

采用激光选区熔化(SLM)技术制备了一种新型高强FeCoNi中熵合金,通过SEM、TEM、EBSD和XRD分析了时效热处理对FeCoNi合金微观组织与力学性能的影响。结果表明:沉积态样品为单相的BCC固溶体,平均晶粒尺寸为4.29μm,显微硬度为HV 336,抗拉强度1010 MPa,伸长率约4%。经过470℃热处理后,在晶界与晶内析出白色颗粒状沉淀相,TEM分析为富Ni的Ni_(3)Fe金属间化合物。Ni_(3)Fe相含量随热处理时间的延长逐渐增加,时效4 h后析出相含量最多为13%,合金平均硬度增至HV 535,与沉积态相比硬度提升了59%,抗拉强度提高到1514 MPa。470℃低温时效热处理使合金组织中产生了纳米级Ni_(3)Fe析出相,同时细化晶粒,且析出相与基体呈现共格关系,显著提高合金强度。

A novel high strength FeCoNi medium entropy alloy fabricated by selective laser melting technology(SLM).The effects of aging heat treatment on the microstructure and mechanical properties of FeCoNi alloy were investigated by SEM,TEM,EBSD and XRD.The results showed that the as-deposited sample was a single-phase BCC solid solution with an average grain size of 4.29μm,microhardness of HV336,ultimate tensile strength of 1010 MPa and elongation of about 4%.After heat treatment at 470℃,white granular precipitates were produced at grain boundaries and within grains,which was analyzed by TEM as Ni-rich Ni_(3)Fe intermetallic compound.The content of Ni_(3)Fe phase gradually increased with the extension of heat treatment time,and the maximum precipitated phase content was 13%after aging for 4 h.The average microhardness of the alloy increased to HV535,the microhardness increases by 59%compared with the as-deposited alloy,and the tensile strength increased to 1514 MPa.The lowtemperature aging heat treatment at 470℃produced nanoscale Ni_(3)Fe precipitated phases in the alloy structure and refined the grains,and the precipitated phases showed a coherent relationship with the matrix,which significantly improved the alloy strength.