激光选区熔化增材制造双相高熵合金组织调控与强化机制

Tailored microstructures and strengthening mechanisms in an additively manufactured dualphase high-entropy alloy via selective laser melting

双相高熵合金因具有优异的综合力学性能而备受关注.本文对激光选区熔化制备的AlCrCuFeNi3.0双相高熵合金微观组织进行了调控,揭示了分层组织形成的机理.研究发现,当激光扫描速度为400 mm s-1时,AlCrCuFeNi3.0成分进入共生区,随着扫描速度的增加,冷却速率增加,该成分将偏离共生区.固液前沿Cr和Fe溶质的富集产生成分过冷,有利于异质形核和等轴晶的形成.近共晶组织与近等轴晶的共同作用有效地抑制了开裂.在拉伸变形过程中,发现了类似于晶界强化的晶间背应力强化现象.同时,由面心立方和有序体心立方(B2)双相纳米结构组成的近共晶组织导致晶内塑性变形不协调,从而产生晶内背应力.而B2相中富铬的纳米析出相发生位错剪切变形,可以强化背应力.此外,本文对多种强化机制进行了物理评估,发现背应力强化显著提高了该合金的力学性能.

Dual-phase high-entropy alloys(DP-HEAs)with excellent strength-ductility combinations have attracted scientific interests.In the present study,the microstructures of AlCrCuFeNi3.0DP-HEA fabricated via selective laser melting(SLM)are rationally adjusted and controlled.The mechanisms engendering the hierarchical microstructures are revealed.It is found that the AlCrCuFeNi3.0fabricated by SLM at the scanning speed of 400 mm s-1falls into the eutectic coupled zone,and increasing the scanning speed will make this composition deviate away from the eutectic coupled zone due to the increased cooling rate.The enrichment of Cr and Fe solutes with large growth restriction values ahead of the solid/liquid interface can develop a constitutional supercooling zone,thus facilitating the heterogeneous nucleation and nearequiaxed grain formation.The synergy of the near-eutectic DP nano-structures and near-equiaxed grains instead of columnar ones effectively suppresses cracking for the as-built DP-HEA.During the tensile deformation,the intergranular back stress hardening similar to the grain-boundary strengthening is discovered.Meanwhile,the near-eutectic microstructures comprised of soft face-centered cubic and hard ordered bodycentered cubic(B2)DP nano-structures lead to plastic strain incompatibility within grains,thus producing the intragranular back stress.The Cr-rich nano-precipitates inside the B2 phase are found to be sheared by dislocation gliding and can complement the back stress.Additionally,multiple strengthening mechanisms are physically evaluated,and the back stress strengthening contributes obviously to the high performances of the as-built DP-HEA.