微晶铸造对K4169合金组织及持久性能的影响

Effect of Micro-Grain Casting Process on Microstructure and Stress Rupture Properties of K4169 Alloy

分别采用普通铸造、细晶铸造和微晶铸造工艺制得了晶粒度为ASTM M9~M7级、ASTM M14~M9级和ASTM 3~5级的K4169合金试样,研究了微晶铸造对K4169合金组织及持久性能的影响。研究结果表明,微晶铸造工艺可显著细化晶粒,降低凝固偏析,减少Laves相和大块MC碳化物,增加γ″相体积分数;使合金704℃/448 MPa条件下的持久性能相比于普通铸造和细晶铸造合金分别提高了621%和44%,达到614.9 h;断裂模式从普通铸造K4169的脆性穿晶断裂转变为微晶铸造K4169的韧性沿晶穿晶混合型断裂。微晶铸造工艺引起的晶粒细化和γ″相体积分数的提高,有效强化了K4169合金,而大块MC碳化物及Laves相的减少,减少了潜在的裂纹萌生、扩展位置,二者共同作用提高了K4169合金的持久寿命,并降低了性能数据分散性。微晶铸造工艺可获得良好的综合力学性能,提升K4169合金机匣、壳体、扩压器等整体结构件在700℃以下的服役性能,有良好的应用前景。

K4169 samples with grain size of ASTM M9~M7,ASTM M14~M9 and ASTM 3~5 were prepared by conventional casting process,fine grain casting process and micro-grain casting process,respectively.The effects of micro-grain casting process on the microstructures and stress rupture properties of K4169 alloy were analyzed.Results show that micro-grain casting process can significantly refine grains,reduce solidification segregation and the content of Laves phase and large bulk MC carbides,increase the volume fraction ofγ″phase,thus improve the mechanical properties of K4169 alloy.The stress rupture life at 704℃/448 MPa of micro-grain K4169 alloy is up to 614.9 h,which is 621%and 44%higher than that of conventional K4169 and fine-grain K4169,respectively.The fracture mode transforms from brittle transgranular fracture of conventional K4169 to ductile mixed-mode fracture(transgranular fracture and intergranular fracture)of micro-grain K4169.Grain refinement and the increased volume fraction ofγ″effectively strengthen K4169 alloy,while the decreases of Laves phase and large bulk MC carbides reduce the potential crack initiation and propagation locations.The combination of the above two points improves the stress rupture life of K4169 alloy and reduces the dispersion of performance data.The micro-grain casting process can obtain good comprehensive mechanical properties and improve the service performance of K4169 alloy below 700℃,which has a good application prospect.