稀土Gd对Ni-Cr-Mo合金热变形行为的影响

Effect of Rare Earth Gd on Thermal Deformation Behavior of Ni-Cr-Mo Alloys

含Gd镍铬钼合金作为乏燃料贮运用中子屏蔽材料具有广阔的应用前景,却在热加工时极易发生开裂,为了优化合金热变形工艺参数,本文以Ni-Cr-Mo合金为研究对象,研究了Gd加入后引起的组织变化。在变形温度为1 000~1 200℃、应变速率为0.01~5 s^(-1)条件下进行等温热压缩实验,计算合金相关材料常数及热变形激活能,构建热加工图并确定热加工窗口,结合微观组织进行分析,研究Gd对合金热变形行为的影响。结果表明,Ni-Cr-Mo合金中加入了1.2%的Gd,合金的变形激活能从472.15 kJ/mol降至422.9 kJ/mol,在热变形时合金的能量消耗效率更高,组织演变更充分,塑性失稳区域由高温向低温逐渐转移,并且增大了合金在1 000~1 060℃,0.01~0.32 s^(-1)低温低应变速率下安全区的面积。合金最佳热加工区间为:0.5真应变量,温度(T)为1 113~1 164℃,应变速率(ε)为0.01~0.2 s^(-1)。Gd在晶界或枝晶间以金属间化合物GdNi_(5)析出,GdNi_(5)相作为硬脆相,在热变形过程中其周围产生较大应变,导致组织中畸变能更高,从而促进周围变形晶粒发生再结晶,降低组织中的残余应变。

As a neutron shielding material for spent fuel storage, Ni-Cr-Mo-Gd alloy has broad application prospects, but it is prone to cracking during thermal working. In order to optimize the hot deformation process parameters of the alloy,this paper focuses on the study of Ni-Cr-Mo alloy, investigating the microstructural changes induced by the addition of Gd. Isothermal hot compression experiments were conducted at deformation temperatures of 1 000 ℃-1 200 ℃ and strain rates of 0. 01 s^(-1)-5 s^(-1) to calculate the relevant material constants and the activation energy for thermal deformation. Thermal working map was established to determine thermal deformation window, while the influence of Gd element on the thermal deformation behavior of the alloy was analyzed in conjunction with the microstructure. The results indicate that the addition of 1. 2% Gd to the Ni-Cr-Mo alloy reduces the deformation activation energy from 472. 15 kJ/mol to 422. 9 kJ/mol. This results in higher energy consumption efficiency during thermal deformation and more comprehensive microstructure evolution. The plastic instability zone gradually shifts from high to low temperatures, expanding the safe deformation zone of the alloy at low temperatures of 1 000 ℃-1 060 ℃ and low strain rates of 0. 01 s^(-1)-0. 32 s^(-1). Optimal thermal deformation zone for alloy is determined to be a true strain of 0. 5 at temperatures of 1 113 ℃-1 164 ℃ and strain rates of 0. 01 s^(-1)-0. 2 s^(-1).Gd precipitates as the intermetallic compound GdNi_(5) at grain boundaries or dendrite interfaces. The presence of GdNi_(5), as a hard brittle phase, leads to significant strain accumulation during the thermal deformation process, resulting in higher stored energy in the microstructure, thereby promoting recrystallization of the surrounding deformed grains and reducing the residual strain in the microstructure.