均匀化热处理对Nb47Ti合金铸锭通道偏析的影响

Effect of Homogenization Heat Treatment on Channel Segregation in Nb47Ti Alloy Ingot

摘要:

Nb47Ti合金在真空自耗电弧熔炼过程中易形成通道偏析，显著降低材料加工性能。采用分子动力学模拟计算，发现Ti-Nb体系在1170 ℃保温时，Ti和Nb的均方位移随着Nb含量的增加而增加，Nb47Ti合金溶质原子Nb的位移振幅及扩散轨迹明显强于基体Ti，说明均匀化对合金微观偏析有改善作用。分析了1170 ℃下5.5和10 h均匀化热处理对Φ520 mm规格Nb47Ti铸锭微区成分、通道偏析的影响。结果表明，均匀化热处理后微区成分偏析因子可下降0.27%和0.53%，但对通道偏析的形貌、数量及尺寸均无明显改善，试验结果与理论计算结果吻合。提高热处理温度或者增加时间，对通道偏析的改善作用极其微弱，且会导致氢含量超标问题。

Abstract:

Channel segregation in Nb47Ti alloy is prone to occur during vacuum arc remelting (VAR), which significantly degrades its processability. Molecular dynamics simulations reveal that for the Ti-Nb system under isothermal holding at 1170 ℃, the mean squared displacement (MSD) of Ti and Nb increases with the increase in Nb content, indicating that homogenization treatment effectively alleviates microsegregation. In Nb47Ti alloy, solute atoms Nb exhibit significantly stronger displacement amplitudes and diffusion trajectories than the Ti matrix. The effects of homogenization heat treatment at 1170 ℃ for 5.5 and 10 h on the microsegregation and channel segregation of Nb47Ti ingot with diameter of 520 mm were analyzed. The results show that the segregation index of microsegregation decreases by 0.27% and 0.53% after homogenization, but no significant improvement is observed in the morphology, quantity, or size of channel segregation. Increasing the heat treatment temperature or prolonging the duration has an extremely minimal effect on reducing channel segregation, and may lead to excessive hydrogen content issues.