热稳定处理时间对TNM合金糊状区组织的影响

Effect of Thermal Stabilization Time on Microstructure of Mushy Zone of TNM Alloy

摘要:

利用真空非自耗电弧炉制备了TNM(Ti-44Al-4Nb-1Mo-0.1B at.%)合金锭,研究其铸态组织形貌,并利用Bridgeman定向凝固装置对TNM合金进行热稳定处理实验,分析热稳定处理时间对合金定向凝固糊状区的影响。实验结果显示,其铸态组织是以(α₂+γ)片层团为主体,网络状B2相、细小的γ相及硼化物分布于片层团间的近片层组织。热稳定处理时,热稳定时间越长、TNM合金固/液界面越平整,界面前沿温度场和溶质场趋向均匀,但从减少坩埚对熔体的污染的角度考虑,热稳定处理时间不宜过长,30~60 min的热稳定时间即可提供平整的定向凝固启动界面。 热稳定处理影响着TNM合金固/液界面附近固液两相中Al元素的分布,进而影响硼化物的分布。

Abstract:

In this paper, the ingots of TNM alloy(Ti-44Al-4Nb-1Mo-0.1B at.%) were obtained using a non-consumable electric arc melting furnace. As-cast microstructure of TNM alloy was investigated. Liquid metal cooling Bridgman-type apparatus was employed in the heat stabilization experiment of TNM alloy and the effect of thermal stabilization time on the mushy zone of TNM alloy during directional solidification has been investigated. The results show the as-cast microstructure of TNM alloy consists of a major of (α₂+γ) lamellar colonies, network-like B2 phase, small γ phase and boride located at the interface of colonies. With the thermal stabilization time increasing, the solid/liquid interface will come to a planar one and the field of temperature and solute in the melt in front of solid/liquid interface will become more homogenous in thermal stabilization test. However, overmuch thermal stabilization time will make the melt contaminated by the crucible. The study shows the thermal stabilization time of 30~60 min is sufficient to provide a planar starting interface for directional solidification. Thermal stabilization affects the distribution of Al in solid and liquid phases near the solid/liquid interface of TNM alloy, and further affects the distribution of borides.