通过改变定向凝固前的保温时间,研究热稳定处理对定向凝固Ti-46Al-0.5W-0.5Si(摩尔分数,％)合金组织和性能的影响.在稳定的温度梯度下(G=20 K/mm),定向凝固启动前试样分别保温5、15、30、45和60 min,然后试样以恒定的速度(ν=30 μm/s)进行定向凝固实验.测量定向凝固组织的一次枝晶间距(λ1)、二次枝晶间距(λ2)、层片间距(λL)和显微硬度(HV),并分析这些参数与热稳定处理时间(t)的关系.λ1、λ2和λL的值随着t的延长而增大,而HV则随着t的延长而减小.在定向凝固启动前,延长热稳定时间有助于获得良好的定向凝固组织,然而,过长的保温时间则会降低合金的力学性能.因此,需要优化定向凝固前的热稳定处理时间.根据实验结果,在当前实验条件下,定向凝固前热稳定处理时间选择30 min,既能够获得良好的定向凝固组织,又能保持合金较高的力学性能.
Effect of thermal stabilization on the microstructure and mechanical property of directionally solidified Ti-46Al-0.5W-0.5Si (mole fraction,％) alloy was investigated.The specimens were thermal stabilized for different time (t) and directionally solidified at a constant growth rate of 30 μm/s and temperature gradient of 20 K/mm.Dependencies of the primary dendritic spacing (λ1),secondary dendritic spacing (λ2),interlamellar spacing (λL) and microhardness (HV) on holding time were determined.The values of the λ1,λ2 and λL increase with the increase oft,and the value of HV decreases with the increase oft.The increase of t is helpful to obtain a good directional solidification structure.However,it reduces the mechanical property of the directionally solidified TiAl alloy.The optimized value of t is about 30 min.
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