Ti-Al合金精密铸件微观缩松预测

根据金属液凝固收缩理论和多孔介质中流体流动原理，建立了离心压力下Ti-Al合金精密铸件中微观缩松缺陷预测的数学模型，采用该模型对Ti-Al增压涡轮铸件进行模拟计算，并进行了实验验证。结果表明，数学模型能够合理反映离心转速，离心半径、温度梯度和冷却速度等重要因素对微观缩松的影响规律，数值模拟结果与实验结果相吻合。分析增压涡轮的计算结果表明，在涡轮轴向，温度梯度值是影响微观缩松度如何分布的主要原因；在涡轮径向，温度梯度、冷却速度和离心半径的共同作用决定着微观缩松度的变化规律。提高温度梯度，降低冷却速度，充分利用离心压力对枝晶间补缩的有效作用，有利于减少涡轮内部的微观缩松，保证叶片和涡轮的组织致密性和力学性能。

RESEARCH ON PREDICTION OF MICROPOROSITY IN Ti-Al ALLOY INVESTMENT CASTING

Based on solidification and shrinkage theory of molten metal and fluid How theory through porous media, a mathematical model of predicting microporosities in Ti-Al alloy investment castings has been established under the condition of centrifugal pressure;. It has been applied t.o numerical simulation of Ti-Al alloy turbocharger, and experimental verification has been carried out. The results show that the model could describe rationally the influence of the rotation speed, eccentricity, temperature gradient, and cooling rate on the microporosities. and the simulation results coincide with experimental results quite well. Application to the rurbocharger indicates that microporosity distribution in axial direction of the turbocharger is influenced chiefly by temperature gradient, while that in radial direction of the turbocharger is affected by temperature gradient, cooling rate and radius of rotation. Several processes should be employed in order to lessen microporosities and improve compactness such as increasing temperature gradient, decreasing cooling rate and taking advantage of centrifugal effect on the feeding through interdentritic fluid flow.