Ti4822合金熔体停止流动机理研究

Analysis on Flow Cessation During Investment Casting of Ti4822 Alloy

低压涡轮工作叶片是目前TiAl合金最成功的应用,但是TiAl合金与常规钛合金相比流动性比较差,这给铸造成形带来了困难,特别是对于薄壁构件。本研究分析了Ti4822合金叶片在熔模精密铸造工艺条件下合金熔体的停止流动机理。通过观察未完整成形的叶片试样组织,发现当叶片厚度小于3 mm时,显微组织主要是等轴晶,由于熔体前端充型过程中温度不断下降,最终使流动停止;当叶片厚度大于3 mm时,显微组织包括等轴晶和柱状晶,柱状晶最终封闭了熔体流动通道,阻止了熔体继续流动。

Low pressure turbine(LPT) blade is the most successful application of TiAl alloy castings now.However,the poor fluidity of TiAl alloy compared with common titanium alloys makes it very difficult to shape completely especially for thin-wall parts.In this work, the flow cessation of Ti4822 alloy was analyzed during the investment casting ofthe blades.The microstructures of the incompletely shaped blade were observed by the optical microscope(OM).The results show that when the thickness of the blade is less than 3 mm, the microstructue of the sample consists of all equiaxed grains.The flow cessation in this case is due to the front end of the melt which becomes gradually cool and stops finally.When the thickness of the blade is more than 3mm, however, the microstructures are composed of both equiaxed grains and columnar grains.The columnar grains mainly exist at the back of the blade, closing the channel of the melt feeding and preventing the melt from flowing.