Ti-47Al-6Nb基排气阀的熔模离心铸造工艺的研究

Centrifugal investment casting of Ti-47Al-6Nb exhaust valves

摘要:

本文研究了高Nb钛铝基排气阀铸件的熔模离心铸造工艺,排气阀铸件的化学成分确定为Ti-47Al-6Nb (at.%),所用型壳材料为锆砂。为了与模拟充型结果进行比较和验证浇注工艺,本文进行了排气阀的离心铸造模壳充型实验。模拟结果表明：模壳充型时间约为3.8s,铸件缺陷沿排气阀中心线分布,特别是在颈部位置处；经过实验验证,模拟结果和实验结果吻合度较好。实验过程中,模壳挂涂所需内层浆料的适宜工艺确定为粉液比是1.5:1,搅拌时间30min。通过对排气阀铸件表面进行XRD测试,结果表明铸型与壳型之间没有明显的界面反应；排气阀铸件的金相组织为典型的层状结构,晶粒尺寸大小在185 - 305μm之间。

Abstract:

The shell mold filling process for high-Nb TiAl alloys exhausts valve castings by centrifugal investment casting is described in the paper. Compositions of the castings and shell mold are Ti-47Al-6Nb (at.%) and Zircon sand, respectively. As a comparison and verification of the simulation results, a series of shell mold filling experiments of centrifugal casting is carried out. Simulation results indicate that the shell mold filling time is about 3.8s; casting defects distribute along the central line of the exhaust valves, especially in the neck position. The comparison shows that the results of the simulation agree with those experiments. The powder/liquid ratio of 1.5:1 and mixing time of 30min is identified as the proper process for the inner layer slurry in the making shell mold process. There are no noticeable interfacial reactions between casting and shell mold using XRD analysis. The metallurgical analysis results reveal that the lamellar structure is the typical structure for the as-cast exhaust valves, with the grain size of 185-305μm.