Effect of SiO_2 concentration in silica sol on interface reaction during titanium alloy investment casting  

作　　者：Ya-meng Wei Ke-hui Hu Zhi-gang Lu 

机构地区：[1]Department of Mechanical Engineering, Tsinghua Universit [2] Beijing 100084, China [2]State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China

出　　处：《China Foundry》2018年第1期23-30,共8页中国铸造（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(Grant No.50875144)

摘　　要：Using silica sol as a binder for titanium investment casting is very attractive due to its good stability and reasonable cost as compared with yttrium sol and zirconium sol. However, the mechanism of interface reaction in the related system remains unclear. In this investigation, the interface reaction between Y_2O_3-SiO_2(YSi) shell mold and titanium alloys was studied. A group of shell molds were prepared by using Y_2O_3 sand and silica sol with different contents of SiO_2. Ti-6Al-4V alloy was cast under vacuum by gravity casting through cold crucible induction melting(CCIM) method. Scanning electron microscopy(SEM) and energy dispersive x-ray spectroscopy(EDS) were employed to characterize the micromorphology and composition of the reaction area, respectively X-ray photoelectron spectroscopy(XPS) was used to confirm the valence state of relevant elements. White ligh interferometer(WLI) was used to obtain the surface topography of Y-Si shells. The results show that the thickness of reaction layers is below 3 μm when the SiO_2 content of silica sol is below 20 wt.%. Whereas, when the SiO_2 content increases to 25 wt.%, the thickness of the reaction layer increases sharply to about 15 μm. There is a good balance between chemical inertness and mechanical performance when the SiO_2 content is between 15 and 20 wt.%. Moreover, it was found that the distribution of SiO_2 and the roughness at the surface of the shell are the key factors that determine the level of reaction.Using silica sol as a binder for titanium investment casting is very attractive due to its good stability and reasonable cost as compared with yttrium sol and zirconium sol. However, the mechanism of interface reaction in the related system remains unclear. In this investigation, the interface reaction between Y_2O_3-SiO_2（YSi） shell mold and titanium alloys was studied. A group of shell molds were prepared by using Y_2O_3 sand and silica sol with different contents of SiO_2. Ti-6Al-4V alloy was cast under vacuum by gravity casting through cold crucible induction melting（CCIM） method. Scanning electron microscopy（SEM） and energy dispersive x-ray spectroscopy（EDS） were employed to characterize the micromorphology and composition of the reaction area, respectively X-ray photoelectron spectroscopy（XPS） was used to confirm the valence state of relevant elements. White ligh interferometer（WLI） was used to obtain the surface topography of Y-Si shells. The results show that the thickness of reaction layers is below 3 μm when the SiO_2 content of silica sol is below 20 wt.%. Whereas, when the SiO_2 content increases to 25 wt.%, the thickness of the reaction layer increases sharply to about 15 μm. There is a good balance between chemical inertness and mechanical performance when the SiO_2 content is between 15 and 20 wt.%. Moreover, it was found that the distribution of SiO_2 and the roughness at the surface of the shell are the key factors that determine the level of reaction.

关 键 词：titanium alloy investment casting Y2O3 silica sol surface roughness 

分 类 号：TG221[金属学及工艺—铸造]