Research progress on refractory composition and deformability of shell molds for TiAl alloy castings

China Foundry, Feb 2018

At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.

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Research progress on refractory composition and deformability of shell molds for TiAl alloy castings

Vo l . Research progress on refractory composition and deformability of shell molds for TiAl alloy castings Document code: A 0 , You-wei Zhang 1 1. Titanium Alloy Division, Shenyang Research Institute of Foundry , Shenyang 110022, China 2. School of Materials Science and Engineering, Shenyang University of Technology , Shenyang 110870 , China 2 Chun-ling Bao At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed. TiAl based alloys; investment casting; shell mold; deformability - Nused as high temperature structural materials. ickel based superalloys are currently widely However, it is more and more difficult to increase the service temperature because of the inherent limitation of superalloys. Due to the co-existence of metallic and covalent bond, intermetallic materials have higher specific strength and rigidity than common metals and better ductility than ceramics, which can be a potential substitute for conventional superalloys. Among these, TiAl based alloys are becoming competitive materials for heat-resistant structural components in aero and auto engines and have great application potential for their low density, at only half of nickel based alloys, as well as good creep resistance and oxidation resistance [ 1 ]. In 2007, the US Boeing company declared that TiAl alloys would be used for low pressure turbine blades in GEnx engine on the 787 airplane, which could reduce the weight of the engine by 800 pounds [ 2 ]. That was a milestone for the application of TiAl alloys to reduce engine weight and prompt the application of TiAl alloys around the world. In recent years, the studies on TiAl alloys were focused on the relationship among process, microstructure and mechanical properties, manufacturing and forming technologies, as well as the TiAl based composite materials [ 3-7 ]. Until now, processes similar to those for nickel based alloys have been developed for manufacturing and forming of TiAl alloys, including ingot metallurgical methods (casting ingot plus thermal mechanical treatment), casting process and powder metallurgy. Casting methods such as investment casting process[ 8 ], permanent mold casting process[ 9 ] and centrifugal casting process[ 10 ] are still the main forming technology for TiAl components for their low cost and net shape advantages over other forming technologies. Among which, the investment casting method is usually used to form parts for aero and auto engine blades and high pressure turbine blade shield plates due to the accurate casting dimensions and high surface quality. Although the investment casting process of TiAl alloys has the advantages of net shape and low cost, problems including cracks, porosities and surface defects are easily found in castings [ 11, 12 ]. The investment casting process consists of several steps in which one of the key steps is production of a ceramic shell since soundness and quality of the ceramic shell has a direct effect on the soundness of the castings [13]. The residual stress and subsequent distortion in castings can be related to the difference between the thermal expansion characteristics of the alloy and the ceramic shell [ 13 ]. Mechanical interaction between the ceramic shell mold and solidifying alloy can cause residual stress, distortion and hot tearing cracks. According to statistics, more than 70% of defects and scraps of TiAl alloy castings are caused by shell mold quality, so the property of the shell mold is an important issue for TiAl alloy precision casting[ 14 ]. To solve these problems, a lot of studies have been carried out on shell molds for TiAl alloy castings in the aspect of compos (...truncated)


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Chun-ling Bao, Shuang-qi Zhang, Yu-yan Ren, You-wei Zhang, Hua-sheng Xie, Jun Zhao. Research progress on refractory composition and deformability of shell molds for TiAl alloy castings, China Foundry, 2018, pp. 1-10, Volume 15, Issue 1, DOI: 10.1007/s41230-018-7022-9