The paper outlines some research work that has been conducted in Harbin Institute of Technology, on the fabrication of TiAl alloys. The review is presented with special emphasis on some different manufacturing routes of TiAl alloys, including investment casting, canned forging and sheet rolling, mechanical milling and rapid solidification. Investment casting has been developed to manufacture near-net shape TiAl blades. Also included are current development of canned forging and rolling for TiAl sheets. Then, TiAl nanocrystalline powders gained through low temperature and two steps mechanical milling were researched. And considerably refined TiAl alloys with Y additions were produced by rapid solidification and the microstructure evolution with Y addition was studied. Details of the processing route and microstructure related to different processing method will be presented.
γ-TiAl components due to their unique properties are on the verge of industrial application for increasing operation temperature and improving energy efficiency, especially in aerospace and automobile areas. This paper describes the recent developments of hot precision processing in ingot metallurgy technology including investment casting, canned forging and sheet rolling of TiAl alloys. Alloys development and the melting technology were discussed. Investment casting of TiAl alloys has been successfully developed to manufacture net-shape components. Research aimed at producing TiAl sheets through canned forging and rolling is introduced.
The fabrication of ceramic moulds with zirconia primary coat for investment casting of gamma titanium aluminide based alloys (hereafter called TiAl alloys) was described in this study. The microstructures and fracture strength of ceramic moulds were characterized. The fracture strength and surface roughness of the ceramic moulds with zirconia primary coat were sufficient for the TiAl investment casting. TiAl blades were used for the technology demonstration in producing TiAl components. TiAl castings produced by the ceramic moulds exhibited an average surface roughness (Ra ) of 6 μm.
In this paper, a preparation method concerning ceramic moulds with zirconia coating used for the investment casting of TiAl alloys has been described. The processing technology of ceramic moulds was verified successfully using the ceramic moulds with zirconia coating prepared by recommended processing parameters. Interfacial reactions between ceramic moulds and TiAl alloys examined by OM (optical microscope), SEM (scanning electron microscopy) and XRD (X-ray diffraction) are presented in this paper. The results reveal that the thickness of interfacial reactions layer was about 20 μm.
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