Development of Titanium Alloy Precision Casting Technology

Quality control for titanium alloy investment castings primarily focuses on controlling shape, size, and defects. Titanium is highly chemically active at high temperatures, easily reacting with the crucible and mold shell, resulting in significant outgassing or undercasting, leading to product scrap. Controlling casting shape and size involves wax pattern deformation, mold shell deformation and cracking, casting solidification deformation, heat treatment/hot isostatic pressing deformation, and welding deformation. Controlling casting defects involves material properties, gating system design, mold shell materials and processes, pouring techniques, and post-processing. The primary challenge in developing high-performance titanium alloys lies in balancing high casting performance with high operational performance. As the operating temperatures of aircraft engine compressors increase, ZTC4 titanium alloy no longer meets the increasingly demanding high-temperature mechanical properties required for aerospace components. Therefore, it is necessary to develop titanium alloys capable of high-temperature casting at 550-650°C, address the process challenges of weld cracking, and improve both thermal strength and thermal stability. The casting and mechanical properties of titanium alloys are largely influenced by their alloy composition. Composition optimization can achieve titanium-based alloys with high casting and mechanical properties, thus meeting the demand for precision castings.

      Currently, aerospace structural components are gradually evolving towards larger, more integrated, and thinner-walled components. my country has achieved breakthroughs in titanium alloy precision castings for aircraft engine intermediate casings, round-to-square casings, and fuel tank frames, and is now capable of producing large-scale, thin-walled, and complex titanium alloy precision castings exceeding 1500 mm in diameter. With improvements in metallurgical quality and dimensional control, the future application prospects of titanium alloy precision castings are promising. However, my country's titanium alloy precision casting technology started relatively late, and compared to the advanced technologies accumulated over decades by the aerospace industries of Western countries like the United States and the United Kingdom, there is a significant gap in production capacity, cost control, and delivery cycles. This has resulted in a relatively small share of Chinese titanium alloy precision castings in the international aerospace supply chain, and the titanium alloy precision casting market has long been monopolized by US companies such as PCC. Aerospace is the core market for precision casting, accounting for approximately 39% of the market share and driving 50% of incremental demand. Future market competition is expected to intensify.

     my country's aerospace industry is currently experiencing rapid development, with localization accelerating amidst the complex international landscape. It is projected that the total demand for precision casting in the domestic aerospace industry will exceed 100 billion yuan in the future, with the titanium alloy precision casting market expected to exceed 10 billion yuan. However, the current output value of titanium alloy precision castings produced by domestic companies does not exceed 2.5 billion yuan, suggesting significant potential for future growth in this sector. This article reviews the current status of titanium alloy precision casting applications in the aerospace sector, introduces the development of titanium alloy precision casting processes, materials, and product applications both domestically and internationally, summarizes current challenges, and proposes future prospects. This article can provide guidance for improving the quality and market competitiveness of domestic titanium alloy precision castings.

1. Titanium Alloy Precision Casting Process Development

    In recent years, with increasing demand for casting quality and the advancement of precision Casting Equipment, titanium alloy precision casting has evolved towards structural uniformity, precise forming, and intelligent process control. As shown in Figure 1,

      The production process for titanium alloy investment castings primarily involves wax pattern production – mold shell production – melting and pouring – and post-processing. First, a wax mold is created using a mold (or additive manufacturing equipment) from a casting model designed using computer-aided design software. This mold is then coated with multiple layers of refractory material to form a shell. The shell is then heated to melt and release the wax. Next, the shell is sintered and ceramicized at high temperatures, and molten titanium alloy is poured into the shell. After the molten metal solidifies and cools, the shell is broken and the casting and gating system are removed. Finally, the casting and gating system undergo post-processing, including cutting, sandblasting, polishing, inspection, pickling, and repair, to obtain the final casting. The development of investment casting technology for large, complex, and heterogeneous components requires a more complex process flow, placing higher demands on the initial gating system and casting process design, mold making equipment, shell processing, and melting equipment. As shown in Table 1, compared with other precision forming technologies, titanium alloy precision casting technology offers a shorter process, lower costs, higher precision, and an integrated design.

    Having worked in the investment casting industry for over 20 years, I have a particular passion for this process and have made many connections with casting experts worldwide. I hope to connect with more colleagues in the precision casting industry to better promote the development of the global investment casting industry.