Reviewed by Lexie CornerMar 11 2025
Researchers from the Beijing Institute of Technology and the Beijing Institute of Aerospace Systems Engineering used wire arc additive manufacturing to create a Super-invar Fe64-Ni32-Co4 (wt%) alloy. The findings were published in the journal Advanced Manufacturing.
The study includes the manufacturing process of a super-invar alloy of WAAM, the relationship between microstructure and G/R, the mechanical properties, and the CTE. The main transfer mode of liquid droplets during the manufacturing process is the liquid bridge transition. According to the thermal simulation results, the formation of the columnar cellular microstructure is associated with the value of G/R. The mechanical properties of the super-invar alloy exhibit anisotropy; the longitudinal specimens have better mechanical properties. The coefficient of thermal expansion of super-invar alloy was measured to be 0.265 × 10-6 K-1 from 20 ℃ to 100 ℃. Image Credit: Shuijun Ye, Lindong Xu, Yueling Guo, Xinglong Di, Qifei Han, Yuanxuan Zheng, Xingchen Li.
The study offered a guide for the quick fabrication of super-invar alloy parts using WAAM, thereby advancing the use of super-invar alloy in aerospace.
Super-Invar alloys, known for their exceptionally low coefficient of thermal expansion (CTE) below the Curie point, hold significant potential for applications demanding high dimensional stability. These include electrical communication, aerospace, precision measurement instruments, and railway transportation.
However, super-invar alloy components are difficult to machine due to their high ductility, significant work hardening, and low heat conductivity. To overcome this challenge, a thin-wall rectangular sample was created using the hot-wire technique based on wire-arc additive manufacturing (WAAM).
The deposition process in WAAM is important because it can affect both the mechanical properties and surface quality of the parts. An industrial high-speed camera was used to monitor the manufacturing process, ensuring its stability.
Researchers identified the liquid bridge transition as the main transfer mode for liquid droplets during the manufacturing process. This mode reduces the impact on the molten pool and leads to a better surface quality of the deposited parts.
The super-invar alloy specimens displayed a unique columnar cellular microstructure. By developing a numerical simulation model, the researchers were able to calculate the solidification rate and temperature gradient.
To verify the accuracy of the temperature simulation, an infrared thermal imager was used to measure the temperature distribution during the actual manufacturing process. The study found that the G/R value is linked to the development of the columnar cellular microstructure.
The uniformity of material deposition and process stability were reflected in the consistent hardness distribution along the deposition direction. The researchers found that the average hardness of the sample was 152HV0.2, and the hardness was evenly spread along the deposition direction.
The super-invar alloy specimens showed mechanical property anisotropy, with longitudinal specimens exhibiting better mechanical properties. Both longitudinal and transverse specimens showed ductile fractures.
The coefficient of thermal expansion of the super-invar alloy is an important parameter for researchers, as it is a low-expansion material. The samples in this study had an extremely low coefficient of thermal expansion, measuring 0.265 × 10-6 K-1 between 20 °C to 100 °C.
Although the team acknowledges the need for further improvements in the manufacturing process, this study provides valuable insights into super-invar alloy components produced by WAAM. The findings establish a foundation for future applications in precision engineering by confirming the mechanical characteristics and thermal expansion properties.
Journal Reference:
Ye, S., et al. (2025) Microstructure and mechanical properties of super-invar alloy fabricated by wire-arc additive manufacturing. Advanced Manufacturing. doi.org/10.55092/am20250005.