Vacuum Brazing of Molybdenum-Copper Alloy with Stainless Steel
Molybdenum copper alloy is a composite material that combines the properties of molybdenum and copper. It has high thermal conductivity, a low coefficient of thermal expansion, and good resistance to high temperatures. Because of these characteristics, it is widely used in high-power electronic devices, heat dissipation components, electronic packaging, and high-temperature structural parts. The low expansion coefficient allows good matching with ceramics and sealing materials, while the heat resistance ensures stable performance in demanding thermal environments.
When joining molybdenum-copper alloy with austenitic stainless steel, several technical challenges arise. The two materials have significantly different thermal expansion coefficients and thermal conductivities, which leads to high residual stress at the joint during heating and cooling. This stress increases the risk of crack formation. In addition, Mo-Cu alloy is highly sensitive to gas impurities. During conventional welding, this sensitivity can result in porosity at the joint, coarse weld microstructures (about 200–500μm), and impurity segregation along grain boundaries during rapid cooling. These issues reduce joint strength and reliability, especially at high temperatures.
To overcome these problems, vacuum brazing is adopted as an effective joining method. The high vacuum environment limits oxidation and reduces gas contamination, resulting in a clean and reliable joint. In this process, BNi2 amorphous nickel-based brazing foil with a thickness of 50-8μm is used, and the joint gap is controlled within 40-80μm to ensure proper capillary flow and diffusion. The brazing alloy composition includes Cr 6.5~7.5%, Si 3.0~5.0%, B 2.7~3.5%, Fe 2.5~3.5%, C≤0.02%, Ni margin. Before brazing, the molybdenum copper alloy and austenitic stainless-steel surfaces are thoroughly cleaned to remove oxides and contaminants. The assembled components are then placed in the uniform temperature zone of a vacuum brazing furnace and evacuated to a vacuum level of 1.33*10^-4 to 1.33*10^-3 Pa. The furnace temperature is raised to 850 °C within 50 minutes and held for 20 minutes for outgassing, followed by heating to 1030 °C within 20 minutes with a 15 minute holding stage, and finally increased to 1090 °C ±10 °C within 15 minutes and held for 10 minutes to ensure complete melting and diffusion of the brazing alloy.
After brazing, furnace heating is stopped, and the assembly is allowed to cool naturally inside the furnace. When the chamber temperature drops below 100 °C, the brazed component is removed.
The joints produced using this vacuum brazing process show low impurity content, high density, and excellent resistance to high temperatures. The joint structure is uniform and free from major defects such as pores and cracks. These joints are suitable for use in precision instruments, electronic packaging systems, and high-temperature resistant components where thermal stability and mechanical reliability are required.
Technical Details:
A Normantherm VF1300 series vacuum brazing furnace is the most suitable choice. In particular, the VF1300-644 vacuum brazing furnace is well matched to this process because it is designed specifically for high-vacuum brazing applications, offers a maximum operating temperature up to 1300 °C, and provides stable temperature uniformity and precise control required for multi-stage heating and holding cycles. Its high-performance vacuum pumping system ensures a clean, low-contamination environment, which is critical for molybdenum copper alloy due to its sensitivity to gas impurities.
Edited by: Shristi Paudyal
© 2026 Normantherm Vacuum Furnace. All rights reserved.
Related Products: Vacuum Brazing Furnace (VF1300 series)