Vacuum Brazing of 18MAR300 Nickel Maraging Steel Joints Based on Additively Manufactured and Conventional Material Grades

Laser powder bed fusion (LPBF) processes offer the best possible design options for the production of highly complex components with unique functionalities. Although the development of additive manufacturing processes is progressing impressively and build rates have already been significantly increased, the economic production of high-volume components is still particularly truncated. Comparatively expensive powders, machine-hour rates, and a limited construction space demonstrate a high demand for joining LPBF components to conventionally manufactured parts. Vacuum brazing is an excellent technology for manufacturing and simultaneous heat treatment of such hybrid components. The aim of this study is to investigate the brazeability and the joint properties of ultrahigh-strength nickel maraging steel 18MAR300 (1.2709, X3NiCoMoTi18-9-5) using BVAg-30 (Ag68Cu27Pd5) as brazing filler metal. For this purpose, the effect of nickel-plated surfaces on the wettability and the microstructure of the joint is studied for conv./conv.-, LPBF/conv.-, and LPBF/LPBF joints. Furthermore, the quasi-static and quasi-dynamic joint strength is evaluated. The results prove that nickel-plated surfaces are vital to achieve a sufficient process control. The coating assures a deoxidized and sealed surface which favors the formation of NiCu(Fe,Pd,Ag) phases within the braze metal thus enhancing the joint strength. In addition, LPBF/LPBF joint features have significantly higher tensile strength than conv./conv. joints (825-627 MPa).