Laser beam welding of 316L stainless steel to Kovar alloy (UNS K94610) lap joint for a space X-ray counterpart collection device

Observation of X-ray counterpart produced by the merger of binary compact star system is of great significance for studying their physical mechanisms. Based on the application requirements of the X-ray counterpart collection device, ring-welded samples of 316L stainless steel and UNS K94610 Kovar alloy were investigated using a continuous wave laser. The effects of heat input on the weld formation, microstructure, mechanical properties, and sealing performance were studied. It was shown that because of the different heat distributions inside and outside the ring weld, the internal profile of the weld cross-section was closer to the circular shape and the columnar crystal growth near the fusion line was longer. Specially, the epitaxial growth was found on the K alloy side. However, the element distribution of the weld was uniform and its crystal structure was austenitic phase. When the heat input was greater than 11.88 J/mm, the tensile strength of the weld was higher than that of the K alloy. The tensile failure locations were at the K alloy BM zone, except for samples with heat input less than 7.92 J/mm. However, when the heat input was greater than 37.50 J/mm, the weld had better sealing performance, and the minimum leak rate could reach 4 × 10⁻¹⁰ Pa·mm³/s.