Solid-State Diffusion Welding of Wrought AISI 304 Stainless Steel to Nimonic AP-1 Superalloy Powder by Hot Isostatic Pressing

摘要

The diffusion welding characteristics of wrought AISI 304 stainless steel to a superalloy powder Nimonic AP-1 were examined in this study. After encapsulation, evacuation and degassing, the welds were hot isostatically pressed (HIPed) in two different cycles, i.e., 1200℃ (2192℉)/3 h/ 147 MPa and 1270℃ (2318℉)/3 h/ 121 MPa. A variation in surface condition of stainless steel was also studied for its influence on properties of the joints. These diffusion-welded joints were characterized for diffusion of alloying elements, microstructural features and tensile properties. Most specimens showed good weld strength for both the hot isostatic pressing (HIP) cycles, except specimens with sand blasted surfaces, which gave negligible ductility because of the presence of sand particles embedded on the surface. In general, the tensile properties of the diffusion welded specimens were limited by the mechanical properties of stainless steel and not the joint interface. The mi-crostructural examination of a HIP welded joint showed a thin weld zone of 30-40 μm. While the stainless steel region of the welded specimen showed a relatively clean structure, the Nimonic AP-1 region showed precipitation of dark particles near the interface extending over 20-60 μm. Electron microprobe analysis of the diffusion welded zone revealed enrichment of titanium-rich particles along prior particle boundaries (PPBs) near the interface. Electron micro-probe analysis further revealed extensive diffusion of Ni, Co and Al elements into stain less steel and that of Fe into Nimonic AP-1 superalloy indicating complex composition of the weld interlayer.