Microwave Hybrid Heating Application for Stainless Steel Joint Analysis: A Fuzzy Logic Study on Microhardness and Evaluation of Microstructural Characteristics Under Cold/Heat Processing

Stainless steel SS304 is commonly used in dental applications due to its greater properties, including high strength, hardness, and corrosion resistance. However, the challenge lies in finding eco-friendly methods for joining SS304 with powder-based metals. This study suggests using microwave hybrid heating (MHH) to join SS304 (15 mm × 7.9 mm × 0.2 mm) and pure tin powder (44 µm and 99% purity). Temperature variations (30 °C to 60 °C) and cold processing (0 °C to 10 °C) were employed to assess microhardness and microstructures. Temperature had a direct impact on microhardness, with higher temperatures leading to increased microhardness. Optimal microhardness (530 HV) was achieved at 60 °C during a 3-min heat treatment. Temperature increases improved microhardness at the joint interface, while cold processing caused slight deformation and grain changes. Heat temperature induced deformation, enhanced grain density and hardness at the fast-cooling rate, particularly at the strongly bonded boundary layer. Experimental and fuzzy logic-predicted values for the zinc joint exhibited promising results with errors below 10%.