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In this work, the effects of post weld heat treatment (PWHT) on the microstructure and mechanical properties of functionally gradient materials (FGM) was investigated. The FGM consisted of five different layers which were mixtures of austenitic stainless steel (type 316L) and ferritic steel (LAS). The ratio of type 316L and LAS powder in each deposition layer was 100:0, 75:25, 50:50, 25:75, and 0:100. FGM samples were successfully fabricated without cracks or delamination by a direct energy deposition process. The sensitization phenomenon of the FGM samples was investigated after PWHT. The PWHTs were conducted at 700oC, 900oC, and 1100oC for 4 hours and the samples were then air-cooled. After PWHT, the annealed specimens were observed by optical and scanning electron microscopy to analyze their microstructure. The occurrence of sensitization was found in the specimen annealed at 700oC. The contents of Cr and C increased substantially along grain boundaries. However, the sensitization did not occur in other samples annealed at 900oC and 1100oC. In the C and D layers of the 1100oC annealed sample, micro-hardness was measured to be very high due to the formation of bainitic ferrite and a lath martensite structure. In addition, a reduction of the austenite fraction was confirmed by Electron Back Scatter Diffraction.

This study investigated the effects of laser power on the microstructure and mechanical properties of functionally gradient materials (FGM) produced by direct energy deposition. The FGM consisted of five different layers, which were a mixture of austenitic stainless steel (Type 316L) and ferritic steel (HSLA). During the direct energy deposition, two different laser power conditions (450W and 380W) were used. The ratio of Type 316L and HSAL at each deposition layers were 100:0, 65:35, 50:50, 25:75, and 0:100. After the direct energy deposition process, no cracks or delamination were seen between layers of the FGM. The effects of laser power on chemical composition and microstructure were not significant. However, as the laser power decreased, tensile strength and elongation changed with a small change in grain size.