In this investigation, the fabrication of functionally graded structures of SS316L to Ni-based alloys were studied, using the novel technique 3D plasma metal deposition. Two Ni-based alloys were used, a heat resistance alloy Ni80-20 and the solid-solution strengthened Ni625. Different configurations were analyzed, for the Ni80-20 a hard transition and a smooth transition with a region of 50% SS316L/50% Ni80-20. Regarding the structures with Ni625, a smooth transition configuration and variations in the heat input were applied. The effect of the process parameters on the geometry of the structures and the microstructures was studied. Microstructure examinations were carried out using optical and scanning electron microscopy. In addition, microhardness analysis were made on the interfaces. In general, the smooth transition of both systems showed a gradual change in the properties. The microstructural results for the SS316L (both systems) showed an austenite matrix with δ-phase. For the mixed zone and the Ni80-20 an austenite (γ) matrix with some M₇C₃ precipitates and laves phase were recognized. The as-built Ni625 microstructure was composed of an austenite (γ) matrix with secondary phases laves and δ-Ni3Nb, and precipitates M₇C₃. The mixed zone exhibited the same phases but with changes in the morphology.

Injection molds are production tools that require detailed analysis based on the quality of the resulting part, the impact on cycle times, and the expected production volume. Cooling channels also play a critical role in mold performance and product quality as they largely determine cycle time. Designs that incorporate conformal cooling channel (CCC) geometries that conform to or align with the part contour are currently being explored as an alternative to conventional cooling channel designs in injection molds. In this study, a simulation of CCC geometries was performed and their effects on mold temperatures and warpage were investigated. Two cross-sectional geometries, circular and square, were selected for a three-factor level design of experiments (DOE) analysis. The response variables used were mold temperatures and part warpage. A cup-shaped part with upper and lower diameters of 54 and 48 mm, respectively, a height of 23 mm and a thickness of 3 mm was used for the injection molded part. A comparison was also made between two materials for the injection mold, steel and polycarbonate. The DOE results showed that the distance between the CCC and the injected part and the diameter or side of the square have significant effects on the response variables for both systems (steel and polycarbonate molds). In addition, a comparison between conventional and conformal cooling channels was analyzed using a cup-shaped part and a less rigid part geometry. The finite element simulation results show a 9.26% reduction in final warpage in the cup-shaped part using CCCs compared with the conventional cooling methods in steel. When using parts with lower geometry stiffness, the use of CCCs reduced final part warpage by 32.4% in metal molds and by 59.8% in polymer molds.

Powder metallurgy and thermal spraying has been used traditionally to manufacture functionally graded materials (FGMs). However, only simple geometries can be made with these processes and the compositional gradients cannot be tailored. These disadvantages can be overcome by employing additive manufacturing (AM). 3D plasma metal deposition (3DPMD) is a new technique that combines the advantages of plasma powder and additive processes. This process allows the production of structures with mixtures of different materials and powder fraction targeting changes in local properties and microstructures. For example, up to four powders, which can be different in terms of chemistry and powder fraction, can be mixed within one layer to adapt the local properties of the structure. The feasibility of functionally graded structures of stainless steel 316L (SS316L) and Ni80-20 alloy was studied. Two configurations, transition between the steel and the Ni-based alloy, were tested. The first one is hard transition, SS316L on the bottom and Ni80-20 on the top. The second one, a smooth transition between both materials was created with 50% of steel and 50% of Ni-based alloy. Optical microscopy and scanning electron microscopy were used to characterize the microstructures. The manufactured part showed good appearance, without any external defects and acceptable geometric accuracy. The layer thickness was around z = 1 mm for both structures. Regarding the microstructural characterization, both materials displayed a dendritic structure. In the SS316L, the microstructure was composed by an austenitic matrix with δ-ferrite located in the grain boundaries. The microstructure of the Ni80-20 was characterized as an austenitic matrix, with some M₇C₃ and M₂₃C₆ precipitates. In addition, the Laves phase was also observed.