Production of nickel based superalloy materials by powder injection molding method and their characterization

In this study; superalloy materials were shaped by PIM method from three distinct nickel based superalloy powders, commercially known as IN718, IN625 and Nimonic 90. In order to determine optimum production and heat treatment parameters, the molded parts were subjected to different sintering and heat treatment cycles and then they were characterized with mechanical tests and microstructural examinations both in sintered and in aged conditions.The experimental studies were initiated by taking SEM images and making master sizer analyses of powder materials to determine particle shapes and size distribution. For preparing feedstocks of all three material powders were mixed with a multi-component binder system which consist of paraffin wax, polypropylene, carnauba wax and stearic acid. The obtained mixtures were granulated and then injection molded in both standard tensile and fracture specimens. To get rid of the polymeric materials from injection molded samples a two-stage debinding process was employed. The first step of debinding process was carried out by solvent debinding. Thermal debinding stage, the second step of debinding, was performed under a high purity argon atmosphere. The parameters of thermal debinding process were determined by TGA (thermogravimetric analysis) which applied for each component of multi-component binder system. According to the data obtained from DSC (differential scanning calorimetry) and dilatometer analyses which employed to debinded samples, sintering operations were carried out at different temperatures for various periods of time under high level vacuum. The samples, reaching to the highest density, were subjected to different heat treatment cycles.After density measurements and XRD (X-ray diffraction) analyses, microstructural characterization of the sintered samples and the aged samples was employed with optical microscope, SEM (scanning electron microscope), TEM (transmission electron microscope) and EDS (energy dispersive spectroscopy) examinations. Mechanical characterization of the samples was performed with hardness measurements, tensile tests, fracture toughness tests and impact tests both in sintered and in aged conditions. In characterization processes, sintering and heat treatment terms which significantly affect the product properties were emphasized in detail. Thus, the effects of production parameters on the product characteristics were determined. It was observed that for the all three materials, the obtained relative density and hardness values increased in parallel with increase in sintering temperature and sintering time. The microstructural and the mechanical properties of materials were significantly affected from the applied heat treatments. It is determined that, the hardness and strength values of all three materials were increased; however the fracture and impact toughness values were decreased due to intermetallic and carbide precipitates that is occurred as a result of heat treatments.