Development and Characterization of Metal Injection Moulded Components in Improving Resistance to High Temperature Wear and Oxidation

Abstract

Metal injection moulding (MIM) is a near-net shape manufacturing technology for producing intricate parts, cost-effectively. MIM comprises combined techniques of plastic injection moulding and powder metallurgy. A wax-based binder system consisting of paraffin wax (PW), low-density polyethylene (LDPE), polyethylene glycol (PEG-600) and stearic acid is established for MIM of powder systems of Cr3C2- NiCr (30% Wt.) +NiCrSiB (70% Wt.), SS316L (70% Wt.) +WC-CrC-Ni (30% Wt.) and Tool Steel. The excellence of the MIM product depends on feedstock characteristics, process parameters of the injection moulding stage as well as debinding and sintering stage. Injection stage is most important as many defects such as phase separation, weld line, voids etc. may occur during injection stage due to improper selection of injection moulding parameters and these defects cannot be repaired in the subsequent debinding and sintering stages. The feedstock was characterized by rheological properties at different temperatures. Injection temperature was determined by the rheological investigation of the feedstock having the 56 % powder loading and 44% binder by volume. The solvent debinding temperature is optimized and defect-free MIM component is obtained at a temperature of 48°C. Sintering process was carried out with the temperature cycle in the range of 1150–1200 °C under hydrogen purged atmosphere. The sintering density achieved was 96%. The MIM components showed good and acceptable shrinkage in linear dimensions. Material behaviour at elevated temperature is becoming an increasing technological importance. Components working at higher temperatures like in land-based gas turbines, power generation boiler tubes, hot sections of aero engine, gas and steam turbine, propulsion bearings, materials processing, and internal combustion engines are subjected to surface friction, wear, oxidation conditions. Service conditions of such components in elevated temperature environments may compromise their mechanical properties resulting in a reduced life cycle. Components working in such adverse conditions demand suitable components processed through near net shape techniques. The proposed MIM compacts are investigated for their resistance to wear and oxidation under laboratory conditions.vi Three types of MIM specimens namely Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). Further, microstructure and mechanical properties were characterized to evaluate their potential for hightemperature application. Dry sliding wear behaviour of MIM specimens are evaluated using a high-temperature pin on disc tribometer. The SS316L+WC-CrC-Ni and Tool Steel MIM specimens displayed a lower coefficient of friction and wear rate in comparison with Cr3C2- NiCr+NiCrSiB. Excellent wear resistance of the MIM specimens is attributed to the solid lubricants effect. Based on the wear rate data, the relative wear resistance of the MIM specimens under dry sliding conditions is arranged in the following sequence: (Tool Steel) > (SS316L+WC-CrC-Ni) > (Cr3C2-NiCr+NiCrSiB) Higher wear resistance of MIM Tool Steel specimens is attributed to the high hardness of Cr3Ni2 phase formed during the sintering process. Thermo cyclic oxidation behaviour of MIM specimens was carried out at 700 °C for 20 cycles. Each cycle consisted of heating at 700 °C for 1 hour, followed by 20 minutes of cooling in the air. The thermogravimetric technique is used to approximate the oxidation kinetics of MIM specimens. The Cr3C2-NiCr+NiCrSiB and SS316L+WCCrC-Ni MIM specimens reported lower weight gain as compared to the Tool steel. Cr3C2-NiCr+NiCrSiB MIM specimens registered less weight gain as compared to SS316L+WC-CrC-Ni which is attributed to the excellent oxidation resistance of NiCrSiB and formation of NiCrO4 along with NiO and Cr2O3 oxides on the surface of MIM specimens. In the present study, the powders of Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are successfully metal injection moulded and sintered to achieve 96% density. Developed MIM components exhibit resistance to high-temperature wear and oxidation which is suitable for components subjected to elevated temperature service conditions.