Study of the Effect of Sintering Temperature on the Physical and Mechanical Properties of MgO–Ni Composite Prepared by Powder Metallurgy

Abstract

This research addressed the preparation and study of a ceramic-metal composite consisting of 65% MgO + 35% Ni using powder metallurgy technology, focusing on studying the effect of sintering temperature within the range (700–1100°C) on the microstructure and mechanical and physical properties of the composite. The results obtained revealed a number of important conclusions, which can be summarized as follows: Scanning electron microscope (SEM) images showed that the prepared composite has a relatively homogeneous microstructure, characterized by a uniform distribution of grains and a clear absence of cracks or large agglomerates, reflecting the efficiency of the preparation and sintering method used. Measurements derived from SEM images also showed that the average grain size gradually increased with increasing sintering temperature, ranging from 165.4 nm to 179.6 nm. This behavior is attributed to improved atomic diffusion and increased grain boundary mobility at higher temperatures. Despite this grain growth, it remained limited and uniform, indicating balanced sintering without excessive grain growth, which is desirable from an application standpoint. The mechanical properties of the composite showed a marked improvement with increasing sintering temperature. Vickers hardness gradually increased from 301.7 HV at 700°C to 367.8 HV at 1100°C. This improvement is attributed to reduced porosity, increased density, and improved cohesion between grains. The high MgO content also played a key role in increasing hardness due to its hard ceramic nature, while the Ni mineral phase contributed to enhancing structural cohesion and reducing brittle fracture susceptibility. Compressive strength showed a limited gradual increase within the range of 320.8–339.6 MPa, indicating the stability of the composite's mechanical behavior and the stability of the compressive strength mechanism as a result of the stability of the chemical composition and the absence of new phases forming with increasing sintering temperature. The wear test results showed a clear decrease in the wear rate with increasing sintering temperature, from 6.82×10⁻⁴ to 3.98×10⁻⁴ mm³/ N·m. This is attributed to increased hardness, improved microstructural cohesion, and reduced porosity, which limits the separation of surface particles during friction. The balanced interaction between the MgO ceramic phase and the Ni metallic phase also contributed to improved wear resistance by combining high hardness with the ability to absorb part of the stresses generated during the wear process. The physical properties of the composite showed a gradual improvement with increasing sintering temperature, with both true and apparent densities increasing, while porosity decreased to less than 3% at all sintering temperatures, indicating the efficiency of the pressing and sintering processes in producing highly compacted and defect-free samples. The thermal conductivity of the composite also increased from 21.8 to 31.2 W/m·K with increasing sintering temperature, as a result of reduced porosity and the formation of effective thermal paths due to the presence of the Ni metal phase within the MgO matrix, with values remaining within the expected range for ceramic-metal composites. In general, it can be concluded that the sintering degree is a decisive factor in controlling the microstructure and improving the mechanical and physical properties of the MgO–Ni composite without the need to change the chemical composition. The results confirm that the prepared compound has good structural stability and mechanical and thermal performance, making it suitable for engineering applications that require materials with high hardness, improved wear resistance, high density, and stability under various loads and thermal conditions.