Effect of Graphite Content on the Physical and Mechanical Properties of Self-Lubricating Iron-Based Composites Fabricated by Powder Metallurgy

Abstract

This study investigated the physical and mechanical properties of a self-lubricating iron-based material reinforced with different weight percentages of graphite. The specimens were prepared using the powder metallurgy technique by designing and fabricating a suitable die for compacting sponge iron powders containing graphite in weight ratios ranging from 0% to 20%, followed by sintering at 1200 °C. The prepared samples were subjected to several laboratory tests, including green strength, green and sintered density, porosity, dimensional changes, hardness, compressive strength, and abrasive wear, to evaluate the effect of graphite content on the physical and mechanical properties. Microscopic examination was also carried out to track microstructural changes and relate them to the obtained results. The findings showed a decrease in porosity and an increase in density after sintering, accompanied by a 24% improvement in hardness. In the abrasive wear test, the addition of graphite reduced the average weight loss by about 74%, with the 1 wt% graphite sample exhibiting the best performance. All graphite-containing samples demonstrated improved wear resistance exceeding 340%, reaching a peak of about 570% for the 1 wt% graphite specimen compared with the pure iron sample. However, samples with higher graphite contents (≥ 5 wt%) showed separation of graphite from the iron matrix during sintering. Microscopic analysis confirmed that from 2.5 wt% graphite onwards, the graphite phase increased in size and formed voids within the structure, leading to deterioration of mechanical properties. The study concluded that incorporating 1 wt% graphite provides the optimum composition, offering an effective balance between self-lubrication and mechanical strength, and is therefore suitable for use in self-lubricating bearings and power transmission components.