Ni–Cr matrix composites reinforced with nano- and micron-sized surface-modified zirconia: Synthesis, microstructure and mechanical properties

Abstract

Ni-20Cr alloy with Ni-coated and uncoated hybrid particle size (nano- and micron) ZrO2 reinforcements (11, 15 and 19 wt. %) were used to prepare oxide dispersion strengthening (ODS) superalloy by powder metallurgy. The resultant composite powders were consolidated through spark plasma sintering (SPS) method. The effect of Ni-coating and the size of zirconia particles on the mechanical and tribological properties of the composites was investigated. According to the hardness and wear results, it was found that the coated reinforcements with the hybrid particle size provide the best properties for the composite. In addition, the results showed that hardness of the composite improves when the zirconia content is increased from 11 to 15 wt.% and afterward with increasing more ZrO2 particles the hardness decreases. The results revealed that the composite sample containing 15 wt.% coated hybrid particle size zirconia, shows the greatest mechanical and tribological properties. Therefore, the composite was considered as the optimal sample. Compared to the Ni-20Cr alloy and 15 wt.% uncoated hybrid particle size ZrO2/Ni-20Cr composite samples, the optimal sample exhibited 54% and 26% increase in Vickers hardness, respectively. Furthermore, the optimal sample showed 39.5% and 11.5% increase in Vickers hardness in comparison with 15 wt.% uncoated and coated micron-sized zirconia reinforced composites, respectively. Regarding (pin-on-disc) tribological behavior, an obvious transition in the wear mechanism was observed with incorporating the coated reinforcements. The dominant wear mechanism changed from adhesion for the Ni-20Cr alloy sample to adhesion/abrasion for uncoated composite and to abrasion wear mechanism in the optimal sample.