Characteristics, high temperature wear and oxidation behavior of boride layer grown on nimonic 80A Ni-based superalloy

Nickel-based superalloy Nimonic 80A was pack-borided in a solid medium at temperatures of 850 degrees C and 950 degrees C for 2 h and 4 h using silicon-free boriding powders. To investigate the effects of the boriding treatments on mechanical properties (hardness, modulus of elasticity, fracture toughness) and high temperature oxidation resistance, the layers grown on the surfaces were characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, and evaluated using microhardness, nanoindentation, wear and oxidation tests. Wear tests were performed on untreated and borided Nimonic 80A alloys using a ball-on-disc tribometer at room temperature and at 500 degrees C under dry sliding conditions. Oxidation tests were carried out in air at 1000 degrees C for 5 h, 25 h and 75 h. Characterization studies revealed a smooth, 22 to 86 mu m thick crack-free boride layer consisting mainly of Ni2B and minor quantities of CrB, Cr2B and Cr5B3 in the borided samples. The hardness and elastic modulus of the boride layer was measured as 15.57-18.95 GPa and 142-217 GPa, respectively. Increasing the boriding temperature and time increased the concentrations of chromium in the boride layer. The hardness and elastic modulus of the boride layer increased with chromium content while its fracture toughness decreased. The boriding treatments improved the dry sliding wear resistance. Increasing boriding time and temperature generally led to a higher wear resistance values. However, the treatments had no significant effect on oxidation resistance. The results of this study show that boriding can significantly improve the wear resistance of Nimonic 80A without compromising its oxidation resistance.

Automated summary

The nickel-based superalloy Nimonic 80A was borided using silicon-free boriding powders at temperatures of 850°C and 950°C for 2-4 hours, resulting in a smooth boride layer mainly composed of Ni2B with minor amounts of CrB, Cr2B, and Cr5B3. The hardness and elastic modulus of the boride layer increased with chromium content, while fracture toughness decreased. Boriding treatments improved dry sliding wear resistance, with higher values achieved with increased time and temperature, although they had no significant effect on oxidation resistance.