Microstructural aspects of plasma transferred arc surfaced Ni-based hardfacing alloy

In the current investigation, nickel-base hardfacing alloy AWS NiCr-B was deposited on austenitic stainless steel substrate 316 LN using the plasma transferred arc-welding process. The deposit was characterized by hardness measurements, microstructural examination and sliding wear assessment. Identification of precipitates was carried out using X-ray diffraction, scanning electron microscope/energy dispersive X-ray analysis (SEM/EDAX), electron probe micro analyzer (EPMA) mappings and line-scan profiles. The microstructure of the hardfacing deposit predominantly consists of the γ-Ni phase and the interdendritic eutectic mixture comprised of γ-nickel and nickel-rich borides. These studies also revealed the presence of chromium-rich carbides and borides in a γ-nickel matrix. The sliding wear behaviour of the hardfacing alloy was investigated in air at three different temperatures viz., room temperature, 300 and 500 °C. The study revealed significant weight loss at room temperature and abrupt decrease at high temperatures. This behaviour at high temperatures has been attributed to the formation of a wear protective oxide layer at the surface during sliding. To evaluate the microstructural stability of the deposit, ageing studies were carried out at 650 °C for 250 h. Microstructural examination and hardness testing revealed that there is no deterioration in the microstructure and that the hardness remains intact. Sliding wear tests at room temperature and at high temperatures also demonstrated that there is no significant change in the weight loss or the wear behaviour after the thermal exposure.