Microstructure and wear characteristics of nickel based hardfacing alloys deposited by plasma transferred arc welding

摘要

In the present investigation, a nickel based hardfacing alloy (AWS NiCr-B) was deposited on an austenitic stainless steel substrate 316LN using the plasma transferred arc welding process. The deposit was characterised by hardness measurements, microstructural examination and sliding wear assessment. Identification of precipitates was carried out using X-ray diffraction and SEM/EDAX. These studies revealed the presence of chromium rich carbides and borides in a γ-Ni matrix. Down to a distance of 1 mm from the interface, the hardness of the deposit was found to be 52 HRC. The sliding wear behaviour of the hardfacing alloy was investigated in air in the room temperature to 550°C range, with a pin on disk configuration using a cylindrical pin with tip radius of 3 mm under loads of 30, 40 and 50 N. Wear experiments were conducted up to a sliding distance of 180 m at a sliding speed of 0·1 m s−1. The elastic modulus and Poisson's ratio of the hardfaced deposits were evaluated by the ultrasonic method and these values were used for calculating initial Hertzian contact stress. The study showed that, while significant wear loss occurred at room temperature, there was practically no measurable weight loss at temperatures of 300 and 550°C. This could be attributed to the formation of an oxide layer at the surface during wear testing.