WEAR BEHAVIOR OF COBALT-BASED ALLOYS IN LASER SURFACE CLADDING

The wear properties and wear mechanism of Stellite No. 6 powder cladded over AISI 1020 low carbon steel have been investigated. The wear resistance of specimens with laser surface cladding overlapping by different amounts (20%, 30% and 50%) was measured using a dry-sand rubber-wheel abrasion test and a block-on-ring wear test at room temperature. Wear tests were also performed at different temperatures (50-degrees-C, 150-degrees-C, 250-degrees-C and 400-degrees-C) with an Schwingung reibung verschleiss (SRV) oscillation friction wear tester under 25 N and 50 N loads. The specimen with 50% overlapping showed the lowest initial wear, together with the highest surface hardness and a smoother surface than the others. The specimen with 50% overlapping also suffered the lowest total weight loss. Weight loss increased with increasing test temperature up to 150-degrees-C, and then decreased with further increases in temperature owing to transfer of material. The average friction coefficient was about the same for all the overlapping ratios at 50-degrees-C. At 150-degrees-C it had a slightly higher value. The wear mechanism was studied by observing worn surfaces through scanning electron microscopy which showed that the surface polish, plastic deformation and ploughing caused by abrasive wear were very significant at 50-degrees-C. Microcracking, fatigue delamination and brittle fracture could also be observed at temperatures above 250-degrees-C.