Microstructure and Wear Behavior of Laser-Aided Direct Metal Deposited Co-285 and Co-285 + WC Coatings

Abstract

The laser-aided direct metal deposition technique was used to form Co-285 superalloy (A) and Co-285 + 30 wt pct WC (B) wear-resistant coatings on 1018 mild steel. Microstructure, element distribution, phases, microhardness distribution, and wear properties of the two coatings were investigated using scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectrometry, scanning transmission electron microscopy (TEM), X-ray diffractometry (XRD), microhardness testing, and wear testing. Results indicate that both of the coatings had dense structures, as well as a metallurgical bonding with the substrate. In addition, coating B had microcracks and randomly distributed undissolved WC particles in it. Coating A was composed of a-Co dendrites, Co 3 W precipitates, and eutectics, while coating B was composed of undissolved WC, Co-rich dendrites, eutectics, and the W-rich third phases with various shapes. Crack behavior in coating B was also discussed. The average microhardness of the matrix in coating B was 751 HV 0.5 , which was almost 1.8 times that of coating A (420 HV 0.5 ). Wear results indicate that the wear resistance of coating B was improved by 6.8 times compared with that of coating A. The improvement in wear resistance is believed to be partially due to the undissolved WC and the formation of large numbers of carbides in the matrix working as wear-resistant phases and partially due to the good bonding between the hard phases and the tough matrix.

Effects of Processing Parameters on the Laser Deposited Co-285 + WC Coatings

“…Figure 1 reveals the microstructure found in the deposited coatings. As similar to that in literature [9], the microstructure varies according to the distance to the undissolved WC particles. In areas close to undissolved WC particles (Fig.…”

“…1(b) and (c)), the microstructure is composed of dendrite (spot 5) and eutectics (spot 4). Phases in the deposited coatings must contain undissolved WC, various carbides and Co-based solid solution as can be concluded from literature [9]. Morphology of the wear groove and the wear suface.…”

“…The value of the two hardness was an average from 10 different measurements. Sliding wear tests were conducted in the same way as described in literaterue [9]. The microstructure of the deposited coatings after the ball-on-disk wear test was observed with SEM and the wear mechanism was explained.…”