Microstructure and mechanical properties of plasma transferred wire arc spray coating on aluminum cylinder bores

Abstract

This study examines the microstructure and mechanical properties of plasma transferred wire arc (PTWA) coating of typical alloyed steel, deposited on diecast aluminum alloy cylinder bores. The coating surface and microstructure were characterized in terms of surface roughness, features (i.e., defects, splats formation mechanisms, distribution of oxides, re-solidified particles, and interfacial metallurgical bonding) using laser scanning confocal microscope, scanning and transmission electron microscope (SEM and TEM). Residual stress through the thickness of the coating was measured using X-ray diffraction (XRD) and hole-drilling method. In post-processed samples, compressive residual stress was measured throughout the coating with a value close to 100 MPa at the interface, resulting from the thermal mismatch between coating and substrate materials. In terms of mechanical properties, coating hardness was estimated at both the micro- and nanoscale and examined the influence of microstructure inhomogeneity on the mechanical performance and failure modes. Three-point bending tests and consequent analysis using the equivalent section method yielded stress-strain properties for both the substrate and coating materials with a maximum coating strength averaging 1480 ± 108 MPa. SEM observation of fracture surfaces showed three modes of failure involving coating delamination and breakage, which is related to the deposition process and the various features within the coating.