Evaluation of the Crystallinity-Index and Physical-Mechanical Properties of Co-based Self-Fluxing Thermal Spray Coatings

In this research paper the crystallinity-index and physical-mechanical properties of Co-based self-fluxing thermal spray coatings produced using APS and HVOF on low-carbon steel substrates were investigated. Advanced characterization methods such as XRD, SEM and TEM as well as DSC thermal analysis were used to evaluate the evolution of phase transformation during thermal spraying processes. The phase analysis results show that the main phase of the thermal spray coatings was α-Co solid solution with FCC crystal structure as well as amorphous phase that produced during rapid solidification of particles over the course of flying on impacting to the substrate. The Crystallinity-index for APS and HVOF coatings was computed around 75% and 80% respectively. The existence of amorphous phase in the matrix was yielded to increase the hardness of the coatings. The average microhardness was estimated around 800 and 500 Vickers for HVOF and APS coatings respectively. In addition the porosity content percentage was calculated about 2.12±0.11 for HVOF and 5.52±0.73 for APS coatings. The adhesion strength test showed that for the APS coating fracture was happened in the interface of the coating / substrate in the form of adhesive, however, for HVOF coating fracture was occurred in glue or the interface of the glue / substrate.