Study on the crystallization behaviors and mechanical properties of reactive plasma sprayed TiCN coatings

In this study, nanostructural TiCN coatings were prepared by reactive plasma spraying micrometer Ti/graphite powders under atmospheric conditions, and the crystallzation behaviors and mechanical properties of as-sprayed coatings were discussed. The results showed that the mechanical properties of as-sprayed coatings depend mainly on the crystallization behavior and resultant morphology of the structure. The sprayed coatings were mainly composed of fully, partically and unmelted particles, which exhibit different crystallization characteristics. Overall, the sprayed coating mainly consisted of columnar grains accompanied by few equixaed grains, and the size of these grains are about 50-100 nm in diameter. In parallel to the substrate/coatings surface direction, columnar grains or columnar dendrites were observed at the partially/unmelted particles and edage of particles. However, in vertical to the substrate surface direction, the coatings were mainly composed of columnar grains accompanied by few equiaxed grains. These different crystallzation behaviors of surface and cross-section resulted in different properties. Especially, the tight columnar grains in cross-sections with multi-long -diameter ratios presented better deformation resistance than that of the surface. Besides, during the coating deposition process, some pores were retained in the coating as 'close pores' and thus the compactness of the cross-sections was higher than that of the surface. In this case, the micro-hardness and indentation toughness on the cross-sections were better than those of the coatings surfaces.