Microstructure evolution and mechanical properties of in-situ bimodal TiC-Fe coatings prepared by reactive plasma spraying

An in-situ synthesis phenomenon of bimodal TiC-Fe coatings is discovered in the reactive thermal spraying of Fe-Ti-C composite powders. The Fe-Ti-C composite powders were prepared by a hybrid spray-drying/pyrolysis technology using a mixture of ferrotitanium (TiFe), graphite and sucrose. The microstructure evolution and mechanical properties of the coatings were investigated. The results showed that the TiC-Fe coatings exhibited an apparent bimodal particle size distribution of submicron and nano TiC particles in the alpha-Fe matrix. The formation of the bimodal distribution structure was revealed as following bi-precipitation mechanism: the first precipitation during the flight process to form submicron TiC particles and the second precipitation in the impact process with rapid cooling to form nano TiC particles. The bimodal TiC-Fe coatings showed high microhardness in various loads due to simultaneous hardening effect from submicron and nano TiC particles. The crack analysis showed that the in-situ bimodal TiC structure hindered the crack initiation and the crack propagation and thus improved the fracture toughness. The bimodal TiC-Fe coatings exhibited high abrasive wear resistance and the wear mechanism transformed from two-body abrasive wear to three-body abrasive wear with the increase of spray distances.