Study of mechanical and metallurgical characteristics of flame sprayed NiCrBSi as-sprayed and continuous compacted coating

Abstract

Thermal spray processes such as high-velocity oxy-fuel and detonation spraying are more commonly used in industries for depositing coating material as compared to flame spray coatings because of better coating properties (high bond strength, low porosity, and high hardness) offered by the high-velocity flame spraying process. The flame spray coatings are economical but are not frequently used because of coarse microstructure, high porosity, and low-hardness-related problems. The above problems associated with flame spraying can be reduced using innovative techniques like hot isostatic pressing and rolling of coated material at high temperature. Mostly these methods are completed in two stages, which in turn make the post-processing of the coating uneconomical. Therefore, in the present investigation an attempt has been made to integrate the coating deposition and post-processing (compaction) of NiCrBSi coating in one step. In the present work, the NiCrBSi flame sprayed coatings after compaction were compared with as-sprayed coatings in terms of microstructure, porosity, and hardness. Field emission scanning electron microscopy and X-ray diffraction analysis of coatings were also carried out for elemental and phase analysis of its micro-constituents. It was observed that continuous compaction of the flame sprayed coating results in higher hardness, reduced porosity, and finer grain size as compared to that of as-sprayed coating.