Microstructure and Phase Composition of NiCrBSi-TiB₂ Vacuum Furnace Fused Flame-Sprayed Coatings

Several studies have revealed that NiCrBSi reinforced with different intermetallic compounds exhibits characteristics that allow the material to be successfully used as a thermally sprayed coating for applications that require wear and corrosion protection. One of such materials is TiB₂, as it has an elevated melting point, high elasticity modulus, increased hardness and good thermal stability. NiCrBSi was mechanically mixed with 5%, 10%, 15% and 20% vol. TiB₂, flame sprayed and subsequently fused in a vacuum furnace. A remelting process under controlled atmosphere offer important advantages like good gas extraction and precise adjustment of temperature. The best performing batch of samples were selected for further analyse of microhardness and porosity measurements. The experimental results show that the thermal cycle created with the aid of the data offered by differential thermal analysis lead to a reduced porosity without affecting the hardness. X-ray diffractometry was used to characterize the phase composition while scanning electron microscopy was employed to investigate the microstructure and phase distribution. Further theoretical aspects regarding the influence of the phase composition on the coatings properties, like hardness or sliding wear conclude the work. (paper)