Microstructure and Improved Thermal Shock Behaviour of an In Situ Formed Metal-Enamel Interlocking Coating

Abstract

A novel metal-enamel interlocking coating was designed and prepared in situ by co-deposition of Ni-enamel composite layer and subsequent air spray of enamel with 10 wt% nanoscale Ni. During the firing process, the external enamel layer was melted and jointed with the enamel particles at the upper part of the Ni-plating layer to form the enamel pegs. Thermal shock tests of pure enamel, enamel with 10 wt% Ni composite and metal-enamel interlocking coatings were conducted at 600 °C in water and static air. The results indicated that the metal-enamel interlocking showed superior thermal shock resistance to both pure enamel and enamel with 10 wt% Ni composite coatings. The enhanced performance was mainly attributed to the advantageous effects of mechanical interlocking of the enamel pegs formed at the enamel/Ni-plating interface. Meanwhile, during thermal shock test, big clusters formed by nanoscale Ni agglomerations were oxidised to be a Ni/NiO core-shell structure while small single nanoscale Ni grains were oxidised completely, which both improved the thermal shock resistance of enamel coating significantly.

Improving the mechanical properties of enamel by nickel nanoparticle addition

“…11,13,21 With the addition of Ni content more than 2 wt.%, the Ni nanoparticle dispersion through the enamel matrix was not uniform, and a large number of particles agglomerated, thereby reducing the probability of formation of a ductile phase near the crack tip. Moreover, the agglomerated Ni nanoparticles were more easily oxidized, 37 and the stress and strain were concentrated in a small area near the crack front. In the absence of the plastic deformation of the ductile phase and crack passivation, the stress was not released, resulting in the crack expansion.…”