Zishuan Fan

Characterization and wear behavior of WC-0.8Co coating on cast steel rolls by electro-spark deposition

Abstract To prepare high wear resistance and high hardness coatings, electro-spark deposition was adopted for depositing an electrode of a mixture of 92wt%WC+8wt%Co on a cast steel roll substrate. The coating was characterized by classical X-ray diffractometer (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The results indicate that the coating shows nanosized particulate structure and dendritic structure including columnar structure and equiaxed structure. The primary phases of the coating contain Fe3W3C, Co3W3C, Fe2C and Si2W. The coating has a low friction coefficient of 0.13, its average wear-resistance is 3.3 times that of the cast steel roll substrate and the main mechanism is abrasive wear. The maximum microhardness value of the coating is about 1573.9 Hv0.3. The study reveals that the electro-spark deposition process has the characteristic of better coating quality and the coating has higher wear resistance and hardness.

Molybdenum based amorphous and nanocrystalline coatings prepared by high velocity oxy-fuel spraying

The high velocity oxy-fuel (HVOF) based thermal spray process has developed as a potential advantageous approach for fabricating various kinds of functional coatings. In this article, the coatings of Mo-based alloy were synthesized using the HVOF process. The microstructure and the mechanical properties of the HVOF-processed coatings were investigated using SEM, TEM, XRD, and hardness and wear tests. Annealing treatment was applied to the as-sprayed coatings to develop the microstructure and its effect on the microstructure and mechanical properties of the coatings was examined. It is found that the HVOF-processed Mo-based alloy coatings are comprised of an amorphous splat matrix embedded with nano-sized crystalline particles. Annealing at temperatures over 950 °C results into crystallization of the amorphous matrix. The mechanical properties of the as-sprayed coatings are enhanced with annealing temperature up to 750 °C and from 950 to 1050 °C, keeps constant between 750 and 950 °C, and reduce over 1050 °C. The change of the mechanical property with the microstructure was illustrated in the study.