High temperature erosion-oxidation behavior of thermal sprayed nickel-chromium and chromium carbide coatings

Abstract

This paper presents the high temperature erosion-oxidation (E-O) behavior of HVOF coatings of Ni20Cr alloy and Cr3C2-25(Ni20Cr). The E-O measurements were made in a test rig in the temperature range 500-850° C, using alumina particles as the erodent at impact velocities in the range 2.5–19.5 ms-1. At low impact velocities the coatings did not exhibit any change in E-O behavior up to 500-600° C, compared to that at 100° C. However at higher temperatures, wastage increased with temperature, reaching a maximum at 700º C and then decreased with further increase in temperature up to 800° C. At temperatures above 800° C, wastage increased again. The E-O mechanism of these two coatings was quite similar. Changes in E-O wastage are attributed to regime change from ‘substrate dominated’ to ‘oxide modified’. At higher erodent impact velocities a significant increase in E-O wastage of the coatings was observed. Using surface roughness as the criterion to compare E-O behavior of the coatings, E-O maps were constructed for the two coatings. Regions corresponding to low, moderate and severe wastage were defined and shown in the maps to aid in qualitative selection of conditions for safe use of the coatings.