Effect of process parameters on microstructure and wear resistance of niobium carbide coatings produced by pack cementation

Abstract

The effects of the proportions of ferrocolumbium powder and ammonium chloride powder in the reaction medium, deposition temperatures, and deposition times on the thickness and mechanical properties of niobium carbide coatings were studied by means of orthogonal experiment. Mathematical analysis was conducted to quantify the influence of these four variables on the pack cementation process to obtain a superior production process with deposition temperature of 950 °C, deposition time of 5 h, proportion of ferrocolumbium powder at 20 wt%, and proportion of ammonium chloride at 5 wt%. The weight values of the experimental process parameters were 60.9% for deposition temperature, deposition time 37.4%, ammonium chloride powder 1.1%, and ferrocolumbium powder 3.1%. Further experiments were conducted with deposition temperatures set to 900 °C, 950 °C, and 1,000 °C, with coatings’ surface microhardness of 925 ± 60 HV0.2, 860 ± 30 HV0.2, and 750 ± 20 HV0.2, respectively. Scanning Electron Microscope (SEM) surface morphology observation, X-ray diffraction (XRD) phase analysis, and grain size calculation showed that the surface phase of the three coatings all are NbC phases, and the grain size (37.0, 42.4, and 57.9 nm, respectively) increased with increasing temperature. The coatings’ roughness decreased as temperature increased, and the 950 °C deposition temperature obtained the best wear resistance.