Tribological Properties of Double-Glow Plasma Surface Niobizing on Low-Carbon Steel

The niobized layer was formed on Q235 low-carbon steel by double-glow plasma surface niobizing to improve its wear resistance. The microstructure, phase composition, and microhardness were determined. The friction and wear properties of the niobized samples and the untreated alloys were tested on a ball-on-disk tribometer by rubbing against GCr15 and silicon nitride (Si₃N₄) balls at room temperature and 400°C, respectively. The results indicated that the alloyed layer that contained a sediment layer and diffusion layer is about 35 μm in thickness, metallurgically adhered to the base metal. Niobium content was gradually decreased along the depth direction from the surface, which was similar to the change in the microhardness. The alloying layer mainly consisted of Nb, Fe₂Nb, and FeNb phases. Under unlubricated sliding conditions, the friction coefficients and the specific wear rates were lower than those of the untreated carbon steel at room and high temperatures. The wear mechanism of the niobized specimen at room temperature is dominated by slightly abrasive wear, whereas the predominant wear mechanism is abrasive wear and fatigue delamination at high temperature.