Crystallization and wear behavior of SiO2-Al2O3-ZrO2-Ba(Sr, Ca)O glass-ceramics added with Cr2O3 by different methods

Crystallization and wear behavior of the SiO2-Al2O3-ZrO2-Ba(Sr, Ca)O based glass-ceramics with addition of Cr2O3 are investigated. On annealing at 1273 K, SiO2 and acicular BaSi2O5 crystallites are precipitated out from the silicate glass-ceramics which thereafter possess high friction coefficient and wear rate. Adding Cr2O3 retards the precipitation of BaSi2O5 and decreases wear resistance. But this retardation effect varies with the way that Cr2O3 is added. When Cr2O3 is added by ball milling, precipitation of BaSi2O5 is only partly retarded, and wear rate is decreased marginally. However, adding Cr2O3 during the smelting process, the precipitation of BaSi2O5 is almost fully prohibited, and BaCrO4 and/or BaCr2O4 substituting BaSi2O5 precipitate out. The nanoscale barium chromates promote the formation at worn surfaces of a lubricating glaze layer that decreases largely the wear rate and friction coefficient.