Crystallization and Wear Behavior of SiO2-Al2O3-ZrO2-Ba(Sr, Ca)O Glass-Ceramics Added with Cr2O3 By Different Methods

Abstract

The merits of glass-ceramics are mainly derived from the refractory crystallites, but controlling crystallization of glass is a complicated process. Although substantial work was conducted on crystallization and its effect on mechanical and thermal properties of glass-ceramics, few were available on the effect of crystallization on friction. In the current work, Cr2O3 was incorporated into a, BaO-rich, SiO2-Al2O3-ZrO2-Ba(Sr, Ca)O based glass system through two methods: (1) melted into the glass; (2) added as foreign ceramic crystallites. After heat treated at high temperature, it transformed to glass-ceramics. Then crystallization and its influence on friction of the glass-ceramics were carefully studied.The results showed that, on annealing at 1173 K, SiO2 and acicular BaSi2O5 crystallites were precipitated out from the silicate glass-ceramics which thereafter possessed high friction coefficient and wear rate. Adding Cr2O3 retarded the precipitation of BaSi2O5 and decreased wear resistance. But this retardation effect varied with the way that Cr2O3 was added. When Cr2O3 was added by ball milling, precipitation of BaSi2O5 was only partly retarded, and wear rate was decreased marginally. However, adding Cr2O3 during the smelting process, the precipitation of BaSi2O5 was almost fully prohibited, and BaCrO4 and/or BaCr2O4 substituting BaSi2O5 precipitated out. The nanoscale barium chromates promoted the formation at worn surfaces of a lubricating glaze layer that decreased largely the wear rate and friction coefficient. Figure 1