Role of Mobile Cations on Microplasticity in Alumino‐Phosphate Glasses

Abstract

Room‐temperature microplastic phenomena in oxide glasses are attributed to the combined effects of densification and shear flow, the origin of which, however, remains speculative. Using atomic force microscopy imaging to analyze the imprint topology created by microindentation in mixed alkali alumino‐phosphate glasses, we show that the amount of matter displaced at the surface is correlated with the alkali mobility. These results lead to the conclusion that mobile alkali assists shear flow processes produced by indentation at room temperature and that these processes correspond to plastic rather than viscous flow.

Mixed alkali effect on Vickers hardness and cracking

“…Thus in the present experiments, performed at constant load, it is presumed that indentation induced densification remained largely unchanged with the ratio of alkali, and that the variations of hardness with alkali ratio (Fig. 2) was due to that of plastic flow, as noted by Faivre et al [6]. They argued that the plastic flow of glass is assisted by the hopping of network modifiers, promoting the slippage of the rigid parts of the network.…”

“…The mixed alkali effect on the Vickers hardness of glasses has been reported previously [6,7]. Faivre et al [6] measured Vickers indentation on an alkali aluminophosphate glass [0.50 P 2 O 5 , 0.04 Al 2 O 3 0.46 xNa 2 O-(1-x)Li 2 O], x = 0, 0.5 and 1, at indentation loads of 100 g and 50 g. The size of the indents varied non-linearly with the relative alkali ratio, x, with the smallest indents on mixed alkali glasses.…”

“…Faivre et al [6] measured Vickers indentation on an alkali aluminophosphate glass [0.50 P 2 O 5 , 0.04 Al 2 O 3 0.46 xNa 2 O-(1-x)Li 2 O], x = 0, 0.5 and 1, at indentation loads of 100 g and 50 g. The size of the indents varied non-linearly with the relative alkali ratio, x, with the smallest indents on mixed alkali glasses. Using atomic force microscopy, they showed less pileup of material at the dent margins of mixed alkali glasses than those of single alkali glasses.…”

Densification contribution as a function of strain rate under indentation of terbium-doped aluminophosphate glass

“…If this conclusion was made for silica glass with a predominant densification mechanism of plastic deformation, it is even more relevant for aluminophosphate glass characterized by higher contribution of shear deformation in comparison with silica glass. The chain-like structure of Q 2 phosphate structural group of the investigated aluminophosphate glass contains a large amount of network modifiers, which facilitates the shear plastic flow along the weak ionic bound interfaces in network modifierrich regions [1,18,34]. The sliding along these interfaces favors the rearrangements of the atoms, which under acting pressure tend to form a more densified structure.…”

“…The sliding along these interfaces favors the rearrangements of the atoms, which under acting pressure tend to form a more densified structure. At the same time, different types of network modifier ions may hamper the shear sliding process [34] that could be an additional factor stimulating the development of densification process. The atomic packing density, calculated using the formulae C g = qRf i V i /Rf i M i , where q is the density, f i is the molar fraction, V i is the molar volume, and M i is the molar mass of each constituent oxide [35], gives the value C g = 0.595 for the investigated glass, adequate value for the development of the densification mechanism of deformation [8,18].…”