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It is known that network modifying ions (such as alkali or alkaline earth ions) make glasses susceptible to aqueous corrosion, resulting in the alteration of their surface layers. However, the effect of the altered layers on the mechanical properties of glasses has not been well understood. In this work we study this effect using the pharmaceutical boroaluminosilicate (BAS) glasses as objects by performing nano- and macroscale mechanical tests. The results show that extending the corrosion time increases the thickness of the alteration layer of the BAS glass. The water-related species in the alteration layer lowers the nanohardness, the reduced modulus, the nanowear resistance and Vickers hardness. The corrosion-induced "silica-like" structure in alteration layer benefits the densification of the subsurface caused by nanoindentation and nanowear, and thereby enhances the fracture toughness of the BAS glass. The correlation between the water content in the alteration layer and the mechanical properties has been revealed. This work is instrumental in the design of the next generation of pharmaceutical glasses with higher toughness. [ABSTRACT FROM AUTHOR]

Thermal tempering is an industrial process widely used to make soda lime silica (SLS) glass panels stronger and tougher. During the tempering process, the upper and bottom sides of the glass may experience different cooling rates, and thus, their properties could be different. This study characterized changes in surface composition and subsurface glass network structures as well as indentation and wear resistance properties of the air‐ and tin‐sides of 6‐mm‐thick SLS window panels faced toward the upper and sliding roller sides during thermal tempering. The results showed that although the chemical and structural differences detected with X‐ray photoelectron spectroscopy and specular reflection infrared spectroscopy are subtle, there are large differences in nanoindentation behaviors and mechanochemical wear properties of the SLS glass surface. The findings of this study provide further insights into the performance difference between the air‐ and tin‐sides of the SLS glass panel treated with thermal tempering. [ABSTRACT FROM AUTHOR]

In this paper, the effect of water immersion and humid weathering on the near‐surface mechanical properties of phosphate laser (PL) glass was investigated using nanoindentation. The results indicate that, in the water immersion condition, the reduced modulus and nano‐hardness of PL glass decrease first, then increase and finally keeps unchanged with the increase in immersion duration; however, in the humid weathering condition, they decrease monotonously. The reaction mechanism occurring between water molecules and the glass network, especially during the later stage of the reaction process, determines the near‐surface mechanical properties and their differences when exposed to water and/or humid air. The results in this paper provide additional insight into the nano‐mechanics of glass surfaces, which also help understand the surface alteration process of phosphate laser glass during machining, storage, and serving in wet environments. [ABSTRACT FROM AUTHOR]

• Nanohardness and elastic modulus of FS and SLS glass decreases with holding time. • Depth recovery of both glasses after nanoindentation and before subsequent AFM measurements increases with holding time. • Densified and shear flow volume of both glasses increase with holding time, but the recovery ratio decreases with holding time. • A model is proposed for the entire indentation process to analyze the creep time-dependent deformation behavior of glass. In this study, the time dependent deformation of soda lime silicate and silica glass surfaces is investigated with nanoindentation creep tests. The results reveal that the nanomechanical properties of both glasses decrease with holding time. In addition, a quick recovery in the residual depth of nanoindentation imprint of both glasses has also been found after the indenter tip is retracted and before atomic force microscopy. Furthermore, the inelastic volume of glass surfaces within nanoindentation tests is quantified into densified and shear flow with annealing, and it is found that both the densified and shear flow volume of both glasses increase with holding time, but the recovery ratio of both glasses decreases with holding time, which is due to a faster increase in indentation volume with holding time compared with densified volume. Finally, a model of creep-induced deformation of glass surfaces is proposed to complement the creep-induced deformation process of silicate glasses. [ABSTRACT FROM AUTHOR]

Highlights: [•] The time dependence of water-induced further indentation damage was addressed. [•] The mechanisms of water-induced crack growth and material collapse were discussed. [•] The effect of water on nanomechanical properties around indentation was investigated. [•] The comparison of crack evolution between phosphate and silicate glass was performed. [ABSTRACT FROM AUTHOR]

Abstract: With a nanoindenter, the radial nanofretting behaviors of amorphous ultrathin carbon nitride (a-CN x ) film on the silicon substrate were investigated by a spherical diamond indenter. The experimental results indicate that the radial nanofretting damage on a-CN x film usually successively experiences the buckling, cracking and detachment of film. These damages can be easily detected by the variation in the apparent contact stiffness. Generally, the initial increase in the contact stiffness indicates the buckling of film; the following sharp decrease in the contact stiffness reveals the initiation and propagation of circular cracks in film; the final stable contact stiffness implies the detachment of film. [Copyright &y& Elsevier]

It is well known that the densification of oxide glass can occur at high contact pressure (typically >5 GPa) under normal indentation conditions. This study reports that when frictional shear is involved, the subsurface densification of glass can occur under low load conditions that would involve completely elastic deformation if the load is applied along the surface normal direction without any interfacial shear. This phenomenon was observed for a borosilicate glass rubbed with a smooth stainless-steel ball in liquid water at a nominal Hertzian contact pressure of ≤0.5 GPa. Under these frictional conditions, subsurface cracking is completely suppressed, and surface wear occurs through mechanochemical reactions. Since the mechanochemical wear track was sufficiently smooth, it was possible to employ a sub-glass transition temperature (sub-T g) annealing method to measure the volume recovery of the densified subsurface region. The friction-induced subsurface densification of the wear track was also confirmed through nanoindentation measurements and dissolution tests in pH 13 aqueous solutions. Molecular dynamics (MD) simulations with a ReaxFF reactive force also suggested that the subsurface structural change can occur readily when friction is involved at low contact pressure conditions. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Human saliva consists of approximately 98% water and a variety of electrolytes and proteins. Those proteins can be selectively adsorbed onto the enamel surface. The cuticular material formed on the enamel surface is termed acquired salivary pellicle (ASP), which is critical for the health of oral mucosa and teeth. The ASP is composed of a inner layer and a outer layer. The lubricating properties of ASP are closely associated with the inner layer. The aim of this research is to characterize the structural and mechanical properties of the inner layer of ASP. In this paper, enamel specimens were immersed for 1 min in human saliva. The ASP formed in vitro within 1 min was studied using a nanoindenter. The results show that the thickness of the inner layer of ASP is approximately 18 nm. Moreover, the inner layer is a heterogeneous pellicle with a gradient in density. From the surface of the inner layer to the enamel surface, the density and mechanical properties gradually increase. The research results may be helpful to extend the understanding of mechanical properties of salivary pellicle and to the oral hygiene industry for diagnose oral diseases. [ABSTRACT FROM AUTHOR]

• The physical and mechanical properties of fused silica are studied after various depths of subsurface damage removal by reactive ion etching process. • Concentration of metal ions contamination in the subsurface of fused silica decreases with the etching depth. • Homogeneity of adsorbed water molecules on fused silica surface increases with the etching depth, especially at higher humidity conditions. • Nanohardness and reduced modulus of fused silica increases with the etching depth. The subsurface damage of polished fused silica can be removed by various post-treatments to improve the strength of fused silica in high energy laser systems, but the evolution of physical and mechanical properties of fused silica after the removal of subsurface damage remains unclear. In this study, the physical and mechanical properties of fused silica are studied after various depths of subsurface damage removal by reactive ion etching process. The results show that as the etching depth increases, the concentration of metal ions contamination in the subsurface of fused silica decreases significantly, the water contact angle of fused silica decreased, while homogeneity of adsorbed water molecules on fused silica surface increases, especially at higher humidity conditions. Furthermore, the nanohardness and reduced modulus of fused silica increases with the etching depth. These results will be helpful for optimizing the manufacturing and lifetime of fused silica in high energy laser systems. [ABSTRACT FROM AUTHOR]

• The nanohardness and reduced modulus of G/SLS glass is higher than that of bare SLS glass. • The nanosratch resistance of G/SLS glass is increased by ∼30%-44% in humid air. • The subsurface damage of G/SLS glass upon nanoindenation and nanoscrach tests are also reduced. • The Vickers hardness and indentation fracture toughness of G/SLS glass is increased. In this work, the role of graphene on indentation and scratch properties of soda lime silicate (SLS) glass is investigated by nanoindentation and nanoscratch as well as Vickers indentation tests. The results show that compared with bare SLS glass, the nanohardness and reduced modulus of graphene coated on SLS (G/SLS) glass are higher, because G/SLS glass surface can accommodate more strain energy through elastic process. The nanoscratch resistance of G/SLS glass is increased by ∼30%-44%, since the monolayer graphene can effectively reduce the friction force and activation volume of SLS glass during the mechanochemical wear process in humid air. Furthermore, the subsurface damage of G/SLS glass upon nanoindentation and nanoscratch tests are reduced, and the Vickers hardness and indentation fracture toughness of G/SLS glass are increased. These results clearly show the monolayer graphene can protect the SLS glass surface from physical contact via both normal and tangential shear tests. [ABSTRACT FROM AUTHOR]

Surface defects or flaws on materials made by physical contacts with foreign objects can deteriorate their mechanical properties and limit technical applications. Thus, understanding the contact-induced subsurface damage is of great importance. Using nanoscale infrared spectroscopy and reactive molecular dynamics simulations, the subsurface structural changes of silica upon nanoindentation and nanoscratch are investigated. The results reveal an elongation of the Si O bond length distribution even after the topographically-elastic contact, indicating a "chemical plasticity" at the sub-Angstrom level. In the plastic region with subsurface densification, the Si O bond is found to be slightly longer than the pristine region, indicating the decrease in molar volume is accompanied with the elongation, not shortening, of the Si O bond. These results elucidate the structural damage of a material upon physical contact cannot be delineated based on the topographic deformation of the surface. [Display omitted] [ABSTRACT FROM AUTHOR]