Effect Of Water Environment On Micro/Nano Mechanical Properties Of Phosphate Laser Glass Surface

Nd-doped phosphate laser glass has been successfully used in the high-peak-power laser systems such as the “National Ignition Facility” manufactured in America,the “Laser Megajoule” manufactured in France and the “Shen guang” series devices manufactured in China due to its excellent optical properties.The high-quality surface can effectively reduce the laser energy caused by the surface defects of the glass.It is necessary to require ultra-high surface quality of the Nd-doped phosphate laser glass,such as super smooth and has no defects.In addition,owing to surface processing of phosphate laser glass carried out in the polishing solution,the coolant,and in the process of storage in the moist atmosphere,so the water molecules will inevitably affect the quality of the glass surface.The interaction between water molecules and glass surface involves several processes,forinstance,hydration,hydrolysis,and leaching reaction.These reactions can change the structure of the glass near-surface and form a so-called alteration layer(also known as surface-reaction layer).Due to the structural variation in the alteration layer,the mechanical properties of the glass near-surface are different from the pristine surface.The specific difference depends on the thickness and structure of the alteration layer.Therefore,it is necessary to investigate the evolution of near-surface mechanical properties of thephosphate glass in different water environments.Therefore,in this paper,the near-surface mechanical properties of the phosphate laser glass in different water environments were measured with a Nanoindenter.The experiment was divided into two parts.1.According to nanoindentation,the near-surface mechanical properties of the phosphate laser glass in various immersion/weathering durations in DI water/humid air were measured with a nanoindenter using the continuous stiffness measurement technique.The evolution of the mechanical properties and the thickness of the alteration layer as a function of immersion/weathering duration were quantified,and the relationship between the evolution rule and reaction mechanism in the two water-containing environments was discussed.2.According to nano-scratch,the friction and wear behaviors of the phosphate glass under various velocities by single direction scratch test in dry air and humid air were comparatively studied.The effect of sliding velocity on the damage and material removal of the phosphate laser glass and the potential wear mechanism in different environment were discovered.Finally,according to the results of EDS?XPS and Raman chemical detection technique,the paper have discussed the effect of the chemical structure,the chemical stability of the glass and the mechanical properties of the glass near-surface.Based on the above researches,the following conclusions were obtained:(1)Water immersion and humid weathering show different effects on the near-surface mechanical properties of phosphate laser glass.After water immersion,the thickness of the alteration layer increases before it decreases,which causes the reduced modulus and nano-hardness to decrease first and then increase.After humid weathering,the thickness of the alteration layer increases monotonously with increase weathering duration,thus,the near-surface mechanical properties weaken persistently.The different reaction mechanisms between water molecules and the glass network in aqueous solution and weathering,especially during the later stage of reaction process,determine the different developments of the near-surface mechanical properties and the alteration layer thickness.(2)During the later stage of the water immersion,network dissolution destroys the pre-existing alteration layer and prevents the formation of a newly stable alteration layer.Thus,the surface mechanical properties move closer to the pristine glass surface with increasing immersion duration.In contrast,during the later stage of the humid weathering,both dissociation and hydrolysis of phosphate chains occur within the glass network,which sustains the growth of the alteration layer and deteriorates the near-surface mechanical properties.(3)Whether in humid air or in dry air,with the increase of sliding velocity,the on-load scratch depth and residual scratch depth decreases.The maximum on-load scratch depth at low sliding velocity is concentrated at the beginning of the scratch.The overall depth of scratch in humid air are larger than that in dry air.This is because the water molecules in humid air destroy the network structure of the glass and further produce tribochemical reaction under the action of stress.On the other hand,in humid air,the alteration layer result in the weaken near-surface mechanical properties,and lead to a larger depth of scratch than that in dry environment.(4)The friction coefficient of the phosphate laser glass in humid air is smaller than that in dry air.The alteration layer on the glass surface in humid air has a certain lubrication effect,the friction coefficient in humid air is smaller than that in the dry condition under all velocities.Furthermore,in dry air,the wear behaviors at the phosphate glass interface is dominated by mechanical wear.