Quantitative analysis of the tribological properties of phosphate glass at the nano- and macro-scales
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Quantitative analysis of the tribological properties of phosphate glass at the nano- and macro-scales Huimin QI1, Wen HU1, Hongtu HE1, Yafeng ZHANG1, Chenfei SONG2, Jiaxin YU1,2,* 1
Key Laboratory of Testing Technology for Manufacturing Process in Ministry of Education, State Key Laboratory of Environment-friendly Energy Materials, Southwest University of Science and Technology, Mianyang 621010, China
2
National United Engineering Laboratory for Advanced Bearing Tribology, Henan University of Science and Technology, Luoyang 471023, China
Received: 11 October 2019 / Revised: 06 January 2020 / Accepted: 09 May 2020
© The author(s) 2020. Abstract: Processing (grinding, polishing) of phosphate laser (PL) glass involves material removal at two vastly different (spatial) scales. In this study, the nano- and macro-tribological properties of PL glass are investigated by rubbing the glass against a SiO2 counter-surface in both dry and humid conditions. The results indicate that the friction of the PL glass/SiO2 pair has opposing trends at the nano- and macroscales. At the nanoscale, the friction coefficient (COF) in humid air is much higher than in dry air, which is attributed to the capillary effect of the absorbed water-film at the interface. At the macroscale, on the other hand, the COF in humid air is lower than in dry air, because the water-related mechanochemical wear makes the worn surface less susceptible to cracking. Material removal for PL glass is better facilitated by humid air than by dry air at both scales, because the stress-enhanced hydrolysis accelerates the material-removal process in glass. Moreover, the material-removal is more sensitive to contact pressure at the macroscale, because stronger mechanical-interaction occurs during material removal at the macroscale with the multi asperity contact mode. At the macroscale, the material removal is more sensitive to contact pressure in humid air compared to dry air. Because almost all mechanical energy is used to remove material in humid air, and most of the mechanical energy is used to produce cracks in PL glass in dry air. The results of this study can help optimize the multi-scale surface processing of optical glasses. Keywords: phosphate glass; friction; wear; water; hydrolysis; tribochemistry
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Introduction
Nd-doped phosphate laser (PL) glasses are an ideal gain medium for high peak-power solid-state lasers because of their high optical energy-storage capacity. For this reason, they are widely used for power amplification in high peak-power lasersystems [1, 2]. To provide a high-quality optical surface, PL glasses need to be processed via grinding to ensure high surface precision. This process * Corresponding author: [email protected]
involves material removal at the macroscale [3]. Subsequently, the PL glasses are polished to provide an ultra-smooth and defect-free surface, which involves material removal at the nanoscale [4]. In both processes, the material removal occurs due to tribological i
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