The scratching mechanism of polycrystallineγ-TiAl alloy was investigated at the atomic scale using the molecular dynamics method,with a focus on the influence of different grain sizes.The analysis encompassed tribolo...The scratching mechanism of polycrystallineγ-TiAl alloy was investigated at the atomic scale using the molecular dynamics method,with a focus on the influence of different grain sizes.The analysis encompassed tribological characteristics,scratch morphology,subsurface defect distribution,temperature variations,and stress states during the scratching process.The findings indicate that the scratch force,number of recovered atoms,and pile-up height exhibit abrupt changes when the critical size is 9.41 nm due to the influence of the inverse Hall-Petch effect.Variations in the number of grain boundaries and randomness of grain orientation result in different accumulation patterns on the scratch surface.Notably,single crystal materials and those with 3.73 nm in grain size display more regular surface morphology.Furthermore,smaller grain size leads to an increase in average coefficient of friction,removed atoms number,and wear rate.While it also causes higher temperatures with a larger range of distributions.Due to the barrier effect of grain boundaries,smaller grains exhibit reduced microscopic defects.Additionally,average von Mises stress and hydrostatic compressive stress at the indenter tip decrease as grain size decreases owing to grain boundary obstruction.展开更多
Polyhedral oligomeric Silsesquioxanes (POSS) derived from vinyltrimethoxysilane (VMS) and modified with titanium tetrabutoxide (TTBO) (PVT) were prepared by sol-gel process catalyzed by hydrochloric acid (molar ratio:...Polyhedral oligomeric Silsesquioxanes (POSS) derived from vinyltrimethoxysilane (VMS) and modified with titanium tetrabutoxide (TTBO) (PVT) were prepared by sol-gel process catalyzed by hydrochloric acid (molar ratio: [HCl]/Si=0.05), and heating at 45 ℃ during 3 days. The PVT films (f-PVT) with different TTBO content, 5, 20 and 25wt% TTBO, were prepared by adding the stoichiometric amount of benzoyl peroxide (BPO) to PVT solutions in ethanol, dip-coating over glass substrates, and curing using an appropriate thermal cycle and time. The hardness and elastic modulus of f-PVT were tested by continuous stiffness measurement (CSM) of nanoindentation, and the tribological behaviors were comparatively investigated with a nanoscratch test. The influence of the different TTBO contents on the mechanical properties of f-PVT was discussed. The scratch and friction coefficient profiles of f-PVT were illustrated. As the results of the test, f-PVT with 20% TTBO showed the better scratch resistance and tribological behavior.展开更多
Purpose–Severe scarcity of natural river sand(RS),exacerbated by environmental protection policies and extraction constraints,has significantly impacted aggregate supply for railway concrete.While manufactured sand(M...Purpose–Severe scarcity of natural river sand(RS),exacerbated by environmental protection policies and extraction constraints,has significantly impacted aggregate supply for railway concrete.While manufactured sand(MS)offers a substitute for RS in railway applications,its widespread adoption in high-strength railway prestressed structures is challenged by lack of drying shrinkage and creep research data on concrete.Design/methodology/approach–High-strength manufactured sand concrete(MSC)was prepared using MS with varying lithologies and stone powder contents.Its drying shrinkage and creep behaviors were evaluated in accordance with the Chinese standard GB/T 50082.The deformation mechanism was analyzed by combining nano-scratch testing.Findings–Compared to RS concrete,MSC from all tested lithologies showed higher drying shrinkage but lower creep deformation.The drying shrinkage rose steadily with increased stone powder content,while the creep strain displayed a distinct non-linear trend,decreasing first before rising.To prepare low-deformation MSC,select high-strength MS and limit stone powder content not greater 10%.Nano-scratch tests indicated that harder MS particles suppress microcracking at the interfacial transition zone(ITZ),improving the creep resistance.The predictive models for drying shrinkage and creep were also developed by incorporating coefficients for stone powder and lithology effects.Originality/value–These findings serve as a foundation for the application of MSC in railway prestressed structures,offering both theoretical and practical guidance.展开更多
基金National Natural Science Foundation of China(52065036,52365018)Natural Science Foundation of Gansu(23JRRA760)+1 种基金Hongliu Outstanding Youth Foundation of Lanzhou University of TechnologyChina Postdoctoral Science Foundation(2023M733583)。
文摘The scratching mechanism of polycrystallineγ-TiAl alloy was investigated at the atomic scale using the molecular dynamics method,with a focus on the influence of different grain sizes.The analysis encompassed tribological characteristics,scratch morphology,subsurface defect distribution,temperature variations,and stress states during the scratching process.The findings indicate that the scratch force,number of recovered atoms,and pile-up height exhibit abrupt changes when the critical size is 9.41 nm due to the influence of the inverse Hall-Petch effect.Variations in the number of grain boundaries and randomness of grain orientation result in different accumulation patterns on the scratch surface.Notably,single crystal materials and those with 3.73 nm in grain size display more regular surface morphology.Furthermore,smaller grain size leads to an increase in average coefficient of friction,removed atoms number,and wear rate.While it also causes higher temperatures with a larger range of distributions.Due to the barrier effect of grain boundaries,smaller grains exhibit reduced microscopic defects.Additionally,average von Mises stress and hydrostatic compressive stress at the indenter tip decrease as grain size decreases owing to grain boundary obstruction.
文摘Polyhedral oligomeric Silsesquioxanes (POSS) derived from vinyltrimethoxysilane (VMS) and modified with titanium tetrabutoxide (TTBO) (PVT) were prepared by sol-gel process catalyzed by hydrochloric acid (molar ratio: [HCl]/Si=0.05), and heating at 45 ℃ during 3 days. The PVT films (f-PVT) with different TTBO content, 5, 20 and 25wt% TTBO, were prepared by adding the stoichiometric amount of benzoyl peroxide (BPO) to PVT solutions in ethanol, dip-coating over glass substrates, and curing using an appropriate thermal cycle and time. The hardness and elastic modulus of f-PVT were tested by continuous stiffness measurement (CSM) of nanoindentation, and the tribological behaviors were comparatively investigated with a nanoscratch test. The influence of the different TTBO contents on the mechanical properties of f-PVT was discussed. The scratch and friction coefficient profiles of f-PVT were illustrated. As the results of the test, f-PVT with 20% TTBO showed the better scratch resistance and tribological behavior.
基金supported by National Natural Science Foundation of China(award no.52408309)National Natural Science Foundation of China(award no.52438002).
文摘Purpose–Severe scarcity of natural river sand(RS),exacerbated by environmental protection policies and extraction constraints,has significantly impacted aggregate supply for railway concrete.While manufactured sand(MS)offers a substitute for RS in railway applications,its widespread adoption in high-strength railway prestressed structures is challenged by lack of drying shrinkage and creep research data on concrete.Design/methodology/approach–High-strength manufactured sand concrete(MSC)was prepared using MS with varying lithologies and stone powder contents.Its drying shrinkage and creep behaviors were evaluated in accordance with the Chinese standard GB/T 50082.The deformation mechanism was analyzed by combining nano-scratch testing.Findings–Compared to RS concrete,MSC from all tested lithologies showed higher drying shrinkage but lower creep deformation.The drying shrinkage rose steadily with increased stone powder content,while the creep strain displayed a distinct non-linear trend,decreasing first before rising.To prepare low-deformation MSC,select high-strength MS and limit stone powder content not greater 10%.Nano-scratch tests indicated that harder MS particles suppress microcracking at the interfacial transition zone(ITZ),improving the creep resistance.The predictive models for drying shrinkage and creep were also developed by incorporating coefficients for stone powder and lithology effects.Originality/value–These findings serve as a foundation for the application of MSC in railway prestressed structures,offering both theoretical and practical guidance.
