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Wear resistant composite layers were fabricated on 38CrMoAl steel by laser processing with NiCr/Cr3C2-CeO2 powders with addition of MoS or WS . The composite layers were heat treated at 150 and 300°C (MoS2), and 300 and 600°C (WS2). Microstructure, phases, microhardness, wear behaviour at room temperature and crack behaviour under loading of the laser processed and heat treated layers were investigated. Results indicate that undissolved MoS2 or WS2 were observed in all the layers. Heat treatment changed the microstructure and phases of all the laser processed layers. When the original majority phase of the laser processed layer was martensite, volume fraction of retained austenite increased after heat treatment; while when the original majority phase was austenite, volume fraction of retained austenite decreased after heat treatment. Full width at half maximum (FWHM) of martensite peaks in the laser processed layer with addition of 20 wt.% MoS2 decreased with heat treatment temperatures, indicating reduced defects in the heat treated layers. Laser processed layers with addition of 10 wt.% MoS2, 10 wt.% or 20 wt.% WS2 without heat treatment showed the best wear resistance while that with addition of 20 wt.% MoS2 showed the best wear resistance after heat treatment at 300°C. The wear mechanism of all the layers is abrasive, adhesive and oxidative wear, accompanied by the formation and removal of oxide film and sulphide containing tribofilms. The oxide film and sulphide lubricating phases formed on the worn surface during sliding wear play an important role in reducing friction and wear loss. Un-dissolved MoS2/WS2 and crack behaviour in case of loading is closely related to the microstructure of the pressed matrix. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) is a competitive innovative surface treatment technique, which can induce compressive residual stresses in metal materials. In this investigation, a modified explicit finite element analysis (FEA) method was used to predict the residual stress distribution in 2050-T8 aluminum alloy induced by LSP. The laser shock sequence was programmed by VDLOAD ABAQUS subroutine. Simulated residual stresses from FEA showed good consistency with open literatures. Based on the method, the effects of LSP parameters such as overlapping percentage, number of impacts, laser power density, laser spot size on the average surface residual stress and average in-depth residual stress of 2050-T8 aluminum alloy were analyzed. [ABSTRACT FROM AUTHOR]

Wear resistant composite layers were fabricated on 38CrMoAl steel by laser processing with NiCr/Cr3C2-CeO2 powders with addition of MoS or WS . The composite layers were heat treated at 150 and 300°C (MoS2), and 300 and 600°C (WS2). Microstructure, phases, microhardness, wear behaviour at room temperature and crack behaviour under loading of the laser processed and heat treated layers were investigated. Results indicate that undissolved MoS2 or WS2 were observed in all the layers. Heat treatment changed the microstructure and phases of all the laser processed layers. When the original majority phase of the laser processed layer was martensite, volume fraction of retained austenite increased after heat treatment; while when the original majority phase was austenite, volume fraction of retained austenite decreased after heat treatment. Full width at half maximum (FWHM) of martensite peaks in the laser processed layer with addition of 20 wt.% MoS2 decreased with heat treatment temperatures, indicating reduced defects in the heat treated layers. Laser processed layers with addition of 10 wt.% MoS2, 10 wt.% or 20 wt.% WS2 without heat treatment showed the best wear resistance while that with addition of 20 wt.% MoS2 showed the best wear resistance after heat treatment at 300°C. The wear mechanism of all the layers is abrasive, adhesive and oxidative wear, accompanied by the formation and removal of oxide film and sulphide containing tribofilms. The oxide film and sulphide lubricating phases formed on the worn surface during sliding wear play an important role in reducing friction and wear loss. Un-dissolved MoS2/WS2 and crack behaviour in case of loading is closely related to the microstructure of the pressed matrix. [ABSTRACT FROM AUTHOR]