Strain-hardening and warm deformation behaviors of extruded Mg-2Sn-0.5Yb alloy(at.%)sheet were investigated in uniaxial tensile test at temperatures of 25-250 ℃ and strain rates of 1×10^(−3) s^(−1)-0.1 s^(−1).The data fit with the Kocks-Mecking type plots were used to show different stages of strain hardening.Besides III-stage and IV-stage,the absence of the II-stage strain hardening at room temperature should be related to the sufficient dynamic recrystallization during extrusion.The decrease of strain hardening ability of the alloy after yielding was attributed to the reduction of dislocation density with increasing testing temperature.Strain rate sensitivity(SRS)was significantly enhanced with increasing temperature,and the corresponding m-value was calculated as 0.07-0.12,which indicated that the deformation mechanism was dominated by the climb-controlled dislocation creep at 200 ℃.Furthermore,the grain boundary sliding(GBS)was activated at 250 ℃,which contributed to the higher SRS.The activation energy was calculated as 213.67 kJ mol^(−1),which was higher than that of lattice diffusion or grain boundary self-diffusion.In addition,the alloy exhibited a quasi superplasticity at 250 ℃ with a strain rate of 1×10^(−3) s^(−1),which was mainly related to the fine microstructure and the presence of the Mg2Sn and Mg2(Sn,Yb)particles.
Nanocrystalline Cu film with a mirror surface finishing is prepared by the electric brush-plating technique. The as- prepared Cu film exhibits a superhydrophilic behavior with an apparent water contact angle smaller than 10°. A subsequent increase in the water contact angle and a final wetting transition from inherent hydrophilicity with water contact angle smaller than 90° to apparent hydrophobicity with water contact angle larger than 90° are observed when the Cu film is subjected to natural aging. Analysis based on the measurement of hardness with nanoindentation and the theory of the bond-order-length-strength correlation reveals that this wetting variation on the Cu film is attributed to the relaxation of residual stress generated during brush-plating deposition and a surface hydrophobization role associated with the broken bond polarization induced by surface nanostructure.
The dry sliding wear behavior of extruded Mg-9Sn and Mg-9Sn-3Yb alloys through pin-on-disc configuration was investigated at room temperature. Coefficient of friction, wear rate and wear resistance of extruded Mg-9Sn and Mg-9Sn-3Yb alloys were measured within a load range of 20-240 N and 20-380 N at a sliding velocity of 0.785 m/s, respectively. The wear tracks, worn surface and wear edge were observed using a scanning electron microscope and an energy dispersive X-ray spectrometer. The results indicated that wear rate, coefficient of friction and wear resistance changed with increasing applied load due to different wear mechanisms. Six wear mechanisms, namely adhesion, abrasion, oxidation, delamination, thermal softening and melting, were observed for both extruded alloys. The extruded Mg-9Sn-3Yb alloy exhibited good wear resistance compared with extruded Mg-9Sn alloy, which was mainly attributed to a large number of volume fraction of Mg2 Sn particles, the formation of thermal stable Mg2（Sn,Yb） particles and good elevated temperature mechanical properties.
Microstructures and mechanical properties of extruded Mg-2Sn-xYb(x=0,0.1,0.5 at.%)sheets were investigated.The grain size of as-cast Mg-2Sn alloy is significantly reduced with increasing Yb concentration.In addition toα-Mg and Mg_(2)Sn phase,some fine Mg_(2)(Sn,Yb)particles are observed in as-cast Mg-2Sn-0.5Yb alloy,but these fine particles are not observed in as-cast Mg-2Sn-0.1Yb alloy due to a high solubility of Yb in Mg matrix.Tensile tests demonstrated that extruded Mg-2Sn-0.5Yb sheet exhibited the highest tensile strength and available elongation to failure at room temperature,while extruded Mg-2Sn-0.1Yb alloy exhibited the highest tensile properties at 100°C and 200°C.The difference in the tensile properties of extruded sheets mainly arises from the different strengthening roles of grain refinement,solid solution strengthening and precipitation strengthening of particles.
