Nano-abrasion Behavior Of Pt(111) And Pt Based Metallic Glasses Under Different Humidity Environments

Akin to oxides glasses,the metallic glasses are capable of a viscous flow in supercooled liquid regime and therefore can be thermo-plastically moulded into complex shapes or components with small geometry and high surface quality.For this reason,the BMG can be applicable in micromechanical systems as micro-devices.The Pt-BMG that displayed a high hardness nearly six times of Pt(111)was expected to have a higher wear resistance according to the Archard’s law,yet the Pt(111)actually performed better.However,due to the different atomic structure characteristics of metallic glass and single crystal,which is believed to be the result of the different deformation mechanism of the two materials.The crystal structure has a movable structural defect--dislocation,which leads to a "work hardening" mechanism during friction and wear behavior.Therefore,it is a great desire to see which is better one in such wear condition where the roles of high hardness and work hardening simultaneously operate.It is necessary to study AFM scratches on atomically flat metallic glass and single crystal at nanometer scale.The contribution of hardness and work hardening to wear resistance of Pt glass and single crystal Pt(111)under multifield environment was studied by atomic force microscope nanoscratch technique.The main conclusions of this paper are as follows:(1)In comparison to the Pt(111),the Pt-BMG has a hardness but exhibits a lower wear resistance,which is due to the presence of work hardening effect in the wear process of Pt(111).The hardening effect is further verified by a significant friction force decrease within scratched region on Pt(111)but no apparent change on Pt-BMG.(2)Under high vacuum condition,the wear rate of Pt-BMG is quite similar with that of Pt(111)in friction tests.Combining with the fact that Pt(111)is softer than Pt-BMG,it can be assumed that the work hardening effect also operates in the wear process between the tip and the surface of the Pt(111).Therefore,the wear performance of metallic surfaces can be viewed as a competition of mechanisms among work hardening,immediate oxidization and hardness/strength,and the dominant mechanism depends on the specific wear conditions.(3)With the increase of the number of cycles,the friction force within scratched region on Pt(111)still has a downward trend.And the metallic glass in the single and low cycle wear conditions,there is no difference between the scratch region and no scratch region,but with the number of cycles increased to ten times,the friction force within scratched region on PtBMG also appeared an obvious downward trend,this is because with the increase of the number of cycles,the net free volume within scratched region continues to decline.Eventually leads to work hardening involved in the wear process on Pt-BMG.