Study On Tribology And Corrosion Behavior Of Mg-based Amorphous Nanolaminates

Amorphous alloy films show great potential for applications in microelectromechanical devices,implantable medical treatment,portable electronic equipment and other fields due to the distinct advantages,such as high hardness,good thermoplastic forming ability,and low surface roughness.Amorphous-based nanolaminates consist of amorphous phase and other materials,which alternately stacked with each other in a two-dimensional direction with nanoscale regulation.Thus the number of heterogeneous interfaces,the composition and the layer thickness are controllable,which is very beneficial for designing and optimizing the properties of amorphous alloy films.In this paper,a series of Mg Cu Y/Co Fe Ta B amorphous/amorphous nanolaminates and Mg Cu Y/Cu amorphous/crystalline nanolaminates were prepared by magnetron sputtering,in which the Mg Cu Y layer thickness(～4 nm)was fixed,while the Co Fe Ta B and Cu layer thicknesses varied at the nanoscale.Then the mechanical,frictional wear,and corrosion behaviors were systematically studied,and the underlying mechanisms were explored.The main conclusions are as follows:Layer thickness dependence of the hardness of Mg Cu Y amorphous-based nanolaminates.For Mg Cu Y/Co Fe Ta B nanolaminates,the hardness of the nanolaminates continue to increase,as the thickness of Co Fe Ta B layer decrease from 80 nm to 4 nm and the volume fraction of the softer Mg Cu Y phase increase from 4.67% to 50%,inducing the highest hardness of nanolaminate with layer thickness of 4 nm,which is 19% higher than that of Co Fe Ta B film.Further analysis suggests the result can be attributed to the hindering effect on shear bands brought by the high density heterogeneous interfaces.For the Mg Cu Y/Cu nanolaminates,the hardness of nanolaminates shows a trend of increasing first and then decreasing,as the thickness of Cu layer decrease from 40 nm to 4 nm and the volume fraction of the Mg Cu Y phase increase from 9.1% to 50%,resulting the highest hardness with a layer thickness of 16 nm,which is 68% higher than that of the Cu films.The experiment results revealed the key role of the change in main plastic deformation mechanisms caused by the decrease of grain size in the Cu layer.The tribological properties of Mg Cu Y amorphous-based nanolaminates are not only related to the hardness but are also influenced by the toughness and plasticity.For Mg Cu Y/Co Fe Ta B nanolaminates,the highest hardness occurr when the Co Fe Ta B layer thickness is 4 nm,corresponding to the lowest wear rate with only 1/40 of that of Mg Cu Y films,comparatively,the friction coefficient reduce about 10%.However,for Mg Cu Y/Cu nanolaminates,the friction coefficient and wear rate of nanolaminates with layer thickness of16 nm are much higher than despite the highest hardness,in which wear rate is 42% higher than that of nanolaminate with layer thickness of 4 nm.It is shown that abrasive wear is the main wear mechanism of Mg-based amorphous nanolaminates.With the decrease of Co Fe Ta B layer thickness or Cu layer thickness,the number of interlayer heterogeneous interfaces rapidly increases,and the plastic deformation ability of nanolaminates is apparently improved,and the friction-induced cracking is effectively suppressed.The Mg Cu Y amorphous-based nanolaminate structure can significantly enhance the corrosion resistance of the corresponding metal films with layer thickness dependence.When the layer thickness of Co Fe Ta B(80 nm)or Cu(40 nm)is larger,the interlayer heterogeneous interfaces of nanolaminates can effectively hinder the corrosive medium penetration and corrosion crack expansion.Moreover,the stronger electric coupling interaction between the adjacent anode layer(Mg Cu Y)and cathode layer(Co Fe Ta B or Cu)results in corrosion paths constantly being deflected from the longitudinal to the lateral,thereby slowing down the corrosion process.