Study Of Ternary Alloy Nanoindentation By Molecular Dynamics Simulation And Experiment

As a special kind of crystalline defects,nanotwinning structure shows excellent mechanical,tribological and thermal properties.Current research of nanotwins mainly focus on single crystal metal,such as Cu,Mg,Al,few studies are centered on nanotwins in engineering alloy materials.Dynamic plastic deformation(DPD),pulsed electrodepositon,et al,have been used to fabricate the nanotwins.However,ultra-low temperature and toxic chemicals are required in these methods,respectively.In addition to experimental research,molecular dynamics(MD)simulation is widely used to investigate the properties and formation of nanotwins,the simulation are maily centered on single crystal mental.In addition,MD simulations are usually performed by directly building nanotwinning model,few studies about nanotwins in a single crystal model have been reported.Therefore,a novel approach is used to fabricating nanotwinning surface,MD models are constructed for single crystal ternary nickel alloy and titanium alloy,the deformation behavior of single crystal ternary alloy and formation mechanism of nanotwins by MD simulations of nanoindentation are analyzed,the main content is as follows:Firstly,a MD simulations of nanoindentation is performed on the constructed single crystal ternary nickel alloy C-2000.The effect of different indentation orientations,indentation speed and model size on the plastic deformation behavior of the material are investigated.Nanotwins and a special kind of fivefold nanotwins are observed in the ternary nickel alloy during the MD simulations of nanoindentation.The deformation mechanism of nanotwins and fivefold twins are elucidated by analyzing the evolution of microstructure under nanoindentation.Sencondly,in order to verify the results of MD simulations in nickel alloy C-2000 under nanoindentation,a nanoindentation experiment is developed to fabricate the nanotwinning surface in nickel alloy C-2000.Hardness of nickel alloy improved significantly at a peak load of 1 N,the large area cycle nanoindentation of nickel alloy are performed at the peak load of 1 N.The treated sample is characterized by the transmission electron microscope(TEM),the coherent twin boundary are observed in the TEM images.Finally,another common aviation material Ti-2Al-2.5Zr alloy is used during MD simulations based on nanoindentation.We construct a MD model using suitable crystal size,indentation speed and indenter size,different types of nanotwinning structure are observed in two different indent orientation of the alloy model,we analyze the deformation mechanism of the two different types of nanotwins.