Properties And Fracture Anisotropy Of Nanolaminated Nickel

According to Hall-Petch relationship,when the grain size decreases,the strength of the material increases.So grain refinement is the most direct and effective way to improve the mechanical properties of metal materials.However,although the ordinary bulk nanocrystalline materials have extremely high strength,their plasticity is very low and they will cause necking instability rapidly.In recent years,some scholars have prepared nano-gradient structure materials and obtained excellent mechanical properties.However,there is a lack of detailed research on deformation physics and microstructures.Therefore,it is not suitable for industrial production.Later,some scholars have prepared nano-laminated structure materials,which have both high strength and good plasticity.and attracted great attention of materials scholars.This papar takes the f.c.c.nickel as an example.On the basis of severe plastic deformation process,bulk nano-laminated nickel were prepared by geometric refinement,and their microstructures,mechanical properties and anisotropic behavior were studied.The main results obtained are as follows.(1)Due to the size limitation of nano-laminated nickel,I developed a micronscale uniaxial tension platform independently,and used this instrument to measure the mechanical properties of micron-scale samples accurately.(2)The size effect of nano-laminated nickel on strength and plasticity was researched by comparing the mechanical properties of macroscopic samples and microscopic samples and analyzing the fracture behavior.It is found that the stress state during the deformation process and microstructure change of the microscopic sample are important factors leading to the size effect.(3)The tensile orientation effect of nano-laminated nickel was studied by comparing the mechanical properties of samples with different orientations.It was found that the parallel lamellar orientation had the highest strength,while the 45 degree orientation sample had the lowest strength,but its plasticity was the best.(4)The effect of tensile orientation on the fracture behavior of nano-laminated nickel was researched by analyzing the fracture behavior of samples with different orientations.It was found that parallel lamellar orientation was the fracture mechanism of microvoid coalescence,dislocation stacking at the boundaries of the TD 45 oriented sample is the main reason for its poor plasticity.(5)By analyzing the mechanical properties and fracture behavior of ND oriented samples,it was found that the fracture behavior of the samples in the vertical lamellar is controlled by the boundary defects.