Research On Ultrasonic Microarray Forming And The Size Effect Of Nanocrystaline Ni-Co Foil Material

In recent years, researches on nanomaterials, micro-electro-mechanical systems and ultrasound-assisted forming are becoming more and more widely. This subject aims to study the micro-arrayed formability of the electro-deposited nanocrystalline Ni-Co foil with the assistance of ultrasonic. Size effect at room temperature and high temperature properties of the nanocrystalline Ni-Co foil were also studied.The structural and mechanical properties of the as-deposited Ni-Co foil were studied by various characterization methods: SEM test indicates the surface of the Ni-Co foil is flat and compact; Energy spectrum analysis shows the dispersion of elements on the surface is uniform, and Ni element makes up 97.52% while Co makes up 2.47%; XRD analysis indicates the crystal structure is simple face-centered cubic,and the grain size ranges from 30 to 50 nm which was calculated by scherrer’s formula;TEM test determines the grain size is about 40nm; Nano-indentation hardness test shows its hardness is 4.724 GPa.Ni-Co foils with different thicknesses were prepared by changing the time for electrodeposition. Micro tensile tests were conducted at room temperature under three conditions, and effects of foil thickness, grain size and strain rate on the mechanical property were studied. The result demonstrates that with the increase of foil thickness,the varation of tensile strength is not significant while the elongation shows the trend to increase with the maximum value of 11.67%; With the increased grain size caused by improved heat treatment temperature, the tensile strength and the elongation are both decreased; With the increase of strain rate, the tensile strength and the elongation are increased firstly but then shows the trend to decrease. High temperature tensile experiment was used to study the high temperature mechanical properties of the Ni-Co foil, and a maximum elongation of 366% was obtained in the tension test at a temperature of 500℃ and at a strain rate of 1.11×10-3s-1.The best micro-arrayed forming part with rigid punch was obtained when the forming temperature, foil thickness and ultrasonic amplitude loading were 500℃,120μm and 20.85μm, respectively. And height-to-diameter ratios of the two punch diameters were 0.4875 and 0.425. The height-to-diameter ratio of the soft-punch forming was increased with the increase of the foil thickness, ultrasonic amplitude and die diameter. The maximum height-to-diameter was obtained with the forming temperature of 500℃, foil thickness of 120μm, ultrasonic amplitude loading of20.85μm and die diameter of 0.6mm, and the value was 0.47.