Study On Microstructure And Properties Of Ni/Ni₃Al Microlaminate Sheets Deposited By EB-PVD

Ni/Ni₃Al microlaminate sheets were successfully synthesized by EB-PVD(Electron Beam Physical Vapor Depositon) technique.The sheets are 200μm²50μm thick and they were studied about morphology,microstructure and mechanical properties. The preliminary simulation of the interphases was also finished.The microlaminate composites prepared by EB-PVD technique have high porosity and the mechanical properties of construction materials are sensitive functions of macroscopic and microscopic faults of structure.So two kinds of as-deposited microlaminate sheets were thermally densified using hot rolling,hot isostatic pressing,hot pressing techniques which were decided by considering the result of differential thermal analysis and the experimental condition.Having examined the composition by EMPA,studied the morphological characteristics by SEM,and probed the phase composition by XRD method,this paper also analyzed the texture,examined the stress-strain curves at room temperature and high temperature and analyzed why the customary linear zone presents nonlinearity in some of them.It was found that while No.1 microlamiate sheet,prepared when the distance between targets and the substrate was 500mm,was growing in the island mode,No.2 microlaminate sheets, prepared when the distance between targets and the substrate was 300mm,was growing in the mode between the island mode and the layer mode. The EB-PVD process has great influence on the layer geometry of microlaminate sheets.Between layers close to the substrate,which were deposited earlier,diffusion processed longer and layer interfaces moved towards each other and even disappear. No.1 microlaminate sheets are mainly composed of Ni solution phase. In as-deposited samples there is no texture and the highestσb andδare 317MPa and 48%;No.2 microlaminate sheets are mainly composed of Ni solution phase and Ni₃Al(γ') phase and they are arranged in alternant layers with (111) and (200) textures in both phases of as-deposited samples. The highestσb andδare 797.9MPa and 66.9%;Compared to as-deposited No.1 microlaminate sheets, there are (111) and (200) textures in hot-rolled No.1 microlaminate sheets,and the strength and elongation percentage of the them at room temperature decreased,while at high temperature the strength was improved and elongation percentage decreased. There are strong (220) texture in Ni solution of hot-rolled No.2 microlaminate sheets. There are (220),(311),(222) textures in hot-isostatic-pressed No.1 microlaminate sheets and the strength and elongation percentage increased at every tested temperature,except for the elongation percentage at 800°C decreased. the strength and elongation percentage of hot-pressed No.2 microlaminate sheets decreased compared to the corresponding as-deposited. Hot isostatic pressing is the most effective thermal densifying technique.Different from the stress-strain curves of ordinary alloy,the part of curves of No.2 microlaminate sheets,corresponding to the customary elastic section, present the nonlinearity and compose a slantwise and elongate's'shape.With the temperature elevated,there are sawtooth fluctuation.The modes of connection on the Ni/Ni₃Al (001) and (110) coherent interphases were analyzed by using Material Studio.In the opinion of energy,one promising mode in the (001) coherent interphase and two promising modes in the (110) coherent interphase were obtained.