Study On The Microstructure And Properties Of Heat-Treated Ni-20.3Cr-4.6Co-2.1Al Sheet Deposited By EB-PVD

The microstructure and mechanical properties of Ni-20.3Cr-4.6Co-2.1Al sheet deposited by Electron Beam Physical Vapor Deposition (EB-PVD) for different technologies of heat-treatment were studied in this thesis. Superalloy sheet was annealed at different temperatures (400℃¹000℃) for different time (2h.4h.16h.30h) in 5×10^-3 Pa vacuum. The microstructure and phase structure of the different states were examined by XRD, OM, SEM, TEM and AFM. Contemporarily tensile properties at ambient and high temperatures of the different states were studied, then fracture pattern and fracture mechanism were analyzed. A kind of the best heattreatmnet was given, which reduced the residual stresses and improved the mechanical properties of materials.The results showed that, the phase structure of as-deposited alloy wasγ-Ni solid solution, not existed second-phase, and diffraction peaks were widen, had asymmetry. Its microstructure was densified structure, without precipitated phase, including twin crystals, dislocations and strain fringe, which was non-equilibrium state. The state of heattreatment was alsoγ-Ni solid solution, With the hoist of temperature and extension of times, the widen phenomenon disappeared, and had well symmetry, the grains along (220) planum grew by preferential orientation rapidly, lattice parameter reduced to a of equilibrium state. The main reason that stresses of macro and microscopic view were eliminated gradually.After annealed by different technologies, the microstructure of planums and cross-sections took on obviously growing by cellular crystal, which existed substructural flaws including twin crystals, dislocations, fault etc. Grains'sizes became larger and arranged regularly, strain fringes were eliminated, dislocations in grains showed themselves different configurations, were clearly provided with crystallographic feature. Accordingly we can obtain equilibrium strcture, in order to eliminate inner stress, improve microstructure and properties.The microhardness and nano-hardness of alloy sheet reduced as the temper- ature increasing, when the different state sheets were drew for normal and high temperatures, tensile strength and yield strength firstly increased then reduced, took on nicer plasticity. Tensile fracture patterns all took on two regions of...