Investigation On The Microstructure And Mechanical Properties Of A Ni-based Single Crystal Superalloy

In the present paper, the mechanical properties and deformation mechanism of a Ni-based single crystal superalloy were investigated and analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).As-cast alloy has obvious dendritic structure,γ' phase has regular cubic shape after full heat treatment. Both yield and tensile strengths reach the minimum value at about 500℃, and they increase to maximum value at 800℃. The trend of ductility with temperature is opposite to that of strength. At low temperatures, shearingγ' particles by single dislocation is the main deformation mechanisum. At high temperatures, the deformation mechanisum was dominated by dislocation bypassingγ' particles. Intermediate temperatures exhibited transitional behavior. At room and intermediate temperatures, the fracture mode exhibits pure shear feature. At high temperature, the fracture mode shows microviod coalesence fracture.The y'particles remain cubic shape at 800℃; at 980℃,γ' particles form fine rafted structure. At intermediate temperature (800℃), the fracture mode shows both pure shear feature and microviod coalessence feature. At high temperature (980℃), the fracture mode turns to be microviod coalessence fracture. At 800℃/850MPa,800℃/1050MPa conditions, the stress rupture deformation mechanisms in proper sequence are stacking faults and dislocation-pair shearingγ' phase; at 980℃/250MPa,980℃/320MPa conditions, the stress rupture deformation mechanism is dislocation bowing, at 980℃/400MPa condition, the stress rupture deformation mechanism is dislocation climbing.The creep curves of alloy exhibit strong stress dependence. At 1010℃/235MPa, 1010℃/248MPa conditions, the creep curves present obviously the steady-state and accelerating creep stages; at 1010℃/340MPa condition, the creep curves only emerge obvious accelerating creep stages.The effect of long-term aging on microstructure and creep properties of a single crystal Ni-based superalloy is investigated, the results showed that theγ' phase always remain cubic distribution after aging 100h at 800℃; theγ' phase gradually connect and raft after aging 1000h at 980℃and aging 500h at 1010℃. Theμphase precipitating in the form of needles and granules when aged more than 500h at 980℃and more than 100h at 1010℃, theμphase gradually increased with the aging time extended at 980℃, while it first increased and then decreased at 1010℃. The creep lives of alloy changed little after long-term aging at 800℃, while it decreased with increasing of aging time and temperatures generally at 980℃and 1010℃.