材料期刊网

研究了晶粒细化对K417G高温合金在760 ℃/645 MPa,900℃/315 MPa和950℃/235 MPa下的蠕变性能的影响.结果表明,晶粒细化对合金蠕变性能的影响与温度和施加应力有关.在760 ℃/645 MPa下合金的蠕变性能随晶粒细化而提高,变形以晶内变形为主;900℃/315 MPa下的蠕变性能随晶粒细化先升高后降低,变形为晶内变形和晶界滑移竞争作用;950 ℃/235 MPa下的蠕变性能随晶粒细化而降低,变形以晶界滑移为主.760℃/645 MPa下,位错切过γ'相,基体通道中没有位错网产生;900℃/315 MPa和950℃/235 MPa下位错通过Orowan机制绕过γ'相,基体通道中产生位错网,并且M23C6在晶内析出.

Grain size is one of the most important parameters which affect the mechanical properties of cast polycrystalline superalloys.To study the effect of grain refinement on the creep behaviors of K417G superalloy,the creep behaviors of K417G superalloy with four grain sizes were investigated at 760 ℃/645 MPa,900 ℃/315 MPa and 950 ℃/235 MPa.The longitudinal section of the fracture surface,crack propagation path,dislocation structure and plastic deformation distribution in the vicinity of the cracks were investigated by using SEM,TEM and EBSD techniques,thus the deformation mechanism and effect of grain refinement on the creep properties of K417G superalloy were determined under different creep conditions.The results showed that the effects of grain refinement on the creep property of the alloy varied with the temperatures and stress.At 760 ℃/645 MPa,grain refinement improved the creep life and reduced the steady-state deformation rate of the alloy.The creep deformation was dominated by intragranular deformation.At 900 ℃/315 MPa,as grain size decreased,the creep life increased firstly and then decreased,while the steady-state deformation rate decreased firstly and then increased.The creep deformation showed a competitive effect ofintragranular deformation and grain boundary sliding.At 950 ℃/235 MPa,the creep life decreased and the steady-state deformation rate increased with the decrease of the grain size.Grain boundary sliding was the main deformation mode.At the same time,grain refinement could cause a refinement of the dendrite and carbide of the alloy,which would also affect the creep behavior of the alloy to a small extent.The TEM observation showed that at 760 ℃/645 MPa,the dislocations interacted with γ'particles through shearing mechanism and no dislocation network was found in the matrix.While at 900 ℃/315 MPa and 950 ℃/235 MPa,the dislocations crossed the γ'particles through Orowan bypass mechanism,dislocation network formed in the matrix,and M23C6 precipitated in the interior of the grains,which had a [001]M23C6//[001]Matix orientation relationship between the M23C6 precipitates and matrix.