摘要
The influence of a longitudinal static magnetic field on microstructures and mechanical properties of Ni_(3)Al-based alloy during directional solidification at the growth speed of 25μm/s and 100μm/s has been experimentally investigated.Results reflected that the utilization of a 0.5 T magnetic field refines the Ni Al dendrites at both speeds of growth.When applying a high magnetic field,the columnar-to-equiaxed transition(CET)occurred at growth speed of 25μm/s and dendrite networks formed at growth speed of 100μm/s.Tensile property results indicated that the refinement of dendrites enhanced both plasticity and ultimate tensile strength of Ni-Al alloy.The change of microstructures and mechanical properties should be attributed to the combined action of the thermoelectric magnetic convection(TEMC)in mushy zone together with the thermoelectric magnetic force(TEMF)acting on the solid.When applying a low magnetic field(0.5 T),the TEMF is too small to fragment the dendrites,and the refined dendrites is mainly due to the TEMC in the interdendritic regions.At a lower growth speed,the TEMF is supposed to strong enough to fragment the dendrites and induce the occurrence of CET under 2 or 4 T.When the growth speed increased to 100μm/s,no obvious CET was observed,but a vertical secondary convection is induced by the circulation in the parallel plane,which promotes the growth of secondary and tertiary branches,leading to the formation of abnormally developed high order dendrites.The hierarchical dendritic structure was suggested to provide a channel for rapid crack propagation and thus degraded the mechanical properties.
基金
supported by National Science and Technology Major Project“Aero engine and Gas Turbine”(2017-VII-00080102)
National Key Research and Development Program of China(No.2019YFA0705300)
National Nature Science Foundation of China(No.51701112 and No.51690162)
Shanghai Rising-Star Program(20QA1403800 and 21QC1401500)
Shanghai Science and Technology Committee(19DZ1100704)。
