Abstract
The influence of a longitudinal static magnetic field on microstructures and mechanical properties of Ni3AI-based alloy during directional solidification at the growth speed of 25 μm/s and 100 μm/s has been experimentally investigated.Results reflected that the utilization of a 0.5 T magnetic field refines the NiAl dendrites at both speeds of growth.When applying a high magnetic field,the columnar-to-equiaxed transition(CET)occurred at growth speed of 25 μm/s and dendrite networks formed at growth speed of 100 μm/s.Tensile property results indicated that the refinement of dendrites enhanced both plastic-ity 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 100 μm/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 den-dritic structure was suggested to provide a channel for rapid crack propagation and thus degraded the mechanical properties.
基金项目
国家科技重大专项(2017-Ⅶ-0008-0102)
国家重点研发计划(2019YFA0705300)
国家自然科学基金(51701112)
国家自然科学基金(51690162)
Shanghai Rising-Star Pro-gram(20QA1403800)
Shanghai Rising-Star Pro-gram(21QC1401500)
Shanghai Science and Technology Committee(19DZ1100704)
Shanghai Synchrotron X-ray Facility(SSRF)on date analysis()
万方数据