Crystallographic Study of Grain Refinement in Ni Alloys with Ni-RE Intermetallics

Abstract Rare earth-doped nickel (Ni-RE) alloys are very attractive for the neutron shielding application for excellent neutron absorption and good mechanical behavior. Ni-RE intermetallics are important for their precipitation reinforcement in Ni alloys. In this work, Ni-RE intermetallics have been founded to be Ni grain refiners, which has been proved both by nucleation crystallography analysis and experiments. Ni-RE intermetallics could work as heterogeneous nucleation well, either different in atomic structures (for example, Ni17RE2, Ni5RE, Ni7RE2, Ni3RE, Ni2RE having matching orientation relationships as (111)Ni // (0004)Ni17Gd2 with [ 1 1 ¯ 0 ] Ni   / /   [ 01 1 ¯ 0 ] Ni17Gd2 , (111)Ni // (0002)Ni5Gd with [ 1 1 ¯ 0 ] Ni   / /   [ 01 1 ¯ 0 ] Ni 5Gd , (111)Ni // (00018)Ni7Gd2 with [ 1 1 ¯ 0 ] Ni   / /   [ 01 1 ¯ 0 ] Ni7Gd2 , (111)Ni // (00012)Ni3Gd with [ 1 1 ¯ 0 ] Ni   / /   [ 01 1 ¯ 0 ] Ni3Gd , (111)Ni // (222)Ni2Gd with [ 1 1 ¯ 0 ] Ni   / /   [ 1 1 ¯ 0 ] Ni2Gd ) or different in rare earth element (for example, (111)Ni // (0002)Ni5RE with [ 1 1 ¯ 0 ] Ni   / /   [ 01 1 ¯ 0 ] Ni5RE is general matching orientation relationships (ORs) of Ni5RE (RE = Sc, Y, La ~ Lu) for Ni grains). When RE dopant mass fraction is 1 wt%, the grain size is reduced from ~50 μm to 15 μm, and the refinement effect reaches the best. The work proposes Ni-RE intermetallics as good heterogeneous nuclei for Ni grains with an atomic level understanding and provides theoretical guidance for high-strength nickel alloy design.