Microstructure design and control of intermetallics

1. Ni_3Al多晶组织控制在适当的变形条件下，通过等温锻造将Ni_3Al三元合金组织控制为等轴再结晶晶粒，并研究了其室温塑性。三元元素含量大于2%的Ni_3Al微合金的延展性可以用有序能来解释，而含Zr或Hf的Ni_3Al微合金的延展性可以归因于清除杂质。后一结论与在超高真空条件下用区细化Ni和Al制备的高纯Ni_3Al具有延展性的事实相一致。采用H_2机械合金化+热压或Ar机械合金化+ HIPing的方法制备了超细晶粒TiAl。与粗晶TiAl相比，超细晶TiAl在较低的应力下变形。超细晶TiAl+Ti_3Al表现出超塑性，超塑性变形后的热处理提高了高温强度。高温压缩变形产物变形织构为TiAl和层状组织TiAl/Ti_3Al。在TiAl中加入三元会产生由金属间化合物、碳化物或氮化物组成的析出物，从而提高高温强度。采用铸锭等温锻造、合金粉末HIP固结和热压反应烧结制备Nb_3AlNb_3Al+Nb两相合金。通过控制合金成分和组织，提高了合金的高温强度和室温断裂韧性。

1. Microstructure control of Ni_3Al polycrystalsMicrostructures of Ni_3Al ternary alloys were controlled to consist of equiaxd, recrystallized grains by isothermal forging under appropriate deformation conditions and ductility at room temperature was investigated. Ductilities of Ni_3Al alloyed with ternary elements of more than 2% are explained by ordering energy, and ductilization of Ni_3Al microalloyed with Zr or Hf is ascribed to scavenging of impurities. The latter conclusion is consistent with the fact that high purity Ni_3Al prepared by using zone-refined Ni and Al in a ultra-high vacuum exhibits ductility.2. Microstructure control of TiAlUtra-fine grained TiAl was obtained by mechanical alloying in H_2 followed by hot pressing or mechanical alloying in Ar followed by HIPing. Ultra-fine grained TiAl deforms under lower stress compared with coarse grained TiAl. Ultra-fine grained TiAl+Ti_3Al exhibits superplasticity and heat treatment after superplastic deformation improves high temperature strength.Compressive deformation at high temperatures products deformation texture for TiAl and for lamellar structured TiAl/Ti_3Al.Ternary additions to TiAl Produce precipitates consisting of intermetallic compounds, carbides or nitrides, thereby increasing high temperature strength.3. Microstructure control of Nb_3AlNb_3Al+Nb two phase alloys were prepared by isothermal forging of ingots, HIP consolidation of alloyed powders or reactive sintering in hot pressing. High temperature strength and fracture toughness at room temperature are improved by controlling alloy composition and microstructure.