Microstructure design and control of intermetallics

1. Ni_3Al多晶合金的组织控制在适当的变形条件下，通过等温锻造将Ni_3Al三元合金的组织控制为等轴再结晶晶粒，并研究了其室温塑性。用有序化能解释了Ni_3Al合金化后的塑性，用Zr或Hf微合金化后的塑性归因于杂质的清除。后一结论与超高真空区熔Ni和Al制备的高纯Ni_3Al具有塑性的事实相一致.采用H_2中机械合金化+热压或Ar中机械合金化+热等静压的方法，获得了TiAl超细晶组织。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具有超塑性，超塑性变形后的热处理可提高高温强度;高温压缩变形可使TiAl和层片状TiAl/Ti_3Al产生形变织构; TiAl中的三元添加物可产生由金属间化合物、碳化物或氮化物组成的析出相，从而提高高温强度.采用铸锭等温锻造、合金粉末热等静压固结和热压反应烧结等方法制备了Nb_3AlNb_3Al+Nb两相合金。通过控制合金成分和显微组织，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.