Alloy Design and Microstructural Control in Ni-based Multi-Intermetallic In-situ Composite Materials

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Using Ni_3Al-Ni_3Nb-Ni_3Ti, Ni_3Al-Ni_3Ti-Ni_3V, Ni_3Al-Ni_3Nb-Ni_3V and Ni_3Si-Ni_3Nb-Ni_3Ti pseudo-ternary alloy systems, the development of multi-intermetallic in-situ composite materials as a candidate of new high-temperature structural materials was performed on alloy design and microstructure control. The following results were obtained from the present study.(1)It was found dual multi-phase microstructure composed of L1_2 and D0_<22> phases was developed in Ni_3Al-Ni_3Ti-Ni_3V and Ni_3Al-Ni_3Nb-Ni_3V pseudo-ternary alloy systems, and had extremely fine microstructure and highly coherent interface structures not only between the upper- and lower-multi-phase microstructures but also between the constituent phases.(2)In Ni_3Si-Ni_3Nb-Ni_3Ti pseudo-ternary alloy system, the precipitation phenomenon due to the solubility change by temperature between two constituent phases, L1_2 and D0_<24> was found to occur and consequently the precipitation strengthening was applicable to the present alloy system.(3)The Ni_3Al-Ni_3Ti-Ni_3V and Ni_3Al-Ni_3Nb-Ni_3V pseudo-ternary alloys displayed the positive temperature dependence of the flow strength and also extremely high high-temperature strength accompanied with reasonable tensile ductility over a wide range of temperatures. In addition, the creep rate and creep rupture life were identical to or superior to those of the most superalloys or advanced superalloys.(4)For the Ni_3Al-Ni_3Ti-Ni_3V pseudo-ternary alloys, fabrication process such as conventional melting, hot-forging and unidirectional solidification processes were found to be applicable, consequently resulting in the mass production, reliability and low-cost.(5)It was shown that the developed multi-intermetallic in-situ composite materials are strongly promising as new high-temperature structural materials.