JOINT STUDY ON THE DEVELOPMENT OF Ni-Al-Ti BASE AUPERALLOYS

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To develop a new type of beta (NiAl : B2) -base superalloy, phase equilibria in the Ni-Al base systems have been investigated and some microstructural controls based on the information of the phase equilibria have been performed. The results obtained are summarized as follows.1, Phase Equilibria in the Ni-Al Base SystemsThe phase equilibria among the beta, gamma (A1), gamma' (L1_2), beta' (L2_1) and eta (D0_<24>) phases in the Ni-Al-Ti, Ni-Al-Fe, Ni-Al-Co and Ni-Al-Ti-base systems were determined mainly by diffusion couple experiment. Thermodynamic analysis and computer calculation of phase diagrams of the Ni-Al, Ni-Ti, Ni-Al-Ti, and Ni-Al-Fe systems were also carried out.2, Microstructural Controlgamma+beta, gamma'+beta and gamma+gamma'+beta multi-phase alloys were obtained by a conventional thermomechanical treatment through the microstructural control. In the Ni-Al-Fe and Ni-Al-Co systems where martensitic transformation occurs in the beta phase, three types of beta+gamma' structure … More s i.e.blocky, fine lamellar and widmanstatten structures, can be obtained.3, Mechanical Properties of Multi-Phase Alloys(1) gamma+beta two-phase alloys ; the introduction of gamma phase improves the ductility drastically and exhibits a good tensile properties at room temperature. This type of alloys shows an excellent oxidation resistance, while high-temperature strength decreases with increasing temperature over 600ﾟC.(2) gamma+beta two-phase alloys ; the alloys with the lamellar structure show an excellent mechanical properties at room temperature. The high-temperature strength is slightly higher than that of the gamma+beta two-phase alloy.(3) gamma'+beta+beta' three-phase alloys ; Ni- (15-25) Al- (7-15) Ti base three-phase alloys exhibit an excellent strength higher than that of some practical superalloys at the temperatures below 700ﾟC,while the increase in ductility is necessary for the practical use.It is concluded from the present study that the Ni-Al base superalloys with the beta matrix have sufficient oxidation resistance and exhibit strength higher than many practical superalloys at the temperatures below 700ﾟC. Less