In order to investigate the diffusivity of both W and Re in Ni-based superalloys, interdiffusion coefficients in Ni-Al-X (X ¼ Re, W) ternary system, which is the fundamental system of Ni-based superalloys, were measured by an experiment using diffusion couples. A modified ternary Boltzmann-Matano method was employed for the evaluation of the interdiffusion coefficients. In the phase of Ni-2.5Al-4.3Re and of Ni-2.4Al-3.3W (mol%), the major interdiffusion coefficients were estimated to beD D The interdiffusion coefficients give the Wagner's interaction parameter between Re and Al, and between W and Al as " ReAl < " WAl < 0, indicating that the ordering tendency exists between Al and Re, and between Al and W.

Interdiffusion coefficients of the refractory elements in Ni-X-Y (X, Y ¼ W, Re, Ru, Al) ternary systems, which are the fundamental systems of Ni-based superalloys, were estimated by a series of experiments using diffusion couples. The modified ternary Boltzmann-Matano method was employed for analyzing the experimental data. The cross interdiffusion coefficients were smaller than the main interdiffusion coefficients in all systems. Especially, the cross interdiffusion coefficientD D Ni ReRu is much smaller by an order of magnitude than the main interdiffusion coefficientD D NiReRe in Ni-Ru-Re system. This result indicates that the thermodynamical interaction parameter (Wagner's interaction parameter) between Ru and Re is negligible, and implies that Ru does not affect the distribution behaviour of Re into and 0 phases.

SynopsisThree steels microalloyed with V, Nb and V & Nb were deformed by torsion at temperatures f rom 900 to 1200 °C and over a strain rate range from about 10_3 to 10 s-'.Within the experimental range covered, typical dynamic recrystallization type flow was observed in all steels. The dynamic recrystallization behavior was analyzed with a special emphasis on the transition from multiple to single peak flows. The grain size of the dynamically recrystallized materials was also measured, and it was able to present as a function of the Zener-Hollomon parameter, Z, without exhibiting any dependence on the initial grain size.The transition condition of flow stress behavior could be reasonably expressed by Z, not as a unique value but by a range of z values. Throughout the range, the transition of flow stress behavior occurred. The correlation of the flow behavior with the resultant microstructure was also considered.

The activation enthalpies and frequency factors for interdiffussion of Al and Re in the -phase of Ni-Al-Re ternary system were estimated by a series of experiments using diffusion couples in the temperature range from 1200 to 1300 C. The method developed by Whittle and Green was applied to obtain the interdiffusion coefficients of the solutes (Al, Re) in the system. The activation enthalpies Q and the frequency factors D D o obtained from the experiments confirmed the slower diffusion of Re than Al. In addition, it was found that the influence of Re on the diffusion of Al in the -phase of Ni-Al-Re system was insignificant.

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