National Research Nuclear University “MEPhI” (Moscow Engineering Physics Institute), Moscow, Russia:

A. V. Shulga, Assistant Professor of a Chair of Physical Problems of Material Science, e-mail: avshulga@mephi.ru

The results of the compression tests of the specimens of the type EP741NP Ni-based rapidly quenched superalloy at the temperatures range of 1100 to 1200 ^оC and investigation of the microstructure features are presented. The specimens were produced from consolidated compacts fabricated by hot isostatic pressing using the rapidly quenched powders produced by the gas atomization technique (GA) and plasma rotating electrode process (PREP). The true stress-strain diagrams were calculated by the electronic data processing using the “compressive load — shortening of specimen” diagrams which were recorded as the initial results of compression tests. An analysis of the stress-strain curves and the features of the microstructure and distribution of boron are presented. The following main methods were used for the specimen investigation: light metallography and autoradiography on boron. Effect of the type of the melt-atomized powder on the level of the consolidated compact flow stress and the features of the microstructures such as “necklace”, ultra high dispersion types were detected. Important feature of the flow behavior of the type EP741NP Ni-based superalloy as-HIPped compacts is
the obvious oscillations of the stress-strain curve at the low temperature 1125 ^оС at the strain rate 10^–3 s^–1. The occurrence of «necklace» microstructure at these temperature and strain rate has confirmed that the reason of the oscillations is dynamic recrystallization. Correlations of the features of stressstrain curves with the microstructure and boron distribution were established. In compacts fabricated using PREP-powders were detected more homogeneous distribution of boron and presence of anomalous granules when compared with GA-powders.

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