Elastoplastic Deformation of a Ni 3 Al-Based Single Crystal Depending on Crystallographic Direction
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Russian Physics Journal, Vol. 63, No. 5, September, 2020 (Russian Original No. 5, May, 2020)
ELASTOPLASTIC DEFORMATION OF A Ni3Al-BASED SINGLE CRYSTAL DEPENDING ON CRYSTALLOGRAPHIC DIRECTION E. V. Tuch,1 Ya. V. Mayer,1 E. A. Strebkova,1 and M. N. Krivosheina1,2
UDC 539.3
The results of a numerical study in a three-dimensional formulation of the processes of elastoplastic deformation of a cubic single crystal based on the Ni3 Al intermetallic (VZHM8) under impact loading are presented. Impact loading is carried out in the [001] direction. The development of deformation processes is studied in the [100] and [010] or [011] and [011] directions. In the former case, the crystallographic directions of the single crystal coincide with the axes of the computational coordinate system and the elastic constants in these directions are the same. In the latter case, only one axis coincides with the [100] crystallographic direction, the other two are rotated by an angle of 45°. It is shown that a change in the elastic constants of a single crystal in new directions results in a change in the volume compressibility in all three directions. This is a consequence of the generalized Hooke's law. In the mathematical model used in this work to describe elastoplastic deformation, it is assumed that the volume compressibility of the single crystal is constant in the region of elastic and plastic deformations. It is shown for the first time that with the above rotation of the coordinate axes in a cubic single crystal, a change in elastoplastic deformations in the direction of the axis of impact loading is observed. Keywords: crystallographic directions, elastic constants, single crystal, dynamic action.
INTRODUCTION The need in new materials, satisfying exclusive requirements on high-temperature strength and heat resistance, for aerospace industry motivates numerous investigations of mechanical properties of single-crystal materials. Due to their structure, single crystals demonstrate high strength characteristics, and a series of nickel-rhenium-ruthenium containing alloys (VZHM6, VZHM8) also possesses high heat-resistance properties [1–6]. Owing to improved mechanical properties, Ni3Al-based single crystal monoaluminide (VZHM8) is widely used in the generation-V gasturbine engines (GTE) [2]. The properties of this alloy are being developed and investigated at the All-Russian Institute of Aviation Materials (VIAM) and the Baranov Central Institute of Aviation Motors (TSIUAM) [1–6], which allows using the results of their research for formulating new problem statements. It is well known that in single crystals with cubic symmetry along three principal crystallographic axes the elastic constants are equal, and when two directions rotate by an angle of 45°, anomalous demonstration of elastic properties is observed: a negative value of the Poisson’s coefficient can appear (auxetic property). In certain planes, auxetic alloys possess a value of the Poisson’s ratio of more than 0.5, which is impossible for isotropic materials. The calculat
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