Parameters of Dislocation Structure and Work Hardening of Ni 3 Ge
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Parameters of Dislocation Structure and Work Hardening of Ni3Ge N.A. Koneva, Yu.V. Solov'eva, V.A. Starenchenko, E.V. Kozlov Tomsk State University of Architecture and Building, Department of Physics, Solyanaya sq. 2, Tomsk 634003, Russia ABSTRACT Orientation dependence of the yield stress temperature anomaly in Ni3Ge single crystals with the L12 structure was investigated during compression tests. The measurements were carried out in the 4.2 K-1000 K temperature interval for two orientations of single crystals, [001] and [ 2 34]. The dislocation structure was studied by TEM. Quantitative measurements of different parameters of dislocation structure were carried out. The values of the scalar dislocation density, ρ, were determined for different temperatures in the deformation interval from the yield stress up to fracture. Temperature dependence of the friction stress τ F (T ) and the interdislocation interaction parameter α (T ) were also obtained. The change in the fraction of straight dislocations as a function of temperature was analyzed. INTRODUCTION Positive temperature dependence of the flow stress appears to be a characteristic property of the intermetallics with the L12 structure. The yield stress and the flow stress are increased considerably with increasing temperature in some temperature intervals. Generally, such behavior is associated with self-locking mechanisms of individual superdislocations, namely with the formation of Kear-Wilsdorf locks. In this connection, a lot of attention is directed towards the experimental studies of the superdislocation fine structure using TEM [1]. Most investigations are carried out on a Ni3Al alloy and its ternary alloys [2]. To understand the mechanisms of deformation and thermal strengthening, it is important to study the evolution of the dislocation structure in different intermetallics. In connection with this, the present work is devoted to the experimental study of the evolution of the parameters of the dislocation structure in a Ni3Ge single crystals with the L12 structure, where a considerable temperature anomaly of mechanical properties was observed [3, 4]. EXPERIMENTAL DETAILS Single crystals of the Ni3Ge were grown using a Chokhralsky technique. Samples with the size of 3.0× 3.0×6.0 mm3 were cut from single crystal ingots using the spark erosion method. The facet orientations were determined by the XRD Laue method. The samples were homogenized at Т=953 оС for 48 hrs. The uniaxial compression tests were carried out for two orientations of single crystals [001] and [ 2 34] with the constant rate of 3.3 × 10-4s-1 using an Instron type test machine in the 4.2-1000 K temperature interval. The shear stresses in the octahedral slip planes were calculated using the τ=m×σ relationship, where m is the Schmid factor of the primary octahedral slip system, σ is the flow stress. The critical resolved shear stress, τ 0 , was considered equal to the flow stress value at ε =0.2 %. Different foil sections were
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examined, particularly in [111], [100], [110] a
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