STRAIN HARDENING OF MONOCRYSTALS OF ALLOY FCC AT MESOLEVEL

The paper presents the analysis of strain hardening in monocrystals of single-phase disordered alloy Ni₃ Fe. These monocrystals are subjected to compression at room temperature. The compression axis is parallel to [001] crystallographic direction. The strain curve of monocrystals with [001] orientation is characterized by several stages conditioned by a certain sequence of substructural transformations. Ni₃ Fe alloy with monocrystals of atomic short-range order possesses an average value of stacking fault energy. Plastic deformation enables the low-energy evolutionary branch of substructure: plane dislocation clusters → knitted structure → striple structure. The linear stage of the alloy strain hardening is connected with the formation of non-homogeneous knitted dislocation structure. TEM images of this structure allow measuring the free distances between the different dislocation locks formed along the dislocation line due to the dislocation intersections of different slip systems. Using the parameters measured for the monocrystal knitted structure, the contribution of strain-hardening mechanisms to shear stress was evaluated. These mechanisms include dislocation intersection, threshold creep, formation and destruction of dislocation junctions, crossing of Lomer–Cottrell and Hirth dislocation barriers and spot defect generation. The formation laws for long-range stresses and elastic interaction between dislocations were studied and the static and dynamic stress contribution to the total stress was determined. To consider the non-homogeneity of knitted dislocation structure, the contributions are detected individually for its dense and loose areas. The estimation of partial contribution made by each mechanism indicates that the main impact to deformation resistance of monocrystals oriented for multiple slip is made by the dislocation hindering, caused by contact interaction between moving and forest dislocations. The deformation growth enables the density increase in the dislocation locks (thresholds and junctions) along the dislocation line, caused by strain hardening of alloy FCC having an atomic short-range order. 

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