In situ Neutron Diffraction Study of Internal Micro‐Stresses Developed by Plastic Elongation in <110> Textured BCC Wires

Abstract

By in situ neutron diffraction during tensile tests of a strongly <100> textured Nb wire, we have shown the development of internal tensile microstresses of the order of 20 % of the flow stress, acting normal to the longitudinally aligned {110} planes. Such stresses are retained as residual stresses upon unloading. They must be taken into account for preventing splitting failures of high strength BCC wires (e.g., highly drawn tungsten filaments or pearlitic steel wires) that, because of the drawing fabrication process, contain a high density of longitudinally oriented brittle interfaces.

Neutron and X-ray diffraction study of residual and internal stress evolution in pearlitic steel during cold drawing

“…As one can see, a significant variation in the mechanical response is found among differently oriented ferrite grains, including a peculiar response of the {200} reflection, cp. [1,2,24]. The present results show a discrepancy with the behavior of high carbon steel studied by Oliver et al [1] and Kanie et al [25].…”

Effect of α–α′ phase separation on notch impact behavior of oxide dispersion strengthened (ODS) Fe20Cr5Al alloy

“…Because of the considerably higher plastic deformation in the S-direction than in the T-direction, the plastic constrain is the S-direction would lead to an increase of r x in the case of LT samples, and of r z in the case of LS sample that would cause delamination perpendicular to the notch base for LT samples and parallel to the notch base for LS samples. (4) The delamination-toughening phenomenon, as introduced by Kimura et al [35], is able to explain the evolution of USE and DBTT observed in LS samples. In the crack-arrester geometry of LS samples, the delamination is thought to relax the triaxial stress condition and to blunt the crack tip.…”

Evolution of Residual Micro Phase and Orientation Dependent Stresses during Cold Wire Drawing

“…consists in the full understanding and the eventual control of the evolving microstructure. Hence, in case of severely cold drawn pearlitic steel wires and filaments, much attention has been paid to the analysis of strengthening mechanisms and strength -(micro)structure relationships including the dissolution of the cementite phase [5][6][7][8][9][10][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Mainly, (i) local high resolution techniques such as Atom Probe Tomography [14,[24][25][26][27] and High-Resolution Transmission Electron Microscopy [9,24] and (ii) integral in situ (neutron/synchrotron) diffraction experiments [3,6,7,[20][21][22] have been used for the investigations.…”

“…Hence, in case of severely cold drawn pearlitic steel wires and filaments, much attention has been paid to the analysis of strengthening mechanisms and strength -(micro)structure relationships including the dissolution of the cementite phase [5][6][7][8][9][10][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Mainly, (i) local high resolution techniques such as Atom Probe Tomography [14,[24][25][26][27] and High-Resolution Transmission Electron Microscopy [9,24] and (ii) integral in situ (neutron/synchrotron) diffraction experiments [3,6,7,[20][21][22] have been used for the investigations. Correspondingly, the microstructural analysis suggested that the (1) phase boundary and (2) dislocation strengthening mechanism and (3) solid solution hardening could be the major contributors to the strength of a nanostructured severely deformed pearlitic steel.…”

“…Hence, as expected for nanostructured material the strength increases with decreasing spacing between the cementite lamellae and/or grain size of ferrite, with the density of dislocations in the ferrite matrix and with the carbon concentration in the ferrite lamellae respectively. Further, in situ/static neutron diffraction studies pointed to the increasing intergranular/residual grain microstresses in heavily drawn wire with increasing true drawing strain and/or increasing carbon content [2,[20][21][22]. It has been suggested that the strengthening mechanism for heavily drawn wire (after rupture and partial dissolution of the cementite phase) should be discussed based on grain size, dislocation density and internal and residual grain microstresses which are not independent from each other.…”