Unraveling cyclic deformation mechanisms of a rolled magnesium alloy using in situ neutron diffraction

Abstract

In the current study, the deformation mechanisms of a rolled magnesium alloy were investigated under cyclic loading using real-time in situ neutron diffraction under a continuous-loading condition. The relationship between the macroscopic cyclic deformation behavior and the microscopic response at the grain level was established. The neutron diffraction results indicate that more and more grains are involved in the twinning and detwinning deformation process with the increase of fatigue cycles. The residual twins appear in the early fatigue life, which is responsible for the cyclic hardening behavior. The asymmetric shape of the hysteresis loop is attributed to the early exhaustion of the detwinning process during compression, which leads to the activation of dislocation slips and rapid strain-hardening. The critical resolved shear stress for the activation of tensile twinning closely depends on the residual strain developed during cyclic loading. In the cycle before the sample fractured, the dislocation slips became active in tension, although the sample was not fully twinned. The increased dislocation density leads to the rise of the stress concentration at weak spots, which is believed to be the main reason for the fatigue failure. The deformation history greatly influences the deformation mechanisms of hexagonal-close-packed-structured magnesium alloy during cyclic loading.

Characterization of Crystallographic Structures Using Bragg-Edge Neutron Imaging at the Spallation Neutron Source

“…A variety of sample environments (load frame, heating furnace, levitation equipment, etc.) have enabled more complex dynamic or real-time microstructure measurements [5][6][7][8][9][10]. Moreover, attenuation-based neutron imaging has been widely adopted to visualize micron-scale structures inside materials (porosity, density inhomogeneity) [11][12][13].…”

Bending Behavior of a Wrought Magnesium Alloy Investigated by the In Situ Pinhole Neutron Diffraction Method

“…A commercial rolled AZ31B Mg alloy plate (chemical composition: 3 wt.% Al, 1 wt.% Zn and Mg as balance) in H24 temper (strain-hardened and partially annealed) was selected for the current research. A typical rolling texture with the HCP crystal c-axis parallel to the normal direction (ND) and perpendicular to the rolling direction (RD) has been analyzed in previous publications [13][14][15][16]. The four-point bending sample was machined using electrical discharge machining (EDM) with 60 mm in length (RD) × 15 mm in width [transverse direction (TD)] × 10 mm in thickness (ND).…”

“…The detwinning process can be activated by a stress/strain reversal in twined grains [10,11]. The majority of research has been focused on the deformation twinning behavior of Mg alloys under uniaxial loading conditions, such as tension, compression, and cyclic loading [12][13][14][15][16][17][18][19][20][21].…”

Event-based processing of neutron scattering data at the Spallation Neutron Source

“…Combining this chopping with the stroboscopic methodology, VULCAN provides the capability for fast real-time operando testing. Users have benefited from these scientific capabilities and conducted a broad range of new research in materials science and engineering, including stress-induced twin reorientation (Pramanick et al, 2011), phase transformation in shapememory alloys (Yang et al, 2017;Wang et al, 2017) and bulk metallic glass composites (Wu et al, 2017), transformationinduced plasticity in alloys (Yu et al, 2014;Huang et al, 2017), twinning/detwinning behaviors in metals (Wu et al, 2013(Wu et al, , 2014(Wu et al, , 2015Xie et al, 2017;Wu & An, 2016), residual stress relaxation in engineering structures (Aba-Perea et al, 2016), domain switching in oxides (Aman et al, 2014), non-equilibrium phase transformation during rapid heating (Yu et al, 2012), cycling and degradation of realistic-format batteries Wang et al, 2012;Liu et al, 2013Liu et al, , 2016, and in situ materials processing and synthesis (Cai, Liu et al, 2013;Chen et al, , 2014Steiner et al, 2016). Specific examples of the use of event data acquisition are chosen from battery charge-discharge, rapid heating of a dual-phase steel and cyclic fatigue-induced martensitic phase transformation.…”