A study of stress relaxation in AZ31 using high-energy X-ray diffraction

Abstract

a b s t r a c tThe micro-plasticity of the Mg alloy AZ31 is explored through high-energy X-ray diffraction (HEXD). Through cyclic loading of the sample, a softening response is found to follow the resolved shear stress for basal slip. Stress relaxation is studied by applying an incremental elongation increase while continuously collecting images from a detector array. The rate exponent associated with a particular reflection is developed by evaluating the average lattice strain in the loading direction from the composite detector image collected at a particular point in time, and then following the time evolution. A distinct rate exponent is identified for grain orientations that have a propensity for slip on second-order pyramidal planes, highlighting the capability to capture the simultaneous action of different deformation mechanisms through HEXD.

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

“…Studies of kinetics are possible, suggesting the possibility for tracking and quantifying temporal bursts in plastic activity. 19 The present work characterizes the dynamics of plastic relaxation events occurring during creep-loading of a polycrystalline titanium alloy, showing that grain-level strains shift, both positively and negatively, in a correlated fashion between grains as time evolves. Measurement of evolving inter-granular strain tensors which yield stress tensors in situ provides a mesoscopic view of the transient response through measures such as the resolved shear stress on a slip system.…”

Grain interaction mechanisms leading to intragranular orientation spread in tensile deformed bulk grains of interstitial-free steel

“…This gives a unique possibility of investigating the behaviour of individual grains and how they interact with their environment. Particular emphasis has been on understanding the deformation behaviour of metals by mapping intra-granular orientation gradients as a function of plastic deformation Lind et al, 2014;Pokharel et al, 2015;Toda et al, 2016) and measuring grain-resolved stresses associated with deformation twinning in hexagonal close packed metals (Abdolvand et al, 2015a(Abdolvand et al, , 2015bAydiner et al, 2009;Bieler et al, 2014;, but also processes such as grain nucleation (West et al, 2009), growth (Poulsen et al, 2011;Schmidt et al, 2004Schmidt et al, , 2008 and coarsening (Dake et al, 2016;Sharma et al, 2012), crack evolution (Cerrone et al, 2015;Chatterjee et al, 2015;Oddershede et al, 2012;Ozturk et al, 2016), stress relaxation (Tang et al, 2015), creep (Schuren et al, 2015) and phase transformations (Barton and Bernier, 2012;Hedström et al, 2010;Offerman et al, 2006) have been investigated using 3DXRD. For completeness applications of 3DXRD to minerals (Borthwick et al, 2012;Hall and Wright, 2015;Sørensen et al, 2012a), deep earth science (Nisr et al, 2014(Nisr et al, , 2012Rosa et al, 2015), nuclear materials (Brown et al, 2014;X.…”

Intermittent plasticity in individual grains: A study using high energy x-ray diffraction

“…Our results may be viewed in light of the “mild to wild” proposal by Weiss et al 35 The preferred modes of basal and prism slip for the AZ31 and Ti-7Al alloys, respectively, do not admit a component of plastic deformation along the c-axis. However, the presence of pyramidal slip in stress relaxation at room temperature is indicated in the studies of AZ31 19,36 . In the present work, one of the most distinctive relaxation events observed in the AZ31 sample was associated with a high resolved shear stress on the 2nd order pyramidal plane.…”

“…As compared to the Ti-7Al, the AZ31 material exhibited a finer grain size of roughly 25 μ m, with many more, but less intense, diffraction spots. The AZ31 sample was fabricated from a 12.7 mm thick annealed and rolled plate 19 . The nominal cross-section of this sample was 2 mm × 2 mm and the gauge length was 10 mm.…”

“…Linear elasticity was used to obtain the stress tensor from lattice strain, with elastic constants from Refs. 24, 19, and 25 for Ti-7Al and AZ31, respectively.…”