Revealing Grain Boundary Sliding from Textures of a Deformed Nanocrystalline Pd–Au Alloy

Employing a recent modeling scheme for grain boundary sliding [Zhao et al. Adv. Eng. Mater. 2017, doi:10.1002/adem.201700212], crystallographic textures were simulated for nanocrystalline fcc metals deformed in shear compression. It is shown that, as grain boundary sliding increases, the texture strength decreases while the signature of the texture type remains the same. Grain boundary sliding affects the texture components differently with respect to intensity and angular position. A comparison of a simulation and an experiment on a Pd–10 atom % Au alloy with a 15 nm grain size reveals that, at room temperature, the predominant deformation mode is grain boundary sliding contributing to strain by about 60%

Revealing Grain Boundary Sliding from Textures of a Deformed Nanocrystalline Pd–Au Alloy

Employing a recent modeling scheme for grain boundary sliding [Zhao et al. Adv. Eng. Mater. 2017, doi:10.1002/adem.201700212], crystallographic textures were simulated for nanocrystalline fcc metals deformed in shear compression. It is shown that, as grain boundary sliding increases, the texture strength decreases while the signature of the texture type remains the same. Grain boundary sliding affects the texture components differently with respect to intensity and angular position. A comparison of a simulation and an experiment on a Pd–10 atom % Au alloy with a 15 nm grain size reveals that, at room temperature, the predominant deformation mode is grain boundary sliding contributing to strain by about 60%

Imparting high-temperature grain stability to an Al-Mg alloy

Al alloys, despite their excellent strength-to-weight ratio, cannot be used at elevated temperatures because of microstructural instability owing to grain growth and precipitate coarsening, thus, leading to a drastic loss in their strength. In this work, we have attempted to address the issue of grain growth by introducing in-situ formed polymer derived ceramics in an Al-Mg alloy. A stable grain structure with minimal loss in hardness when exposed to 450 °C and 550 °C for 1 hour was obtained due to the particle pinning of the grain boundaries by the Zener mechanism.This work was supported by the French State through the program “Investment in the future” operated by the National Re- search Agency (ANR) and referenced by ANR-11-LABX-0 0 08-01 (LabEx DAMAS). Abhishek Pariyar acknowledges the Ph.D. scholarship awarded by the Ministry of Human Resource Development, Govt. of India

The New Plastic Flow Machining Process for Producing Thin Sheets

A new severe plastic deformation (SPD) process called plastic flow machining (PFM) was recently proposed to produce thin sheets with gradient structures. In the present paper, the role of the die geometry is investigated by studying the effects of the produced sheet thickness (h) on the material properties of commercial pure Aluminum (Al1050) processed by PFM. The obtained experimental results show that an increase of h in the range of 0.65 to 1.5 mm improved the formation efficiency of the sheet. Microstructures of the produced sheets show gradient structures with an average grain size varying from 0.8 to 3.81 µm across the sheet thickness. Both experiments and finite element (FE) simulations document that the degree of the gradient in the microstructure became more significant when h was increased. Sheets produced by PFM exhibited a better strength-ductility balance than sheets obtained in other SPD processes. Tensile strength of 160–175 MPa and total ductility of 18–25% were obtained for the processed samples after PFM. A rise of h from 0.65 to 1.5 mm lowered the strength but enhanced the ductility of the produced sheet, which is due to the coarser microstructure at larger values of h

Effects of processing conditions on texture and microstructure evolution in extra-low carbon steel during multi-pass asymmetric rolling

Multi-pass rolling was carried out on extra-low carbon steel at room temperature by imposing different ratios of asymmetry in the roll-diameters as well as by conventional mode. The aim of this study is to understand the effect of shear deformation due to the asymmetric conditions on the development of the rolling texture and the possibilities of propagating the shear deformation into the mid-thickness area of the sheet. The trends of the measured texture developments in both symmetric and asymmetric rolling indicate their dependence primarily on the stability and fraction of the Goss {110}<001> and the rotated cube {001}<111> orientations. The effects of asymmetry conditions were further examined on the microstructure evolution and were correlated to the increased orientation inhomogeneity and grain fragmentation. Both texture and microstructure development showed their dependence on the applied thickness reduction per pass, on the total thickness reduction of the sheet as well as on the degree of the imposed asymmetry. It was found that shear textures can be obtained by asymmetric rolling at conditions where all three parameters-asymmetry ratio, strain in one pass, and the total accumulated strain-are as large as possible

Modeling the effect of primary and secondary twinning on texture evolution during severe plastic deformation of a twinning-induced plasticity steel

Modeling the effect of deformation twinning and the ensuing twin-twin- and slip-twin-induced hardening is a long-standing problem in computational mechanical metallurgy of materials that deform by both slip and twinning. In this work, we address this effect using the twin volume transfer method, which obviates the need of any cumbersome criterion for twin variant selection. Additionally, this method is capable of capturing, at the same time, secondary or double twinning, which is particularly important for modeling in large strain regimes. We validate our modeling methodology by simulating the behavior of an Fe-23Mn-1.5Al-0.3C twinning-induced plasticity (TWIP) steel under large strain conditions, experimentally achieved in this work through equal-channel angular pressing (ECAP) for up to two passes in a 90&deg; die following route BC at 300 &deg;C. Each possible twin variant, whether nucleating inside the parent grain or inside a potential primary twin variant was predefined in the initial list of orientations as possible grain of the polycrystal with zero initial volume fraction. A novelty of our approach is to take into account the loss of coherency of the twins with their parent matrix under large strains, obstructing progressively their further growth. This effect has been captured by attenuating growth rates of twins as a function of their rotation away from their perfect twin orientation, dubbed here as &ldquo;disorientation&rdquo; with respect to the mother grain&rsquo;s lattice. The simulated textures and the hardening under tensile strain showed very good agreement with experimental characterization and mechanical testing results. Furthermore, upper-bound Taylor deformation was found to be operational for the TWIP steel deformation when all the above ingredients of twinning are captured, indicating that self-consistent schemes can be bypassed. <br /

Asymmetric rolling of interstitial-free steel using differential roll diameters. Part II : microstructure and annealing effects

The effects of annealing on the microstructure, texture, tensile properties, and R value evolution of an IF steel sheet after room-temperature symmetric and asymmetric rolling were examined. Simulations were carried out to obtain R values from the experimental textures using the viscoplastic self-consistent polycrystal plasticity model. The investigation revealed the variations in the textures due to annealing and symmetric/asymmetric rolling and showed that the R values correlate strongly with the evolution of the texture. An optimum heat treatment for the balance of strength, ductility, and deep drawability was found to be at 873 K (600 _C) for 30 minutes

Evidence for diagnosis of early chronic pancreatitis after three episodes of acute pancreatitis : a cross-sectional multicentre international study with experimental animal model

Chronic pancreatitis (CP) is an end-stage disease with no specific therapy; therefore, an early diagnosis is of crucial importance. In this study, data from 1315 and 318 patients were analysed from acute pancreatitis (AP) and CP registries, respectively. The population from the AP registry was divided into AP (n=983), recurrent AP (RAP, n=270) and CP (n=62) groups. The prevalence of CP in combination with AP, RAP2, RAP3, RAP4 and RAP5+was 0%, 1%, 16%, 50% and 47%, respectively, suggesting that three or more episodes of AP is a strong risk factor for CP. Laboratory, imaging and clinical biomarkers highlighted that patients with RAP3+do not show a significant difference between RAPs and CP. Data from CP registries showed 98% of patients had at least one AP and the average number of episodes was four. We mimicked the human RAPs in a mouse model and found that three or more episodes of AP cause early chronic-like morphological changes in the pancreas. We concluded that three or more attacks of AP with no morphological changes to the pancreas could be considered as early CP (ECP).The new diagnostic criteria for ECP allow the majority of CP patients to be diagnosed earlier. They can be used in hospitals with no additional costs in healthcare.Peer reviewe