查看更多>>摘要：Deformation twinning is another important phenomenon besides dislocation slip during the plastic deformation of metals and alloys. In this work, the plastic deformation behavior of coarse-grained aluminum with high stacking fault energy was studied by in-situ tensile TEM. The results show that deformation twins appear at the crack tip under continuous applied stress, and the thickness of deformation twin increases with the appearance of incoherent twin boundaries (ITBs). Further analysis shows that Frank partial dislocation in deformation twins is decomposed into perfect dislocation and Shockley partial dislocation under the action of applied stress. These perfect dislocation and Shockley partial dislocation can slip along the crystal planes and react to form the dislocation combinations that constitute the ITB. The results of this work provide a new way for researchers to understand the role of ITBs on deformation twins and the formation of dislocation combinations in ITBs.
查看更多>>摘要：We report the role of grain boundary segregation on microstructure development during hot-rolling of Mg-3Al0.8Zn-0.4Mn (mass%, AZ31) alloy. Annealing at 420 degrees C before hot-rolling induces strong grain boundary segregation of Al and Zn, forming thin solute-depleted regions near the grain boundaries. This facilitates dynamic recrystallization at the grain boundaries and induces strong basal texture. On the other hand, annealing at 500 degrees C reduces the grain boundary segregation, hindering the dynamic recrystallization during hot-rolling. As a result, a weak rolling-direction-split texture occurs during subsequent annealing, and this improves the stretch formability of the AZ31 alloy sheet.
Park, KwangjaeWang, JianKobashi, MakotoHirayama, Yusuke...
6页
查看更多>>摘要：The Sm-Co bulk magnet prepared in this work using unique Sm-Co alloy nanopowder as a precursor prepared by the lox oxygen-induction thermal plasma (LO-ITP) process displays a giant coercivity of 4.1 MA/m (52 kOe) at 300 K, which is the highest coercivity among the reported rare-earth permanent bulk magnets with high density. The Sm-Co magnet has a high coercivity of 2.4 MA/m (30 kOe) at 473 K and 1.6 MA/m (20 kOe) at 573 K, which shows the good temperature coefficient of coercivity of-0.22%/K. The well-organized microstructure with fine Sm-Co alloy single-crystal grains with an average grain size of 0.63 mu m, sharp grain boundary, and better crystallinity, leads to a huge coercivity and remarkable thermal stability.
Li, B. S.Sen, H. S.Daghbouj, N.AlMotasem, A. T....
6页
查看更多>>摘要：SiC is considered a perspective material in advanced nuclear systems as well as for electronic or spintronic applications, which require an ion implantation process. In this regard, two sets of 6H-SiC samples were implanted with i) 2.5 MeV Fe ions and ii) 2.5 MeV Fe ions and co-implanted 500 keV He ions at room temperature and then annealed at 1500 degrees C for 2 h. The microstructure evolution and Fe diffusion behavior before and after annealing were characterized and analyzed. After annealing, Fe concentration is enhanced close to the surface in the Fe-implanted sample, whereas in the co-implanted system, Fe atoms are redistributed into two distinct, spatially separated regions (close to the surface, and around the He-induced defects). The reason behind this finding is explained from an energetic point of view by using ab initio simulations. Technologically, the preexisting cavities can be used to control the Fe diffusion.
查看更多>>摘要：A novel concept of microstructure design involving warm rolling and low-temperature annealing has been proposed to greatly improve the strength-ductility combination of medium Mn steel. The unique transformation induced plasticity has been triggered by firstly microbands and secondly deformation twins, enhancing the ductility significantly and the reasonable dislocation density in non-recrystallized austenite grains increases the yield strength greatly. The individual contribution of solid solution strengthening, grain boundary strengthening, V-precipitates strengthening and dislocation strengthening to yield strength is discussed by constitutive models, in which the tangled dislocation plays a dominant role. Best strength-ductility combination with yield strength (1239MPa), ultimate tensile strength (1341MPa), total elongation (41.8%) and product of strength and elongation (56.1GPa.%) has been obtained, which are comparable and superior to the reported medium-Mn steels.
查看更多>>摘要：Mechanical properties of a coarse-grained hexagonal close packed (hcp) single phase Mg-Sc alloy with two different textures, randomized (through body centered cubic (bcc) to hcp transformation) or weakened (through only cold rolling) texture, was investigated. Alloys of both the textures showed high elongation of over 30% with a moderately high ultimate tensile strength of about 240 MPa. Transmission electron microscopy (TEM) observations showed that both a- and c- component dislocations were activated in the grain interiors, over 20 mu m away from grain boundaries. Thus, pyramidal <c+a> slip can be activated in grain interiors of a coarse-grained Mg-Sc alloy.
查看更多>>摘要：In metals with homogeneous microstructure, whether there is a critical grain size, and exactly at which, that enables the optimal strength-ductility synergy alongside the trade-off relation? Here, this issue is investigated in the recrystallized CrCoNi medium entropy alloys across a wide grain size range of 0.23-108 mu m. Results reveal that there is indeed a critical grain size of-2 mu m at which the product of yield strength (-800 MPa) and uniform elongation (>30%) reaches the maximum, i.e., achieving the optimal strength-ductility synergy. Physics behind this critical grain size are explored by microstructure examination: (i) reduced grain size renders short dislo-cation slip path for high strength; (ii) low initial dislocation density and dense grain/twin boundaries enables effective accumulation of defects for consistent work hardening during plastic deformation.
Pinho, RuiTkach, AlexanderCarpenter, Michael A.Noudem, Jacques...
6页
查看更多>>摘要：An alternative sintering methodology, Spark Plasma Texturing (SPT), allowed us to prepare 98.0% dense leadfree piezoelectric (K1-xNax)NbO3 (KNN) ceramics with a homogenous microstructure of small grains. In this work, Resonant Ultrasound Spectroscopy (RUS) was used to measure bulk, K, and shear, G, moduli of SPT KNN for comparison with conventionally sintered (CS) KNN. SPT fabrication resulted in the highest elastic moduli K = 120.3 GPa (127.7 GPa for 100% density) and G = 45.47 GPa (47.2 GPa for 100% density) ever reported for KNN ceramics. Moreover, by collecting RUS data in situ as a function of temperature, phase transitions at temperatures of 464 and 688 K for CS KNN, and 443 and 643 K for SPT KNN ceramics were determined. Low acoustic loss in the stability field of the cubic phase indicated that the ceramics were mechanically robust, while high loss in the stability fields of the tetragonal and orthorhombic structures demonstrated high mobility of ferroelastic domain walls.
查看更多>>摘要：Structural and magnetic properties of CoMn0.88Cu0.12Ge have been investigated using X-ray diffraction and differential scanning calorimetry (DSC) accompanied with investigation of magnetic properties under applied hydrostatic pressure up to 12 kbar. The orthorhombic crystal structure (TiNiSi-type), which is dominant at low temperatures, turns into the hexagonal one (Ni2In-type), slightly above 200 K. The structural transition is of the first-order type as confirmed by presence of distinct thermal hysteresis. The ac magnetic measurements indicate a ferromagnetic order below 238 K, followed by additional anomaly at lower temperatures - the latter one being related to the structural transition. Application of hydrostatic pressure leads to temperature separation of the purely magnetic transition, whose Curie temperature increases with applied pressure, and the magnetostructural transition characterized by decreasing critical temperature. Comparison of the DSC data for the investigated compound and the isostructural CoMn0.95Cu0.05Ge has made it possible to determine both the structural and magnetic components of entropy change.
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Elsevier