查看更多>>摘要：A chemical heterogeneity of Mn is introduced into the parent austenite of a Fe-0.2C-2Mn steel. The Mn-rich regions in the parent austenite is substantially stabilized by a promoted C partitioning during the austenite to ferrite transformation, without which these regions cannot be preserved as retained austenite. Following this strategy, a multiphase microstructure is achieved which presents a better combination of strength (ultimate strength of 977 MPa) and ductility (uniform elongation of 17.9%) as compared with that of other Si-or Al-added AHSSs of similar compositions. The results here suggest an alternative, yet a simple route, to acquire retained austenite in advanced high strength steels without the need of Si and Al alloying.
查看更多>>摘要：This study elucidates the influence of Nb addition on the mechanical and actuation response of the (Ni49.5Ti35.5Hf15)90Nb10 high temperature shape memory alloy (HTSMA) wires and presents the microstructure evolution of Nb with the drawing process. The change in morphology of beta-Nb from network structure to nanowires greatly increases the yield strength of the NiTiHfNb alloy followed by an ascending stress plateau. The fatigue life of the (Ni49.5Ti35.5Hf15)90Nb10 wire is 7754 cycles with remarkably stable actuation strain of 2.3% under 418 MPa. The concept of in-situ nanowire composite is applied to HTSMAs for the first time and our finding implies the promising practical applications of NiTiHfNb wires in high temperature actuators.
查看更多>>摘要：In this paper, the tensile fracture energies of smooth and pre-cracked specimens of a carbide-free bainitic steel at various loading rates were investigated. It is demonstrated that the tensile fracture energy of smooth specimen decreases gradually with increasing the loading rate and this is related to the gradually decreased TRIP effect due to less amount of martensitic transformation at higher loading rates. However, the tensile fracture energy of pre-cracked specimen increases with the increase of loading rate and this is associated with more M and M/A islands concentrated at the crack tip at lower loading rates.
Church, N. L.Talbot, C. E. P.Wise, G. J.Shah, O. Y., I...
4页
查看更多>>摘要：Metastable beta-Ti alloys based on the Ti-Nb system are of commercial interest as they undergo a reversible martensitic transformation that offers damping capabilities. However, their use is currently limited by a low yield stress compared to other alternatives such as NiTi. Here, we show how this limitation can be overcome by the in situ formation of the Ti3Sn phase concurrent with recrystalisation. The Zener pinning resulting from the Ti3Sn precipitates provides significant Hall-Petch strengthening leading to a yield stress in excess of 1 GPa, more than double that of similar alloys, whilst still allowing conventional processing routes. This has the potential to provide Ti-Nb yield stresses that can rival those of NiTi, addressing one of the biggest challenges for this class of alloys.
查看更多>>摘要：Metal hydride electrodes have been widely used for aqueous rechargeable batteries with good wide temperature performance compared to lithium-ion batteries. For the first time, the design and application of Nb-doped metal hydride electrode with excellent overcharge resistance in this study for La0.46Ce0.42xPr0.03Nd0.08Zr0.02NbxNi4.41Mn0.36Al0.28 (x = 0, 0.05 or 0.1). The ratio of capacity retention after the 100th cycle for charging 420 and 360 mAh g-1 increases from 86.99% (x = 0) to 99.93% (x = 0.1) at 25 degrees C, and from 83.95% (x = 0) to 99.28% for (x = 0.1) at 50 degrees C. Furthermore, the capacity of simulated wide temperature and overcharge experiment at -20 degrees C increases from 86.3 mAh g-1 (x = 0) to 217.8 mAh g-1 (x = 0.1) after the 100th cycle at 50 degrees C, due to the increase of overcharge resistance. This material makes it a promising candidate as electrode material for wide temperature applications.
查看更多>>摘要：The electric field-induced strain in lead-free piezoceramics is generally limited to less than 0.4%, which hinders their practical applications such as actuator. Herein we report a new composition of 0.94Bi(0.5)Na(0.5)TiO(30.06)Ba(0.85)Ca(0.15)Ti(0.9)Zr(0.1)O(3-x)Li(0.06)(K0.5Na0.5)(0.94)NbO3 (BNT-BCZT-xLKNN) ceramics by adding two modifiers (i. e., Li-0.06(K0.5Na0.5)(0.94)NbO3 and Ba0.85Ca0.15Ti0.9Zr0.1O3) featuring with a morphotropic phase boundary (MPB) into the Bi0.5Na0.5TiO3 system. The BNT-BCZT-0.02LKNN shows a high strain of 0.5% as well as a strain-electric field ratio (S-max/E-max) of 625 pm/V, which is one of the best performances compared with reported lead-free piezoceramics. Rietveld refinement and microstructure analysis confirmed the existence of tetragonal (P4bm) and rhombohedral (R3c) phases, and a small part of ferroelectric domains embedded into relaxors according to the PFM, both facilitating the relaxor-to-ferroelectric transformation under an external electric field. As a result, a high strain is obtained in the BNT-BCZT-LKNN system. Our work provides an effective strategy for designing novel lead-free materials with high strain.
查看更多>>摘要：The relationship of solid solution carbon and electrical resistivity in retained austenite was investigated by using as-quenched martensitic specimens of Fe-10mass%Ni alloys with added carbon up to 0.9 mass%. With increasing carbon content, the volume fraction of retained austenite increased, and simultaneously, the electrical resistivity of the bulk specimen also increased. Four-types of multi-phase models were applied to evaluate the electrical resistivity of each phase. As a result, the electrical resistivity of retained austenite was found to be increased with the increment of solute carbon concentration monotonously. The dependence of the solute carbon concentration (C-sol) on the electrical resistivity of retained austenite (Delta(rho gamma)) could be formulated as Delta(rho gamma) [m Omega.mm] = 0.26 x C-sol [mass%].
Mikhaylovskaya, Anastasia V.Yakovtseva, Olga A.Tabachkova, Natalia Yu.Langdon, Terence G....
5页
查看更多>>摘要：During superplastic deformation of microduplex-structured brasses, the strain is primarily localized in the beta-phase where deformation occurs by grain boundary sliding (GBS) and dislocation slip/creep mechanisms. Dynamic recrystallization and twinning were observed in the b.c.c. beta-phase leading to a transformation of the initial coarse beta-phase grains with average sizes of -4-5 mu m to ultrafine grains with sizes below 1 mu m. Alloying with Al refined the beta-grains, improved the superplastic behavior and reduced the occurrence of residual cavitation.
查看更多>>摘要：Interaction between a matrix prismatic <c>edge dislocation and a migrating (10 <(1)over bar > 2) twin boundary results in extended basal <a> mixed dislocations in the twin lattice. The interaction between the resultant <a> dislocation and the migrating twin boundary is studied using molecular dynamics simulations. The <a> dislocation tends to detach from or connect to the twin boundary, when its slip plane intersects a compression or extension site of the twin boundary. When the <a> dislocation connects to the twin boundary, connection always occurs with a 90 Shockley partial and a basal-prismatic (BP) or prismatic-basal (PB) two-atomic-layer-height step, depending on whether the Burgers vector direction of the Shockley partial points away from or towards the twin boundary. The BP or PB two-atomic-layer-height step is sessile, in contrast to those that are not connected to such <a> dislocation.
NSTL
Elsevier