Soto-Medina, SujeilyRijal, BiswasSachdev, Anil K.Hennig, Richard G....
8页
查看更多>>摘要：Automotive applications need low-cost, lightweight, high-temperature alloys to increase vehicle efficiency. The Al-Fe-Si system provides an opportunity to develop such a material, as it consists of three low-cost elements that are all abundant in nature. Specifically, the tau 11-Al4Fe1.7Si ternary intermetallic phase is a high-temperature, lightweight phase with high strength and good corrosion resistance. However, this phase exhibits a narrow compositional range of stability, resulting in undesirable microstructures forming during solidification and processing, limiting its use in potential applications. Density functional theory (DFT) calculations and a thermodynamically-driven experimental approach utilizing diffusion couples were employed to study the effect of Mn on the stability and composition range of tau 11-Al4Fe1.7Si. The DFT calculations showed a decrease in the energy of the structure when alloying with Mn. Experimental results confirmed the predictions from the DFT calculations, indicating that alloying with Mn increases the compositional range, and thus the processability of this phase. New phase diagrams and equilibria are proposed by exploring and determining phase boundaries for the tau 11-Al4Fe1.7Si phase with Mn.
查看更多>>摘要：The kinetics of glass transition and the fragility of Zr55Cu30Al10Ni5 and (Zr55Cu30Al10Ni5)98Nb2 metallic glasses were investigated by the calorimetric measurements. The Nb minor addition narrows the width of glass transition, accelerates the relaxation process during glass transition, and decreases the energy barrier of glass transition. In addition, the fragility was evaluated in terms of the kinetic fragility index. While both alloys can be classified as intermediate glass formers, the Nb minor addition remarkably decreases the fragility and a stronger glass is achieved by the microalloying process. The lower fragility in the Nb-containing alloy is accompanied by higher degree of short-range ordering inferred from structural characterizations, formation of nanoscale chemical heterogeneities evidenced from the energy-dispersive X-ray spectroscopy (EDS) results, and deteriorated plasticity evaluated from the bending experiments. Our results highlight positive correlations between the fragility and the plasticity of the studied glasses.
查看更多>>摘要：Evolution of an initial nearly-lamellar (gamma+alpha(2)+beta(0)) structure of a new cast beta-solidifying TiAl-based alloy Ti-44.5Al2V-1Nb-2Cr-0.1Gd (at.%) after isothermal exposures at 800 degrees C for up to 10,000 h has been systematically investigated using SEM, TEM, EDS, and XRD analyses. During the exposures the alloy microstructure degraded by the alpha(2) laths and beta(0) phase dissolution, resulting in coarsening of lamellar structure and rising of the gamma phase volume fraction. A 2.5- and 3-fold increase in the number of nano-sized gadolinium oxide (Gd2O3) particles have been observed after 10,000-h exposure in lamellar colonies and in grain boundaries, respectively. The gadolinium oxides had monoclinic (C2/m) and cubic (Ia-3) structures and precipitated predominantly along gamma/alpha(2) and gamma/beta(0) interfaces and inside the gamma lamellae. Furthermore, the applied creep loading was found to contribute significantly to the precipitation process of Gd2O3 nano-particles, since dislocation networks being the sites for their preferred formation. Nanohardness of the gamma phase increased from 4.4 +/- 0.3 to 5.0 +/- 0.4 GPa after the exposures, but no changes were observed for the beta 0 phase. As a result of structure evolution the tensile strengths reduced by 10-12 and 11-14 % measured at 20 and 750 degrees C testing temperatures, respectively. Meanwhile, the plastic elongation values remained essentially unchanged. We interpret this as insignificant effect of the precipitation of Gd-rich oxide nano-particles on the alloy ductility.
查看更多>>摘要：Nickel-based single crystal alloys are widely used in aerospace, national defense and other fields because of their excellent properties (excellent strength, high temperature creep resistance and corrosion resistance). At present, its machining accuracy is very high, and high machining surface quality is required. In the sub nano and near atomic scale (SN-NAS) cutting process, the crystal orientation of workpiece has an important impact on the internal dislocation nucleation and expansion and surface material removal. These changes will affect the evolution process of subsurface defects and have an important impact on the surface quality. The SN-NAS cutting models are established, and the relationship between dislocation emission and energy change is deduced. The cutting models of nickel-based single crystal alloys with different crystal orientations were established by the molecular dynamics method. It is found that dislocations are emitted along the direction perpendicular to the cutting surface. Due to the different crystal orientation of the workpiece, the dislocation slip direction presents anisotropy. The plastic deformation of the workpiece is closely related to dislocation slip and stacking fault propagation. Due to the difference in lattice arrangement, dislocation slip orientation and surface energy, the surface roughness shows strong anisotropy. The work hardening behavior is determined by the change of micro defect structure and dislocation density in the workpiece. At the same time, it is closely related to the movement of material slip system and the self-hardening and latent-hardening of dislocations. This study analyzes the formation mechanism of the subsurface deformation layer and how the change of crystal orientation affects the evolution of the subsurface deformation layer, so as to provide technical support for the development of SN-NAS cutting of nickel-based alloy.
查看更多>>摘要：Nanoporous metal-based actuators show advantages over conventional piezoelectric ceramics and conducting polymers, but are mainly limited to noble metals. Herein, we design a series of ternary Al-Ni-Cu alloys with variable Ni/Cu ratios to investigate their dealloying behaviors as well as electrochemical actuation performances. The change of the Ni/Cu ratio influences the microstructure and phase constituent of the as-cast Al-Ni-Cu alloys. Specially, an Al-3(Ni, Cu)(2) phase is identified in all the Al-Ni-Cu alloys, and its amount and composition alter with the Ni/Cu ratio. Furthermore, the corrosion-resistant Al-3(Ni, Cu)(2) phase significantly affects the dealloying behaviors of the ternary Al-Ni-Cu precursors. Additionally, the as-dealloyed Al-Ni-Cu alloys show good electrochemical actuation performance, which is associated with the existence of efficient nanoporous (np) components (np-Cu and np-Ni). The largest strain amplitude and strain rate could reach up to 0.9% and 6.6 x 10(-4) s(-1), respectively. Compared with noble metal-based actuators, the large strain amplitude and strain rate, as well as the lower material cost, make nanoporous Al-Ni-Cu alloy a potential actuation material for practical applications.
查看更多>>摘要：A new experimental method is proposed to quantify the site-occupancy of substitutional solute elements in multi-component intermetallics from atom probe tomography data and is applied to the L12 ordered gamma' phase in the top, middle and bottom regions of an electron powder bed fusion produced IN-738LC build. Ti, W and Ta are found to substitute almost exclusively for the beta sites. Cr and Mo show mixed behaviour with a higher proportion substituting for the beta sites. Co also shows mixed behaviour but with a higher proportion substituting for the alpha sites. While gamma' maintains an almost constant chemistry and site-preference behaviour throughout the build, the relative site-occupancy ratio is observed to change, particularly for Co and Mo. The results suggest that local changes in thermal history inherent to metal additive manufacturing processes may induce changes to the resultant site-occupancy of gamma'. The method described here improves the experimental quantification of the local atomic site-occupancy, enabling an assessment of the substitutional solute element fractions occurring at the alpha and beta sites in L1(2) ordered structures. This is important in multi-component intermetallics because of the burgeoning interest in relating the elastic and plastic properties of these structures to their site-occupancy.
查看更多>>摘要：Introducing the second phase into high-entropy alloy through composition design is an effective strategy to further improve its mechanical properties. In this work, a novel Fe(35)Cr(35)Ni(15)Al(12)Ti(3 )HEA was successfully designed and prepared with arc-melting method. Its microstructure, phase constitution, mechanical properties, and strengthening mechanisms were systematically investigated. A uniform distribution of high-density semi coherent L2(1) and coherent B2 precipitates in the BCC matrix was achieved. Significantly, the HEA possesses outstanding mechanical properties, with true compressive yield strength of 1308.0 MPa, maximum compressive strength of 1803.8 MPa and maximum compressive strain of 86.8%, which are much higher than most similar HEAs reported previously. The excellent mechanical properties could be ascribed to the precipitation strengthening and solid-solution strengthening induced by fine B2 and uniform distribution of L2(1) precipitates.& nbsp;& nbsp;
Mohamed, A. K.Palacheva, V. V.Cheverikin, V. V.Vershinina, T. N....
12页
查看更多>>摘要：Significant differences between the properties of Fe-Ga alloys (Galfenols) in their metastable and equilibrium states, as well as discrepancies between existing Fe-Ga phase diagrams and for the transition rates for the metastable to equilibrium state have been detected and discussed. In view of both the fundamental understanding and the technological importance of these alloys, the exact knowledge of the equilibrium phase diagram, metastable phases, and the transition rates between different phase states towards equilibrium are necessary and require further clarification. We have studied the influence of alloy composition, annealing temperature and annealing time (up to 1800 h) on the metastable-to-equilibrium phase transitions in binary Fe-Ga using a coherent set of complementing methods, including diffraction methods (X-ray and neutron diffraction), scanning electron microscopy, and electron backscatter diffraction. We propose several important changes to the low-temperature part of the binary Fe-Ga diagram close to the Fe-rich corner and a new method based on interdiffusion couples for varying the structure and phase states of Fe-Ga alloys.
查看更多>>摘要：A bamboo-like grain structure was obtained in melt-extraction Au7Cu5Al4 microwires via cyclic heat treatment. The superelasticity and two-way shape memory properties were investigated by performing uniaxial cyclic tensile tests and mechanically constrained thermal cycling, respectively. The superelasticity of bamboo-grained microwires was improved significantly duo to a reduction in the constraints caused by triple junctions. A recoverable strain of ~3% was achieved over a wide temperature range of 358-423 K for the bamboo-grained microwire, which exhibited excellent cyclic stability under a stress of up to 470 MPa. The two-way shape memory properties were determined by conducting load-biased thermal cycling tests, and a recoverable strain of 1.2% with a maximum work output of 1.2 J cm-3 was achieved under a stress of 100 MPa. The results indicate that the Au-Cu-Al shape memory alloy is a potential candidate for small-sized actuators operating in harsh environments.
查看更多>>摘要：A forced cooling system with three cooling plates was designed to assist laser remelting, and the effects of forced cooling on the microstructure and properties of Fe-based amorphous composite coatings prepared by laser remelting were studied. Results show that the content and size of the precipitated crystalline phase decrease, and the crystallites become finer with an increase in the temperature gradient of the forced cooling device. When the temperature of the cooling plate drops to 200 K, the precipitation of the strengthening phase M23(CB)6 is inhibited, and only the alpha-Fe phase precipitates, which has a good toughening effect. The hardness of the coating decreases because the precipitation of the strengthening phase is inhibited. The wear and corrosion resistances of the coatings are significantly improved because of an increase in the content of the amorphous phase and solid solution strengthening of the alpha-Fe phase. However, lowering the temperature of the cooling plate does not result in better performance. At a cooling plate temperature of 200 K, the wear resistance of the coating is the best because the appropriate amount of alpha-Fe phase plays a toughening effect.
NSTL
Elsevier