•The initial cyclic softening followed by cyclic hardening behavior is observed.•The dislocation rearrangement process promotes initial cyclic softening behavior.•The martensite formation results in ...the cyclic hardening behavior of SLM 304L.
Considering the relationship between austenite stability and strain level, the cyclic response curves are obtained for SLM 304L under different strain amplitude at R = 0.3. The results indicate that since the microstructure characteristics shift from stacking faults (SFs) at low strain amplitude to martensite and twins at high strain amplitude, the cyclic softening behavior transitions to cyclic hardening behavior. Besides, it also indicates that high strain levels can overcome the influence of initial microstructure on fatigue performance, presenting a new sight to understand the relationship between cyclic hardening and martensite transformation.
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W–Cu alloys are typically used for heat sinks, radiation shielding or high performance contact materials. Their immiscibility leads to interpenetrating structures, with typically ...smallest microstructural length scales on the order of several micrometres. This work focusses on tuning this length scale from the atomic level to the nanometre and submicron range. This is made possible by exploiting the two constituents’ immiscibility in thermodynamic equilibrium as well as the lack of Cu segregation to W grain-boundaries, thus allowing for the growth of the two phases. The system is studied in the complete concentration range and microstructure is related to both mechanical and electronic properties.
(left) Plot showing effect of Ta occupancy on formation energy for Co0.75Al0.125Mo0.125−xTax intermetallic phase in competing DO19 and L12 ordered structures. (middle) Dark field image taken along ...001 zone axis using 100 superlattice L12 ordered spot and (right) APT reconstruction delineated using 10% Al isosurface showing γ′ precipitates (red color) in Co–10Al–5Mo–2Ta heat treated alloy. Display omitted
The present paper reports a new class of Co based superalloys that has γ–γ′ microstructure and exhibits much lower density compared to other commercially available Co superalloys including Co–Al–W based alloys. The basic composition is Co–10Al–5Mo (at%) with addition of 2at% Ta for stabilization of γ′ phase. The γ–γ′ microstructure evolves through solutionising and aging treatment. Using first principles calculations, we observe that Ta plays a crucial role in stabilizing γ′ phase. By addition of Ta in the basic stoichiometric composition Co3(Al, Mo), the enthalpy of formation (ΔHf) of L12 structure (γ′ phase) becomes more negative in comparison to DO19 structure. The ΔHf of the L12 structure becomes further more negative by the occupancy of Ni and Ti atoms in the lattice suggesting an increase in the stability of the γ′ precipitates. Among large number of alloys studied experimentally, the paper presents results of detailed investigations on Co–10Al–5Mo–2Ta, Co–30Ni–10Al–5Mo–2Ta and Co–30Ni–10Al–5Mo–2Ta–2Ti. To evaluate the role alloying elements, atom probe tomography investigations were carried out to obtain partition coefficients for the constituent elements. The results show strong partitioning of Ni, Al, Ta and Ti in ordered γ′ precipitates.
Failure of metals II: Fatigue Pineau, André; McDowell, David L.; Busso, Esteban P. ...
Acta biomaterialia,
04/2016, Volume:
107
Journal Article
Peer reviewed
Open access
In this interpretive review, fatigue in metallic systems is considered primarily from the perspective of interactions between the microstructure, the deformation mode and the mechanical state at both ...low and high temperatures. In Part 1 the development and early propagation of cracks is considered in terms of the basic damage mechanisms and the relative size of the crack with respect to applicable microstructural feature(s). In this section, a multistage grain scale approach to microstructure-sensitive fatigue crack formation and growth is presented which uses Fatigue Indicator Parameters (FIPs) to correlate these processes. Various FIPs parameters are discussed in terms of their indication of the state of fatigue. The development and early crack propagation is considered in the context of microstructure and notches, and probabilistic aspects of the notch fatigue problem are discussed. These features are integrated into a systematic approach for the selection of fatigue resistant microstructures for given applications. In Part 2, attention is focused on Ni-base superalloys and the interaction between oxidation, creep and microstructure (including coatings) in the formation and propagation of cracks. This part of the overview addresses both experimental and modelling aspects. Methodologies based upon fundamental physical processes are presented for understanding and predicting the development and propagation of fatigue cracks, including effects of sequential oxide type formation and of creep on either restraining or accelerating damage by oxidation. The variable fatigue resistance of discs in jet engines is seen to depend upon the variability of microstructure and its influence on the severity of creep/oxidation interactions. All of these factors are considered in the practical case where both temperature and loading parameters vary simultaneously (thermomechanical fatigue). A physics-based life prediction model considering the interactions of deformation and environmental damage is reviewed in terms of its applicability to life prediction of components.
In this study, the electrical conductivity characteristics of SmBaCo2O5+d (SBCO) and SmBa0.5Sr0.5Co2O5+d (SBSCO) were measured and analyzed by changing the characteristics of the microstructure from ...dense microstructure to porous microstructure for the cathode application in solid oxide fuel cells. SBCO and SBSCO comprised of the dense microstructure showed metal insulator transition (MIT) and metallic behavior, respectively. In SBCO, when the oxygen partial pressure is reduced, the conductivity value decreases, and the conductivity behavior changes to the behavior of a semiconductor. However, the electrical conductivity behavior of SBSCO did not change even when the oxygen partial pressure was decreased. The electrical conductivities of the porous cathodes were lower than those of the dense cathodes due to the discontinuous electric path, but all porous cathodes showed semiconductor behavior. The conductivity value decreases when the oxygen partial pressure decreases, but the general conductivity behavior of the samples with a porous microstructure does not change under N2 atmosphere. The porous cathode showed the highest electrical conductivity when Pt lines were led to the top of the cathode. In this case, a relatively high electrical conductivity was measured using the method of measuring multiple conductivities at different temperatures while decreasing the measurement temperature starting from a high temperature rather than the method of measuring while raising the temperature starting from a low temperature. In the dense cathode, higher electrical conductivities were measured when a low current was applied, but in the porous cathode, the same electrical conductivity values were measured regardless of the applied current values.
•All porous cathodes were shown to display semiconductor conductivity behavior.•The electrical conductivity of the sample in which the Pt line was printed on the cathode surface was the highest.•Dense cathodes have higher electrical conductivity when a low current is applied.•Porous cathodes have no difference in electrical conductivity with respect to the applied current value.
•A6B2O17 high entropy ceramics are successfully prepared by spark plasma sintering.•The sintering densification behavior of the ceramics are investigated.•A6B2O17 ceramics have good hardness (16 GPa) ...and fracture toughness (2.3 MPa·m1/2).•A6B2O17 ceramics show good high temperature thermal stability.
A6B2O17 (A = Hf, Zr; B = Ta, Nb) high entropy ceramics are successfully prepared by solid state reaction combined with spark plasma sintering. The sintering densification behavior, structure characteristics and mechanical properties of the ceramics are investigated. High entropy A6B2O17 ceramics have good hardness (∼16 GPa) and fracture toughness (∼2.3 MPa·m1/2). The fracture toughness of A6B2O17 ceramics is independent of its components, but only related to its structure. The phase structure remains unchanged after annealing at 1300 °C for 24 h, indicating a good high temperature thermal stability.
Ceramics with engineered porosity are promising materials for a number of functional and structural applications including thermal insulation, filters, bio-scaffolds for tissue engineering, and ...preforms for composite fabrication. In this application based review of advanced porous ceramics, the microstructure of porous components is discussed in terms of the necessary features required to achieve the ideal properties for the intended application. The processing methods that are capable of producing the required microstructure are addressed. Those methods which allow the pore structure to be tailored or controlled are considered the most favorable processing techniques.
The microstructure of the B1-type TiC formed during solidification and its mechanical properties were investigated using arc-melted Fe–Ti–C ternary alloys. The TiC formed at relatively high ...temperatures in the liquid as the primary phase exhibited a dendritic shape. With decreasing temperature and/or decreasing Ti and C content in the liquid, the morphology of the TiC changed to a cubic shape with a {001}TiC habit plane, a plate shape with a {011}TiC habit plane, and a needle shape with a preferential growth direction of TiC. The morphology of the TiC was characterized by the anisotropy of its surface energy and its growth rate. The cubic shape with a {001}TiC habit plane was formed as a result of the {001}TiC surface exhibiting the lowest surface energy among the TiC surfaces. However, the plate shape with a {011}TiC habit plane and the needle shape with a TiC preferential growth direction likely formed because the slowest and fastest growth rates corresponded to the TiC and TiC directions, respectively. At room temperature, the alloy with dendritic TiC was fractured in the elastic deformation region because TiC exhibited no plastic deformation. However, the results obtained at 800°C suggested that the TiC exhibited plastic deformability and that the alloy with the dendritic TiC was also plastically deformed.
Electrodeposited nanocrystalline Ni-W alloy coatings are projected as potential alternatives for hard chrome (HCr) coatings owing to their comparable hardness and superior corrosion resistance. ...However, the limited strain hardening ability of the nanocrystalline Ni-W coatings manifests in their poor resistance towards solid particle erosion involving a high strain-rate (>103 s−1) deformation. In the present study, a novel microstructural engineering strategy has been implemented to enhance the strain hardening ability of the nanocrystalline Ni-W coatings without compromising on their strength/hardness. Ni-W multilayer coatings composed of alternatively stacked soft (2.6 GPa) and hard (8.5 GPa) Ni-W layers were developed using the pulse reverse electrodeposition technique. Further, to investigate the effect of individual layer thickness (λ), multilayer coatings with different λ were deposited. Solid particle erosion testing using the angular SiO2 particles showed that the multilayer coatings (irrespective of λ) exhibit superior erosion resistance compared to the homogeneous nanocrystalline Ni-15W at both oblique (θ = 30°) and normal (θ = 90°) impact conditions. The post-erosion microstructural analysis of the multilayer coatings revealed that the hard Ni-W layers undergo uniform strain (ε > 50 %) without cracking due to the constrained co-deformation imposed by the surrounding soft Ni-W layers. Therefore, the enhanced erosion resistance of the multilayer coatings is attributed to the effective dissipation of impact energy through co-deformation of the individual hard and soft Ni-W layers.
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•Ni-W multilayered coatings through pulse reverse electrodeposition.•Improved solid particle erosion resistance due to multilayering.•Erosion is independent of impact angle at layer thickness of 0.1 μm.•Co-deformation of multilayers controls erosion behavior.
TauFactor is a MatLab application for efficiently calculating the tortuosity factor, as well as volume fractions, surface areas and triple phase boundary densities, from image based microstructural ...data. The tortuosity factor quantifies the apparent decrease in diffusive transport resulting from convolutions of the flow paths through porous media. TauFactor was originally developed to improve the understanding of electrode microstructures for batteries and fuel cells; however, the tortuosity factor has been of interest to a wide range of disciplines for over a century, including geoscience, biology and optics. It is still common practice to use correlations, such as that developed by Bruggeman, to approximate the tortuosity factor, but in recent years the increasing availability of 3D imaging techniques has spurred interest in calculating this quantity more directly. This tool provides a fast and accurate computational platform applicable to the big datasets (>108 voxels) typical of modern tomography, without requiring high computational power.
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