Materialia最新文献

The low-cost Bi_1-xSb_x crystal has been considered the best low-temperature material for its high electrical properties, which also can generate high effective thermal conductivity, revealing a high potential in heat dissipation. However, the weak mechanical strength hinders practical applications. Herein, we firstly grew the Bi_1-xSb_x crystal by the Bridgeman method, then cleaved the crystal into slabs with different sizes for hot-pressing. The obtained materials exhibited a high bending strength of 72 MPa, which is twofold that of Bi_1-xSb_x [001]-direction. Furthermore, the hot-pressed Bi_1-xSb_x samples show high electrical conductivities, being similar to those of the single crystals, resulting in the high record power factor of 78 μW·cm^-1·K^-2 @110 K and 38 μW·cm^-1·K^-2 @300 K among the hot-pressed poly-crystalline Bi_1-xSb_x. This high electrical performance is beneficial to the applications of heat dissipation. Therefore, this work proves an effective way to simultaneously improve the mechanical and thermoelectric properties of Bi_1-xSb_x alloys.

Carbon fiber-reinforced plastic (CFRP) sheets were dissimilarly edge-joined with anodized A6061 Al alloy sheets by copper electrodeposition. A high bonding strength of 137 MPa was attained following a series of pretreatments including etching in KMnO₄ + NaOH hot aqueous solution, anodization at 2 V vs. SUS316 cathode in 1 mol L^˗1 H₂SO₄, and sulfonation in hot concentrated H₂SO₄. The anodization physically cleaned the carbon fiber (CF) surface in CFRP. The chemical surface properties of the CFs were modified by the anodization, introducing crystallographic defects and CO groups. This physical and chemical modification of CFs in CFRP resulted in good adhesion of the electrodeposited copper.

The application of lattice structures in porous titanium implants has emerged as a promising approach in the load-bearing orthopaedic implant industry. Complex-shaped medical implants have been effectively produced using metal AM techniques. However, there remains ambiguity regarding the suitable porous lattice structure, which significantly influences bone formation. The study aims to evaluate and compare the tissue ingrowth capability of different porous lattice structure implants on their surface using mechanoregulatory tissue differentiation algorithm. Computer-aided design (CAD) models of five topologies, namely cubic, X-shape, cubic centre, face centre, and octet, were created using Solidworks with similar porosities (60 %). Further, the study entailed the 3D microscale modelling of regular porous structured implants with five distinct repeating cells on their surface were constructed using Solidworks. Additionally, five FE microscale models of bone-implant interface were modelled, with each model representing a distinct porous lattice structure implant. Lattice tissue ingrowth behaviour is evaluated by employing a mechanobiological algorithm to every FE microscale model. The bone ingrowth efficiencies of the five porous lattice structure implants were ranked. By observing the results, it was found that each lattice structure displays distinct tissue differentiation behaviour. Results demonstrate that highest bone tissue ingrowth was seen in implant with cubic lattice followed by FCC, octet, cubic centre, and X-shape lattice structure implant. Among the five lattice structure implants analysed, the X-shape lattice structure implant promotes lowest bone tissue ingrowth. Overall, the findings derived from this study have the potential to improve Ti6Al4V prosthetic devices inserted in different human anatomical regions.

A semi-phenomenological model mimicking the full-time process of stress corrosion cracking (SCC) is proposed, and its attractive characteristics can be summarised as follows. Firstly, the role played by the hydrostatic pressure gradient at a crack tip in anodic dissolution is centralised by the proposed partial differential equation system, so as to formulate the interplay of load and corrosion in a mechanistic manner. As a result, the model can naturally reproduce the repeated film rupture mechanism that is believed central to general SCC phenomena. Secondly, the model implementation is extremely efficient, outputting a full-life SCC prediction within a few seconds on a normal laptop computer. Thirdly, a general rule for model calibration is introduced against limited experimental data, enabling its predictability over SCC indices that are not experimentally trackable. The efficacy and the generality of the proposed model are examined with three SCC scenarios, including (a) Inconel 600 alloys in nuclear pipelines, (b) stainless steels in oil pipelines, and (c) magnesium alloys used as structural materials in blood vessels. It is shown that SCC indices such as the SCC incubation period, which may be too long to be experimentally measured, can be quickly predicted with the present model after being calibrated.

Mg-Ca-Zn-Mn alloys are promising for applications in biodegradable bone fixation devices. The Zn/Ca atomic ratio in the compositions of these alloys is important to their corrosion and mechanical properties. This paper investigated the Zn/Ca ratio using a phase-focused approach based on CALPHAD (CALculation of PHAse Diagrams) modeling and experimental validation. Six Mg-0.5Ca-xZn-0.5Mn (all wt.%) alloys were cast with x = 0.96, 1.15, 1.47, 1.69, 1.94, and 3.81 so that the Zn/Ca atomic ratio spanned from 1.18 to 4.66. The microstructure is studied in the as-cast, solution-treated, and as-rolled conditions. A critical ratio was determined to be 2.77, above which Mg₂Ca phase can be suppressed in as-cast microstructure. In the solution-treated condition, a Zn/Ca ratio of less than 2.0 was required to dissolve the Ca₂Mg₆Zn₃ phase. Alloys below 2.0 Zn/Ca were found to have yield strength of 300 MPa and a corrosion rate of 0.25 to 0.3 mg/cm²/day as measured by both weight loss and hydrogen evolution. In alloys above 2.0 Zn/Ca, the yield strength decreased to 280 MPa and the corrosion rate measured by weight-loss increased to 0.5 mg/cm²/day. Above the critical ratio, the yield strength was the highest at 347 MPa but a corrosion rate of 0.4 mg/cm²/day. The Zn/Ca region with the best combination of corrosion resistance and mechanical properties is between 1.18 and 1.8 (in rolled sheet condition), which provides important guidance for biomedical Mg-Ca-Zn alloy design and optimization.

A bio-compatible Ti-25 wt% Nb alloy fabricated from a blend of pure elemental powders using laser powder bed fusion additive manufacturing technique. The present work investigated the effects of processing conditions on the evolution of microstructures and its consequential material attributes, such as mechanical properties and corrosion performance. Thermal management strategies comprising laser powers of 200 W and 300 W in complement with a shorter scan length (1 mm) and substrate preheating above $\beta$-transus temperature (1123 K) were considered to achieve complete dissolution of niobium particles. The microstructure in the 200 W sample showed thin $\alpha ”$ martensite needles in $\beta$ matrix while martensite laths in the 300 W condition appear coarse and were twice the area fraction compared to that in 200 W build. On the other hand, microstructures in the heated substrate sample exhibited the evolution of $\alpha$ and $\beta$ phases. A multi-scale finite element method based thermo-kinetic model spanning from melt pool scale to the component scale was incorporated to understand the mechanism of the evolution of microstructures during liquid–solid and solid–solid state transformation. Electrochemical performance in the simulated body fluid of the printed alloys was found to be significantly affected by the presence of martensite fractions. Both mechanical and corrosion behaviors were favorably influenced by adoption of the substrate preheating during additive manufacturing due to promotion of diffusional transformation of $\beta$ to $\alpha$ transformation at the expense of martensitic transformation.

The critical stress for cutting of a void and He bubble (generically referred to as a cavity) by edge and screw dislocations has been determined for FCC Fe_0.70Cr_0.20Ni_0.10—close to 300-series stainless steel—over a range of cavity spacings, diameters, pressures, and glide plane positions. The results exhibit anomalous trends with spacing, diameter, and pressure when compared with classical theories for obstacle hardening. These anomalies are attributed to elastic anisotropy and the wide extended dislocation core in low stacking fault energy metals, indicating that caution must be exercised when using perfect dislocations in isotropic solids to study void and bubble hardening. In many simulations with screw dislocations, cross-slip was observed at the void/bubble surface, leading to an additional contribution to strengthening. We refer to this phenomenon as cavity cross-slip locking, and argue that it may be an important contributor to void and bubble hardening.

Voronoi tessellation was innovatively applied to interpret the high-resolution atomic-scale micrographs of the Cr-W-C ternary M₂₃C₆ with and without irradiation to provide mechanistic insight into the phase stability under irradiation. A W concentration-dependent radiation-induced amorphization behavior was observed and the amorphization was confirmed in the 4 W sample (∼12 at.%W). Analysis of the local crystal structure using Voronoi diagrams shows that the average size of each Voronoi cell and its standard deviation are affected by irradiation and W concentration. In addition, the standard deviation of the Voronoi cell size, which is considered an indicator of the uncertainty of the atomic column positions, is also plotted as a function of the lattice parameter change. This mathematical analysis indicates that a higher W concentration tends to cause a more severe disordering of the atomic distribution upon irradiation, which is directly correlated with the occurrence of amorphization.

With the aim of further exploiting the trade-off between formability and strength in Al alloys, this study addresses the influence of Cu in Al-Mg-Si alloys that achieve simultaneously high strength and high ductility via cluster hardening. The study carefully examines the mechanical properties and strain hardening behavior of various Mg/Si ratios with and without Cu and compares the effects of pre-aging and atypical long-term low-temperature aging treatments at 100°C to conventional heat treatments. Interestingly, in all cases adding Cu improved ductility. In the extremal case cluster hardening plus the addition of Cu quadruples elongation, while keeping yield strength similar to the classical T6 state. The results of the study are discussed with a focus on the dense distribution of clusters and partial hardening phases based on atom probe tomography data. Most importantly, the cluster-hardened alloys exhibit pronounced strain-hardening properties, which we evaluate using a Kocks-Mecking approach in combination with a microstructural analysis in the pre-aging and long-term aging condition. The key finding of the study involves the role of Cu in refining clusters/precipitates, where it causes a substantial increase in number density and volume fraction. This refinement, in combination with strain-induced clustering, contributes significantly to improving the alloys’ overall mechanical performance and underlines the central role of Cu in tailoring microstructural features, especially in alloys primarily strengthened by clusters.