Materialia最新文献

Swift heavy ion (SHI) irradiation deposits large amount of energy in the target material which thereby influences the structural features of the sample. In this work, the structural response of CdSe material has been studied under high energetic 120 MeV SHI irradiation. The long-range structural modifications of CdSe under SHI have been analyzed using Rietveld study. On the other hand, the short-range behavior of SHI irradiated CdSe has been studied using Pair distribution function (PDF), which can be interpreted as a distance map between two atoms in terms of a PDF peak. The small-box structural refinement of the samples has been performed using the PDFgui package for the study of modifications in the atomic arrangement after the SHI irradiation. In addition to this, structural characteristics such as unit cell parameters as determined from long-range (Rietveld) refinement are compared to that obtained from short-range (small-box) refinement. Moreover, atomic displacement factor for CdSe also has been determined to study the atomic disorder in the nanocrystal under the influence SHI irradiation. Finally, impact of SHI induced stress generated on the CdSe sample and its influence also has been studied based on the width of the PDF peak.

The present work investigates the effect of different type of hold on the change in microstructure and cyclic life. i.e., number of cycles to failure of the 304LN grade austenitic stainless steel at an elevated temperature. The strain-controlled low cycle fatigue and creep-fatigue interaction tests were carried out in air at 540 °C for constant total strain amplitude levels of ± 0.5 % and ± 0.7 %. The duration of hold-time was maintained at a constant level of 600 s at peak tensile, compressive and both peak tensile-compressive strain during different creep-fatigue interaction tests. Due to incorporation of creep damage, the cyclic life of the creep-fatigue interaction-tested samples has been found to be lower than that of the low cycle fatigue-tested samples. The tensile-hold appears to have maximum impact on reduction in cyclic life during creep-fatigue interaction tests followed by tension-compression hold and compressive hold. The scanning electron microscopy and electron back scattered diffraction analyses of creep-fatigue interaction-tested samples have revealed that the grain size coarsening, reduction in twin boundary fraction and increase in average Kernel Average Misorientation are the key factors in reduction of cyclic life.

There is renewed interest in refractory alloys that possess higher service temperatures than incumbent Ni-based superalloys (e.g., ⪆1100 °C). This study provides a review of the high-temperature constitutive responses of Nb-alloys measured over a wide range of temperatures (≈860 °C < T < ≈1760 °C) and strain rates (≈10^–9 s^-1< $\dot{\epsilon }$ < ≈10^–1 s^-1). Nevertheless, the extant data is sparse and informed materials selection decisions require constitutive expressions to interpolate and reliably extrapolate. The Larson-Miller parameter approach to describe creep-life provides a conservative estimate of material response at the highest temperatures and lowest strain rates, whereas the Sellars-Tegart model describes both steady-state creep and high-temperature tensile test data with a single, universal equation. A minimum flow stress based on the combination of these two models is proposed for design considerations to address the overprediction of strength that can arise from applying one or the other independently. This effort highlights the fact that refractory alloys exhibit strain rate sensitive flow strengths in the temperature range of interest for applications. The roles of alloying, thermomechanical processing, and impurity levels are discussed, and highlight the fact that these advanced Nb-alloys evidence Class 1 (Class A) solute drag controlled creep behavior, except the carbide precipitation strengthened alloy, D-43. In addition, the high-temperature strengths are confirmed to be strongly correlated with alloy melting point.

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.