Scripta Materialia最新文献

The ability to control the stress-induced phase transformation of the shape memory alloy, NiTi, is an important technological challenge that must be understood for their wide application in devices that can exploit their reversible strain properties. This study elucidates the direct relationship between dislocation density and the martensitic, B19' & R-phase transformations, including its formation temperature from interrupted annealing of rolled NiTi samples. Deformation is shown to determine the enthalpy change required for the B2→R→B19' transformation, with associated transformation temperatures being modifiable via dislocation density and recovery processes. Recovery is shown to be rapid, highly heterogeneous and sensitive to crystal orientation. Grains with a 〈100〉 direction close to the macroscopic rolling direction recover more rapidly than 〈110〉 and 〈111〉 orientated grains. Considered to be governed by processing induced residual stresses and resultant crystallographic dependent annihilation/slip pathways, there are opportunities to tune B2→R→B19' transformation on either a grain-averaged or an orientation dependant per-grain basis.

The fracture behavior of a duplex stainless steel processed by laser powder bed fusion (LPBF) from mixed 25Cr + 5 wt.% Ni powders (i.e., 25Cr-5Ni) was compared to 25Cr that was processed without Ni but additionally heat-treated (i.e., 25Cr-HT) to give similar phase fractions of austenite and ferrite but with different micro and mesostructures. The 25Cr-5Ni alloy exhibited high yield strength (828–958 MPa) and good fracture toughness (122–167 MPa√m) while requiring no post heat-treatment after LPBF fabrication. In contrast, the 25Cr-HT alloy gave somewhat lower strength and higher fracture toughness in a classic strength-toughness trade-off due to the elimination of the high dislocation density from the LPBF process. While powder mixing induces somewhat more anisotropic properties due to a coarser mesostructure phase distribution, the results demonstrate an approach to develop LPBF processed duplex stainless steels that don't require costly post heat treatments.

Post-irradiation evaluation was performed on a 316 stainless steel baffle former bolt harvested after 40 years of service in a pressurized water reactor. Microstructure analysis revealed the presence of defect-free dislocation channels and strain-induced twins, indicative of loading at a stress level close to yield stress at least once while in service. Primary radiation-induced Ni/Si precipitates were likely destroyed during channel and twin formation, and secondary, significantly coarser Ni/Si precipitates formed inside the newly formed dislocation channels and along ∑3 boundaries during the continued irradiation. Complex chemistry inside the strain-induced features may overlap with dislocation pileups and impact localized corrosion and material long-term performance.

The application range of 2:17 Sm-Co magnets is limited by poor mechanical properties. This study investigates the effects of adding Sm₂O₃ during ball milling and introducing O₂ during jet milling on the mechanical and magnetic properties of 2:17 Sm-Co magnets. With increasing oxygen content, the flexural strength in both Sm₂O₃-added and O₂-added magnets was enhanced. Flexural strength in Sm₂O₃-added magnets increased by 18.5 % with oxygen content (x) rising from 0.07 wt.% to 0.46 wt.%, while in O₂-added magnets, a 43.0 % increase was observed with oxygen content (x) from 0.08 wt.% to 0.41 wt.%. The uniform dispersion of Sm₂O₃ and its grain refinement effect contribute to superior mechanical properties in O₂-added magnets. It can be foreseen that compensation with a certain Sm content can achieve a combination of magnetic and mechanical properties. This study provides insights for developing magnets with exceptional overall performance.

Density Functional Theory calculations of self-interstitial atom clusters in bcc Fe unexpectedly show that from ∼9–14 self-interstitial atoms, an intriguing new family of sessile ⟨100⟩ clusters, surrounded by ⟨110⟩ dumbbells, are more stable than highly mobile clusters of parallel ⟨111⟩ dumbbells. The ⟨110⟩ edge dumbbells find a favorable location in terms of strain energy on the tensile side around the edges of the ⟨100⟩ center, thus stabilizing the clusters. These sessile clusters might explain resistivity recovery results that suggested an absence of glissile self-interstitial clusters up to large cluster sizes in irradiated Fe, while smaller self-interstitial atom clusters likely would have been present. The mechanism of non-parallel edge interstitials stabilizing an otherwise higher energy interstitial loop is also found in some fcc metals.

This study focuses on the impact of off-eutectic microstructures on mechanical properties in ternary Mo-Si-Ti alloys, namely Ti-rich Mo-18Si-72Ti and Mo-16.5Si-72Ti, in relation to the well-researched eutectic, two-phase Mo-20Si-52.8Ti alloy. The microstructure of these alloys consists of a Ti-rich body-centered cubic solid solution (Ti,Mo,Si)_ss and a hexagonal silicide phase (Ti,Mo)₅Si₃. Notably, the off-eutectic alloys exhibit remarkable compression ductility at 800 °C, distinguishing it from Mo-20Si-52.8Ti. The directionally solidified (DS) specimens of the Ti-rich alloys display higher strength compared to the arc-melted specimens. This enhanced strength is attributed to the multiple precipitation strengthening events present, despite the increase in the length scale of individual phases which further enhances the fracture toughness.

Glasses in the TeO₂-ZnO-Bi₂O₃ system were prepared with up to 2.5 mol% of Yb₂O₃ using standard melting process and their crystallization process was investigated for the first time. No concentration quenching was observed. The thermal treatment leads to surface precipitation of crystals, the composition of which depends on the Yb₂O₃ content. The addition of Yb₂O₃ in the tellurite network promotes the precipitation of Bi₂Te₄O₁₁ crystals at the expense of Zn₂Te₃O₈ crystals. The growing of these crystals in the low Yb³⁺ concentrated glass during a thermal treatment increases the interaction between the Yb³⁺ ions leading to an enhancement of the Yb³⁺ emission properties which reach those of highly Yb³⁺ concentrated tellurite glass. Our study suggests that a thermal treatment can be a practical alternative to increase the emission efficiency of the glass prepared with 0.5 mol% of Yb₂O₃ to the level of the as-prepared glass doped with 2.5 mol% of Yb₂O₃.

Interfacial behavior in composites significantly influences their properties. Ag-based composites reinforced with Ti₃AlC₂ (a MAX phase) are promising for electrical contacts. However, interdiffusion between the Ag matrix and Ti₃AlC₂ increases impurities in the Ag matrix, adversely affecting electrical resistance and raising operational temperatures. To address this, we developed a novel partial etching pretreatment that selectively etches Al atoms from the near-surface region of Ti₃AlC₂, creating a Ti₃C₂ surface layer. This innovative approach confines interdiffusion mainly within the Ti₃C₂ layer, preserving the Ag matrix's high electrical conductivity. Experimental results for Ag-based composites with 10 wt.% of Ti₃AlC₂, subjected to 0.5 h etching, show a significant 51 % reduction in electrical resistivity with only a 10 % decrease in mechanical properties compared to Ag/Ti₃AlC₂. These findings underscore the effectiveness of manipulating A-site elements in Ti₃AlC₂ to enhance the performance of Ag-based composites, offering valuable insights for advanced electrical material design.

The optical transmission, the wavelength and temperature dependence of the Verdet constant as well as the thermally induced depolarization in a Zn₄B₆O₁₃ crystal were investigated. The analytical dependence of the Verdet constant on wavelength and temperature, which describes well the experimental data in the 240–1100 nm range, was obtained. The small coefficient of linear expansion and its isotropy significantly suppressed thermally induced depolarization associated with thermally induced linear birefringence caused by the photo-elastic effect, while the diamagnetic nature of the material ensured the absence of thermally induced depolarization associated with the temperature dependence of the Verdet constant. The results revealed that Zn₄B₆O₁₃ is highly suitable for the wavelength range of 248–350 nm and can be used as a magneto-optical material for an optical isolator for high-average-power UV lasers.