Effect of deep cryogenic treatment on carbon segregation in Cr8Mo2SiV tool steel during tempering

Carbon segregation in Cr8Mo2SiV tool steel after common heat treatment (CHT) and deep cryogenic treatment (DCT) has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) extraction replica and three-dimensional atom probe (3DAP) tests. The XRD results show that most of the retained austenite transformed to martensite after DCT. The TEM results confirm the transformation of blocky retained austenite to twin martensite during DCT. The 3DAP results reveal the segregation of carbon atoms and the maximum carbon fraction in carbon-rich regions increases after DCT. The peak carbon concentration in carbon-rich regions of SDC99 steel after CHT and DCT are 8 at. % and 15 at. %, respectively. The segregated carbon atoms grew into nuclei for nanoscale carbides precipitation on subsequent tempering.     

Chemistry and morphology of β′ precipitates in an aged Mg-Nd-Y-Zr alloy

While the Mg–Y–Nd system is used for industrial applications, the details of the precipitation sequence and exact role of each alloying element during ageing have not been fully quantified. Focusing on WE43, a Mg–Y–Nd alloy containing Zr, the chemistry of β′ precipitates and matrix during isothermal ageing at 250 °C is investigated using atom probe tomography. Precipitate morphologies and compositions are compared with previous electron microscopy observations, and the roles of the alloying elements are discussed.     

Precipitation of γ’ during cooling of nickel-base superalloy Haynes 282

ABSTRACT

Cooling-induced precipitation of the strengthening γ’ phase is commonly investigated in Ni-base superalloys with a high γ’ volume fraction, where it is used to control the final microstructure and properties. Less is known about the phase separation in low-volume-fraction alloys during cooling, although the microstructural state after cooling from solution treatment is known to affect subsequent heat-treatment steps. We use atomic-scale characterisation of Ni-base superalloy Haynes 282 (equilibrium γ’ volume fraction around 20%) to show that air cooling after solution or carbide stabilisation results in precipitation of nm-sized γ’ particles, whereas precipitation was suppressed during water quenching. The solution treatment has a significant effect on the hardness and γ’ precipitation during air cooling from the subsequent carbide stabilisation temperature. Also, the carbide-stabilisation treatment itself affects the γ’ precipitation during subsequent air cooling.     

Secondary ageing in Al-Cu-Mg

Secondary ageing, that is microstructural evolution occurring at room temperature after short heating at temperatures above the metastable phase boundary of Guinier-Preston zones, has been studied for an Al-Cu-Mg alloy with a high Cu-to-Mg ratio. Combined data from positron annihilation spectroscopy, Vickers microhardness measurements and differential scanning calorimetry show that, on secondary ageing after 5 or 7min at 190°C, firstly, hardening takes place at a rate nine to 16 times slower than natural age hardening; secondly, vacancies slowly released by Cu-rich aggregates formed during the heat treatment at 190°C promote further formation of solute aggregates, with a time-dependent chemical composition; thirdly, the thermal stability of the structures formed during secondary ageing increases with increasing dwell time at room temperature; and, fourthly, solute aggregates formed at 190°C undergo a structural reorganization and possibly a change in the composition, leading to species with a different thermal stability. The slow release of vacancies from Cu-rich aggregates is proposed as one of the limiting factors of the hardening rate.     

Formation of omega and Ti2Ni phases in a residual Ti–Ni–Ti multilayer between stainless steel and zirconia after bonding at 1173 K

Stainless steel (316L) and 8 mol pct Y₂O₃-stabilized zirconia (8Y-ZrO₂) were bonded using a Ti–Ni–Ti multilayer at 1173 K (900 °C) for 1 h. Cross-sectional transmission electron microscopy specimens were prepared by an innovative focused ion beam plus lift-out technique. In addition to acicular α-Ti, the dissolution of Fe, Cr, and Ni diffusing outwards from 316L into β-Ti led to the precipitation of the omega (ω) phase with different variants in the residual Ti foil between 316L and Ni. The ω-phase was not found in the residual Ti foil between Ni and 8Y-ZrO₂, while Ti₂Ni precipitates were precipitated in some α-Ti grains owing to the exclusion of Ni from the β-Ti.     

重离子放射治疗技术实践场域中的伦理问题及治理

重离子放射治疗技术既有因技术突破带来的无限发展的前景,也有因技术不确定性带来的风险和挑战。以重离子放射治疗技术为研究对象,从实践伦理的角度出发,分析重离子放射治疗技术在研发、投产、临床应用三个实践场域中的伦理问题,发现其在研发领域存在技术不确定性、投产领域存在社会价值和科学有效性争议、临床使用场域存在技术价值冲突等问题。在深入分析三个场域存在的风险和伦理问题的基础之上,提出了加强风险评估和伦理约束、增强公众对重离子放射治疗技术的认知和参与度、加强重离子放射治疗技术的全球治理的相关建议。

     

大学生场依存性─－独立性认知方式分析

对二十一个学科专业１５２６名大学生的场依存性─－独立性认知方式进行调查所获得的新近常模资料表明：大学生场依存性─－独立性个体差异的群体分布是正态性的,其总体平均水平以《认知方式图形测验》成绩作指标为１３．７（ｓ为４．６）。在此基础上,对文献所报道的影响场依存性─－独立性发展水平的两个因素作了进一步的研究分析,发现,大学生场依存性─－独立性的性别差异非常接近显著水平;专业分化是不依赖于性别因素而导致大学生场依存性─－独立性水平显著不同的主要因素．     

Influence of properties of layered silicate minerals on adsorbed DNA surface affinity,self-assembly and nanopatterning

We report on the specific interaction between DNA and some mica-family minerals and other layered silicate structures. The interaction depends on mineral surface's crystallography, chemistry and potential. These properties are responsible for a remarkable variety of adsorption mechanisms and can be used to modulate surface self-assembly and nanopatterning of DNA. The controlled deposition of DNA onto non-conductive mineral regions with atomically flat boundaries has very attractive applications in nano-biotechnology (for example, microelectronics, microarrays and sensors). In addition, the extreme affinity discovered for some mineral surfaces, together with their ability to organize the DNA molecules, could be an indication of their catalytic potential. It may also have had relevance in the prebiotic environment, with important implications for the earth and life sciences.     

Investigations of the optical spectra and EPR g-factors for the tetragonal Ce3+ centers in YPO4 and LuPO4 crystals

The optical spectral band positions and EPR g-factors (g_‖ , g _⊥) for the tetragonal Ce³⁺ centers in YPO₄ and LuPO₄ crystals with the zircon-structure are calculated using a complete diagonalization (of the energy matrix) method (CDM) related to 4f¹ ions in tetragonal symmetry. In this method, the Zeeman interaction term are added to the Hamiltonian in the conventional CDM and so no perturbation calculations are required to obtain the g factors. The crystal-field parameters used in the calculations are obtained from the superposition model in which the local lattice relaxation related to the bonding lengths is considered. The calculated results are in reasonable agreement with the experimental values. It is found that the four observed optical bands for both the systems can be attributed to Ce³⁺ ions in a tetragonal crystal field.