Measurement of high temperature phase stability and thermophysical properties of alloy 740

In the present study, the characterisation of phase stability and measurement of different thermophysical properties of alloy 740 has been carried out. The transformation temperatures including liquidus/solidus and corresponding enthalpy of transformation have been measured for different phase changes up to melting using dynamic calorimetry. Further, the enthalpy increment data have been measured in the temperature range of 473–1473?K to obtain the heat capacity using static calorimetry. The present calorimetric data have been analysed in corroboration with the results obtained using JMatPro and Thermo-Calc simulation. In addition, the temperature dependence of other thermophysical properties such as thermal expansivity, density, thermal diffusivity and thermal conductivity are also measured in the range of 300–1473?K using thermomechanical analyser and laser flash method.     

Mechanical properties and thermal stability of nitrogen incorporated diamond-like carbon films

The nitrogen incorporated diamond-like carbon films were deposited on Si (100) substrates by arc ion plating (AIP) under different N₂ content in the gas mixture of Ar and N₂. The influence of N₂ content on the film microstructure and mechanical properties was studied by atomic force microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nanoindentation. It was found that the hardness (H), elastic modulus (E), elastic recovery (R) and plastic resistance parameter (H/E) decrease with increasing the nitrogen content. The decrease of mechanical properties of DLC films resulted from nitrogen incorporation was associated with total sp³ carbon bond content and N-sp³C bond content. The structural modification as well as mechanical properties of the annealed nitrogen incorporated diamond-like carbon films was investigated as a function of annealing temperature. Raman spectra indicate that the I_D/I_G ratio starts to increase and G peak position shifts upward at the annealing temperature over 500 °C. The hardness and elastic modulus of thermally annealed nitrogen incorporated DLC films decreased slightly at lower annealing temperature and then significantly decreased at higher annealing temperature. The strong covalent bonding between C and N atoms is expected to be effective on their thermal stability enhancement.     

The stability of insulin in solid formulations containing melezitose and starch. Effects of processing and excipients

Solid insulin formulations obtained by different methods of preparation were compared with respect to chemical stability and morphology. Spray- and freeze-drying, solution enhanced dispersion by supercritical fluids (SEDS) and precipitation into starch microspheres were the methods used for preparation of solid powders. The excipients applied were melezitose, starch, and sodium taurocholate. The stability of the samples was evaluated after storage in open containers at 25°C and 30% RH for 6 months.

All samples were amorphous after processing and storage as detected by XRD, except for the starch microspheres which were semi-crystalline. The spray- and freeze-dried samples containing melezitose and sodium taurocholate experienced a significant water uptake during storage, resulting in changes in morphology and disappearance of Tg. However, the chemical stability of these samples did not seem to be affected by the water uptake. Changes in morphology were not observed for the SEDS powders and the starch microspheres.

The chemical stability of the samples was assessed by HPLC. In general, conventional spray- and freeze drying resulted in samples with higher chemical stability compared to SEDS powders and starch microspheres. Nevertheless, the excipients applied were observed to be of major importance, and further optimization of the formulation as well as processing conditions may lead to slightly different conclusions.     

Cr-Si-Ni电阻薄膜在模拟环境中的电学稳定性及腐蚀行为

研究了磁控溅射法制备的Cr-Si-Ni电阻薄膜在不同模拟环境介质溶液中的电学稳定性及腐蚀行为.结果表明,500℃热处理后纳米晶结构的Cr-Si-Ni电阻薄膜在25℃的模拟海洋、工业、酸性及碱性环境介质溶液中浸泡240h后,薄膜试样的相对电阻变化值(ΔR/R)分别为0.27%、0.08%、0.96%、3.31%.说明薄膜在上述4种环境中电学稳定性和耐腐蚀性能从高到低依次为:工业环境、海洋环境、酸性环境、碱性环境.薄膜在4种溶液中都能发生自钝化现象而在膜层表面形成SiO2保护层,形成的钝化膜在模拟的工业环境中最稳定.     

Mechanical properties and thermal stability of a Cu-based bulk metallic glass microalloyed with silicon

(Cu₄₂Zr₄₂Al₈Ag₈)_{100? x} Si _x (x?=?0?～?1) amorphous alloy rods of 2–6?mm diameter were prepared by Cu-mold drop casting. The thermal properties, microstructure evolution, and mechanical properties were studied by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness test, and compression test. The XRD result revealed that all as-quenched (Cu₄₂Zr₄₂Al₈Ag₈)_100?x Si _x alloy rods exhibited a broad diffraction pattern in the amorphous phase. The (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 alloy was found to possess the highest glass forming ability (GFA) as well as the best thermal stability among all tested samples. In addition, both its hardness and yield strength were increased by the microalloyed Si content. The fracture strength and the plastic strain of (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 amorphous alloy can reach 2000?MPa and 3.5 %.     

反应射频磁控溅射法制备HfTaO薄膜的热稳定性和光学性能

采用反应射频磁控溅射技术制备HfTaO薄膜,利用X射线衍射(XRD)分析了薄膜的微结构,通过紫外-可见光分光光度计测量了薄膜的透过谱,计算了薄膜的折射率和禁带宽度,利用原子力显微镜观察了薄膜的表面形貌。结果表明,随着Ta掺入量(10%,26%,50%)的增加,HfTaO薄膜的结晶化温度分别为800、900、950℃,Ta掺入量继续增加到72%,经过950℃退火处理的HfTaO薄膜仍然保持非晶态,具有优良的热稳定性。AFM形貌分析显示非晶HfTaO薄膜表面非常平整。在550nm处薄膜折射率n随着Ta掺入量的增大而增大,n的变化区间为1.90～2.15。同时HfTaO薄膜的光学带隙Eg随着Ta掺入量的增大而逐渐减小,Eg的变化区间为4.15～5.29eV。     

Tensile properties and thermal stability of ZnO-coated aluminum borate whiskers reinforced 2024Al composite

ZnO-coated aluminum borate whiskers reinforced 2024Al composite was fabricated by squeeze casting. Interfacial microstructures and tensile properties of the composite in as-cast and after thermal exposure were investigated. Fracture mechanisms of the composite in as-cast and after thermal exposure were also investigated. The results show that ZnO coating of the whiskers reacts with molten 2024Al and MgAl₂O₄ forms at the interface during squeeze casting. On the one hand, the interfacial reaction between ZnO and 2024Al can improve the wettability of the whiskers by molten 2024Al, increasing the tensile properties of as-cast composite. On the other hand, during thermal exposure, MgAl₂O₄ at the interface can effectively hinder serious interfacial reactions between the whiskers and magnesium in the matrix of 2024Al, improving the thermal stability of the composite at high temperatures.     

Effect of nitrogen addition on the properties and thermal stability of fluorinated amorphous carbon films

Continuous fluorinated amorphous carbon (a-C : F) films doped with nitrogen (a-C : F : N) were deposited by plasma enhanced chemical vapor deposition using CF₄ and C₂H₂ gases as precursors with the addition of N₂ gas. The surface morphologies, chemical compositions, deposition rates, thermal stability and mechanical properties of these films varied with the deposition parameters, including CF₄ and N₂ feed gas concentrations, processing pressure, plasma power and substrate temperature. With increasing N₂ feed gas concentration, the nitrogen content of the a-C : F : N films increased to about 6 at.% and contributed to higher mechanical properties. After thermal annealing, the a-C : F films with higher fluorine contents exhibited more obvious fluorine release and extensive film thickness shrinkage, whereas the a-C : F : N films with higher contents of nitrogen doping yielded less composition variations, smaller thickness shrinkages, higher mechanical properties, and conclusively better thermal stability.     

球磨Mg0.97La0.03Ni合金的热稳定性及电性能研究

采用XRD、DTA、SEM及电池性能测试仪等对球磨Mg0.97La0.03Ni合金的结构、形貌、活化性能、热稳定性、电化学稳定性及容量衰减机理等进行了详细的研究。结果表明：样品的热稳定性及循环稳定性随着球磨时间的延长而增加。经400r／min球磨50h的样品在第二次活化时即达到最大值450mAh／g．经25次循环充放电后．该样品的容量与其最大值相比下降了53％．容量衰减的主要原因有：在循环充放电过程中．非晶体逐渐分解生成Mg2NiH4和Ni等晶体相，同时在颗粒表面形成腐蚀产物Mg(OH)2等。     

Measuring spatial variations of weak layer and slab properties with regard to snow slope stability

Spatial variations of weak layer and slab properties are believed to affect snow slope stability. To quantify spatial variability at the slope scale, penetration resistance was measured with a high-resolution snow micro-penetrometer (SMP) in a partly randomized grid pattern. The grid design consisted of 46 SMP measurement locations. In addition, a full snow profile and 20 compression tests as well as a Rutschblock test at the snow profile location were performed within the grid. Fifteen slopes of different aspects were sampled of which 11 could be analysed. Weak layer and slab properties were characterised using non-spatial as well as spatial statistics and results were related to slope stability. The geostatistical analysis revealed that in more than half of the cases a range could be determined. Slab layers tended to have more spatial structure than the weak layer. Though some trends are apparent, firm conclusions on the dependence of slope stability on spatial variations were not possible due to the limited range of snow conditions in the dataset, and the fact that the definition of slope stability remains elusive. Based on our limited data set, we can therefore not specify the conditions when spatial variations of weak layer and slab properties are most relevant for snow slab release.     

The effect of particle morphology on the physical stability of pharmaceutical powder mixtures: the effect of surface roughness of the carrier on the stability of ordered mixtures

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.     

Phase stability,physical properties and strengthening mechanisms of concentrated solid solution alloys

We review recent research developments in a special class of multicomponent concentrated solid solution alloys (CSAs) – of which the recently discovered high entropy alloys (HEAs) are exemplars – that offer a new paradigm for the development of next generation structural materials. This review focuses on the role of inherent extreme chemical complexity on the phase stability, electronic, transport, and mechanical properties of this remarkable class of disordered solid solution alloys. Both experimental observations and theoretical models indicate that the phase stability of HEAs goes beyond the original conjecture that these alloys are stabilized by configurational/mixing entropy; rather, it results from competition between the homogeneously disordered phase and phase separation/intermetallic compound formation. Although the number of single-phase HEAs with equiatomic composition is limited, those that do exist often exhibit remarkable electronic, magnetic, transport, and mechanical properties. For the mechanical response, we discuss the solution strengthening mechanism which governs the strength and deformation behaviors of the CSAs, as well as the increasing evidence that low stacking fault energies (deformation twinning) plays an important role in the low temperature strength and ductility of CrMnFeCoNi related alloys. We also review the current understanding of the role of the number and type of alloy elements in determining the electronic, magnetic, and transport properties, in particular the dominant role of magnetic interactions in the properties of 3d-transition metal based alloys. Finally, we emphasize that, despite rapid progress in characterization and understanding of the phase stability and physical/mechanical responses of CSAs, there remain significant challenges to fully exploring the new paradigm that these alloys represent.     

Thermal stability and mechanical properties of nanostructured Ti–24Nb–4Zr–7.9Sn alloy

Thermal stability of the nanostructured grains of cold-rolled Ti–24Nb–4Zr–7.9Sn alloy and corresponding variations in mechanical properties were investigated. The activation energy for grain growth was found distinct below and above the ( + β)/β transus of 950 K, with values of 47 and 206 kJ/mol, respectively. Due to the pinning effect of the precipitates at β grain boundaries, grains sizes can be maintained at less than 100 nm during prolonged annealing at temperatures up to 773 K, and are less than 1 μm for annealing temperature up to 923 K and time up to 2 h. Annealing above the β transus resulted in coarse grains with sizes of tens of micrometers in less than 2 h. Tensile and hardness tests showed rapid strengthening with the increase of annealing time below 773 K, which was attributed to both the rapid formation of nano-sized precipitates and the slow growth rate of β grains. By adjusting the grain size of the cold-rolled material the high strength/low Young's modulus match desirable for implant applications can be improved over the hot-rolled bars with coarse grains.     

Structure,optical properties and thermal stability of Al2O3-WC nanocomposite ceramic spectrally selective solar absorbers

Traditional metal-dielectric composite coating has found important application in spectrally selective solar absorbers. However, fine metal particles can easily diffuse, congregate, or be oxidized at high temperature, which causes deterioration in the optical properties. In this work, we report a new spectrally selective solar absorber coating, composed of low Al₂O₃ ceramic volume fraction (Al₂O₃(L)-WC) layer, high Al₂O₃ ceramic volume fraction (Al₂O₃(H)-WC layer) and Al₂O₃ antireflection layer. The features of our work are: 1) compared with the metal-dielectric composites concept, Al₂O₃-WC nanocomposite ceramic successfully achieves the all-ceramic concept, which exhibits a high solar absorptance of 0.94 and a low thermal emittance of 0.08, 2) Al₂O₃ and WC act as filler material and host material, respectively, which are different from traditional concept, 3) Al₂O₃-WC nanocomposite ceramic solar absorber coating exhibits good thermal stability at 600 °C. In addition, the solar absorber coating is successfully modelled by a commercial optical simulation programme, the result of which agrees with the experimental results.     

Effect of microstructure morphology on mechanical properties of quenching and partitioning steel

In order to illuminate the relationship between microstructure morphology and final properties of the quenching and partitioning(Q&P) steel, the samples with different microstructure morphology (equiaxed and lamellar) and same volume fraction of each phase are obtained by controlling the initial microstructure and Q&P heat treatment. Because of the feature of microstructure morphology, a large yield ratio and total elongation are obtained in the lamellar sample though yield strength and ultimate tensile strength are relatively lower than that of equiaxed sample. Moreover, the lamellar sample produces a continuous work-hardening rate and better the fracture toughness compared to the equiaxed sample. Thus the lamellar sample is more suitable to be used as automotive structural components.     

Effect of water activity and temperature on the stability of creatine during storage

Creatine degradation to creatinine, which has no biological activity, in combinations of glycerol and pH 4.0 buffer solutions followed first-order kinetics up to a point where degradation started to level off, generally beyond the first half-life. Practical data are reported for a wide range of water activity (a_w) values (0.31–0.983) at 4°C, 23°C, and 35°C. Creatine degradation did not exhibit a dilution effect, that is a decrease in rate about an a_w of 0.7, as is found for both microbiological growth and chemical reactions in semisolid food matrix systems. The temperature dependence obeyed the Arrhenius relationship with an energy of activation of about 20 kcal/mol at a_w ≥ 0.68 increasing to 23 kcal/mole below that a_w. In addition, a semilog plot of half-life as a function of a_w at each temperature follows a predicted straight line. The pH and assumed liquid viscosity increase through increased glycerol concentration were not able to completely explain the decrease in rate of degradation as a function of a_w. Furthermore, we confirmed that creatine stability in the crystal form is very high as long as it does not reach the deliquescence state.     

Tuning austenite stability in a medium Mn steel and relationship to structure and mechanical properties

We study here the underlying factors that govern the stability of austenite in a medium Mn (Fe–0.18C–11Mn–3.8Al) (wt-%) steel. In this regard, a novel heat treatment involving intercritical quenching and tempering was designed to obtain high total elongation (TEL) and high ultimate tensile strength (UTS) in the cold-rolled steel. And the UTS and TEL approached 920–1150?MPa and 35–65%, respectively. The product of TEL and UTS (PSE) exceeded 40?GPa%, with a maximum value of 60?GPa%. A detailed analysis of microstructure before and after tensile deformation revealed that the TRIP effect occurred and the stability of austenite was predominantly governed by the grain sizes of austenite rather than the orientation of austenite grains. The theoretical analysis of work hardening data suggested that the superior elongation of medium Mn TRIP steel is related to the high stability of austenite and the cooperative deformation of ferrite.     

Intermethod comparison of the particle size distributions of colloidal silica nanoparticles

There can be a large variation in the measured diameter of nanoparticles depending on which method is used. In this work, we have strived to accurately determine the mean particle diameter of 30–40 nm colloidal silica particles by using six different techniques. A quantitative agreement between the particle size distributions was obtained by scanning electron microscopy (SEM), and electrospray-scanning mobility particle sizer (ES-SMPS). However, transmission electron microscopy gave a distribution shifted to smaller sizes. After confirming that the magnification calibration was consistent, this was attributed to sample preparation artifacts. The hydrodynamic diameter, d _h , was determined by dynamic light scattering (DLS) both in batch mode, and hyphenated with sedimentation field flow fractionation. Surprisingly the d _h were smaller than the SEM, and ES-SMPS diameters. A plausible explanation for the smaller sizes found with DLS is that a permeable gel layer forms on the particle surface. Results from nanoparticle tracking analysis were strongly biased towards larger diameters, most likely because the silica particles provide low refractive index contrast. Calculations confirmed that the sensitivity is, depending on the shape of the laser beam, strongly size dependent for particles with diameters close to the visualization limit.     

Hydrogen storing and electrical properties of hyperbranched polymers-based nanoporous materials

Hydrogen storage and electrical properties of different hyperbranched polymer systems beside a nanocomposite are studied. The polymers examined are aliphatic hyperbranched poly urea (P-Urea), polyamide amine (PAMAM) and polyamide amine/vanadium oxide (PAMAM/VO_x) nanocomposite. At 80 K and up to 20 bar hydrogen pressure, the hydrogen storage capacity of hyperbranched P-Urea reached 1.6 wt%, 0.9 wt% in case of PAMAM and 0.6 wt% for VO_x. The hydrogen storage capacity significantly enhanced when PAMAM and VO_x form a nanocomposite and increased up to 2 wt%. At 298 K and up to 20 bar, all the samples did not show measurable hydrogen uptake. Electrical properties of the samples are also investigated; the measurements showed complete insulating behavior at hydrogenation measuring temperature. These investigations ensure that the polymer conductivity does not play a role in hydrogen uptake, also hyperbranched polymers are promising materials for hydrogen storage.     

成形条件对PAN初生纤维结晶及力学性能的影响

为了制备具有良好可牵伸性能的PAN初生纤维,利用XRD、纤维强伸度仪、SEM等手段,分析了纺丝液温度、凝固浴温度和喷丝速度对初生纤维结晶和力学性能的影响。结果表明降低纺丝液温度和凝固浴温度减弱了PAN初生纤维的结晶能力,其中凝固浴温度的作用效果更为明显,结晶度的下降有利于提高初生纤维的断裂伸长率,而不会造成断裂强度的降低。加快喷丝速度能促进PAN初生纤维成形过程中的拉伸变形,有效降低了初生纤维的纤度并提高了其可牵伸性能。