Effect of swaging on microstructure and mechanical properties of liquid-phase sintered 93W-4.9(Ni,Co)-2.1Fe alloy

The effect of swaging on the microstructure and mechanical properties of 93W-4.9Ni-2.1Fe alloy was investigated. The alloy was prepared by liquid-phase sintering under hydrogen atmosphere followed by vacuum heat treatment and swaging at 600 °C with different area reductions (ranging from 15.0% to 84.8%). The as-swaged alloy with area reduction 84.8% exhibits the highest ultimate tensile strength (about 1490 MPa) and the lowest elongation (about 2.5%), which has been attributed to higher fraction of tungsten cleavage. For the as-sintered alloys, the fracture modes are a combination of the ductile rupture of W-Ni-Fe-Co matrix, transgranular cleavage of the tungsten particles, W-W interfacial segregation and W-M interfacial debonding, whereas transgranular cleavage of the tungsten particles is the main characteristic in the as-swaged alloy. Transmission electron microscopy images indicate that tungsten grains and W-Ni-Fe-Co matrix phase are composed of high-density dislocations. Based on the results, when running the swaging of 93W-4.9(Ni, Co)-2.1Fe alloy at 600 °C, the strengthening mechanism can be mainly due to the working-hardening.     

Crystallization and thermal expansion behavior of lithium zinc silicate sealing glass

Effect of heat treatment schedule on the crystallization and thermal expansion behavior of a lithium zinc silicate glass system was investigated by differential scanning calorimeter (DSC), X-ray diffraction, and linear thermal expansion test. Two well-defined crystallization exothermic peaks were observed from the DSC trace. According to the apparent activation energies and avrami parameter values calculated from the two crystallization exothermal peaks, the first crystallization exothermal peak was attributed to a combining surface and internal crystallization behavior, while the second one was found to be internal crystallization. Additionally, the phase evolution and the thermal expansion behavior with increasing heat treatment temperature were found to be closely related. Interestingly, it was found in comparison with previous reports that addition of CaO varies the phase composition of the resulting glass–ceramic in an opposite way to K₂O and the deep rooted reason has been discussed which may cast light on the modulation of properties of glass–ceramic involved crystalline phase of quartz or cristobalite. At last, average thermal expansion coefficient of 7.99–15.38×10⁻⁶ K⁻¹ in the temperature range of 25–400 °C has been obtained with different heat treatment schedules.     

Co3O4 microtubules derived from a biotemplated method for improved lithium storage performance

A simple and effective biotemplated method is applied to fabricate porous microtubular cobalt oxide by infiltration of cotton fiber with a cobalt nitrate solution, followed by annealing at 500 °C in air. The as-obtained Co₃O₄ have been characterized by: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), N₂ adsorption and desorption measurements, and thermal analysis (TG). According to these results, the as-prepared Co₃O₄ display a perfect tubular morphology and mesoporous features. The electrochemical performance of the as-obtained sample was studied for use as a lithium-ion battery anode material by cyclic voltammetry (CV), and charge-discharge and electrochemical impedance spectroscopy (ESI) measurements. Compared to bulk Co₃O₄ and previously reported nanostructured Co₃O₄ electrodes, mesoporous microtubular Co₃O₄ show an improved lithium storage properties, which can be attributed to their unique morphology, large specific surface area and mesoporous feature.     

Effect of process parameters on microstructure and properties of laser welded joints of aluminum/steel with Ni/Cu interlayer

The effects of laser parameters and interlayer material on the microstructure and properties of the welded joint between 6061 aluminum alloy and stainless steel were studied. The results show that the density and microstructure of the welded joint can be optimized by changing the laser power with 0.05 mm Cu foil and 0.1 mm Ni foil as interlayer. A large number of new Cu–Al binary phases were found near the aluminum alloy, which effectively inhibited the formation of the binary brittle phase of Fe–Al. The maximum shear force of 1350.96 N was obtained with laser power of 2200 W. The shear force of the welded joint increased to 1754.73 N when the thickness of the Cu foil thickness changed to 0.02 mm.     

Thermal,mechanical and electrical properties of hard B4C,BCN, ZrBC and ZrBCN ceramics

We study the thermal, mechanical and electrical properties of B₄C, BCN, ZrBC and ZrBCN ceramics prepared in the form of thin films by magnetron sputtering. We focus on the effect of Zr_x(B₄C)_1−x sputter target composition, the N₂+Ar discharge gas mixture composition, the deposition temperature and the annealing temperature after the deposition. The thermal properties of interest include thermal conductivity (observed in the range 1.3–7.3 W m⁻¹ K⁻¹), heat capacity (0.37–1.6×10³ J kg⁻¹ K⁻¹ or 1.9–4.1×10⁶ Jm⁻³ K⁻¹), thermal effusivity (1.6–4.5×10³ J m⁻² s^−1/2 K⁻¹) and thermal diffusivity (0.38–2.6×10⁻⁶ m² s⁻¹). We discuss the relationships between materials composition, preparation conditions, structure, thermal properties, temperature dependence of the thermal properties and other (mechanical and electrical) properties. We find that the materials structure (amorphous×crystalline hexagonal ZrB₂-like×nanocrystalline cubic ZrN-like), more than the composition, is the crucial factor determining the thermal conductivity and other properties. The results are particularly important for the design of future ceramic materials combining tailored thermal properties, mechanical properties, electrical conductivity and oxidation resistance.     

A chromium carbide coating in-situ formed on C/C composites by the novel reactive wetting strategy to enhance oxidation resistance

A chromium carbide (Cr-C) coating in-situ formed on the C/C substrate is successfully prepared by a novel reactive wetting strategy. The interfacial microstructure and oxidation resistance of coated C/C composites are investigated in detail. The as-prepared coating mainly consists of Cr₂₃C₆ and Cr₇C₃, forming a tight joining with the C/C substrate. Compared to uncoated samples, the oxidation weight loss of coated C/C composites is substantially reduced at high temperatures. Furthermore, the hardness of coated C/C composites is significantly increased, enhancing their ability to resist external damage. This reactive wetting strategy can also be used to prepare uniform coatings on C/C composites with complex grooved structure or large size. Surprisingly, coated C/C composites possess a low weight gain of 3.7% due to thin coating (< 10 µm), which can maintain their advantage of low density.     

A 2D image-based multiphysics model for lifetime evaluation and failure scenario analysis of self-healing ceramic-matrix mini-composites under a tensile load

We propose a multi-physics numerical model for a self-healing ceramic matrix mini-composite under tensile load. Crack averaged PDEs are proposed for the transport of oxygen and of all the chemical species involved in the healing process and studied in the dimensionless form to perform the most appropriate discretization choices concerning time integration, and boundary conditions. Concerning the fibres’ degradation, a slow crack growth model explicitly dependent on the environmental parameters is calibrated using a particular exact solution and integrated numerically in the general case. The tow failure results from the statistical distribution of the fibres’ initial strength, the slow crack growth kinetics, and the load transfer following fibres breakage. The lifetime prediction capabilities of the model, as well as the effect of temperature, spatial variation of the statistical distribution of fibres strength, and applied load, are investigated highlighting the influence of the diffusion/reaction processes (healing) on the fibre breakage scenarios.     

Softening of hydroxyapatite by vacancies: A first principles investigation

First-principles plane-wave calculations were performed to investigate the influences of intrinsic vacancy on the stability and elastic properties of hydroxyapatite (HA). Five types of vacancies, i.e. H, O, OH, Ca, and Ca^2 + vacancy, were considered. Formation energies were evaluated and compared with experimental measurements. It was shown that HA with a Ca^2 + vacancy is the most stable one among the considered systems. Elastic constants were estimated via curves of total energy against strain. Bulk, shear and Young's moduli, and Poisson's ratio are also evaluated to compare with the experimental value. The elastic properties of HA are significantly affected by the vacancy. Vacancy can soften HA via reducing its elastic moduli. The HA with Ca^2 + vacancy is the softest one among the considered systems. Electronic structures of HA with vacancy are also analyzed to explain the softening mechanisms.     

Wetting of AgCu-Ti filler on porous Si3N4 ceramic and brazing of the ceramic to TiAl alloy

The effect of Ti content on the wettability of AgCu-Ti filler on porous Si₃N₄ ceramic was studied by the sessile drop method. AgCu-2 wt% Ti filler alloy showed a minimum contact angle of 14.6° on porous Si₃N₄ ceramic during the isothermal wetting process. The mechanism of AgCu-Ti filler wetting on porous Si₃N₄ ceramic is clarified in this paper. Porous Si₃N₄ ceramic was brazed to TiAl alloy using AgCu-xTi (x = 0, 2 wt%, 4 wt%, 6 wt%, 8 wt%) filler alloy at 880 °C for 10 min. The effect of Ti content on the interfacial microstructure and mechanical properties of porous-Si₃N₄/AgCu-xTi/TiAl joints are studied. The typical interfacial microstructure of p-Si₃N₄/AgCu-Ti/TiAl joint is p-Si₃N₄/penetration layer (Ag(s,s)+Si₃N₄+TiN+Ti₅Si₃)/Ag(s,s)+Cu(s,s)+TiCu/AlCu₂Ti/TiAl. The maximum shearing strength of the brazed joint was 14.17 MPa and fracture that occurred during the shearing test propagated in the porous Si₃N₄ ceramic substrate for the formation of the penetration layer.     

A powerful estimation scheme with the error-in-variables-model for nonlinear cases: Reactivity ratio estimation examples

This paper gives an overview of the error-in-variables-model (EVM) procedure for parameter estimation with nonlinear models. It is shown that the nested-iterative EVM algorithm, used in this work, is efficient and powerful, since it provides both true values of the variables and the best estimates of the parameters. The step by step illustration along with evaluation techniques for results, are followed by further discussion about the importance and advantages of combining EVM with design of experiments strategies. With the focus on the performance of the EVM algorithm, an illustrative example of reactivity ratio estimation in copolymerization is included, with single-response (composition data) and multi-response (triad fraction data) scenarios.