On the thermodynamic stability of intermetallic phases in the AA6111 aluminum alloy

An experimental investigation of both as-cast and heat-treated AA6111 alloys pointed to the quaternary phase Al₁₆(Fe,Mn)₄Si₃ as the dominant intermetallic phase. Weight fractions of this phase were determined by extracting it from the alloys via a selective dissolution of the FCC matrix in boiling phenol. The fractions found were significantly greater than those predicted by thermodynamic modeling. In an attempt to resolve the contradiction, it was assumed that the thermodynamic stability of the quaternary phase reported in literature had been underestimated. In order to refine its thermodynamic characteristics, conditions of phase equilibria in which Al₁₆(Fe,Mn)₄Si₃ participated were handled within the framework of the CALPHAD method.     

Enzymatic hydrolysis of lysine diisocyanate based polyurethanes and segmented polyurethane ureas by various proteases

This work studies the enzymatic degradation of polyurethanes (PUs) and segmented polyurethane ureas (SPUUs) derived from lysine diisocyanate (LDI) by various proteases. Thiol proteases, such as papain, bromelain, and ficin, showed high activity on PUs. Protease K and chymotrypsin also hydrolyzed the PUs. For almost all SPUUs, papain showed high activity. For example, LDI/poly(caprolactone) diol (M_w = 1250)/ethylene diamine (2/1/1) was hydrolyzed to 43% under the same conditions. The water-soluble degradation products of a polyurethane, LDI/BD (1/1), and two model compounds treated with papain were studied with NMR and GPC analysis. From the results, it was evident that the pendant methyl ester group in LDI was rapidly hydrolyzed, followed by slow hydrolysis of urethane bonds in the backbone chain.     

Interface structure and mechanical properties of the brazed joint of TiC cermet and steel

A commercially available Ag–Cu braze alloy foil with Zn was used to join TiC cermet and steel. According to the experimental observations, the interface structure is (Cu, Ni)/Ag (s.s.) + Cu (s.s.)/(Cu, Ni)/(Cu, Ni) + (Fe, Ni) from TiC cermet to steel side. With increased brazing temperature or time, the amounts of (Cu, Ni) near the base metals/Ag–31Cu–23Zn interface and (Cu, Ni) + (Fe, Ni) near the Ag–31Cu–23Zn/steel interface increase, while the amount of Ag (s.s.) + Cu (s.s.) in the middle of the braze alloy decreases. The whole joining process consists of diffusion and solution among atoms of the braze alloy foil and base metals. The maximum shear strength is 120.7 MPa for the joint brazed at 850 °C for 10 min.     

Global optimum of microstructure parameters in the CMWP line-profile-analysis method by combining Marquardt-Levenberg and Monte-Carlo procedures

Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimization procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncertainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters of the microstructure.     

Skin layer of A380 aluminium alloy die castings and its blistering during solution treatment

Skin layer is a characteristic microstructure of aluminium die castings, which would effect the surface blistering during solution treatment. In this study, the microstructures of skin layer were investigated by the methods of optical microscope (OM), scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). High resolution X-ray CT was used to compare the skin layer with normal surface before and after solution treatment. With the aid of computational fluid dynamics (CFD), the formation mechanism of the skin layer was discussed based on microstructure distribution, solute segregation, porosity distribution and surface blistering. The results suggested that the skin layer is related to a succession of complex processes before the filling process finished. Pore clusters or laminar defects would be formed in skin layers during solution treatment and cause severe surface blistering.     

The study on oxygen bubbles of anodic alumina based on high purity aluminum

U–t curve has been determined in anodic oxidation of high purity aluminum in two kinds of electrolytes. The formation of the barrier anodic aluminum oxide (AAO) film, the transformation from the barrier film to the porous one and the development of the porous film were analyzed in detail through the SEM micrograph. It was proposed that the porous films have developed from where they used to be seen as the phase of the formation of barrier films. The generation of O₂ in metal/film interface goes with the formation of porous films, so that the AAO film, whether or not it has begun to transform from barrier type to porous type, can be judged by observing if O₂ separates out or not.     

An equilibrium model for the crystallization of high silica zeolites

A simple equilibrium model is proposed to explain the change in pH which occurs when high silica zeolites are crystallized from gels. The model shows that for a given concentration of quaternary ammonium ions the highest increases in pH are associated with the most stable zeolite, and that the yields depend primarily on the stoichiometry of the reaction mixture. For reaction mixtures which are buffered by amines the model shows that the increase in pH is reduced and the yields are substantially increased.     

High carrier mobility and remarkable photovoltaic performance of two-dimensional Ruddlesden–Popper organic–inorganic metal halides (PA)2(MA)2M3I10 for perovskite solar cell applications

Two-dimensional Ruddlesden–Popper (2DRP) metal halides have attracted extensive attention in photovoltaic applications due to their high stability, low self-doping levels and long-lived free carriers. Among them, (PA)₂(MA)₂Pb₃I₁₀ presents itself as a superior candidate, demonstrating greater moisture resistance and improved heat and light stability over many other 2DRP metal halides. This study takes on the opportunity to search for lead-free alternatives by investigating the optoelectronic and carrier transport properties, as well as the photovoltaic performance of such (PA)₂(MA)₂M₃I₁₀ type metal halides as the photovoltaic absorber, where M = Pb, Cd, Cr, Cu, Ge, Mn, Ni, Sn, Yb, Zn. Our results indicate that the bandgap of (PA)₂(MA)₂M₃I₁₀ can be tuned to the optimum photovoltaic application range of 0.9–1.6 eV, along with improved optical and enhanced photo-response capacity, when Sn, Cd, Mn, Ge, and Zn are used to replace Pb. In particular, (PA)₂(MA)₂Zn₃I₁₀ possesses the largest Stokes shift and Huang-Rhys factor, while showing the best photoluminescence tendency and broadest emission nature. (PA)₂(MA)₂Ge₃I₁₀ displays the most excellent of carrier transport capacities with high mobilities of 73 cm² V⁻¹ s⁻¹ and 43 cm² V⁻¹ s⁻¹ for electron and hole carriers, respectively, which are even comparable to that of 3D counterparts. Furthermore, (PA)₂(MA)₂Zn₃I₁₀ is predicted to have the highest power conversion efficiency of 23.36% based on an empirical energy loss (0.5 eV), which is quite close to the Shockley–Queisser limit, thereby featuring it as a suitable absorber for photovoltaic applications. These findings shed light on new strategies for designing and developing lead-free 2DRP metal halides targeted at future applications in photovoltaic solar cell devices.     

Giant photoresponsivity of transfer free grown fluorographene – MoS2 heterostructured ultra-stable transistors

Development of metal dichalcogenides based air and water stable opto-electronic devices is a bottleneck in their commercial implementation. Here we address this issue by the direct catalyst-free deposition of fluorographene (FG) protective layer over monolayer MoS₂ (MS), where such an atomic interface is found to be providing enormous photoresponse and chemical stability to the device. Electric field modulated (ionic liquid (IL) electrolyte based top-gated) photodetectors are developed with MS only and FG-MS heterostructure, where the MS photodetector has the responsivity of ~1.3 A/W (with V_GS = 0 V while unstable with IL gating) while that of FG-MS is ~2000 A/W (with V_GS = 0 V and ~8000 A/W with V_GS = 1.5 V, and the detectivity ~10¹³). This giant photoresponse of the FG-MS is validated with the help of ultrafast transient absorption spectroscopy assisted charge carrier dynamics studies at different temperatures. The broad optical response (350–850 nm) of the FG-MS is found to be intact not only in IL based gating but also after exposing in water for a month or heat treated in air at 200 °C. Interfacing and capping with FG, developed via the direct growth method, are found to be ideal for realizing high shelf-life and good responsivity photodetectors and solar cells of several other monolayer TMDs too, while available for wafer-scale manufacture.