Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process

Metal foams, now one of research foci, are a newclass of materials with low densities and novel physi-cal, mechanical, thermal, electrical and acoustic prop-erties[1—8]. Demands from high-tech make Al alloyfoam, which has much higher specific strength than ofpure Al foam, the new development focus[9—11]. Melt foaming process is one of the approaches tofabricate Al foam and Al alloy foam and their porestructure (pore diameter and porosity) has close rela-tionship with the thermal decompo…     

Thermodynamics and kinetics of hydrogen absorption–desorption of vanadium synthesized by aluminothermy

This paper studies the addition (0–40% w/w) of natural zeolite (NZ, 84% clinoptilolite) in blended cements made with Portland cement (PC) with low and medium C₃A content. The isothermal calorimetry was used to understand the effect of NZ on the early cement hydration. For low C₃A cement, the addition of NZ produces mainly a dilution effect and then the heat released curve is similar to plain cement with lower intensity. For medium C₃A cement, the curve shows the C₃S peak in advance and a high intensity of third peak attributed to C₃A hydration. The high cation fixed of NZ reduces the ions concentration (especially alkalis) in the mixing water stimulating the PC hydration. The flowability decreases when the NZ replacement level increases. Results of Fratini’s test show that NZ with both PCs used presents slow pozzolanic activity. At early age, XRD and FTIR analyses confirm that hydration products are the same as that of the corresponding PC and the CH is progressively reduced after 28 days and some AFm phases (hemi- and monocarboaluminate) appear depending on the NZ percentage and the PC used. For low replacement levels, the compressive strength is higher than the corresponding PC from 2 to 28 days. For high replacement levels, the early compressive strength is lower than that of corresponding plain PC and the pozzolanic reaction improves the later compressive strength of blended cements.     

Anodizing parameters optimization of Ti–6Al–4V titanium alloy using response surface methodology

The present paper depicts application of response surface methodology (RSM) for optimizing the anodizing parameters of Ti–6Al–4V (TA6V) titanium alloy. Three operating parameters, i.e., voltage (V), temperature (T) and time (t), are designed as factors by using RSM design. Reliable regression models were established between the input parameters and the given responses, namely oxide thickness (e), Vickers hardness (Hv) and polarization resistance (R_p) with regression coefficients multiples of 0.940, 0.925, 0.865, respectively, indicating good agreement between the experimental values and those predicted using the quadratic model.The predicted values of V (42.67 V), t (45.9 min) and T (29.5 °C) are the optimal anodization combination leading to a TiO₂ layer with the best compromise between the oxide thickness (28.7 μm), Vickers hardness (321.90) and bias resistance (6.37 MΩ cm²). It was observed that the hardness characteristic is more affected by anodizing time and temperature, and less sensitive to voltage and parameter interactions. Polarization resistance is strongly influenced by voltage, modestly influenced by anodizing time and temperature, and less sensitive to parameter interactions. Moreover, higher anodizing parameters lead to higher thickness. Therefore, RMS could be a suitable method to optimize anodizing parameters of titanium alloys.     

Crystallisation kinetics and structure of modified Zn–Al–Cu alloys

The present paper reports induced glass transition dynamics appeared in porous silica (PSi) and nonporous silica (NPSi) nanoparticles. The size of these spherical particles is 5–15 nm for PSi and 15–20 nm for NPSi. PSi shows two glass transitions (Tg1 and Tg2) on heating, whereas NPSi shows one glass transition (Tg). The NPSi shows Tg at a higher temperature than PSi. PSi shows an exothermic transition on cooling, whereas NPSi shows no transition on cooling. Both Tgs appeared in PSi show dynamic behavior with the existence of positive activation energy. Both Tgs are reversible in PSi, whereas NPSi shows only one and irreversible Tg. The observed glass transitions in PSi and NPSi follow the configuron percolation model and show thermodynamic quasi-equilibrium with percolation threshold (fc) <1. The silica nanoparticles show induced glass transitions because of the presence of weak hydrogen bonds (HB) and a weak van der Waal force present in PSi, whereas the lack of porosity in NPSi shows irreversible Tg with stronger HB. The porosity of PSi makes it more reactive and dynamic due to its capillary behavior and shows its applicability in medical sciences, whereas the stability of NPSi makes it important for industrial research.     

Crystallization behavior of ternary γ–γ′ Co–Al–W alloy

Journal of Thermal Analysis and Calorimetry - In the investigation, crystallization behavior of ternary γ–γ′ alloy based on Co–Al–W system was analyzed. The alloy...     

Influence of Sr addition on microstructure of the hypereutectic Zn–Al–Cu alloy

Journal of Thermal Analysis and Calorimetry - The purpose of the presented work is to answer the questions: how does the addition of strontium to the Zn–8Al–1Cu alloy crystallisation...     

Mechanoelectrochemical synthesis and properties of porous nano-Ti–6Al–4V alloy with hydroxyapatite layer for biomedical applications

Formation of porous morphology in nanocrystalline mechanically alloyed and electrochemically etched Ti–6Al–4V biomedical alloy was investigated. The alloy was electrochemically etched in a mixture of H₃PO₄ and HF. The electrochemical etching results in broad range from micro(nano)-macropores formation in the surface layer, with diameter in the range of 3 nm–60 µm. On the etched surface hydroxyapatite was electrochemically deposited by using 0.042 M Ca(NO₃)₂ + 0.025 (NH₄)₂HPO₄ + 0.1M HCl electrolyte. In this way bioactive surface was prepared. The pores in the surface acts as anchors for the hydroxyapatite, which grows inside them. Due to the porous morphology, the etched as well as HA deposited surface is promising for hard tissue implant applications. The nanocrystalline alloy has a nanohardness and Young modulus in the range of 993–1275 HV and 137–162 GPa, respectively.     

Potentiostatic versus galvanostatic electrodeposition of nanocrystalline Al–Mg alloy powders

Nanocrystalline supersaturated dendritic Al–Mg powders were electrodeposited using potentiostatic and galvanostatic techniques under equal-charge conditions. In potentiostatic deposition morphology depended on applied potential: featherlike at lower and globular at higher potentials. Galvanostatic deposits yielded both morphologies at any current density. Morphological evolution was observed in galvanostatic deposits from featherlike to globular. Independent of deposition technique face-centered cubic Al(+Mg) phase with ∼7 atom% Mg (featherlike) with/without ∼20 atom% Mg (smooth globular) composition formed at lower applied/realized potentials (or deposition rates). Higher applied/realized potentials showed hexagonal close packed Mg(+Al) phase with ∼80 atom% Mg (rough globules) over smooth globules. Potentiostatic and galvanostatic deposits were compared for their morphologies, phases, and compositions.     

Evolution of Fe-based intermetallic phases during homogenization of Al–Fe hypoeutectic alloy

Journal of Thermal Analysis and Calorimetry - Homogenization heat treatment is the first step in the processing of aluminium alloys, which for most alloys is carried out before any deformation...     

Transport Coefficients of Hydrogen and Argon–Hydrogen Plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of hydrogen and mixtures of argon and hydrogen at high temperatures are presented. Combined ordinary, pressure, temperature, and electric field diffusion coefficients are also given for the mixtures. The calculations, which assume local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30,000 K. The results are compared with those of previously published studies. Generally, the agreement is reasonable; those discrepancies that exist are attributed to the improved values of some of the collision integrals used here in calculating the transport coefficients.     

Electrochemical performance of Mg–9Al–1Zn alloy in aqueous medium

A systematic study on the corrosion and passivation behavior of AZ91D alloy in relation to the influence of concentration, temperature, pH, and immersion time was made in aqueous sulfate solution using electrochemical techniques including open-circuit potential, potentiodynamic polarization and impedance spectroscopy. It was found that the corrosion and pitting potentials (E _corr and E _pit) of the alloy drift to more active values with increasing either concentration (0.01–1.0 M) or temperature (278–338 K) of the test solution, suggesting that sulfate solution enhances the alloy dissolution, particularly at higher temperatures. On the other hand, values of the total film resistance (R _T) indicate that neutral solution (pH 7.0) supports the formation of a better protective layer on AZ91D surface than alkaline (pH 12.5) or acidic (pH 1.0) medium. The growth of a protective film on the alloy surface at short immersion times (up to ∼50 h) is evinced by a rapid positive evolution of E _corr and fast decrease in the corrosion rate (i _corr). However, for a long-term exposure (up to 500 h) E _corr drifts negatively and i _corr increases due to breakdown of the protective film, which causes a decrease in the alloy stability. Fitting the impedance data to equivalent circuit models suitable to each behavior assisted to explore the mechanism for the attack of the sample surface at various testing times. The results obtained from the three studied electrochemical techniques are in good agreement.     

Computer-aided cooling curve thermal analysis of near eutectic Al–Si–Cu–Fe alloy

The effects of bismuth (Bi), antimony (Sb) and strontium (Sr) additions on the characteristic parameters of the evolution of aluminium dendrites in a near eutectic Al–11.3Si–2Cu–0.4Fe alloy during solidification at different cooling rates (0.6–2 °C) were investigated by computer-aided cooling curve thermal analysis (CA-CCTA). Nucleation temperature ( $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ ) is defined with a new approach based on second derivative cooling curve. The results showed that $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ increased with increasing cooling rate but both the growth temperature ( $ T_{\text{G}}^{{\alpha {\text{ - Al}}}} $ ) and the coherency temperature (T _DCP) decreased. Increase in the temperature difference for dendrite coherency ( $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} - T_{\text{DCP}} $ ) with increasing cooling rate indicate a wider range of temperature before the dendrite can impinge on each other and higher fraction solid ( $ f_{\text{S}}^{\text{DCP}} $ ). Additions of Bi, Sb and Sr to the base alloy produced only a minor effect on $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ . Additions of Bi and Sb resulted in an increase in fraction solid and an increase of 30 % in the value of $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} \, - \,T_{\text{G}}^{{\alpha {\text{ - Al}}}} $ to almost 13 °C.     

Effect of grain refinements on the microstructure and thermal behaviour of Mg–Li–Al alloy

Journal of Thermal Analysis and Calorimetry - The light as-cast Mg–9Li–1.5Al alloys were manufactured and modified by 0.2 mass% Zr, commercial 0.2 mass% TiBor and 0.2 mass% AlSr master...     

Effects of vanadium and cadmium on transformation temperatures of Cu–Al–Mn shape memory alloy

Cu-based quaternary shape memory alloys were extensively investigated alloy in last decade. In this study, Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were produced by arc melting. We have investigated the effects of the alloying elements on the characteristic transformation temperatures, variations in structure and microstructure. The characterization of the transformation temperatures was studied by the differential scanning calorimetry. It was observed that the addition of the vanadium and cadmium decreases the characteristic transformation temperatures. The structural changes of the samples were studied by X-ray diffraction measurements and optical microscope observations. The crystal structure of the martensite Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were identified as M18 at room temperature. The crystallite sizes of the alloys were determined. The microstructure of the alloy was studied with the help of optical microscope and V-type martensites with different orientations were detected. Microhardness value of the alloys were found between 194 and 211 Hv.