In situ surface Raman study of the induced codeposition mechanism of Ni–Mo alloys

The induced codeposition of molybdenum with nickel on a Ni–Cu alloy electrode has been investigated by means of in situ surface Raman spectroscopy to obtain information about the codeposition mechanism during electrodeposition of Ni–Mo alloys. The experimental results show that, in the NiSO₄-free solution, molybdate can only be reduced to a mixture of polyvalent molybdenum oxides and/or hydroxide, while, in the case where NiSO₄ coexisted in the solution, molybdate is first reduced to Mo(IV) oxide, which, as an intermediate, subsequently is reduced to molybdenum in alloy under the catalysis of inducing nickel.     

Crystallization behavior of Mg–Cu–Y amorphous alloy

Amorphous Mg₆₁Cu₂₄Y₁₅ ribbons were manufactured by melt-spinning at wheel speeds in the range 5?C20?ms^?1. The crystallization behavior of amorphous ribbons was investigated by a combination of differential scanning calorimetry (DSC) and X-ray diffractometry. DSC measurements showed that the amorphous ribbons exhibit distinct glass transition temperature and wide supercooled liquid region before crystallization. During continuous heating three exothermic peaks and two endothermic peaks were observed. The characteristic thermodynamic parameters such as T _g, T _x , ??T _x , and T _rg are around 432?C439, 478?C485, 46?C54?K, and 0.55?C0.56, respectively. Isothermal annealing DSC traces for this amorphous alloy, the first crystallization peak showed a clear incubation period and Avrami exponent was found to be 2.30?C2.74, which indicate that the transformation reaction involved nucleation and three-dimensional diffusion controlled growth. Mechanical properties of the as-quenched and subsequently annealed ribbons were examined by Vickers microhardness (HV) measurements. Results showed that microhardness of the as-quenched ribbons were about 309?HV. However, the results also showed that microhardness of the rapidly solidified ribbons increases with the increasing temperature.     

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...     

Electrical resistivity feature of Cu–Sn–(Bi) alloy melts

The temperature dependence of electrical resistivity of Cu–Sn alloys, along with Cu–Sn–Bi alloys, has been investigated in a wide temperature range using the DC four-probe technique. Evidently abnormal changes are observed on ρ–T curves of these alloys. The result reveals that the irreversible and reversible changes on these ρ–Tcurves indicate the existence of the metastable microinhomogeneous structure and microheterogeneous structure (including some short range orders) of the Cu–Sn and Cu–Sn–Bi alloy melts, respectively. Furthermore, the addition of Bi increases the metastable microheterogeneity in the first heating process of Cu–Sn melts.     

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...     

Thermal behavior of the Cu–22.55 at.%Al alloy with small Ag additions

In this study the effect of Ag additions on the thermal behavior of the Cu–22.55 at.%Al alloy was studied using electrical resistivity measurements, in situ X-ray diffractometry, differential scanning calorimetry, and optical microscopy. The results indicated that Ag additions do not change the phase transformations sequence in the studied alloys, but modify its critical temperatures due to a change on entropy of system. It was verified that at the cooling rate of 10 K/min the decomposition of β phase into (α + γ₁) is incomplete, but for lower cooling rates than 1.0 K/min this reaction is completed.     

Electrochemical formation of a cesium–tin alloy in an amide-type ionic liquid

Electrochemical formation of cesium–tin alloys in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing 0.5 M CsTFSA has been studied. Cathodic decomposition of BMPTFSA on a platinum electrode was suppressed by addition of CsTFSA, suggesting that Cs⁺ accumulated on the electrode surface and hindered the reduction of BMPTFSA. Multiple cathodic current peaks were observed on a tin electrode in the ionic liquid. Energy-dispersive X-ray analysis and X-ray diffraction results suggested formation of cesium–tin alloys after potentiostatic cathodic reduction on the tin electrode at room temperature.     

Influence of dose and ion concentration on formation of binary Al–Ni alloy nanoclusters

Colloidal Al–Ni nanoclusters were prepared in an aqueous polyvinyl alcohol solution containing aluminum chloride and nickel chloride as metal precursors, polyvinyl alcohol as a capping agent, isopropanol as a scavenger of hydroxyl radicals, and distilled water as a solvent. Gamma irradiations were carried out in a ⁶⁰Co gamma source chamber at doses up to 100 kGy. The nanocluster properties were characterized by transmission electron microscopy (TEM), UV–visible spectrophotometry, and X-ray diffraction (XRD). By controlling the dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increase of precursor concentration and decreased with increase of dose. This is owing to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.     

Studies of chemical–catalytic formation of Ni–Re (Mo,W)–B alloys

The paper briefly reviews the studies of the processes of formation of Ni–Re–B, Ni–Mo–B, and Ni–W–B triple alloys using the method of chemical–catalytic reduction of metal ions and their properties.     

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.     

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.     

Calorimetric studies of Ag–Sn–Cu dental amalgam alloy powders and their amalgams

The methods of directed crystallization and thermal analysis were used to construct the section Cu_0.19Fe_0.33S_0.48–Cu_0.31Fe_0.23S_0.46 of the liquid–solid diagram of the Cu–Fe–S system. Pyrrhotite solid solution (Fe, Cu)S_1±δ (Poss) and nonstoichiometric isocubanite Cu_1.1Fe_2.0S_3.0 (Icb*) form from melt (L) successively. Isocubanite forms at 970 °C by peritectic reaction L + Poss → Icb*. At 930 °C, peritectic reaction L + Icb* → Iss proceeds with formation of intermediate solid solution with average composition Cu_1.0Fe_1.2S_2.0 (Iss). On the basis of the results from this paper and earlier published works, we built a fragment of liquidus surface for the Cu–Fe–S system in the crystallization field of nonstoichiometric isocubanite and stoichiometric isocubanite CuFe₂S₃ (Icb).     

Effect of morphology and precipitation of Si phase on thermal properties of Al–Si–Mg–Cu foundry alloy

Journal of Thermal Analysis and Calorimetry - In this study, CuAl13?xTax (% mass x?=?1; 1.5; 2; 2.5) shape-memory alloys were produced through arc-melting method. Phase...     

Thermal parameters determination of Co–Al–W as-cast alloy homogenization by DTA analysis

The γ–γ′ Co-based superalloys are newly developed class of refractory alloys which may replace commercial Ni-based superalloys owing to their favorable properties at high temperature. In case of new Co-based superalloys, the heat treatment aims to obtain microstructure composed of appropriate volume fraction of small cuboidal γ′-Co₃(Al,W) precipitates within the γ-Co matrix. However, due to a high tendency to interdendritic segregations of alloying elements, the alloys based on Co–Al–W system should be normally homogenized before further steps of heat treatment (solutionizing and aging). In this study, thermal analysis was applied for determination of temperature range for primary heat treatment of the Co–9Al–9W (at.%). The differential thermal analysis (DTA) measurements were carried out on the thermal analyzer NETZSCH STA 449 F3 Jupiter. On the base of obtained results, respectively, solvus of γ′ phase and solidus temperatures were determined, as well as the thermal range of Co₃W (DO₁₉) phase precipitation. As a consequence, the heat treatment without homogenizing (only solution and aging) was proposed as a most suitable way to obtain beneficial microstructure.     

Effects of Zr addition on solidification characteristics of Al–Zn–Mg–Cu alloy using thermal analysis

The effect of Zr as a grain refiner on the solidification behavior, micro- and macrostructure of a new Al–Zn–Mg–Cu aluminum super-high strength alloy containing high Zn content was studied. The addition of 2 mass% Zr reduced the grain size from 1500 to 190 μm. Moreover, the dendritic structure of the alloy altered from a coarse, elongated and non-uniform morphology to a rosette-like shape and more uniform one. The parameters of liquidus region of cooling curve obtained from thermal analysis were in a good correlation with grain size results. The maximum of first derivative in the liquidus region was introduced beside recalescence undercooling which could predict the grain refinement level even after disappearing of recalescence in the cooling curve. Furthermore, the addition of 1 mass% Zr enhanced fraction of solid in dendrite coherency point from 21 to 31% and lessened the amounts of porosity from 2.3 to 1.4%.     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Electrodeposition of Co–W coatings from boron gluconate electrolyte with a soluble tungsten anode

Conditions were determined in which an active anodic dissolution of tungsten is observed in a borongluconate electrolyte used to obtain Co–W coatings (pH ~6.5) and the nature of critical currents of transition to the passivation was found, which makes it possible to use the tungsten anode as a soluble electrode. The anodic dissolution of tungsten occurs under these conditions with a current efficiency of 90–100%, which, in contrast to the case of a graphite anode, does not lead to an additional oxidation of the electrolyte components and polymerization in solution; in combination with the decrease in the concentration of tungstate ions, this reduces the electrolyte performance. It was shown that the use of a soluble tungsten anode in obtaining nanocrystalline cobalt–tungsten coating can improve the electrolyte performance due to the rise in the current efficiency of electrodeposition and to the increase in the microhardness of the coatings in comparison with the case of an insoluble graphite anode.