Effect of Ti-Zr addition on the microstructure and the arc chopping current of melt-spun CuCr ribbon

The microstructure and the arc chopping current of melt-spun Cu₇₁Cr₂₉ ribbon added by Ti-Zr are studied in the article. The results reveal that the melt spinning could partly restrain the liquid phase separation of CuCr alloys because it has a high cooling rate (about 10⁶ K/s), the size of the Cr rich phase from liquid phase separation in the Cu₇₁Cr₂₉ microstructure can be decreased from the micron-scale to about 250 nm by using melt spinning. On the melt-spun base, alloying by Ti-Zr could further decrease the size of the Cr rich phase from 250 nm to about 100 nm. For nano-grained CuCr alloys, its lower arc chopping current is advantageous to the use of contact and the circuitry protect, its long arc trace route and high velocity of spot direction motion could mitigate the partial ablate of cathode surface and the lifetime of contact could be prolonged.     

Synthesis of CuCr and CuCrAg alloy with nano-ceramic dispersion by mechanical alloying and consolidation by laser assisted sintering

Cu-4.5Cr and Cu-4.5Cr-3Ag (in wt%) alloys without or with 10 wt% nanocrystalline Al₂O₃ and ZrO₂ dispersion have been synthesized by mechanical alloying or milling and consolidated by laser assisted sintering in Ar atmosphere. Microstructural characterization by scanning and transmission electron microscopy and phase analysis by X-ray diffraction suggest that the alloyed matrix undergoes significant grain growth after sintering while the dispersoids retain their ultrafine size and uniform distribution in the matrix. The dispersion of nano-Al₂O₃ is more effective than that of nano-ZrO₂ in enhancing the mechanical properties due to the smaller initial particle size of Al₂O₃ than that of ZrO₂. In general, laser sintering of mechanically alloyed Cu-4.5Cr and Cu-4.5Cr-3Ag alloys with 10 wt% nanocrystalline Al₂O₃ at 100 W laser power and 1-2 mm s⁻¹ scan speed yields the optimum combination of high density (7.1-7.5 mg m⁻³), hardness (165-225 VHN), wear resistance and electrical conductivity (13-20% IACS).     

Synthesis and structural properties of Ni–20Cr–2Y2O3 nanocomposite alloy prepared by a very high energy mechanical milling

Ni–20Cr–2Y₂O₃ nanocomposite alloys were synthesized by a very high energy ball milling (applied milling energy, ∼180 kJ g⁻¹ hit; milling speed, ∼1000 rpm) using the coarse yttria (Y₂O₃; ∼50 μm) starting powders, and their formation behavior was investigated with particular attention paid to Y₂O₃ particles. Homogeneous Ni–20Cr–2Y₂O₃ nanocomposite alloy powders were achieved in a short milling time of 40 min; the Cr elements were almost fully alloyed into the Ni lattice, and simultaneously the original coarse cubic Y₂O₃ particles were transformed into extremely fine monoclinic nanocrystals. Thermal consolidation by spark plasma sintering induced homogeneous precipitations of the Y–Cr–O nano-clustered oxides (mean diameter d_m ∼12 nm), which were identified as an orthorhombic YCrO₃ structure (space group Pnma, a = 0.5523 nm).     

Electrochemical properties of (La1−xTix)0.67Mg0.33Ni2.75Co0.25 (x = 0-0.20, at%) hydrogen storage alloys

(La_1−xTi_x)_0.67Mg_0.33Ni_2.75Co_0.25 (x = 0, 0.05, 0.10, 0.15 and 0.20, at%) alloys are synthesized by arc-melting and subsequent heat solid-liquid diffusing techniques, and the crystalline structures and electrochemical properties of the alloys are investigated systematically. The structural analysis results show that all the alloys mainly consist of (La, Mg)Ni₃ phase with the rhombohedral PuNi₃-type structure and LaNi₅ phase with the hexagonal CaCu₅-type structure. However, when the Ti content is higher than 0.10, a little amount of TiNi₃ phase start to form. Electrochemical measurements show that the alloy electrodes could be activated to their maximum discharge capacity within four cycles, the maximum discharge capacity is around 321.9-384.6 mAh g⁻¹, both the cyclic stability and the high-rate discharge ability first increased and then decrease with increasing x. All the results show that a little amount of Ti substitution for La in AB₃-type hydrogen storage alloys is effective to the improvement of the overall electrochemical properties.     

Devitrification of Zr-Ni-Al-Cu-Ti(Nb,Ta) glassy alloys

The devitrification behavior and phase formation in Zr_65-55Ni₁₀Al_7.5Cu_7.5Ti_5-10(Nb,Ta)_5-10 metallic glass have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. It has been found that mutual addition of Ti and Ta/Nb benefits the formation of nanoscale icosahedral phase in the glassy phase on heating and the oxygen content in the alloy makes significant influence on the devitrification behavior of these alloys. At the same time in Nb-bearing alloys and alloys containing 5 at.% Ta icosahedral phase was found to coexist with crystalline one.     

Synthesis, structural and magnetic studies of the CuCr1−xRhxO2 delafossite solid solution with 0 ≤ x ≤ 0.2

The CuCr_1−xRh_xO₂ series is investigated by X-ray diffraction, magnetization measurements and Raman spectroscopy on ceramic samples. It is found that a delafossite solid solution is maintained up to x = 0.2 in CuCr_1−xRh_xO₂. The small observed variation in cell parameters is consistent with the small difference between the ionic radii of Cr³⁺ and Rh³⁺. A significant broadening of X-ray reflections is observed and when analyzed using the Williamson-Hall relationship showed that the strain generated by Rh substitution is strongly anisotropic, affecting mainly (Cr,Rh)-O bonds in the ab plane. Room temperature Raman spectra displayed three main Raman active modes. All modes shift to lower frequency and undergo significant changes in intensity with increasing Rh content, showing the effect of Rh atoms on the M³⁺-O bond strength. The magnetic behavior of CuCr_1−xRh_xO₂ samples was investigated as a function of temperature and applied field. At high temperature paramagnetic behavior, and at low temperature, evidence for weak ferromagnetism, reinforced by a hysteresis loop at 4 K is observed. The magnetic behavior of CuCr_1−xRh_xO₂ is attributed to the disorder of Cr and Rh in octahedral sites resulting in short-range Cr-O-Cr and Cr-O-Rh interactions, which give rise to short-range weak ferromagnetism.     

Effects of Cr addition on grindability of cast Ti–10Zr based alloys

The present study was undertaken to investigate the microstructure, microhardness and grindability of a series of cast Ti–10Zr–xCr alloys with 1, 3, 5, 7 and 10 wt.% Cr. The grindability of Ti–10Zr and Ti–10Zr–xCr alloys was evaluated by measuring the amount of metal volume removed after grinding for 1 min at each of the four rotational speeds of the wheel (500, 750, 1000 or 1200 m min⁻¹), with the goal of developing a titanium alloy possessing superior grindability than commercially pure titanium (c.p. Ti). The results indicate that the structure of Ti–10Zr–xCr alloys is sensitive to the Cr content. With Cr contents higher than 3 wt.%, the equi-axed β phase began to be retained, while ω phase was found in the Ti–10Zr–3Cr, Ti–10Zr–5Cr and Ti–10Zr–7Cr alloys. The largest quantity of ω phase and the highest microhardness values were found in the Ti–10Zr–5Cr alloy. The grinding rates of the Ti–10Zr based alloys showed a similar tendency to the microhardness. The Ti–10Zr–5Cr alloy exhibited the best grindability, especially at 500, 750 and 1000 m min⁻¹. Its grinding rate at 1000 m min⁻¹ was about 2.6 times that of c.p. Ti, and the grinding ratio was approximately 2.7 times that of c.p. Ti. This study concluded that because Cr can not only harden Titanium, but also improve its grindability, the Ti–10Zr–5Cr alloy has a great potential for use as a dental machining alloy.     

Effect of heat treatment on microstructure and wear behavior of Al–Si alloys with various iron contents

Effect of T6 heat treatment on microstructure and wear behavior of hypoeutectic Al–Si alloys with iron contents of 0.15, 0.7 and 1.2 wt% was studied. Dry sliding wear tests were performed on a pin-on-disk tribometer under normal loads of 20, 30 and 40 N. The alloy with 0.7 wt% iron showed the highest wear resistance before the heat treatment under the loads tested. T6 heat treatment improved the wear resistance of the alloys with different iron contents compared to the non-heat treated 0.7 wt% iron alloy under all applied loads. The improvements in the wear can be attributed to the decrease of length and volume fraction of hard and brittle β-Al₅FeSi iron-rich intermetallics and spherodization of the coarse eutectic silicon particles by diffusion of iron and silicon into the matrix upon solution heat treatment. The change in the morphology of the phase particles reduced the probability of nucleation and propagation of subsurface cracks and increased the wear resistance in the samples.     

The effect of Si additions on the sintering and sintered microstructure and mechanical properties of Ti-3Ni alloy

Thermodynamic predictions suggest that silicon has the potential to be a potent sintering aid for Ti-Ni alloys because small additions of Si lower the solidus of Ti-Ni alloys appreciably (>200 °C by 1 wt.% Si). A systematic study has been made of the effect of Si on the sintering of a Ti-3Ni alloy at 1300 °C. The sintered density increased from 91.8% theoretical density (TD) to 99.2%TD with increasing Si from 0% to 2%. Microstructural examination reveals that coarse particles and/or continuous networks of Ti₅Si₃ form along grain boundaries when the addition of Si exceeds 1%. The grain boundary Ti₅Si₃ phase leads to predominantly intergranular fracture and therefore a sharp decrease in ductility concomitant with increased tensile strengths. The optimum addition of Si is proposed to be ≤1%. Dilatometry experiments reveal different shrinkage behaviours with respect to different Si contents. Interrupted differential scanning calorimetry (DSC) experiments and corresponding X-ray diffraction (XRD) analyses clarify the sequence of phase formation during heating. The results provide a useful basis for powder metallurgy (PM) Ti alloy design with Si.     

Improved activation and hydrogen storage properties of a Mg85Ni15 melt-spun alloy via surface treatment with NH4 solution

An amorphous Mg₈₅Ni₁₅ melt-spun hydrogen storage alloy, processed by submersion in an aqueous solution of NH₄⁺, is able to absorb nearly 5 mass% hydrogen at 473 K during the first hydrogenation cycle. The nanocrystalline microstructure formed during devitrification of the metallic glass is preserved by the lower required activation temperature of the NH₄⁺-treated material compared to the as-spun material; and the kinetics of subsequent absorption/desorption cycles at 573 K are dramatically improved. The material activated at 473 K exhibits a decrease in hydride decomposition temperature by 30 K, observed via DSC and TPD experiments, compared to a sample activated at 573 K. The NH₄⁺-treatment of a glassy alloy presented here provides a practical alternative to ball milling for forming a nanocrystalline material and facilitating activation, requiring much less time and a more commercially scalable option.     

Nanocrystalline Hf and Ta containing FeCo based alloys for high frequency applications

FeCo based nanocrystalline materials have excellent soft magnetic properties even at high temperature, but are limited to low frequency applications due to their relatively low electrical resistivities, ρ_e, resulting in high eddy current losses. Amorphous alloys of (Fe₈₁Co₁₉)₈₄M₉B₇ where M = (Hf, HfTa, Ta) were prepared by meltspinning and annealed for increasing times at their respective crystallization temperatures. The nanocrystalline alloys had coercivities less than 0.4 Oe and saturation inductions greater than 1 T. The electrical resistivities of the amorphous ribbons were all similar with values of ρ_e ? 180 μΩ cm. After annealing at the crystallization temperature, the M = Ta alloy had the largest ρ_e of 140 ± 3 μΩ cm. The Ta alloy also had the best high frequency properties, with an initial permeability of 822 at 1 MHz.     

Phase transitions in alloys of the Ni–Mo system

The structure of Ni–20 at.% Mo and Ni–25 at.% Mo alloys heat treated at different temperatures was studied by the method of transmission electron microscopy. X-ray photoelectron spectroscopy was used to detect the sign of the chemical interaction between Ni and Mo atoms at different temperatures. It is shown that at high temperatures the tendency toward phase separation takes place. The system of additional reflections at positions {1 ½ 0} on the electron diffraction patterns testifies that the precipitation of crystalline bcc Mo particles begins in the liquid solution. At 900 °C and below, the tendency toward ordering leads to the precipitation of the particles of the chemical compounds. A body-centered tetragonal phase Ni₄Mo (D1_a) is formed in the Ni–20 at.% Mo alloy. In the Ni–25 at.% Mo alloy, the formation of the Ni₃Mo (D0₂₂) chemical compound from the A1 solid solution has gone through the intervening stage of the Ni₄Mo (D1_a) and Ni₂Mo (Pt₂Mo) formation.     

Growth of single-phase CuInGaSe2 photo-absorbing alloy films by the selenization method using diethylselenide as a less-hazardous Se source

Selenization growth of purely single-phase, polycrystalline CuIn_1 − xGa_xSe₂ (0 ≤ x ≤ 1) alloy films was demonstrated using a less-hazardous metalorganic selenide, diethylselenide [(C₂H₅)₂Se: DESe], without additional thermal annealing. Approximately 2.0-μm-thick films of the alloys exhibited X-ray diffraction peaks originating exclusively from the chalcopyrite structure. Low temperature photoluminescence spectra of the alloy films were dominated by a couple of characteristic donor-acceptor pair emissions that are particular to the state-of-the-art CuInGaSe₂ photo-absorbing layers.     

Effect of P on crystallization behavior and soft-magnetic properties of Fe83.3Si4Cu0.7B12 − xPx nanocrystalline soft-magnetic alloys

The P content dependences of the crystallization behavior, thermal stability and soft-magnetic properties of high Fe content Fe_83.3Si₄Cu_0.7B_12 − xP_x (x = 0 to 8) nanocrystalline soft-magnetic alloys were investigated. P addition is very effective in widening the optimum annealing temperature range and refining of bcc-Fe grain size in addition to the increasing of nanocrystalline grain density. Uniform nanocrystalline bcc-Fe grains with average size of about 20 nm and number density of 10²³-10²⁴ /m³ were prepared at around x = 6-8 for the annealed Fe_83.3Si₄Cu_0.7B_12 − xP_x alloys. The coercivity H_c markedly decreases with increasing x and exhibits a minimum at around x = 6-8, while the saturation magnetic flux density B_s shows a slight decrease. Fe_83.3Si₄Cu_0.7B₆P₆ nanocrystalline alloy exhibits excellent soft-magnetic properties with a high saturation magnetic flux density B_s of 1.77 T, low coercivity H_c of 4.2 A/m and high effective permeability μ_e of 11,600 at 1 kHz.     

Effect of micro-alloying chromium on the corrosion resistance of nanocrystalline nickel aluminide intermetallic produced by mechanical alloying process

In this study, Ni₅₀Al_50 − xCr_x nanocrystalline intermetallic compound was synthesized by using the high energy mechanical milling of pure Ni, Al and Cr elemental powders for 16 h. The morphological investigation was done by using the optical and scanning electron microscope. The corrosion behavior of the samples was studied by using the electrochemical impedance spectroscopy in 3.5% NaCl solution. The results showed that when the micro-alloying Cr content is increased, the particles distribution is modified and the size of particles is decreased. Therefore the passive film which is formed on the surface of samples is less porous, so the corrosion resistance is increased.     

Fabrication of tungsten-based metallic glasses by low purity industrial raw materials

Quaternary W₃₀Fe₃₈B_32−xC_x (x = 5, 7, 10, 13, 15 at.%) alloys have been investigated by melt-spinning method to produce metallic glasses using low purity industrial raw materials. The phase structure of these ribbons is investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The thermal stabilities of W₃₀Fe₃₈B_32−xC_x (x = 5, 7, 10, 13, 15 at.%) alloys are analyzed by differential scanning calorimeter (DSC). It is found that W₃₀Fe₃₈B₂₂C₁₀ metallic glass with 45 μm in thickness and 2 mm width can be successfully fabricated. And other alloys with the same thickness and width as W₃₀Fe₃₈B₂₂C₁₀ alloy are observed with some crystalline peaks on the halo patterns. The DSC measurements show that each alloy undergoes a two-step crystallization with the onset temperature of the first crystallization being as high as 984-1067 K. Vickers hardness and density values of W₃₀Fe₃₈B_32−xC_x (x = 7, 10, 13, 15 at.%) alloys at room temperature are 11.9-12.8 GPa and 14.5 g/cm³ at least, respectively. The effect of C addition on GFA in the W-Fe-B alloy system is discussed.     

Microstructures and mechanical properties of bulk nanocrystalline Fe3Al materials with 5, 10 and 15 wt.% Cr prepared by aluminothermic reaction

Bulk nanocrystalline Fe₃Al based materials with 5, 10 and 15 wt.% Cr were prepared by aluminothermic reaction, in which melts were superheated about 1500 K before solidification. Microstructures of the materials were investigated by optical microscope, electron probe microscope, X-ray diffraction and transmission electron microscope. It was shown that microstructure of the materials consist of nanocrystalline matrix phase, which was composed of Fe, Al and Cr elements, and a small amount of contamination. The nanocrystalline phase was disordered bcc structure, and which did not change with Cr content. Average grain sizes of the nanocrystalline phase of the materials with 5, 10 and 15 wt.% Cr were 33, 21 and 37 nm, respectively. Compressive properties and hardness of the materials were tested. It indicated that the materials had a considerable plastic deformation and were not fractured in compression. Yield strength of the materials were about three times higher but hardness were a little lower than those of Fe₃Al material with coarsen grain. The hardness and yield strength of the materials varied slightly with Cr content and that of the material with 10 wt.% Cr was slightly lower. Average grain sizes of the materials decreased and texture changes appeared after the compression.     

Effect of rare earth Y addition on the microstructure and mechanical properties of high entropy AlCoCrCuNiTi alloys

A series of AlCoCrCuNiTiY_x (x values in molar ratio, x = 0, 0.5, 0.8, 1.0) alloys have been prepared using vacuum arc melting. Classical high entropy diffraction peaks corresponding to a BCC crystal structure and some Cu, Cr peaks are observed for the AlCoCrCuNiTi alloy. However, with the incorporation of rare earth element Y, the BCC diffraction peaks disappeared and were replaced by new compounds like Cu₂Y and AlNi₂Ti. A typical cast dendrite structure with Cu-rich dendritic regions and Cr-rich rosette-like shape precipitations are found in the AlCoCrCuNiTi alloy. In the AlCoCrCuNiTiY_x alloys, Y segregated preferentially to Cu and combined as bulky Cu₂Y compound. The maximum stress of the AlCoCrCuNiTi alloy is 1495 MPa, but reduces intensively after the incorporation of Y due to the formation of bulky Cu₂Y. For all the alloys, the compressive fracture mechanism is observed to be cleavage fracture.     

Effects of Al and Zn additions on mechanical properties and precipitation behaviors of Mg-Sn alloy system

For the Mg-Sn-Al alloys, the ultimate strength (UTS) of an extruded Mg-9wt.%Al-2wt.%Sn alloy reached 390 MPa. TEM observation indicated that plate-like Mg₁₇Al₁₂ precipitates having Burgers orientation relationship with the matrix are responsible for the strength. This alloy also exhibits an age hardening behavior: the peak hardness appears after 15-20 h of heat treatment at 473 K. On the other hand, the UTS of the Mg-Mg-Sn-Zn alloys are on the order of 300 MPa. The precipitates in these alloys are composed of the Mg₂Sn and MgZn₂ particles. It was found that these phases often precipitate together, suggesting that the MgZn₂ phase can act as a nucleation sites for Mg₂Sn.     

Microstructures and mechanical responses of powder metallurgy non-combustive magnesium extruded alloy by rapid solidification process in mass production

Spinning Water Atomization Process (SWAP), which was one of the rapid solidification processes, promised to produce coarse non-combustible magnesium alloy powder with 1–4 mm length, having fine α-Mg grains and Al₂Ca intermetallic compounds. It had economical and safe benefits in producing coarse Mg alloy powders with very fine microstructures in the mass production process due to its extreme high solidification rate compared to the conventional atomization process. AMX602 (Mg–6%Al–0.5%Mn–2%Ca) powders were compacted at room temperature. Their green compacts with a relative density of about 85% were heated at 573–673 K for 300 s in Ar gas atmosphere, and immediately consolidated by hot extrusion. Microstructure observation and evaluation of mechanical properties of the extruded AMX602 alloys were carried out. The uniform and fine microstructures with grains less than 0.45–0.8 μm via dynamic recrystallization during hot extrusion were observed, and were much small compared to the extruded AMX602 alloy fabricated by using cast ingot. The extremely fine intermetallic compounds 200–500 nm diameter were uniformly distributed in the matrix of powder metallurgy (P/M) extruded alloys. These microstructures caused excellent mechanical properties of the wrought alloys. For example, in the case of AMX602 alloys extruded at 573 K, the tensile strength (TS) of 447 MPa, yield stress (YS) of 425 MPa and 9.6% elongation were obtained.