Hydrogen permeation properties of Pd-coated Ni−Nb−Ti−Zr amorphous alloys

Hydrogen permeability of Pd-coated Ni₆₀Nb₁₅Ti₁₅Zr₁₀ and Ni₆₀Nb₂₀Ti₁₅Zr₅ amorphous alloys was measured in the temperature range of 673 K to 773 K and was compared with the results obtained using Ni₆₀Nb₄₀, a binary amorphous alloy. The permeability thus measured was found to increase moderately increasing temperature. A long-term permeation test for the Pd-coated Ni₆₀Nb₁₅Ti₁₅Zr₁₀ amorphous alloy revealed high permeation stability up to 16.6 h.     

Embrittlement of Pd-coated Ni−Nb−Ti−Zr amorphous alloys during hydrogen permeation

In this study, we report results of an investigation into the failure of Ni₆₀Nb₁₅Ti₁₅Zr₁₀ amorphous alloys occurring during hydrogen permeation performed at 473 K and 573 K. However, the amorphous membrane did not fail during test performed at higher temperatures (673 K and 773 K). The failure of the Pd-coated Ni₆₀Nb₁₅Ti₁₅Zr₁₀ amorphous ribbon is attributed to the cracking of the hydrogenated Pd coating induced by the formation of α′ hydride phase in the low temperature range. 0     

Cold resistance of low-carbon Mn−Ni−Mo−V steels for pressure vessels

Conclusions  

Pretreatment-free Ni−P plating on magnesium alloy at low temperatures

Electrochemically promoted electroless plating (EPEP) was used for the application of pretreatment-free Ni?P coating on AM60B magnesium alloy at low temperatures and the obtained coating was characterized by SEM, AFM, EDS and XRD techniques. Compact, uniform, and medium-phosphorus Ni?P coating with mixed crystalline?amorphous microstructure was obtained by applying a cathodic current density of 4 mA/cm² at 50 °C. Also, island-like nickel clusters were deposited on the alloy surface under the same plating condition but without applying the cathodic current. In addition, the durability of the magnesium alloy against corrosion was strongly improved after plating via EPEP technique which was revealed by electrochemical examinations in 3.5% NaCl (mass fraction) corrosive electrolyte. The results of the electrochemical examinations were confirmed by microscopic observations. Thickness, microhardness, porosity and adhesive strength of the deposits were also qualified.     

Ag−P

Tear Out PagesAlloy Phase Diagrams

Ag−P     

Phase transformation behavior and shape memory characteristics of Ti−Ni−Si alloys

Transformation behavior, microstructures and shape memory characteristics of Ti−(50−X)Ni−XSi (X=2, 4, 6 at.%) and (50−X)Ti−Ni−XSi (X=2, 5, 7, 10 at.%) alloys were investigated by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, electrical resistivity measurements and constant load thermal cycling tests. Ti₅Si₃, Ni₁₆Ti₆Si₇ and Ni₄Ti₄Si₇ were formed in Ti−(50−X)Ni−XSi alloys, while Ti₅Si₄, Ni₃Si, Ni₃Ti₂ and Ni₃Ti₂Si were found in (50−X)Ti−Ni−XSi alloys. The total amount of silicides increased with increasing Si content, irrespective of Si content. The B2→B19 transformation occurred in Ti−(50−X)Ni−XSi alloys, and their transformation temperatures appeared to be almost constant. Transformation elongation associated with the B2→B19 transformation decreased with increasing Si content. In contrast to Ti−(50−X)Ni−XSi alloys, a transformation accompanied with structural change did not occur in (50−X)Ti−Ni−XSi alloys.     

Effect of thermal treatment and ball milling on microstructure and phase transformation of Ni−Mn−Ga−Nb alloys

To clarify phase transformation evolution of Nb-doped Ni−Mn−Ga bulk alloys after aging and ball milling, the microstructure and phase transformation of the aged and ball-milled dual-phase Nb-doped Ni−Mn−Ga alloys were investigated by SEM, EDS, XRD, DSC and susceptibility measurements. The as-cast alloys were mainly composed of the second phase with layer-shape and presented a reduced martensitic transformation with increasing the second phase content. The second phase transformed from layer-shape to dense bar-shape and the martensitic transformation was enhanced after being quenched at 1173 K. After aging at 673 and 873 K, the 3% Nb alloy with less second phase exhibited a single-step phase transformation, whereas the 6% Nb and 9% Nb alloys with more second phase exhibited a two-step martensitic transformation and Curie transition. The martensitic transformation and Curie transition of the as-milled dual-phase particles disappeared and were retrieved after annealing at 1073 K due to the recovery of high ordered structure of the matrix.     

Formation of reversed austenite during tempering of 14Cr−7Ni−0.3Nb−0.7Mo−0.03C super martensitic stainless steel

Reversed austenite transformation and existence of retained austenite during tempering of the super martensitic stainless steel of Fe-14Cr-7Ni-0.3Nb-0.7Mo-0.03C were studied by means of experiments on microstructure and X-ray diffraction, and tensile and hardness tests. Acicular type retained austenite at the lath boundary of martensite with the interior appeared after solution annealing. This retained austenite still existed, and reversed austenite was not formed, with tempering up to 24h at 450°C. The reversed austenite began to form above 550°C, and the volume fraction of reversed austenite decreased with increasing tempering temperature after showing a maximum value of 19.2% at 650°C. This maximum volume fraction of reversed austenite was responsible for the lowest value of strength and hardness. The Ni contents of plate type reversed austenite and the surrounding matrix increased and decreased respectively, implying that the reversed austenite was formed as a result of nickel diffusion. The orientation relationships between reversed austenite and the surrounding matrix showed a K-S relationship of and.     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Electrodeposition and corrosion behavior of Zn−Ni−Mn alloy coatings deposited from alkaline solution

The potentiostatic electrodeposition of Zn−Ni−Mn was carried out in an alkaline solution with the addition of Mn salt. The effects of electrolyte Mn²⁺ concentration and deposition potential on the surface morphology, phase structure and corrosion behavior of coatings were studied. The results of corrosion polarization showed that the presence of higher Mn content in Zn−Ni−Mn coatings could lead to the formation of a good passive layer with a 7-fold increase in R_p of coating and a significant decrease in the corrosion current density compared to those of Zn−Ni coating. The XRD and the XPS analyses from the surface of Zn−Ni−Mn after corrosion test showed that the passive layer was composed of zinc hydroxide chloride, zinc oxide, zinc hydroxide carbonate, and manganese oxides.     

Effect of composition and heat treatment on the structure and properties of Fe−Ni−Be invar alloys

Conclusions Addition of Be (0.5–1%) to Fe–Ni invar alloys provides dispersion hardening after quenching and aging, with retention of a low (close to invar) value of LCTE. Increase of the Be concentration in alloy 36N is accompanied by an increase in LCTE in the quenched as well as the aged condition, and increase of the Ni concentration to 38–41% at a fixed concentration of Be leads to a decreased value of LCTE in the aged alloys, approaching that of the alloy 36N. The optimum composition range for Fe–Ni–Be alloys in which the best combination of properties can be obtained — low value of LCTE (3.10^–6, K^–1) and higher strength (_0.2910 N/mm², _u1100 N/mm²) — was determined to be (39–40% Ni, 0.7–0.8% Be). The alloy 40NL (40% Ni, 0.8% Be) is proposed as a high strength invar alloy.I. P. Bardin Central Scientific-Research Institute for Ferrous Metallurgy (TsNIIChERMET). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 33–36, February, 1992.     

New Fe−Co−Ni−Cu−Al−Ti Alloy for Single-Crystal Permanent Magnets

A new alloy intended for single-crystal permanent magnets has been suggested. The new alloy has been designed based on the well-known Fe?Co?Ni?Cu?Al?Ti system and contains to 1 wt % Hf. The alloy demonstrates an enhanced potential ability for single-crystal forming in the course of unidirectional solidification of ingot. Single-crystal permanent magnets manufactured from this alloy are characterized by a high level of magnetic properties. When designing the new alloy, computer simulation of the phase composition and calculations of solidification parameters of complex metallic systems have been performed using the Thermo-Calc software and calculation and experimental procedures based on quantitative metallographic analysis of quenched structures. After the corresponding heat treatment, the content of high-magnetic phase in the alloy is 10% higher than that in available analogous alloys.     

Microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler alloy

The influence of brazing temperature and brazing time on the microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler was investigated using SEM, EDS, XRD and universal testing machine. Results show that all the brazed joints mainly consist of four reaction layers regardless of the brazing temperature and brazing time. The thickness of the brazed seam and the average shear strength of the joint increase firstly and then decrease with brazing temperature in the range of 1090−1170 °C and brazing time varying from 0 to 20 min. The maximum shear strength of 262 MPa is obtained at 1150 °C for 10 min. The brittle Al₃NiTi₂ and TiNi₃ intermetallics are the main controlling factors for the crack generation and deterioration of joint strength. The fracture surface is characterized as typical cleavage fracture and it mainly consists of massive brittle Al₃NiTi₂ intermetallics.     

Microstructure of carbide precipitates in L12−Ni3Al and L10−TiAl

The crystallographic structures of carbide formed in Ni₃Al- and TiAl-based intermetallics containing carbon are investigated in this study using transmission electron microscopy. In an L1₂-ordered Ni₃Al alloy with 4 mol.% of chromium and 0.2 mol.% to 3.0 mol.% of carbon, fine octahedral precipitates of M₂₃C₆ type carbide were formed in the matrix by aging at temperatures around 973 K after solution annealing at 1423 K. TEM examination revealed that the M₂₃C₆ phase and the matrix lattices have a cube-cube orientation relationship and maintain partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the M₂₃C₆ precipitates adopt a rod-like morphology elongated parallel to the <100> directions. In L1₀-ordered TiAl containing from 0.1 mol.% to 2.0 mol.% carbon, TEM observations reveal that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the L1₀ matrix appear in the matrix mainly at dislocations. Selected-area electron diffraction (SAED) patterns analyses showed that the needle-shaped precipitate is perovskite-type Ti₃AlC. The orientation relationship between the Ti₃AlC and the L1₀ matrix was found to be (001)_Ti3AlC//(001)_{L10 matrix} and [010]_Ti3AlC//[010]_{L10 matrix}. By aging at higher temperatures or for a longer period at 1073 K, plate-like precipitates of Ti₂AlC with a hexagonal structure form on the {111} planes of the L1₀ matrix. The orientation relationship between the Ti₂AlC and the L1₀ matrix is (0001)_Ti2AlC//(111)_{L10 matrix} and Ti2AlC//L10 matrix.     

Formation of pre-silicide layers below Ni1−xPtxSi/Si interfaces

The formation of a pre-silicide layer below Ni_1?xPt_xSi films is reported with structure and composition distinctly different from previously observed diffusion layers. It was found that during two-step rapid thermal annealing Ni interstitial diffusion can kinetically dominate over the formation of Ni silicide, which results in a metastable pre-silicide layer. Aberration corrected scanning transmission electron microscopy experiments have revealed Ni to occupy interstitial and substitutional sites in the pre-silicide layer. Rapid thermal annealing and Pt alloying determines the stoichiometry and thickness of the layer, while the point defect configurations give rise to lowering of the associated Schottky barrier heights. The pre-silicide layer effectively limits diffusion of Ni into the substrate and therefore allows for the low-temperature growth of Ni₂Si and NiSi.