Effect of technological parameters on the mutual penetration of copper and iron in laser cladding of steel with a copper–nickel alloy

A copper–nickel alloy was deposited on steel using a powerful fibre laser. Beads of different height and width were produced by varying the process parameters. The results of metallographic examination show that at optimum cladding conditions there are areas of unmelted steel. In areas where the steel is melted the penetration depth, the width of the transition zone from steel to copper, the depth of penetration of the cracks caused by the Rehbinder effect and the content of the iron phase in the copper layer are lower than in other conditions.     

Structural evolution and phase formation in cold-rolled aluminum–nickel multilayers

Multilayer samples of nickel and aluminum with the compositions of Al–20 at% Ni and Al–25 at% Ni were prepared by the repeated folding and cold rolling (F&R) of elemental foils. Characterization by X-ray diffraction, scanning electron microscopy and transmission electron microscopy/selected-area electron diffraction reveals that the rolling procedure results in a decrease in thickness of the elemental layers to below 0.1 μm and a reduction in grain size to below 50 nm, but does not induce formation of an intermediate phase. Differential scanning calorimetry (DSC) measurements on samples subjected to different numbers of F&R cycles show double exotherms related to an initial nucleation and lateral growth and a subsequent thickening of reactively formed Al₃Ni. The DSC data agree qualitatively with predictions of an existing kinetic model for multilayer reactions, but a decisively improved quantitative fit is obtained when a distribution of layer spacings is considered, rather than a well-defined modulation wavelength. The modified kinetic model can be inverted to yield information on the evolution of the distribution of layer sizes during deformation from DSC data.     

Hydrogen absorption and desorption in a B2 single-phase Ti–22Al–27Nb alloy before and after deformation

The effects of deformation on the hydrogen absorption/desorption behavior of a B2 single-phase Ti–22Al–27Nb (at.%) alloy were investigated mainly by measuring the static pressure–composition (P–C) isotherms from room temperature to 100°C for specimens quenched from 1200°C and deformed to 5–∼90% in compression or by cold-rolling. β hydride is formed at a very low hydrogen pressure similarly to bcc hydrogen absorbing alloys. In as-quenched specimens, further absorption to γ hydride is sluggish and there is no obviously reverse γ→β hydride transformation. Both the β→γ and reverse γ→β hydride transformations are promoted by deformation. The best hydrogen absorption/desorption properties are attained in specimens deformed to 5–10%, the deformation structure of which consists of well-aligned and uniformly distributed <111> screw dislocations. The beneficial effects of deformation on the hydrogen absorption/desorption behavior of the alloy are interpreted in terms of similarities between atomic displacements around straight screw dislocations and those taking place during the β–γ hydride transformation.     

Microstructures and properties analysis of dissimilar metal joint in the friction stir welded copper to aluminum alloy

This paper mainly concentrated on the feasibility of friction stir welding of dissimilar metal of aluminum alloy to copper （I2） and a preliminary analysis of welding parameters influencing on the microstructures and properties of joint was carried out. The results indicated that the thickness of workpiece played an important role in the welding parameters which could succeed in the friction stir welding of dissimilar metal of copper to aluminum alloy, and the parameters were proved to be a narrow choice. The interfacial region between copper and aluminum in the dissimilar joint was not uniformly mixed, constituted with part of incomplete mixing zone, complete mixing zone, dispersion zone and the most region＇ s boundary was obvious. Meantime a kind banded structure with inhomogeneous width was formed. The intermetallic compounds generated during friction stir welding in the interfacial region were mainly CugAl4, Al2Cu etc, and their hardness was higher than oihers.     

Structure formation and properties of a copper–aluminum joint produced by ultrasound-assisted explosive welding

The effect of ultrasound-assisted explosive welding on the structure formation and the properties of copper–aluminum joints is studied. Ultrasound-assisted explosive welding improves the quality of formed copper–aluminum joints, i.e., enhances their strength and significantly reduces the amount of fused metal over the entire weldability range. It is shown that ultrasound-assisted explosive welding can noticeably extend the weldability range of the copper–aluminum pair to obtain equal-in-strength joints with minimum structural heterogeneity in the wide welding range.     

Effect of barium on the refinement of primary aluminum and eutectics in a hypoeutectic Al-Si alloy

The effect of barium on the refinement of primary aluminum and on the modification of eutectics in a hypoeutec-tic aluminum-silicon alloy was investigated. The results indicate that barium not only modifies the eutectic silicon but also refines the primary aluminum and there is a relationship between the retained barium and the second spacing of primary aluminum. Experiments of barium-treated commercial Al-Si hypoeutectic alloy show that barium is a better modifier than sodium when there is a longer holding time.     

Cavity formation and early growth in a superplastic Al–Mg alloy

Knowledge of the exact physical mechanism of cavity formation and early growth is important for the prediction of the extent of internal damage following superplastic deformation. To this end, the early stages of cavitation in a superplastic Al–Mg–Mn–Cu alloy have been experimentally studied and reported here. Small cavities (<0.5 μm) were detected by scanning electron microscopy and the number of cavities per unit volume was monitored by image analysis through optical microscopy. Before deformation, some cavities were seen at the particle–matrix interfaces. However, during tensile deformation in the temperature range of 450–550°C (and strain rates ∼10⁻⁴ to 10⁻² s⁻¹), additional cavities emerge and grow. Most cavities are observed at the interface between particles and the matrix from submicrometer size range, and grow initially along the interface. This suggests that early cavity growth is by matrix/particle decohesion, possibly starting from interfacial defects, and this growth has rapid kinetics. The density of observable cavities increases with strain, i.e. “nucleation” is continuous. The number of cavities increases at higher strain rates and at lower test temperatures. This is due to the higher flow stresses, reduced strain-rate sensitivity and poorer diffusional accommodation process, which assist in the initial growth of the submicrometer and nanoscale interface defects. But the evidence for diffusional cavity growth in the initial stages was not found.     

A study of the diffusion zone in steel 07Kh16N6 and granulated nickel alloy ÉP741NP formed in the process of hot isostatic pressing

Conclusions  

Corrosion and anodic oxidation of copper in 1-butyl-3-methylimidazolium bromide–copper(II) bromide ionic liquid

Using the gravimetric and polarization methods, the corrosion behavior of copper in 1-butyl-3-methylimidazolium bromide (BMImBr) ionic liquid in its pure state and with additions of CuBr₂ (from 0.4 to 1.2 mol kg^–1) has been investigated. It is found that the corrosion in naturally aerated BMImBr ionic liquid is accompanied by oxygen depolarization. Copper dibromide in BMImBr–CuBr₂ ionic liquid plays the role of an oxidant, and the rate of copper corrosion in this case is higher by about an order of magnitude than for the pure ionic liquid. The method of cyclic voltammetry shows that the anodic dissolution of copper in BMImBr–CuBr₂ ionic liquid proceeds via the EC mechanism. It is shown that the chemical-reaction rate of dissolving the surface layer and the rate of copper corrosion (according to gravimetric and polarization data) are comparable. Copper corrosion in the studied ionic liquid is accompanied by the effect of surface polishing, as is confirmed by the atomic force microscopy and profilography.     

Defects caused by precipitation of in liquid copper–nickel–aluminium–bronze alloys dissolved carbon and removal by treatment of melt

Castings made of copper–nickel–aluminium bronze (CuAl₁₀Fe₅Ni₅) alloys regularly show defects in the thick, slowly solidifying parts of the castings, which give rise to rejections. Metallographic examination has been made on material of scrap castings showing porosity accompanied with film-like inclusions located beside the iron rich κ_II phases. Investigations of large failed cast structures of copper–nickel–aluminium bronze show the same characteristic defects on which fatigue cracks initiate and grow. Investigation has been made to the nature and the cause of appearance of the film-like inclusions. Microanalysis indicates a high intensity of carbon at the place of the film-like inclusions. Hereafter, an investigation has been made into the solubility of carbon in liquid copper–nickel–aluminium bronze, and it is found that besides hydrogen, also carbon is soluble in copper–nickel–aluminium bronze alloys. The appearance of the carbon as flakes in the fracture surface of materials with defects does suspect there is a nucleating effect on the formation of microporosity causing the defects. To prevent the formation of the casting defects by the interaction between solved hydrogen and carbon, it is necessary to remove the carbon as far as possible by treatment of the melt.     

Role of the structural state of a copper–beryllium alloy in the formation of its tribotechnical properties

The influence of the structural state of a copper–beryllium alloy on its resistance to friction fracture under adhesion interaction and abrasive wear has been investigated. It has been shown that the elastic interphase deformations that cause the tension of the crystal lattice of the particles of precipitated phase brings about a decrease in the wear resistance of the alloy at a retained high hardness. The relaxation of interphase deformations during the aging process leads to a significant increase in the wear resistance of the alloy, despite the reduction its hardness.     

A comparative study of microstructure,oxidation resistance,mechanical, and tribological properties of coatings in Mo–B–(N), Cr–B–(N) and Ti–B–(N) systems

M–B–(N) (M = Mo, Cr, Ti) coatings were obtained by the magnetron sputtering of MoB, CrB₂, TiB, and TiB₂ targets in argon and in gaseous mixtures of argon with nitrogen. The structure and composition of the coatings have been investigated using scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. The mechanical and tribological properties of the coatings have been determined by nanoindentation, scratch-testing, and ball-on-disk tribological tests. The experiments on estimating the oxidation resistance of coatings were carried out in a temperature range of 600–1000°С. A distinctive feature of TiB₂ coatings was their high hardness (61 GPa). The Cr–B–(N) coatings had high maximum oxidation resistance (900°С (CrB₂) and 1000°С (Cr–B–N)) and possessed high resistance to the diffusion of elements from the metallic substrate up to a temperature of 1000°С. The Mo–B–N coatings were significantly inferior to the Ti–B–(N) and Cr–B–(N) coatings in their mechanical properties and oxidation resistance, as well as had а tendency to oxidize in air atmosphere after long exposure at room temperature. All of the coatings with nitrogen possessed a low coefficient of friction (in a range of 0.3–0.5) and low relative wear ((0.8–1.2) × 10^–6 mm3 N^–1 m^–1.     

Microstructural analysis of modification and grain refinement in a hypoeutectic Al–Si alloy

Abstract

It is well known that in hypoeutectic Al–Si alloys addition of titanium boride refines primary aluminium and addition of strontium modifies eutectic silicon. In this work their individual and simultaneous effect on both features has been investigated quantitatively. On the basis of experimental observations and quantitative analysis, it was concluded that an addition of 0·002 wt-% titanium almost halves grain size of primary aluminium in an ingot of A356, cast in a bar-shaped copper mould. Combining 0·002 wt-% titanium (as Al–3Ti–B) with 0·02 wt-% strontium resulted in a decrease in this grain refinement. However, an addition of 0·02 wt-% strontium has a slight refinement effect on primary aluminium phase. In order to quantify the effect of addition on eutectic silicon readily, as-cast specimens were heat-treated. It was observed that the number of eutectic silicon particles in Sr-modified specimens increased in a higher level compared to a Sr + Ti treated specimen. It was also found that Ti slightly influences the size of eutectic silicon particles.     

Phase transformations and phase equilibria in a Ti–37% Al–20% Mn alloy

The solid-state phase transformations and phase equilibria in a Ti–37 at% Al–20 at% Mn alloy have been investigated. The alloy was prepared by plasma-arc melting and the microstructures of high-temperature-annealed and water-quenched or furnace-cooled samples were studied. The results show that at 1235°C β-phase and (Mn,Al)₂Ti (Laves phase) are present whereas below 1000°C the phases (γ+α/α₂+(Mn,Al)₂Ti) are formed. A comparison between calculated equilibrium phase compositions and values measured by EDXA shows reasonable agreement for the β, γ and α/α₂ phases over a range of temperatures but agreement for the (Mn,Al)₂Ti phase is less good, particularly at the higher temperatures. The transformation kinetics in this system appear to be sluggish and true equilibrium does not appear to have been achieved in all samples annealed below 1145°C. DTA analysis was also undertaken and the heating thermogram obtained is interpreted with the aid of the calculated phase equilibria.     

Corrosion behaviour of experimental copper–antimony–molybdenum carbon steels in industrial and marine atmospheres and in a sulphuric acid aqueous solution

Low alloyed carbon steels are used in several applications as in automotive, home appliances and civil industries. Sb-bearing steels have been developed to withstand acid condensation, mainly to exhibit corrosion resistance to sulphuric acid aqueous solutions. This work is aimed at studying the corrosion resistance of three experimental low alloyed carbon steels with additions of copper, antimony and molybdenum using the electrochemical impedance spectroscopy (EIS) in a sulphuric acid aqueous solution, and field tests in industrial and marine atmospheres. The field tests showed the mass loss of antimony–molybdenum carbon steels was higher compared to that of other steels. The alloyed carbon steels with copper and antimony additions showed the highest atmospheric corrosion resistance evaluated by using field tests in industrial and marine environments. The molybdenum-bearing steels showed the highest corrosion resistance in a sulphuric acid solution, measured by using the EIS.     

Corrosion and corrosive-wear behaviors of a high strength and toughness Cu–15Ni–8Sn alloy in seawater

The Cu–15Ni–8Sn alloy with high strength and toughness is a common bearing alloy, while it is often subjected to premature failure in service due to corrosion and wear. Therefore, the corrosion and wear behaviors of an ultra-high-strength and toughness Cu–15Ni–8Sn (wt%) alloy fabricated by hot isostatic pressing were investigated in this study. The results indicated that intergranular corrosion and pits were observed when the studied alloy was immersed into seawater for 30 days. When the Cu–15Ni–8Sn alloy slid in seawater, there was a synergistic effect between corrosion and wear. With the increase of normal load, the synergistic effect weakened initially and then enhanced the interaction between corrosion and wear changed from negative to positive, and the main wear mechanisms transferred from abrasive wear into delamination.     

Crystallography and morphology of nanosized Cr particles in a Cu–0.2% Cr alloy

The crystallography and morphology of nanosized Cr precipitate particles in a Cu matrix have been examined using an aged Cu–0.20 mass% Cr alloy at 773 K. By HRTEM observations, the Cr particles were found to have the b.c.c. structure even for sizes smaller than 10 nm. The orientation relationships between the fine Cr particles and the Cu matrix were analyzed by observing Moiré fringes. Two distinct orientation relationships were found: one close to the Kurdjumov–Sachs relationship and the other close to the Nishiyama–Wassermann relationship. The particles exhibited major facet planes: (533)_f/(134)_b for the Kurdjumov–Sachs particles and (533)_f/(035)_b for the Nishiyama–Wassermann particles. The relative stability of the two types of Cr particles is discussed by adopting the invariant-line concept and the eigenvectors of the transformation.