Brazing copper to alumina using reactive CuAgTi alloys

The purpose of this work was to describe and discuss the fundamental issues involved in reactive brazing of alumina to copper by CuAgTi alloys. The method used to bring the Ti to the CuAg braze enabled the Ti concentration in the braze to be varied to a large extent (from 0.8 to 6 wt.%). It was then possible to study the effects of this parameter on the interfacial chemistry and joint microstructure, as well as on the mechanical performance of the brazing joints, characterized by tensile tests. The mechanical strength of metal/alumina joints processed by reactive brazing was also compared with data obtained using a standard metallization process.     

Corrosion behaviour of Al–29at%Co alloy in aqueous NaCl

Microstructure and corrosion behaviour of a binary Al–29 at%Co alloy have been studied. The alloy was prepared by arc-melting of Al and Co in high purity Ar and rapidly solidified on a water-cooled Cu mould. The alloy chemical composition and microstructure were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Furthermore, the corrosion behaviour was studied by potentiodynamic polarization in aqueous NaCl (0.6 mol dm⁻³) at room temperature. The alloy was found to consist of three phases: hexagonal Al₅Co₂, Z-phase and AlCo (β). The corrosion resistance of different intermetallic phases is characterized. The results are compared to previously published results of Al–TM (TM = transition metal) alloys.     

Fireside corrosion degradation of ferritic alloys at 600 °C in oxy-fired conditions

This paper reports the results of a study carried out to investigate the effects of simulated coal/biomass combustion conditions on the fireside corrosion. The 1000 h deposit recoat exposure (5 × 200 h cycles) was carried out at 600 °C. In these tests ferritic alloys were used 15Mo3, T22, T23 and T91. Kinetics data were generated for the alloys exposed using both traditional weight change methods and metal loss measurements. The highest rate of corrosion based on EDX results occurred under D1 deposit where provoke mainly by the formation of alkali iron tri-sulphate phase.     

Mechanistic studies of corrosion product flaking on copper and copper-based alloys in marine environments

The mechanism of corrosion product flaking on bare copper sheet and three copper-based alloys in chloride rich environments has been explored through field and laboratory exposures. The tendency for flaking is much more pronounced on Cu and Cu–4 wt%Sn than on Cu–15 wt%Zn and Cu–5 wt%Al–5 wt%Zn. This difference is explained by the initial formation of zinc and zinc–aluminum hydroxycarbonates on Cu15Zn and Cu5Al5Zn, which delays the formation of CuCl, a precursor of Cu₂(OH)₃Cl. As a result, the observed volume expansion during transformation of CuCl to Cu₂(OH)₃Cl, and concomitant corrosion product flaking, is less severe on Cu15Zn and Cu5Al5Zn than on Cu and Cu4Sn.     

Effect of small amounts of alloyed tin on the electrochemical behaviour of aluminium in sodium chloride solution

Binary model AlSn alloys containing 30–1000 ppm (by weight) Sn were investigated by electrochemical polarization in 5 wt% chloride solution and subsequent characterization of corrosion morphology. In the homogenized and rolled condition, tin concentration only slightly affected electrochemical behaviour up to 500 ppm, and the pitting potentials were all about −0.8 V_SCE. However, alloy containing 1000 ppm Sn was significantly activated by lowering of the passivity-breakdown potential to −1.38 V_SCE. Annealing at 300 °C caused significant segregation of Sn to the metal surface, and all specimens, independent of bulk Sn concentration, became nearly similarly active with breakdown potentials around −1.2 V_SCE. Corrosion on 300 °C-annealed specimens was uniformly distributed by polarization below the bulk pitting potential of −0.76 V_SCE. Moreover, the activation effect was temporary, and corrosion was significantly reduced as the segregated Sn was etched away from the surface. Thick oxide, formed during water quenching on high Sn concentration samples, containing 500 and 1000 ppm Sn, introduced partial passivation during polarization test. Annealing at 600 °C caused increasing activation with increasing Sn concentration, caused by Sn enrichment at the metal surface by dealloying of aluminium during anodic polarization in chloride solution. Corrosion was localized in the form of grain boundary corrosion for alloyed Sn concentration less than and equal to 500 ppm and pitting following the triple grain boundaries for 1000 ppm.     

Corrosion of Inconel 690 and Inconel 693 in an iron phosphate glass melt

The isothermal corrosion behavior between 1000 °C and 1190 °C of Inconel 690 and 693 in an iron phosphate glass melt containing 26 wt.% of a simulated Hanford low activity nuclear waste (LAW) was investigated. At least three distinct corrosion processes were recognized for both alloys over different temperature ranges. Inconel 690 and 693 both display the best corrosion resistance at an intermediate temperature range (Inconel 690: 1050–1100 °C; Inconel 693: 1050–1165 °C), and more severe corrosion at both lower and higher temperatures. In general, Inconel 693 is less reactive over a wider temperature range than Inconel 690.     

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

The corrosion behavior of Cu–Al–Be shape memory alloys with different microstructures and Be content in a 3.5% NaCl solution was studied by weight loss, cyclic anodic polarization and chronoamperometric measurements. The beryllium has a beneficial effect in β alloys. A pitting potential of −100 mV/SCE was found by anodic polarization tests for all the studied alloys, corresponding to the formation of pits produced by severe dealuminization. Samples with precipitates were more susceptible to pit formation. The corrosion behavior is strongly affected by the alloy microstructural conditions, and the β samples present higher pitting resistance and repassivation ability.     

Susceptibility of Ti–6Al–4V alloy to stress corrosion cracking in a Lewis-neutral aluminium chloride–1-ethyl-3-methylimidazolium chloride ionic liquid

The susceptibility of Ti–6Al–4 V alloy to stress corrosion cracking (SCC) in a Lewis neutral AlCl₃–EMIC ionic liquid (IL) was investigated employing U-bend tests. The results indicated that cracking initiated at the α/β phase boundary, propagated intergranularly, followed by transgranular cracking and failed in dimple mode under overloaded stress.     

Comparative study of stress corrosion cracking susceptibility of Fe18Cr10Mn- and Fe18Cr10Mn1Ni-based high nitrogen stainless steels

The stress corrosion cracking (SCC) behavior of Fe18Cr10Mn1Ni(0.3–0.8)N alloys was investigated in aqueous NaCl environment by using slow strain rate test method, and the results were compared to those of Ni-free counterparts. The addition of N tended to improve the SCC resistance of Fe18Cr10Mn- and Fe18Cr10Mn1Ni-based alloys. The alloying Ni magnified the beneficial effect of N on the SCC susceptibility and, eventually, the Fe18Cr10Mn0.8N alloy was immune to SCC in 2 M NaCl solution at 50 °C. The SCC behavior of the present alloys was found to be closely related to the repassivation tendency and the resistance to pitting corrosion.     

Determination of the critical flow velocities for erosion–corrosion of passive materials under impingement by NaCl solution containing sand

Transition from passivation to erosion–corrosion at the critical flow velocity (CFV) is of interest for corrosion engineers. This transition phenomenon on 304 stainless steel and a Fe-based amorphous coating was investigated under impingement by sand-containing NaCl solution. Mass loss measurement, open-circuit potential monitoring and potentiostatic test were employed to determine the CFV. The CFV values defined via the three approaches are consistent, about 10 m/s for 304 stainless steel and 15 m/s for the coating. The CFV decreases with increasing the sand concentration. It may serve as an effective tool for evaluating the erosion–corrosion resistance of passive materials.     

Microstructural characterization of diamond/CBN grains steel braze joint interface using Cu–Sn–Ti active filler alloy

In order to develop the new generation superhard abrasive tools of diamond and cubic boron nitride (CBN), the brazing joint experiments of diamond/CBN crystals and AISI 1045 steel matrix using Cu–Sn–Ti active filler powder alloy were investigated in vacuum furnace. The brazing temperature was 930 °C and the dwelling time was 20 min. Interfacial characteristics of the brazing joint among the diamond/CBN grains, the active filler layer and the steel substrate were analyzed using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction techniques. The results indicated that Ti element in the Cu–Sn–Ti alloys diffused preferentially to the surface of diamond/CBN grits to form a Ti-rich reaction layer in the brazed joints by microanalyses. Moreover, the TiC, TiN and TiB₂ phases in diamond/CBN interface and Cu–Ti phase in steel interface were confirmed by X-ray diffraction phase analysis. The wetting and bonding reactions on diamond/CBN by melting Cu–Sn–Ti alloy were realized through the interfacial reaction products like TiC, TiN and TiB₂ compounds during the brazing process. The adhesive strength experiments of the joint interfaces revealed that the grains were not pulled out from the bond interface. The reliable bonding strength of brazed diamond/CBN grains to the steel substrate can meet the application requirements of high efficiency machining in the industrial field.     

Effect of N and C on stress corrosion cracking susceptibility of austenitic Fe18Cr10Mn-based stainless steels

Stress corrosion cracking (SCC) susceptibility of austenitic Fe18Cr10Mn alloys with 0.3N, 0.6N and 0.3N0.3C was investigated in aqueous chloride environment using a slow strain rate test method. The SCC susceptibility of Fe18Cr10Mn alloys in 2 M NaCl solution at 50 °C under constant anodic potential condition decreased with increase in N content from 0.3 to 0.6 wt%, and with addition of 0.3 wt% C to the Fe18Cr10Mn0.3N alloys. The present study strongly suggested that the beneficial effects of N and C on the SCC behavior of Fe18Cr10Mn alloys would be associated with the resistance to pitting corrosion initiation and the repassivation kinetics.     

Annealing effects on the corrosion resistance of ultrafine-grained pure titanium

The effect of annealing on the corrosion behaviour of the ultrafine-grained pure titanium (Ti) produced by high-ratio differential speed rolling was examined in a 0.5 M H₂SO₄ solution using potentiodynamic polarisation and weight loss methods. The results indicated that post-rolling annealing significantly affected the corrosion resistance of ultrafine-grained Ti. It was concluded that annealing treatments leading to a decrease in dislocation density and residual stress while maintaining an ultrafine grain size and strong basal texture can allow for the development of pure Ti with a good combination of high strength and high corrosion resistance.     

Hot corrosion of Ti–46Al–8Ta (at.%) intermetallic alloy

Hot corrosion behaviour of a fully lamellar Ti–46Al–8Ta (at.%) alloy was studied in air under thermal cycling conditions (20-h cycles) at 700 and 800 °C. The samples were purposely contaminated with salt deposits consisting of NaCl or Na₂SO₄ or a mixture of these. The progress of degradation was followed by mass change measurements and visual inspection. Post-exposure examination involved scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The composition of salt deposits clearly influenced the rate and type of corrosion. Sodium chloride appeared especially harmful because of the formation of volatile chloride species.     

2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: Electrochemistry, 3D-profilometry,and XPS surface analysis

2-Mercaptobenzoxazole (MBOH) was studied as a corrosion inhibitor for Cu in 3 wt.% NaCl solution using EIS, a potentiodynamic curve, 3D-profilometry, and XPS measurements. It was shown that Cu corrosion in solution containing MBOH follows kinetic-controlled and diffusion-controlled processes and that MBOH is a mixed-type inhibitor. The diffusion coefficient of the Cu ions travelling through the solid surface layers was estimated to be on the order of 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. It was also demonstrated that the Cu(I)–MBOH complex is formed on the Cu surface and that the thickness of this surface layer is 1.4 ± 0.4 nm.     

Magnetron-sputtered oxidation protection coatings for Mo–Si–B alloys

Oxidation protective Mo–70Al, Mo–37Si–15B and Mo–46Si–24B (at.%) coatings with 5–10 μm thickness were deposited on Mo–9Si–8B alloys by magnetron sputtering; and their oxidation behavior was studied at 800, 1000 and 1300 °C in air. On the Mo–70Al layer a dense aluminum borate scale grew at 800 °C; however, this coating rapidly degraded at 1000 °C linked to substrate oxidation at uncoated areas. The Mo–37Si–15B and Mo–46Si–24B layers provided oxidation protection to the Mo–Si–B alloy at 800 and 1000 °C for up to 100 h due to formation of a borosilicate scale. The latter coating was protective for short times even at 1300 °C.     

Surface characterization of oxides grown on the Ti–13Nb–13Zr alloy and their corrosion protection

Oxide films were formed on the biocompatible alloy Ti–13Nb–13Zr in a phosphate buffer at open-circuit potential (E_oc), potentiodynamically up to 8 V, or by micro-arc oxidation (MAO) at 300 V. Their electrochemical properties were assessed in a phosphate buffer saline solution (PBS). EIS and SEM results showed that the E_oc and potentiodynamically formed oxide films were compact and behave as a monolayer, while the MAO oxide was a bilayered film (compact inner and porous outer layers). Open-circuit potential and EIS resistance values indicated that the MAO oxide provides the best corrosion protection for the alloy in PBS.     

Corrosion of ultra-high-purity Mg in 3.5% NaCl solution saturated with Mg(OH)2

Corrosion was evaluated for ultra-high-purity magnesium (Mg) immersed in 3.5% NaCl solution saturated with Mg(OH)₂. The intrinsic corrosion rate measured with weight loss, P_W = 0.25 ± 0.07 mm y⁻¹, was slightly smaller than that for high-purity Mg. Some specimens had somewhat higher corrosion rates attributed to localised corrosion. The average corrosion rate measured from hydrogen evolution, P_AH, was lower than that measured with weight loss, P_W, attributed to dissolution of some hydrogen in the Mg specimen. The amount of dissolution under electrochemical control was a small amount of the total dissolution. A new hydride dissolution mechanism is suggested.     

Erosion–corrosion of HVOF-sprayed Fe-based amorphous metallic coating under impingement by a sand-containing NaCl solution

Erosion–corrosion (E–C) behaviour of a Fe-based amorphous metallic coating (AMC) compared with 304 stainless steel (304 s.s.) was studied under a slurry impingement condition in a sand-containing NaCl solution. AMC exhibited much higher resistance to E–C than 304 s.s. The weight loss reached the maximum at an impact angle of 90° and the critical flow velocity was about 15 m/s for AMC, while 45° and 9 m/s for 304 s.s. The increment in passive current density under impingement for AMC was about 10 times lower than 304 s.s. Passive films formed at different impact velocities were of different thicknesses.     

Development of carbon nanotubes reinforced hydroxyapatite composite coatings on titanium by electrodeposition method

Carbon nanotubes (CNTs) are outstanding reinforcement material for imparting strength and toughness to brittle hydroxyapatite (HAP). This work reports the electrodeposition of CNTs reinforced HAP on titanium substrate at −1.4 V vs. SCE during 30 min with the functionalised CNTs concentration ranging from 0 to 2 wt.%. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX), high resolution transmission electron microscopy (HRTEM), mechanical and biological studies were used to characterise the coatings. Also, the corrosion resistance of the coatings was evaluated by electrochemical techniques in simulated body fluid (SBF) solution.