► We examine corrosion behaviour of Cu–Al–Ni shape memory alloy. ► Adsorption of chloride ions leads to the decrease of
E
OCP and the breakdown of the protective surface oxide film. ► Polarization ...behaviour was determinated by the dissolution of copper to soluble cuprous chloride ion complex (CuCl
2
−). ► The microstructure consisted of grains with martensite plates. ► After corrosion testing occured of corrosion products at Cu–Al–Ni surface.
The corrosive behaviour of Cu–Al–Ni shape memory alloy in deaerated 0.5
M NaCl solution at 20
°C was studied by means of open circuit potential measurements, linear polarization, potentiodynamic polarization measurements, cyclic voltammetry and electrochemical impedance spectroscopy measurements. The electrode surface was examined by light microscope, SEM, XRD and EDX methods. The polarization measurements have shown that corrosive behaviour of Cu–Al–Ni alloy in NaCl solution was dominated by the Cu component. The results of impedance measurements at open circuit potential have shown that the overall impedance of the system increases with immersion time due to continuous growth of the passive film on the alloy surface. The XRD and EDX analysis showed the presence of copper, aluminium and nickel compounds, Cu-oxides and Cu-chlorides on alloy surface.
•We examine transformation kinetics of austenite during isothermal annealing of heat-resistant stainless steel.•Long-time exposure to high temperatures 600–900°C leads to microstructural ...changes.•Sigma phase particles occurred in the form of network of plates.•After fracture occurred intercrystalline brittle mode of fracture surfaces.•The increase in hardness was associated with annealing duration and content of sigma phase.
In this work, the results of the transformation kinetics of austenite heat-resistant stainless steel (AISI 310S) with 2.27wt.% silicon were presented. The results of microstructural and fractography analysis, as well as the results of hardness after the isothermal heat treatment of the steel in the temperature range from 600 to 900°C at different annealing times (from 1 to 956h) are shown. It was found that the microstructure of steel after isothermal annealing consisted of austenite, carbide (M23C6) and σ-phase. The number of σ-phase precipitates increases with higher annealing times. In longer annealed steel samples the significant coarsening of precipitates was observed, as well as a large amount of σ-phase particles in the form of a chain and a network of plates. Precipitates were both observed at grain boundaries and within austenite grains. σ-phase precipitation involves two mechanisms: transformation γ→Cr23C6→σ and transformation γ→α′→σ. The hardness began to increase after 48h of annealing at a temperature of 600°C, while in the temperature range of 700–900°C the hardness increased with annealing times higher than 8h. The slope of hardness curve is caused by microstructural changes. The fracture surface mode was intercrystalline brittle. Relatively large dimples can be related to large particles of precipitates which occurred after long annealing times.
The influence of different heat treatment temperatures on microstructural and mechanical properties of CuAlNi shape memory alloy was determined. The samples were investigated in as-cast state and ...heat treated state at three different temperatures (700°C, 740°C and 780°C). The heat treatment was conducted at above mentioned temperatures for a very short period of time (2min) followed by water quenching (WQ). The microstructures in all samples were martensitic, and only in the sample that was heat treated at 780°C after tensile testing small particles of some other phase were observed. According to tensile testing measurement, some samples show better results, but insufficient elasticity for proceeding to cold plastic deformation processes. Fractographic analysis shows the intergranular type of fracture in the area of columnar grains and the transgranular type of fracture in the centre of the sample where the equiaxial grains appear. The microhardnesses of the samples were in the range between 239 and 305 HV10.
•Microstructural and fracture analysis of CuAlNi SMA were analyzed.•The influence of heat treatment on failure was determined.•Fracture surface analysis showed intergranular and transgranular type of fracture.•Elongation of the alloy was very low.•Hardness of alloy was very high.
The electrochemical behavior of folic acid (FA), at the electrochemically prepared ex situ bismuth film (BiF) on glassy carbon electrode, clearly indicates electrocatalytic nature of the prepared ...film toward FA reduction (at –0.55 V). Scanning electron microscopy is used for morphological characterization of the prepared BiF. Accordingly, we establishing an electrochemical procedure based on square wave cathodic stripping voltammetry, preceded by accumulation of FA on the BiF electrode (BiFE). This analytical method is optimized and its analytical performance is presented. This electrode displays a two linear response range: 0.1 to 1.0 μmol L–1 and 1.0–10.0 μmol L–1 with sensitivity of 20.10 μA μmol–1 L and 2.28 μA μmol–1 L, respectively. Developed method was validated in compliance with spectrophotometric method. Excellent recovery and standard deviation obtained with BiFE revealed great analytical potential of the proposed method which was applied for the determination of FA in pharmaceuticals formulation.
This work is licensed under a Creative Commons Attribution 4.0 International License .
•Thermodynamics of the metal alloys.•CALPHAD method and optimized thermodynamic parameters for calculation of alloys properties.•Microstructure of Cu-rich region of the Cu–Al–Ag system using scanning ...electron microscopy with energy dispersive X-ray spectroscopy.
Copper rich region in shape memory Cu–Al–Ag system was experimentally investigated using DTA and calculated using optimized thermodynamic parameters according to CALPHAD method. Overall composition alloys were chosen along three vertical sections with constant copper content of 70, 80 and 90at%. Experimentally determined solidus and liquidus temperatures were compared with the results of thermodynamic calculation and good mutual agreement was noticed.
The influence of different chloride ion concentration (0.1 %, 0.5 %, 0.9 % and 1.5 % NaCl solution) on the electrochemical behaviour of the cast CuAlNi alloy was examined with electrochemical ...techniques (open circuit potential measurements, linear and potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS)). After polarization measurements, electrode surfaces were examined with an optical microscope and the SEM/EDS analysis. Polarization measurements revealed that an increase in chloride ion concentration leads to an increase of the corrosion current density values and a decrease of the polarization resistance values, which indicated a higher corrosion attack on the alloy. The examination of alloy surfaces with an optical microscope and the SEM/EDS analysis has shown that there is no indication of pitting corrosion in the 0.1% NaCl solution, but pits were clearly visible on the samples which were examined in the higher chloride concentration solutions. The EDS analysis has shown the existence of copper oxide on the electrode surface and a presence of a small percentage of aluminium in the form of aluminium oxide.
CuAlNi shape memory alloys (SMA) belongs to a group of alloys that exhibit shape memory effect which is related to the thermoelastic martensitic transformation. In this paper the influence of heat ...treatment (quenching and tempering) on fracture surface morphology of the CuAlNi SMA after tensile testing was examined by scanning electron microscope. It is observed a small difference on alloys mechanical properties and surface morphology between casted and quenched (850°C/60'/WQ) condition. But after tempering at 300 °C/60'/WQ the mechanical properties and surface morphology is drastically changed. In both states (casted and quenched) can be noticed a transgranular type of fracture showing that the small amount of plastic deformation occurred, and along long oriented grains it is observed an intergranular type of fracture. After tempering the CuAlNi sample shows mostly intergranular type of fracture after tensile testing.
Failure of steel pipes for hot air supply Gojić, Mirko; Nagode, Aleš; Kosec, Borut ...
Engineering failure analysis,
12/2011, Letnik:
18, Številka:
8
Journal Article
Recenzirano
► We examine microstructure and fracture of stainless steel AISI 310S. ► Pipes were tested after long life application (between 2 and 3
years) at temperatures 600–650
°C. ► Microstructure consisted ...from σ-phase, sporadically carbides and austenite matrix. ► Fracture surface was transgranular brittle fracture with clevage morphology.
Pack aluminization process is one of the possible production methods to improve oxidation resistance at high temperatures of various types of metallic materials. It is a chemo-thermal process where ...products are embedded in the powder mixture, consisting of Al powder, halide activator NH4Ű, and inert diluent ARO3 powder, and annealed at high temperature. This exposure to high temperature causes the Al diffusion into the base material and formation of the aluminide surface layer. During the component service at elevated temperatures, the oxidation resistance is obtained due to the constant formation of an aluminium oxide film that forms on the aluminide surface layer and acts as an oxygen impermeable barrier. In the present study, FeCrAl and the NiCr heat resistant alloys in the form of 1mm thick sheet were aluminized at various process parameters. The effect of time, temperature, concentration of aluminium and halide activator in the powder mixture as well as the influence of furnace atmosphere on coating formation mechanism, mass gain and the thickness of the aluminide diffusion layer was evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy and micro hardness analytic techniques. Isothermal exposure tests at 1200 °C for 24h in air were conducted and compared with untreated samples for high temperature oxidation resistance estimation.
PDF
