Mattsson's Solution Research Articles

Material Influence on Mitigation of Stress Corrosion Cracking Via Laser Shock Peening

Stress corrosion cracking is a phenomenon that can lead to sudden failure of metallic components. Here, we use laser shock peening (LSP) as a surface treatment for mitigation of stress corrosion cracking (SCC), and explore how the material differences of 304 stainless steel, 4140 high strength steel, and 260 brass affect their mitigation. Cathodic charging of the samples in 1 M sulfuric acid was performed to accelerate hydrogen uptake. Nontreated stainless steel samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0–8%, indicative that LSP keeps hydrogen from permeating into the metal. Similarly for the high strength steel, LSP treating limited the hardness changes from hydrogen to less than 5%. Mechanical U-bends subjected to Mattsson's solution, NaCl, and MgCl2 environments are analyzed, to determine changes in fracture morphology. LSP treating increased the time to failure by 65% for the stainless steel, and by 40% for the high strength steel. LSP treating of the brass showed no improvement in U-bend tests. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, and a finite element model comparing induced stresses is developed. Detection of any deformation induced martensite phases, which may be detrimental, is performed using X-ray diffraction. We find LSP to be beneficial for stainless and high strength steels but does not improve brass's SCC resistance. With our analysis methods, we provide a description accounting for differences between the materials, and subsequently highlight important processing considerations for implementation of the process.

The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work.

Study on the role of tarnishing film in stress-corrosion cracking of brass in Mattsson's solution

In this paper, the influence of tarnishing film-induced stress and tarnishing film-induced brittle cracking on stress-corrosion cracking (SCC) of brass in Mattsson’s solution are investigated using hydrogen charging. Results showed that the SCC susceptibility of brass in Mattsson’s solution increased with the increase of tarnishing film-induced tensile stress. Also, the film-induced brittle cracking showed little effect on SCC susceptibility. From the results obtained, an improved SCC mechanism is proposed to explain the role of the tarnishing film-induced stress and the film-induced brittle cracking in SCC of brass in Mattsson’s solution. It seems that the film-induced brittle cracking is responsible for crack initiation of ductile brass. Also, the SCC susceptibility of brass in Mattsson’s solution was controlled by the growth rate of tarnishing film. Hydrogen enhanced the SCC susceptibility, which can be ascribed to the fact that hydrogen facilitates the tarnishing film growth.

Tarnishing film-induced brittle cracking of brass

Tarnishing film was developed on the brass surface in Mattsson's solution at room temperature. The filmed brass was removed from the solution, dried, and subjected to a slow strain rate (loading speed = 0.5 mm/min) in air for studying the effect of the film on crack propagation in the brass substrate. It was observed that initial cracks started to emerge in the film and then propagated to the brass matrix in a brittle intergranular manner. However, it changed into a ductile mode after removing the deposited film. The galvanic current between platinum wire and filmed brass sample in Mattson's solution was investigated. The results showed that periodic current fluctuations were observed when the sample was under a constant applied load. These observations showed that the film rupture-formation occurred at cracks under the stress-corrosion cracking condition.

Stress corrosion cracking properties of environmentally friendly unleaded brasses containing bismuth in Mattsson's solution

The purpose of the present investigation was to study the stress corrosion cracking (SCC) properties of environmentally friendly Bi-brasses in Mattsson's solution (0.05 M copper sulfate and 0.5 M ammonium sulfate, pH 7.4) at room temperature. Three unleaded brasses with Bi content ranging from 1 to 3 wt.% and a conventional leaded brass for comparison were investigated. The effect of Bi on SCC of unleaded brasses was studied through polarization test, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and slow strain rate tests (SSRT). Potentiodynamic polarization studies indicated that the corrosion resistance of Bi-containing brasses was improved as the content of Bi, which shown passivating characteristic in Mattsson's solution, increased. The Pb- and Bi-containing brasses presented an inductive behavior on impedance data in low frequency region at the open-circuit potential (OCP). Such behavior could be attributed to the adsorption process on the alloy surface. The observed dezincified layers after SSRT should be particularly good initiators of SCC as they could induce tensile stress. As the content of Bi increased, the thickness of dezincified layer and the volume fraction of preferentially attacked phase decreased, therefore, SCC resistance of the Bi-containing brasses was improved.

Electrochemical Noise Generation during Stress Corrosion Cracking of Alpha-Brass

Abstract An investigation of the electrochemical noise generation during the stress corrosion cracking (SCC) of alpha-brass was conducted in Mattsson solution (ammoniacal copper sulfate solution) o...

The Environmentally Assisted Failure of Cusil in Mattsson's Solution

Abstract The stress corrosion cracking (SCC) behavior of a CuAg eutectic (∼72% Ag) has been investigated in Mattsson's solution. The first stage in the environmentally assisted fracture process consists of preferential dissolution of copper from the eutectic, leaving a brittle, Ag-rich outer layer. The dissolution process is controlled by diffusion through this porous outer region. In the second stage, as the true tensile stress of the unattacked portion exceeds the ultimate tensile strength, fracture occurs by ductile rupture.

The inhibitive effect of extraneous ion addition on stress corrosion cracking of alpha-brass

The addition of ammonium chloride, cobalt sulphate, cesium sulphate and ethylene diamine to a Mattsson solution and the addition of ammonium sulphate to the Pugh solution have been found to produce an inhibitive effect on the stress corrosion cracking of alpha-brass in these solutions. Ammonium chloride and ammonium sulphate additions affect the tarnish formation on the specimen as well as the cracking pattern. Electrochemical polarization studies have also been carried out with these two additives. The observations have been explained in the light of adsorption of these ionic species at selected sites on the metal surface and their possible interference with the cathodic reactions.

The effects of crosshead speed and temperature on the stress corrosion cracking of Cu-30% Zn alloy in ammoniacal solution

Stress corrosion cracking (s.c.c. of Cu-30% Zn alloy in Mattsson's solution (0.05 mol/l CuSO 4 + 0.5 mol/l (NH 4) 2SO 4, pH 7.2) was investigated as a function of temperature (298 K–323 K) and crosshead speed (10 −5 mm/min to 1 mm/min). Crack propagation behaviour in a crosshead speed of 10 −4 mm/min at 298 K was also studied. All tests were carried out using a slow strain rate technique. Cracks occurred intergranularly under all experimental conditions used. At high crosshead speeds (5 × 10 −3 mm/min to 1 mm/min) the susceptibility to s.c.c. increased with increasing temperature. At slow crosshead speeds, however, an inverse effect of temperature on the susceptibility was revealed. Constant crack velocities were obtained in both specimens with or without surface coating, and the velocity in the coated specimen was lower than that in the uncoated specimen by one order of magnitude. Scanning electron microscopic examination revealed that ahead of intergranular cracks small corrosion pits were formed along grain boundaries. Based on the above experimental results, the mechanism of intergranular s.c.c. of Cu-30%Zn alloy was discussed by considering the growth rate of microcrack formed along grain boundary and the corrosion rate (or repassivation rate) of the microcrack.

The Inhibitive Effect of Benzotriazole on Stress Corrosion Cracking of α-Brass in Mattsson's Solution

The Inhibitive Effect of Benzotriazole on Stress Corrosion Cracking of α-Brass in Mattsson's Solution

Auger spectral analysis of oxide films on brass—a quantitative method

Auger spectral analysis of the black tarnish films formed on 64/36 brass after immersion in Mattsson's solution in the pH range 7.17–7.35 gives a composition Cu 2O containing 4–5 at.%Zn(II). A method of quantitative analysis of the differential Auger spectra without the use of spectral standards is proposed. The method is tested for a spectrum of pure Cu 2O.

Fracture of Tarnish Films on α-Brass

Abstract A study of the fracture of tarnish films on a 70/30 brass in pH 7.2 Mattsson's solution reveals that the film fractures transgranularly. Stressed metal specimens in the same solution crack intergranularly. The results are in disagreement with the reputed tarnish film rupture mechanism.

The formation of cuprous oxide films on α-brass stress-corrosion fracture surfaces

A study has been made of the nature of the fracture surface of α-brass specimens after failure by stress-corrosion cracking in pH 7·2 Mattsson's solution. The yellow colour of the stress-corrosion fracture surface points to a possible inadequacy in the “tarnish-rupture” model of the mechanism of this instance of stress-corrosion. The techniques of cathodic reduction and chemical dissolution have been used to remove any oxide present on the original fracture surface. On subsequent re-immersion in pH 7·2 Mattsson's solution, the stress-corrosion fracture surface remains untarnished, whereas the mechanical fracture surface rapidly acquires a black tarnish film. Comparison of plateau lengths obtained on further cathodic reduction has shown that for equivalent times of re-immersion, a much thicker film forms on the mechanical fracture region than on the stress-corrosion region of the fracture surface. The experimental results are interpreted as being inconsistent with the “tarnish-rupture” model but consistent with a stress-corrosion mechanism involving dezincification at the crack tip.

Mechanism of scc of α-brass in Mattsson's solution under potentiostatic conditions

SCC of α-brass in Mattsson's solution has been studied under potentiostatic anodic and cathodic polarization. In annealed samples, anodic polarization brings in a minimum in cracking time accompanied by a transition in cracking mode from intergranular to transgranular. The range of potential giving maximum susceptibility to cracking has been found to be independent of Cu content and pH of the test solution, but dependent on cold work. Cathodic polarization increases the resistance to cracking, and in cold-worked samples, where the cracking is initially transgranular, a transition to intergranular has been observed on cathodic polarization. SCC has been encountered also in a non-Cu-containing solution. These observations strongly suggest a mechanism based on a shift in active anodic and cathodic sites on polarization and adsorption playing an important role in the cracking process.

On the relation between stress-relief annealing, ordering and stress-corrosion cracking susceptibility in three copper alloys

The effects of post-forming heat treatments on the scc susceptibility in ammoniacal environments of three new commercial copper alloys (CDA Alloys 619, 638 and 688) have been investigated. The stress-corrosion susceptibility was evaluated semi-quantitatively using pre-formed U-bend specimens exposed to environments of moist ammonia and Mattsson's solution. Short time (30 min) heat treatments at various temps. (within the range 250–600°F) were carried out on the preformed U-bend specimens. During subsequent stress-corrosion testing the specimens were stressed elastically, with little further plastic deformation being introduced. The heat treatments used resulted in differing degrees of residual stress relief in the pre-formed U-bend specimens and also in the formation of differing amounts of order in the alloys; these latter effects were evaluated using differential thermal analysis techniques. The stress-corrosion data, expressed as per cent springback with time, are interpreted in terms of the amount of residual stress relief and the degree of ordering. An optimum stress-relief anneal temp. for maximum stress-corrosion resistance of formed components is recommended for each alloy. Results of a metallographic examination of failed specimens are also reported.

Ammoniacal Stress Corrosion Cracking of Alpha-Brass

Abstract Stress corrosion cracking of Cu-29.38 zinc in Mattsson's ammoniacal solution has been studied over the pH range 5.9 to 8.0. Electron diffraction studies conducted on the actual stress corr...

Relationship between stress—corrosion cracking and strain rate in alpha brass

Stress—corrosion cracking of Cu—30%Zn alloy under the constant strain rate in the range of 6·6 × 10 −6 s −1 to 1·1 × 10 −2 s −1 was investigated in Mattsson's solution (pH 7·2) (for inter-granular cracking) and in 1 M/L NH 4OH + 0·25 M/L CuCl 2 aqueous solution (pH 11·0) (for transgranular cracking). Within strain rates of 6·6 × 10 −6 s −1 for intergranular cracking and of 1·1 × 10 −5 s −1 for transgranular cracking, the rate-controlling step of stress—corrosion cracking corresponds to the slip step formation. Exceeding the above strain rates the s c c is controlled by the corrosion, where the rate-controlling mechanism requires the activation energy of about 18·7 Kcal/mol. When the strain rate exceeds 1·1 × 10 −3 s −1, intergranular s c c never occurs at room temperature. Width of crack tip increases with increase of strain rate for intergranular cracking, while decreases for transgranular cracking.

Transition in Mode of Cracking and Effect of Cold Reduction on Stress Corrosion Cracking in Copper-Manganese Alloys

Abstract Effect of cold reduction on the stress corrosion behavior of copper-manganese alloys in the range of 7 to 23% manganese has been studied using Mattsson's solution as the corrosive medium. ...

An Empirical Relationship Between Time of Cracking and Variation in Composition in Stress Corrosion Studies in Mattsson's Solution

An empirical equation has been derived for quantitative determination of the contribution by different chemical and physical factors towards the total cracking time in the stress corrosion cracking of copper-manganese alloys in Mattsson's solution. Three alloys containing 3·9 to 8·1 % of Mn, showing intergranular cracking, have been studied at different pH and copper concentrations of the solution and the results were used for the formulation of the equation. Cracking times calculated from the proposed equation for any set of variables were shown to correspond well with the observed values within allowable limits of deviation.

Stress-Corrosion Cracking of Alpha Brass in CusO4/(Nh4)2SO4Solution

AbstractThe role of different variables on stress-corrosion cracking of alpha brass in copper sulphate/ammonium sulphate solution (Mattsson's solution) has been investigated with annealed directly loaded wires. Composition, pH, ageing and other variables of the solution have been found to play an important part in controlling cracking susceptibility. The results are discussed in terms of the chemistry of the system based on the potential/pH diagram.