Jianqiu Wang

Comparison of Corrosion Resistance of UNS N06690TT and UNS N08800SN in Simulated Primary Water with Various Concentrations of Dissolved Oxygen

Corrosion behaviors of UNS N06690TT and N08800SN in simulated pressurized water reactor (PWR) primary water containing three concentrations of dissolved oxygen (DO) was studied by open-circuit pote...

Effects of microstructure and temperature on corrosion behavior of Sn–3.0Ag–0.5Cu lead-free solder

The heterogeneous microstructure of solder could be obtained when cooling rate of the solder joint was not even, which would affect the corrosion behavior of solder during service. The ambient temperature would also affect the corrosion behavior of solder joint. In this paper, the effects of microstructure and temperature on the corrosion behavior of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated. The various microstructures of SAC305 lead-free solder were obtained by cooling specimens in air and furnace. Compared to the fine-fibrous Ag3Sn phase inside the commercial SAC305 solder, platelet-like Ag3Sn formed as cooling speed decreasing. The polarization behavior of SAC305 solders in 3.5 wt.% NaCl solution was not significantly affected by various microstructures, but sensitive to temperature.

A review of the influence of hydrogen on the mechanical properties of DP, TRIP, and TWIP advanced high-strength steels for auto construction

Abstract The literature is reviewed regarding the influence of hydrogen on dual-phase (DP), transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP) steels. Hydrogen influences DP steels by decreasing ductility while strengths are largely unaffected. TRIP steels may be susceptible to hydrogen embrittlement (HE) as indicated by the loss of ductility and some brittle fracture features. The literature on the influence of hydrogen on TWIP steels was inconsistent. Some researchers found no significant influence of hydrogen on TWIP steel properties and fully ductile fractures, whereas others found a significant loss of ductility and strength due to hydrogen and some brittle features. Possible countermeasures for HE are tempering for DP and TRIP steels and aluminum alloying for TWIP steels.

Effects of Surface State and Applied Stress on Stress Corrosion Cracking of Alloy 690TT in Lead-containing Caustic Solution

The effects of surface state and applied stress on the stress corrosion cracking (SCC) behaviors of thermally treated (TT) Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 degrees C were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit (ground), shot-peened (SP) and electro-polished (EP) and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.

Effect of Hydrogen on Corrosion and Stress Corrosion Cracking of AZ91 Alloy in Aqueous Solutions

The effect of hydrogen on the corrosion and stress corrosion cracking of the magnesium AZ91 alloy has been investigated in aqueous solutions. Hydrogen produced by corrosion in water diffuses into, and reacts with the Mg matrix to form hydride. Some of the hydrogen accumulates at hydride/Mg matrix (or secondary phase) interfaces as a consequence of slow hydride formation and the incompatibility of the hydride with the Mg matrix (or secondary phase), and combines to form molecular hydrogen. This leads to the development of a local pressure at the hydride/Mg matrix (or secondary phase) interface. The expansion stress caused by hydride formation and the local hydrogen pressure due to its accumulation result in brittle fracture of hydride. These two combined effects promote both the corrosion rate of the AZ91 alloy, and crack initiation and propagation even in the absence of an external load. Hydrogen absorption leads to a dramatic deterioration in the mechanical properties of the AZ91 alloy, indicating that hydrogen embrittlement is responsible for transgulanar stress corrosion cracking in aqueous solutions.

Microstructure, Residual Strain and Stress Corrosion Cracking Behavior in 316L Heat-Affected Zone

Austenitic stainless steels are usually chosen to make many components of nuclear power plants (NPPs). However, their microstructure in the heat-affected zone (HAZ) will change during the welding process. Some failures of the weld joints, mainly stress corrosion cracking (SCC), have been found to be located in the HAZ. In this research, the microstructure, micro-hardness, residual strain and SCC behavior at different locations of the 316L HAZ cut from a safe-end dissimilar metal weld joint were studied. However, traditional optical microscope observation could not find any microstructural difference between the HAZ and the base metal, higher residual strain and micro-hardness, and higher fraction of random high-angle grain boundaries were found in the HAZ than in the base metal when studied by using electron back-scattering diffraction scanning and micro-hardness test. What’s more, the residual strain, the micro-hardness and the fraction of random grain boundaries decreased, while the fraction of coincidence site lattice grain boundaries increased with increasing the distance from the fusion boundary in 316L HAZ. Creviced bent beam test was applied to evaluate the SCC susceptibility at different locations of 316L HAZ and base metal. It was found that the HAZ had higher SCC susceptibility than the base metal and SCC resistance increased when increasing the distance from the fusion boundary in 316L HAZ.

Characterisation of rust formed on carbon steel after exposure to open atmosphere in Qinghai salt lake region

Abstract The rust layer formed on carbon steel after 1 year exposure to Qinghai salt lake atmosphere was characterised by the following complementary techniques: X-ray diffraction, infrared transmission spectroscopy, scanning electron microscopy and energy dispersive X-ray. The crystalline components of the rust layers consisted primarily of β-FeOOH, γ-FeOOH and iowaite [Mg4Fe(OH)8OCl.4H2O]. δ-FeOOH, ferrihydrite and amorphous rust were also found. Most corrosion products were contained in the inner layer, while foreign particles were mainly distributed in the outer layer. Energy dispersive X-ray and linear scanning results indicated that Cl and Mg elements were rich in the whole rust layer, in which case they will have had an important influence on the corrosion process of carbon steel in the salt lake atmospheric conditions.

Corrosion behavior of Sn-3.0Ag-0.5Cu lead-free solder joints

Abstract The aim of this study is to evaluate the corrosion behavior of Sn-3.0Ag-0.5Cu (SAC305) lead-free solder joint using salt spray test. The presence of Cu pad accelerates the dissolution of Sn from solder joints into corrosive medium because of galvanic corrosion mechanism. So, the solder joint was easily corroded in corrosive environment than SAC305 solder bar. During salt spray test, pitting corrosion begin from the solidification cracks in the solder joints, which will lead to a decrease of the reliability of solder joints and shorten the life of electronic devices.

Oxidation and Electrochemical Behavior of Monolayer-Graphene-Coated Copper in Simulated Primary Water

In high-temperature and high-pressure water, traditional anticorrosion approaches are not suitable to be used to protect structural materials from oxidation and corrosion. In this study, monolayer graphene was explored as a barrier to protect the materials from degradation. The oxidation and corrosion rate of the monolayer-graphene-coated copper is much lower than that of the bare copper, suggesting that the monolayer graphene can effectively protect the copper from oxidation and corrosion in the simulated primary water of pressurized water reactors.

Pitting growth rate on Alloy 800 in chloride solutions containing thiosulphate: image analysis assessment

ABSTRACT The growth rate of pits formed on Alloy 800 in chloride solutions containing various thiosulphate concentrations was assessed by potentiostatic polarisation, in situ corrosion image observation, and image analysis. The pitting growth rate was a function of solution chemistry: in chloride solution pits were small but numerous, in chloride + thiosulphate solution, the pits were large. Competitive adsorption on Alloy 800 of chloride and thiosulphate ions affected the pitting potential and therefore the pitting growth rate on the metal. The reduction of thiosulphate to elemental sulphur accelerated the pitting growth rate in chloride + thiosulphate solutions.