No abstract

Electrochemical migration is caused by the adsorption of water and the bias voltages between the electrodes or pads which form an electric circuit or in the solders used to connect the parts. This work focused on the elucidation of the mechanisms of electrochemical migration of pure Sn, Sn37Pb, and Sn55Pb solders in electronics. The electrochemical migration behavior was discussed on the basis of the polarization behavior of SnPb solders. After the water drop test, the time to failure decreased with increasing Pb content in Cl solution and increased with increasing Pb content in SO 4 2 solution. In the case of the SnPb solder alloys, the pitting potential, the passive current density, the cathodic current density and the efficiency of cathodic deposition of the alloying elements were closely related to the resistance of the electrochemical migration.

No abstract

Biometals need high corrosion resistance since metallic implants in the body should be biocompatible and metal ion release should be minimized. In this work, we designed three kinds of super stainless steel and adjusted the alloying elements to obtain different microstructures. Super stainless steels contain larger amounts of Cr, Mo, W, and N than commercial alloys. These elements play a very important role in localized corrosion and, thus, their effects can be represented by the "pitting resistance equivalent number (PREN)." This work focused on the behavior which can arise when the bare surface of an implant in the body is exposed during walking, heavy exercise, and so on. Among the experimental alloys examined herein, Alloy Al and 316L stainless steels were mildly cytotoxic, whereas the other super austenitic, duplex, and ferritic stainless steels were noncytotoxic. This behavior is primarily related to the passive current and pitting resistance of the alloys. When the PREN value was increased, the passivation behavior in simulated body solution was totally different from that in acidic chloride solution and, thus, the Cr(2)O(3)/Cr(OH)(3) and [Metal oxide]/[Metal + Metal oxide] ratios of the passive film in the simulated body solution were larger than those in acidic chloride solution. Also, the critical current density in simulated body solution increased and, thus, active dissolution may induce metal ion release into the body when the PREN value and Ni content are increased. This behavior was closely related to the presence of EDTA in the simulated body solution.

Electrochemical migration occurs via electrochemical processes. When a water film forms on the electric circuit and then a bias voltage is applied, the metallic ions dissolve from the anode and move to the cathode. At the cathode, the metallic ions react with the electrons and then form dendrites. Thus, a short circuit failure of the electronic components occurs. This study focuses on the relationship between the electrochemical migration (ECM) susceptibility of SnPb solders and the composition of the dendrites on the basis of electrochemical techniques. It was found that the ECM susceptibility of SnPb solder alloys was affected by the chloride and sulfate ions. After the water drop test, the composition of the dendrites was primarily Pb mixed with Sn, regardless the dissolution/composition ratio of the solder alloys. However, only Sn was detected in the dendrites formed in the acidic solution. The dissolution of the metal from the anode influenced the failure time, and the pH of the corrosion environment significantly changed the composition of the dendrites formed on the cathode. The composition of the dendrites was proven to be closely related to the cathodic deposition efficiency of the ions dissolved from the anode.

The introduction of tensile residual stress has led to the induction of damage such as fatigue, corrosion fatigue, and stress corrosion cracking (SCC) in stainless steel in association with the influence of environments, components, surface defects, and corrosive factors during its use. Compressive residual stress can be achieved through various techniques. Among several methods, laser peening can be more attractive as it creates regularity on the surface with a high-quality surface finish. However, there is very little research on heavily peened surface and cross-section of stainless steel with very deep compressive residual stress. This work focused on welding and laser peening and the influence of Al coating on the microstructural changes in 304L stainless steel. The specimen obtained by laser peening had a very deep compressive residual stress of over 1 mm and was evaluated based on microstructural and hardness analysis. Therefore, a model for microstructural change by laser peening on welded 304L stainless steel was proposed.

Dry canisters used in nuclear power plants can be subject to localized corrosion, including stress corrosion cracking. External and residual tensile stress can facilitate the occurrence of stress corrosion cracking. Residual stress can arise from welding and plastic deformation. Mitigation methods of residual stress depend upon the energy used and include laser peening, ultrasonic peening, ultrasonic nanocrystal surface modification, shot peening, or water jet peening. Among these, laser peening technology irradiates a continuous laser beam on the surface of metals and alloys at short intervals to add compressive residual stress as a shock wave is caused. This research studied the effect of laser peening with/without a thin aluminum layer on the corrosion properties of welded 304L stainless steel. The intergranular corrosion rate of the laser-peened specimen was a little faster than the rate of the non-peened specimen. However, laser peening enhanced the polarization properties of the cross-section of 304L stainless steel, while the properties of the surface were reduced by laser peening. This behavior was discussed on the basis of the microstructure and residual stress.

There is a need to destroy both military and civilian hazardous waste and urgency, mandated by public concern over traditional waste handling methodologies, to safe and efficient alternative technologies. One very effective process for the destruction of such waste is supercritical water oxidation (SCWO). Nevertheless, corrosion of the materials of fabrication is a serious concern. This work intends to obtain the fundamental data for developing the corrosion resistant steel for the construction of SCWO system. The effects of various factors on the corrosion resistance of flat, welded, and U-bend 316L stainless steels in Trimsol solution were studied. Corroded product on surface was composed of multi-layer with oxides and salts, and dealloying was observed. Major corrosion phenomena of 316L stainless steel under SCWO condition were intergranular corrosion, pitting corrosion, SCC, and erosion corrosion. This work focused on the elucidation of corrosion mechanism of 316L stainless steel in SCWO environment.