This paper reviewed the corrosion resistance of various dental alloys evaluated in the light of their released ions in vitro experiments, and showed the examples in which original corrosion resistance was lowered by the factors such as dental casting, polishing and contact with other metals. The trends of the dental alloy development suggested by the new gold alloys with safety to organism were discussed.
Corrosion measurement techniques and its experimental results of metallic biomaterials in vivo and in vitro are reviewed. The corrosion phenomena of metallic biomaterials used for artificial joints, bone plates, etc. are discussed based on empirical data. Dissolution, open circuit potential, repassivation potential, and repassivation current are measured. Also, polarization, AC impedance, and surface analyses are employed in the field of biomaterials. However, test solutions used for the measurements are characteristic in biomaterial research. The compositions of the solutions are simulated as body fluid, controlling temperature, pH, and dissolved oxygen concentration.
Recently, irradiation assisted stress corrosion cracking (IASCC) of austenitic stainless steels for core internal components materials become a subject of discussion in light water reactors (LWRs). IASCC has not been found in Pressurized Water Reactors (PWRs). However, the authors have investigated on the possibility of IASCC of austenitic stainless steels for core internal materials so as to be able to estimate the degradation of PWR plants up to the end of their lifetime. In this study, in order to verify the hypothetical that the IASCC in PWRs shall be caused by the primary water stress corrosion cracking (PWSCC) as a result of radiation induced segregation (RIS) at grain boundaries, the authors simulated RIS at grain boundaries of austenitic stainless steels based on previous study and estimated RIS tendency after long time operation. And the authors melted the test alloys whose bulk compositions simulated the grain boundary compositions of irradiated austenitic stainless steels and made clear chromium-nickel-silicon compositions for PWSCC susceptibility area in austenitic alloys by slow strain rate tensile (SSRT) test.
Cavitation damage in hydraulic machines is still unavoidable as the downsizing and the increase in their power continues. One of the characteristic features of cavitation erosion involves the removal of metallic material, which occurs after an incubation period, during which no mass loss, but plastic deformation of the surface, occurs. The current methods for predicting the amount of erosion damage inflicted upon metallic materials in a cavitating environment are based on the mass of the material which is lost. As a consequence, the erosion-resistance of a material cannot be determined until a measurable amount of mass loss has occurred. In this study, in order to quickly evaluate the erosion-resistance of metallic materials, the plastic deformation behavior of metallic materials during the incubation period was analyzed. The increment of the surface area was determined from the material surface profile data, measured through a surface roughness meter, to establish a good index for evaluating cavitation erosion development on the surface, as well as the intensity of the cavitation attack. According to the index, the incubation period of cavitation erosion is to be divided into two periods. In the first period, the rate of surface area increment is related to the hardness of the metallic material, and in the second period to the strain hardening exponent. These results can then be applied to the rapid determination of the level of erosion-resistance, in turn leading to a rapid prediction of the service life of the material.
One of the characteristic features of cavitation erosion involves the removal of metallic material, which occurs after an incubation period, during which no mass loss, but plastic deformation of the surface, occurs. The current methods for predicting the amount of erosion damage inflicted upon metallic material in a cavitatiog environment are based on the mass of the material which is lost. As a consequence, the erosion-resistance of a material cannot be determined until a measurable amount of mass loss has occurred. In this study, in order to estimate the damage rate during the mass loss period, the plastic deformation behavior in the incubation period as well as in the mass loss period was analyzed. The increment of the surface area was determined from material surface profile data, measured through a surface roughness meter, and proved to be a good index for quantitatively evaluating the development of surface plastic deformation. It increased with testing duration, reaching a constant value after the incubation period. The value was related to the size of particles, which were separated from the damage surface. The value of the surface increment at the end of incubation period was closely related to the maximum strain which the surface can bear. This value can be used for estimating the cavitation damage rate.
The corrosion behavior of polyamide plastics immersed in sulfuric acid solution was investigated. The degree of degradation was evaluated by the changes of weight, flexural strength, and molecular weight. The flexural strength rapidly decreased after the onset of immersion due to water absorption. A part of decreased flexural strength recovered by drying. Color changed layer was observed by using optical microscope, and the generation of crack was also observed in scanning electron microscopic photographs. The thickness of color changed layer agreed with that of crack depth. The average molecular weight of polyamide decreased by immersion in sulfuric acid solution. It was recognized by X-ray microanalyzer that sulfuric acid molecules penetrated into the inside of the color changed layer. Thus, color changed layer was formed by the extreme decrease of molecular weight, and color unchanged layer was also degraded by the penetration of sulfuric acid.
It has been reported by the authors that Al2O3/Al/Al2O3/Al multilayer and Al2O3⋅Nb composite films have self-healing ability. The aim of this study is to make clear the most preferable composition of the Al2O3⋅Nb composite film for self-healing and presume the self-healing mechanism of the films. Al2O3⋅Nb composite films with various composition were prepared on an Fe thin film formed on a glass substrate by ion-beam-sputter deposition. The self-healing ability was evaluated by the repassivation behavior of potential and current on specimens just after giving a knife-scratch in 1.0kmol·m-3 Na2SO4 and NaCl solutions. The chemical state of constituent elements of the composite films was analyzed by XPS and the micro- and crystal structures of the films were examined by TEM. The surface of the specimens after scratching was analyzed by AES combined with Ar+ ion sputtering. The activation and repassivation behavior of potential and current on the specimens after scratching showed the specimens, except for those with high Nb content, have the self-healing ability in a Na2SO4 solution. However, the specimen that has a mole composition ratio of Al2O3: Nb=92:8 only showed the self-healing ability in a NaCl solution. The XPS analysis showed that the oxidation state of Nb in the composite films changed with composition. The AES analysis revealed that the composite films were not removed completely by scratching. Most of composite films with plastic deformation adhered on the Fe film after scratching. These results show that the defects generated by scratching should be microscopicically small. The self-healing should results from filling up the defects with oxides generated by the oxidation of Nb metal and/or lower valance Nb oxides in the films.