Materials Science Forum Vols. 475-479

Abstract: Vapor-, electro-, and electroless-deposits have usually strong fiber textures. When annealed, the deposits undergo recrystallization or abnormal grain growth to reduce their energy stored during deposition. The driving force for recrystallization is mainly caused by dislocations, whereas that for abnormal grain growth is due to the grain boundary, surface, interface, and strain energies. During recrystallization and abnormal grain growth, the texture change can take place. The recrystallization and abnormal grain growth textures are in general of fiber type. However, copper interconnects are subjected to non-planar stress state due to geometric constraints during room temperature and/or elevated temperature annealing. The annealing textures of the thin films and copper interconnects are discussed in terms of the minimization of the surface, interface, and strain energies, the grain boundary energy and mobility, and the strain-energy-release maximization.

Abstract: Due to the ultrafine grains (or domains or particles) and a high density of grain boundaries (or generally interfaces) in nanostructured materials, many properties and performance of the materials are expected to be significantly varied with respect to their coarse-grained counterparts. Extensive investigations over the past decays indicated that the nanostructured metals do possess some novel properties that may find technological applications in industry. In this talk, a brief survey of current status of investigations on properties of nanostructured metals will be summarized with emphasis on the following properties.

Abstract: In order to diminish the industrial pollution to maintain the sustainable development and to reduce the cost of the steel production, a unified technology combining plastic forming and heat treatment for some steel parts production is suggested. This article mainly concerns part theoretical foundation of such technology, i.e. the thermodynamic and kinetic models of the ferrite and pearlite transformations under external stress. Simulation of the ferrite fraction after continuous cooling under stress in a low-alloyed steel is presented. The effects of stresses on bainitic and martensitic transformations are also briefly introduced. The unified technology seems favorable to be realized in manufacturing practice.

Abstract: Structural refinement in interstitial free (IF) steels has been obtained by three different methods: (i) deformation by cold or warm rolling, (ii) martensitic transformation and (iii) a combination of a martensitic transformation and plastic deformation. For all these processes, the refinement is discussed in terms of grain subdivision by high angle boundaries and dislocation boundaries on length scales from the micrometer level to the nanometer dimension. The characteristics of the subdividing boundaries are discussed, leading to the formulation of strength-structural relationship for IF steel in the deformed state.

Abstract: A lot of works for developing the structural nano-materials have been performed all over the world in recent years. Severe deformation techniques like HPT, ECPA and ARB have been applied to different materials such as Al, Cu, Ti and several steels. Such techniques greatly reduced the grain size and improved the yield and tensile strengths. However, the elongation of the materials is greatly decreased due to the small amount of work hardening, and these techniques do not seem suitable for the mass production. Therefore, this study has been carried out as a fundamental research for developing austenitic steels with high strength and good elongation using a conventional rolling and annealing processes. Fe-0.1%C-10%Cr-5%Ni-8%Mn alloy was melted, homogenized, hot rolled, and cold rolled at room temperature to transform γ austenite to α ’ martensite. After that, the specimens were annealed just above its reverse transformation finish temperature (Af) to obtain the fine reversed austenite grains. The grain size of the metastable austenitic steel was successfully refined to less than 200nm by repeating rolling and annealing processes. The resultant nanocrystalline material shows not only high strength but also large elongation because the work hardening ability is enhanced by the strain-induced martensitic transformation during the tensile test.

Abstract: The concept of deformation-enhanced transformation of ferrite in plain low carbon steel is introduced. The characteristics are presented. Systematic works conclude that deformation significantly enhances the ferrite transformation of undercooled austenite in plain low carbon steel. Nucleation is the dominant process of the transformation. Until the completion of the transformation, nucleation is always repeated, especially at the zone in front of the newly formed ferrite grains, which restrict the grain growth and lead to formation of very fine ferrite grains. Three stages of kinetics are clearly shown from the experimental measurement, which correspond to nucleation at grain boundaries, at the zone in front of newly formed ferrite grains and within residual austenite.

Abstract: The iron rust phase has been analyzed by using EPMA, TEM and EIS after simulating marine corrosion tests. The ultrafine grained (UFG) weathering steel containing Si and Al showed higher corrosion resistance than carbon steel in the test. Si and Al were identified as Si 2+ and Al 3+ in the complex oxide of inner rust by EPMA and TEM. It was demonstrated by EIS that the resistance at the low frequency region corresponded to that of corrosion reaction of rusted steels (Rt). The Rt value of this steel increased after the continuous formation of inner rust, which implied that Si and Al took part in the conversion of complex oxides into fine structure that prevented the penetration of Cl ions.

Abstract: An ACM (Atmospheric Corrosion Monitor) type corrosion sensor, consisting of a Fe-Ag galvanic couple was developed and applied for the evaluation of corrosivity of atmospheric environments. The sensor was designed considering mass-production and good reproducibility of results, making it convenient for long-term corrosion data acquisition. Besides the sensor output, I, temperature, relative humidity (RH) were also recorded by a microcomputer. By analyzing the magnitude and time variation of I, the occurrence and duration of rain, dew and dry periods, Train, Tdew and Tdry, respectively, could be distinguished and determined. And by referencing to the empirical I-RH calibrating curve, the amount of deposited sea salt, Ws, could also be estimated. It was also found that the corrosion loss could be estimated in both indoor and outdoor sites by analyzing sensor output. Corrosivities of some kinds of exposure sites, not only outdoor environments but also indoor environments, were evaluated by using the ACM sensor.