Defect and Diffusion Forum Vols. 326-328

Abstract: In heat resistant materials, the microstructural change occurs due to atomic diffusion and it affects directly to their mechanical properties. It is known that the state of this microstructural change can be represented by the system free energy, and therefore evaluation of this free energy is useful for the damage analysis of the materials. In this study, change in the system free energy of FG-HAZ in 9Cr heat resistant ferritic steels was estimated with creep time on the basis of a series of experiments. As a result, it was found that system free energy decreased with creep time and the decreasing rate was accelerated by applied stress. The change in the system free energy expressed as a function of applied stress makes it possible for, the microstructural state of the steel to predict an arbitrary creep condition.

Abstract: The mainly property of thin solid films technologies is their adhesion to the substrates. Because of its good wear resistance and its low coefficient of friction against steel, TiC is an attractive coating material for wear applications such as bearing components. The adhesion of TiC coatings, however suffers from insufficient reproducibility, which is probably due to uncontrolled process parameters. In our work pure titanium thin films of approximately 0.6 µm in thickness were prepared on 100C6 stainless steel substrates by cathodic sputtering. The samples were subjected to secondary vacuum annealing at a temperature between 400 and 1000°C for 30 min. The reaction between substrates and thin films was characterized using an x-ray diffractometer (XRD). Surface morphology and elements diffusion evaluations were carried out by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The interaction substrates-thin films is accompanied by nucleation and growth of titanium carbide as a function of annealing temperature. By the SEM and EDS results, it appears clearly that the diffusion of manganese to the external layers leads to the destruction of adhesion especially at high temperatures.

Abstract: In this work, the results of a dilatometric study of alloys on the base of the Al-Fe system were presented. Thermal expansion investigations of the alloys of the Al-Fe system with concentration of Al equal to - 38, 48, 58 at.% were also presented. The alloys were obtained by classical casting technique. The thermal expansion studies of the alloys were carried out by dilatometric analysis method using a Setsys thermal analyzer made by Setaram. A linear thermal expansion coefficient α was calculated using standard methods. A temperature dependence of the α coefficient was noted. The results are an important supplement of knowledge on the alloys of the Al-Fe system.

Abstract: Designing a drying process for porous type fabrics using traditional linear heat transfer models may be inefficiency because the drying characteristics in the process are usually nonlinear. Using nonlinear approaches to describe the heat/mass flow could be better for many industrial application cases. The paper as presented here is a study for an analytical model using differential form nonlinear equations to describe heat transfer and moisture diffusion process using air as the processing medium. Experimental findings were used to evaluate the performance of the studied model. Relationships between the model parameters and fabric physical properties were determined for further used in the design of drying equipment.

Abstract: The results of running a quasi two-dimensional experimental benchmark for horizontal directional solidification of binary Sn-3 wt.%Pb alloy in a rectangular region are presented. The computation was performed using the GIGAN software and two models to simulate the mushy zone were compared, namely, the one based on the equilibrium approach and the non-equilibrium one.

Abstract: The paper presents the complexity of the thermo-mechanical phenomena in multi-component porous material during thermal shock and heat transfer, including identification of its behavior by Hot Distortion Plus^® test, elastic/plastic interpretation and modelling using Comsol system on the example of granular material (quartz sand bonded by selected resins used for mould production in foundry industry).

Abstract: Discontinuities in cast products, obtained from a liquid state of an alloy, are the result of phenomena occurring during multiphase system crystallization. On the one hand, compacted defects as a shrinkage pipe are relatively easy to eliminate. On the other hand, it is known that presence of fine shrinkage and gas porosity is unavoidable. Detectability of these dispersed discontinuities depends on type of inspection method applied. Structure, including intensity and location of porosity zones, is dependent on the type of the alloy, casting configuration and conception of technological solution, related with control of velocity of the heat extraction to the mould. Thus, mechanical properties in the volume of a casting are not homogenous and are strongly reduced only in the zones of porosity. However, in strength calculations of cast products, this obvious fact is not taken into consideration. The rule of material homogeneity is applied instead, along with drastic increase of factor of safety. The paper indicates benefits of precise determination of limits of porosity zones located in the casting, using the NTD methods (for example, Phased Array ultrasonic tomography). Coordinates of porosity zones in 3D, introduced into CAD geometry and assigned with different properties allow to estimate the actual state of stress and strain of real object using FEM methods (systems like Ansys, Comsol). Load justified by operating conditions and application of tolerance of damage rule, with simultaneous reference to the limited state of stress according to LOV (Loss of Volume) and LEFM (Linear Elastic Fracture Mechanics) methods should find their place in design procedures of cast products, which will allow for better use of material and reduction of weight of the casting. This approach, named Tolerance of damage concerning the castings is the motto of this paper.

Abstract: Hydrogen entering into steel affects its electrochemical properties and may enhance the susceptibility to environmental degradation. The present work has been aimed at further clarifying the effect of hydrogenation on the corrosion behaviour and passivity of highly-alloyed stainless steels. The results were discussed by taking into account hydrogen charged samples and without hydrogen. The corrosion resistance to pitting was qualified with the cyclic polarization curves. The conclusion is that hydrogen may deteriorated the passive film stability and corrosion resistance to pitting of highly-alloyed stainless steel. Furthermore, the presence of hydrogen in passive films increases corrosion current density, decreasing the potential of the film breakdown and repassivation potential. It was also found that the degree of susceptibility to hydrogen-enhanced pitting corrosion was dependent on the type of steel.

Abstract: The hydrogen diffuses and accumulates at the stress concentration area like a crack tip and it causes hydrogen embrittlement. To clarify the mechanism of hydrogen embrittlement, it is important to obtain the hydrogen concentration behavior. However, experimental detection is not feasible due to the high diffusivity of hydrogen and numerical analyses have been preceded. In this paper, by using a finite element and finite difference coupled method at which the diffusion analysis is performed by FDM coupled with the stress analysis by FEM, the analyses of hydrogen diffusion were conducted under cyclic loading conditions.

Abstract: In this paper, the vacancy migration in Cu interconnect of large scale integration caused by stress induced voiding was calculated using the α multiplication method. Then, the effect of weight coefficient, α, on stress induced vacancy diffusion analysis was investigated and the validity of the α multiplication method was verified. Furthermore, the method of the vacancy diffusion analysis coupled with thermal stress analysis which can consider the history of thermal stress due to temperature changes was proposed. The results of the vacancy diffusion analysis coupled with the thermal stress analysis were compared with the analytical results of the vacancy migration without the effect of history of thermal stress. As a result, the maximum site of vacancy accumulation was found to be qualitatively in good agreement between them. However, the quantitative value of maximum vacancy concentration obtained by the vacancy diffusion analysis coupled with thermal stress analysis was found to be much higher and the vacancy distribution is found to be much more localized.