Materials Science Forum Vol. 812

Abstract: Microgeometrical characteristics of the surface of engineering components operating in wear condition are important features influencing the wear process of the tribological system. Beside the widely used common 2D roughness parameters – e.g. the R_a, arithmetical mean roughness, R_z, ten point mean roughness, or R_mr, material ratio, etc. – the 3D roughness features (S_a, S_z S_mr) provide potentially new means for geometrical description of the operating surfaces. Our paper aims at contributing an overview on the available 2D and 3D features, giving their definition and their potential use in multi-scale characterization of components used especially in wear type loading conditions. An interesting question is the relationship between the 2D and 3D roughness parameters and their information content, relating to tribological problems. Besides giving a systematic overview of the most important parameters applicable in wear analyses we also present examples of 2D and 3D roughness data determined on surface of nitrocarburised steels, as well as silicon nitride ceramics. A special emphasis is placed on those parameters which can be most efficiently used during wear damage analyses of ceramic materials.

Abstract: The so-called phase diagram is one of the oldest but at the same time one of the most useful method for the material science. The role of algorithms and software calculating the phase diagram have an extraordinary importance in the industrial and research-development applications because remarkable advantages can be obtained by installing these software or the detailed and exact data base developed by them into either the simulation programs or into the everyday production (process-control, checking). In our present paper, the investigation of data-requirement of calculation method of ESTPHAD phase diagram is described by processing binary-and ternary systems.

Abstract: From the lattice orientation of a sample, elements of the Nye-tensor can be determined. With the help of Nye’s tensor, dislocation density can be calculated for the certain sample. Since the measures were carried out with scanning electronmicroscope (SEM), just superficial orientations can be measured. Hence the Nye-tensor is an incomplete matrix, with five elements. Because of the absence of the other four elements just a quasi-dislocation density can be obtained. The algorithm of the calculation was programmed on the language C#.

Abstract: In the design of metalworking technologies, one of the most important amount is the flow stress of the material. A few experimental method can be used to measure it. The most commonly used tests to determine the flow curve of materials include upsetting of cylindrical or prismatic specimens, tension or torsion tests. In our work, the determination method of flow curve were investigated based on the principle of virtual power with cold working conditions. The experimental method, cylindrical upsetting, was executed on the Gleeble 3800 thermo-mechanical simulator. The goal was to determine reliable flow curve for large plastic strain. The results showed that reliable flow stress values were obtainable in equivalent plastic strain range of 0 to 0.7 by continuous cylindrical upsetting.

Abstract: To classify quantitatively the topological structure of all carbon fullerene molecules (fullerene graphs) we suggest a novel two-step method based on the following concept: As a first step, the duals of the fullerene graphs are generated, and as a second step, by using two molecular descriptors called Zagreb indices, we construct appropriately defined topological indices for structural characterization of fullerene isomers. Performing comparative tests on the set of C40 fullerene isomers, it will be demonstrated that the method suggested can be efficiently applicable to the stability prediction of fullerene-like materials.

Abstract: The austenitization of steels can occur in a wide variety of initial microstructures. In this study we addressed the transformation of banded pearlite steels. Banded pearlite initial structures similar to the real ones were created. In these structures the entire transformation process was simulated whose part processes are nucleation and grain growth. The nucleation is described by a free energy based model, and the Fick II. diffusion equation by using Finite Difference Method describes the grain growth. These models have been coupled in cellular automata simulations.