In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 10 No. 1 March 2004


Strengthening of the surface layer microstructure with a laser beam; 3–9

Regita Bendikienë, Sangaudas Chodoèinskas, and Edmundas Pupelis

Abstract. Wear resistance and durability of the products depend on the nature of the solid solution and microstructure. Minimal wear have materials with optimum alloyed solid solution and fine particles, usually carbide inclusions. Such a structure is difficult to obtain using traditional methods of manufacturing. Blanks of alloyed steels have coarse grains and carbide inclusions of undesirable shape, arranged discretely. To change such a microstructure is impossible. Therefore the purpose of the present paper is to create a desirable microstructure using micrographical laser beam treatment and to evaluate the influence of treatment parameters and point drawing to wear resistance of the surface layer.

Key words: wear resistance, surface strengthening, laser treatment.

Melting and modification by producing ductile iron castings; 10–17

Stasys Boèkus and Aloyzas Dobrovolskis

Abstract. The effect of charge materials, melting conditions, section size, spheroidizing and inoculation methods on the chemical composition of melt and the matrix microstructure of ductile iron castings has been investigated. Results show that the amount of pig iron in the charge and the section size have a significant effect on the amount of ferrite in ductile iron castings. The increase of the temperature and holding duration of the melt in an induction furnace decreases the carbon content and increases the silicon content. The intensity of spheroidizing affects the carbon and residual magnesium contents in the ductile iron castings.

Key words: ductile iron, charge, spheroidizing, inoculation, metallic matrix.

Adsorption distribution of the ion associates and ion-exchange at the water/1,2-dichloroethane interface by extracting with cesium dicarbollyde; 18–22

Tatyana Borisova

Abstract. The paper presents evaluation of the distribution ratios of dicarbollylcobaltate (III) of alkali metal salts and of the voluminous constant of exchange of sodium by magnesium on a monolayer. A comparison of these values, calculated by different methods, has been made and the influence of counterions on the surface activity of cesium dicarbollyde is investigated. Interfacial tension isotherms have been used to study the adsorption at the water/1,2-dichloroethane interface and to evaluate the above-mentioned values.

Key words: dicarbollylcobaltate (III) anion, interface, interfacial tension, isotherm, drop-volume method.

Preparation of nanosized W- and WC-based powders and their processing; 23–29

Janis Grabis, Ilmars Zalite, Dzidra Jankovica, and Dzintra Rasmane

Abstract. Nanosized particles of tungsten and WC1–x or W2C with the average particle size of 10–14 nm have been prepared by evaporation and reduction of oxide by hydrogen, ammonia, or hydrocarbones in the radio-frequency nitrogen plasma. The consolidation of carbides containing nanoparticles by hot pressing at 1800 °C provides formation of a single WC-phase bulk material with the fine-grained microstructure.

Key words: nanosized materials, W-based powders, nitrogen plasma.

Laser ablation for 3D nanometric imaging of solids; 30–38

Ilmar Kink, Vambola Kisand, Kristjan Saal, Tanel Tätte, Madis Lobjakas, and Ants Lõhmus

Abstract. A new method for subsurface nanometric imaging is proposed that combines scanning probe microscopy and laser ablation techniques. The feasibility of the method was tested on mica samples by studying laser radiation interaction with the mica surface. The ablation of the samples was characterized as functions of deposited radiation energy and of the number of laser pulses. Additional examples of applicability of the method are presented using more complex samples such as a TiC : Ni compound and a biological tooth.

Key words: SPM, laser ablation, three-dimensional imaging.

Testing hardened steel targets for dynamic hardness; 39–44

Ilmar Kleis and Toomas Remi

Abstract. In literature no information can be found about any recognized method of testing steels harder than 350 HV for dynamic hardness, neither about its numerical values for different steels, needed for the prediction of erosion resistance of steels. This paper represents a new method for the determination of dynamic hardness properties of hard materials and discusses the test data obtained on steels with hardness range of 360–820 HV.

Key words: hardened steels, dynamic hardness, dynamic-to-static hardness relationship.

Adapting the energetic erosion theory to hardened steels; 45–52

Ilmar Kleis and Toomas Remi

Abstract. This paper presents the ways and means of transformation of the existing energetic theory into a modified form, applicable for hardened steels by predicting their erosion rate in order to obtain a close correlation between the calculated values and test data. Differently from the initial form of the theory, employing static hardness for the estimation of particle penetration depth into the target surface, the modified theory utilizes dynamic hardness. More specified is the determination of the particle shape factor since besides its geometry the effect of crushing strength and angle of incidence are taken into account. In comparison with the values used before, for particles of extra high crushing strength as manufactured corundum impacting against hardened steel target, the shape factor may obtain values three times higher than normally expected.

Key words: erosion, wear, hardened steel, dynamic hardness.

Correction of the short-term forecast of high-voltage power consumption; 53–62

Taivo Kangilaski and Vladimir Jaanimägi

Abstract. This paper describes and proves an algorithm for approximating the high-voltage power forecasted consumption with a model function. The first and second derivatives are used to describe the real consumption function. The algorithm is used in Eesti Energia AS for the analysis and technical management of large-scale transmission networks.

Key words: short-term forecast, high-voltage power consumption, function approximation.

Copyright Transfer Agreement; 63