In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 9 No. 4 December 2003


Special issue on engineering materials and tribology



Foreword; 245

Jakob Kübarsepp and Priit Kulu

Evaluation of deformation methods of Cu-Al2O3 systems with quality factor; 246–251

Michal Besterci, Katarína Sülleiová, and Priit Kulu

Abstract. Quality of Cu-Al2O3 composite materials, prepared vith powder metallurgy, is assessed on the basis of the analysis of the deformation processes. Powder mixture was prepared by grinding Cu and Al2O3 particles. After the compaction, the materials were deformed by extrusion, forging, and isostacic pressing. Their microstructure and mechanical properties were qualitatively evaluated. By comparison of these three deformation technologies we found isotropic micro­structure in the materials forged and isostatically pressed. The materials, deformed by hot isostatic pressing, which possessed a low residual porosity (< 1%), showed optimum properties (the ultimate tensile strength and reduction of the area).

Key words: Cu-Al2O3 composites, powder metallurgy, deformation process, mechanical properties, microstructure, quality factor.

Plastic flow of BCC metals at monotonous static and dynamic cyclic loading; 252–260

Antanas Ciuplys, Jonas Vilys, Vytautas Ciuplys, and Valdas Kvedaras

Abstract. This paper deals with the relation between the physical yield plateau and multicycle fatigue disintegration peculiarities. Low carbon steel 20 yield plateau alteration kinetics during the cyclic loading has been investigated. For this purpose samples were loaded cyclically by a fixed load for a number of cycles and after that abruptly statically stretched. It was established that plastic flow of BCC metals on the surface takes place similarly during the monotonous static and dynamic cyclic loading.

Key words: metals, mechanical properties, surface layer, cyclic loading, physical fatigue limit, yield plateau.

Elevated temperature wear of chromium carbide based cermets; 261–271

Irina Hussainova and Maksim Antonov

Abstract. Good thermomechanical properties, combined with low density and bulk chemical stability at temperatures approaching 1300 °C, make chromium carbide based composites of interest for a variety of wear-resistant applications and especially for applications at elevated temperatures. The purpose of this work is to study the erosion behaviour of Cr3C2-Ni cermets at room and elevated temperatures of 300 and 600 °C. Systematic studies of the influence of the impact variables on the collision process have been carried out using silica particles. The erosion of ceramic-metal composites is associated with the combination of ductile and brittle modes of wear and material behaviour is influenced by both microstructure and test conditions. The high temperature oxidation behaviour of Cr3C2-Ni has been investigated to show the advantage of these materials over conventional cemented carbides at elevated temperatures.

Key words: erosion, composites, microstructure, high temperature wear, oxidation.

Durability of advanced TiC-base cermets; 272–280

Heinrich Klaasen, Jakob Kübarsepp, and Irina Preis

Abstract. Mechanical and wear behaviour of some advanced cemented carbides, prospective for metalforming, TiC-base cermets and WC-base hardmetals differing in composition and binder structure have been analysed in a set of tests including durability (blanking performance and fatigue endurance) complemented by SEM. It was found that the blanking performance (durability during blanking of sheet metals) of a cemented carbide is controlled by its adhesive wear resistance and fatigue sensitivity (slope of the Wöhler curve). In respect to blanking performance and fatigue endurance, the advantage of advanced steel-bonded TiC-base cermet over the conventional WC-base hardmetal used in metalforming has been revealed.

Key words: cemented carbide, cermet, hardmetal, blanking die, fatigue, wear.

Determination of residual stresses in a galvanic coating; 281–292

Alexander Ryabchikov, Harri Lille, and Jakub Kõo

Abstract. A method for the determination of residual stresses in a galvanic coating by measuring the longitudinal deformation of a straight strip (ribbon) substrate was elaborated. For this purpose, an experimental measuring system was designed. Experiments were carried out using a nickel coating deposited bilaterally from Watt’s electrolyte on a copper or brass strip substrate, and residual stresses were calculated. An equipment for fixing the strip substrate at one end and a load with a calibrated weight at the other was designed. The longitudinal displacement of the free end of the substrate, depending on the coating thickness, was determined by measuring the deformation of the elastic element. The effect of the rigidity of the elastic element on residual stresses was investigated. The results are compared with the literature data.

Key words: residual stress, strip substrate, elastic element, longitudinal deformation, galvanic coating, measuring system.

Spray parameter optimization and tribological properties of thermally sprayed quasicrystalline and partially quasicrystalline coatings; 293–303

Erja Turunen, Tommi Varis, Kari Vierimaa, and Simo-Pekka Hannula

Abstract. Good tribological properties and low coefficient of friction have previously been reported for thermally sprayed quasicrystalline coatings. In this paper HVOF spray parameter optimization and tribological properties of quasicrystalline coatings, manufactured from three different compositions, is discussed. On-line diagnostics measurements and splat studies were performed to optimize spray parameters of HVOF. Quasicrystalline coatings were produced and the coating microstructure was analysed. Large amount of wear and friction tests were performed to determine the tribological properties of quasicrystalline coating. Relatively high values of the coefficient of friction were obtained in the PoD-test. These tests yielded friction values varying typically between 0.4–0.6 independent of the counter material.

Key words: high velocity oxy-fuel (HVOF) spraying, quasicrystalline coatings, friction, wear, microstructure.

Applications of recycled hardmetal powder; 304–316

Sergei Zimakov, Toomas Pihl, Priit Kulu, Maksim Antonov, and Valdek Mikli

Abstract. This paper is devoted to the study of hardmetal powders of different particle shape, produced from used hardmetal by a mechanical disintegrator milling technology. The WC-15Co hardmetal powder of 0.2 to 0.5 mm with angular and round particle shape has been investigated. Particle granularity is characterized by the mean particle size and the angularity of milled powders is described by the so-called “spike parameter”. The influence of the hardmetal particle angularity on the erosion rate of different metallic materials has been determined. The experiments showed that this parameter is crucial in abrasive particle shape characterization. The wear resistance of composite coatings, based on self-fluxing alloy and hardmetal powders of different particle shape, was studied. These coatings showed minimal difference in their wear resistance.

Key words: hardmetal powder, angularity, abrasivity, powder coatings, wear resistance.

Instructions to authors; 317–319

Copyright Transfer Agreement; 320

Contents of volume 9; 321–322