Investigation was focused on resistance of Astaloy CrL type sintered material to contact fatigue. The material in two versions (0·3 and 0·7 wt-%C) was covered with TiCN coating. The results show that resistance to contact fatigue increased substantially, up to the value of about 3410±90 MPa. This increase was influenced primarily by the properties of coating. In this case, the impact of the matrix was of secondary importance. The results obtained in the evaluation of life in terms of contact fatigue were confronted with those of the microscopic observation of generation and propagation of cracks leading to the formation of pitting, as well as with other tests. It describes the impact of contact fatigue stress to changes in the material at the point of application. A special section is devoted to the use of finite element method (FEM) for simulation of the Hertzian stress and changes during contact strain.

The article deals with the influence of laser beams, which when acting on materials affect their surface. Depending on the intensity of exposure and the speed of displacement of the beam, due to the heating of the material and the subsequent cooling, there occurs the change in the pattern of the surface and of course to a change in the properties in the volume that was exposed to the temperature changes. For the tests the sintered material based on iron powder type Astaloy CrL and CrM containing 0.7% C was used. Results showed that by the appropriate combination of laser parameters it was be possible to obtain the same structures as by using the technology of "sinterhardening". Compared to sintered state, the hardness of the surface of a material CrL +0.7% C values increased from 248 to 911 -1000 and at material CrM +0.7% C values from 450 to 1043 -1100 HV 0.05, depending on the velocity of displacement of the beam. The same is true for the values of microhardness. Hardness values reflect the structural changes that occur in the material due to rapid heating and subsequent rapid cooling. The first tests of this technology demonstrated its high variability and the potentials of replacing classical procedures.Keywords: laser hardening, sintered material, structure, hardness IntroductionLaser hardening is one of the new technologies, which is currently widely used in the manufacture of machine parts. The principle of laser quenching consists in the rapid heating of the material surface by laser, short holding time at temperature followed by cooling, heat dissipation due to thermal conductivity of the material. A significant advantage of the heat treatment is its speed, quality and especially stable reproducibility. In addition, it provides low thermal load to the ambient material, minimum distortions, low surface oxidation and prevents formation of surface cracks. It is also possible to arrange for local hardening only at the desired location, to control the depth of hardening and the resulting hardness. The temperature is in many cases controlled on-line by a pyrometer directly integrated in the optics. Typical applications include local hardening of molds, tools, gears and racks, guide surfaces, parts of transmissions, shafts, cams and turbine blades and vanes [1][2][3][4][5]. Nowadays, when in the engineering practice, powder metallurgy product are increasingly promoted, knowing the possibilities of using this type of heat treatment at this type steels is quite real. In the actual powder metallurgy practice in connection with the development of steels for highly stressed components, such alloyed materials has been introduced, which following heat treatment by hardening are able to achieve the desired mechanical properties. In addition to conventional quenching, by some suitably alloyed materials, there are currently method in use

In this article, we propose the parameters of a battery that would be suitable for the conceptual design of a small training aircraft. The mass design of the battery is based on the requirements for real training flights performed by students in pilot training. Such a serial hybrid propulsion aircraft could be used in our UNIZA aviation, training and education center for pilot training. Due to socio-political pressures in reducing emissions generated by vehicles, there has also been massive research in the aviation industry in the field of hybrid and electric aircraft propulsion. In the introduction, the article deals with the energy sources used in aircraft propulsion. In hybrid propulsion, a combination of aviation fuel and electricity is used as the energy source. The required total energy must choose a suitable combination of these two energy sources. The biggest drawback of batteries that can be used in hybrid systems is their low energy density. Low energy density means that larger and heavier batteries need to be used to achieve the required performance, which is their main disadvantage. Therefore, it is necessary to find a suitable compromise between the hybrid’s percentage, i.e., the ratio between conventional and electric drive. We applied the hybrid aircraft system’s calculations to the real training flights to determine the necessary parameters of the hybrid aircraft suitable for pilot training. This calculation will help in obtaining an idea of the basic parameters of the hybrid drive and the battery parameters, which are necessary for particular applications in the training aircraft. The performed calculations of the hybrid configuration and, especially, the determination of the battery of the hybrid propulsion parameters provide the basic information necessary for the design of the hybrid system of a small training aircraft. These outputs can be used to determine the parameters of batteries that would be used in hybrid systems. A limiting factor to consider with hybrid aircrafts is that the aircraft must be charged on the ground before the flight, which poses interesting logistical and infrastructure problems at the airport.

The article deals with the assessment of material characteristics of the two types of steels. One was produced some 100 years ago and used in the construction of barracks in the former so-called" Saffron garden "site in Kosice. In connection with the reconstruction there arose the need to review the eligibility of steel for further use in the new project. Within the framework of reconstruction a new steel produced in the current circumstances was used. Conducted analysis at booth steel specimens reveals extensive difference especially in steel microsture homogeneity, considerably incluencing their mechanical properties. These results will help by reconstructional Works especially for engineers responsible for architecture and for Structural engineers, because public safety is the most important issue.

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