STRENGTH AND HIGH-PLASTICITY MATERIALS FRACTURE MECHANISMS UNDER DISCRETE WATER-DROPLET FLOW

The field research results of the austenitic steel wear under the droplet impact erosion are presented. The stages of the erosive wear origin and development are considered. The leading part of the side cracks in the forming and growth of the erosion fracture craters, as specified in Marshall-Lawn model, is shown by the high-resolution scanning electron microscopy technique

Estimation of erosion resistance of hardened metal alloys under conditions of droplet impact

Introduction. The phenomenon of the droplet impingement erosion which develops in the metallic materials at the frequencies of drop collisions of 50 ... 200 s-1 and velocities of 150 ... 600 m/s is considered. The comparative estimability of the wear resistance of materials of various structural classes and with different levels of mechanical properties is investigated. The major goal of the work is the development of a computational and analytical model of erosion wear of hardened materials. In parallel, the problem of the criterial evaluation of materials, with the help of which they could be attributed to plastic or reinforced materials and then used as a corresponding model of the fatigue failure mechanics, is solved.Materials and Methods. The well-known dependences of the fracture mechanics and the fatigue theory of Paris-Erdogan are used for the computational and analytical estimates of the erosion resistance of materials. The calculated expressions parameters are obtained on the basis of the bench erosion test results and scanning electron microscopy data of samples of 20Cr13 steel with a martensitic structure.Research Results. It is suggested to use limiting state diagrams of the ductile and durable materials as their classification criterion. In particular, the initial and critical size of the brittle fracture can be determined on the basis of such a diagram of the hardened materials. These values are used in the basic model to calculate the erosion resistance of the material. Based on theParis equation from the fatigue theory of ParisErdogan, a computational and analytical model for estimating the erosion resistance of the hardened materials is developed and scientifically proven. Their surface degradation occurs according to the mechanism of nucleation and development of cracks of the clasped type. The calculation data are presented for samples of martensitic 20Cr13 steel using the experimentally obtained parameters of theParis equation.Discussion and Conclusions. The results obtained are relevant for the selection, optimization or development of the erosionresistant materials for high-speed blades of the steam-gas turbine and compressor equipment operating under the conditions of condensate formation

DERIVATIZATION OF PHOTOACTIVE STRUCTURES SI(N+)/SI(P)/SI(P+) THROUGH ION-BEAM CRYSTALLIZATION

The physical and mathematical mass-transfer model of the ion-beam crystallization method is developed. The derivatization of photoactive structures Si(n+)/Si(p)/Si(p+) on 100 mm substrates through ion-beam crystallization is considered. The optimum conditions for the process: residual pressure in the growth chamber — 10−4 Pa; the substrate temperature — 550 °C; ion current density — 2 mA/cm2; acceleration voltage — 400 V; target — substrate distance — 150 mm are determined. The scanning electron microscopy data show that the grown photoactive structures have closely a faultless surface. The results demonstrate that the photoactive structures Si(n+)/Si(p)/Si(p+) offer the external quantum efficiency over 90 % in the wavelength range of 550—900 nm (spectrum AM 1.5) under the following conditions: front layer thickness Si(n+) — 100 nm; donor doping density n+ = 5∙1018 cm−3; layer thickness Si(p) — 130 μm; acceptor doping density p = 2∙1016 cm−3; layer thickness Si(p+) — 500 nm; acceptor doping density p+ = 1∙1018 cm−3

To problem of hydrogen embrittlement of steel at droplet impingement erosion

Introduction. The work is devoted to the problem of the hydrogen saturation of steel parts skin at their high-speed impacts with a water-drop flow. A hypothesis of the water molecules dissociation at high-speed drop impacts was suggested in a number of papers. This hypothesis was confirmed by some experimental data. The effect of this dissociation is hydrogen embrittlement of the metal surface layer. The work objective is the calculation and experimental verification of the given mechanism of the erosion destruction of the steel surface. Materials and Methods. Energy equations of various ways of the water molecules dissociation are considered for the calculation-analytical estimates. The Tate and van der Waals equations are used with allowance for the change in the phase states of water at impact. Experimental data are obtained on the basis of spectral analysis using visible monochromatic (qualitative analysis) and infrared (quantitative analysis) emissions. Research Results. An improved calculation apparatus is proposed to determine the energy level of the water molecules dissociation and free hydrogen release with account for the compressibility of water at achievable impact speeds. The results of spectral studies of bubble tracks formed on the experimental steel samples under the bench erosion tests are presented. The spectral analysis shows that the tracks are composed of air bubbles. Free hydrogen is not detected in them. Discussion and Conclusions. The calculated and experimental data obtained in this paper do not give grounds for confirming the hypothesis of hydrogen dissociation under the water-drop impacts with a steel surface in the impact velocity range of 200-600 m / s. Therefore, the mechanism of hydrogen embrittlement, apparently, should be excluded from the number of additive components of the droplet impingement erosive wear

PREDICTION OF TITANIUM ALLOYS EROSIVE WEAR UNDER LONG-TERM DROPLET-IMPACT EFFECT

The approximating model for the definition of the steam turbines blades wear rate under the continuous operation through the droplet-impact erosion is built on the ground of the comparative analysis of the stand test data of the titanium alloy samples

Morphological features and mechanics of destruction of materials with different structures under impact drop cyclic loading

The process of erosion destruction of steels with austenitic, sorbitol and martensitic structure under the influence of high-speed liquid-drop collisions is studied. The characteristics of the morphological features and mechanisms of the process of surface degradation of steels with different structures are given. Their classification criterion is proposed on the basis of the diagrams of limiting states. Based on the theory of Paris-Erdogan, the computational and analytical model of the fatigue fracture of martensitic steel has been developed