Cavitation wear of Eurofer 97, Cr18Ni10Ti and 42HNM alloys

The microstructure, hardness and cavitation wear of Eurofer 97, Cr18Ni10Ti and 42HNM have been investigated. It was revealed that the cavitation resistance of the 42HNM alloy is by an order of magnitude higher than that of the Cr18Ni10Ti steel and 16 times higher than that of the Eurofer 97 steel. Alloy 42HNM has the highest microhardness (249 kg/mm2) of all the investigated materials, which explains its high cavitation resistance. The microhardness values of the Cr18Ni10Ti steel and the Eurofer 97 were 196.2 kg/mm2 and 207.2 kg/mm2, respectively. The rate of cavitation wear of the austenitic steel Cr18Ni10Ti is 2.6 times lower than that of the martensitic Eurofer 97.

Assessment of tribotechnical properties and resistance to wear of plasma coatings

In order to determine the operating conditions of parts for which restoration of worn surfaces is acceptable by the method of plasma spraying of various powder alloys, contact fatigue tests were carried out under cyclic contact impulse loading. In addition, tribotechnical tests were carried out with various wear-resistant coatings under conditions of liquid sliding friction. Bench and operational tests showed the use of coatings obtained using modern plasma technologies, the feasibility of protecting parts operating in conditions of corrosion, waterjet and cavitation wear, as well as in sliding friction. The coating sprayed with Ni-Al intermetallic alloy powder provides the most reliable protection against shock cyclic impact and abrasion during liquid friction than other materials studied. Coating with wear-resistant self-fluxing powder Ni-Cr-B-Si-C alloy, hardened by solid carboboride phases, without its additional heat treatment for restoration of surfaces working in sliding friction pairs, is not recommended.

Mechanism of Cavitation Wear of a Low-Friction Composite Coating CrN+WC/C Deposed on Ferritic-Pearlitic P265GH and Austenitic X2CrNi18-9 (304L) Steels

In order to meet the expectations of the global industry in areas such as: energy, heating, aviation, automotive, railway, chemical, petrochemical, oil, gas, river and marine sectors, where material wear processes may occur due to the flow of water gas and steam or their mixtures with various degree of saturation at different pressures, the authors of this article have conducted research on the resistance to cavitation wear of a low-friction composite anti-wear PVD coating in the form of chromium nitride and tungsten carbide (CrN+WC/C) deposited by a physical method on the surface of structural elements in the form of cavitation generators operating in extreme conditions of cavitation wear. Structural elements were examined made of steel with the ferritic-perlitic structure of the P265GH grade and with the austenitic chromium-nickel structure of the X2CrNi18-9 (304L) grade with a protective composite low-friction coating applied onto their surfaces by the Physical Vapour Deposition (PVD) technique, intended for operation in the cavitation wear environment. In order to obtain the results, the investigations of mass loss and roughness profile changes were conducted and the analysis of structural-metallographic morphology changes on the surfaces of structural elements was performed using a scanning electron microscope at voltages accelerating from 5 to 20kV using secondary electrons detection. The results of cavitation wear on the surface of structural elements were obtained using a digital microscope operating in 4K technology with a progressive scanning system.

Prediction of cavitation wear resistance of metallic materials based on the results of measuring the roughness of a worn surface

A method is proposed for predicting the relative cavitation wear resistance of metallic materials using the ratio of the durations of their incubation periods of wear, based on measuring the rate of increase in surface roughness during the incubation period. The experiments were carried out in fresh water and artificial seawater. Keywords: cavitation wear, metal alloy, relative wear resistance, incubation period, surface roughness. [email protected]

Shock Waves as dominant Mechanism for Cavitation damage

In this paper, the mechanism of energy transfer from cavitation bubbles to solids is demonstrated as shock waves. To identify this mechanism, cavitation bubble structures, the corresponding damaged surface, and the wear particles in vibratory erosion tests on pure aluminum Al-99.999 using high-speed and SEM photography were observed. The eroded surface morphology was in the form of large swellings (hundreds of micrometers), which embodies the plastic flow. Results indicate that large swelling regions formed in a few seconds are caused by shock pressure waves and not by a microjet only several micrometers in size. The observed surface erosion and falling particles make it clear that the mechanism of cavitation wear is fatigue failure.

Measuring diameter of water jets affecting propeller blade surface under cavitation wear

The article analyses the structure of cavitated areas of the ship propeller blades made from aluminum bronzes with different composition. The most informative zones of cavitation wear are the cold-hardening zone and the peripheral one that help estimate the mechanical parameters causing the cavities to collapse. The dents formed on the metal surface in the process of hydrodynamic cavitation wear have spherical parts on their bottoms, in which it is possible to inscribe a circle of a definite diameter. There were conducted the experiments on forcing the ball indentors into the surface of different metal alloys. The first run of the experiments includes forcing of a steel ball with a diameter of 1.588 mm into the surface of 33 alloys with different hardness under the loads of 1 470, 980 and 588 N. The impression diameters were measured using Brinell magnifying glass. There has been found the power dependence between deformation of dents on the metals tested under hydrodynamic cavitation and hardness of the materials, which is similar to the dependence of deformation after forcing the ball indentors into the alloys of different hardness. The second run of the experiments included modeling the cold-hardening zone of the cavitation wear area by repeated forcing the ball indentors with the diameters of 1.588, 2.5, 3.175 and 5.0 mm into the bronze BrAZhNMts9-4-4-1 plates with area of 100 × 50 × 20 mm. Forcing was made into the side 100 × 50 mm previously ground and polished. The equal strain rate in impressions of different diameters was observed during forcing. A direct proportional relationship was obtained between the arithmetic mean deviation of the surface profile and the indenter diameter. The arithmetical mean deviation of the assessed profile of the side plotted against the ball indentor yields a direct proportional relationship. Using the dependence for the case of cavitation attack on the propeller blades helps to infer that the diameter of water jets striking against the propeller blade surface with diameter of 3 700 mm makes about 10 mm. The obtained value allows to choose reasonably the experimental equipment and the parameters of testing the ship propeller materials for cavitation wear.

Study of failures of reciprocating medium-speed diesel engines

The article is focused upon the problems of reciprocating diesel engines. The main reason for the failure of cylinder-piston group (CPG) parts is insufficient strength, wear resistance, and resistance of the metal structure to vibration. There are studied the following periods of engine operation: running-in period; period of normal operation; period of intensive wear. In the burn-in period, the main cause of CPG failures is scuffing, when finger breaking or ring groove chipping take place. Sudden failures during normal operation occur due to the wear of the bushings to the limit size. In the third period of intensive wear the main cause of metal failures is the ultimate wear by cavitation erosion and breakage of the bushing collar. The block diagram of the CPG system with serial connection of elements is given. The rate of CPG failures is illustrated depending on the time of operation. It has been found that the failure rate during the running-in period due to scuffing is reduced because of stabilization of the structure, dimensions and mechanical properties of the piston at operating temperatures (300–350°C). The failure rate of the normal period of operation depends on the increase in the abrasive wear resistance of the metal of bushings, increased hardness, due to the replacement of gray cast iron with lamellar graphite by gray cast iron with vermicular graphite or by high-strength cast iron with spherical graphite inclusions. There are listed the positive and negative qualities of aluminum alloys in comparison with cast iron. Variants of damage to cylinder liners are considered in detail. The most dangerous defect in the bushing is the cracks in the upper liner collar, as a result of which about 40% of the cylinder bushings must be replaced. The formulas for calculating the actual wear rate of the CPG parts during the first (end of warranty periods), medium and major overhauls are given. The failure rate of the last period of operation (intensive wear) is reduced by reducing vibration in the CPG system, reducing the amplitude of forced vibrations and reducing the size of the thermal gap between the sleeve and the piston, increasing the rigidity of the sleeve. The rate of cavitation wear of modernized and conventional bushings is determined, the influence of the bushing stiffness on cracks under the shoulder and on cavitation wear up to the maximum permissible thickness is considered.