Effect of microstructure on the erosion and impact damage of sintered silicon nitride

The erosion rates and impact damage of two sintered silicon nitride materials with identical compositions but different microstructures were determined as a function of impacting particle (SiC) kinetic energy and temperature (25–1000° C) using a slinger-type erosion apparatus. The coarse-grained silicon nitride had significantly better resistance to impact damage than the fine-grained material. Crack-microstructure interactions were characterized using scanning electron microscopy and showed that crack-bridging was an important toughening mechanism in the coarse-grained material. Post-impact strength data were significantly less than those predicted from the indentation-strength data, due to impact flaws linking up prior to fracture. Consistent with its greater fracture resistance, the erosion rate of the coarse-grained material was less than that of the fine-grained material for erosion at 25 deg, and was independent of erosion temperature.     

Flux rate effects in the erosive wear of elastomers

The variation of erosion rate with particle flux was studied for five elastomers (natural rubber and epoxidized natural rubber, both with and without antioxidant, and butyl rubber) whilst subject to erosion by 120m silica particles at 50 m sec^–1. Th.e erosion rate was found to increase at low particle fluxes, for the elastomers without antioxidant. Infrared spectroscopy showed that there was a considerable degree of oxygen incorporation into the elastomer surface during erosion. Studies with an intermittent erosion stream suggest that a transient reaction occurs on impact causing degradation of the elastomer surface, which can account for the variation of erosion rate with particle flux. Studies with a range of erodent particles (silica, alumina, silicon carbide and soda-lime glass beads) showed that the degradation is more pronounced for hydrophilic particles.     

A model for calculating the erosion of a composite material

We generalize experimental data and present a model for calculating the erosion of some composite materials subject to impact by solid particles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 3, pp. 395–404, September, 1979.     

Fundamental relations of erosion kinetics

The relations between the kinetic parameters and the erosion characteristics of various materials subjected to the action of a particle stream are established for transition to the quasisteady phase.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 5, pp. 709–716, May, 1987.     

Computational simulation of thermally sprayed WC–Co powder

WC–Co cemented carbides are a class of hard composite materials of great technological importance. They are widely used as tool materials in a large variety of applications that have high demands on hardness and toughness, including mining, turning, cutting and milling. The HVOF (high velocity oxygen fuel) technology has been very successful in spraying wear resistant WC–Co coatings with higher density, superior bond strengths and less decarburization than many other thermal spray processes, attributed mainly to its high particle impact velocities and relatively low peak particle temperatures. The degree of decomposition and bond strength is directly related to relevant particle parameters such as velocity, temperature and state of melting or solidification. These are consecutively related to process parameters such as powder particle size distribution, carrier gas flow rate, and fuel type employed. To obtain detailed particle data important for thermal spraying, mathematical models are developed in the present paper to predict the particle dynamic behavior in a liquid fuelled HVOF thermal spray gun. The particle transport equations are coupled with the three-dimensional, chemically reacting, turbulent gas flow, and solved in a Lagrangian manner. The melting and solidification within the particles as a result of heat exchange with the surrounding gas flow is solved numerically. The in-flight characteristics of WC–Co particles are studied and the effects of carrier gas parameters on particle behavior are examined. The results demonstrate that WC–Co particles smaller than 5 μm in diameter undergo melting and solidification prior to impact while most particles never reach liquid state during the HVOF thermal spraying. The flow rate of carrier gas has considerable influence on particle dynamics as well as deposition on substrate. At higher flow rate the powder particles are redirected further away from the substrate center, while smaller flow rate results in better heating, higher impact velocity and deposition closer to the substrate center.     

Action of a rectangular pulse of a neodymium laser on porous metal targets

By the method of laser probing the erosion products of porous metal targets of Al and W under the action of a rectangular radiation pulse of a neodymium laser are investigated. The diameters of metal particles in the erosion flame measured using an electron microscope and using laser probing are fairly close, which indicates the reliability of control of particle sizes in real time by the laser probing method. The possibility of decreasing the particle sizes by reevaporating them is shown.A. N. Sevchenko Research Institute of Applied Physical Problems, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 2, pp. 179–183, February, 1994.     

Solid particle erosion resistance of ductile wrought superalloys and their weld overlay coatings

The elevated temperature (400°C) erosion behaviour of six weld overlay coatings and wrought alloys of similar compositions, was analysed and the relative ranking of their erosion resistance has been developed. Microhardness tests performed on eroded samples showed that all materials experienced significant plastic deformation. No relationship was observed between hardness of the coatings at 400°C and their erosion resistance. A new toughness parameter was developed based on the measured area under the microhardness profile curve, which represents the ability of a material to absorb impact energy. This parameter correlated well with erosion resistance for both weld overlays and wrought alloys. Also, for the wrought alloys, an increase in area under the true stress–strain curve or tensile toughness, corresponded to an increase in erosion resistance. The physical significance of the toughness parameter is discussed along with relationships between hardness, tensile properties and erosion resistance. © 1998 Chapman & Hall     

Densification and microstructure development during the sintering of submicrometre magnesium oxide particles prepared by a vapour-phase oxidation process

The densification behaviour and microstructure development of MgO compacts fired from room temperature up to 1700°C at a heating rate of 10°C min^–1 were examined. Starting materials were seven kinds of MgO powder with primary particle sizes ranging from 11–261 nm; these powders were produced by a vapour-phase oxidation process. The original powders contained agglomerates, due to the spontaneous coagulation of primary particles, which ranged in size from 100–500 nm. The MgO compacts densified during firing by three types of sintering: sintering within agglomerates; sintering between agglomerates and grains; and rearrangement of agglomerates and grains. The MgO compact with the lowest primary particle size (11 nm) densified by the first and second types of sintering, but the effects of these two types of sintering decreased when the primary particle size became 44 nm; here the rearrangement of agglomerates and grains primarily contributed to densification of the compact. All three types of densification became less complete with further increases in primary particle size up to 261 nm. The relative densities of the MgO compacts with smaller primary particle sizes (11–44 nm) became 96–98% when the compacts were fired up to 1700°C.     

Review Processes and influencing parameters of the solid particle erosion of polymers and their composites

The solid particle erosion behaviour of polymers and polymeric composites has been reviewed. Attention was paid to the effects of testing variables (e.g., erodent type, size and flux, impact angle) and target material characteristics (e.g., crystallinity, crosslink density, reinforcement content and arrangement). The occurring failure mechanisms were classified and discussed. Various predictions and models proposed to describe the erosion rate (ER) were listed and their suitability was checked. Recommendations were given how to solve some open questions related to the structure—erosion resistance relationships for polymers and polymeric composites.     

Similarity Criteria for Dusting of Plastic Materials

We propose a system of similarity criteria and criteria formulas that have made it possible to generalize the available experimental data on the erosion of plastic materials (metals) by particles, impacting with them at a right angle, with a rootmeansquare error of 30%. The experimental data analyzed have been obtained under the following conditions: velocity of the particles, 10–300 m/sec; temperature of the obstacle, room temperature–0.8T _m ; ratio between the densities of the particle flux and the obstacle material, 0.3–3; diameter of the particles, 40–3000 m. A formula for generalizing experimental data on the erosion of materials by particles incident on their surface at different angles has been obtained.     

Relaxation processes in electrodynamic plasma acceleration

Relaxation processes which occur in a plasma during its electrodynamic acceleration are analyzed. The corresponding mass-transfer equations are solved with an account of Joule erosion of the electrodes, particle diffusion, charge exchange, and the delay of mass separation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 3, pp. 517–526, March, 1970.     

Laboratory scale erosion testing of a wear resistant glass–ceramic

Abstract

The testing of erosion resistant materials is usually performed on laboratory scale test rigs under accelerated wear conditions. The validity of this is questionable because of the dependence of wear mechanisms on a variety of impact parameters. Data are presented that have been obtained from such tests on a glass–ceramic (Silceram) which has been developed as a low-cost erosion resistant lining material. Various impact conditions have been investigated, including impact angle, particle velocity, and impact frequency. The data concerning the effects of particle velocity show very good agreement with one particular erosion model, although there is an apparent dependence on other test variables.

MST/611     

Effect of pores and acicular eutectic silicon particles on the performance of Al–Si–Mg (AS7G03) casting

Excellent castability, corrosion resistance and high specific strength has made cast Al–Si–Mg alloys a suitable candidate material for various aerospace application. Aluminium alloy casting AS7G03, belonging to Al–Si–Mg series of cast alloy in Y23 condition, is being used as outlet adaptor of liquid propellant tank for Indian space programme. During developmental stage, one of the castings namely oxidizer tank outlet adaptor failed and parted in to two pieces during the proof pressure test (PPT) at 22 bar.This paper brings out the details of investigation and correlates the effect of pores and acicular unmodified silicon particle on the performance of the material.     

Effects of the Starting Material and Hydrothermal Treatment Conditions on the Crystallization of Ultrafine Silica

The effects of the starting material and hydrothermal crystallization conditions on the phase composition and particle size of the resulting nanocrystalline silica powders were studied. Hydrothermal treatment of silica gels, xerogels, and Aerosils in water and aqueous NaF and NaOH solutions at temperatures in the range 250–500°C and pressures of up to 100 MPa causes gradual dehydration and densification of the materials, accompanied by the formation of crystalline SiO₂ varieties, such as more or less ordered opaline silicas, cristobalite, keatite, and quartz. The extent and rate of these transformations, as well as the particle size of the crystallizing phases, depend on the starting material and the process parameters: temperature, pressure, duration, and environment. The best precursors to nanocrystalline silica with a particle size of 20–35 nm are silica gels and Aerosils treated in water at 250–300°C and 100 MPa.     

Hybrid lattice particle modeling: Theoretical considerations for a 2D elastic spring network for dynamic fracture simulations

A new hybrid lattice particle modeling (HLPM) scheme is proposed. The particle–particle interaction is derived from lattice modeling (LM) theory, whereas the computational scheme follows particle modeling (PM) technique. The newly proposed HLPM considers different particle interaction schemes, involving not only particles in the nearest neighborhood, but also the second nearest neighborhood. Different mesh structures with triangular or rectangular unit cells can be used. The current paper is concerned with the mathematical derivations of elastic interaction between contiguous particles in 2D lattice networks, accounting for different types of linkage mechanism and different shapes of lattice. Axial (α) and combined axial-angular (α − β) models are considered. Derivations are based on the equivalence of strain energy stored in a unit cell with its associated continuum structure in the case of in-plane elasticity. Conventional PM technique was restricted to a fixed Poisson’s ratio and had a strong bias in crack propagation direction, as a result of the geometry of the adopted lattice network. The current HLPM is free from the above-mentioned deficiencies and can be applied to a wide range of impact and dynamic fracture failure problems. Although the current analysis is based on the linear elastic spring model, inelastic considerations can be easily implemented, as HLPM has the same force interaction scheme as PM, based on the Lennard–Jones potential.     

Effects of blockage and erosion on the filtration of suspensions

A model of filtration is considered which takes into account blockage (colmatation) and erosion (suffosion) of the pores using a generalized relationship between permeability and porosity.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 2, pp. 244–250, February, 1990.     

Collision of polymer particle with rigid barrier

The article establishes a correlation of the relaxation spectrum with the dissipation of kinetic energy of a polymer particle upon impact.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 909–916, December, 1986.     

Shock compaction of AlMgSi0.5 spheres

Shock compaction of AlMgSi0.5 was realized by using a LEXAN projectile with a velocity of 1655 ms^–1. The dynamic pressure in the zone of impact was 8 GPa in the sample in the target at room temperature. The sample consisted of spheres of two particle size fractions (100–200 m and 200–315 m) separated in layers through which the same shock wave was passing. The appearance of non-porous interparticle contacts in the impact zone, with the content of melted areas up to 10% was detected in the case of the larger particle fraction only. Smaller particles had no tendency to form the strong interparticle contacts, not even in the first layers in the direction of the shock wave. TEM analysis showed the presence of an intensively deformed structure in the zone of the planar shock wave, as well as the structures with very poor signs of recovery and recrystallization in particle contact areas. The hardening effect of the shock wave was obvious, so that microhardness in the zone of the planar wave in larger particles had reached the value of 120 Hv, much higher than the microhardness of the initial powder (70 Hv).