Correlation between solid particle erosion of metals and their melting energies

A new correlation is presented for the ductile erosive wear of metals by an impinging stream of abrasive particles. The specific erosion energy (the kinetic energy per unit volume of metal removed) is shown to be directly proportional to the melting energy per unit volume of the target metal. By analogy with grinding, this direct correlation is attributed to the extreme strains and strain rates which characterize the erosion process, thereby leading to near adiabatic plastic deformation of the metal to its energy limit.     

Flux effects in solid particle erosion

Systematic measurements of the steady state erosion rate as a function of erodent particle flux were made for a range of different erosion conditions. A significant decrease in erosion rate with increasing flux was observed. A first-order particle collision model was developed that provides a physical basis for describing the flux effect. The data confirm the exponential dependence of the erosion rate on flux predicted by the model. Further analysis of the data within the context of the collision model also provides new insight into the particle impact process.     

Some aspects of solid particle erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It was shown that the erosive wear resistance of cermets can not be estimated only by hardness, characterizing resistance to penetration. The differences in wear resistance between cermet materials with equal hardness levels can be attributed to differences in their resistance to fracture and fracture toughness. The mechanism of erosion depends first on testing conditions. The present paper discusses some features of the material removal process during particle-wall collision. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

Correlation between solid particle erosion of cermets and particle impact dynamics

Since the erosion rate depends on energy exchange between particle and material, a reformulation and solution of the equations of two solid bodies collision is presented and adapted to the calculation of the energy absorbed by a material surface during impact of a spherical particle onto a plain target. It has been observed that energy loss is a strong function of dynamic coefficients named as coefficient of velocity restitution after impact, k, and coefficient of dynamic friction, f. The new method and experimental equipment for the coefficients determination are described. It was shown that energy consumption during application may be an appropriate guide for the material selection in the conditions of erosive wear.     

Single solid particle impact erosion damage on polypropylene

The literature on the erosion of polymers is reviewed. Single-particle impacts by spheres of 4 mm diameter have been carried out at various angles and speeds on polypropylene. The crater types are classified and plotted on a “deformation map”. High speed photography was used to record the impacts and any material loss. Both ductile (the drawing out of filaments) and brittle (the fracturing of blocks of polymer) erosion processes were observed. The surface finish of the specimens is an important variable in the latter mechanism.     

The role of adiabatic shear in solid particle erosion

A comparison is made of the deformation produced when titanium and mild steel target specimens are impacted obliquely by flat-ended cylindrical projectiles. The impact process is studied by high speed photography; it is shown that whereas in mild steel material is not removed from the surface but merely displaced, in titanium, the displaced material detaches by a process involving the formation of adiabatic shear bands. Attention is drawn to the influence of susceptibility to adiabatic shear on resistance to solid particle erosion.     

Analysis of interlaboratory test results of solid particle impingement erosion

During the development of a standard method for solid particle impingement erosion testing of materials, a number of interlaboratory test comparisons were conducted. In this paper the results of four test series involving twelve laboratories in total are described. The measurements were carried out with considerable care using the gas jet type of erosion tester, involving nearly the same conditions and test parameters on two different materials, a low carbon steel and a stainless steel. The final results indicated a high degree of within-laboratory precision and a moderate degree of between-laboratory precision of erosion loss determinations. A need for standard materials was identified to control sources of measurement bias between laboratories. The principal source of random error in these studies was believed to be associated with the measurements of particle impact velocity.     

Particle size distribution effects on the solid particle erosion of brittle materials

The effects of distributions of projectile size and velocity on the erosion of brittle materials were assessed. Strong dependences of the steady state erosion rate on the width of the particle size distribution and on the velocity characteristics of the erosion equipment were predicted. The predictions were confirmed by experiment. The results indicate that careful design of controlled erosion experiments is essential in order to avoid misleading predictions of in-service erosion rates. The implications of the analysis for the interpretation of threshold effects and for experiments designed to verify erosion theories are also discussed.     

Investigation on solid particle erosion behaviour of polyetherimide and its composites

The present investigation reports about, the solid particle erosion behaviour of randomly oriented short E-glass, carbon fibre and solid lubricants (PTFE, graphite, MoS₂) filled polyetherimide (PEI) composites. The erosion rates (ERs) of these composites have been evaluated at different impingement angles (15–90°) and impact velocities (30–88 m/s). Mechanical properties such as tensile strength (S), ultimate elongation to fracture (e), hardness (H_V), Izod impact strength (I) and shear strength (S_s) seems to be controlling the erosion rate of PEI and its composites. Polyetherimide and its glass, carbon fibre reinforced composites showed semi-ductile erosion behaviour with peak erosion rate at 60° impingement angle. However, glass fibre reinforced PEI composite filled with solid lubricants showed peak erosion rate at 60° impingement angle for impact velocities of 30 and 88 m/s, whereas for intermediate velocities (52 and 60 m/s) peak erosion rate observed at 30° impingement angle. It is observed that 20% (w/w) glass fibre reinforcement helps in improving erosive wear resistance of neat PEI matrix. Erosion efficiency (η) values (0.23–8.2%) indicate micro-ploughing and micro-cutting dominant wear mechanisms. The morphology of eroded surfaces was examined by using scanning electron microscopy (SEM). Possible erosion mechanisms are discussed.     

The erosion of aluminum by solid particle impingement at normal incidence

A rotating arm apparatus was used to study the erosion of polycrystalline aluminum by 1.58 mm diameter WC-6% Co spheres impinging at normal incidence. Dynamic hardness values were obtained from measurements of the impact craters and compared with corresponding quasi-static values. In addition, material removal was monitored gravimetrically, and quantitative information was obtained on threshold and incubation phenomena and steady state erosion behavior. The variation of the velocity dependence of erosion with the number of particle impacts was derived from these data. Supporting scanning electron microscope studies suggest that the mechanism of material removal responsible for ductile erosion at near normal incidence is somewhat different from that which operates at shallower angles. The similarities and differences between these mechanisms are discussed, and it is suggested that together they account for the characteristic variation of ductile erosion with angle of impingement.     

Effects of hardness on the solid particle erosion mechanisms in AISI 1060 steel

The mechanisms of mass loss were studied using impacts of single particles (WC spheres $\text{3}\text{16}$ in in diameter) for a 0.6% C steel (AISI 1060 steel) heat treated to give hardnesses of 12, 45 or 60 HRC. Both oblique and near-normal angles of impact were used. A new foil laminate was developed to measure rebound velocity and angle. Velocities of 100–200 m s^?1 were studied. A measurable mass loss was found only at 200 m s^?1. At a hardness of 12 HRC the mode of metal loss involved the loss of shear lips. At 60 HRC the dominant loss mode involves the intersection of adiabatic shear bands (ASBs) and shows a maximum mass loss at near-normal impact. The material with a hardness of 45 HRC shows both modes of mass loss and a maximum mass loss rate at oblique (30°) impact. ASBs on the surface and welding of target material to the impacting ball indicate a high temperature at the surface. However, the material welded to the particle is not a significant fraction of the material lost.     

The halo effect in jet impingement solid particle erosion testing of ductile metals

Two different areas of erosion occur on flat test specimens exposed to gas—solid particle erosive streams where the stream diameter is smaller than the specimen surface dimensions. The inner area accounts for the majority of the weight loss. This area sees the set test conditions of velocity and impingement angle. Erosion also occurs outside this area in an area designated the “halo area”. The weight loss in this area depends on the impingement angle of the particles and ranges from as high as 25% of the total weight loss at 15° to 3% of the total weight loss at 60°. A definite boundary was observed between the two areas. This halo erosion effect was found to be primarily due to the velocity distribution of the particles in a cone around the principal column of particles striking the specimen. A secondary effect is the change in the true angle of the particles striking the specimen from the set angle.     

Influence of impingement angle on solid particle erosion of carbon fabric reinforced polyetherimide composite

Polyetherimide (PEI) composite reinforced with plain weave carbon fabric (CF) (40% by volume) was developed and characterized for physical and mechanical properties. The erosive wear behaviour of PEI and its composite was evaluated using silica sand particles at a constant impact velocity but varying angles of impingement. It was confirmed that though all the mechanical properties of PEI improved substantially by CF reinforcement, the erosion resistance (W_R) deteriorated by a factor of almost four–six times at all angles of impingement. Both materials showed minimum wear at normal incidence (90° impingement). In spite of the fact that PEI is not a very ductile polymer (elongation to break-60%), it showed maximum wear at 15° which is a characteristic of ductile and semi-ductile mode of failure. The composite (elongation to break-1%) also showed highest wear at 30° (impingement at 15° was not studied). These phenomena were explained using scanning electron micrographs of the eroded surfaces.     

Effects of fibre content and relative fibre-orientation on the solid particle erosion of GF/PP composites

The erosive wear behaviour of glass fibre (GF) reinforced thermoplastic polypropylene (PP) composites was studied in a modified sandblasting apparatus as a function of the impact angle (30, 60 and 90°), relative fibre-orientation (parallel Pa and perpendicular Pe), fibre length (discontinuous, continuous) and fibre content (40–60 wt.%).The results showed a strong dependence of the erosive wear on the relative fibre-orientation at low impact angles (30°), but hardly any difference for 60 and 90° impact angles. In contrast, the fibre length did not affect the erosive wear behaviour especially at high impact angles.The inclusion of brittle GF led to higher erosive wear rates (ER) of the GF/PP composites; the higher the fibre content, the higher was the ER. Nevertheless, the composites still failed in a ductile manner. Different approaches proposed to describe the relationship between ER and fibre content were applied. Best results were generally delivered with the inverse rule of mixture. The modified rule of mixtures proposed for abrasive wear do not seem to apply for erosive wear.     

Solid particle erosion of mullite

The solid particle erosion of mullite (3Al₂O₃·2SiO₂ plus approximately 12% glass phase) was investigated using angular A1₂O₃ particles whose mean diameters D were varied between 23 and 270 μm. A range of impact angles α between 15° and 90° was used and the impact velocity V was varied from 60 to 100 m s^?1. The results of these experiments are in agreement with the general predictions of the two models developed to describe erosion in brittle materials on the basis of the formation of lateral cracks. The velocity exponent of the steady state erosion rate ΔW is between 2.2 and 2.8, being larger for smaller particles. For normal incidence, $\text{ΔW ∝ D}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ in accord with both theories. For α > 15° only the normal component of velocity need be considered, but for smaller α there is evidence of plasticity both in the α dependence of ΔW and as observed using scanning electron microscopy.     

Mechanisms of solid particle erosive wear for 90° impact on copper and iron

High purity copper single crystals and fully annealed polycrystalline α-Fe were eroded by glass spheres 70 μm in diameter suspended in an argon gas stream and travelling normal to the target surface at 122 m s^?1. Detailed scanning electron microscopy of eroded surfaces, together with transmission electron microscopy of erosion debris, was performed. It was observed that the surfaces developed a stable hill-and-valley topology not reported previously. The mechanism of material removal was plowing on the hillsides and flaking due to subsurface crack propagation in the valleys. Subsurface voids were created independently of second-phase particles and evidence existed for a local temperature rise at the surface.     

Nozzle passage aerodynamic design to reduce solid particle erosion of a supercritical steam turbine control stage

The solid particle erosion on the control stage nozzle of supercritical steam turbines can be reduced by using suitable nozzle passage design to control the particle impacting velocity and impacting angle. In this paper, two nozzle designs with tip endwall contouring/an aft-loaded vane profile respectively are presented. Furthermore, anti-erosion performances of these two nozzles for a supercritical steam turbine control stage are numerically analysed by means of a three-dimensional particle trajectory tracking technique combined with an erosion model of 12Cr steel impacted by iron oxide particle at 500 °C, which is developed based on the available experimental data. The three-dimensional solid particle moving behaviors, particle impacting positions, impacting parameters and local erosion rate distributions on the nozzle surface are computed and compared with those of a straight endwall nozzle under same conditions. The results show that the contoured endwall nozzle design can decrease the particle impacting velocity and thus reduce particle erosion damage effectively. Compared with the straight endwall nozzle the maximum local erosion rate and the severely eroded area on the pressure surface of presented endwall contouring nozzle are decreased by a factor of 40% and 30%, respectively. However, in comparison to the straight endwall nozzle the maximum local erosion rate of the aft-loaded nozzle is increased by a factor of 25% and the severely eroded surface area is about the same due to higher impacting velocity and larger impacting angle and hence the anti-erosion performance is not improved.