Decrease In Erosion Rate Research Articles

Erosion resistance of refractory alloys modified by ion beams

The objective of the present research is the critical analysis of test results, dedicated to the effect of ion-beam irradiation conditions upon the sand particle erosion resistance of refractory alloys. Gas turbine engine compressor blades, produced with titanium alloys (VT9 and VT18U) as well as refractory steels (EP866sh and EP718ID) were used as the study objects. The ion implantation and irradiation of targets for the high-power pulsed ion beam were accomplished by means of Delta, Raduga-2 and Temp-M accelerators. The irradiation conditions were varied within the following ranges: B, N, C, La, Pd, Sm and Hf ion implantation — E = 30–80 keV (ion energy), j = 40–5·10 3 μA/cm 2 (ion current density), f = 30 Hz (pulse frequency), D = 10 16–2 10 19 ion/cm 2 (irradiation dose); high-power pulsed ion-beam irradiation — ions of carbon (60–70%) and protons, E = 250–300 keV, j = 40–200 A/cm 2, τ = 50 ns (pulse duration), n = 3–10 pulses (number of pulses). After irradiation some targets were subjected to vacuum annealing for 2 h at their service temperature. Erosion tests of initial and irradiated blades were performed in vacuum on the gas-dynamical branches with a sand load to 200 mg/mm 2 at the particle velocity of 200 m/s. The average size of the sand particles was equal to 80–120 μm. The target surface state prior to and after erosion tests was studied by Auger electron spectroscopy, scanning electron microscopy, transmission electron microscopy, optical metallography and X-ray structural analysis. The fracture surface was studied by optical and electron fractography. The test results showed that the erosion resistance of blades, subjected to the ion-beam irradiation with post-process vacuum annealing at the optimum conditions, could be increased by 20–200% depending on the type of implanted ion. This positive effect of ion-beam treatment on the erosion resistance of refractory alloy blades is evidently connected with strengthening the material in the surface layer with thickness of 1 μm (ion implantation) up to 10 μm (high-power pulsed ion-beam irradiation). Using electron fractography it was found, that the erosion resistance increase was associated both with the type change of craters created during beginning stages of the erosion tests and with the decrease of erosion rate due to the surface microrelief formed during the fracture incubation period (“start–inertial” mechanism of fracture).

Scarp retreat versus pinned drainage divide in the formation of the Drakensberg escarpment, southern Africa

The dramatic escarpment bounding the Drakensberg-Maluti mountainland has long been regarded as a classic example of a topographic feature formed by scarp retreat processes. However, this view has recently been challenged on the basis of apatite fission track (AFT) and cosmogenic isotope data, which are argued to be inconsistent with a uniform rate of scarp retreat from the original position of continental break-up. It was suggested rather, that the evolution and present position of the escarpment was controlled primarily by a pre-existing inland drainage divide. Numeric surface process models have been used to support this interpretation, although these rely on a large number of unconstrained variables, and thus do not provide unique solutions. However, several lines of direct geological field evidence support the scarp retreat model for the evolution of the Drakensberg escarpment. The Drakensberg-Maluti Mountains in southern Africa are formed by a ~1000 m thick sequence of Karoo basalts, capping Karoo sediments. This mountainland has an approximately rectangular shape, surrounded by orthogonal escarpments, except in the southwest, where it is dissected by the deeply incised Orange River. In detail, these marginal scarps are everywhere double topographic features, reflecting two resistant layers that form prominent cliffs: the thick upper basalt flows, and the Clarens Formation sandstone at the base to the lava sequence. Moreover, in the Drakensberg-Maluti example, the presence of inland-facing escarpments reveals that escarpment formation is not exclusively related to processes that occur at or adjacent to the site of continental break-up. These direct geomorphological and geological observations demonstrate that resistant units are the dominant influence in escarpment formation. Headward retreat of large waterfalls on major rivers over considerable distances (10–100 km) provides clear field evidence that scarps formed by resistant lithologies will not invariably degrade as a result of the existence of an inland drainage divide, as has been argued on the basis of surface process modelling. Several complementary factors provide a ready explanation for apparent inconsistencies in the scarp retreat model that were identified from the AFT and cosmogenic isotope studies. The Drakensberg-Maluti mountains are surrounded by a dense network of dolerite dykes that were contemporary with, and supplied, the Karoo basalts. The massive lava flows capping the modern escarpment therefore probably originally extended at least to the edge of the dyke network. The advance inland of an erosion front, initiated by continental break-up, would have slowed dramatically where such massive lava flows were encountered. Tectonic processes, climate changes, and possibly plant evolution may have compounded this decrease in erosion rates. Although these latter factors are not readily quantified, they were probably subordinate to the dominant lithological control that we invoke. Escarpments may thus form and persist over long periods, extending from the time of continental break-up to the present, independently of inland drainage divides. These field observations must be taken into consideration when assigning values to the numerous unconstrained variables used in surface process models.

Simulation of Erosion in Drilling Tools for the Oil and Gas Industry

Abstract Erosion is a form of wear that has been found on the drilling tools used in the oil and gas industry that can, in some cases, severely shorten the life of the tools. In spite of its importance, there has been virtually no attention paid to it in drilling engineering research. This paper focuses on the modelling of erosion and the application of the developed models to improve the design of drilling tools. The mechanism of erosion, which is controlled primarily by the impact velocity and angle, has been formulated based on experimental and theoretical work done in material science. These algorithms were developed for transient simulations of the erosion of any surface in 2D geometry. Based on these, an "Erosion Simulator(1)" has been written, which is able, in combination with any computational fluid dynamics (CFD) software, to simulate erosion in downhole tools. Actual data from TESCO Corporation casing drilling tools(2) has been used to calibrate the physics of the process and validate the software. The simulator has been used to modify the geometry of the under-reamer casing-drilling tool, which resulted in a substantial decrease in erosion rate and therefore an increase in the tool's life. Introduction Erosion, as a form of material wear, has been reported in many areas of the oil and gas industry. An example of erosion in drilling tools is the TESCO Corporation (hereinafter TESCO) "underreamer" tool used in casing drilling(1) (see Figures 1 and 2). Erosion in the drilling industry is important because it can lead to an increase in time and cost of operation. In the case of drilling tool failure from erosion, eroded parts must be replaced. This will cause unexpected extra rig time in order to pull out the drill string and run it with new parts into the wellbore. Besides the cost of operation, erosion may be dangerous. Tool failure can cause a blowoutand be a potential for loss of lives. This paper focuses on an erosion simulation in order to understand and predict erosion phenomena in drilling tools, with the ultimate goal of improving tool design and extending its life. History of Erosion Research Erosion (i.e., a form of wear) occurs when fluid containing solid particles impacts a solid surface. The intensity of erosion is commonly measured as a specific weight loss (rate of material removal from the surface) and expressed as Er (the weight of material removed by unit weight of impacting particles). During the 1960s and 1970s, a number of important experiments were done in the area of metal wear that laid the foundation for the current understanding of the phenomena. Erosion experiments during that period covered impact velocities up to 550 m/s and particle sizes of up to 1,000 μm [Tilly(3)]. Different velocities and particles can cause different types of damage. During this time, scientists and researchers determined the relationship between erosion rate, the type of material, size of particles, velocity, and angle of impact.

Oligocene to Holocene erosion and glacial history in Marie Byrd Land, West Antarctica, inferred from exhumation of the Dorrel Rock intrusive complex and from volcano morphologies

The Dorrel Rock intrusive complex in Marie Byrd Land, West Antarctica, consists of a coarse-grained gabbro cut by fine-grained benmoreite and trachyte dikes, all exposed in a single nunatak. It is the only exposed plutonic body related to late Cenozoic volcanism in this part of the West Antarctic rift system. Our 40 Ar- 39 Ar age determinations indicate emplacement of the gabbro took place ca. 34 Ma, followed by dike injection at ca. 33.5 Ma. Marie Byrd Land volcanoes are all younger than ca. 27–29 Ma, and lie on a low-relief Late Cretaceous erosion surface that has been disrupted by block faulting and dome uplift since late Oligocene time. The erosion surface and overlying volcanoes are well preserved, but in contrast, we estimate that at least 3 km of overburden has been eroded away to expose the gabbro. This anomaly is most easily explained if most of the exhumation took place during a period of rapid erosion between ca. 34 Ma and 27–29 Ma and was followed by a pronounced decrease in erosion rate in the late Oligocene. Temporal anomalies in the degree of dissection of volcanic edifices, together with evidence from hydrovolcanic deposits, suggest there was an ice cap in Marie Byrd Land in the late Oligocene and that inland (200+ km) volcanoes were being actively eroded by glaciers until ca. 15 Ma. This is consistent with seismic and stratigraphic work in the Ross Sea, which documents at least two expansions of the West Antarctic Ice Sheet in the early mid-Miocene. We find that rates of glacial erosion in Marie Byrd Land increase significantly with nearness to the coast, and in nonresistant rock. Thus, the observation that inland volcanoes younger than ca. 15 Ma show no effects of glacial erosion, except for one with a basal section of weak tuffs, suggests that a transition from warm-based to cold-based glaciers took place around 15 Ma. These findings are similar to many of those reported from well-studied McMurdo Sound and Ross Sea localities, so they provide a wider regional picture of middle to late Cenozoic climatic and surficialgeologic events in Antarctica.

Erosion behavior of thermal sprayed, recycled polymer and ethylene–methacrylic acid composite coatings

Polymer consumption is increasing and the recycling rate is 30–40 wt.%. Thus any process or application that uses recycled plastic residue will be looked upon with favor. It has been demonstrated that post-consumer commingled polymer, or PCCP, coatings can be produced by thermal spraying. Furthermore, polymeric coatings are widely used as protective coatings against solid particle erosion. Therefore, in this paper the erosion behavior of thermal spray coatings that have some PCCP material is investigated. The coatings were produced using a low velocity combustion thermal spray process and a PCCP mixed with different levels of virgin ethylene–methacrylic acid co-polymer (EMAA). The erosion rates using 50 μm alumina were determined at impact angles of 30° and 90°. The wear features were analyzed by scanning electron microscopy and profilometry. The results exhibited brittle wear features, consistent with the relationship between erosion rates and mechanical properties of the polymers. However, a decrease in erosion rate with an increase in impact angle, from 30° to 90°, indicates ductile behavior during erosion.

Climatic forcing of erosion, landscape, and tectonics in the Bhutan Himalayas

A fundamental objective in studies of climate-erosion-tectonics coupling is to document convincing correlation between observable indicators of these processes on the scale of a mountain range. The eastern Himalayas are a unique range to quantify the contribution of tectonics and climate to long-term erosion rates, because uniform and steady tectonics have persisted for several million years, while monsoonal precipitation patterns have varied in space and time. Specifically, the rise of the Shillong plateau, the only orographic barrier in the Himalayan foreland, has reduced the mean annual precipitation downwind in the eastern Bhutan Himalaya at the Miocene-Pliocene transition. Apatite fission-track (AFT) analyses of 45 bedrock samples from an E-W transect along Bhutan indicate faster long-term erosion rates outside of the rain shadow in the west (1.0‐1.8 mm/yr) than inside of it in the east (0.55‐0.85 mm/yr). Furthermore, an AFT vertical profile in the latter segment reveals a deceleration in erosion rates sometime after 5.9 Ma. In this drier segment of Bhutan, there are remnants of a relict landscape formed under a wetter climate that has not yet equilibrated to the present climatic conditions. Uplift and preservation of the paleolandscape are a result of a climate-induced decrease in erosion rates, rather than of an increase in rock uplift rate. This study documents not only a compelling spatial correlation between long-term erosion and precipitation rates, but also a climatically driven erosion-rate change on the scale of the eastern Himalayas, a change that, in turn, likely influences that region’s recent tectonic evolution.

Feast to famine: Sediment supply control on Laramide basin fill

Erosion of Laramide-style uplifts in the western United States exerted an important first-order influence on Paleogene sedimentation by controlling sediment supply rates to adjacent closed basins. During the latest Cretaceous through Paleocene, these uplifts exposed thick intervals of mud-rich Upper Cretaceous foreland basin fill, which was quickly eroded and redeposited. Cretaceous sedimentary lithologies dominate Paleocene conglomerate clast compositions, and the volume of eroded foreland basin strata is approximately twice the volume of preserved Paleocene basin fill. As a result of this sediment oversupply, clastic alluvial and paludal facies dominate Paleocene strata, and are associated with relatively shallow and ephemeral freshwater lake facies. In contrast, large, long-lived, carbonate-producing lakes occupied several of the basins during the Eocene. Basement-derived clasts (granite, quartzite, and other metamorphic rocks) simultaneously became abundant in lower Eocene conglomerate. We propose that Eocene lakes developed primarily due to exposure of erosion-resistant lithologies within cores of Laramide uplifts. The resultant decrease in erosion rate starved adjacent basins of sediment, allowing the widespread and prolonged deposition of organic-rich lacustrine mudstone. These observations suggest that geomorphic evolution of the surrounding landscape should be considered as a potentially important influence on sedimentation in many other interior basins, in addition to more conventionally interpreted tectonic and climatic controls.

Oligocene to Holocene erosion and glacial history in Marie Byrd Land, West Antarctica, inferred from exhumation of the Dorrel Rock intrusive complex and from volcano morphologies

Research Article| July 01, 2006 Oligocene to Holocene erosion and glacial history in Marie Byrd Land, West Antarctica, inferred from exhumation of the Dorrel Rock intrusive complex and from volcano morphologies Sergio Rocchi; Sergio Rocchi 1Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I56126 Pisa, Italy Search for other works by this author on: GSW Google Scholar Wesley E. LeMasurier; Wesley E. LeMasurier 2Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Gianfranco Di Vincenzo Gianfranco Di Vincenzo 3Istituto di Geoscienze e Georisorse (IGG), Consiglio Nazionale delle Ricerche (CNR), Via Moruzzi 1, I56124 Pisa, Italy Search for other works by this author on: GSW Google Scholar GSA Bulletin (2006) 118 (7-8): 991–1005. https://doi.org/10.1130/B25675.1 Article history received: 14 Jul 2004 rev-recd: 27 Jan 2006 accepted: 24 Mar 2006 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Sergio Rocchi, Wesley E. LeMasurier, Gianfranco Di Vincenzo; Oligocene to Holocene erosion and glacial history in Marie Byrd Land, West Antarctica, inferred from exhumation of the Dorrel Rock intrusive complex and from volcano morphologies. GSA Bulletin 2006;; 118 (7-8): 991–1005. doi: https://doi.org/10.1130/B25675.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Dorrel Rock intrusive complex in Marie Byrd Land, West Antarctica, consists of a coarse-grained gabbro cut by fine-grained benmoreite and trachyte dikes, all exposed in a single nunatak. It is the only exposed plutonic body related to late Cenozoic volcanism in this part of the West Antarctic rift system. Our 40Ar-39Ar age determinations indicate emplacement of the gabbro took place ca. 34 Ma, followed by dike injection at ca. 33.5 Ma. Marie Byrd Land volcanoes are all younger than ca. 27–29 Ma, and lie on a low-relief Late Cretaceous erosion surface that has been disrupted by block faulting and dome uplift since late Oligocene time. The erosion surface and overlying volcanoes are well preserved, but in contrast, we estimate that at least 3 km of overburden has been eroded away to expose the gabbro. This anomaly is most easily explained if most of the exhumation took place during a period of rapid erosion between ca. 34 Ma and 27–29 Ma and was followed by a pronounced decrease in erosion rate in the late Oligocene.Temporal anomalies in the degree of dissection of volcanic edifices, together with evidence from hydrovolcanic deposits, suggest there was an ice cap in Marie Byrd Land in the late Oligocene and that inland (200+ km) volcanoes were being actively eroded by glaciers until ca. 15 Ma. This is consistent with seismic and stratigraphic work in the Ross Sea, which documents at least two expansions of the West Antarctic Ice Sheet in the early mid-Miocene. We find that rates of glacial erosion in Marie Byrd Land increase significantly with nearness to the coast, and in nonresistant rock. Thus, the observation that inland volcanoes younger than ca. 15 Ma show no effects of glacial erosion, except for one with a basal section of weak tuffs, suggests that a transition from warm-based to cold-based glaciers took place around 15 Ma. These findings are similar to many of those reported from well-studied McMurdo Sound and Ross Sea localities, so they provide a wider regional picture of middle to late Cenozoic climatic and surficialgeologic events in Antarctica. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Analysis and simulation of erosion in drilling tools

Erosion has been reported in the drilling tools used in the oil and gas industry. This paper focuses on the development of erosion modeling techniques and the application of the developed models to improve the design of drilling tools. Mechanisms of erosion have been formulated based on experimental and theoretical work done in the material science. The model adopted combines the two well known types of erosion (ductile and brittle) in a single model, in which the erosion is controlled primarily by the particle impact velocity and impact angle, as well as other secondary variables. Algorithms were developed for transient simulation of the erosion of any surface in 2D tool geometry. Because the erosion changes the geometry of the tool, which in turn changes the flow field, the algorithms must combine the moving boundary problem with the solution of the flow in the tool. Based on the theory developed, an “erosion simulator” has been written, which can use as a flow component any computational fluid dynamics (CFD) software. Actual data from TESCO Corporation casing drilling tools has been used to calibrate the physics of the process and validate the software. A general agreement between the two was obtained, but the validation process also identified areas of future laboratory and theoretical research needed. As an example of the ability of the software to identify “hot spots” in the tool design, the simulator has been used to modify the geometry of the “under-reamer casing-drilling tool”. This resulted in a substantial decrease in erosion rate and therefore increased life of the tool.

Peak or centroid — which parameter is better suited for quantifying apparent marker locations in low‐energy sputter depth profiling with reactive primary ion beams?

AbstractSilicon samples containing narrow boron markers were depth profiled using normally incident 0.25–1 keV O2+ ion beams in combination with secondary ion mass spectrometry (SIMS). The profiles revealed significant deviations from ideal delta distributions, either as tails or shoulders. All tracer profiles exhibited the well‐known apparent shift towards the surface, which is due to the initial decrease in erosion rate. The peak positions, $\catcode`@=11\def\curvedhat#1{\vbox{\offinterlineskip\ialign{##\crcr\hfil$\scriptscriptstyle\frown$\hfil\crcr\hfil{#1}\hfil\crcr}}}\curvedhat{z}$, showed a much more pronounced non‐linear energy‐dependent shift than the centroids, 〈z〉, up to a factor of 2 stronger. To evaluate the form of measured profiles, a reduced shape parameter is defined as Δ = 〈z〉 − $\catcode`@=11\def\curvedhat#1{\vbox{\offinterlineskip\ialign{##\crcr\hfil$\scriptscriptstyle\frown$\hfil\crcr\hfil{#1}\hfil\crcr}}}\curvedhat{z}$. For ideal deltas, this parameter can be calculated using the analytical resolution function (rf) after Dowsett et al. Depending on the orientation and magnitude of the tracer distortions, the measured values of Δ differed from Δrf by up to 0.8 nm. This difference is attributed to the fact that the ‘weight’ of the distortions gives rise to a corresponding change of 〈z〉. The results imply that (relative) marker locations are determined more safely from $\catcode`@=11\def\curvedhat#1{\vbox{\offinterlineskip\ialign{##\crcr\hfil$\scriptscriptstyle\frown$\hfil\crcr\hfil{#1}\hfil\crcr}}}\curvedhat{z}$ than from 〈z〉. Copyright © 2001 John Wiley & Sons, Ltd.

A re-examination of the ‘particle size effect’ in slurry erosion

The nature and significance of what has been called the ‘particle size effect’ on the rate of slurry erosion and the problem of its experimental evaluation are discussed. Experiments involving the change of erodent particle size in typical laboratory test equipment, while revealing a decrease in erosion rate with decreasing erodent particle size, also produce significant changes in the slurry flow conditions and particle motion which, unless evaluated quantitatively, will mask the nature of the particle size effect. Some model for the rate of material removal must be assumed to allow comparison between the conditions examined. We assume this to be the rate of dissipation of erodent particle kinetic energy at impact. Wear results have been obtained using a slurry pot erosion tester (for which the flow conditions about, and impact conditions on, the 6 mm diameter cylindrical specimens have been modelled and experimentally confirmed), using 0.94 wt.% suspensions of SiC (varying in mean particle size from 14 to 780 μm) in diesel oil for aluminium and Pyrex glass. For aluminium no damage threshold was observed and the experimental erosion rate varied as d p 2 over the whole particle size range. A contribution to this of d p was found to be ascribable to fluid flow changes in the experimental apparatus and the remaining contribution of d p between 100 and 780 μm tentatively assigned to the decrease in surface energy of debris particles with increasing particle size. Below 100 μm there is a transition from wear by particle impact to wear by wet abrasion by particles moving across the surface. Quantitative analysis of erosion rates on the basis of particle impact energies was not possible in this range. For Pyrex glass, erosion wear was measured only between 390 and 780 μm and was found to vary as d p 4. This dependence was made up of d p for fluid flow changes, d p for debris particle size and d p 2 for the influence of an energy threshold for damage of between 2 and 8 μJ for each particle impact. After taking flow conditions and squeeze film retardation at impact into account, it is concluded that there is no fundamental change in the interaction between impacting erodent particles and the wearing surface with increasing particle size between 100 and 780 μm.

Erosion rates on Mars and implications for climate change: Constraints from the Pathfinder landing site

The observation that the Mars Pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1.8–3.5 Ga allows quantitative constraints to be placed on the rate of change of the site since that time. The abundance of erosional features such as an exhumed former soil horizon, sculpted wind tails, ripplelike and other lag deposits, and ventifacts (fluted and grooved rocks) all suggest the site has undergone net deflation or loss of 3–7 cm of material. The presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand‐size particles entrained in the wind. Most ventifacts probably formed soon after the catastrophic flood, which likely introduced a large, fresh supply of sand‐size particles distributed across the rocky plain. The strongest winds blew toward the northwest during this time, resulting in the sculpting of ventifacts, deflation of the surface, collections of dunes within Big Crater and other lows, and possibly preferentially eroding small crater rims. The predominant wind direction changed to blow toward the southwest, similar to today. These winds further deflated the surface, completed the deposition of sand‐size material in dunes and ultimately trapped these dunes in lows. The erosional features observed by Pathfinder indicate extremely low longterm deflation rates of 0.01–0.04 nm/yr since the end of the Hesperian (1.8–3.5 Ga) similar to less precise rates of <1 nm/yr based on the preservation of craters at the Viking 1 and Pathfinder landing sites. Short‐term redistribution rates (deposition and removal) of atmospheric dust at the Pathfinder landing site and preexisting dust and sand at other locations on Mars are up to 105nm/yr. Estimates of erosion rates on Mars show a rapid decrease by 3–6 orders of magnitude from 102–104nm/yr in Noachian terrains (characterized by rimless, flat‐floored craters and valley networks) to the exceedingly slow rates (10−2–10−1nm/yr) operating during the Hesperian and Amazonian. Noachian erosion rates comparable to low continental denudation rates on Earth are consistent with erosion by running water and perhaps a more clement climate. The rapid decrease in erosion rates is consistent with a major climatic change during the Noachian, at the tail end of heavy bombardment, and a cold, dry, desiccating climate similar to today's since that time.

Plasma-facing materials mixing and mixed material properties

Tungsten-doped amorphous carbon films with 0–9.5 at.% W concentration were produced by magnetron sputtering and exposed to deuterium plasmas applying different ion energies and fluences. The partial C and W erosion rates were determined from the C and W areal density changes, respectively, measured by Rutherford backscattering spectrometry. For W-doped films the erosion rate decreases with increasing W concentration and incident fluence. During deuterium plasma exposure carbon is preferentially eroded while tungsten atoms accumulate at the surface leading to the formation of a W-rich layer, which decreases the removal efficiency and leads to a continuous decrease of the erosion rate. At 30 eV/D incident energy a relatively compact W-rich layer is formed on films with higher (⩾5%) W concentration which protects the carbon underneath from further erosion. For films with lower (⩽2.5%) W concentration the erosion rate decreases, but the erosion process does not stop because the W-rich layer has a high porosity. Reactive neutral species can penetrate through this porous layer and react with carbon atoms below it. At 100 eV/D incident energy the erosion rate is significantly higher compared with 30 eV/D. In addition, slight tungsten sputtering is observed due to the presence of a small fraction of D+ plasma ions which impinge with 300 eV/D.

Isolating Erosivity and Erodibility Components in Erosion by Rain-Impacted Flow

Erosion experiments were performed using 3.7 mm raindrops impacting flows over various sized sands. The results from these experiments, when combined with data from previous experiments using other drop sizes, enabled the effects of flow and rain to be isolated from the effect of the eroding surface. Although the rate of decrease in erosion rate with flow depth was observed to vary with drop size when drops impact flows deeper than about 4 mm, raindrop size may not have a significant influence on the erosion rate when shallower flows are impacted by medium-to-large raindrops. However, this is not the case for smaller drops and for medium-to-large drops traveling at much less than their terminal velocities.

On the particle size effect in slurry erosion

The erosion rates of cylindrical steel specimens tested at a constant speed of 18.7 m s −1 in an erosion pot tester using 1.2 wt.% suspension of SiC in oil for particle diameters between 20 and 500 μm have been determined. The rate of particle impact on unit area of the surface at the stagnation line of erosion specimens was established as a function of particle size by short-time erosion tests, allowing a calculation of the mean mass removed for each particle impact as a function of particle size. These values were compared with the kinetic energy of particles using impact velocity values derived from a model of suspension flow. Results show that the decrease in erosion rate with decreasing particle size for suspensions of constant solids loading reflects the decrease in the proportion of particles impacting the target surface as well as the decrease in impact velocity. A value of about 24 kJ g −1is tentatively suggested for the energy of removal of P110 steel by erosion. It is concluded that for these dilute suspensions with particle sizes greater than about 100 μm the erosion rate is proportional to the kinetic energy dissipated by particles during impact, but for particle sizes less than 100 μm other metal removal mechanisms become increasingly significant.

Solid Particle Erosion of Brittle Materials (Part 6)

Al2O3-SiC composites containing up to 30wt% SiC particle or whisker were hot-pressed at 1500°-1850°C for 1h under 25MN·m-2, and their erosive wear was studied using SiC and Al2O3 abrasives. The erosion rate of Al2O3-SiC composites decreased with an increase in SiC content regardless of the abrasive. The erosion rate of Al2O3 containing 30wt% SiC whisker was four times smaller than that for pure Al2O3. The decrease in erosion rate was related to the increase of hardness and fracture toughness of composites due to SiC addition. The composites were considered to be homogeneous from erosive wear characteristics.

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.

Effect of the arc velocity on the cathode erosion rate in argon-nitrogen mixtures

Erosion measurements on a copper cathode are reported. The 100 A arc, driven by a magnetic field, runs continuously for up to 30 min between two concentric cylindrical electrodes. Argon-nitrogen gas mixtures in various proportions are blown through the electrode gap. The erosion rate in argon is drastically reduced by the addition of only 1% nitrogen and is further reduced as the nitrogen content increases in the gas mixtures. The decrease in erosion rate is found to be correlated to an increase in arc velocity.