Material Loss Rate Research Articles

Inferring genomic flux in bacteria.

Acquisition and loss of genetic material are essential forces in bacterial microevolution. They have been repeatedly linked with adaptation of lineages to new lifestyles, and in particular, pathogenicity. Comparative genomics has the potential to elucidate this genetic flux, but there are many methodological challenges involved in inferring evolutionary events from collections of genome sequences. Here we describe a model-based method for using whole-genome sequences to infer the patterns of genome content evolution. A fundamental property of our model is that it allows the rates at which genetic elements are gained or lost to vary in time and from one lineage to another. Our approach is purely sequence based, and does not rely on gene identification. We show how inference can be performed under our model and illustrate its use on three datasets from Francisella tularensis, Streptococcus pyogenes, and Escherichia coli. In all three examples, we found interesting variations in the rates of genetic material gain and loss, which strongly correlate with their lifestyle. The algorithms we describe are implemented in a computer software named GenoPlast.

Rubber abrasion at steady state

Blade abrasion devices have previously been used to investigate the abrasion resistance of different elastomers. Despite extensive investigation the exact mechanisms that are present during abrasion continue to be the subject of debate. This investigation examines the effect of the normal and frictional forces on the rate and direction of crack growth during the abrasion process. Comparison is drawn between the rates of material loss as measured experimentally on two different styrene butadiene rubber compounds under a range of test conditions. For each set of conditions the representative stored energy release rate is calculated using a finite element analysis technique on a model of a specific abrasion asperity contacting a sliding rigid abrader. It is therefore possible to plot a graph of the stored energy release rate versus crack growth rate for an abrasion process. This is compared with an independently measured cyclic fatigue crack growth rate versus stored energy release rate. The correlation between these two independent tests was excellent. From this work insight into the nature of abrasion is gained.

A Probabilistic Model to Characterize Erosion-Oxidation Damage on Boiler Grade Steel Impacted by Solid Particle

A probabilistic model based methodology has been applied to describe the relative rate of material loss from the steel surface subjected to simultaneous action of high temperature oxidation and mechanical erosion. Growth of the oxide scales is treated deterministically and erosion is described using an established probabilistic modeling methodology. Oxidation is described with a parabolic growth law to quantify the rate of growth of the oxide scales, namely, nickel, iron, and chromium, respectively. In consonance with the published model, erosion is treated using a probabilistic methodology as spatially random phenomena on the oxide surface. The model has been applied to predict the relative erosive loss of material as a function of time resulted as a consequence of influence oxidation on mechanical erosion in a synergetic manner.

Numerical study on fatigue damage properties of cavitation erosion for rigid metal materials

Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated that the components of different materials exhibited various fatigue lives under the same external conditions. When the groove depth was extended, the initiation crack life decreased rapidly, while the true stress amplitude was increased simultaneously. This gave an important explanation to the accelerating material loss rate during cavitation erosion. However, when the groove depth was fixed and the length varied, the fatigue life became complex, more fluctuant than that happened in depth. The results also indicate that the fatigue effect of cavitation plays an important role in contributing to the formation and propagation of characteristic pits.

A systematic erosion–corrosion study of two stainless steels in marine conditions via experimental design

Erosion–corrosion performance of two stainless steels (UNS S32760 and UNS S31603) for marine applications has been assessed under liquid–solid impingement conditions in 3.5% NaCl. The total material loss rate and the components of mechanical erosion, electrochemical corrosion and their synergistic interactions have been determined under various conditions. The major environmental parameters considered are solid loading, flow velocity and fluid temperature. For the two stainless steels, a quantitative analysis of the damage showed mechanical erosion to be the dominant process under erosion–corrosion over the range of conditions considered. A full two-level factorial experimental design method was applied to study the individual effects of each parameter as well as their interactive contributions to the overall material degradation. The analysis shows that the interactions between environmental factors all accelerate mass loss during the erosion–corrosion process and the interactive effect between velocity and sand loading is the greatest. Fluid temperature has the smallest effect of the three parameters. Some guidelines to assist in material selection for erosion–corrosion and progress towards prediction of erosion–corrosion in marine applications are discussed in this paper.

Corrosion and mechanical-microstructural aspects of dissimilar joints of Ti–6Al–4V and Al plates

In this study, Ti–6Al–4V and Al plates were joined by explosive welding at various explosive loads. Tensile-shear, bending, hardness, microstructure and corrosion behaviours of the explosively joined samples were investigated. At the end of the tensile-shear tests carried out according to ASTM D 3165-95 standard, no seperation was observed in the interfaces of the joined samples. The results of the bending tests also showed no sign of any distinctive seperation, crack and tear in the interfaces. The highest hardness values were measured in regions next to interfaces. The optical microscope and SEM examinations revealed that an increment in wavelength and amplitude was observed with increasing explosive load. It is seen from the corrosion test results that materials loss was high at the beginning of the corossion tests but the rate of material loss decreased later on. Furthermore, increasing deformation with increasing explosive load increased the materials loss in corrosion tests.

Assessing Metal Matrix Composites for Corrosion and Erosion-Corrosion Applications in the Oil Sands Industry

Abstract Erosion-corrosion that arises when materials are transporting aqueous slurries can be a significant problem in the oil sands industry. Interactions between erosion and corrosion are complex and, as such, it is difficult to determine the rate of material loss with sufficient accuracy for the reliable prediction of equipment lifetime. A combination of electrochemical and gravimetric techniques were used in this study to assess erosion-corrosion rates under liquid-solid impingement in a simulated recycle cooling water environment containing 5 wt% solids at 25°C and 65°C. One material that has been successfully used on critical production equipment is tungsten carbide (WC) metal matrix composite (MMC) applied to the surface as a weld overlay. Four WC-based hardfacing overlays with different particle size distributions were investigated in this study. These overlays comprised 65 wt% WC hard phase with a metal matrix binder consisting of mainly Ni, Cr, Si, B, and Fe. The MMC overlays were applied using...

Coastal landslide material loss rates associated with severe climatic events

Deep-seated landslides along the California coast deliver large amounts of material to the nearshore littoral environment. Landslide movement, a combined result of slope base undercutting by waves and ground saturation, is highly episodic. Movement occurs primarily during periods of high rainfall and large waves, such as those associated with El Nino events. This analysis applies remote-sensing techniques to quantify the volumetric net loss rates at three specific landslide sites along the Big Sur coast over three approximately decadal time periods, two of which contained the largest El Nino events of the twentieth century. High-resolution historical terrain models were compared in order to provide surface- elevation change data for each landslide complex. To determine the material influx to the littoral system, the landslide complexes were divided into upper and lower slopes, and the surface-elevation change was converted to a volume loss. Some material lost from the upper slope was deposited at the slope base, not into the littoral system. We describe a method to calculate the net loss that omits the deposition volumes from the upper slope. Loss rates were found to be substantially higher during the periods in which El Nino events occurred. This is especially true during the period of the 1997–1998 El Nino, when 75% of the total material volume was lost, and loss rates were as much as sixteen times higher than during non–El Nino periods.

Micro-engineered first wall tungsten armor for high average power laser fusion energy systems

The high average power laser program is developing an inertial fusion energy demonstration power reactor with a solid first wall chamber. The first wall (FW) will be subject to high energy density radiation and high doses of high energy helium implantation. Tungsten has been identified as the candidate material for a FW armor. The fundamental concern is long term thermo-mechanical survivability of the armor against the effects of high temperature pulsed operation and exfoliation due to the retention of implanted helium. Even if a solid tungsten armor coating would survive the high temperature cyclic operation with minimal failure, the high helium implantation and retention would result in unacceptable material loss rates. Micro-engineered materials, such as castellated structures, plasma sprayed nano-porous coatings and refractory foams are suggested as a first wall armor material to address these fundamental concerns. A micro-engineered FW armor would have to be designed with specific geometric features that tolerate high cyclic heating loads and recycle most of the implanted helium without any significant failure. Micro-engineered materials are briefly reviewed. In particular, plasma-sprayed nano-porous tungsten and tungsten foams are assessed for their potential to accommodate inertial fusion specific loads. Tests show that nano-porous plasma spray coatings can be manufactured with high permeability to helium gas, while retaining relatively high thermal conductivities. Tungsten foams where shown to be able to overcome thermo-mechanical loads by cell rotation and deformation. Helium implantation tests have shown, that pulsed implantation and heating releases significant levels of implanted helium. Helium implantation and release from tungsten was modeled using an expanded kinetic rate theory, to include the effects of pulsed implantations and thermal cycles. Although, significant challenges remain micro-engineered materials are shown to constitute potential candidate FW armor materials.

Erosion–corrosion behaviour of WC-based MMCs in liquid–solid slurries

In the oilsands industry erosive wear and erosion–corrosion can cause high rates of material loss, particularly in the hydrotransport system where corrosive slurries are encountered. Metal Matrix Composites (MMCs), comprising a ductile binder with a reinforcing hard phase, are seeing greater applications as coatings and hardfacing for critical components, where there is a requirement for high durability. In this paper the erosion–corrosion performance of WC-MMCs applied by the PTA process is evaluated. Four MMCs, with varying WC-size range, all with a Ni–Cr–Si–B matrix, have been considered. The erosion–corrosion behaviour of the MMCs is compared to UNS S31603 austenitic stainless steel. The material degradation is assessed as a function of sand particle size and sand loading. The materials were eroded by two sizes of silica sand with stream velocities of 10 and 17 m/s at 65 °C. The solid loading (wt.%) was varied from 1%, 5%, 10%, 15% and 20% with most tests being conducted at 1% and 5%. With the smaller sand size the MMCs showed considerably reduced damage due to erosion–corrosion compared to UNS S31603. Using the coarse sand, the MMCs show inferior resistance to erosion–corrosion compared to UNS S31603; the finding are explained by careful consideration of the material degradation mechanisms.

The rolling sliding wear response of conventionally processed and spray formed high speed steel at ambient and elevated temperature

The effect of spray forming on the wear properties of a 1.2C–3.4W–8.9Cr–4.3V–2.7Mo high speed steel is described. The microstructure, fracture behaviour and wear response of the spray cast materials are compared with those of conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale for both grain size and carbide size. In addition, large primary and interconnected eutectic carbides observed in the conventionally cast material were replaced by a more uniform distribution of discrete globular carbides in the spray cast material. This refinement is shown to give rise to an increase in the resistance to fracture. Wear testing was undertaken in the rolling/sliding configuration (8% slippage) at 300 N against an M2 tool steel counterface in the temperature range 20–650 °C. The wear rate of the conventional material was significantly higher than that of the spray cast material at all temperatures. Both adhesive and oxidative wear mechanisms were observed, with the latter becoming more prominent as the test temperature increased. Surface degradation occurred preferentially at the carbide/matrix interface for both materials, but was particularly prominent in the Fe/M 2C–M 6C eutectic regions and at large primary VC carbides in the conventionally cast material, resulting in higher rates of material loss in these regions. The improvement in wear resistance observed for the spray formed material can be directly attributed to the refinement of both primary and eutectic carbide phases and the elimination of microsegregation. The laboratory observations are compared to a worn surface of a spun cast hot mill work roll of nominally the same composition following a normal campaign in the roughing stands of a hot rolling mill. This showed that the wear mechanisms in the field were reproduced in the laboratory. The relationship between process parameters microstructure and wear mechanisms is discussed.

Plasma interaction with liquid lithium: Measurements of retention and erosion

This paper reports on recent studies of high flux deuterium and helium plasma interaction with liquid lithium in the Pisces–B edge plasma simulator facility. Deuterium retention is explored as a function of plasma ion fluence in the range 6×10 19–4×10 22 atoms cm −2 and exposure temperatures of 523–673 K. The results are consistent with full uptake of the deuterium ions incident on the liquid metal surface, independent of the temperature of the liquid lithium. Full uptake continues until the sample is volumetrically converted to lithium deuteride. Helium retention is not observed for fluences up to 5×10 21 He atoms cm −2. Measurements of the erosion of lithium are found to be consistent with physical sputtering for the lithium solid phase. However, a mechanism that provides an increased evaporative-like yield and is related to ion impact events on the surface, dominates during the liquid phase leading to an enhanced loss rate for liquid lithium that is greater than the expected loss rate due to evaporation at elevated temperatures. Further, the material loss rate is found to depend linearly on the incident ion flux, even at very high temperature.

The effect of an impinging liquid-solid jet on the electrochemical corrosion of stainless steels

Stainless steels rely on their passive film for corrosion protection in saline environments and localised disruption of the passive film can lead to high local rates of material loss. Materials which exhibit passivity in static conditions are often susceptible to erosion-corrosion under severe hydrodynamic regimes. In this paper the corrosion behaviour of two superaustenitic (UNS S31254 and UNS S32654) and one superduplex (UNS S32750) stainless steels was examined in static conditions at a range of temperatures from 18 °C to 70 °C and during exposure to an impinging saline jet containing varying concentrations of solid particles. In static conditions the materials exhibit decreasing resistance to passivity breakdown as the temperature is increased and a critical breakdown temperature for UNS S31254 and UNS S32750 was identified. Under liquid-solid impingement the materials exhibit an active regime near to the free corrosion potential followed by a stabilised current regime as more positive potentials. The complex electrochemical response is dependent on the material grade and the solid particle concentration. Also in the paper assessment of the recovery' of the stainless steels after exposure to slurry impingement is addressed.

Erosion of a High-Carbon Steel in Coal and Bottom-Ash Slurries

This paper discusses the observations made during erosive wear testing of a high-carbon steel (0.65% C) in coal and bottom-ash slurries. The slurry was made by separately dispersing 30% coal and bottom ash (collected from a thermal power plant) in tap water. The tests were performed using a sample rotation method in the slurry at a fixed linear velocity of 5 m/s for different traversal distances at room temperature. To see the influence of microstructural features on slurry wear response, the steel was subjected to hardening and annealing heat treatments. Test results indicate that material loss of the specimens increased with traversal distance in all cases. Further, the hardened steel showed a lower rate of material loss when compared with steel in an annealed condition in either of the test environments. Moreover, irrespective of heat-treatment conditions, the samples revealed significantly higher material loss when tested in the bottom-ash slurry than in the coal slurry. The higher rate of material removal in the case of the former was attributed to the more efficient transfer of the kinetic energy of the moving (hard) bottom-ash particles to the specimen surface than in the case of the softer coal particles. Fracture of coal particles as a result of impact during the course of slurry erosion further supported the view. Results have been explained on the basis of the characteristics of the affected surfaces and changes in the morphology of the erodent particles after the test.

Wear of titanium carbide reinforced metal matrix composites

The wear resistance of eight titanium carbide (TiC) reinforced metal matrix composites was investigated under different wear conditions. The TiC particles were dispersed in various steel and nickel matrices using a powder metallurgy (P/M) technique. Volume fraction of TiC particles in these composites varied between 0.35 and 0.45. The microstructure of each material was characterized using scanning electron microscopy (SEM), light optical microscopy, and X-ray diffraction (XRD). A high-stress abrasion test (pin abrasion), a low-stress abrasion test (dry-sand/rubber-wheel (DSRW)), an abrasion–impact test (impeller-in-drum) and an erosion test were utilized to understand the wear behavior of these materials under different conditions. While in the low-stress abrasion environment, finer TiC particles (with smaller interparticle spacing) provided better wear resistance, the coarser TiC particles were more effective in protecting the softer matrix from abrasion in the high-stress environment. On the other hand, variation in TiC size did not affect the rate of material loss in the impact–abrasion test. Erosion rate was unchanged with hardness of the composites.

Heat treatment of cathodic arc deposited amorphous hard carbon films

Amorphous hard carbon films of varying sp 2/sp 3 fractions were deposited on Si using filtered cathodic arc deposition with pulsed biasing. The films were heat treated in air at temperatures up to 550°C. Raman investigation and nanoindentation were performed to study the modification of the films caused by the heat treatment. It was found that films containing a high sp 3 fraction sustain their hardness for temperatures at least up to 400°C, their structure for temperatures up to 500°C, and show a low rate of material loss during heat treatment. Films containing a low sp 3 fraction graphitize during heat treatment, show changes in structure and hardness, and have a high rate of material loss.

Erosion and corrosion properties of WC coatings and duplex stainless steel in sand-containing synthetic sea water

Two different thermally sprayed coatings have been investigated with respect to erosion and corrosion resistance and compared with a duplex stainless steel. The coatings consist of WC particles in a metal binder, one with a pure Co binder and one with a binder consisting of mainly Ni, Cr, Co and Fe. The materials have been exposed to flowing synthetic sea water containing sand. The test equipment consists of an inner rotating cylinder and an outer stationary cylinder. In between there is a 4 mm gap through which synthetic sea water flows. The cylinder walls are divided into ring-shaped specimens. Less sand attacks the inner cylinder than the outer owing to centrifugal forces. Weight loss rates were determined by weighing the specimens. In addition, corrosion rates were determined by electrochemical measurements. By cathodic protection of the specimens the rate of erosion was found. In that way, the relative importance of the corrosion and erosion rates has been studied. The results show that the corrosion properties of the coatings strongly affect the material loss rate. Coatings with a highly corroding matrix, such as Co, suffer from a strong synergistic effect where the corrosion gives enhanced erosion. This effect can be more than three times as high as the corrosion itself. It is also seen that the weight loss rates vary with exposure time, being larger from the start. This is an important issue to consider when testing these materials. Modelling of the flow conditions has been performed to determine sand particle energy and the angle of attack on the surface.

Combined erosion and corrosion of thermal sprayed WC and CrC coatings

This paper presents investigations of the combined effect of erosion and corrosion on one stainless steel and four different thermal sprayed coatings with carbide particles in a metal matrix. The materials were exposed to flowing synthetic sea water containing sand. Pure erosion, electrochemical corrosion and total material loss were determined at different sand concentrations. The effect of exposure time was also studied. The results show that erosion is the dominating process at high sand concentrations while corrosion is important at lower concentrations. The relative importance depends on the material. The corrosion resistance of the metal matrix has great influence on the total material loss rate. For the coating with lowest corrosion resistance there seems to be a synergistic effect between the mechanical and electrochemical processes.

Evaluation of deterioration mechanisms and roll life of different roll materials

Evaluation of wear loss of rolls in operation is very difficult since the rolling conditions are hard to keep under control. To solve this problem a high temperature test rig was designed. A conventional roll material was compared to a hot work tool steel. The main wear mechanisms were different. The conventional roll grade was mainly subjected to thermal fatigue as could be expected. The hot work tool steel was mainly sublected to abrasive wear, and no evidence of thermal fatigue was found. The rate of material loss was 6 times higher in the hot work tool steel, but when the deterioration caused by thermal fatigue of the cast iron is taken into consideration, the deterioration rate was of the same order in both materials. The friction between the hot steel and the roll materials were of the same order

Effect of sulphuric acid concentration on the rate of tribocorrosion of iron

Corrosion and tribocorrosion tests of iron in sulphuric acid at different concentrations were performed in order to elucidate the relationship between corrosion and wear and the role of surface films. Coefficient of friction, material loss rates and surface morphology of iron rubbing against alumina were monitored in sulphuric acid solutions of concentrations ranging from 2 M up to 18 M. It was found that the material removal rate under tribocorrosion as a function of acid concentration reaches a maximum at 8 M. The simultaneous action of wear and corrosion may significantly affect the material removal mechanisms observed under static corrosion conditions. The films formed by corrosion products at the iron surface are responsible for surface smoothing.