On the construction of wear maps for Y-TZP dental ceramics in aqueous environments: pH, exposure time and impact angle effects

The object of this work was to evaluate the particulate erosion performance of Y-TZP (Yttria Tetragonal Zirconia Polycrystalline), used in the construction of artificial teeth, at various pH values, impact angles and exposure times. The results showed that the highest degradation recorded was in acidic environments. However, the incubation time to high wastage was also affected by impact angle and exposure time. Wear maps were constructed, based on the results, identifying wastage regimes for the material as a function of the exposure conditions. In addition, a wear map was generated based on the observed phase transformations for the material.     

Erosion-corrosion mapping of Fe in aqueous slurries: some views on a new rationale for defining the erosion-corrosion interaction

In studies of erosion-corrosion of materials in aqueous conditions, there have been various attempts to define regimes of interaction. Such regimes indicate whether erosion or corrosion may dominate the wastage mechanism. However, intermediate regimes in which corrosion and erosion interact with each other may lead to situations where the wastage is far greater than the sum of the processes acting separately.A common method of defining erosion-corrosion interactions has been to distinguish between the regime in which erosion enhances the corrosion rate (the so called “additive effect” because the corrosion contribution can be measured electrochemically and thus added to the erosion contribution to assess the overall wastage rate) and the regime where corrosion enhances erosion (the so-called “synergistic” effect). However, regimes of erosion-corrosion, where corrosion impedes the erosion are also of great importance mechanistically, and usually these are termed as exhibiting “negative synergism”. Defining the conditions in which a transition from “positive” to “negative synergism” occurs, is useful in order to optimize the parameters to minimize the wastage rate.This paper reviews the rationale that has been used to define erosion-corrosion regimes in aqueous conditions as part of a study of the erosion-corrosion of Fe at various pHs. The mathematical definitions are discussed in relation to practical erosion-corrosion problems. In addition, a new “antagonistic” erosion-corrosion regime is proposed to properly define the concept of “negative synergism”.     

Estimation of Incubation Time of Cavitation Erosion for Various Cavitating Conditions

Estimations have been made, resulting in a general method for the prediction of the incubation time for cavitation erosion using various cavitating conditions and materials. From a single erosion test, the incubation time can be estimated for various conditions and materials by plotting the mass loss as a function of exposure time to cavitation on a log–log scale.     

Modelling particulate erosion–corrosion regime transitions for Al/Al2O3 and Cu/Al2O3 MMCs in aqueous conditions

Very little research effort has been directed at development of models of erosion–corrosion of composite materials. This is because, in part, the understanding of the erosion–corrosion mechanisms of such materials is poor. In addition, although there has been a significant degree of effort in the development of models for erosion of MMCs, there are still difficulties in applying such models to the laboratory trends on erosion rate.In this paper, the methodology for mapping erosion–corrosion processes in aqueous slurries was extended to particulate composites. An inverse rule of mixtures was used for the construction of the erosion model for the particulate MMCs. The corrosion rate calculation was evaluated with reference to the matrix material.The erosion–corrosion maps for composites showed significant dependency on pH and applied potential. In addition, the corrosion resistance of the matrix material was observed to affect the regime boundaries. Materials maps were generated based on the results to show the optimum composite composition for exposure to the environment.     

Erosion-corrosion regimes: number, nomenclature and justification?

In studies of elevated temperature erosion by solid particles in oxidizing gaseous environments, several regimes of interaction have been identified. These regimes define whether wastage occurs predominantly due to erosion of the alloy substrate, corrosion of the substrate, or a mechanism intermediate between these processes, and various criteria for the transitions between such regimes have been identified by different investigators. In such cases, the possible number and nomenclature of regimes can sometimes be unclear.The purpose of this paper is to review all the available information on the various erosion-corrosion regimes which have been identified. The similarities and the differences between the various approaches to defining regimes are discussed. In addition, the criteria for their identification are evaluated critically. The importance of the identification of such regimes is discussed. The use of such information to establish zones of minimum wastage on erosion-corrosion maps is demonstrated. In addition, the ability of such regimes to identify variations in erosion-corrosion rate with the main erosion-corrosion variables is indicated.     

Mapping tribo-corrosion processes in dry and in aqueous conditions: some new directions for the new millennium

Tribo-corrosion is the term which describes the interaction between a tribological process with corrosion. This process may include sliding or abrasive wear, erosion by solid particles or liquid impact, or cavitation, fretting or fatigue. Corrosion environments may be complex; they can be alternately dry (i.e. at elevated temperatures) or wet aqueous conditions at room temperatures. Significant progress has been made in the study of tribo-corrosion in the past 20 years. Erosion–corrosion in particular has received much attention, because of the increasing prevalence in minerals processing and in the oil and gas industries. Mechanistic maps for such processes have been generated, showing the transitions between the tribo-corrosion regimes as a function of tribological and corrosive variables. This paper reviews the recent research in the area, from the inception of the initial wear map, to current work in the area. The significance of the various maps will be discussed, and their potential application to “real” environments will be described. New directions for the work will be highlighted with emphasis on extension to advanced materials and a wider range of variables.     

Erosion–corrosion performance of high-Cr cast iron alloys in flowing liquid–solid slurries

In many slurry transportation systems, such as in FGD (Flue Gas Desulphurization) and chemical processing applications, corrosion and erosion are the two main mechanisms of material degradation of the pump wet-end components including pump casing, impeller and liners. The performance of a selected material is mostly dependent upon its relative corrosion and erosion resistance to the service environment. In these cases erosion, corrosion and the related synergistic effects can be very complicated since they are affected by numerous factors including solid and slurry properties, chemical contents, hydraulic conditions and temperatures. In this experimental study, sliding Coriolis erosion testing has been performed with various corrosion factors such as pH value, chlorides content and temperature to evaluate the erosion–corrosion resistance of some high-alloyed white cast irons containing different levels of chromium and other elements. Optical microscope and SEM-EDS have also been used to examine microstructure and surface conditions of tested materials. Results indicated that material loss due to corrosion factors increased as acidity-chlorides and temperature increased. At relatively high corrosion intensity, the white cast irons with higher alloy content (especially chromium) clearly showed improved corrosion resistance and combined erosion–corrosion resistance over those with lower alloy content. Under certain corrosion and hydraulic conditions, particle size is perhaps the single most influential factor on erosion–corrosion rate of the high-Cr cast iron alloys. Relatively large particles are much more effective than small ones at removing both the corroded surface layer and the fresh material, causing substantially higher rate of material loss. Some other related factors have also been addressed.     

Micro-abrasion resistance of thermochemically treated steels in aqueous solutions: Mechanisms, maps, materials selection

The area of micro-abrasion is an interesting and relatively recent area in tribo-testing methodologies, where small particles of less than 10 μm are employed between interacting surfaces. It is topical for a number of reasons; its direct relation to the mechanisms of the wear process in bio-tribological applications, ease in conducting tests and the good repeatability of the test results. It has widespread applications in conditions used in the space and offshore industries to bio-engineering for artificial joints and implants.There have been many recent studies on the micro-abrasion performance of materials, ranging from work basic metals to nano-structured coatings. However, no significant work is reported on the micro-abrasion resistance of thermochemically treated steels. Hence, this paper looks at the performance of two thermochemically treated steels, Tenifer bath nitride stainless steel (T-SS) and vanadized carbon steel (V-CS) in such conditions with reference to the stainless steel (SS) by varying the applied load and sliding distance.The results indicated that T-SS demonstrates exceptionally poor resistance to micro-abrasion. It was observed that the heat treatment process and properties of the hardened layer (hardness and thickness) are extremely important in determining the micro-abrasion resistance of such steels. Finally, the results were used to develop micro-abrasion mechanism and wastage maps, which can be used to optimize the surface treated materials for micro-abrasion resistance.     

Erosion-corrosion of Fe- and Ni-based tubes and coatings in a fluidized bed test rig during exposure to HCl- and SO2-containing atmospheres

Tubes made from five commercial alloys (Fe9Cr1Mo, 304L, Esshete 1250, 353 MA and Inconel 625) as well as two coating materials (Inconel 625 and Metco 8443) deposited on low alloyed steel tubes were exposed to different atmospheres in a laboratory fluidized bed test rig at 550 °C for 3 weeks (504 h). The atmospheres were air, air + 50 ppm HCl and air + 50 ppm SO₂. Excluding the Metco 8443 coating, all materials show the lowest wastage rate in the SO₂-containing atmosphere. For all exposure conditions, the best overall performance is shown by the Fe9Cr1Mo alloy. The circumferential wastage profiles recorded on tubes exposed in air and air + 50 ppm HCl show an erosion pattern with two maxima (Type A behaviour), while the tubes recorded in the SO₂-containing atmosphere display only one maximum (Type B behaviour).     

Some Views on the Mapping of Erosion of Coated Composites In Tidal Turbine Simulated Conditions

This article presents a study of the erosion resistance of coated and uncoated polymer matrix composites for tidal turbine conditions. It focuses on the development of comparative erosive wear mode and mechanism maps for such materials. In our earlier work, testing of glass-fiber-reinforced polymer composites for tribological applications in marine simulated conditions, several erosion-related issues were highlighted. The combined effects of the NaCl solution and sand dramatically enhanced the erosive wear of the uncoated specimens. In order to address those issues, an erosion-resistant polymeric coating was applied to the composite and tested in marine simulated conditions with an extended range of sand particle size. The test results of the uncoated and coated composite have been compared in this research by erosive wear mode and mechanism maps techniques. These maps reveal that the coating has enhanced the erosion resistance. These findings provide significant progress toward materials selection approaches to manufacture of tidal turbine blades.     

Erosion wear and mechanical properties of plasma-sprayed nickel- and iron-based coatings subjected to service conditions in boilers

The erosion wear and mechanical properties after exposure to simulated industrial service conditions in boilers of nickel-based, iron-based and chromium–nickel plasma-sprayed coatings on carbon steel and stainless steel have been obtained. These types of coatings are used as heat transfer and structural elements in boilers. Different tests simulating boiler service conditions under standard and extreme situations were carried out at 400, 600 and 800°C in a laboratory combustion unit. The influence of high temperature oxidation processes on the adherence, microhardness, microstructure, and wear erosion behaviour of both base materials and coatings have been evaluated.     

Particle-surface interactions during the erosion of aluminide-coated MarM002

Particle-surface interactions during the erosion of a nickel aluminide coating were assessed using a single-impact technique. It is shown that the erosive response is a function of the surface scale thickness and the temperature, with the temperature not only influencing the surface scale plasticity but also determining the contribution of the coating substrate to the impact process. In this respect the ductile-to-brittle transition temperature of the coating is of particular importance.Under a wide range of conditions typical of those found in gas turbines the erosion of aluminide coatings is shown to be controlled by the formation and removal of surface scales. This implies that the use of aluminide coatings will increase the erosion resistance of typical turbine blade materials because of the superior oxidation and corrosion resistance of this coating. This increase in erosion resistance will be particularly significant at higher operating temperatures, above 900 °C.     

Erosion—corrosion characteristics of a 2.25 Cr-1 Mo steel exposed at low particle velocities

The erosion-corrosion characteristics of a 2.25 Cr-1 Mo steel at low particle velocities and elevated temperatures were determined using a nozzle type laboratory erosion tester. The tests were performed with 180–360 μm angular alumina particles at 60° angle of impingement at low particle velocities of 2.6–8.2 m/s and in the temperature interval 20–600°C. The steel was tested both in the as-received condition as well as in two preoxidized conditions. The erosion-corrosion rate of the steel, both in the as-received and in the preoxidized conditions, was found to increase with increasing particle velocity. In contrast, the wastage rates were relatively independent of temperature in the temperature range investigated, the only exception being specimens exposed to the lowest particle velocity (2.6 m/s) at the very highest temperature, i.e. 600°C, which displayed a drastic increase in wastage. Specimens preoxidized at 700°C exhibited a somewhat higher erosion rate compared with non-preoxidized specimens and specimens preoxidized at 500°C. Microscopy revealed four different major wastage mechanisms, i.e. (i) plastic deformation, cracking and micro chipping of surface material of a size corresponding to the area impinged by eroding particles, (ii) chipping of somewhat larger oxide fragments (up to 10–15 μm in diameter), (iii) chipping or spalling of relatively large oxide fragments (up to 30–50 μm in diameter), and (iv) spalling along the steel-oxide interface or within an oxide layer due to cohesive failure, of larger (up to 500 μm in diameter) oxide layer fragments. In the present study extensive spalling was only observed for non-preoxidized specimens exposed to the lowest particle velocity (2.6 m/s) and the two highest specimen temperatures (550°C and 600°C).     

High temperature erosion of Ti(Mo)C–Ni cermets

The resistance of Ti(Mo)C–Ni cermets of different binder content to solid particle erosion was evaluated at 25, 350 and 650 °C. The elevated temperature erosion of cermets containing 40, 50, 60, 70 and 80 wt.% of titanium carbides and produced from the powder of initially different ratios of Ni to Mo were tested with the help of specially designed centrifugal particle accelerator using silica as the abrasive. Erosion rate was related to both microstructure developed during sintering and materials removal mechanisms operating at the test conditions (impact angle of particles jet was 30° and 90° and velocity was 50 ms⁻¹). The erosion rate decreases with the increase of TiC and Mo contents in the composite. At 650 °C the process of tribo-oxidation affected the material performance to a great extent. The morphology of the worn surface was analyzed with SEM to determine the erosion mechanisms.     

Some views on the construction of bio-tribo-corrosion maps for Titanium alloys in Hank's solution: Particle concentration and applied loads effects

The micro-abrasion-corrosion behavior of a Ti alloy in Hank's solution was investigated using various electrochemical and microscopy techniques. The effects of applied load and particle concentration were assessed for various corrosion, wear and wear-corrosion components of the wastage. Electrochemical potentiodynamic and potentiostatic tests were carried out to assess the effects of tribological variables on the wastage rate. The results were used to generate micro-abrasion-corrosion mechanism, wastage and synergy maps. The potential application of such maps to optimize the materials for total replacement bio-implants is addressed in this paper.     

Particle erosion behaviour of boiler tube materials at elevated temperature

The particle erosion behaviour of typical boiler tube materials, including carbon steel, low alloy steels and austenitic steels, at elevated temperatures up to 650 °C was studied using irregularly shaped silica particles. Using 304 steel, the influence of various factors, namely particle concentration, velocity and impingement angle, was examined. The erosion behaviour did not seem to differ significantly from that obtained at room temperature. The erosion rate was a linear function of the particle concentration. The velocity exponents obtained at 300 and 650 °C were both approximately 2.8. The peak impingement angle was at acute angles of 20° – 30°, with a tendency for the peak angle to be slightly higher at 300 °C than at 650 °C. However, the temperature effect was clearly observed in that the erosion rate at acute impingement angles increased significantly with the temperature suggesting that the steel tends to show a behaviour more typical of ductile materials as the temperature is increased. The erosion morphologies at low angles indicated cutting for every temperature used and the lengths of the cutting tracks obtained at 20° also increased with temperature.The erosion rate varied significantly between materials, e.g. the alloy (Incoloy) 800 eroded the most and the 12Cr-1Mo-V steel eroded the least at every temperature used, although every material showed an increase in the erosion rate with temperature. From an attempt to compare the erosion rate data obtained at 20° for every material at every temperature with the tensile properties of the steels, it was found that the yield strength of materials correlates reasonably well with the erosion rate. The erosion rate was apparently proportional to the reciprocal of the yield strength, suggesting that the flow stress included in Finnie's cutting theory may be conveniently substituted by the yield strength multiplied by a constant.     

Particle concentration and size effects on the erosion-corrosion of pure metals in aqueous slurries

In previous studies of erosion-corrosion, several different theories have been developed to produce a model which represents the relationship between particle erosion and chemical corrosion. Regimes in the models define how the two mechanisms behave relative to one another, whether it is erosion dominated, corrosion dominated. This paper investigates the effect of particle and target material on the erosion-corrosion mechanisms. The performance of Fe as the target material will be modelled when considering particle concentration and size. A comparison is made between the erosion-corrosion mechanisms of Fe, Ni, Al and Cu under different conditions of particle size and concentration. By producing several maps, the regimes and wastage rates predicted as functions of velocity and applied potential will be discussed.     

Mapping erosion–corrosion of carbon steel in oil–water solutions: Effects of velocity and applied potential

In this study, the erosion–corrosion performance of carbon steel was investigated in crude oil, reservoir water, and a mixture of both solutions at a range of applied potentials, velocities and impact angle. The application of such work is to upstream and downstream oilfield conditions, where the proportions of hydrocarbon and water may vary during the extraction process over time. Following exposure of the carbon steel in the crude oil, the extent of erosion was greater than that of corrosion, whilst in the reservoir water, the erosion and corrosion contributions were similar. Regimes of erosion–corrosion were proposed based on the variation in erosion behaviour at various impact angles and applied potentials in the environments studied. Mechanistic changes were identified on erosion–corrosion maps as a function of velocity and applied potential at various impact angles, indicating important transitions in erosion–corrosion processes in the oil/water environments.     

Mapping erosion-corrosion of carbon steel in oil exploration conditions: Some new approaches to characterizing mechanisms and synergies

Erosion by solid particles in oil/water slurries is a technologically important area. In such conditions, it is necessary to distinguish between the effects of the sand, aqueous environment, and the oil. Erosion-corrosion maps provide a means of identification between erosion-corrosion regimes as a function of erosion and corrosion parameters. However, there has been no work carried out to map the effects of parameters in oil/water slurries. This paper investigates the effect of erosion-corrosion on carbon steel in oil field production and maps the results. Distinctions between “synergistic” and “additive” erosion-corrosion behaviour are superimposed on the maps in the various environments.