Control and evaluation of particle impact conditions in a sand erosion test facility

For the prediction of actual damage to plant component materials and for making the erosion mechanisms clear, it is important to control and to evaluate the particle impact conditions in a testing facility. A sand blast type erosion test rig, which can achieve the particle impact velocities up to 135 m s⁻¹ and a wide range of impact angles has been constructed. The key factors in particle impact conditions of particle flux, impact velocity and impact angle were examined. The relative distance between particles and particle size was discussed, as the particle flux affected erosion rate of material. A new method was proposed to determine particle velocities in this facility. The theoretical velocity of the particle calculated by the equations of particle motion was compared with the experimental results. The divergence of particles from a geometrical angle was evaluated by measuring surface roughness of the specimens. Although some spread of the particles were observed surrounding the central damage area of the specimen surface, the greatest amount of damage was concentrated in the center. As a result, it was found that particle impact conditions were well controlled in this testing unit.     

疏浚管道金属材料冲蚀磨损性能*

疏浚工程中,输送管道内壁面受到泥砂浆的持续冲刷,导致管道冲蚀磨损严重。为选择输合理的输送管道材质,以提高疏浚管道的抗冲蚀性能,降低其维修和更换频率,采用冲蚀试验与理论分析的方法,以常见管材Q235为参照对象,对比5种可用于制作耐磨排泥管道的耐磨金属材料的冲蚀性能,包括Cr15铸铁、Cr26铸铁、Fedur®40合金、中锰钢、信铬钢。根据材料表面扫描电镜(SEM)图像,分析不同冲蚀角度下材料磨损类型。结果表明：冲蚀磨损过程中,各耐磨金属材料同时承受多种磨损作用,合金材料中起支撑作用的软质组分容易因切削、塑性疲劳断裂等因素而被剥离,而较硬的碳化物等组分则在松动后容易被颗粒撞击脱落;除Q235外,其余材料的磨损率均随着冲蚀角度的增加而增大;信铬钢、Fedur®40合金在中、小冲蚀角度下的耐磨性能表现优秀,若价格与加工性能合适,建议选作疏浚管道金属材料。     

基于CFD数值模拟的异面三通管冲蚀磨损规律研究*

针对管道在输送过程中,由流体中固态颗粒产生的冲蚀磨损导致的失效问题,通过CFD-DPM模型开展关于不同流速、颗粒直径、含砂体积比和异面管夹角对异面三通冲蚀磨损性能影响的分析。结果表明：三管交汇处的弯面是管道主要发生冲蚀磨损的位置,水平两管弯头上侧管壁处是受损最为严重的部位;在流速2~10 m/s、含砂体积比1%~9%、异面管夹角90°~150°、颗粒直径0.1~0.5 mm时,管道的最大冲蚀率随着流速增大呈指数型增长,冲蚀面积明显扩张;低流速下,含砂体积比对最大冲蚀率影响较弱,高流速下,最大冲蚀率与含砂体积比呈线性正相关;异面管夹角的增大降低了管道对固体颗粒的流动约束性,其冲蚀率呈线性减小;最大冲蚀率随颗粒直径的增大整体呈现平缓上升的趋势,大颗粒产生的冲蚀破坏相比小颗粒更为集中一些。     

FEM analysis of erosive wear

Surface damage caused by the impact of dispersed particles in gas or liquid flow is called “erosion”. Much attention has been paid to this phenomenon as one of the most serious problems to be solved, particularly concerning pipe-bends or valves in pneumatic conveying systems. But the phenomena of erosive wear are so complicated and vary depending on the factors of not only the kinds of material, hardness, shapes, sizes and mechanical properties of the particles, but also of blasting angles and velocity.

For the purpose of this study, mild steel was prepared and erosion wear tests were carried out. Steel grits were impacted against target materials at different incident angles. The results showed that the wear losses varied markedly as a function of the impact angles, and that the maximum wear occurred at specific angles. Maximum wear occurred at 20–30° for mild steel, and 60° for ductile iron. This impact angle dependence of wear was simulated by Tabor’s theory and FEM which could analyze the plastic deformation of alloy surface as a result of a single particle impact. In the case of both mild steel and ductile cast iron, it was found that the impact angles play a very important and valid role in the corrosion process.     

Erosive wear on ceramic materials obtained from solid residuals and volcanic ashes

In this study, the performance of ceramic materials that were subjected to solid particle erosion was analyzed. This research was performed to characterize the materials in relation to the wear process. The materials could be used in the construction of devices and machine components that are commonly exposed to environments where volatile, abrasive particles typically cause a high rate of wear. The types of composites used in this study could have useful applications in mechanical components, automotive coatings, etc. These materials are usually obtained from solid residuals and volcanic ashes, in which clay and epoxy resin were used as binders.The erosion testing was performed in accordance with the ASTM G76-95 standard. The samples had a rectangular shape, and their dimensions were 50×25 mm² and 10 mm in thickness. The abrasive particles used were angular silicon carbide (SiC) with a particle size of 420-450 μm. The tests were performed using three different incident angles (30°, 45° and 90°) with a particle velocity of 24±2 m/s. The abrasive flow rate was 70 g/min. The particle velocity and the abrasive flow rate were low in all the tests to reduce the interaction between the incident particles and the rebounding particles in the system. Additionally, the total time of each test was 10 min, and the specimens were removed every 2 min to determine the amount of mass lost. The test specimens were located a distance of 7 mm from the shot blast. The surface of the specimens was examined with a scanning electron microscope (SEM), which characterized the erosive wear damage.The results indicated that all of the ceramic materials reached their maximum erosion rate at an incident angle of 90°. The erosion rate was significantly decreased when the angle of incidence was 30°. Additionally, the ceramics that consisted of volcanic ashes and sand mixed with epoxy resin gave a better erosion resistance compared with the materials that were combined with clay. It was assumed that the combination that was mixed with epoxy resin produced a more compact structure in the specimens, which resulted in a less severe attack of the particles that were acting on the surface of the material. The sand and the volcanic ashes that were mixed with clay, which had the poorest performance in the tests, exhibited similar behavior.It was also observed that the damaged area was extended in all of the cases that used an incident angle of 45°, whereas the depth of the wear scars was higher when an incident angle of 90° (normal incidence) was used. The wear scars were characterized by an elliptical shape at 30° and 45°, which is a characteristic feature when the specimens are impacted at low-impact angles (α≤45°), whereas a circular shape was observed at 90°.     

Characterization and solid particle erosion behavior of plasma sprayed alumina and calcia-stabilized zirconia coatings on Al-6061 substrate

Repeated impact by solid particles causes erosion and degradation of engineering components. In internal combustion engines, during combustion, hot gases are generated in large quantity which causes erosion of cylinder, combustion chamber, exhaust system, etc. In this work, two types of plasma sprayed coating systems were developed on Al-6061 substrate. For each system, a systematic microstructural study was carried out to understand changes occurred after spraying. Mechanical properties like density, adhesion strength and hardness of coatings were determined. A solid particle erosion test was conducted on coating systems according to ASTM G-76-02 and results were correlated with the microstructural and subsequent mechanical property change. It was observed that volume erosion is more at 45° angle of impact and shows that behavior is in between ductile and brittle. This work also discusses the mechanism involved in erosion wear of plasma sprayed coating systems.     

The effect of TBC morphology and aging on the erosion rate of EB-PVD TBCs

Since thermal barrier coatings (TBCs) have been used in gas turbines most of the research conducted on them has involved the bond coat and the growth of the thermally grown oxide (TGO) as failure of the bond coat and the TGO were considered to be the primary causes of failure. Erosion of TBCs has been considered as a secondary problem and as such received less attention. Most of the initial work on the erosion of TBCs covered the effects of velocity and impact angle on the erosion rates of both plasma sprayed (PS) and electron beam physical vapour deposited (EB-PVD) TBCs and compared the differences between the two deposition systems. It must be noted that most of the tests were conducted on coatings in the as received condition. This paper aims at expanding the understanding of the erosion of EB-PVD TBCs by examining the effects of TBC morphology, column diameter, column inclination angle and the effects of aging and sintering on the erosion rates of EB-PVD TBCs. The paper also looks at how erosion rate changes as the coating is eroded through to the bond coat.The paper also looks at the mechanisms of foreign object damage of EB-PVD TBCs under a range of different impact conditions. The different damage mechanisms have been identified and related to the size and impact velocity of the impacting particles. The effect of temperature on the plasticity and hence the mechanisms are also discussed, while mapping is used to set the boundary limits for the different types of damage mechanisms that have been identified. It was found that at temperatures above 800 °C the coatings can accommodate a large degree of plastic deformation, while at room temperature there is a greater degree of cracking, for similar types of FOD impact. The 800 °C is not necessarily a limit, but the temperature at which the coatings were tested, and the limiting temperature could in fact be significantly lower. It was found that, all else being equal, erosion rate decreases with a decrease in the column diameter, while aging results in an increase in the erosion rate, dependent on the aging temperature and time. A decrease in the inclination angle of the columns with respect to the substrate increases the erosion rate, when the inclination angle is less than 60° the erosion rate increases catastrophically. These effects are all discussed and explained in terms of erosion mechanisms and mechanical properties in the paper.     

Experimental verification of a model of erosion due to the impact of rigid single angular particles on fully plastic targets

A previously described rigid-plastic model of the erosion of ductile targets by the impact of single angular particles was experimentally verified over a wide range of particle angularities, incident angles of attack, and incident orientation angles. The model assumes that the particle is perfectly rigid and thus is non-deforming, while the target material response is fully plastic, so that elastic rebound effects are neglected.Measurements of particle rebound kinematics, crater volume, and crater shape revealed generally good agreement with those predicted by the rigid-plastic model, and erosion mechanisms resulting from particles tumbling either forwards or backwards, were identified. For highly angular particles, target material removal sometimes occurred due to tunnelling of the particles below the target surface, leading to early break-off of a machined chip, behaviour that could not be predicted by the rigid-plastic model. Besides providing insights into fundamental erosion mechanisms, the results of the present study can be used to predict particle rebound kinematics, crucial for simulations of erosive streams which take into account interference between incident and rebounding particles.     

三相磨料射流作用下材料的破坏机理研究

针对一种新型磨料射流形式，从摩擦学角度出发，分析材料在其作用下的破坏机理。结果表明材料磨蚀主要由冲蚀磨损、气蚀破坏以及它们的共混蚀损作用造成的。特别是共混蚀损，它是三相流中一种独特的现象，相互制约，相互促进，加速了材料的破坏。     

黄河砂冲击下水轮机用钢冲蚀攻角效应

研究了黄河砂冲击下水轮机有20SiMn钢和0CrNi5Mo钢冲蚀攻角效应。结果表明：冲蚀分为孕育期、增加期和稳定期三个过程；低攻角“增重”小于大攻角；攻角增加，冲蚀率增大。水轮机用钢冲蚀攻角效应奇异性与黄河砂冲击下“变形冲蚀”、“切削”和“二次冲蚀”的相对作用大小有关。     

Three-body impact wear study on conventional and new P/M + HIPed wear resistant materials

A new hammer-mill type impact wear testing facility was built for impact wear testing and characterization. Tests with the hammer-mill impact wear device were carried out on conventional wear resistant materials such as Mn-steels of different compositions, white cast iron, and on new P/M+HIPed wear resistant materials. To verify the validity in using this laboratory wear testing apparatus, wear behavior and worn surfaces obtained on conventional and new Mn-steels generated from this device were compared with wear phenomena and worn surfaces developed in industrial applications, i.e. from certain types of rock crushers. The strain hardening effect in different Mn-steel grades was studied first. Second, the wear resistance of materials with different properties was studied using two different grades of abrasive. With silica sand (high hardness, low compressive strength), conventional Mn-steel and white cast iron perform in a manner comparable with the P/M+HIPed materials. With volcanite sand (low hardness, very high compressive strength), the P/M+HIPed wear resistant materials appear to have the best wear resistance.     

Combined experimental and numerical approach for wear prediction in feed pipes

Within this work, a combined experimental and numerical approach to fundamentally understand erosive wear in feed pipes was initiated. By experimental lab-scale testing, it was shown that erosion rates strongly depend on the material's properties and testing conditions. Steel wear was more pronounced at higher impact angle, whereas low impact angle was more critical for rubber. Lab-tests results distinguish from empirical erosion models because material dependent critical impact energies and fatigue phenomena cannot be considered there. A CFD–DEM approach was conducted for simulation of particulate flow in pipes. In addition, long term wear measurements were done to gain data of the wear progress. Although further validation and testing are necessary, very promising results on erosion prediction could be achieved.     

Measurements of plastic strain around indentations caused by the impact of round and angular particles, and the origin of erosion

The aim of this paper is to examine plastic strain distributions around indentations and to consider the mechanisms of erosion damage caused by solid particle impact. A WC ball and an angular SiC particle of 3 mm in diameter were used to compare the effect of particle shape on plastic strain. Measurements of principal shearing strain distributions around the indentations were performed on surfaces of aluminum, iron and cast iron at impact angles of 20°, 30°, 40°, 60° and 90° at impact velocities from 50 to 200 m s⁻¹. It was found that the impact angle dependence was roughly consistent with the maximum principal shearing strain and erosion damage data, which have been published in previous papers and obtained during additional works in this study. The surface topography of the impact craters suggested that depth, contact area and volume of indentation are affected by the particle density and the hardness of both particle and target material. Measurements of volume ratio of lips to craters proved that material removal did not necessarily occur at a single impact of the WC ball, but occurred at the impact of the angular SiC particle at low impact angles. It is concluded that the origin of erosion is probably attributed to the conjoint actions of high plastic strains followed by subsequent removal and the cutting process caused by particle impact.     

Numerical Study of Impact Behaviors of Angular Particles on Metallic Surface Using Smoothed Particle Hydrodynamics

Modeling and studying the impact behaviors of angular particles is critical in understanding the mechanisms of erosive wear on solid surfaces. This article focuses on effective mesh-free model based on the smoothed particle hydrodynamics (SPH) method to simulate impacts of angular particles on metallic surfaces. The predicted results are compared with the available experimental data, and good agreement has been achieved. Our simulations under different incident conditions successfully reproduce the general impact behaviors of angular particles, including rotating behavior and rebound behavior, which enables detailed examinations of erosion mechanisms. We find that the rotating behaviors are mainly determined by initial orientation and impact angle, whereas impact velocity has little effect. For backward impact involving a prying-off action, there generally exsits a critical impact velocity below which the cutting process would never be finished, which may result in a rebound angle greater than 90°. Further, multiple and overlapping impacts are simulated to reveal the effect of a pre-created crater on the subsequent impact. The results demonstrate the ability of the present model to handle the extremely deformed surface by overlapping impacts. The proposed SPH model and the present study could be useful in the study of erosive wear on the surface of metal devices that carry granular substances.     

An erosion-based model for abrasive waterjet turning of ductile materials

This paper presents an attempt to model the abrasive waterjet (AWJ) turning process considering material removal from the circumference of a rotating cylindrical specimen. The methodology involves the use of Finnie's theory of erosion to estimate the volume of material removed by the impacting abrasive particles. The proposed model considers the impact of jet at an angle to the workpiece surface to account for the curvature of the workpiece. Unlike earlier works, this model considers the continuous change in local impact angle caused by the change in workpiece diameter. The flow stress of the workpiece material is determined using a novel experiment involving the same abrasive and workpiece materials. The adequacy of the proposed model is examined through AWJ turning tests under various process parameter combinations. The final diameters predicted by the model are found to be in good agreement with the experimental results.     

Solid particle erosion of diamond coatings under non-normal impact angles

This paper describes an erosion study, which examines the effect of impact angle on the erosion behaviour of diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were 37–60 μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194 μm at a particle velocity of 268 m s⁻¹. The impact angles used were 30, 45, 60 and 90°. The results show that the damage features, termed “pin-holes” are generated at all angles, though the number of impacts required for pin-hole initiation is significantly increased at lower angles. This work provides useful information in attempting to explain the mechanism by which damage is generated during the high velocity sand erosion of CVD diamond.     

离心压缩机叶轮材料FV520B冲蚀规律和机理的研究

利用高速冲蚀试验系统,以7 μm、10 μm、14 μm多角氧化铝微粒为冲蚀颗粒,在120 ~ 210 m/s冲击速度范围内,对离心式压缩机叶轮材料FV520B在模拟压缩机叶轮高速粒子冲蚀环境下的冲蚀规律进行了系统的试验研究。对冲蚀表面形貌进行分析,研究冲蚀磨损机理。结果表明：参与冲蚀的粒子质量在5 ~ 80 g之间时,冲蚀率先增加后减小即为冲蚀过渡期,冲蚀粒子质量大于80 g后冲蚀率趋于平稳,进入冲蚀稳定期;高、低强度的两种FV520B材料,均呈现出典型的塑性材料的冲蚀特性,最大冲蚀率分别出现在24°、18°的冲击角度附近;高强度FV520B在24°和90°冲击角度时的速度指数分别为3.37和3.68,速度指数随冲击角度的增大而增大;FV520B冲蚀磨损的实质是微切削与变形磨损共同作用,在低角度冲蚀时,以微切削磨损为主,而在大于60°的高角度冲蚀,以变形磨损为主。     

Development of 1232°C (2250°F) Erosion and Impact Tests for Thermal Barrier Coatings

High temperature erosion and impact texts were developed for evaluation of thermal barrier coating (TBC) systems that are being generated for the High-Speed Civil Transport supersonic aircraft under NASA's Enabling Propulsion Materials program. The TBC-coated test specimen is a 6.1-mm (0.24-inch) diameter cylindrical pin. Twelve pins are mounted on a carousel with a pitch diameter of 46 mm (1.813 inch). This carousel is rotated at 500 rpm, 50 mm (two inches) from the combustor exhaust of a burner rig, while the TBC temperature is controlled at 1232°C (2250°F) using a pyrometer. The particulate is injected radially into the combustor in two horizontally opposed positions.

Two separate types of particulate are used in the tests: 50-micron and 560-micron crushed alumina. The effects of the 50-micron erosion and 560-micron impact tests are quite different, but in each case excellent similarity is seen between damage to test specimens and that of commercial engine service hardware. The temperature of the impinging particulate is above 1450°C (2642°F), and the particulate velocities were determined to be. 174 and 9 meter/second (570 and 30 feel/second), respectively, for the 50-micron and 560-micron materials.

A mathematical expression was developed for erosion wear as a function of particle size, velocity, hardness and density. The ranges over which these parameters were varied are particle size 10 to 180 micron, velocity 107 to 332 meter per second, hardness 820 to 2100 kg/mm² Knoop, density 2.2 to 5.7 gram/cc. Erosion wear is linear with the accumulated mass of eroding particulate used. Impact wear caused by 560-micron alumina is distinctly nonlinear.     

Solid particle erosion behaviour of hardfacing deposits on cast iron—Influence of deposit microstructure and erodent particles

Solid particle erosion (SPE) behaviour of different hardfacing electrodes deposited on gray cast iron (ASTM 2500) was studied using quartz sand and iron ore as erodent particles. Erosion test was carried out as per ASTM G76 test method. Considerable differences in erosion rates were found among different hardfacing electrodes at normal impact. Both volume fraction of carbides and type of carbides played an important role in the erosion behaviour of the deposits when quartz sand was used as erodent particles. On the other hand, only volume fraction of carbides irrespective of carbide type mainly controlled the erosion rate of the same deposits when iron ore was used as erodent particles. Such difference is attributed due to difference in metal removal mechanisms by the two erodent particles used. Hard quartz sand particles were capable of causing damage to most of the carbides while relatively softer iron ore particles were unable to fracture any carbides present in the microstructures. Furthermore, relatively brittle matrix led to high erosion rate which is significant in case of quartz sand as erodent, but not in case of iron ore particles. Like abrasion resistance, hardness is not a true index of erosion resistance of hardfacing deposits.     

Determination of particle impacts and impact energy in the erosion of X65 carbon steel using acoustic emission technique

An in-situ acoustic emission (AE) monitoring technique has been implemented in a submerged jet impingement (SIJ) system in an effort to investigate the effect of sand particle impact on the degradation mechanism of X65 carbon steel pipeline material in erosion conditions.A detailed analysis of the acoustic events' count rate enabled the number of impacts per second to be quantified for a range of flow velocities (7, 10, 15 m/s) and solid loadings (0, 50, 200, 500 mg/L) in a nitrogen-saturated solution at 50 °C. The number of impacts obtained from acoustic signals showed a strong agreement with theoretical prediction for flow velocities 7 and 10 m/s. A deviation between practical readings and theory is observed for flow velocity of 15 m/s which may be due to error from detected emissions of multiple rebounded particles.Computational fluid dynamics (CFD) was used in conjunction with particle tracking to model the impingement system and predict the velocity and impact angle distribution on the surface of the sample. Data was used to predict the kinetic energy of the impacts and was correlated with the measured AE energy and material loss from gravimetric analysis. The results demonstrate that AE is a useful technique for quantifying and predicting the erosion damage of X65 pipeline material in an erosion–corrosion environment.