Modelling the erosion rate in micro abrasive air jet machining of glasses

Micro abrasive jet machining (MAJM) is an economical and efficient technology for micro-machining of brittle material like glasses. The erosion of brittle materials by solid micro-particles is a complex process in which material is removed from the target surface by brittle fractures. The rate of material removal is one of the most important quantities for a machining process. Predictive mathematical models for the erosion rates in micro-hole drilling and micro-channel cutting on glasses with an abrasive air jet are developed. A dimensional analysis technique is used to formulate the models as functions of the particle impact parameters, target material properties and the major process parameters that are known to affect the erosion process of brittle materials. The predictive capability of the models is assessed and verified by an experimental investigation covering a range of the common process parameters such as air pressure, abrasive mass flow rate, stand-off distance and machining time (for hole machining) or traverse speed (for channel machining). It shows that model predictions are in good agreement with the experimental results.     

Correlation between solid particle erosion of metals and their melting energies

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

Analysis of particulate erosion

A general analysis is developed for the erosion of materials whereby material is removed through a process of erosion pit nucleation and growth. This model is applicable to a variety of materials exposed to liquid drop impingement and impingement by rounded solid particles. A fundamental limitation of the model is that material removal has to occur as a preferential process.     

Observation and modeling research of high-velocity flushing effect on the performance of BEAM

Blasting erosion arc machining (BEAM) is a novel high efficiency electrical erosion process, which is characterized by a powerful multi-hole inner flushing. In order to study the influence of the high-velocity flushing on the performance of BEAM, a single discharge experiment is carried out on a specially designed observation apparatus, and the phenomena that occurred during the discharge is observed using a high-speed video camera. During the discharge process, a spray cloud of the removed debris near the downstream side of the discharging point is captured by the camera. Tail shaped crater and erosion-corrosion features are also found on the workpiece and electrode surfaces, respectively. These observed phenomena imply that the high-velocity flushing can greatly improve the melting metal removal from the molten pool thereby improving the material removal rate (MRR). For purpose of exploring the mechanism behind, the flow field and pressure distribution of the high-velocity flushing are analyzed by using computational fluid dynamic (CFD) method. The analyzed results indicate that a low-pressure suction effect exists on the downstream side of the electrodes. With the help of the low-pressure suction effect, the high-velocity flushing can continuously take the molten metal out of the molten pool during the discharge, resulting in the reduction of the overheating of the molten metal and improve the efficiency of the discharging energy. Thereby, the work in this paper helps to explain why the high-velocity flushing can markedly promote the material removal rate.     

Study of particle erosion damage in Haynes Stellite 6B I: Scanning electron microscopy of eroded surfaces

The erosion behavior of metals and alloys by solid particles entrained in relatively slow moving gases is of current interest as a result of ongoing efforts in coal conversion and the consequent production of dust-laden gases. Haynes Stellite 6B represents a typical alloy used for erosive wear resistance in such situations and also provides an appropriate alloy for the study of the mechanisms of erosion because it comprises essentially large brittle carbide phases in a ductile matrix. A scanning electron microscope study of the surface of Stellite 6B after erosion by alumina particles is described, and the types of erosion damage incurred by the ductile metal matrix and the brittle carbides are characterized. The only mechanism of material loss of the ductile metal for which positive evidence was found was cutting, with the possibility that fracture on a very fine scale may also be involved. The mechanism of material removal from the carbides appeared to be by surface crack interlinkage. Under the conditions studied, corners of the eroding alumina particles were found to break off and to adhere to the alloy or carbide surface; at the highest impact velocity studied an extensive layer of embedded alumina fragments was built up on the alloy surface and probably modified its erosion behavior.     

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。     

Chromium�Cmanganese iron alloy system design cast in metal and sand moulds for erosion resistance: a positron lifetime study

Erosion characteristics of high chromium (Cr, 16?C19%) alloy cast iron with 5% and 10% manganese (Mn) prepared in metal and sand moulds through induction melting are investigated using jet erosion test setup in both as-cast and heat-treated conditions. The samples were characterised for hardness and microstructural properties. A new and novel non-destructive evaluation technique namely positron lifetime spectroscopy has also been used for the first time to characterise the microstructure of the material in terms of defects and their concentration. We found that the hardness decreases irrespective of the sample condition when the mould type is changed from metal to sand, On the other hand, the erosion volume loss shows an increasing trend. Since the macroscopic properties have a bearing on the microstructure, good credence is obtained from the microstructural features as seen from light and scanning electron micrographs. Faster cooling in the metal mould yielded fine carbide precipitation on the surface. The defect size and their concentration derived from positron method are higher for sand mould compared to metal mould. Lower erosion loss corresponds to smaller size defects in metal mould are the results of quicker heat transfer in the metal mould compared to the sand mould. Heat treatment effects are clearly seen as the reduced concentration of defects and spherodisation of carbides points to this. The erosion loss with respect to the defects size and concentration correlate very well.     

A new model for the erosion of metals at normal incidence

A new theoretical model is proposed for the erosion of metals by particles at normal incidence. The model employs a criterion of critical plastic strain to determine when the material will be removed. This critical plastic strain is defined as the strain at which the deformation in the target localizes and hence results in the lip formation. It is shown that, under typical erosion conditions, the “localization” model is more appropriate than the “fatigue” models. Finally, it is demonstrated that the new model predicts quite well all the essential features of the normal impact erosion process.     

MICRO-COURSE OF CAVITATION EROSION

By cavitation tests and scanning electron microscope （SEM） microanalysis, the micro-appearance of cavitation samples is studied. It is the first time that the micro-appearance of metals is pursued successfully. According to the changing course of the micro-appearance of metals, the damaging course of cavitation erosion is determined. The destructive way of collapsing bubbles on the metal surface is known. Firstly cavitation pinholes appear on the metal surface, then cracks generate and grow under the action of collapsing bubbles. When cracks connect each other, small pieces are removed from pinhole wall and pinholes develop into cavitation pits. When the previous surface is removed completely, new pinholes are produced again on the new surface. A pinhole is the result of the powerful striking of a micro-liquid jet ejected by a large collapsed bubble near the surface. At some stages, cracks grow in the way of fatigue. The corrosion phenomenon is observed during the cavitation erosion. The cavitation pattern can be used to explain the cavitation pregnancy and the changing regulation of sample surface.     

Erosion of a strong aluminum alloy

The erosion of a strong aluminum alloy (7075-T6) and annealed commercially pure aluminum was modelled with impacts by ball bearings of diameter 5 mm at velocities of 140–185 m s^?1. Single impacts caused significant erosive loss only at low impact angles (20°–35°). Single impacts normal to the surface removed negligible amounts of metal. Erosion by impacts normal to the surface occurred only when the deformation field from one impact overlapped that of an earlier impact.Erosion resistance, as measured by velocity threshold for weight loss, was much lower for the high strength 7075-T6 alloy than for pure aluminum. Thus alloying for strength diminishes erosion resistance. Treatments that improve the fracture toughness of the 7075 alloy did not improve erosion resistances.Metal left the target as one or two chips per impact. These separated along narrow bands of intense shear. While particle impacts always deform the surface, it is postulated that this deformation results in metal loss (erosion) only when a shear instability (adiabatic shear) develops under the ball prior to the tensile stresses set up in the surface upon particle rebound.     

Analysis of boiler-tube erosion by the technique of acoustic emission Part I. Mechanical erosion

This paper investigates the mechanical erosion of the metal tubes in bagasse-fired boilers with the aid of the acoustic emission technique. By studying the material removal under various collision conditions, the paper analyzes the dependence of the erosion wear upon the impact angle, velocity, size and concentration of the particles. It was found that the material removal mechanisms were mainly dependent on the particle collision angle and fell into four regimes characterized by rubbing and scratching, cutting and cracking, forging and extrusion as well as sputtering and adhesion. The highest wear rate took place with the cutting and cracking mechanism when the particle collision angle was in the range of 20–30°. The variation of the acoustic emission energy confirmed the conclusions. Finally, three simple formulae were developed to show the dependence of the erosion wear upon the main erosion parameters.     

The role of adiabatic shear in solid particle erosion

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

Solid Particle Erosion Behavior of WC-CoCr Nanostructured Coating

In the present study, solid particle erosion resistance of high-velocity oxy-fuel (HVOF)-sprayed WC-CoCr coatings was evaluated. Erosion testing was conducted using alumina (Al₂O₃) powder as the erodent with three different impact angles (30, 60, and 90°) and impact velocity was kept constant. The coatings were deposited using two different powders; one was composed of conventional WC particles and second one contained nanoscale particles mixed with CoCr binder material. Erosion testing was carried out at room temperature using an air-jet erosion test setup. The effect of varying impact angles was studied and discussed with the help of scanning electron microscopy images of worn surfaces of coatings. The results showed that coating properties like microhardness and fracture toughness have a strong influence on the erosion behavior. During erosion testing, material was removed by fracturing and pullout of WC grains from the binder matrix. The morphology of the eroded surface also showed cutting, lip, and groove formation in the binder matrix caused by the repetitive impacts of erodent particles. It was observed that coating with nano-WC grains exhibited higher erosion resistance compared to conventional coating.     

Evaluation of a semi-empirical model in predicting erosion–corrosion

The phenomenon of erosion–corrosion has been studied extensively by various investigators but no accurate model has been developed to predict the interactions between erosion and corrosion. This is mainly attributed to the complexity of the interactions that generate either a synergistic or antagonistic wear effect for a particular material in a certain environment. A semi-empirical model has recently been developed at the University of Southampton which incorporates dynamic Hertzian contact mechanics to model the damage during particle impact and accommodates the effect of erodent deforming the surface leading to an increased corrosion activity. The model was found to have good agreement with erosion–corrosion rates of carbon steel. The aim of this paper is to evaluate the robustness of this semi-empirical model by testing it on a passive metal. UNS S31603 was chosen due to its inherent passivity to corrosion. A slurry pot erosion tester was used as the test rig to perform the experiments. It was found that this passive metal produces high synergistic levels when exposed to erosion–corrosion in 0.3 M HCl with variation in erodent concentrations and flow velocities. SEM and surface profilometry show typical ductile material behaviour with cutting mechanism and deformation mechanism occurring simultaneously. A wear map is presented and it is observed that the increase in velocity and sand concentration causes the material to shift from a corrosion–erosion dominated region to an erosion–corrosion dominated region. This paper will also evaluate the semi-empirical model and discuss its applicability in predicting erosion–corrosion.     

Erosion in rocket motor nozzles

Examination of the nozzle assemblies of solid propellant rocket motors has shown that erosion of molybdenum inserts occurs by three distinct processes. Wear was initiated by the physical erosion of the steel nozzle body due to particles in the gas stream. Material removed in this manner wetted and alloyed with the surface of the molybdenum inserts in the high temperature reducing gas flame to form a low melting point Fe-Mo-C eutectic alloy. Subsequent liquid metal erosion occurred by blasting of the continuously forming liquid eutectic from the surface of the nozzle by the high velocity gas stream. Finally, additional erosion at the insert throat occurred by the rapid ingress of oxygen to grain boundaries; this weakened the cohesion between the grains and allowed whole grains to be eroded from the surface by the gas stream.     

Particulate erosion of NiO scales

The erosion behavior of brittle oxide scales on ductile alloy substrates is not well known. The oxidation of commercially pure nickel in an air furnace at 1000°C produces relatively thick NiO scales which provide a base for an investigation of the erosion behavior of scales of more complex alloys. The NiO scales formed consisted of two distinct layers, a columnar outer layer and a fine-grained porous inner layer. The erosion testing was conducted at room temperature using an air blast tester. Angular SiC particles were used at velocities V_p of 100 and 30 m s^?1, and at impingement angles α of 20° and 90°.Erosion damage of the NiO scales was observed and interpreted using simplified postulates based on fracture propagation concepts. The NiO duplex scale is removed in a two-step mechanism. Plastic flow indentation and lateral crack growth in the columnar outer layer is the first step in the erosion mechanism. In the second step, pits are produced from hertzian cone fractures formed in the inner layer. The oxide is removed by the chipping away of the cracked scale of the outer and inner layers, which enlarges the pits. At greater velocities, particle sizes and impingement angles the erosion of the thinner oxide scales to the bare nickel occurred in times of the order of seconds. It was observed that the strengths of the bonds between the two scale layers and between the scale and the metal substrate were directly related to the erosion behavior. NiO scales thicker than 50μm introduced some protection during the initial period of erosion of the outer scale. The microstructure, mechanical properties and bonding state of the oxide layers are important parameters in the erosion behavior of oxide scales.     

新型陶瓷喷砂嘴的制备及其应用

分析了喷砂嘴材料和结构的发展情况,采用热压烧结工艺制备出了B4C/(W,Ti)C新型陶瓷喷砂嘴,结果表明随(W,Ti)C含量的增加,陶瓷喷嘴材料的致密度显著增加,晶粒显著细化,保温时间大大缩短,抗弯强度和断裂韧性大大提高;以SiC为冲蚀磨料进行的喷砂冲蚀试验证明了新型陶瓷喷砂嘴的抗冲蚀磨损能力远高于金属、硬质合金和其它陶瓷喷嘴。     

Investigation into erosion rate of AISI 4340 steel during wire electrical discharge turning process

Wire electrical discharge turning (WEDT) process was developed to generate cylindrical form on any electrically conductive material applied in aerospace and automotive industry. The mechanism of metal removal in WEDT process is by means of successive spark discharge. Each spark results in the formation of crater. In the present work, a new model is proposed to predict the erosion rate of each spark for a given discharge energy. A new method is proposed to measure the crater depth from 2D roughness profile of the machined component. The proposed model is validated by conducting experiments on AISI 4340 steel and the results obtained are presented in the paper. It is observed that the results are in close proximity with the experimental values at low discharge energy. The stochastic erosion mechanism of WEDT process is analyzed using scanning electron microscope images of spark eroded wire. Using the proposed model the erosion rate can be controlled and better surface characteristic of machined surface can be achieved.     

Cavitation erosion characteristics of poly(methyl methacrylate) in a rotating disk device

Experimental results pertaining to the initiation, dynamics and mechanism of cavitation erosion on poly(methyl methacrylate) specimens tested in a rotating disk device are described in detail. Erosion normally starts at the location nearest to the center of rotation (CR). As the exposure time to cavitation increases, additional erosion areas or sites appear away from the CR and secondary erosion (induced by eroded pits) spreads upstream and merges with the main pit. The microcracks increase in density towards the end of the incubation period and transform into macrocracks in most cases. A study of light optical photographs and scanning electron micrographs of the eroded area shows that material particles are removed from the network of cracks because of crack joining and pits indicate particle debris. Optical degradation (loss of transmittance) is observed to be greater on the back of the specimen than on the front.     

三相射流去毛刺工艺的试验研究

金属切削毛刺是影响精密零件棱边质量及使用性能的主要因素之一。三相射流去毛刺技术是一种柔性工艺方法。三相射流去毛刺的作用过程和机理非常复杂,不仅与射流及作用条件有关,而且与材料的性质及毛刺的形状密切相关。通过正交试验,分析了三相射流工作条件对材料去除量和冲蚀深度的影响,讨论了磨料粒度与加工表面粗糙度的关系。