Masanobu Matsumura

The impact angle dependence of erosion damage caused by solid particle impact

Abstract The dependence on the impact angle of erosion damage caused by solid particle impact was characterized on several kinds of material, as expressed by a trigonometric function of both impact angle and material hardness. Erosion tests were conducted on five metallic materials, a ceramic and a plastic material using silica sand particles (mean particle size 325 μm) at impact angles from 3° to 90°, up to an impact velocity of 130 m s−1. The geometry of the specimen and the nozzle tip were devised in order to obtain erosion damage at shallow impact angles less than 20°. The reproducibility of erosion damage obtained under these conditions was consistent with that of standard erosion tests. The detailed erosion damage at shallow impact angles made the dependence of impact angle clear. Although the amount of erosion damage commonly increased with the increase in impact velocity, it was found that the dependence of the erosion damage of metallic materials on impact angle was independent of the impact velocity within 50–130 m s−1 in terms of the relative erosion damage normalized by that at a normal impact angle. This allowed simplification of the equation for erosion damage curves. It was recognized that the maximum erosion damage and the shape of the damage curves shifted monotonically according to the material hardness, which is considered generally to be correlated with other mechanical properties. As a result, the normalized erosion damage curves for tested materials were basically correlated with a trigonometric function in which constants and exponents depended on the impact conditions, except for the impact velocity, if the properties of the particles were fixed. Moreover, in the case of metallic materials, the values related to the hardness. This simulation probably enables an estimation of erosion damage at a given impact angle from that at the normal impact angle.

Relationship between surface hardness and erosion damage caused by solid particle impact

Abstract A model for erosion caused by solid particles was studied and an equation based upon the relationship between dynamic indentation and the hardness of the material was proposed. This equation was established by the relationship between the surface hardness and the erosion damage to the materials. Erosion tests using a gas gun unit were conducted on five materials over a wide range of hardness values (Hv number 9–1100) up to an impact velocity of 150 m s −1 . An increase in the hardness was seen on the fully eroded surfaces obtained in the cases of iron and aluminium, but a decrease was seen in the case of quenched carbon tool steel. No change in the hardness was seen in the cases of the acrylic resin and nylon. The hardness of the eroded surfaces, as opposed to that of the non-eroded surfaces, slightly improved the correlation with erosion damage, but it was not necessarily sound. The softening observed on the eroded surface of the quenched carbon tool steel specimen suggested that heat was generated during the impact of the particles and also that the surface hardness during the course of erosion was different from that both before and after erosion. The temperature increase of an iron leaf sample owing to the impact of a 3.18 mm steel ball or silica sand particles pointed to a transiently high temperature on the impacted surface and the possibility of softening during the course of the erosion process. As a result, the surface hardness of each material estimated with respect to work hardening and softening reasonably correlated with the erosion damage. Also, numerical formulation and the soundness of this equation were discussed through many erosion tests under various conditions.

Critical impact velocity in the solid particles impact erosion of metallic materials

Abstract Solid particles impact erosion of metallic materials proceeds through two kinds of damage processes. One is the removal of material due to repeated plastic deformation, and the other is cutting. These processes occur simultaneously and the ratio of each contribution to the total damage depends not only on the impact angle (the predominant parameter) but also on the impact velocity. As the impact velocity goes down, a solid particle tends not to skid on the target material surface, and hence the cutting damage is reduced. At a certain lower velocity, the particle does not skid at all, resulting in no cutting damage but plastic deformation damage only. This velocity was defined as the “critical impact velocity”. In this study, the methodology to determine the critical velocity through a measurement of the coefficient of friction was established, that is, the dynamic friction coefficient during skidding and the static friction coefficient during rolling without skidding. In order to measure the coefficient of friction at the moment of particle impact, a rotating target apparatus was developed. The critical impact velocity thus determined depended on the hardness of both material and particle, as well as on the shape and size of the solid particles.

Slurry erosion of plasma-sprayed ceramic coatings

Abstract Abrasive resistances of engineering components encountering the attack of erosive environments during operation can be improved by ceramic coatings on their surfaces with a optimum techniques of plasma spraying. The present paper mainly studied abrasive properties of a series of ceramic coatings with different low pressure plasma spray (LPPS) and combined LPPS/APPS (atmospheric pressure plasma spray) methods, in comparison with that of SUS 329J1 dual phase stainless steel, in the jet-in-slit and the rotating specimen testers. The erosive environments were selected as silica sand slurry and fly ash(x%)+gypsum(y%) slurries, respectively. The test results from the two testers did not always coincide although they did in general. The paper summarizes the possible reasons and the implications of the distinctions. In addition, the impact frequency, velocity and angle of particles on the surfaces of the specimens were measured and calculated, and they were used to explain the wear properties of ceramic coatings. Generally, ceramic coatings, such as Cr2O3 and Al2O3, have much improved wear resistance. But the advantages of their wear properties are decreased with increasing impingement angle. In the fly ash(x%)+gypsum(y%) slurry environments which are usually existed in the desulphurizers of thermal power plants, the most deleterious environment for the pumps is pure fly ash (fly ash(100%)+gypsum(0%) slurry.

Improvement of corrosion resistance of materials coated with a Cr2O3/NiCr dilayer using a sealing treatment

Abstract A sealing treatment has been applied to diminish the effects of the pores and micro-cracks on the corrosion properties of the plasma-sprayed Cr 2 O 3 /NiCr dilayer coatings. This treatment decreased the porosity both in the ceramic and in the NiCr dilayer and effectively improved the corrosion resistance. The sealing treatment involved the use of polymethyl silicon and vinyl methyl silicon. Two compositions of plasma sprayed Cr 2 O 3 /NiCr dilayer coated materials (Cr 2 O 3 /80NiCr/316 and Cr 2 O 3 /50NiCr/316) were studied. Optical microscopy and scanning electron microscopy demonstrated that all of the open pores in Cr 2 O 3 /NiCr dilayer were blocked by the sealant resin and only closed pores were remained. The ceramic and sealing resin formed a compact layer without open pores, which protected the materials beneath against corrosion. Corrosion tests of the sealed and unsealed specimens showed that the corrosion resistance of the Cr 2 O 3 /NiCr dilayer coated materials increased markedly after the sealing treatment. Electrochemical experiments showed that after the sealing treatment the difference in corrosion resistance between the sealed Cr 2 O 3 /80NiCr/316 and Cr 2 O 3 /50NiCr/316 was very small probably because the corrosive environment served to mask the effect of the 80NiCr and 50NiCr on the corrosion properties of the dilayer coated materials. Sealed specimens showed small weight grains due to the absorption of water in the resin.

The solid particle erosion behavior of Al18B4O33 whisker-reinforced AC4C Al alloy matrix composites

Abstract Steady-state solid particle erosion of squeeze-cast AC4C Al alloy and 19.5 vol.% Al 18 B 4 O 33 whisker/AC4C Al composites was investigated at room temperature. Experiments were performed with angular silica sand having four velocities (55 m s −1 , 140 m s −1 , 198 m s −1 and 243 m s −1 ) and at impact angle in the range 15° to 90°. The eroded surface and subsurface were observed using scanning electron and optical microscopy. The results indicated that erosion characteristics of the composites was affected by the particle velocity and impact angle. Steady-state rate was found to increase with the addition of whisker to the matrix alloy at high particle velocities or upon increasing impact angle. High erosion rate in the whisker reinforced composites can be attributed to reduced ductility. In addition to plastic deformation, flaking, gouging and microcutting, for the composites, fragmentation and dislodgement of Al 18 B 4 O 33 whisker occurred with impact of particles. At low particle velocity and shallow impact angle, the whisker at the surface can act as protective reinforcement to resist the microcutting and microploughing action. The erosion resistance for the Al 18 B 4 O 33 /AC4C Al composites was improved as a result of whisker addition.

Theoretical equation of the critical impact velocity in solid particles impact erosion

In the previous paper (Yabuki and Matsumura, this issue), the critical impact velocity in the erosion of metallic materials by solid particles impact was experimentally determined. In this paper, the critical impact velocity was theoretically derived through analyzing the behavior of the material surface obliquely impacted by a spherical solid particle, where the material is strained tangentially to the surface in the direction of particle movement. As the extent of strain goes over the elastic limit, the impacted solid particle does skid over the surface, which brings about wear (to the surface) by cutting. The threshold strain was theoretically derived as a function of the impact velocity and the rotating velocities as well as the duration of particle surface contact. Those parameters which characterized the impact behavior were derived from the coefficient of friction and the rebounding coefficient, all of which were obtained from the mechanical properties of the target material and particle, and other factors concerning the particle. Consequently, the theoretical value of the critical impact velocity was given solely as a function of the mechanical properties of the target and the particle. The calculated critical impact velocity attained the lowest value at a low impact angle, and a good correlation was found between the critical velocity determined by experiment and that predicted by the theoretical equation.

Slurry erosion properties of ceramic coatings

Abstract The effectiveness of ceramic coatings on pump impellers used in the acidic gypsum-fly ash slurry environments in desulphurisers was assessed by using two kinds of slurry erosion tester. The experimental results from the two testers did not always coincide, although in general they did. The possible reasons and the implications of this distinction between the two testers were discussed, and the following conclusions were reached: (1) Generally, although ceramic coatings, in particular Cr 2 O 3 and Al 2 O 3 , have much improved slurry erosion resistance, the resistance of ceramic coatings to slurry-erosion is closely related to the techniques of plasma spraying. At optimum manufacturing conditions, ceramic coatings are about two times as resistant as the base metal (SUS329J1); (2) Vickers hardness ( H v ) is an effective parameter for the assessment of slurry erosion properties of ceramic coatings, as well as bulk ceramics; (3) The most deleterious environment for slurry pumps used in desulphurisers is pure fly ash, therefore, fly ash should be removed as much as possible before desulphurising in thermal power plants.

The anti-slurry erosion properties of polyethylene for sewerage pipe use

Abstract Sewerage systems are more common in Japan. The pipes and fittings in the systems are exposed not only to a corrosive environment, but also to the impact by solid particles contained in mud drains, resulting in an erosive wear on the surface. A strategy for coping with these problems involves replacing the more traditionally used iron and steel pipes with polymeric materials, which have excellent anti-corrosion properties. In this study, a slurry erosion test were carried out using a jet-in-slit apparatus on seven types of polyethylenes, three other types of polymers, and two types of iron and steels, thoroughly taking into account the fact that erosion damage is highly dependent on the impact angle of the particles. As a result, all the polyethylenes proved to have excellent anti-erosion properties, compared with the other materials over the entire range of particle impact angle. Further, a model was proposed to account the impact angle dependency of the erosion damage. The model aided in clarifying the reasons why the erosion rate of the polyethylenes is satisfactorily correlated with a complex parameter in which the fracture energy and the elastic modulus are combined.

The effect of NiCr intermediate layer on corrosion behavior of Cr2O3 ceramic coated materials

Abstract The NiCr plasma-sprayed deposition, as an intermediate layer, is normally used to improve the adhesion between the metal substrate and the ceramic coating. Defects, such as pores and micro-cracks, generally exist in the ceramic layer, and lead to corrosion beneath the coating. The present work used plasma-sprayed specimens, such as the Cr2O3 ceramic coatings with and without a NiCr intermediate layer and the single NiCr coatings, etc. which were deposited on a SUS316L stainless steel substrate. The results of corrosion tests and electrochemical experiments indicated that the corrosion resistance of the 80NiCr (80Ni–20Cr) coating was weaker than that of the SUS316 substrate, while that of 50NiCr (50Ni–50Cr) was better than that of the substrate. The existence of 80NiCr plasma-sprayed intermediate layer decreased the corrosion resistance of the Cr2O3 ceramic coated specimen, while the 50NiCr increased it. The microstructure analysis demonstrated that both the 80NiCr and 50NiCr plasma-sprayed coatings consisted of the matrix and a second-phase structure. Energy dispersive spectroscopy (EDS), wave dispersive spectroscopy (WDS) and X-ray diffractometry (XRD) analysis showed that the components of the matrix and the second-phase in 50NiCr were different from those in 80NiCr. In addition, this paper preliminarily discusses the corrosion mechanism of 80NiCr and 50NiCr intermediate layers. The different chromium content in the matrix of the 80NiCr and 50NiCr coatings might have caused the difference in the corrosion resistance between them. It can be predicted that the decrease of porosity by means of plasma spraying or sealing treatment of the ceramic coating, as well as by regulating the components of the NiCr intermediate layer, would improve the corrosion resistance of Cr2O3 ceramic coated materials.