Dry Erosion Research Articles

Improvement of erosion and erosion–corrosion resistance of AISI420 stainless steel by low temperature plasma nitriding

Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N 2 + 75% H 2 atmosphere at low temperature (350 °C) and normal temperature (550 °C) for 15 h. The composition, microstructure, microhardness profiles, residual stress profiles and electrochemical impedance spectrum analyses of the nitrided samples were examined. The influence of plasma nitriding on the erosion and erosion–corrosion resistance of AISI 420 martensitic stainless steel was investigated using a jet solid particle erosion tester and a slurry erosion–corrosion tester. Results showed that the 350 °C nitriding layer was dominated by ɛ-Fe 3N and α N phase, a supersaturated nitrogen solid solution. However, nitrogen would react with Cr in the steel to form CrN precipitates directly during 550 °C nitriding, which would lead to the depletion of Cr in the solid solution phase of the nitrided layer. Both 350 and 550 °C plasma nitriding could improve the erosion resistance of AISI420 stainless steel under dry erosion, but the former showed better results. In both neutral and acid environment, while the erosion–corrosion resistance of AISI 420 was improved by means of 350 °C nitriding, it was decreased through 550 °C nitriding.

Wear performance of sandwich structured WC–Co–Cr thermally sprayed coatings using different intermediate layers

Cermet based WC–Co–Cr thermally sprayed coatings are known for their good wear and corrosion performance. Different intermediate layers with various deposition processes were performed between cermet WC–Co–Cr coatings to form a sandwich structure to enhance adhesion and to damp particle impacts during erosion. As the outer cermet layer exhibits high hardness against abrasion whereas the intermediate layer is ductile to damp the shock due to particle impact in erosion, sandwich coatings might have potential improvement in life time of coated tools used in mining, drilling, cutting and grinding. Adhesion tests were performed and the tribological behavior of cermet coating and sandwich structured materials was mainly investigated with dry erosion and high pressure slurry jet erosion tests with 30° and 90° impinging angles to study wear mechanism and particle impact at interfaces between coatings. In this work, the adhesive strength of different coatings was measured for each combination. Cermet coating, combinations of Ni–Cr 80–20 and Ni-plating showed high strength value. In spite of the low erosive wear rate Ni–Cr 80–20, the metallographic examination revealed many cracks within this coating due to the particle erosion at high pressures that has been found to drive microcracks through the interfaces between splats leading to flaking of the sprayed coatings. The electrochemically deposited interlayer showed better tribological performance under metallographic observation, because of its homogeneous microstructure, since the electrochemical deposition does not provide splat formation. Consequently, the absence of discrete interfaces limits crack initiation within the coating and at the interface. However, the microstructure of the interlayer is known to be related to coating deposition process such as microsplats and oxide formation in spraying process. Therefore, the influence of microstructure on wear mechanism was investigated.

Evaluation of porcelain enamels of directional signs used in the UAE

Blue coloured enamel coatings on 3003 aluminium alloy panels have been produced. The enamels used to produce the coatings were of similar compositions except for titanium dioxide, colouring and other metal oxides. The first enamel composition was a standard one as recommended by the supplier and contains 7% of the expensive opacifier titanium dioxide. This recommended composition has been modified to form the second enamel. Higher amounts of the less expensive colouring and other metal oxides were added on the expense of titanium dioxide which was reduced to 1%. Different firing temperatures and enamel slip fineness were used to produce the modified enamel coatings. Scanning electron microscopy, accelerated weathering, spalling and dry erosion tests have been used to evaluate different enamel coatings. Results have shown that the modified enamel composition has produced coatings of comparable quality as compared to coatings produced using the supplier recommended composition. Firing the modified enamel below 500 °C results in enamel coatings of inferior quality, whereas firing at temperatures above 525 °C produces coatings of good performance. Coatings produced using small fineness have resulted in enamel coatings having pores of relatively smaller sizes.

Beneficial effect of oxygen-active elements on the resistance of aluminide coatings to corrosive erosion and dry erosion

Oxygen-active elements such as yttrium and cerium are often used to improve the performance of high-temperature alloys. Recent studies demonstrate that the oxygen-active elements are also beneficial to the wear resistance of materials in corrosive environments or at elevated temperatures. In this work, the effect of yttrium and cerium on the corrosive erosion of an aluminide coating on 1030 steel at ambient temperature, in sulfuric and salty slurries, respectively, were investigated. The microstructure of the aluminide coatings was investigated using optical microscopy and transmission electron microscopy (TEM). The distribution of yttrium or cerium in the diffusion layer was analyzed using energy-dispersive spectroscopy (EDS), and the microhardness of the coating also was determined. The corrosion rate, polarization behavior and corrosive erosion of the Y/Ce-containing aluminide coatings, as well as their dry sand erosion at different temperatures from 30 to 190°C were evaluated. The results showed that the oxygen-active elements significantly increased the resistance of the aluminide coatings to corrosive erosion in silica-containing sulfuric acid slurry and silica-containing salt slurry, respectively. The modified aluminide coating also manifested a higher resistance to corrosion at ambient temperature, as well as to dry sand erosion at different temperatures.

Improvements of the microstructure and erosion resistance of boron carbide with additives

A series of test materials were produced from boron carbide (B4C) powders with additions of either boron in amounts up to 60 wt.%, silicon (4 wt.%) or silicon and silicon carbide (4 wt.% and 30 wt.%, respectively). The powder mixtures were densified by encapsulation hot-isostatic pressing. The test materials where evaluated in dry particle erosion tests with silicon carbide grits. Particular attention was given to the relation between the microstructure and the composition.It was found that boron additions up to 20 wt.%, decreased the average grain size and reduced the porosity of the boron carbide. A material with 60 wt.% boron exhibited very low porosity and supreme resistance to particle erosion. The erosion resistance was also significantly improved by additions of silicon and silicon carbide.The favorable effects of boron, silicon and silicon carbide are discussed in terms of their influence on microstructural parameters, such as grain size, porosity, grain boundaries and reduction of free carbon.

Effects of cerium on dry sand erosion and corrosive erosion of aluminide coating on 1030 steel

Effects of cerium on dry sand erosion and corrosive erosion of aluminide coating on 1030 steel

Modification of Aluminide Coating with Yttrium for Improved Resistance to Corrosive Erosion

Aluminide coatings on a mild steel substrate were modified by using an oxygen-active element, yttrium, for improved resistance to corrosive erosion. The performance of the yttrium-containing coating during the following three erosion conditions was evaluated: dry sand erosion at different temperatures, erosion in a dilute NaCl slurry containing 30% silica sand, and erosion in a dilute H2SO4 slurry containing 30% silica sand. Results of the study demonstrated that yttrium significantly improved the resistance of the aluminide coating to both corrosive erosion and dry sand erosion.

Looking beyond the millennium: critical issues in the evaluation of materials performance for resistance to erosive wear in corrosive conditions

Advances in the study of erosive wear in corrosive conditions have lead to improved understanding of the performance of materials in such conditions. Through mapping the materials degradation as a function of the main process parameters, the most favourable operating conditions may be identified. The maps, albeit still in their infancy, provide the basis for addressing materials problems in erosion–corrosion environments in a non-empirical fashion. Where do we go from here? Much experimental work still needs to be carried out to understand the mechanisms of erosion–corrosion of the wide range of materials and coatings available for combating erosion–corrosion damage. Based on such work, mechanistic models of the damage processes need to be continually developed and refined in order that a sound basis can be generated for the construction of such maps from theoretical methods. This paper summarizes the recent work carried out on the development of materials performance maps both in wet and dry erosion–corrosion conditions. The future challenges for the research community of the work in this area are described. An outline route map through which these important developments may be carried out is also described.

Comparison of slurry and dry erosion behaviour of some HVOF thermal sprayed coatings

The performance of 10 high velocity oxy-fuel (HVOF) sprayed coatings has been evaluated under both dry particle and slurry erosion conditions at 90° and 20° impingement angles. The coatings were six WC cermets with Co- or Ni-based matrices, a Cr 3C 2–NiCr composite and three metallic alloys. Slurry jet erosion experiments were carried out using a 9 wt.% alumina/water slurry with 35 and 200 μm angular alumina particles, at an impingement velocity of 15 m/s and flow rate of 18 l/min in a re-circulating loop apparatus. Dry erosion was effected in a once-through mode with 50 μm diameter alumina particles at a velocity of 84 m/s and feed rate of 2 g/min. Dry erosion rates three orders of magnitude greater than slurry erosion rates were due mainly to the differences in actual particle-target impact velocities. Coating composition, microstructural integrity and hardness were the major determinants of relative erosion resistance in all tests, with matrix corrosion resistance influencing the surface damage resistance of cermets in longer duration aqueous slurry tests.

Parametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil moisture for arid and semi-arid areas

Abstract. Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account for the influence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension) are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w' (depending on the soil texture), these capillary forces are considered as not strong enough to significantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w' is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coefficients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w' and soil clay content has been established. The erosion threshold ratios simulated for different soil textures were found to be in good agreement with the experimental data.Key words. Atmospheric composition and structure (Aerosols and particles) · Hydrology (soil moisture)

Abrasive Blasting of Metal Matrix Composites

This paper investigates the feasibility of dry erosion by blasting alumina erodent on aluminum composite reinforced with silicon carbide particles. The erosion rate is dependent on the erodent velocity and the matrix hardness. Two different material removal mechanisms are observed due to different attack angles. Blasting between 30-60° is recommended for optimum erosion rate and surface quality. Material removal mechanisms and surface quality of blasted and ground composites are compared. Although its erosion rate is two orders of magnitude less than that for rough grinding, dry blasting is suitable as a finishing process of composites with irregular contours.

Peculiarities of erosion-corrosion processes

Investigations have been carried out on an erosion-corrosion apparatus to investigate the behaviour of corrosion-resistant highalloy iron-base materials containing hard phases. These materials had been optimized for increased wear resistance under complex stress conditions. As expected, in dry erosion tests, very low mass losses were established; there was little difference between the materials. Also, in corrosive environments (NaCl, H 2SO 4), the materials showed good stability; however, the duplex structures were superior to the martensitic ones. The combination of erosion and corrosion produced large differences and, in some cases, markedly reduced resistance to damage. These results confirmed observations that it is impossible to deduce the environmentally influenced mechanical behaviour of an alloy from its behaviour in separate corrosion and erosion experiments. The basic mechanisms underlying these processes have been investigated only tentatively.

Dry erosion of epoxy/rubber composites

AbstractThe dry erosion behavior of epoxy/waste rubber composites has been investigated as a function of rubber content, air pressure (particle velocity), and impact angle. Morphological aspects have also been examined. The experimental data have been explained by means of an analytic equation derived from the crack propagation physics.

The Distribution and Spread of Alien Vascular Plants on Prince Edward Island

Surveys of alien plants at subantarctic Prince Edward Island in 2001 show that the ranges of all three introduced species have increased since the last survey in 1998. Poa annua, the longest-established species, increased its range substantially after 1987, prior to which it was confined to a single site for more than 20 years. It remains largely restricted to sites characterized by intense disturbance by seals and seabirds. Sagina procumbens, the most recently discovered alien plant, has spread even more rapidly (up to 800 m year−1) and has colonized the west coast of the island (a leap of at least 3 km). Unlike Poa annua, it is not restricted to animal-disturbed areas, although its seeds probably are dispersed by both birds and fur seals. Cerastium fontanum also continues to spread at the island, but remains confined to the western coastal plain, where it occurs mostly on dry feldmark slopes or erosion scars. All three species have expanded their ranges faster than at Marion Island, possibly because of a warmer recent climate and higher densities of seabirds and seals at Prince Edward Island. The ranges of alien plants are likely to continue to expand, with S. procumbens causing considerable changes in the island's terrestrial ecology.