K. M. Emara

Investigation Into Cavitation Erosion Pits

Cavitation erosion pits and their effects on erosion progression were investigated in detail for SUS 304 stainless steel, α + β brass (60/40), and pure aluminum (Al-99.999 and Al-99.92) by means of vibratory erosion. Two kinds of erosion pits were found on the specimen surfaces, one by microjet impact and the other by shockwave blow. Systematic observations of the feature of microjet-pits with the testing time showed that the sizes and shapes of microjet-pits did not change at all and such pits scarcely played an important role in developing the erosion. Moreover, the feature morphology of eroded surfaces, and dislodged particles and their large sizes revealed that microjet-pits had a limited effect on erosion and that the predominant failure was a fatigue process.

Design and Performance of Slurry Erosion Tester

A slurry whirling arm erosion test ring was constructed and a series of erosion tests andpost-erosion analysis were carried out using a paint erosion indication technique. Thepattern of the paint removal presented a highly visual and accelerated map for theerosion process and its behavior. Also, the erosion rate of paint removal was investigatedunder a number of erosion variables. It was observed that the rebounding of the erodentparticles from the sample surface play an important role in developing erosion for thistester. The erosion pattern showed that the effect of the rebound particles depends on theimpact velocity and impingement angle. It was also observed that the erosion behavior ofpaint as a function of impingement angle, impact velocity, and erosion time was similarto that reported in literature for engineering materials. The slurry whirling arm erosiontester seems to be promising for simulating the slurry process in real cases.

Fractal Characterization of Slurry Eroded Surfaces at Different Impact Angles

In the present work, the topographical images of slurry erosion surfaces at different impact angles were quantified using fractal analysis. The study showed that the variation of fractal value of slope of linearized power spectral density with the impact angle is largely similar to the relationship between the erosion rate and the impact angle. Both the fractal value and erosion rate were maximum at 45 deg and 90 deg for ductile and brittle materials, respectively. It was found also that the variation of fractal values versus the impact angle has a general trend that does not depend on magnification factor. The fractal features to the eroded surfaces along different directions showed high directionality at oblique impact angle and were symmetrical at normal impact.

Effect of Impact Angle on Slurry Erosion Behavior and Mechanisms of Carburized AISI 5117 Steel

The paper reports a study of slurry erosion of carburized AISI 5117 steel using whirling-arm rig. The study is mainly focused on studying the erosion wear resistance properties of AISI 5117 steel after carburizing at different impact angles. The mechanisms of erosion wear at different impact angles are presented using SEM examination of eroded samples. In addition, the SEM images of eroded samples at different stages are presented for better understanding of erosion mechanisms at different angles. The tests were carried out with particle concentration of 1 wt %, and the impact velocity of slurry stream was 15 m/s. Silica sand having a nominal size range of 250 – 355 μm was used as an erodent. The results showed that, carburizing process of steel increased the erosion resistance and hardness compared with untreated material for all impact angles. The erosion resistance of AISI 5117 steel increases by 70, 57, 60 and 36 % at an impact angle of 30o, 45o, 60o and 90o, respectively as result of carburizing, i.e. the effectiveness of carburizing was the highest at low impact angles. Treated and untreated specimens behave as ductile material, and the maximum mass loss appears at impact angle of 45 o . Plough grooves and cutting lips appears for acute impact angle, but the material extrusions are for normal impact angles. The erosion traces are wider and deeper for untreated specimens comparing by the shallower and superficial ones for the carburized specimens.

Stepwise Erosion as a Method for Investigating the Wear Mechanisms at Different Impact Angles in Slurry Erosion

In the present work, stepwise erosion technique was carried out to investigate in detail the influence of impact angle on the erosion process of AISI 5117 steel. The number of impact sites and their morphologies at different impact angles were investigated using scanning electron microscope (SEM) examination and image analysis. The tests were carried out with particle concentration of 1wt. %, and the impact velocity of slurry stream was 15m/s. Silica sand—which has a nominal size range of 250‐355lm—was used as an erodent, using whirling-arm test rig. The results have shown that the number of craters, as expected, increases with the increase in the mass of erodent for all impact angles and this number decreases with the increase of the impact angle. In addition, the counted number of craters is larger than the calculated number of particles at any stage for all impact angles. This may be explained by the effect of the rebound effect of particles, the irregular shape for these particles, and particle fragmentation. The effect of impact angle based on the impact crater shape can be divided into two regions; the first region for h � 60 deg and the second region for h � 75 deg. The shape of the craters is related to the dominant erosion mechanisms of plowing and microcutting in the first region and indentation and lip extrusion in the second region. In the first region, the length of the tracks decreases with the increase of impact angle. The calculated size ranges are from few micrometers to 100lm for the first region and to 50lm in the second region. Chipping of the former impact sites by subsequent impact particles plays an important role in developing erosion. [DOI: 10.1115/1.4026420]