Low Impact Angles Research Articles

Microstructure and tribological properties of CrN and CrSiCN coatings

Abstract Three CrN based coatings were deposited on 17-4PH precipitation hardening stainless steel substrate using plasma enhanced magnetron sputtering (PEMS) technique. The three coatings evaluated in this study assumed the nominal compositions of Cr 0.68 N 0.32 (sample CrN), Cr 0.55 Si 0.013 C 0.14 N 0.3 (sample CrSiCN-1), and Cr 0.43 Si 0.034 C 0.25 N 0.29 (Sample CrSiCN-2) . The microstructure, mechanical properties and wear and erosion resistance of the coatings were evaluated to examine the effect of Si and C additions to CrN. The results indicated that with the incorporation of Si and C, the microstructure transformed from hexagonal Cr 2 N (for CrN coating) to B1 structure containing crystalline Si 3 N 4 (for CrSiCN-2). The initial addition of Si (1.3 at.%) and C resulted in increase of hardness ( H ), Young's modulus ( E ) and the ratio of H 3 /E 2 . With further increase in Si (3.4 at.%) and C, the hardness and Young's modulus decreased. The coefficient of friction was observed to decrease with the addition of Si and C, irrespective of microstructure changes. The combination of reduced coefficient of friction and microstructure modifications has resulted in improved wear resistance for sample CrSiCN-2 (with a wear rate ∼ 60% lower than CrN). The erosion resistance test results showed brittle erosion characteristics for samples CrN and CrSiCN-1 where erosion rate increased with erodent impingement angle and reached the highest rate at 75° and 90°, respectively. CrSiCN-2 coating, while exhibiting higher erosion rate at low impingement angle, demonstrated reduced erosion rate at higher angle due to the ductile nature of the coating under erosion test condition.

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 mm 2 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°.

Erosion properties of Fe based amorphous/nanocrystalline coatings prepared by wire arc spraying process

Fe–Cr–B–Si–Mn–Nb–Y and Fe–B–Si–Nb–Cr amorphous/nanocrystalline coatings were fabricated by wire arc spray process. The microstructure and phase compositions of the coatings were characterised by means of SEM, EDAX and XRD. The formation mechanism of amorphous phase and nanocrystalline phase was discussed. The elevated temperature erosion behaviour of the coatings was also investigated using an air solid particle erosion rig. The microstructures of the coatings consist of amorphous phase and α-(Fe,Cr) nanocrystalline phase. Both coatings are fully dense with low porosity. The coatings exhibit better erosion resistance at lower impact angles. With increasing erosion temperature, the erosion rates of the coatings decrease. The Fe–B–Si–Nb–Cr coating has better elevated temperature erosion resistance than that of the Fe–Cr–B–Si–Mn–Nb–Y coating.

The SPH method for simulating a viscoelastic drop impact and spreading on an inclined plate

In the present work, the phenomenon of an Oldroyd-B drop impact and spreading on an inclined rigid plate at low impact angles is simulated numerically using the smoothed particle hydrodynamics (SPH) method. In order to remove the unphysical phenomenon of fracture and particle clustering in fluid stretching which is the so-called tensile instability, an artificial stress term is employed which has been successfully proposed in simulations of elastic solids. Particularly, the effects of surface inclination and the different regimes of drop impact and spreading on an inclined surface are investigated. The numerical results show the capability of the proposed scheme in handing the unsteady viscoelastic free surface flows. All numerical results of using the SPH method are in agreement with the available data.

Erosion–corrosion behavior of plastic mold steel in solid/aqueous slurry

Erosion–corrosion behavior of a precipitation hardenable plastic mold steel (NAK80) has been investigated by using a rotated slurry erosion rig containing a slurry comprising 20 wt% Al2O3 particle and 3.5% NaCl solution. The erosion–corrosion rate and the synergism between erosion and corrosion have been determined under various conditions. The major environmental parameters considered are impact angle, impact velocity, and particle size. Post-test examination was conducted to identify the material degradation mechanism involved. The erosion–corrosion mechanisms of NAK80 mold steel at high-impact angles are dominated by the formation of impact pits, dissolution of metallic matrix, and plastic deformation fatigue spalling, whereas at low-impact angles, the mechanisms are dominated by the formation of impact pits, dissolution of metallic matrix, fatigue cracks, and cutting. The observed synergism between these mechanisms is much more accentuated at an oblique impact angle than that at a normal impact angle. At a given impact angle, the erosion–corrosion rate is found to increase with the impact velocity and the size of solid particles. The maximum peak of the erosion rates lies at oblique angles between 30° and 45°, whereas the maximum peak of the erosion–corrosion rates appears at 45°, and the erosion–corrosion rate is higher than the erosion rate alone at all angles examined. There is a positive synergism between erosion and corrosion for NAK80 mold steel in solid/aqueous slurry. The synergistic effect is 40–60% of the total weight loss. The contribution of synergism to the total weight loss depends upon the impact velocity; however, it is almost independent of the impact angle and particle size.

Fracture characteristics of high impact polystyrene under impact fatigue loadings

This study analyses the impact properties of high impact polystyrene (HIPS). HIPS is one of the well-known toughened polymers. The high toughness is given by the rubbery phase. The impact fatigue behavior of HIPS was studied with a Ceast pendulum type tester (Resil 25). The fracture mechanisms were examined with a scanning electron microscopy. The nature of crack initiation and propagation was investigated for small impact angles and three different spans. The impact angles of charpy hammer were chosen as 5°, 10°, 15°, 20°, and 25°. The fracture characteristics varied with the impact angle, the number of impacts, and the distance between supports. The rate of crack propagation was high at higher impact angles with lower endurance, and low at lower impact angles with higher endurance.

Performance and wear characteristics of ceramic, cemented carbide, and metal nozzles used in coal–water–slurry boilers

Ceramics, cemented carbides, and metals were prepared to be used as nozzles in CWS boilers. CWS burning tests in a boiler with these nozzles were carried out. The erosion wear resistance of these nozzles was compared by determining their erosion rates and hole diameter variation. Results showed that the life of the ceramic nozzles is about 30 times high than that of the metal nozzles. The wear types at the nozzle wall surface differed in various positions. The nozzle center wall section suffers form abrasive impact under low impact angles, and the damage at the center wall mainly occurs by plowing and plastic deformation for metals, and by polishing action for carbides and ceramics. The primary wear mechanisms at the exit of ceramic nozzle exhibited thermal shock damage with chipping owing to the greater thermal stresses.

Solid particle erosion of unidirectional fibre reinforced thermoplastic composites

In the present study, the solid particle erosion behaviour of neat PEEK matrix and unidirectional glass fibre (GF) and carbon fibre (CF) reinforced polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) composites has been studied. The erosion experiments have been carried out by using silica sand particles (200±50μm) as an erodent. Steady state erosion rates of these composites have been evaluated at different impact angles and impact velocities. The neat PEEK exhibited peak erosion rate at 30° impingement angle whereas the composites exhibited a semi-ductile behaviour with peak erosion rate at 60° impact angle. The erosion rate of the glass fibre reinforced composites was higher than that of the carbon fibre reinforced composites. The results show that the fibre orientation has a significant influence on erosion rate only at lower impact angles. The erosion rate of the composites was higher when the particles impact perpendicular to the fibre direction than parallel to the fibres. The morphology of eroded surfaces was observed under scanning electron microscope and damage mechanisms were discussed.

High Velocity Oblique Impact and Coefficient of Restitution for Head Disk Interface Operational Shock

With the increased use of hard disk drives (HDDs) in mobile and consumer applications combined with the requirement of higher areal density, there is enhanced focus on reducing head disk spacing, and consequently there is higher susceptibility of slider/disk impact damage during HDD operation. To investigate this impact process, a dynamic elastic-plastic finite element model of a sphere (representing a slider corner) obliquely impacting a thin-film disk was created to study the effect of the slider corner radius and the impact velocity on critical contact parameters. To characterize the energy losses due to the operational shock impact damage, the coefficient of restitution for oblique elastic-plastic impact was studied using the finite element model. A modification to an existing physics-based elastic-plastic oblique impact coefficient of restitution model was proposed to accurately predict the energy losses for a rigid sphere impacting a half-space. The analytical model results compared favorably to the finite element results for the range from low impact angles (primarily normal impacts) to high impact angles (primarily tangential impacts).

Influence of austenization temperature on the erosion behavior of austempered ductile irons

The erosion behavior of austempered ductile irons austenized at different temperatures was studied. The results indicate that the erosion rate well correlates with the mechanical properties. At high impact angles, increasing ductility and mechanical energy density results in decreasing erosion rate, whereas increasing hardness reduces the erosion rate at low impact angles.

Sand erosion testing of novel compositions of hard ceramics

The sand erosion rates of novel compositions of hard ceramics such as tungsten carbide, silicon nitride, silicon carbide, and partially stabilized zirconia have been tested in air-sand erosion facilities. A new testing facility that ensured stable and reproducible erosion testing with sand velocities and concentrations up to 250 m/s and 5 wt% in air, respectively, was built at IMI. Special rig design features allowed accurate sand consumption monitoring during each test. High-speed photography was used to determine the sand velocity distribution at each test setting. Parallel testing of these materials in the benchmark facility at the University of Southampton elucidated the test parameters critical for reproducibility of the results in different test configurations. High-speed visualization of the sand impact on the material surface demonstrated fragmentation of almost every sand particle in the range of velocities of 60 m/s and higher. The evidence of extensive fragmentation contributed to understanding the origin of the erosion resistance of hard ceramics. The values of the velocity exponent ( n) were typical of those reported in literature. However, unlike the expected erosion behavior of a brittle material, an ultrafine grained binderless tungsten carbide was more erosive at low impact angle.

Possible reasons of shock melt deficiency in the Bosumtwi drill cores

Abstract— Pre‐drilling numerical modeling of the Bosumtwi impact event predicted a 200 m thick coherent melt layer, as well as abundant highly shocked target material within the central part of the crater structure. However, these predictions are in disagreement with data from drill core obtained in 2004–2005. Here I provide a brief overview of previous results and discuss possible reasons behind melt deficiency, such as specific impact scenarios (low impact velocity and/or low impact angle), and specific target properties (different composition, high porosity, high content of volatiles). I conclude that the most likely explanation is the dispersion of impactites due to the vaporization of pore water, which was not included in the original numerical model.

Effect of impingement angle on slurry erosion behaviour and mechanisms of 1017 steel and high-chromium white cast iron

In the present work a series of systematic erosion tests were carried out to investigate the influence of impingement angle on erosion mechanisms of 1017 steel and high-Cr white cast iron using a slurry whirling-arm test rig. Scanning electron microscopy (SEM), image analysis system, optical microscopy as well as gravimetric and microhardness measurements were utilized to identify the slurry erosion process. Test results showed that, the effect of impingement angle on erosion mechanisms of 1017 steel has three regions. In the first region ( θ ≤ 15°) shallow ploughing and particle rolling were the dominant erosion mechanisms, microcutting and deep ploughing in the second region (15° < θ < 75°), while indentations and material extrusion prevailed in the third region ( θ ≥ 75°). For high-Cr white cast iron the test results showed that, the erosion mechanisms involved both plastic deformation of the ductile matrix and brittle fracture of the carbides. At low impingement angles (up to 45°) observations of microphotographs of the impacted surfaces revealed that, plastic deformation of the ductile matrix was the dominant erosion mechanism and the carbides fracture was negligible which lead to small erosion rate. Whereas, at high impingement angles (greater than 45°) gross fracture and cracking of the carbides were the main erosion mechanisms in addition to indentation with extruded lips of the ductile matrix.

Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

The precise cause and timing of the Cretaceous–Paleocene (K–P) mass extinction 65 Ma ago remains a matter of debate. Many advocate that the extinction was caused by a meteorite impact at Chicxulub, Mexico, and a number of potential kill-mechanisms have been proposed for this. Although we now have good constraints on the size of this impact and chemistry of the target rocks, estimates of its environmental consequences are hindered by a lack of knowledge about the obliquity of this impact. An oblique impact is likely to have been far more catastrophic than a sub-vertical one, because greater volumes of volatiles would have been released into the atmosphere. The principal purpose of this study was to characterize shocked quartz within distal K–P ejecta, to investigate whether the quartz distribution carried a signature of the direction and angle of impact. Our analyses show that the total number, maximum and average size of shocked quartz grains all decrease gradually with paleodistance from Chicxulub. We do not find particularly high abundances in Pacific sites relative to Atlantic and European sites, as has been previously reported, and the size-distribution around Chicxulub is relatively symmetric. Ejecta samples at any one site display features that are indicative of a wide range of shock pressures, but the mean degree of shock increases with paleodistance. These shock- and size-distributions are both consistent with the K–P layer having been formed by a single impact at Chicxulub. One site in the South Atlantic contains quartz indicating an anomalously high average shock degree, that may be indicative of an oblique impact with an uprange direction to the southeast ± 45°. The apparent continuous coverage of proximal ejecta in this quadrant of the crater, however, suggests a relatively high impact angle of > 45°. We conclude that some of the more extreme predictions of the environmental consequences of a low-angle impact at Chicxulub are probably not applicable.

Dopant profiling in NixSi1−x gates with secondary-ion-mass spectroscopy

To study the dynamics of dopant redistribution during the silicidation process, accurate secondary-ion-mass spectroscopy (SIMS) profiles of the dopant and matrix elements are needed in partially Ni silicided gates. A point-to-point calibration method was developed to quantify the SIMS profiles, taking into account the strong dependence of the ionization probabilities of As and B on the Ni content. The Ni and Si intensities, which are needed to monitor the variation in matrix composition, are influenced strongly by the used SIMS conditions. The Ni is pushed forward very effectively by an O2+ beam, when low impact angles are used. But also the use of Cs+ beam induces a serious broadening of the Ni profile. To identify the potential artifacts the sample is analyzed from the front and the back side. The use of backside SIMS turns out to be necessary to obtain accurate SIMS profiles of the Ni.

Particle Erosion of SUS403 Tempered Martensitic Stainless Steel

The particle erosion behavior of SUS403 martensitic stainless steel tempered with five different temperatures range from 200 to 600°C were studied as a function of impact angle and hardness. The results indicate that the dominated mechanisms for material removal are cutting and extrusion at low and high impact angles, respectively. A transition of mechanism mixed by cutting and extrusion occurs at medium impact angle. Grain boundary cracking is often found for all impact angles that seem to be one of the major erosion mechanisms for two-phase materials mixed with martensite and ferrite. The erosion rate of all the experimental materials increases first, and then decreases with increase in impact angle. Thus, the maximum erosion rate occurs at the angle between 30° and 45°. At 15° and 30° of impingement, the erosion rate is virtually independent of hardness. While impact angles exceed than 30°, erosion rate increases with increasing hardness.

Impact of droplets onto inclined surfaces

Drop impacts onto dry walls and liquid films at low impact angles and low normal Weber numbers are experimentally investigated. Measurements were performed using a high spatial resolution CCD camera and short exposure times, yielding both qualitative and quantitative information about the impact. Whereas a droplet generally deposits on the surface for high impact angles, a rebound can occur at lower angles and for smooth or wetted surfaces. No rebound is observed for rough surfaces. A low viscous liquid (water) will either rebound or deposit on smooth or wetted surfaces. A high viscous liquid (glycerin) may also disjoin into two droplets, depending on the impact angle. A correlation is presented for the size of the secondary droplet. A further correlation quantifies the critical impact angle at which rebounding first occurs in terms of the normal Weber number.

Experimental study on erosive wear of some metallic materials using Coriolis wear testing approach

The erosive wear behavior of selected high chromium white iron and aluminum alloys have been experimentally studied by means of Coriolis wear testing and microscopic examinations. Test results suggested that high chromium white iron and aluminum alloy represent two different groups of metallic materials, “hard-brittle” and “soft-ductile,” which experienced significantly different wear patterns and mechanisms in Coriolis wear testing. It appeared that the material loss on white iron samples was generated mostly by sliding wear along with a limited amount of low angle impact fatigue cracking from solid particles in slurry. In contrast, aluminum alloy suffered its weight loss at a much higher rate by the combination of mechanisms including sliding wear and low angle impact wear through microscale deformation, cutting, plowing and work hardening. In the present study, the correlation between wear rate and particle size on the tested materials was discussed. It is proposed that Coriolis wear testing is a valuable and practical approach to simulate and study erosive wear behaviors of materials within a centrifugal pump or similar slurry transportation systems. Factors which should be considered in wear modeling and prediction have also been addressed.

A technical note on grit embedment following abrasive water-jet milling of a titanium alloy

Abrasive water-jet (AWJ) technology is routinely used to cut materials that are difficult to cut by other methods. However, whilst the technology for through-cutting of materials is mature, the process is also being developed for controlled depth milling (CDM) of materials since other processes such as chemi-milling are under increased pressure due to legislative restrictions and costs associated with effluent disposal. Grit embedment and surface morphology is considered to be an issue for the service life of components manufactured by AWJ-CDM, especially in environments where fatigue failure is a concern. In the current work, the effects of milling parameters (namely jet-workpiece traverse speed, jet impingement angle, milling direction and grit size) on the surface morphology and degree of grit embedment are investigated for the milling of a titanium alloy (Ti6Al4V) with garnet grit. Up to 40% of the area of a milled surface has been shown to consist of embedded grit. It has been demonstrated that grit embedment can be minimized either by milling with a high jet traverse speed at low impingement angles or by low speed milling at jet impingement angles up to 45° in the backward direction only. However, even in the best cases, 5% of the area of a milled surface was composed of embedded grit. The levels of grit embedment and development of surface morphology have been observed to depend upon complex interactions of the various processing parameters, and a rationale for the observed behaviour has been proposed.

529 窒化ケイ素セラミックスのアブレイシブジェット加工特性(OS11 研削・砥粒加工)

Abrasive jet machining (AJM) attracts attention as ultra-fine processing technology to brittle material, such as glass and ceramics. This study investigates the effect of impact angle on machining efficiency and surface roughness. The AJM test to which the impact angle was changed, were carried out that a part of fracture mode was changed to ductile mode when an impact angle becomes small. Consequently, machining efficiency. was improved in the conditions of a small impact angle. Moreover, it was shown that surface roughness was improved in the condition of a very low impact angle.