Shallow Impact Angles Research Articles

Nozzle fouling in cold spray: Material transfer between Ni particles and WC-Co substrates at shallow impact angles and elevated surface temperatures

Experimental and theoretical investigations of nozzle clogging in WC-Co cold spray nozzles using nickel powder were conducted. Computational fluid dynamics (CFD) was used to show that the highest particle impact kinetic energy density occurs just downstream of the nozzle throat, where clogging is common. CFD also showed particles impact the nozzle wall at angles between 0.3°–5°, with smaller particles having higher velocities and temperatures. An experimental setup was used to investigate the effects of substrate temperature, surface roughness, and incidence angles on material deposition. Scanning electron microscopy revealed nickel particles smeared on the substrate surface, with more deposition on smoother surfaces. Energy dispersive X-ray spectroscopy (EDS) showed more nickel deposited at higher substrate temperatures and lower impact angles. Finite element simulations indicated nickel powder reaches temperatures above its melting point while sliding along the WC-Co substrate and predicted localized melting. Particle smearing is identified as the cause of nozzle clogging based on experimental and simulation results.

Exploring the effect of ELM and code-coupling frequencies on plasma and material modeling of dynamic recycling in divertors

Integrated modeling of plasma-surface interactions provides a comprehensive and self-consistent description of the system, moving the field closer to developing predictive and design capabilities for plasma facing components. One such workflow, including descriptions for the scrape-off-layer plasma, ion-surface interactions and the sub-surface evolution, was previously used to address steady-state scenarios and has recently been extended to incorporate time-dependence and two-way information flow. The new model can address dynamic recycling in transient scenarios, such as the application presented in this paper: the evolution of W samples pre-damaged by helium and exposed to ELMy H-mode plasmas in the DIII-D DiMES. A first set of simulations explored the effect of ELM frequency. This study was discussed in detail in this conference’s proceedings and is summarized here. The 2nd set of simulations, which is the focus of this paper, explores the effect of code-coupling frequency. These simulations include initial SOLPS solutions converged to the inter-ELM state, ion impact energy (E in) and angles (A in) calculated by hPIC2, and an improved heat transfer description in Xolotl. The model predicts increases in particle fluxes and decreases in heat fluxes by 10%–20% with the coupling time-step. Compared with the first set of simulations, the less shallow impact angle leads to smaller reflection rates and significant D implantation. The higher fraction of implanted flux (and deeper), in particular during ELMs, increases the accumulated D content in the W near-surface region. Future expansion of the workflow includes coupling to hPIC2 and GITR to ensure accurate descriptions of E in and A in, and W impurity transport.

Dimensional Effects of Hybrid Bond Layers on CFRP Metallized by Ti Cold Spray

Hybrid bond layers (BLs) were designed, fabricated, and evaluated for cold spray metallization of CFRP. The bond layers consisted of metal mesh embedded in a polymer film adhesive co-cured to the CFRP. Efforts were devoted to identifying the critical opening ratio—i.e., the ratio of mesh opening size to powder diameter, for deposition of an adherent coating. Analysis of powder deposited at mesh openings show a transition from erosion (at a mesh opening ratio of 6.4) to mechanical interlocking and formation of a continuous coating with decreasing opening ratio. Selection of opening ratio yielded either (a) a grid of consolidated thin-walled deposits atop mesh wires separated by microchannel openings, or (b) densified coatings of cold-sprayed Ti. The effective opening ratio increased with increasing diameter ratio—i.e., the ratio of wire diameter to powder size, a consequence of eroded wire peripheries at shallow impact angles. These findings inform the design of future hybrid BLs, in concert with the selection of powder size, for cold spray metallization of CFRP.

Erosion behavior of laser cladded Colmonoy-6 + 50%WC on SS410 steel under accelerated slurry erosion testing

Erosion due to slurry has an indispensable effect on the lifespan and operating efficiency of hydro machine components. To mitigate this effect, laser cladding may prove as a cost-effective choice to improve the surface properties of various hydro machine components. In this research work, a laser cladding of Colmonoy-6 + 50%WC powder on the surface of SS410 steel was deposited using high-power diode laser at optimized levels of operating parameters. The deposited coating was characterized with regard to different mechanical and metallurgical properties. The effect of various factors such as slurry concentration, erodent particle size, impact velocity, and impact angle on slurry erosion behavior of uncoated and laser cladded substrate was analyzed. The Colmonoy-6 + 50%WC cladded specimens exhibited significantly better slurry erosion resistance in comparison with uncoated SS410 steel specimens under all slurry erosion conditions. Impact velocity was observed to be a maximum contributor to slurry erosion, followed by impact angle, average particle size and slurry concentration. The SEM micrographs of eroded cladded surfaces showed signatures of lip formation & fracture sites, micro-cutting, ploughing, and wear marks at a shallow impact angle in Colmonoy-6 pool, however, for normal impact, the existence of cracks in WC particles were observed.

Solid particle erosion behavior of melt-infiltrated SiC/SiC ceramic matrix composites (CMCs) in a simulated turbine engine environment

The erosion behavior of a melt infiltrated SiC/SiC ceramic matrix composite was investigated under a more representative engine environment. A special experimental facility was setup to simulate the turbine engine conditions. The influence of the operating parameters such as particle velocity, particle size, temperature, erodent concentration and impingement angle were investigated. In addition, room temperature studies were also conducted under the same operating parameters for comparison. Eroded sites were investigated under the scanning electron microscope (SEM) to understand the erosion mechanisms. The results indicate that erosion rate increased with increase in particle velocity, size and temperature. Also, at shallow impact angles the CMC shown to exhibit ductile like mode of erosion as opposed to brittle fracture mode at normal impact angles was observed. The erosion rate decreased with increase in erodent concentration which may be related to a particle shielding effect.

Influence of thickness of hydrophobic polytetrafluoroethylene (PTFE) coatings on cavitation erosion of hydro-machinery steel SS410

Hydrophobic materials have the potential to replace the existing surface modification materials to combat the problem of cavitation erosion (CE), owing to their various capabilities like self-cleaning, anti-corrosion, anti-fogging, anti-icing, anti-fouling, and drag-reduction. Polytetrafluoroethylene (PTFE) as a hydrophobic material exhibits specific combination of properties such as low friction coefficient, chemically neutral, good impact strength and considerable thermal firmness, that allow PTFE to be used in a wide range of applications. Therefore, in this work, an effort has been made to explore the effect of thickness of hydrophobic PTFE coatings on CE of the hydro-machinery SS410 steel. Hydrophobic PTFE coatings with three variable thicknesses have been prepared on the hydro-machinery SS410 steel using sintering process. Using high-velocity submerged water jet cavitation erosion test rig, CE behaviour of PTFE coated and bare SS410 steel was evaluated under various combinations of operating parameters: namely jet velocity, stand-off distance (SOD), and impact angle. Contact angle was reported to be increased with the decrease in the thickness of PTFE layer, which may be due to the increased surface roughness of PTFE layer with decrease in thickness. CE resistance of PTFE coated material with a maximum thickness of 121 μm, was found to be highest for all the combinations of operating parameters, which may be attributed to its lowest fracture toughness and better cushioning effect. Further, it was observed that CE of the coated and SS410 steel was found to be maximum at the chosen maximum velocity, normal impact angle, and intermediate SOD. The signatures of pits with circular and elongated morphology were observed for normal and shallow impact angles, respectively. In case of lowest PTFE layer thickness, overlapped pits with relatively higher depth were observed, which might be responsible for higher CE of the same amongst all the PTFE coatings.

Erosion under turbulent slurry flow: An experimental determination of particle impact angle, impact direction, and distribution thereof by image processing

In turbulent flows, the extent of erosive wear is given by particle impacts caused deviated from nominal flow by turbulent fluctuations. This paper describes an experimental determination of particle impact angle and impact direction distributions from collective wear scar features by image analysis. A slurry pot is used to produce wear damage on copper in exposure to a dilute slurry of glass beads. Degradation is evaluated by weight loss, and topography data for the image analysis is acquired by non-contact 3D profilometry. The results reveal that most of the kinetic energy is transferred by the tangential component of the impact velocity at shallow impact angles, regardless the particle size. Particle impact conditions do not distribute Gaussian and a statistical cut-off angle is established.

Failure analysis on unexpected perforation of heat exchanger tube in methacrylic acid reboiler of specialty chemical plant

Heat exchanger tubes are regarded as a vulnerable component of reboilers due to different working conditions between tube side medium and shell side medium. In this paper, an unexpected perforation failure of heat exchanger tube that occurred in methacrylic acid reboiler of a German world's leading specialty chemical plant was investigated in depth. Macro observation showed that the perforation presented concave appearance both on the inner and outer walls of the failed tube. This was fairly different from the appearance of perforations reported in the past literatures. Comprehensive analysis finally reveled that this unique failure was caused by unreasonable flushing operation of steel water gun with the initial water pressure of 2300 kgf/cm2. It produced several irregular shallow indentations on the inner wall of a tube at first. Erosion then happened with a shallow impact angle in the indentations where pits were gradually formed. After a period of operation, the selective local erosion was accelerated by the occurrence of vortex erosion on the pits, resulting in perforation failure. Countermeasures were thus put forward to avoid the recurrence of similar failure. Considering that this kind of perforation failure in heat exchanger tubes caused by improper flushing operation is seldom reported in the world, the achievement given by this paper would be very conducive to enhance the safety maintenance management of similar equipment.

Dynamics and wall collision of inertial particles in a solid–liquid turbulent channel flow

The dynamics and wall collision of inertial particles were investigated in non-isotropic turbulence of a horizontal liquid channel flow. The inertial particles were $125~\unicode[STIX]{x03BC}\text{m}$ glass beads at a volumetric concentration of 0.03 %. The bead-laden flow and the unladen base case had the same volumetric flow rates, with a shear Reynolds number, $Re_{\unicode[STIX]{x1D70F}}$, of the unladen flow equal to 410 based on the half-channel height and friction velocity. Lagrangian measurements of three-dimensional trajectories of both fluid tracers and glass beads were obtained using time-resolved particle tracking velocimetry based on the shake-the-box algorithm of Schanz et al. (Exp. Fluids, vol. 57, no. 5, 2016, pp. 1–27). The analysis showed that on average the near-wall glass beads decelerate in the streamwise direction, while farther away from the wall, the streamwise acceleration of the glass beads became positive. The ejection motions provided a local maximum streamwise acceleration above the buffer layer by transporting glass beads to high velocity layers and exposing them to a high drag force in the streamwise direction. Conversely, the sweep motion made the maximum contribution to the average streamwise deceleration of glass beads in the near-wall region. The wall-normal acceleration of the beads was positive in the vicinity of the wall, and it became negative farther from the wall. The investigation showed that the glass beads with sweeping motion had the maximum momentum, streamwise deceleration, and wall-normal acceleration among all the beads close to the wall and these values increased with increasing their trajectory angle. The investigation of the beads that collided with the wall showed that those with shallow impact angles (less than $1.5^{\circ }$) typically slide along the wall. The sliding beads had a small streamwise momentum exchange of ${\sim}5\,\%$ during these events. The duration of their sliding motion could be as much as five times the inner time scale of the unladen flow. The wall-normal velocity of these beads after sliding was greater than their wall-normal velocity before sliding, and was associated with the rotation induced lift force. Beads with impact angles greater than $1.5^{\circ }$ had shorter interaction times with the wall and smaller streamwise and wall-normal restitution ratios.

Solid particle erosion of refractories: A critical discussion of two test standards

Solid particle erosion is a key topic in many industrial applications. Within this work two standardised solid particle erosion test rigs usable for refractories with different working principles will be compared, namely i) the American ASTM C704 standard “Standard Test Method for Abrasion Resistance of Refractory Materials at Room Temperature”, which in fact is a gas blast solid particle erosion test, and ii) the Russian GOST 23.201 “Gas Abrasive Wear Testing of Materials and Coatings with Centrifugal Accelerator” with a centrifugal acceleration disc for the particles. In order to compare the test systems, various ceramic wear protection materials were chosen, featuring heterogeneous microstructures and coarse grain sizes. The particle speed in the ASTM C704 was measured with a high speed camera to be 65 m/s. This speed then was used at both test rigs and samples were impinged at 45° and 90° impact angle with SiC erosive.A comparison of the tests showed similar results at shallow impact angle for materials featuring a slight difference in wear resistance between phases (constituents). For materials containing sufficiently harder phases, the GOST produced lower wear rates.

Erosion of Mild Steel for Engineering Design and Applications

The erosion characteristics of mild steel have been evaluated for a variety of test parameters using dry compressed air jet test rig under room temperature. Random-shaped silica sand (SiO2) is selected to account as erodent size within the range of 300–600 μm. The impact velocity within 30–50 m/s, impact angle of 15° to 90°, and standoff distance of 15–25 mm were set as the operating test conditions to be maintained in the present study. The extreme level of erosion was obtained at 15° impingement angle, which demonstrates the ductile nature of the examined mild steel. Increasing the impact angle also increases kinetic energy; as a result, erosive wear was increased and standoff distance was reduced. Erosive wear was increased because the flax concentration was increased in all test conditions. SEM and 3D SEM were also utilized to analyze the surface damage propagation and determine the causes of the erosive wear behavior. SEM micrographs of the eroded surfaces show that, at shallow impact angles, the material is mainly removed by the platelet mechanism and material is displaced in the direction of flow in all tested materials. The elemental compositions of the eroded test material at different percentages of mild steel were analyzed by EDX.

Effect of Impacting Particle Kinetic Energy on Slurry Erosion Wear

In the present investigation, the effect of kinetic energy of different materials of the same-sized solid particles is examined on copper as target material using slurry pot tester. Quartz, Silicon carbide and Alumina are the impacting solid particles used for conducting trials. It is understood that the kinetic energy and stress concentration of impacting particles on target surface are responsible for material removal from the target surface, also the effect of erodent property like its shape and density is more dominant at shallow impact angles compared to higher impact angles. However, it is reported in literature that the exponent of velocity varies from 1.87 to 4.00 for ductile materials. Thus, different materials with the same-sized solid particles at constant kinetic energy were used to conduct the experiments. It is observed that for three different materials mass loss for the same mean particle size is nearly constant at 90° orientation angle but variation is found in 30° orientation angle. Further, the SEM micrographs of these solid particles show that alumina have sharp edges and angular nature. Silicon carbide is sub-angular in nature while quartz is blocky in nature. SEM micrographs of eroded surfaces show that at shallow impact angles the material is mainly removed by the platelet mechanism and material is displaced in the direction of flow. Also it is observed that increasing the velocity for quartz particle increases the crater length as compared to other two materials. Erosion wear was found more when alumina are used as the impacting particle due to their angular nature. At normal impact, indentation craters with rim are observed with significance increase in crater size when quartz is used as impacting particles.

An Experimental Study of the Abrasive Water Jet Micro-Machining Process for Quartz Crystals

An experimental study of the machining process for micro-channels on a brittle quartz crystal material by an abrasive slurry jet (ASJ) is presented. A statistical experiment design considering the major process variables is conducted, and the machined surface morphology and channelling performance are analysed to understand the micro-machining process. It is found that a good channel top edge appearance and bottom surface quality without wavy patterns can be achieved by employing relatively small particles at shallow jet impact angles. The major channel performance measures, i.e. material removal rate (MRR) and channel depth, are then discussed with respect to the process parameters. It shows that with a proper control of the process variables, the abrasive water jet (AWJ) technology can be used for the micro-machining of brittle materials with high quality and productivity.

Erosion wear behavior of laser clad surfaces of low carbon austenitic steel

Austenitic steel surfaces are laser cladded using a 4 kW continuous wave CO 2 laser with coaxial powder feeding nozzle to investigate the improvement in slurry erosion characteristics. Colmonoy-6 and Inconel-625 are cladded on AISI 316L steel and AISI 304L steel, respectively by laser cladding. Initially, single-pass clad track is overlaid to optimize the laser processing parameters, namely scanning speed and powder feed rate to obtained a sound clad. Minimum cracks, porosity and distortion were found at scanning speed of 0.1 m/min and powder feed rate of 12 g/min. For these parameters, the dilution was 17.33% for Colmonoy-6 and 40% for Inconel-625. To clad large surface area, the optimized laser processing parameters were used to deposit the clad tracks with 60% overlap. Maximum surface hardness of 746 VHN is obtained in case of Colmonoy-6 clad on AISI 316L steel and is 352 VHN in case of Inconel-625 clad on AISI 304L steel. EDAX analysis shows higher degree of mixing of substrate material in the clad pool of Inconel-625 than Colmonoy-6. The results of slurry erosion test of Colmonoy-6 clad surface have shown improvement in erosion resistance of the order of 1.75–4.5 times of the substrate AISI 316L steel at all impact angles and the maximum wear angle has also increased which can be attributed to the increase in the surface hardness. However, Inconel-625 laser clad surface has shown little improvement in erosion resistance of the substrate AISI 304L steel at shallow impact angles with no significant improvement at normal impact condition. The SEM micrographs of worn out Colmonoy-6 clad surfaces at shallow impact angles show that the material is removed mainly by micro-cutting which increases with increase in the impact angle.

Glancing-Blow Impact Forces by a Barge Train on a Lock Approach Wall

In 1993 Headquarters, U.S. Army Corps of Engineers, issued the first formal Corps-wide analysis procedure providing guidance for analyzing the effects of barge impact loading on navigation structures. The guidance was rescinded in 2001 due to concerns about the conservatism of the computed results for usual and unusual loadings and accuracy with shallow approach impact angles and direct head-on impact. This paper addresses the interpretation of full-scale, low-velocity, controlled barge train (15-barge) impact experiments conducted at the decommissioned Gallipolis Lock at Robert C. Byrd Lock and Dam, Gallipolis Ferry, W.V. Two sets of methodologies were used to interpret the barge-to-wall impact data: (1) the use of the equations of equilibrium combined with an assumed value for the coefficient of friction between the barge train and the stiff-to-rigid wall, and (2) the energy method. A simplified empirical correlation is presented to calculate the maximum impact force as a function of the linear momentum normal to the wall using forces measured during these full-scale impact experiments. This empirical correlation is the basis for new Corps guidance for calculating glancing-blow impact forces.

The erosion-corrosion resistance of uncoated and aluminized 12% chromium ferritic steels under fluidized-bed conditions at elevated temperature

In this paper, some results from a study of the erosion-corrosion resistance of uncoated and aluminized 12% chromium steel in a fluidized-bed rig are reported. The aims of the research are to establish and compare the erosion-corrosion resistance of these materials for possible applications as heat exchangers in future power plants, and to obtain an increased understanding on their behaviour and mutual superiority in a range of conditions. Damage to the uncoated 12% chromium steel occurs by an oxidation-affected erosion process under all the studied conditions, with spallation of scale being the primary mechanism of material wastage. At a temperature of 550 °C, the uncoated steel follows the typical angle-dependence of a brittle material, while, at temperatures above 550 °C, it follows an angle-dependence that is more typical of a ductile material. This change in the angle-dependence with temperature is related to characteristics, i.e. uniformity, adhesion and density, of the formed oxide scales. The rate of material wastage increases with increase in speed and temperature, due to the development of thicker, more uniform and more dense oxide scales, that promote more severe scale spallation. The erosion-corrosion behaviour of the aluminized 12% chromium steel changes in the temperature range from 600°C to 650 °C. This is due to a shift from a brittle-like to a ductile-like angle-dependence and to a more rapid oxide scale build-up at temperatures above 600 °C. At an impact angle of 30° and at 550 °C and 600 °C, the prevailing erosion-corrosion process for the aluminized steel is oxidation-affected erosion. At 650 °C and 700 °C for an impact angle of 90°, the primary erosion-corrosion mode is essentially erosion-enhanced oxidation. The results of the study have also demonstrated that the Al 5 Fe 2 coating deposited by pack aluminization offers enhanced protection against erosion-corrosion at shallow impact angles at 550 °C and 600 °C and at steeper impact angles at 700 °C.

Damage behaviour of metallic materials caused by subsonic to hypervelocity particle impact

The aim of this paper is to investigate fundamental damage behaviour of metallic materials such as aluminium, mild steel and titanium, which typically have different crystal structures, by the single impact from low velocity to hypervelocity. An ordinary gas gun unit was used up to an velocity of 200 ms −1 and a two-stage light gas gun unit was used from 300 to 5500 ms −1 in this study. Impact tests by a WC ball were performed on the three metallic materials at various impact velocities and at normal angle. Indentation shapes on a cross-sectional surface and the ratios of crater diameter and depth to the diameter of the WC ball were examined. Three modes were recognized in indentation configurations independent of the type of materials. Average contact pressure, which was obtained by the impact energy divided by indentation volume, showed not only a mechanical property of the target material during the impact process but also fracture strength of the projectile. A single particle impact test at a shallow impact angle and at a hypervelocity showed large material removal in spite of its single impact and intimated the difference in mechanisms of the material removal between subsonic and hypervelocity impacts.

High-speed hydrodynamic wear of steel-fibre reinforced hydraulic concrete

The paper reports about an investigation of the erosion resistance of two types of hydraulic concrete, namely a plain hydraulic concrete (PC) and a steel-fibre reinforced hydraulic concrete (FRC). The flow erosion was simulated by high-speed water jets with velocities up to 234 m/s and impact angles of 15° and 90°, respectively. A general relationship could be found between relative erosion rate (g/g) and process parameters: E R∝ v F n f( θ), with n between 1.1 and 1.25. However, it was shown that the type of pump used for the experiments was critical to these results. The reason was that water flow velocity and water mass flow rate could not be varied independently. If the absolute erosion rate (g/s)—characterised by a constant water mass flow rate—was considered, a modified relationship E ̇ R ∝v F n+qf(θ) was derived, where q considered water volume effects. Values for q were about unity. In general, erosion rate decreased if the concrete was reinforced. However, the influence of the fibre reinforcement was more pronounced for the lower impact angle. This is explained by the formation of a ‘shadow zone’ behind the fibres in case of shallow impact angle.

Hydro-abrasive erosion of steel-fibre reinforced hydraulic concrete

In this paper, hydro-abrasive erosion tests on plain concrete (PC) and on steel-fibre reinforced concrete (FRC) are performed, and the erosion behaviour of the materials for different erosion conditions is investigated. Effects of suspension velocity, impact angle and solid content have been studied in detail. Two major erosion modes are identified. When the impact angle is shallow (15°), the damage is caused mainly by cutting the cement matrix and exposing the aggregates. However, at orthogonal impact, the formation and development of fatigue cracks in the concrete is the main cause of erosion. The addition of steel fibres provides a reinforcement to improve the erosion resistance of hydraulic concrete at shallow impact angles (15°) only. For low suspension velocities (ca. 60 m/s), fibre reinforcement and solid abrasive content do not influence the erosion rate favourably. For higher suspension velocities, abrasive content becomes important.

837 球形粒子の超音速衝突による金属材料の変形挙動 : 固体粒子衝突エロージョンの超音速領域への展開

Hypervelocity impact tests were conducted with a 2-stage light gas gun test rig. Impact velocities were up to 5500 ms^<-1> in order to investigate the deformation behavior of target materials caused by hypervelocity impact of a spherical projectile. The deformation behavior was compared with that at relatively low impact velocities. The deformation behavior showed a mechanical property of target material under low impact velocities but showed fracture strength of a projectile of WC at a hypervelocity. Huge material removal by the hypervelocity impact of a projectile was observed at an shallow impact angle for the aluminum specimen.