Primary Mechanism Of Material Removal Research Articles

Research on the Erosion Law and Protective Measures of L360N Steel for Surface Pipelines Used in Shale Gas Extraction.

The erosion of surface pipelines induced by proppant flowback during shale gas production is significant. The surface pipelines in a shale gas field in the Sichuan Basin experienced perforation failures after only five months of service. To investigate the erosion features of L360N, coatings, and ceramics and optimize the selection of two protective materials, a gas-solid two-phase flow jet erosion experimental device was used to explore the erosion resistance of L360N, coatings, and ceramics under different impact velocities (15 m/s, 20 m/s, and 30 m/s). An energy dispersive spectroscope, a scanning electron microscope, and a laser confocal microscope were employed to analyze erosion morphologies. With the increase in flow velocity, the erosion depth and erosion rate of L360N, coating, and ceramic increased and peaked under an impact velocity of 30 m/s. The maximum erosion rate and maximum erosion depth of L360N were, respectively, 0.0350 mg/g and 37.5365 µm. Its primary material removal mechanism was the plowing of solid particles, and microcracks were distributed on the material surface under high flow velocities. The maximum erosion rate and maximum erosion depth of the coating were, respectively, 0.0217 mg/g and 18.9964 µm. The detachment of matrix caused by plowing is the main material removal mechanism. The maximum erosion rate and maximum erosion depth of ceramics were, respectively, 0.0108 mg/g and 12.4856 µm. The erosion mechanisms were micro-cutting and plowing. Under different particle impact velocities, different erosion morphologies were observed, but the primary erosion mechanism was the same. The erosion resistance of the ceramics was higher than that of the coatings. Therefore, ceramic lining materials could be used to protect the easily eroded parts, such as pipeline bends and tees, and reduce the failure rate by more than 93%. The study provided the data and theoretical basis for the theoretical study on oil and gas pipeline erosion and pipeline material selection.

Effect of various phase fractions of bainite, retained austenite, intercritical ferrite and pearlite on the wear behaviour of multiphase steels

In this study, the dry sliding wear behaviour of multiphase steels (MPS) was investigated with the help of a pin/ball-on-disc wear setup. The newly developed high strength and highly ductile MPS specimens consisting of various fractions of bainite, retained austenite, intercritical ferrite and pearlite, were obtained by a combination of continuous cooling for different times (0 s, 10 s, 20 s and 40 s) after austenitization followed by isothermal heat treatment at various temperatures (300 °C, 350 °C and 400 °C) for 10 min from a moderately high C (∼0.67 wt%) - high Si (∼1.71 wt%) steel. The worn-out surfaces and wear debris revealed that the primary material removal mechanism was of abrasive types. Wear scars were seen like a ploughed field-like structure. The depth of wear scars and amount of material collected at the periphery were affected by various phases and their fractions in the MPS specimens. The wear behaviour of the multiphase steels was affected by the distribution of plastic deformation due to continuous sliding of wear ball and application of loads on the surface of MPS specimens which was analysed by hardness variation of the sub-surfaces beneath the wear scars. At a particular austempering temperature, the wear volume loss and specific wear rate of the MPS specimens increased with the increase of continuous cooling time irrespective of the applied wear loads, and it was attributed to the formation of softer intercritical ferrite as well as pearlite formed due to longer continuous cooling. However, the bainitic structure formed by austempering without continuous cooling led to the highest wear resistance irrespective of the isothermal temperatures.

Enhanced cavitation erosion resistance of a friction stir processed high entropy alloy

Friction stir processing of an Al0.1CoCrFeNi high entropy alloy (HEA) was performed at controlled cooling conditions (ambient and liquid submerged). Microstructural and mechanical characterization of the processed and as-cast HEAs was evaluated using electron backscat-ter diffraction, micro-hardness testing and nanoindentation. HEA under the submerged cooling condition showed elongated grains (10 µm) with fine equiaxed grains (2 µm) along the boundary compared to the coarser grain (∼2 mm) of as-cast HEA. The hardness showed remarkable improvements with four (submerged cooling condition) and three (ambient cooling condition) times that of as-cast HEA (HV ∼150). The enhanced hardness is attributed to the significant grain refinement in the processed HEAs. Cavitation erosion behavior was observed for samples using an ultrasonication method. All of the HEAs showed better cavitation erosion resistance than the stainless steel 316L. The sample processed under a submerged liquid condition showed approximately 20 and 2 times greater erosion resistance than stainless steel 316L and as-cast HEA, respectively. The enhanced erosion resistances of the processed HEAs correlate to their increased hardness, resistance to plasticity, and better yield strength than the as-cast HEA. The surface of the tested samples showed nucleation and pit growth, and plastic deformation of the material followed by fatigue-controlled disintegration as the primary material removal mechanism.

Research on removal function of fluid hydrodynamic fixed abrasive grinding

Fluid hydrodynamic fixed abrasive grinding (FHFAG) is now evolving into a promising finishing method underpinning the major advances across grinding and lapping sciences. While the advances have been startling, the key unmet challenge to date is the theoretical basis of removal function. Here, we approach this challenge by presenting a fully coupled flow deformation model. Given the separation function on microchannel from the grits fixed on the grinding pad, hydrodynamic pressure distribution with many dynamic pressure peaks and basic film thickness can be described theoretically. Combining with primary material removal mechanism the removal function of FHFAG was achieved. The experimental results showed a strong agreement with the prediction removal function model and its practicability has also been verified.

A molecular dynamics investigation into nanoscale scratching mechanism of polycrystalline silicon carbide

In this study, 3D molecular dynamics simulations were conducted to investigate the nanoscale scratching mechanism of polycrystalline SiC constructed by Voronoi site-rotation and cut method. The scratching process, SiC crystal structure evaluation, scratching force, stress, and temperature, surface morphology, and subsurface damage (SSD) were discussed after simulation. The results indicate that the ductile scratching process of polycrystalline SiC could be achieved in the nanoscale depth of cut through the amorphous crystal structure phase transition, which is the primary material removal mechanism in nanoscale SiC scratching. The silicon atom can penetrate into the diamond grit which may cause the wear of diamond tool. The disorder grain boundary (GB) atoms can transit to hexagonal diamond structure and generate dislocation during the scratching. Furthermore, the higher scratching speed results in smaller scratching force, smaller normal stress, and higher temperature due to the larger impaction breaking more SiC bonds, which makes the SiC material more ductile and easier to remove. The tangential stress shows great dependence on the grain and GB geometry and position due to the stress concentration in the GB. It is also found that the higher scratching speed encourages the pileup atoms in the front of grit to flowing to the grit side to form the groove protrusion, which can get a shallower SSD thickness and a wider SSD layer. SSD results also indicate that at least three types of the material removal mechanism – amorphous transition, intergranular fracture, and transgranular fracture – exists in the polycrystalline SiC scratching process.

Melt dynamics and melt-through time in continuous wave laser heating of metal films: Contributions of the recoil vapor pressure and Marangoni effects

The relative contributions of evaporation and melt expulsion due to the recoil vapor pressure and Marangoni effects to the laser damage and melt dynamics in continuous wave (CW) laser interactions with free-standing aluminum films are evaluated in two-phase hydrodynamic simulations. In order the establish the dominant damage mechanisms in different irradiation regimes, the results of hydrodynamic simulations are compared with the predictions of several simplified models that only account for a subset of the involved processes. The hydrodynamic simulations performed in the range of film thickness from 0.2mm to 4mm and laser spot radius from 0.1mm to 1cm reveal only a marginal effect of the Marangoni stresses on the overall picture of melt flow and the melt-through time. The recoil pressure effect, on the contrary, is capable of strongly decreasing the melt-through time in a certain range of laser intensity. At laser intensities below this range the melting process is largely defined by heat transfer in the radial direction, while at laser intensities above this range the thickness of the molten pool and the efficiency of melt expulsion decrease and evaporation becomes the primary mechanism of material removal from the center of the laser spot. The range of laser intensities where the melt-through time is controlled by the recoil pressure effect is not unique and depends on the film thickness. A simple two-phase one-dimensional thermal model of laser melting, where melt expulsion due to the recoil pressure effect is accounted for based on the Bernoulli integral, is developed and found to be capable of accurate prediction of the melt-through time above a certain level of laser intensity. The one-dimensional thermal model captures all qualitative trends revealed in the direct hydrodynamic simulations and can be used as a robust engineering tool for the first-order estimation of the conditions for CW laser damage of metal films.

Investigation of subsurface damage considering the abrasive particle rotation in brittle material grinding

Brittle materials are prone to brittle fracture which is a primary mechanism of material removal in grinding process. Subsurface damage (SSD) strongly affects the quality of grinding surface which is necessary to be evaluated in brittle material grinding. In this paper, the theoretical analysis of SSD is presented in detail considering the effect of abrasive particle rotation along with the wheel. With the increasing rotation angle of abrasive particle, both the median and lateral cracks incline gradually. Moreover, SSD could disappear below the final grinding surface when the rotation angle of abrasive particle reaches a certain critical value. In addition, the grinding depth, the wheel diameter, and the ratio of wheel speed to workpiece speed influence the rotation angle of an abrasive particle; the effects of these parameters on SSD depth are also studied in detail by theoretical analysis and numerical simulation. The larger wheel diameter and the larger ratio of wheel speed to workpiece speed can obtain a smaller SSD depth, but the effect of grinding depth is unapparent due to the kinematic characteristics of the grinding process. The results are meaningful and helpful in predicting SSD depth and selecting the reasonable grinding parameters to obtain a good surface quality in brittle material grinding.

Investigation on feed direction cutting force in ultrasonic vibration-assisted grinding of dental ceramics

The feasibility of ultrasonic vibration-assisted grinding in dental restoration has been preliminarily proved. Improving the machining quality of zirconia ceramics by controlling cutting force is the focus of the researchers. However, the existing feed direction cutting force model for ultrasonic vibration-assisted grinding does not take the ultrasonic vibration amplitude and frequency into account. This paper presents a mathematical model for feed direction cutting force in ultrasonic vibration-assisted grinding of zirconia under the consideration of amplitude and frequency, and assuming that brittle fracture is the primary mechanism of material removal in ultrasonic vibration-assisted grinding of zirconia. The effects of amplitude and frequency on the motion, effective cutting distance, and theoretical removal of an abrasive particle have been analyzed. Besides, the number of active abrasive particles is calculated with analyzing the influences of lateral cracks and ultrasonic vibration. The variation laws of cutting force and penetration depth of an abrasive particle during ultrasonic vibration-assisted grinding have also been analyzed. Therefore, the relationship between feed direction cutting force and input variables is predicted through the developed model. Finally, pilot experiments are conducted for the mathematical model verification. Experimental results show that the trends of input variables for feed direction cutting force agree well with the trends of the developed cutting force model. Hence, the mathematical model can be applied to evaluate the feed direction cutting force in ultrasonic vibration-assisted grinding of zirconia ceramics.

Study of alternating current flow in micro-EDM through real-time pulse counting

Following the general guidance on the influence of the machining polarity in micro-EDM, usually a straight polarity is applied (with the tool electrode being connected to the negative pole of the generator output), since the bombarding of the “light” electrons on the workpiece is assumed to be the primary material removal mechanism. Therefore, a flipping of the polarity in the micro-EDM machining process shall result in a high volumetric relative wear, which has been experimentally verified. The initial objective of this research is to reduce the tool wear by inserting a diode in the discharge circuit to block the reverse current flow. However, in the experiments an even higher volumetric relative wear has been observed with the inclusion of a diode. To investigate in depth the influence of the alternating current flow on the tool-material interaction, a pulse counting method based on the detection of the current peak has been proposed to count the number of effective pulses. This counting of the effective sparks enables the subsequent analysis of the mean material removal per discharge and tool wear per discharge. The analysis of the measurements obtained in both sparking cases, with a diode and without a diode, indicates that the reverse current is contributing positively to the material removal on the workpiece and the volumetric relative wear. Therefore, it is not economically proper to block the reverse the current flow in micro-EDM milling. At lower open voltage, the simple empirical linear model without reverse current flow can still serve as a reference for the in-situ tool wear prediction and the subsequent tool wear compensation. However, a correction to the model has to be made at a setting of higher open voltage.

Theoretical model for cutting force in rotary ultrasonic milling of dental zirconia ceramics

Rotary ultrasonic machining or ultrasonic vibration assisted grinding has superior performance in machining hard and brittle materials, such as dental zirconia ceramics. However, there are few reports about cutting force modeling of rotary ultrasonic milling (RUM) for dental ceramics, especially for cutting force model in feed direction. In this study, the theoretical model of cutting force both in axial direction and feed direction is proposed under the assumption that brittle fracture is the primary mechanism of material removal in RUM of dental ceramics. The effective cutting time and material removal volume have been analyzed to develop the cutting force model. Besides, the number of active abrasive particles has been calculated for the first time during the modeling. The effect of overlapping and intersection of fracture zone in peripheral direction on material removal volume has also been considered via the parameters K 1 and K 2. In addition, the relationships between the cutting force and input variables are revealed through the theoretical model. Finally, pilot experiments of RUM on dental zirconia ceramics are conducted to verify the theoretical model. The experimental results are consistent well with the model predictions. Therefore, the theoretical model can be applied to evaluate the cutting force in RUM of dental ceramics.

Study on the system matching of ultrasonic vibration assisted grinding for hard and brittle materials processing

Ultrasonic vibration assisted grinding (UAG) is an effective processing method for hard and brittle materials. Compared with common grinding (CG), both of grinding force and workpiece surface quality is improved by UAG, but the principle of improvement is still unclear. In order to reveal the mechanism of grinding force reduction and grinding quality improvement in UAG, this paper presents a mathematical model for system matching in UAG of brittle materials. Assuming that brittle fracture is the primary mechanism of material removal in UAG of brittle materials, the system matching model is developed step by step. On the basis of this mathematical model, the mechanism of grinding force reduction and surface roughness forming are discussed. The advantage of UAG processing brittle materials is pointed out in theory. Using the model developed, influences of input variables on grinding force are predicted. These predicted influences are compared with those determined experimentally. This model can serve as a useful foundation for development of grinding force models in UAG of brittle materials and models to predict surface roughness in UAG.

On ultrahigh velocity micro-particle impact on steels – A multiple impact study

A computational model is presented to investigate the ultrahigh-velocity multiple particle impact process on steels. It uses a Monte Carlo framework to model the stochastic nature of the particle flow and the finite element (FE) method to model the individual particle impact process, while considering the thermal diffusion process. The model predictions show a reasonably good agreement with the corresponding experimental data using a high-tensile steel specimen at various conditions. A simulation study using the model is then conducted and shows that it is essential to consider thermal diffusion which causes the temperature at the impact site to rapidly cool down in a multiple particle impact process. As a consequence, the impact result is impact-sequence and impact-time dependent. The study reveals that inertia-induced fracture is the primary material removal mechanism at the normal impacts, while the thermal instability-driven failure, or specifically the adiabatic shear banding (ASB) induced failure, as well as the elongation-induced fractures are the two major material removal mechanisms at oblique impact angles. These failures occur at the pile-up lips (at normal and oblique impact angles) and the crater bottom (at oblique impact angles). It is the thermal-instability-driven failure that contributes to the higher material removal rate at oblique impact angles.

Experimental investigation and characterization of nano-scale dry electro-machining

This paper presents an experimental investigation and characterization of a novel technique of nanoscale electro-machining (EM) in atmospheric air, named dry nano-EM, by using scanning tunneling microscopy (STM) as the platform for nanomachining. The electro-machining has been conducted in near field by maintaining a gap distance of 1–2nm between the Platinum–Iridium [Pt–Ir (80:20)] tool electrode and atomically flat gold substrate with the air as dielectric medium. An in situ process of evaluating the tool quality before and after machining has been used by monitoring the current–displacement (I–Z) spectroscopy curves. The mechanism of dry nano-EM has been presented as well as the machining performance of the process has been evaluated. Based on the observations, it has been established that field induced evaporation due to intense heat generated at the gap width is the primary mechanism of material removal in dry nano-EM. The experimental results show that dry nano-EM is capable of fabricating consistent nano-features with good repeatability. The volume of material removal increases almost linearly with increasing number of features machined and machining time, indicating the consistency in the dimensions of the nano-features. Finally, dry nano-EM is established as a technique capable of machining 50–100 features in a pre-defined manner with average feature size of 7.5–10nm in a single pass, thus suitable for nano-patterning in atomically flat electrically conducting surfaces.

Microstructure and sliding wear resistance of an Al–12 wt.% Si/TiC laser clad coating

Metal matrix composite coatings consisting of an Al–12wt.% Si-alloy matrix reinforced with TiC were prepared by laser cladding from mixtures of Al–12wt.% Si alloy and TiC powders. For the processing parameters used (power density 200MW/m2 and interaction time 0.3s), a small proportion of TiC dissolves in the melt, resulting in a microstructure composed of 34vol.% of TiC and 3vol.% of Ti3SiC2 particles dispersed in a matrix consisting of proeutectic α-Al dendrites and α-Al+Si eutectic. The coating material presents a hardness of 165HV and a wear coefficient of 2.24×10−5mm3/(Nm) in ball-on-plate dry sliding wear tests, using quenched and tempered AISI 440C martensitic stainless steel as the counterbody material. Analysis of the worn surfaces showed that the sliding motion of the contacting bodies leads to the formation of a tribolayer consisting of Fe oxides, as well as metallic phases. On the basis of theoretical calculations it is suggested that the primary material removal mechanism involves the propagation of cracks through the thickness of this tribolayer, followed by crack channeling and debonding of tribolayer fragments.

A cutting force model for rotary ultrasonic machining of brittle materials

Knowing cutting force in rotary ultrasonic machining (RUM) can help optimizing input variables. RUM of brittle materials has been investigated both experimentally and theoretically. However, there are no reports on cutting force models for RUM of brittle materials. This paper presents a mechanistic model for cutting force in RUM of brittle materials. Assuming that brittle fracture is the primary mechanism of material removal in RUM of brittle materials, the cutting force model is developed step by step. On the basis of this mechanistic model, relationships between cutting force and input variables (such as spindle speed, feed rate, ultrasonic vibration amplitude, abrasive size, and abrasive concentration) are predicted. Experiments are conducted for model verification and experimental results agree well with model predictions.

Wear of bulk ceramics in micro-scale abrasion—The role of abrasive shape and hardness and its relevance to testing of ceramic coatings

There is a wide body of literature wherein the micro-scale abrasion test has been employed to assess the behaviour of a range of vapour-deposited ceramic coatings. However, the fundamentals of the micro-scale abrasion process with ceramic materials in general (both in monolithic form and as coatings) are not well understood. In this work, the micro-scale abrasive wear behaviour of a range of brittle materials was examined as a function of abrasive particle type and applied load. The three types of abrasive particle slurries were alumina, silicon carbide and diamond, of similar size distributions and all suspended in water. It was shown that the relative wear rates of the materials depended strongly upon the abrasive type selected. When the abrasives were harder than the testpiece in question, the behaviour was dominated by the angularity and the particle size distribution of the abrasive. High angularity and wide size distributions, observed with alumina and silicon carbide abrasives, resulted in the applied load being carried by a small number of abrasive particles which resulted in lateral fracture and high rates of wear, whereas blocky abrasives (such as diamond) resulted in the load being carried by a larger number of particles and thus lateral fracture being restricted with correspondingly low rates of wear. However, when the abrasives were either softer or not significantly harder than the testpieces, the relative hardnesses dominated the operative wear mechanisms. In previous work, it has been shown that ball roughness in the micro-scale abrasion test promotes abrasive entrainment into the wear zone throughout the test. In this work, it has been shown that high testpiece roughness as developed in the wear scar (due to lateral fracture being the primary mechanism of material removal) hinders further abrasive particle entrainment, and that testpieces which wear with a smooth surface morphology (by plastic flow rather than by brittle fracture) exhibit enhanced particle entrainment under conditions (such as high applied load) where other materials are demonstrating limited entrainment.

Time scale effects in laser material removal: a review

In laser material removal using a continuous wave or long-pulsed laser, the primary material removal mechanism melts with molten metal often ejected by an assisting oxygen jet. Interactions between heat transfer, oxygen diffusion, and gas dy- namics have been studied. In laser machining using a Q-switched solid state laser with pulse width on the order of nanoseconds, the primary material removal mechanism is ablation, but substantial melting is still present if a metallic material is concerned. Two mechanisms, ablation and melting, are modeled together and the property discontinuity and boundary conditions at the liquid/vapor interface are provided. When the laser pulse width further reduces to the order of picoseconds or femtoseconds, as in a Ti:sapphire laser, the dominant material removal mechanism changes yet again, with little thermal damage and wavelength independence observed. Thermal aspects are examined in the context of the short timescales of these pulses compared with the timescale of photon-electron-lattice interactions. Research needs in laser ma- terial removal in each of the three time regimes are discussed.

A Mechanistic Approach to the Prediction of Material Removal Rates in Rotary Ultrasonic Machining

An approach to modeling the material removal rate (MRR) during rotary ultrasonic machining (RUM) of ceramics is proposed and applied to predicting the MRR for the case of magnesia stabilized zirconia. The model, a first attempt at predicting the MRR in RUM, is based on the assumption that brittle fracture is the primary mechanism of material removal. To justify this assumption, a model parameter (which models the ratio of the fractured volume to the indented volume of a single diamond particle) is shown to be invariant for most machining conditions. The model is mechanistic in the sense that this parameter can be observed experimentally from a few experiments for a particular material and then used in prediction of MRR over a wide range of process parameters. This is demonstrated for magnesia stabilized zirconia, where very good predictions are obtained using an estimate of this single parameter. On the basis of this model, relations between the material removal rate and the controllable machining parameters are deduced. These relationships agree well with the trends observed by experimental observations made by other investigators.

Sliding wear characteristics of non-equilibrium Cu-Pb alloys

The sliding wear behavior of copper-lead alloys was studied as a function of lead content (10, 20, 40 and 60 wt.%) using a pin-on-disk test system. The specific wear rate increased with lead content up to 40 wt.% after which a drop in wear rate was observed. No correlation existed between the hardness and sliding wear of these alloys. A study of wear mechanisms shows that oxidative wear is the primary material removal mechanism at low contact pressures, while plastic deformation and adhesion are the rate-controlling mechanisms at high contact pressures.

Effect of carbide size on the abrasion of cobalt-base powder metallurgy alloys

A study of the effect of carbide size on the abrasion resistance of two cobalt-base powder metallurgy alloys, alloys 6 and 19, was conducted using low stress abrasion with a relatively hard abrasive, A1 2O 3. Specimens of each alloy were produced with different carbide sizes but with a constant carbide volume fraction. The wear test results show a monotonie decrease in wear rate with increasing carbide size. Scanning electron microscopy of the worn surfaces and of wear debris particles shows that the primary material removal mechanism is micromachining. Small carbides provide little resistance to micromachining because of the fact that many of them are contained entirely in the volume of micromachining chips. The large carbides must be directly cut by the abrasive particles. Other less frequently observed material removal mechanisms included direct carbide pull-out and the formation of large pits in fine carbide specimens. These processes are considered secondary in the present work, but they may have greater importance in wear by relatively soft abrasives which do not cut chips from the carbide phase of these alloys. Some indication of this is provided by limited studies using a relatively soft abrasive, rounded quartz.