Predominant Mechanism Of Material Removal Research Articles

A new monitor model to detect damages in surface and subsurface during cup grinding process of BK7 optical glass: a new optimization model for energy damage

Grinding is known as the most widely used method of forming borosilicate optical glass (BK7). Due to the brittle nature of the BK7 glass, the predominant mechanism of material removal will be fracture. So, the surface under grinding will have surface (surface roughness) and subsurface damage. These damages will cause a decrease in mechanical resistance and performance. Modeling of surface and subsurface damages due to the grinding process using cup grinding tool has not been subjected in recent investigations. To do this, the surface roughness effects are investigated by changes in grinding parameters such as cutting speed, feed rate, cutting depth and table speed. Moreover, based on the experiments, the relationship between surface roughness and grinding parameters is simulated and the average error was 5.77%. In the second phase of the experiments, angular polishing method is used and subsurface morphologies are investigated by SEM and the depths of these damages are measured. Experimental results are compared with that of the Li theoretical model. Based on the results, the experimental and theoretical results have well consistency. In the end, based on the Li model, a new model based on the relationship between subsurface damage and grinding parameters is conducted.

Influence of laser surface nanotexturing on the friction behaviour of the silicon/sapphire system

The aim of the present work was to investigate the influence of textures consisting of Laser-Induced Periodic Surface Structures (LIPSS) on the friction coefficient of silicon under unlubricated conditions, using nanoscale friction tests. The tests were performed on 〈111〉 single crystal wafers of p-doped silicon. Surface texturing was performed by a direct writing technique, using 560 fs pulses of 1030 nm wavelength radiation and parameters allowing large areas with a uniform LIPSS texture to be obtained. The tribological tests were performed in air using a ball-on-flat nanotribometer with 3 mm diameter sapphire balls as counterbodies. The wear scars were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The friction coefficient of polished Si remains approximately constant during the tests and is independent of the applied load, with values in the range 0.12–0.14. The morphology of the wear scars indicated that the predominant material removal mechanism is mild oxidative wear, independently of the testing conditions used, which explains the low values of the friction coefficient measured. The LIPSS texture leads to an increase of the friction coefficient, in particular in the perpendicular sliding direction. The friction coefficient increases with the applied load and is larger for the perpendicular sliding direction than for the parallel sliding direction, the difference increasing with increasing load. The morphology of the wear scars showed that the predominant wear regime remains oxidative wear, but significant contributions of plastic deformation and ploughing appear. This plastic deformation in Si, which is brittle at room temperature, shows that significant surface heating is being caused by the interaction of the asperities in motion and under load. This temperature increase also accelerates surface oxidation and increases the wear rate. Surface temperature calculations showed that the temperature increase is larger for the perpendicular sliding direction than for the parallel one, which explains the difference of friction coefficient observed in the two directions.

Precision superabrasive grinding of plasma sprayed ceramic coatings

In this investigation, a set of plasma sprayed ceramic oxide coatings were surface ground using super abrasive wheel. The surface integrity and grindability aspects of the coated surface were studied. During the grinding process, low grinding forces and specific grinding energy were observed and these observations pointed toward micro brittle fracture to be the predominant material removal mechanism in all cases. SEM and FIB milling of the ground samples also revealed that material removal is primarily owing to micro-fracture rather than micro-cutting. This is also corroborated by short broken chip formation during grinding. Further, the nature of the chips did not vary with change in grinding parameters. The surface topography showed signatures of micro-fracture, plowing and rubbing only. The ground surface harbors residual stress. However, this stress, unlike metals, does not have a thermal origin. This is attributed to retention of material properties by the ceramic coatings at the grinding temperature.

Mechanisms of the formation of low spatial frequency LIPSS on Ni/ Ti reactive multilayers

The present paper aims at investigating the mechanisms of imprinting LIPSS (laser-induced periodic surface structures), arrangements of parallel ripples with a periodicity slightly smaller than the radiation wavelength, on metallic surfaces. To this end, Ni/Ti multi-layered samples produced by magnetron sputtering were textured with LIPSS using a 1030 nm, 560 fs pulse duration laser and pulse frequency of 1 kHz, and the resulting surfaces were investigated by scanning and transmission electron microscopies. The results obtained show that the core of the ripples remains in the solid state during the laser treatment, except for a layer of material about 30 nm thick at the valleys and 65–130 nm thick at the top of the crests, which melts and solidifies forming NiTi with an amorphous structure. A layer of ablation debris composed of amorphous NiTi nanoparticles was redeposited on the LIPSS crests. The results achieved indicate that the periodic variation of the absorbed radiation intensity leads to a variation of the predominant ablation mechanisms and, consequently, of the ablation rate, thus explaining the rippled surface topography. The comparison with theoretical predictions suggests that in the intensity maxima (corresponding to the valleys) the material is removed by liquid spallation, while at its minima (the crests) the predominant material removal mechanism is melting and vaporization. These results support Sipe et al LIPSS formation theory and are in contradiction with the theories that explain the formation of LIPSS by convective fluid flow or self-organized mass transport of a laser-induced instability.

An Experimental Approach to Determine the Critical Depth of Cut in Brittle-to-Ductile Phase Transition During End Milling of Soda-Lime Glass

Plastic deformation is a predominant material removal mechanism in machining of ductile materials, but it is a big challenge to achieve it in cases of brittle materials. Soda-lime glass is a very useful engineering material. Due to its favorable thermal, corrosion resistance and fine chemical properties, its common applications are in the manufacture of products like mirrors, lenses, semiconductor, and optical, bio-medical and microelectronics components. Nevertheless, owing to its brittleness due to its low fracture toughness, machining of soda-lime glass is practically impossible under normal cutting conditions. Though recent investigations have shown that machining of such brittle material is possible using ductile mode machining under controlled cutting parameters and tool geometry, it remains a challenging task. This paper focuses on identification of the critical axial depth of cut under specific feed per tooth and cutting speed in high-speed end milling of soda-lime glass. A two-fluted solid end mill of 4 mm diameter was used with cutting speed ranging from 377 to 628 m/min and feed rate from 5 to 20 mm/min to investigate the phenomenon of transition from plowing to ductile and ductile to brittle machining mode. The work piece was placed at a specific angle to facilitate machining at gradual increment in depths for different feed rates and cutting speeds combinations. At the highest available cutting speed, three phases (plowing, ductile, and brittle) were observed at a specific feed rate, resulting in a critical depth of cut 51.943 \({\rm \mu}\)m and chip thickness approximately 198 nm.

The influence of phase gradient within the micro arc oxidation (MAO) coatings on mechanical and tribological behaviors

The alumina coatings of 100μm thickness were deposited on 6061 T6 Al-alloy through micro arc oxidation (MAO) technique. The phase composition across the coating thickness was evaluated using step-wise grinding followed by X-ray diffraction analysis. The microhardness and elastic modulus were measured through micro and nano indentation techniques respectively on the mounted and polished coating cross-sections as a function of distance from substrate–coating interface. The coatings represent typical graded composite of α-Al2O3 and γ-Al2O3 phases and accompanied by the corresponding hardness and modulus gradients across the coating thickness. Tribological performance of MAO coatings was evaluated through pin-on-disc wear test under dry (un-lubricated) conditions. The results obtained suggest that the transition from γ-Al2O3 rich surface sub-layers to α-Al2O3 rich inner sub-layers is gradual. On the basis of the above experimental results, the critical interrelationships between the coating phase composition, hardness distribution, modulus distribution and the accompanied sliding wear loss have been established. It was found that the simple rule of mixture explains (ROM) the hardness and modulus distributions as a function of phase gradient across the coating thickness while the inverse rule of mixture (I-ROM) is applicable in the case of sliding wear–phase gradient relationship. Further, the relationships established were utilized to evaluate the mechanical and tribological properties of pure α-Al2O3 and γ-Al2O3 phases. The properties of gamma alumina such as hardness, elastic modulus and sliding wear resistance have been reported for the first time in the present work. Further, the worn surface examination indicates that the formation of mechanically mixed layer (MML) which subsequently undergoes abrasive wear and micro-crack induced chipping as the predominant material removal mechanism during dry sliding wear tests.

Microstructure and wear properties of laser deposited WC–12%Co composites

Laser engineered net shaping (LENS™) has been used to create dense WC–12%Co composite coatings on stainless steel substrates. Low heat input and controlled atmosphere with oxygen content less than 10 ppm resulted in minimum interface dilution, carbide dissolution and uniform carbide distribution. Under present experimental conditions, coatings produced at laser energy input of 365 and 465 J/mm 3 showed similar phase constituents, hardness and wear rate. The coating hardness varied between 1171 and 1181 HV with an average dry sliding specific wear rate in the range of 3 × 10 −6 mm 3/Nm and 6.5 × 10 −6 mm 3/Nm against Si 3N 4 ball. Deformation and extrusion of cobalt phase followed by fracture and removal of carbide particles was found to be a predominant material removal mechanism in the present laser deposited WC–Co coatings. The influence of laser energy input on the microstructural and wear properties of WC–12%Co composites coatings are reported in this article.

Slurry wear characteristics of zinc-based alloys: Effects of sand content of slurry, silicon addition to alloy system and traversal distance

This investigation deals with the observations pertaining to the effects of specimen and slurry compositions as well as traversal distance on the slurry wear response of a zinc-based alloy. The composition of the alloy was altered by adding 4% silicon to it. The slurry composition was varied through changing the concentration of the sand particles in the range of 0–60% that were suspended in the (liquid) electrolyte. The electrolyte contained 4 g sodium chloride and 5 mL concentrated sulphuric acid dissolved in 10 L of water. The slurry wear tests were conducted at a speed of 7.02 m/s over the traversal distance range of 15–500 km. The wear rate increased initially with traversal distance, attained a maximum and decreased thereafter irrespective of the specimen and test environment. However, the wear rate peaks were less prominent in the liquid plus sand environments than the liquid-only medium. Further, the wear rate peak in the liquid-only medium appeared at a shorter traversal distance than the one in the sand containing slurries. Addition of sand particles to the electrolyte reduced the wear rate of the samples to 5%–15% depending on the sand concentration of the slurry. Moreover, intermediate (40%) sand content led to a maximum wear rate when compared with in the liquid plus sand media. However, this maximum was still less than in the liquid-only medium. The silicon containing alloy suffered from higher wear rates than the silicon free alloy samples when tested in the liquid-only medium. On the contrary, the trend reversed in liquid plus 20% and 40% sand environments whereas a mixed response was noted in the slurry containing 60% sand. In the latter case, the presence of silicon proved deleterious initially while an opposite trend was observed at longer traversal distances. The wear response of the samples was discussed in terms of specific features of their microconstituents like silicon and the predominant material removal mechanism in a given set of experimental conditions. The observed behaviour of the alloys was also substantiated further through the characteristics of their affected surface and subsurface regions.

An experimental study of optical glass machining

Owing to brittleness and hardness, optical glass is one of the materials that is most difficult to cut. Nevertheless, as the threshold value of the undeformed chip thickness is reached, brittle materials undergo a transition from the brittle to the ductile machining region. Below this threshold, it is believed that the energy required to propagate cracks is larger than the energy required for plastic deformation. Thus, plastic deformation is the predominant mechanism of material removal in machining these materials in this mode. An experimental study is conducted to diamond-cut BK7 glass in ductile mode. As an effective rake angle plays a more important role than a nominal rake angle does, a discussion about this effective angle is carried out in the paper. The investigation presents the feasibility of achieving nanometric surfaces. Power spectral density (PSD) analysis on the machined surfaces shows the difference between the characteristics of the two modes. During the experiments, it is recognised that tool wear is a severe problem. Further study is in process to improve the cutting tool life.

An experimental study of edge radius effect on cutting single crystal silicon

According to the hypothesis of ductile machining, brittle materials undergo a transition from brittle to ductile mode once a critical undeformed chip thickness is reached. Below this threshold, the energy required to propagate cracks is believed to be larger than the energy required for plastic deformation, so that plastic deformation is the predominant mechanism of material removal in machining these materials in this mode. An experimental study is conducted using diamond cutting for machining single crystal silicon. Analysis of the machined surfaces under a scanning electron microscope (SEM) and an atomic force microscope (AFM) identifies the brittle region and the ductile region. The study shows that the effect of the cutting edge radius possesses a critical importance in the cutting operation. Experimental results of taper cutting show a substantial difference in surface topography with diamond cutting tools of 0° rake angle and an extreme negative rake angle. Cutting with a diamond cutting tool of 0° rake angle could be in a ductile mode if the undeformed chip thickness is less than a critical value, while a ductile mode cutting using the latter tool could not be found in various undeformed chip thicknesses.

Ultra-Precision Cutting for ZKN7 Glass

There is an immense need to obtain nanometric surface finish on optical glasses owing to the advantage of improved performance of the components. Thus, the use of ultra-precision machining becomes critical. According to the hypothesis of ductile machining, all materials, regardless of their hardness and brittleness, will undergo a transition from brittle to ductile machining region below a critical undeformed chip thickness. Below this threshold, the energy required to propagate cracks is believed to be larger than the energy required for plastic deformation, so that plastic deformation is the predominant mechanism of material removal in machining these materials. However, the mere use of ultra-precision machining for this brittle material would not yield mirror surface finish. Therefore, experiments were conducted using diamond cutting for machining ZKN7 glass. Based on the experimental work, a new strategy was proposed for obtaining nanometric surface finish and the cutting mechanism was studied in detail. A new method for measuring the sharpness of the cutting tools was introduced using the confocal laser scanning microscopy. Also, in this paper an alternative approach was recommended for the fracture toughness measurement of brittle materials.

The damage mechanisms of several plasma-sprayed ceramic coatings in controlled scratching

The damage mechanisms of several widely used plasma-sprayed ceramic coatings were studied by single point scratch tests using diamond indenters. The ceramic coatings investigated were Al 2O 3, Al 2O 3/13% TiO 2 and Cr 2O 3. Single scratching on polished virgin surface, repeated scratching over the same track and parallel interacting scratching were investigated. Microstructures of the coatings, their surface and subsurface damage patterns due to the scratching, and the morphology of wear debris were examined. It was found that the unique microstructure of the coatings determined their wear and related damage mechanisms. The predominant mechanism of material removal in the scratching of Al 2O 3 and Al 2O 3/13% TiO 2 coatings was microfracture within the plastic region, which takes place preferentially at pre-existing microcracks and micropores and is driven by plastic strain. The mechanism of material removal in the scratching of the Cr 2O 3 coating depended on contact load and contact geometry. When the contact load was less than a critical value that was related to contact geometry, the predominant mechanism of material removal was the same as that of Al 2O 3 and Al 2O 3/13% TiO 2 coatings. When the contact load exceeded the critical value, the predominant mechanism of material removal was macro-fracture controlled by lateral cracking.

Erosion–corrosion characteristics of squeeze cast aluminium alloy/SiC composites in water and sodium chloride solutions containing sand

The erosion–corrosion behaviour of a squeeze cast aluminium alloy (Al–Cu) dispersed with either 10 vol.-%SiC particles or SiC fibres was investigated in slurry environments of 3%NaCl (aqueous) + 40 wt-% sand and water + 40 wt-% sand over a range of test durations at a linear speed of 7·06 m s-1. Test results indicated higher weight loss for the SiC composites than for the matrix alloy in 3%NaCl + 40 wt-% sand while the reverse trend was noted when the tests were conducted in water + 40 wt-% sand. Severe attack around the dispersoid/matrix and precipitate/matrix interfaces by the NaCl environment caused loosening of the dispersoid phase followed by the subsequent removal of the dispersoids. This resulted in a higher weight loss for composites than for the base alloy in NaCl containing sand. Corrosion processes appear to dominate in this case. The lower weight loss of the composites compared with the matrix alloy in water + 40% sand could be attributed to the protection provided by the SiC phase to the softer matrix. Erosion appears to be the predominant mechanism of material removal in this case. Furthermore, the SiC fibre composite suffered from more weight loss than that containing SiC particles in both the test environments. Results have been explained on the basis of analysis of eroded–corroded surfaces and subsurface regions.

Wear mechanism of plasma-sprayed alumina coating in sliding contacts with harder asperities

The wear mechanism of plasma-sprayed alumina was studied by scratching a model alumina coating using a diamond indenter. Single scratching on polished virgin surface, repeated scratching over the same track and parallel interacting scratching were investigated. The predominant mechanism of material removal was found to be microfracture within the quasi-plastic zone, which takes place preferentially at splat boundaries and pre-existing cracks and is driven by inelastic strain. When scratching was made on a virgin surface the wear rate was relatively low, but when parallel scratches interacted, subsequent scratching was made on already heavily strained material, thus, the wear rate was much higher. The wear debris produced during single and parallel interacting scratching was in the form of small angular particles whose dimensions were related to the splat structure and pre-existing cracks. In repeated scratching over the same track, surface material experienced repeated inelastic deformation and, thus, crack development at the splat boundaries, and this resulted in the production of thin platelet wear debris.

Slurry erosive wear characteristics of a hard faced steel: effect of experimental parameters

Wear properties of engineering components encountering slurry conditions during operation can be improved by overlaying with a wear resistant material. The present paper discusses the effects of different experimental conditions on the wear rate of a low carbon steel on overlaying with a wear resistant material. Distance has a mixed effect on the wear rate. Further, wear rate increases with increase in the sand content in slurry from 20 to 30% but decreases at 40% for all speeds of rotation. Again, wear rate is increased on increasing the speed of rotation from 600 to 800 rpm but decreases remarkably at 1000 rpm. Attempts have been made to explain the wear rate variation behaviour by observing the worn surface through scanning electron microscopic studies. It has been observed that at the lowest speed of rotation and minimum sand content, the predominant mechanism of material removal is erosion, whereas on increasing either than sand content or the speed of rotation, abrasion effects are also observed. At the maximum speed of rotation and sand content, abrasion effects are predominant. Keeping in mind that material removal by abrasion is less than that due to erosion, the variation of wear rate with speed and sand content are explained.

Surface failure mechanisms of NiCrMo steel under lubricated sliding

An investigation of the sliding wear behaviour of a nickelchromiummolybdenum steel under lubricated conditions has been undertaken. After an appropriate running-in procedure that avoids surface roughening, the predominant material-removal mechanism during mild wear is delamination. Surface failure and scuffing under lubricated conditions occur above a transition load of 290 N. The onset of severe wear is associated with adhesive transfer, at which stage delamination and abrasion are also important mechanisms. A layer of plasticity develops immediately below the sliding surface, the thickness of which increases with the applied load. Cracks initiate within this layer, particularly at embedded debris particles, and propagate parallel to the sliding interface to generate delaminated platelets.

Dry Sliding Wear Response of a Modified Zinc-Based Alloy

An attempt has been made in this investigation to characterize the sliding wear response of a modified zinc-based alloy at the sliding speed of 2.68 m/s over a range of applied pressures. A conventional zinc-based alloy (conforming to ZA 27) and a leaded-tin bronze (conforming to SAE 660) were also subjected to identical test conditions in order to assess the (wear) performance of the modified (zinc-based) alloy. A correlation has been established between the nature of the various microconstituents and the wear response of the alloys. Wear mechanisms have also been studied through the examination of wear surfaces, subsurfaces and debris. The study clearly indicates that the presence of nickel and silicon comprising microconstituents led to a considerably increased wear and seizure resistance of the modified zinc-based alloy over its conventional counterpart. Further, zinc-based alloys attained better wear resistance (prior to seizure) but inferior seizure pressure when compared with those of the bronze. As far as the extent of frictional heating is concerned, the conventional zinc-based alloy suffered from a maximum extent of heating while the bronze experienced the minimum. The response of the modified zinc-based alloy was intermediate between the two in this context. The modified alloy also attained improved thermal stability than the conventional (zinc-based) alloy. In general, (microcracking assisted) adhesion was the predominant mechanism of material removal. However, abrasion was also observed to contribute to material loss. The zinc-based alloys experienced considerable wear induced subsurface deformation and formation of a stable transfer layer while such observations were weakly made in the case of the bronze due to the cracking tendency of the latter.

Microstructure and solid particle erosion of carbon-based materials used for the protection of highly porous carbon-carbon composite thermal insulation

Multiparticle erosion tests were performed on candidate coating (colloidal graphite paints) and cladding (dense carbon–carbon composites and graphite foil) materials employed to protect porous carbon–carbon composite thermal insulation in vacuum and inert-gas furnaces that utilize inert gas quenching. The dependence of the erosion rate on the angle of incidence of the erodent was examined and related to the microstructure and the mechanisms of material removal as observed by SEM. In addition, the effect of a thin chemical vapour deposited (CVD) carbon layer on top of a colloidal graphite paint coating and a graphite foil clad was investigated. The coating and cladding materials displayed a greater erosion resistance at all angles of incidence compared to the porous carbon–carbon composite. In general, the greatest erosion rate was found at an angle of incidence of 90°, where the erodent stream is perpendicular to the erosion surface, and brittle fracture was the predominant mechanism of material removal. The exception was the graphite foil material which displayed maximum erosion at an angle of incidence of 60°. For this material, two mechanisms were effective: disruption of the graphite flakes, which are mainly held together by mechanical locking, and a ploughing-like mechanism. The addition of a thin CVD carbon layer to colloidal graphite paint improved performance, whereas the erosion resistance of the graphite foil was slightly degraded as the CVD layer was too thin to prevent the ploughing-like mechanism.

Effect of Grain Size on Scratch Interactions and Material Removal in Alumina

Dramatic effects of scratch interactions on material removal are observed in alumina. A series of parallel scratches are made in aluminas with different grain sizes to investigate the influence of scratch interactions on the material removal process in abrasive machining. The separation distance between the two scratches and the normal load are varied and subsurface microfracture and damage modes are examined to assess the mechanisms of material removal. A very small amount of material is removed when the separation distance between the two parallel scratches is large or when the two scratches completely overlap. However, at intermediate distances the volume of material removed increases dramatically as a result of the interactions between the two scratches. The maximum amount of material removed and the corresponding distance between the two scratches are found to depend strongly on the grain size and the load. Observations of surface and subsurface damage reveal that grain dislodgement is the predominant mechanism of material removal, irrespective of the grain size. The relation between grain size, scratch interactions, and the material removal process in grinding and abrasive machining of ceramics is discussed in terms of the short‐crack toughness of ceramics.

Ductile-Regime Grinding: A New Technology for Machining Brittle Materials

Because of recent advances in precision engineering that allow controlled grinding infeed rates as small as several nanometers per grinding wheel revolution, it is possible to grind brittle materials so that the predominant material-removal mechanism is plastic-flow and not fracture. This process is known as ductile-regime grinding. When brittle materials are ground through a process of plastic deformation, surface finishes similar to those achieved in polishing or lapping are produced. Unlike polishing or lapping, however, grinding is a deterministic process, permitting finely controlled contour accuracy and complex shapes. In this paper, the development of a research apparatus capable of ductile-regime grinding is described. Furthermore, an analytical and experimental investigation of the infeed rates necessary for ductile-regime grinding of brittle materials is presented. Finally, a model is proposed, relating the grinding infeed rate necessary for ductile material-removal with the properties of the brittle workpiece material.