Nanocutting mechanism of 6H-SiC investigated by scanning electron microscope online observation and stress-assisted and ion implant-assisted approaches

Nanocutting mechanism of single crystal 6H-SiC is investigated through a novel scanning electron microscope setup in this paper. Various undeformed chip thicknesses on (0001) orientation are adopted in the nanocutting experiments. Phase transformation and dislocation activities involved in the 6H-SiC nanocutting process are also characterized and analyzed. Two methods of stress-assisted and ion implant-assisted nanocutting are studied to improve 6H-SiC ductile machining ability. Results show that stress-assisted method can effectively decrease the hydrostatic stress and help to activate dislocation motion and ductile machining; ion implant-induced damages are helpful to improve the ductile machining ability from MD simulation and continuous nanocutting experiments under the online observation platform.Peer reviewe

Ultra-high precision machining of contact lens polymers

Contact lens manufacture requires a high level of accuracy and surface integrity in the range of a few nanometres. Amidst numerous optical manufacturing techniques, single-point diamond turning is widely employed in the making of contact lenses due to its capability of producing optical surfaces of complex shapes and nanometric accuracy. For process optimisation, it is ideal to assess the effects of various conditions and also establish their relationships with the surface finish. Presently, there is little information available on the performance of single point diamond turning when machining contact lens polymers. Therefore, the research work undertaken herewith is aimed at testing known facts in contact lens diamond turning and investigating the performance of ultra-high precision manufacturing of contact lens polymers. Experimental tests were conducted on Roflufocon E, which is a commercially available contact lens polymer and on Precitech Nanoform Ultra-grind 250 precision machining. Tests were performed at varying cutting feeds, speed and depth of cut. Initial experimental tests investigated the influence of process factors affecting surface finish in the UHPM of lenses. The acquired data were statistically analysed using Response Surface Method (RSM) to create a model of the process. Subsequently, a model which uses Runge-Kutta’s fourth order non-linear finite series scheme was developed and adapted to deduce the force occurring at the tool tip. These forces were also statistically analysed and modelled to also predict the effects process factors have on cutting force. Further experimental tests were aimed at establishing the presence of the triboelectric wear phenomena occurring during polymer machining and identifying the most influential process factors. Results indicate that feed rate is a significant factor in the generation of high optical surface quality. In addition, the depth of cut was identified as a significant factor in the generation of low surface roughness in lenses. The influence some of these process factors had was notably linked to triboelectric effects. This tribological effect was generated from the continuous rubbing action of magnetised chips on the cutting tool. This further stresses the presence of high static charging during cutting. Moderately humid cutting conditions presented an adequate means for static charge control and displayed improved surface finishes. In all experimental tests, the feed rate was identified as the most significant factor within the range of cutting parameters employed. Hence, the results validated the fact that feed rate had a high influence in polymer machining. The work also established the relationship on how surface roughness of an optical lens responded to monitoring signals and parameters such as force, feed, speed and depth of cut during machining and it generated models for prediction of surface finishes and appropriate selection of parameters. Furthermore, the study provides a molecular simulation analysis for validating observed conditions occurring at the nanometric scale in polymer machining. This is novel in molecular polymer modelling. The outcome of this research has contributed significantly to the body of knowledge and has provided basic information in the area of precision manufacturing of optical components of high surface integrity such as contact lenses. The application of the research findings presented here cuts across various fields such as medicine, semi-conductors, aerospace, defence, telecom, lasers, instrumentation and life sciences

Influence of microstructure on the cutting behaviour of silicon

We use molecular dynamics simulation to study the mechanisms of plasticity during cutting of monocrystalline and polycrystalline silicon. Three scenarios are considered: (i) cutting a single crystal silicon workpiece with a single crystal diamond tool, (ii) cutting a polysilicon workpiece with a single crystal diamond tool, and (iii) cutting a single crystal silicon workpiece with a polycrystalline diamond tool. A long-range analytical bond order potential is used in the simulations, providing a more accurate picture of the atomic-scale mechanisms of brittle fracture, ductile plasticity, and structural changes in silicon. The MD simulation results show a unique phenomenon of brittle cracking typically inclined at an angle of 45°–55° to the cut surface, leading to the formation of periodic arrays of nanogrooves in monocrystalline silicon, which is a new insight into previously published results. Furthermore, during cutting, silicon is found to undergo solid-state directional amorphisation without prior Si–I to Si-II (beta tin) transformation, which is in direct contrast to many previously published MD studies on this topic. Our simulations also predict that the propensity for amorphisation is significantly higher in single crystal silicon than in polysilicon, signifying that grain boundaries eases the material removal process

An atomistic investigation on the nanometric cutting mechanism of hard, brittle materials

The demand for ultra precision machined devices and components is growing at a rapid pace in various areas such as the aerospace, energy, optical, electronics and bio-medical industries. Because of their outstanding engineering properties such as high refractive index, wide energy bandgap and low mass density, there is a continuing requirement for developments in manufacturing methods for hard, brittle materials. Accordingly, an assessment of the nanometric cutting of the optical materials silicon and silicon carbide (SiC), which are ostensibly hard and brittle, has been undertaken. Using an approach of parallel molecular dynamics simulations with a three-body potential energy function combined with experimental characterization, this thesis provides a quantitative understanding of the ductile-regime machining of silicon and SiC (polytypes: 3C, 4H and 6H SiC), and the mechanism by which a diamond tool wears during the process. The distinctive MD algorithm developed in this work provides a comprehensive analysis of thermal effects, high pressure phase transformation, tool wear (both chemical and abrasive), influence of crystal anisotropy, cutting forces and machining stresses (hydrostatic and von Mises), hitherto not done so far. The calculated stress state in the cutting zone during nanometric cutting of single crystal silicon indicated Herzfeld–Mott transition (metallization) due to high pressure phase transformation (HPPT) of silicon under the influence of deviatoric stress conditions. Consequently, the transformation of pristine silicon to β-silicon (Si-II) was found to be the likely reason for the observed ductility of bulk silicon during its nanoscale cutting. Tribochemical formation of silicon carbide through a solid state single phase reaction between the diamond tool and silicon workpiece in tandem with sp3-sp2 disorder of carbon atoms from the diamond tool up to a cutting temperature of 959 K has been suggested as the most likely mechanism through which a diamond cutting tool wears while cutting silicon. The recently developed dislocation extraction algorithm (DXA) was employed to detect the nucleation of dislocations in the MD simulations of varying cutting orientation and cutting direction. Interestingly, despite of being a compound of silicon and carbon, silicon carbide (SiC) exhibited characteristics more like diamond, e.g. both SiC iii workpiece and diamond cutting tool were found to undergo sp3-sp2 transition during the nanometric cutting of single crystal SiC. Also, cleavage was found to be the dominant mechanism of material removal on the (111) crystal orientation. Based on the overall analysis, it was found that 3C-SiC offers ease of deformation on either (111) , (110) or (100) setups. The simulated orthogonal components of thrust force in 3C-SiC showed a variation of up to 45% while the resultant cutting forces showed a variation of 37% suggesting that 3C-SiC is anisotropic in its ease of deformation. The simulation results for three major polytypes of SiC and for silicon indicated that 4H-SiC would produce the best sub-surface integrity followed by 3C-SiC, silicon and 6H-SiC. While, silicon and SiC were found to undergo HPPT which governs the ductility in these hard, brittle materials, corresponding evidence of HPPT during the SPDT of polycrystalline reaction bonded SiC (RB-SiC) was not observed. It was found that, since the grain orientation changes from one crystal to another in polycrystalline SiC, the cutting tool experiences work material with different crystallographic orientations and directions of cutting. Thus, some of the grain boundaries cause the individual grains to slide along the easy cleavage direction. Consequently, the cutting chips in RB-SiC are not deformed by plastic mechanisms alone, but rather a combination of phase transformation at the grain boundaries and cleavage of the grains both proceed in tandem. Also, the specific-cutting energy required to machine polycrystalline SiC was found to be lower than that required to machine single crystal SiC. Correspondingly, a relatively inferior machined surface finish is expected with a polycrystalline SiC. Based on the simulation model developed, a novel method has been proposed for the quantitative assessment of tool wear from the MD simulations. This model can be utilized for the comparison of tool wear for various simulation studies concerning graphitization of diamond tools. Finally, based on the theoretical simulation results, a novel method of machining is proposed to suppress tool wear and to obtain a better quality of the machined surface during machining of difficult-to-machine materials

Исследования пластичного режима резания хрупких материалов (обзор)

Рассмотрены теоретические и экспериментальные исследования пластичного режима резания хрупких материалов (полупроводников, керамики и стекла). Пластичный режим резания основан на осуществлении фазовых переходов под давлением в обрабатываемом материале с последующим срезом трансформированного аморфного слоя, что позволяет избежать образования трещин. Рассмотрены работы по изучению фазовых переходов в хрупких материалах при индентировании, царапании, трении и резании. Показано, что глубина резания, радиус округления кромки резца, толщина формируемой стружки, угол наклона режущей грани резца, кристаллографическая ориентация обрабатываемого материала и алмазного инструмента, тип смазочно-охлаждающей жидкости являются определяющими параметрами для реализации пластичного режима резания.Розглянуто теоретичні та експериментальні дослідження пластичного режиму різання крихких матеріалів (напівпровідників, кераміки та скла). Пластичнийрежим різання базується на здійсненні фазових переходів під тиском в оброблюваному матеріалі з подальшим зрізанням трансформованого аморфного шару, що дозволяє уникнути утворення тріщин. Розглянуто роботи з вивчення фазових переходів у крихких матеріалах при індентуванні, дряпанні, терті і різанні. Показано, що глибина різання, радіус округлення різальної кромки різця, товщина стружки, кут нахилу ріжучої грані різця, кристалографічна орієнтація оброблюваного матеріалу і алмазного інструменту, тип мастильно-охолоджувальної рідини і деякі інші параметри є визначальними для реалізації пластичного режиму різання.Theoretical and experimental studies of ductile regime cutting of brittle materials (semiconductors, ceramics and glass) were considered. The ductile mode cutting is connected with implementation high-pressure phase transformations that occur in the machined brittle materials with following removal of the transformed amorphous layer, which permits to avoid cracking. The investigations of phase transformation in brittle materials at indentation, scratching, friction and cutting were reviewed. It is shown that the cutting depth, the tool cutting edge radius, the undeformed chip thickness, the tool rake angle, crystallographic orientation of the machined material and the diamond tool, the cutting lubricants and some others parameters are critical for maintaining the ductile mode

Influence of temperature on the anisotropic cutting behaviour of single crystal silicon: A molecular dynamics simulation investigation

Using molecular dynamics (MD) simulation, this paper investigates anisotropic cutting behaviour of single crystal silicon in vacuum under a wide range of substrate temperatures (300 K, 500 K, 750 K, 850 K, 1173 K and 1500 K). Specific cutting energy, force ratio, stress in the cutting zone and cutting temperature were the indicators used to quantify the differences in the cutting behaviour of silicon. A key observation was that the specific cutting energy required to cut the (1 1 1) surface of silicon and the von Mises stress to yield the silicon reduces by 25% and 32%, respectively, at 1173 K compared to what is required at 300 K. The room temperature cutting anisotropy in the von Mises stress and the room temperature cutting anisotropy in the specific cutting energy (work done by the tool in removing unit volume of material) were obtained as 12% and 16%, respectively. It was observed that this changes to 20% and 40%, respectively, when cutting was performed at 1500 K, signifying a very strong correlation between the anisotropy observed during cutting and the machining temperature. Furthermore, using the atomic strain criterion, the width of primary shear zone was found to vary with the orientation of workpiece surface and temperature i.e. it remains narrower while cutting the (1 1 1) surface of silicon or at higher machining temperatures. A major anecdote of the study based on the potential function employed in the study is that, irrespective of the cutting plane or the cutting temperature, the state of the cutting edge of the diamond tool did not show direct diamond to graphitic phase transformation

Investigation of cutting mechanics in single point diamond turning of silicon

As a kind of brittle material, silicon will undergo brittle fracture at atmospheric pressure in conventional scale machining. Studies in the last two decades on hard and brittle materials including silicon, germanium, silicon nitride and silicon carbide have demonstrated ductile regime machining using single point diamond turning (SPDT) process. The mirror-like surface finish can be achieved in SPDT provided appropriate tool geometry and cutting parameters including feed rate, depth of cut and cutting speed are adopted.The research work in this thesis is based on combined experimental and numerical smoothed particle hydrodynamics (SPH) studies to provide an inclusive understanding of SPDT of silicon. A global perspective of tool and workpiece condition using experimental studies along with localized chip formation and stress distribution analysis using distinctive SPH approach offer a comprehensive insight of cutting mechanics of silicon and diamond tool wear. In SPH modelling of SPDT of silicon, the distribution of von Mises and hydrostatic stress at incipient and steady-state was found to provide the conditions pertinent to material failure, phase transformation, and ductile mode machining. The pressure-sensitive Drucker Prager (DP) material constitutive model was adopted to predict the machining response behaviour of silicon during SPDT. Inverse parametric analysis based on indentation test was carried out to determine the unknown DP parameters of silicon by analysing the loading-unloading curve for different DP parameters. A very first experimental study was conducted to determine Johnson-Cook (J-C) model constants for silicon. High strain rate compression tests using split Hopkinson pressure bar (SHPB) test as well as quasi-static tests using Instron fatigue testing machine were conducted to determine J-C model constants.The capability of diamond tools to maintain expedient conditions for high-pressure phase transformation (HPPT) as a function of rake angle and tool wear were investigated experimentally as well as using SPH approach. The proportional relationship of cutting forces magnitude and tool wear was found to differ owing to wear contour with different rake angles that influence the distribution of stresses and uniform hydrostatic pressure under the tool cutting edge. A new quantitative evaluation parameter for the tool wear resistance performance based on the cutting distance was also proposed. It was also found that the machinability of silicon could be improved by adopting novel surface defect machining (SDM) method.The ductile to brittle transition (DBT) with the progressive tool wear was found to initiate with the formation of lateral cracks at low tool wear volume which transform into brittle pitting damage at higher tool edge degradation. A significant variation in resistance to shear deformation as well as position shift of the maximum stress values was observed with the progressive tool wear. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of the new and worn diamond tools.As a kind of brittle material, silicon will undergo brittle fracture at atmospheric pressure in conventional scale machining. Studies in the last two decades on hard and brittle materials including silicon, germanium, silicon nitride and silicon carbide have demonstrated ductile regime machining using single point diamond turning (SPDT) process. The mirror-like surface finish can be achieved in SPDT provided appropriate tool geometry and cutting parameters including feed rate, depth of cut and cutting speed are adopted.The research work in this thesis is based on combined experimental and numerical smoothed particle hydrodynamics (SPH) studies to provide an inclusive understanding of SPDT of silicon. A global perspective of tool and workpiece condition using experimental studies along with localized chip formation and stress distribution analysis using distinctive SPH approach offer a comprehensive insight of cutting mechanics of silicon and diamond tool wear. In SPH modelling of SPDT of silicon, the distribution of von Mises and hydrostatic stress at incipient and steady-state was found to provide the conditions pertinent to material failure, phase transformation, and ductile mode machining. The pressure-sensitive Drucker Prager (DP) material constitutive model was adopted to predict the machining response behaviour of silicon during SPDT. Inverse parametric analysis based on indentation test was carried out to determine the unknown DP parameters of silicon by analysing the loading-unloading curve for different DP parameters. A very first experimental study was conducted to determine Johnson-Cook (J-C) model constants for silicon. High strain rate compression tests using split Hopkinson pressure bar (SHPB) test as well as quasi-static tests using Instron fatigue testing machine were conducted to determine J-C model constants.The capability of diamond tools to maintain expedient conditions for high-pressure phase transformation (HPPT) as a function of rake angle and tool wear were investigated experimentally as well as using SPH approach. The proportional relationship of cutting forces magnitude and tool wear was found to differ owing to wear contour with different rake angles that influence the distribution of stresses and uniform hydrostatic pressure under the tool cutting edge. A new quantitative evaluation parameter for the tool wear resistance performance based on the cutting distance was also proposed. It was also found that the machinability of silicon could be improved by adopting novel surface defect machining (SDM) method.The ductile to brittle transition (DBT) with the progressive tool wear was found to initiate with the formation of lateral cracks at low tool wear volume which transform into brittle pitting damage at higher tool edge degradation. A significant variation in resistance to shear deformation as well as position shift of the maximum stress values was observed with the progressive tool wear. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of the new and worn diamond tools

An investigation of mechanics in nanomachining of Gallium Arsenide

The first two decades of the 21st Century have seen a wide exploitation of Gallium Arsenide (GaAs) in photoemitter device, microwave devices, hall element, solar cell, wireless communication as well as quantum computation device due to its superior material properties, such as higher temperature resistance, higher electronic mobility and energy gap that outperforms silicon. Ultra-precision multiplex two dimensional (2D) or three dimensional (3D) free-form nanostructures are often required on GaAs-based devices, such as radio frequency power amplifiers and switches used in the 5G smart mobile wireless communication. However, GaAs is extremely difficult to machine as its elastic modulus, Knoop hardness and fracture toughness are lower than other semiconductor materials such as silicon and germanium. This PhD thesis investigated the mechanics of nanomachining of GaAs through molecular dynamics (MD) simulation combined with single point diamond turning (SPDT) and atomic force microscope (AFM) based experimental characterization in order to realise ductile-regime nanomachining of GaAs, which is the most important motivation behind this thesis. The investigation of mechanics of nanomachining of GaAs included studies on cutting temperature, cutting forces, origin ductile plasticity, atomic scale friction, formation mechanism of sub-surface damage, wear mechanism of diamond cutting tool. Machinability of GaAs at elevated temperature was also studied in order to develop thermally-assisted nanomachining process in the future to facilitate plastic material deformation and removal. This thesis contributed to address the knowledge gaps such as what is the incipient plasticity, how does the sub-surface damage form and how does the diamond cutting tool wear during nanomachining of GaAs. Firstly, this thesis investigated the cutting zone temperature, cutting forces and origin of plasticity of GaAs material, including single crystal GaAs and polycrystalline GaAs during SPDT process. The experimental and MD simulation study showed GaAs has a strong anisotropic machinability. The simulation results indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was only observed during cutting of polycrystalline GaAs, not for single-crystal GaAs. Secondly, this thesis studied the atomic scale friction during AFM-based nanomachining process. a strong size effect was observed when the scratch depths are below 2 nm in MD simulations and 15 nm from the AFM experiments respectively. A strong quantitative corroboration was obtained between the MD simulations and the AFM experiments in the specific scratch energy and more qualitative corroboration with the pile up and the kinetic coefficient of friction. This conclusion suggested that the specific scratch energy is insensitive to the tool geometry and the speed of scratch used in this investigation but the pile up and kinetic coefficient of friction are dependent on the geometry of the tool tip. Thirdly, this thesis investigated formation mechanism of sub-surface damage and wear mechanism of diamond cutting tool during nanomachining of GaAs. Transmission Electron Microscope (TEM) measurement of sub-surface of machined nanogrooves on GaAs and MD simulation of dislocation movement indicated the dual slip mechanisms i.e. shuffle-set slip mechanism and glide-set slip mechanism, and the creation of dislocation loops, multi dislocation nodes, and dislocation junctions governed the formation mechanism of sub-surface damage of GaAs during nanomachining process. Elastic-plastic deformation at the apex of the diamond tip was observed in MD simulations. Meanwhile, a transition of the diamond tip from its initial cubic diamond lattice structure sp3 hybridization to graphite lattice structure sp2 hybridization was revealed. Graphitization was, therefore, found to be the dominant wear mechanism of the diamond tip during nanometric cutting of single crystal GaAs. Finally, in MD simulations study of cutting performance at elevated temperature, hotter conditions resulted in the reduction of cutting forces by 25% however, the kinetic coefficient of friction went up by about 8%. While material removal rate was found to increase with the increase of the substrate temperature, it was accompanied by an increase of the sub-surface damage in the substrate. Moreover, a phenomenon of chip densification was found to occur during hot cutting which referred to the fact that the amorphous cutting chips obtained from cutting at low temperature will have lower density than the chips obtained from cutting at higher temperatures.The first two decades of the 21st Century have seen a wide exploitation of Gallium Arsenide (GaAs) in photoemitter device, microwave devices, hall element, solar cell, wireless communication as well as quantum computation device due to its superior material properties, such as higher temperature resistance, higher electronic mobility and energy gap that outperforms silicon. Ultra-precision multiplex two dimensional (2D) or three dimensional (3D) free-form nanostructures are often required on GaAs-based devices, such as radio frequency power amplifiers and switches used in the 5G smart mobile wireless communication. However, GaAs is extremely difficult to machine as its elastic modulus, Knoop hardness and fracture toughness are lower than other semiconductor materials such as silicon and germanium. This PhD thesis investigated the mechanics of nanomachining of GaAs through molecular dynamics (MD) simulation combined with single point diamond turning (SPDT) and atomic force microscope (AFM) based experimental characterization in order to realise ductile-regime nanomachining of GaAs, which is the most important motivation behind this thesis. The investigation of mechanics of nanomachining of GaAs included studies on cutting temperature, cutting forces, origin ductile plasticity, atomic scale friction, formation mechanism of sub-surface damage, wear mechanism of diamond cutting tool. Machinability of GaAs at elevated temperature was also studied in order to develop thermally-assisted nanomachining process in the future to facilitate plastic material deformation and removal. This thesis contributed to address the knowledge gaps such as what is the incipient plasticity, how does the sub-surface damage form and how does the diamond cutting tool wear during nanomachining of GaAs. Firstly, this thesis investigated the cutting zone temperature, cutting forces and origin of plasticity of GaAs material, including single crystal GaAs and polycrystalline GaAs during SPDT process. The experimental and MD simulation study showed GaAs has a strong anisotropic machinability. The simulation results indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was only observed during cutting of polycrystalline GaAs, not for single-crystal GaAs. Secondly, this thesis studied the atomic scale friction during AFM-based nanomachining process. a strong size effect was observed when the scratch depths are below 2 nm in MD simulations and 15 nm from the AFM experiments respectively. A strong quantitative corroboration was obtained between the MD simulations and the AFM experiments in the specific scratch energy and more qualitative corroboration with the pile up and the kinetic coefficient of friction. This conclusion suggested that the specific scratch energy is insensitive to the tool geometry and the speed of scratch used in this investigation but the pile up and kinetic coefficient of friction are dependent on the geometry of the tool tip. Thirdly, this thesis investigated formation mechanism of sub-surface damage and wear mechanism of diamond cutting tool during nanomachining of GaAs. Transmission Electron Microscope (TEM) measurement of sub-surface of machined nanogrooves on GaAs and MD simulation of dislocation movement indicated the dual slip mechanisms i.e. shuffle-set slip mechanism and glide-set slip mechanism, and the creation of dislocation loops, multi dislocation nodes, and dislocation junctions governed the formation mechanism of sub-surface damage of GaAs during nanomachining process. Elastic-plastic deformation at the apex of the diamond tip was observed in MD simulations. Meanwhile, a transition of the diamond tip from its initial cubic diamond lattice structure sp3 hybridization to graphite lattice structure sp2 hybridization was revealed. Graphitization was, therefore, found to be the dominant wear mechanism of the diamond tip during nanometric cutting of single crystal GaAs. Finally, in MD simulations study of cutting performance at elevated temperature, hotter conditions resulted in the reduction of cutting forces by 25% however, the kinetic coefficient of friction went up by about 8%. While material removal rate was found to increase with the increase of the substrate temperature, it was accompanied by an increase of the sub-surface damage in the substrate. Moreover, a phenomenon of chip densification was found to occur during hot cutting which referred to the fact that the amorphous cutting chips obtained from cutting at low temperature will have lower density than the chips obtained from cutting at higher temperatures

An investigation on the mechanics of nanometric cutting for hard-brittle materials at elevated temperatures

Due to their exceptional physical and chemical properties such as high strength, high thermal conductivity, high stability at high temperature, high resistance to shocks, low thermal expansion and low density, silicon and silicon carbide (SiC) have become consummate candidates for optoelectronics, semiconductor and tribological applications. In particular, 3C-SiC, as a zinc blende structured SiC, possesses the highest fracture toughness, hardness, electron mobility and electron saturation velocity amongst the SiC polytypes. Thus, it has drawn substantial attention as a candidate substrate material for nano-devices which require high performance in extreme environments.Nanometric cutting is a promising ultra precision manufacturing process for manufacturing of 3D silicon and SiC based components which require submicron form accuracy and nanometric smooth finish. However, silicon and 3C-SiC have poor machinability at room temperature due to their relatively low fracture toughness and high hardness. A common understanding is that the yield strength and hardness of silicon and 3C-SiC will reduce under high temperature. As such, their fracture toughness increase which will ease plastic deformation and improve their machinabilities primarily as a result of thermally-generated intrinsic defects and thermal softening processes. However, the extent has never been reported although this knowhow could be vital in implementing the hot machining of silicon and SiC with the assistance of laser processing.This dissertation aims to gain an in-depth understanding of nanoscale mechanisms involved in nanometric cutting of hard-brittle materials such as silicon and 3C-SiC at elevated temperatures through molecular dynamics (MD) simulation and experimental trials. To this end, three-dimensional MD models of nanometric cutting were developed and different types of interatomic potential functions i.e. Tersoff, modified Tersoff, ABOP and SW were adopted to describe the interactions between atoms. In order to obtain reliable results, the equilibrium lattice constants were calculated at different temperatures for the employed potential functions. To perform the MD simulations, LAMMPS software was employed on a HPC service which was coupled with OVITO to visualise and post-process the atomistic data. Material flow behaviour, cutting chip characteristics, cutting forces and specific cutting energy, yielding stresses, stress and temperature on the cutting edge of the diamond tool, tool wear, defect-mediated plasticity and amorphization processes were calculated and analysed to quantify the differences in the cutting behaviour at different temperatures. Furthermore, In-situ high temperature nanoscratching (~500°C) of silicon wafer under reduced oxygen condition through an overpressure of pure Argon was carried out using a Berkovich tip with a ramp load at low and high scratching speeds. Ex-situ Raman spectroscopy and AFM analysis were performed to characterize high pressure phase transformation, nanoscratch topography, nanoscratch hardness and condition of the nanoindenter tip in nanoscratching at room and elevated temperatures.MD simulation results showed that the workpiece atoms underneath the cutting tool experienced a rotational flow akin to fluids. Moreover, the degree of flow in terms of vorticity was found higher on the (111) crystal plane, signifying better machinability on this orientation. Furthermore, it was observed that the degree of turbulence in the machining zone increases linearly with machining operation temperature. The cutting temperature showed significant dependence on the location and position of the stagnation region in the cutting zone of the substrate. In general, when cutting was performed on the (111) plane, the stagnation region (irrespective of the cutting temperature) was observed to locate at an upper position than that for the (010) and (110) planes. Also, at high temperatures, the stagnation region was observed to shift downwards than what was observed at room temperature. Another point of interest was the increase of subsurface deformation depth of the workpiece while cutting the (111) crystal plane at elevated temperatures.;Dislocation nucleation and formation of stacking faults were identified in conjunction with amorphization of silicon as the meditators of crystal plasticity in single crystal silicon during nanometric cutting process on different crystallographic planes at various temperatures. MD simulations revealed strong anisotropic dependence behaviour of dislocation activation and stacking fault formation. Likewise, while cutting 3C-SiC on the (110), formation and subsequent annihilation of stacking fault-couple at high temperatures, i.e. 2000 K and 3000 K, and generation of the cross-junctions between pairs of counter stacking faults meditated by the gliding of Shockley partials at 3000 K were observed. An observation of particular interest, while cutting 3C-SiC, was the shift to the (110) cleavage at cutting temperatures higher than 2000 K. The initial response of both the silicon and 3C-SiC substrates was found to be solid-state amorphization for all the studied cases. Further analysis through virtual X-ray diffraction (XRD) and radial distribution function (RDF) showed the crystal quality and structural changes of the substrate during nanometric cutting. No symptom of any atom-by-atom attrition wear and plastic deformation of the diamond cutting tool was observed during nanometric cutting of silicon irrespective of the cutting plane or the cutting temperature under vacuum condition. However, while cutting 3C-SiC, cutting tool showed severe wear and plastic deformation. It was found that the atom-by-atom attrition wear and plastic deformation of the diamond cutting tool could be alleviated while cutting 3C-SiC at high temperatures. Nevertheless, chemical wear i.e. dissolution-diffusion and adhesion wear is plausible to be accelerated at high temperatures.Raman spectroscopy was successfully used to identify the formation of metastable silicon phases during nanoscratching experiments at room and high temperatures. The probability of forming high pressure phases of Si-III and Si-XII was found to increase above the threshold load of 5 mN during room temperature nanoscratching experiment at low scratching speed. At high scratching speed, small remnants of Si-XII and Si-III phases were detected when the scratching load was greater than a threshold value i.e. ~9.5 mN. When high temperature nanoscratching was carried out at low and high speeds, no remnants of polymorph phases were observed along the nanoscratch residual track, suggesting the transition of metastable silicon phases (Si-III and Si-XII) into thermodynamic stable Si-I. Further analysis using AFM showed that the residual scratch morphologies and nanoscratch hardness were profoundly influenced by the temperature and scratching speed.Due to their exceptional physical and chemical properties such as high strength, high thermal conductivity, high stability at high temperature, high resistance to shocks, low thermal expansion and low density, silicon and silicon carbide (SiC) have become consummate candidates for optoelectronics, semiconductor and tribological applications. In particular, 3C-SiC, as a zinc blende structured SiC, possesses the highest fracture toughness, hardness, electron mobility and electron saturation velocity amongst the SiC polytypes. Thus, it has drawn substantial attention as a candidate substrate material for nano-devices which require high performance in extreme environments.Nanometric cutting is a promising ultra precision manufacturing process for manufacturing of 3D silicon and SiC based components which require submicron form accuracy and nanometric smooth finish. However, silicon and 3C-SiC have poor machinability at room temperature due to their relatively low fracture toughness and high hardness. A common understanding is that the yield strength and hardness of silicon and 3C-SiC will reduce under high temperature. As such, their fracture toughness increase which will ease plastic deformation and improve their machinabilities primarily as a result of thermally-generated intrinsic defects and thermal softening processes. However, the extent has never been reported although this knowhow could be vital in implementing the hot machining of silicon and SiC with the assistance of laser processing.This dissertation aims to gain an in-depth understanding of nanoscale mechanisms involved in nanometric cutting of hard-brittle materials such as silicon and 3C-SiC at elevated temperatures through molecular dynamics (MD) simulation and experimental trials. To this end, three-dimensional MD models of nanometric cutting were developed and different types of interatomic potential functions i.e. Tersoff, modified Tersoff, ABOP and SW were adopted to describe the interactions between atoms. In order to obtain reliable results, the equilibrium lattice constants were calculated at different temperatures for the employed potential functions. To perform the MD simulations, LAMMPS software was employed on a HPC service which was coupled with OVITO to visualise and post-process the atomistic data. Material flow behaviour, cutting chip characteristics, cutting forces and specific cutting energy, yielding stresses, stress and temperature on the cutting edge of the diamond tool, tool wear, defect-mediated plasticity and amorphization processes were calculated and analysed to quantify the differences in the cutting behaviour at different temperatures. Furthermore, In-situ high temperature nanoscratching (~500°C) of silicon wafer under reduced oxygen condition through an overpressure of pure Argon was carried out using a Berkovich tip with a ramp load at low and high scratching speeds. Ex-situ Raman spectroscopy and AFM analysis were performed to characterize high pressure phase transformation, nanoscratch topography, nanoscratch hardness and condition of the nanoindenter tip in nanoscratching at room and elevated temperatures.MD simulation results showed that the workpiece atoms underneath the cutting tool experienced a rotational flow akin to fluids. Moreover, the degree of flow in terms of vorticity was found higher on the (111) crystal plane, signifying better machinability on this orientation. Furthermore, it was observed that the degree of turbulence in the machining zone increases linearly with machining operation temperature. The cutting temperature showed significant dependence on the location and position of the stagnation region in the cutting zone of the substrate. In general, when cutting was performed on the (111) plane, the stagnation region (irrespective of the cutting temperature) was observed to locate at an upper position than that for the (010) and (110) planes. Also, at high temperatures, the stagnation region was observed to shift downwards than what was observed at room temperature. Another point of interest was the increase of subsurface deformation depth of the workpiece while cutting the (111) crystal plane at elevated temperatures.;Dislocation nucleation and formation of stacking faults were identified in conjunction with amorphization of silicon as the meditators of crystal plasticity in single crystal silicon during nanometric cutting process on different crystallographic planes at various temperatures. MD simulations revealed strong anisotropic dependence behaviour of dislocation activation and stacking fault formation. Likewise, while cutting 3C-SiC on the (110), formation and subsequent annihilation of stacking fault-couple at high temperatures, i.e. 2000 K and 3000 K, and generation of the cross-junctions between pairs of counter stacking faults meditated by the gliding of Shockley partials at 3000 K were observed. An observation of particular interest, while cutting 3C-SiC, was the shift to the (110) cleavage at cutting temperatures higher than 2000 K. The initial response of both the silicon and 3C-SiC substrates was found to be solid-state amorphization for all the studied cases. Further analysis through virtual X-ray diffraction (XRD) and radial distribution function (RDF) showed the crystal quality and structural changes of the substrate during nanometric cutting. No symptom of any atom-by-atom attrition wear and plastic deformation of the diamond cutting tool was observed during nanometric cutting of silicon irrespective of the cutting plane or the cutting temperature under vacuum condition. However, while cutting 3C-SiC, cutting tool showed severe wear and plastic deformation. It was found that the atom-by-atom attrition wear and plastic deformation of the diamond cutting tool could be alleviated while cutting 3C-SiC at high temperatures. Nevertheless, chemical wear i.e. dissolution-diffusion and adhesion wear is plausible to be accelerated at high temperatures.Raman spectroscopy was successfully used to identify the formation of metastable silicon phases during nanoscratching experiments at room and high temperatures. The probability of forming high pressure phases of Si-III and Si-XII was found to increase above the threshold load of 5 mN during room temperature nanoscratching experiment at low scratching speed. At high scratching speed, small remnants of Si-XII and Si-III phases were detected when the scratching load was greater than a threshold value i.e. ~9.5 mN. When high temperature nanoscratching was carried out at low and high speeds, no remnants of polymorph phases were observed along the nanoscratch residual track, suggesting the transition of metastable silicon phases (Si-III and Si-XII) into thermodynamic stable Si-I. Further analysis using AFM showed that the residual scratch morphologies and nanoscratch hardness were profoundly influenced by the temperature and scratching speed