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The tribological behavior of traditional oil-in-water (O/W) lubricants (1.0 wt.%) and nano-TiO2 additive lubricants (1.0–9.0 wt.%) during micro rolling of titanium foils were analyzed. In this study, the surface morphologies of titanium foils under various lubrication conditions were assessed, and the corresponding lubrication mechanisms were revealed. The tribological behavior of nano-TiO2 additive lubricants during micro rolling of titanium foils was also explored through a series of characterization methods. The utilization of nano-TiO2 additive lubricants in micro rolling reduces the surface roughness of titanium foils. Moreover, it effectively inhibits the generation of indentations and cracks during rolling processes, enhancing the surface quality of rolled specimens. Additionally, owing to the synergism of rolling, tribo-film, mending and polishing effects of the nanoparticles, both the rolling force and surface roughness were minimized by using lubricants containing 3.0 wt.% TiO2 nanoparticles. Overall, an optimal concentration (3.0 wt.%) of TiO2 nanoparticles in water-based nanolubricants was obtained with enhanced tribological properties and lubrication performance during micro rolling of titanium foils. [ABSTRACT FROM AUTHOR]

In this work, an experimental investigation on the lubrication performance of water-based nanolubricant with TiO2 as nanoadditives was performed. The nanolubricants show excellent dispersibility and stability within 5 days after preparation. Additionally, the results show that the concentration of TiO2 nanoparticles significantly affects the lubrication performance of the prepared nanolubricant during microrolling. The excessive nanoparticles lead to agglomeration at the contact area, while the limited nanoparticles can hardly work during rolling processes. Instead, for a nanolubricant with 3.0 wt% of TiO2 nanoparticles, the nanolubricant is able to feed abundant nanoparticles continuously to the rubbing zone with little agglomeration, improving the surface quality of copper foils during microrolling. [ABSTRACT FROM AUTHOR]

To improve the quality of products produced from microforming, various nanolubricants have been applied in the field of micromanufacturing in recent years. In this paper, the effects of glycerol-based lubricant containing TiO2 NPs (NPs) on micro deep drawing (MDD) of austenitic stainless steel (ASS) SUS301 were studied, and the lubrication mechanism involved was discussed. The MDD experiments were conducted with the SUS301 foils under dry, 1, 2, and 4 wt% TiO2 NP lubrication conditions. The results show that the use of the TiO2 nanolubricants can significantly improve the quality of the drawn cups in terms of decreased wrinkling and surface roughness. Besides, the concentration of TiO2 NPs influences lubricity by reducing friction during the MDD process. The peak drawing force is the lowest when 2 wt% nanolubricant is applied, which drops to 72.54 N from 77.38 N under dry conditions. The micro cup drawn under 2 wt% TiO2 nanolubricant has the best quality among those obtained under all the lubrication conditions. The lubrication mechanisms are derived from the mending effects of TiO2 NPs and the formation of thin lubricant films associated with the open lubricant pockets (OLPs) and close lubricant pocket (CLPs) theory in the MDD. The CLPs function as reservoirs that retain lubricants to counteract the load pressure, whereas the OLPs lead to lubricant leakage due to the higher flow resistance. It was found that the lubricant film and NPs are insufficient at a low concentration (1 wt%), while the lubrication performance can be enhanced with increased NP concentration. However, there exist apparent agglomerations on the surface of the produced micro cup when using 4 wt% nanolubricant, which greatly deteriorates the lubricant performance in the MDD process. It is concluded that the lubricant containing 2 wt% TiO2 NPs demonstrates the best lubrication performance during the MDD of ASS SUS301. [ABSTRACT FROM AUTHOR]

Micro deep drawing (MDD) is a fundamental process in microforming which has wide applications in micro electromechanical system (MEMS) and biological engineering. Titanium possesses excellent mechanical properties and biocompatibility, which makes it a preferred material in micromanufacturing. In this study, eco-friendly and low-cost water-based TiO2 nanolubricants were developed and applied in the MDD with 40 μm-thick pure titanium foils. The lubricants consisting of TiO2 nanoparticles (NPs), 10 wt% glycerol, 0.1 wt% sodium dodecyl-benzene sulfonate (SDBS) and balanced water were synthesised in a facile process. The MDD with 40 μm-thick pure titanium was carried out using the lubricants with varying concentrations of 0.5, 1.0 and 2.0 wt%. The results show that the formability of micro cups could be significantly improved when the nanolubricants are applied. Especially, the use of 1.0 wt% TiO2 nanolubricant demonstrates the best lubrication performance by significantly reducing the final drawing forces, and surface roughness, and the wrinkles by up to 24.2%, 12.55% and 4.82%, respectively. The lubrication mechanisms including the ball bearing and mending effects of NPs on open lubricant pockets (OLPs) and close lubricant pockets (CLPs) areas were then revealed through microstructure observation. [ABSTRACT FROM AUTHOR]

Effects of various lubrication conditions on macroscale deep drawing have been investigated extensively while in microscale due to the open and closed lubrication pocket theory and friction coefficient escalation, proper lubricant concern becomes severe. Microforming is used to produce lighter and more energy-effective products accordingly; in this study, magnesium-lithium (Mg-Li) alloy is chosen to form a superior micro-cup due to its ultralight weight with outstanding ductility. Mg-Li is a new material in microscale; consequently, to study the mechanical properties, a heat treatment process is performed. The dry and oil lubrication conditions are chosen as benchmarks to investigate effects of TiO2 oil-based nano-additive lubricant. Finite element (FE) modelling has been conducted and the simulated results are agreed well with the experimental results where the drawing force is significantly affected by the nano-particle. The formed cup quality regarding the surface roughness has been evaluated extensively by consideration of various parameters and the quality improvement is substantial. [ABSTRACT FROM AUTHOR]

The formation and performance of oxide scale on a low-alloy steel were investigated during hot rolling at 850 and 950 °C under various lubrication conditions, including benchmarks (dry condition and water) and water-based nanolubricants containing various concentrations of nano-TiO2 from 1.0 to 8.0 wt%. The results showed that the addition of nano-TiO2 particles in the lubricant significantly reduced the thickness of oxide scale and surface oxide roughness. The reduction reached the maximum when the concentration of TiO2 was 4.0 wt%. Detailed oxide phase characterisation and oxide component fraction determination revealed that hot rolling destroyed the conventional multi-layer oxide scale and promoted magnetite and haematite formation because of easy access of oxygen from the deformed structure. The effect of TiO2 was explained by the decrease in the rolling force, which led to a higher fraction of dense retaining wustite and therefore reduced the extent of further oxidation. Increasing temperature did not change the trend of lubrication effect but raised the rate of steel oxidation in general. [ABSTRACT FROM AUTHOR]

Surface asperities take a large part of a thin blank in micro-sheet forming processes. Contact and friction significantly affect micro-sheet forming and cannot be simplified as homogeneous in simulation. Material heterogeneity of the blank further affects the friction and its impact becomes significant in micro-scale. In this study, a FE model representing surface morphology of SUS304 sheets was built for micro deep drawing simulation. Each node on the blank model had the same height as an asperity. Key surface morphological characters of the blank can be presented with a proper mesh density. The material size effects were presented via refined material properties assignment based on sheets’ microstructures. Due to the initial surface morphology, wear accumulation and thickness distribution were significantly affected. Experimental results well validated prediction of worst worn area on drawn cup mouth in simulation. Surface roughening which affects shape accuracy in the micro-scale was affected by the wear behaviour during the drawing process. Thus, different roughening behaviours at three divided areas on the drawn cup were wall explained. [ABSTRACT FROM AUTHOR]

The stress state is an important parameter in metal forming processes, which significantly influences the strain state and microstructure of products, affecting their surface qualities. In order to make the metal products have a good surface quality, the surface stress state must be optimised. In this study, two classical methods, the upper bound method and the crystal plasticity finite element method, were investigated. The differences between the two methods were discussed in regard to the model, the velocity field, and the strain field. Then the related surface roughness is deduced. [ABSTRACT FROM AUTHOR]

The breakaway oxidation behaviour of ferritic stainless steels 430, 443 and 445 has been investigated at 1150 °C in humid air. The oxidation kinetics exhibited significant differences among the three ferritic stainless steels. A uniform and steady growing oxide scale was developed on the 430 steel with an even steel/oxide interface. Local breakdown of the initially protective oxide scale occurred and oxide nodules were developed on the 443 and 445 stainless steels, resulting in irregular and rough steel/oxide interfaces. The breakaway oxidation behaviour was significantly influenced by the microstructure and the composition of the oxide scale. The Mn-Cr spinel oxide formed on top of the Cr 2 O 3 scale in Mo alloying 445 steel can greatly minimise the Cr depletion. [ABSTRACT FROM AUTHOR]

Surface roughness, compared with tiny sizes of micro products, can be relatively large and has significant influences on micro forming processes and products’ quality. In this study, a voronoi finite element model that considers size effects of material was developed. Next the surface roughness information was assigned to this voronoi model through different elemental thickness distributions. Furthermore, springback simulation was conducted for the micro deep drawn circular cups. Simulation results demonstrate that the surface roughness with consideration of size effects has significant influences on the overall springback, the drawability represented by the minimum thickness and products’ quality regarding thickness evenness and shape accuracy. This study also shows that the results from the new models are close to the experimental results concerning the diameter of cup mouth and the maximum drawing force. The developed model for the micro deep drawing is accurate and beneficial for the development of micro deep drawing process. [ABSTRACT FROM AUTHOR]

Physical parameters such as microscopic roughness become very important in micro forming process due to increasing surface to volume ratio. As a very important phenomenon in metal forming process, friction size effects are becoming more attracting for researchers because traditional models are not reliable. In this study, the micro rolling deformation characterization has been investigated with SUS 304 stainless steel considering the effect of lubricant, and there exists a sticking area in the contact zone. The evolution of surface roughness and oil film thickness are analyzed. The foil thickness plays an important role in the tribological features of rolling. All the results have been verified experimentally via the desktop 2-Hi micro rolling mills. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, a multi-factor coupling dynamic model of a rolling mill system for a dynamic roll gap during an unsteady lubrication process was developed on the basis of the rolling theory, lubrication and the friction theory, and the mechanical vibration theory. The multi-factor coupling model of interfacial film binding was coupled with the rolling force model, dynamic roll gap interface friction model and work roll movement model. The corresponding distributions of friction and pressure at varying surface roughness and times were systematically analyzed during the unsteady mixed lubrication process. The effects of the main processing parameters on the critical speed and amplitude for self-excited vertical vibration were investigated. [Copyright &y& Elsevier]

Abstract: During the uniaxial planar compression of annealed aluminum alloy, a novel approach to determine surface asperity flattening (roughness R a ) is employed by analyzing the evolution of surface microtexture. With an increase in gauged reduction, surface asperity tends to be flattened, and strain hardening increases. Lubrication can constrain the surface asperity flattening process. Development of surface asperity features shows the obvious dependency on [111] orientation. In-grain slips contribute significantly to the evolution of surface microtexture. Influence of deformation twins (brass orientation) on the evolution of microtexture is not obvious under our current experimental conditions. [Copyright &y& Elsevier]

Micro-hydromechanical deep drawing (MHDD) is a promising micro-manufacturing technology to fabricate micro-metallic products in batch scale. Size effects significantly affect MHDD regarding both material properties and friction. Hydraulic pressure on the blank and its development differ from that in conventional hydromechanical deep drawing. Combined influence of fluid pressure, surface roughness and material inhomogeneity of the blank was investigated in this study via MHDD experiments and advanced FE simulation considering strong fluid-solid interaction (FSI) and size effects. The MHDD experiments under different hydraulic pressures were conducted using the annealed foil followed by the advanced FE simulation. The foil can be successfully drawn into micro-cups, however, wrinkles occurred under high hydraulic pressures. Wrinkle height and number are affected by hydraulic pressure and size effects. Average hydraulic pressure on the blank is lower than the inlet pressure, and pressure development on the blank depends on location and is complex, due to transition of sealing between the blank and die. The maximum drawing force increases, while the contact forces and pressures on the blank holder and die decrease with an increase of hydraulic pressure. Optimal hydraulic pressure for MHDD should be determined with consideration of size effects and MHDD tool geometry. • Micro-hydromechanical deep drawing experiments and advanced simulation with consideration of FSI, material surface morphology and inhomogeneity were conducted. • Change of the sealing between the blank and die significantly affects mean and local hydraulic pressure development on the blank, which further impacts MHDD. • Hydraulic pressure reduces contact forces and maximum contact pressures on both blank holder and die, which benefits wear behaviour of MHDD tools. • Integrated effect of hydraulic pressure and size effects influences wrinkling. • Optimal hydraulic pressure should be determined with consideration of foil's properties and MHDD tool geometry. [ABSTRACT FROM AUTHOR]

Eco-friendly and low-cost water-based nanolubricants containing rutile TiO2 nanoparticles (NPs) were developed for accelerating their applications in industrial-scale hot steel rolling. The lubrication performance of developed nanolubricants was evaluated in a 2-high Hille 100 experimental rolling mill at a rolling temperature of 850 °C in comparison to that of pure water. The results indicate that the use of nanolubricant enables one to decrease the rolling force, reduce the surface roughness and the oxide scale thickness, and enhance the surface hardness. In particular, the nanolubricant consisting of 4 wt % TiO2, 10 wt % glycerol, 0.2 wt % sodium dodecyl benzene sulfonate (SDBS) and 1 wt % Snailcool exhibits the best lubrication performance by lowering the rolling force, surface roughness and oxide scale thickness by up to 8.1%, 53.7% and 50%, respectively. The surface hardness is increased by 4.4%. The corresponding lubrication mechanisms are attributed to its superior wettability and thermal conductivity associated with the synergistic effect of rolling, mending and laminae forming that are contributed by TiO2 NPs. [ABSTRACT FROM AUTHOR]

A comprehensive research on the flat rolling deformation characterization of microwire has been conducted systematically through finite element simulation and testified by the results from the experimental analysis. The obtained results are compared in terms of lateral spread, geometrical characteristic, contact area width and surface roughness considering the effects of pass reduction and initial wire diameter. The size effect has been identified and surface layer modeling has been set up based on surface grain share and grain size distribution. The numerical method combined with varied flow stress has been verified by experimental value with a maximum difference of 3.7% for the 1.5 mm wire. With the increase of the height reduction, the curvature radius is decreased while the lateral spread and contact area width are increased. Surface roughness evolution in the range of 0.52–0.85 µm for the rolled wire has also been investigated. [ABSTRACT FROM AUTHOR]

Hot rolling tests of a low-alloy steel were conducted at a rolling temperature of 850 °C under different lubrication conditions, including benchmarks (dry condition and water) and water-based nanolubricants containing different concentrations of nano-TiO2 from 1.0 to 8.0 wt%. The effects of nanolubricants on rolling force, surface roughness, thickness of oxide scale, and microstructure were systematically investigated through varying nano-TiO2 concentrations. The results show that the application of nanolubricants can decrease the rolling force, surface roughness and oxide scale thickness of rolled steels, and refine ferrite grains. In particular, the nanolubricant containing an optimal concentration (4.0 wt%) of nano-TiO2 demonstrates the best lubrication performance, owing to the synergistic effect of lubricating film, rolling, polishing, and mending generated by nano-TiO2. [ABSTRACT FROM AUTHOR]

• Crystal plasticity finite element model exhibits higher accuracy in evaluation of surface roughness and thickness distribution of cups fabricated by micro deep drawing. • The magnitude of surface roughness S z is almost linearly dependent on the average grain size of austenitic stainless steel foils. • The brass components are beneficial to the formation of drawn cups with uniform thickness distribution and the absence of severe defects. The present work involves the numerical simulation and experimental study on the surface roughness evolution and heterogeneous plastic deformation (strain localization and concomitant surface morphology evolution) in grain scale of micro deep drawn parts of austenitic stainless steel (ASS) 304 foils. A three-dimensional modeling framework was used to simulate the micro deep drawing (MDD) process. The simulation involved the development of a Voronoi-based polycrystalline geometry model (VPGM), a multi-stress-strain response model, and a crystal plasticity finite element methods (CPFEM) model. The results indicate that CPFEM model exhibits higher accuracy in the localized stress and strain, thickness distribution fluctuation and surface roughness evolution of the fabricated parts compared to multi-stress-strain response model. Therefore, the plastic deformation heterogeneity in MDD is in-depth discussed based on CPFEM model. The results show that the coarse-grained foils correspond to the intense strain localization, which is the main cause of surface roughening. Considering the average grain size is close to the thickness of ASS foils, mounding features on the rough surface may readily develop further into potentially fractured sites during deformation. On the other hand, crystal orientation influence plastic deformation by affecting the slip behavior of materials. The effect of crystal orientations including {011} 〈211〉 (Brass), {011} 〈100〉 (Goss), and {112} 〈110〉 components on deformation is discussed. The results indicate a strong correlation between the magnitude of the Schmid's factor and the ease of deformation. Additionally, variations in Schmid's factor across different directions result in differences in deformation accumulation, which affects the thickness distribution along the radial direction and the distribution of earrings and wrinkles along the circumferential direction of the fabricated micro parts. [ABSTRACT FROM AUTHOR]

In this paper, hot rolling tests of low-carbon steel were carried out on a 2-high Hille 100 experimental rolling mill at various speeds and reductions. The rolling temperatures were between 1000 and 1030 °C. Nitrogen protection was used to control the scale thickness when the test samples were heated in the furnace and cooled in a cooling box. The rolling forces, rolling torques and scale thicknesses before and after rolling were measured. Surface characteristics of the steel samples were analyzed with SEM and Atomic Force Microscope (AFM). X-ray diffraction was performed to characterize the phase composition of the scale layers. The effects of scale thickness on rolling force and torque were also investigated. [Copyright &y& Elsevier]

Experimental simulation of oxidation scales during hot strip rolling was carried out on a GLEEBLE-3500 thermo-mechanical simulator. Specimens made of low carbon mild steel were exposed to air and water mist for 0.6–160 s at 800, 900 and 1000 °C. The atmosphere before and after carrying out oxidation was carefully controlled in order to get designated period of time of oxidation at constant temperature. Surface profile characteristics before and after oxidation were examined with atomic force microscope (AFM). An explicit surface profile transformation after oxidation was exhibited by the three-dimensional images from AFM. Oxide scale surface characteristics were investigated with roughness, section, power spectrum and particle distribution analysis. [Copyright &y& Elsevier]

Thin strip with varying thickness, a novel structural and functional material, is fabricated by micro flexible rolling, and has three thickness features including the thicker zone, the thinner zone and the transition zone. Rolling and roll lifting speeds determine the thickness distributions, and have a great influence on the surface roughness, then the final product quality which is of significant importance for thin materials in subsequent processing. In this study, surface roughness alteration of aluminium alloy strips during micro flexible rolling was investigated with considering the influences of rolling speeds, roll lifting speeds, thickness ratios (the ratio of the thicker zone to the thinner zone) and lubrication conditions, and the mechanisms were discussed. The results show that rolling parameters have a significant effect on the alteration of surface roughness from the thicker zone to the thinner zone along the rolling direction. The experimental observations indicate that the surface roughness of thin strips with varying thicknesses presents a decreasing tendency with the increase of contact area results from downward rolling phase along the transition zone, however, it is constantly higher than that in the upward rolling phase. • Surface roughness alters in different thickness zones and rolling phases. • Directional skewness of asperities varies on the smoother and rougher roll cases. • The alteration of surface roughness with diverse rolling and roll lifting speeds. • Oil pool results in surface roughness alteration between different rolling phases. [ABSTRACT FROM AUTHOR]

In this paper, oil-in-water (O/W) based nanolubricants containing TiO 2 nanoparticles were developed to reduce the rolling force and improve the surface quality of rolled 304 stainless steel product. Practical hot rolling tests with and without application of lubricant were conducted to systematically investigate the effects of the developed O/W based nanolubricants on the rolling force, surface roughness, oxide scale thickness and tribological behaviour. The obtained results indicate that the nanoparticles can enter the deform zone with oil droplets to take a lubrication effect. The optimal lubrication effect can be achieved when the O/W (1% oil mass fraction) based nanolubricant with a TiO 2 mass fraction of 1.5% was applied. The microstructure of oxide scales formed on the hot rolled sample was not significantly affected by TiO 2 nanoparticles in the O/W based lubricant, but the oxide scale growth could be induced by TiO 2 nanoparticles. A discontinuous thin SiO 2 layer at the substrate-scale interface was observed. It can effectively reduce the formation of iron-rich oxides. The novel nanolubricant has a great potential to be applied in the hot steel rolling, to realise the cost-effective and environmental-friendly manufacturing process. [ABSTRACT FROM AUTHOR]

In this study, the micro deep drawing (MDD) experiments of an austenitic stainless steel with 40 μm in thickness were conducted using the lubricants containing different mass fractions of graphene nanosheets (GNS) in ethanol. Prior to the MDD tests, the lubricants with GNS concentrations of 5, 10, and 15 mg/ml were synthesised by mixing different amounts of GNS with pure ethanol, and then sprayed uniformly on the blank surface. The friction-reduction mechanisms of the GNS in the MDD were discussed by analysing the profile and surface roughness of the microcups. The results indicated that the GNS could reduce the friction and improve the surface quality of the micro products during the MDD process. In particular, the lubricant with 10 mg/ml GNS enabled the lowest drawing force, wrinkling, and surface roughness of the drawn microcup. These findings contribute to a better understanding of the friction-reduction mechanisms of using GNS in the MDD of materials. • The coating behaviour of the graphene lubricants are compared. • The role of graphene lubricant in micro deep drawing is shown to be important in reducing the friction. • The effect of utilising graphene lubricants for improving the quality of the micro cups is demonstrated. [ABSTRACT FROM AUTHOR]

Oil-in-water (O/W) emulsion is widely applied as a lubricant during hot rolling process. For reducing environmental impact caused by O/W emulsion, a novel nano-TiO 2 additive O/W lubricant with improved stability and reduced coefficient of friction (COF) is developed. Little research, however, has been focused on the growth behaviour of oxide scale formed on the workpiece surface and its effects on the tribological property of nano-TiO 2 additive O/W lubricant. In the current work, oxidation tests of high strength steel were conducted to investigate the growth behaviour of oxide scale and obtain different surface morphologies of the oxide scale. Ball-on-disk tribological tests under a temperature of 80 °C were carried out to investigate the effects of surface morphology of oxide scale on the tribological behaviour under nano-TiO 2 additive O/W lubrication. The performance of the new developed lubricant was evaluated by hot rolling process. The growth mechanism of oxide scale and the modified oxide scale growth model were proposed. Tribological results indicate that oxide scale plays an important role in the tribological behaviour of nano-TiO 2 additive O/W lubricant. A reduction in surface roughness can result in a decrease of COF, while the COF will increase if the surface roughness reduces too much because some of the nano-TiO 2 particles cannot go through the contact area to play a positive role in lubrication. [ABSTRACT FROM AUTHOR]

To comprehend the role of water-based nanolubricant in micro flexible rolling, corresponding characterisation with respect to different concentrations of nanolubricants, surface roughness variation subjected to each micro flexible rolling phase and dispersion of nanoparticles (NPs) were studied systematically. The results reveal that increasing NPs get trapped into the surfaces from the thicker zone to the thinner zone. Downward transition zone with favourable deformation features leads to the smoother surface roughness. Nanolubricants can effectively decrease rolling traces due to the beneficial nanolubrication mechanisms. Notably, the maximum reduction for rolling force is around 18% for the case under 2.0 wt% nanolubricant rolling condition. The current study provides great potential insights in how nanolubrication takes effect in microforming areas. • Water-based nanolubricants distinctly reduce the rolling forces during micro flexible rolling. • Increasing NPs get trapped into the surfaces from the thicker zone to the thinner zone. • Downward transition zone with favourable deformation features leads to the smoother surface roughness. • More remained NPs are detected near the middle area along the transverse direction of the specimen. • Water-based nanolubricants can effectively decrease rolling traces due to the beneficial nanolubrication mechanisms. [ABSTRACT FROM AUTHOR]

Water-based slurries with silica (SiO 2) nanoparticles, graphene oxide (GO) nanosheets and GO/SiO 2 hybrid nanostructures as abrasives were synthesised in order to achieve a high-efficiency and low-damage lapping. Tribological characteristics of SiO 2 , GO and GO/SiO 2 nanoslurries were systematically investigated to optimise slurry formulae, and the lubricating mechanisms involved were revealed based on the analyses of worn surfaces and used slurries. Machining performance of the optimised slurries was then examined in the fixed abrasive lapping of glass substrates in terms of surface quality and material removal. The GO/SiO 2 slurry of 0.16 wt.% at a mass ratio of 1:1 generated a lubricating layer consisting of C deposited and SiO 2 dynamic films at the rubbing interface. This improved friction and wear conditions at the contact, producing a significantly lower COF and a better worn surface quality than those slurries containing only GO or SiO 2. The lapping with the GO/SiO 2 slurry thus reduced the surface damage on glass and achieved a crack-free subsurface. In comparison with a conventional lapping, the new lapping process resulted in a 35% reduction in surface roughness, but a 28% increase in material removal rate. Such improvements were attributed to the synergistic lubrication behaviour of the formed nanostructures of GO/SiO 2 in water. [ABSTRACT FROM AUTHOR]