Cube Corner Indenter Research Articles

Theoretical and experimental investigation of vibration-assisted scratching silicon

Interaction between tip and workpiece plays a crucial role in determining the scratching depth in Vibration-assisted Tip Based Nanofabrication (VTBN), which is more complicated than that of conventional scratching (without vibration-assisted). To establish the relationship between the scratching depth and machining parameters, a cubecorner indenter is employed to conduct VTBN procedure. The indenter is simplified as a cone to calculate the contact model in both 1D groove and 2D surface machining processes. An instantaneous normal load model is established based on the developed tip-workpiece contact model. Due to the variation of instantaneous contact area, effective contact area is put forward for the first time to predict the normal load. Effects of vibration frequency and amplitude on the normal load and surface quality are analyzed based on the proposed model. Experimental results show that higher frequency and larger amplitude will reduce the effective contact area. Vibration can increase the scratching depth and width without enlarging the cutting force. Furthermore, the inconsistency caused by scratching directions in conventional scratching is also overcome during VTBN.

Influence of mechanical properties on material deformation behavior of different ceramics in scratching

To understand the differences in material removal behavior during grinding for different ceramics, scratching of Al2O3, AlN, Si3N4 and ZrO2 (3Y-TZP) ceramics by a cube-corner diamond indenter was investigated in this paper. Scratching characteristics, including material deformation, scratching force, coefficient of friction (COF) and scratching damage of different ceramics were compared and analyzed. Elastic recovery rate model and stress field model were built to analyze the mechanism of material deformation and scratching damage during scratching on different ceramics. The results demonstrated that material deformation behaviors vary significantly, and depend on mechanical properties of the ceramics. Ceramics with higher hardness exhibit shallower penetration depth of scratching, while higher fracture toughness results in shorter maximum surface damage distance. Elastic recovery rate model can predict the extent of material deformation. The ceramic with the highest elastic recovery rate is Al2O3, followed by Si3N4, ZrO2, and finally AlN. Elastic recovery rate decreases with increase in force. In stress field model, AlN exhibits the highest maximum principal stress, followed by Al2O3 and Si3N4, with ZrO2 displaying the lowest stress. These distribution patterns are consistent with the results of scratching damage pattern.

The damage mechanism in copper studied using in situ TEM nanoindentation.

Copper (Cu) has a soft-plastic nature, which makes it susceptible to damages from scratching or abrasive machining, such as lapping and polishing. It is a challenge to control these damages as the damage mechanism is elusive. Nonetheless, controlling damages is essential, especially on the atomic surfaces of Cu. To interpret the damage mechanism, in situ transmission electron microscopy (TEM) nanoindentation was performed using a cube-corner indenter with a radius of 57 nm at a loading speed of 5 nm s-1. Experimental results showed that damages originate from dislocations, evolve to stack faults, and then form broken crystallites. When the indentation depth was 45 nm at a load of 20 μN, damages comprised dislocations and stacking faults. After increasing the depth to 67 nm and load to 30 μN, the formation of broken crystallites initiated; and the critical depth was 67 nm. To validate the damage mechanism, fixed-abrasive lapping, mechanical polishing, and chemical mechanical polishing (CMP) were conducted. Firstly, a novel green CMP slurry containing silica, hydrogen peroxide, and aspartic acid was developed. After CMP, a surface roughness Ra of 0.2 nm was achieved with a scanning area of 50 μm × 50 μm; and the thickness of the damaged layer was 3.1 nm, which included a few micro-stacking faults. Lapping and mechanical polishing were carried out using a silicon carbide plate and cerium slurry, with surface roughness Ra values of 16.42 and 1.74 nm, respectively. The damaged layer of the former with a thickness of 300 nm comprised broken crystallites, dislocations, and stacking faults and that of the latter with a thickness of 33 nm involved several stacking faults. This verifies that the damage mechanism derived from in situ TEM nanoindentation is in agreement with lapping and polishing. These outcomes propose new insights into understanding the origin of damages and controlling them, as well as obtaining atomic surfaces using a novel green CMP technique for soft-plastic metals.

Orientation-dependent hardness of Mo3Si studied by cube-corner nanoindentation

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Investigation of cutting depth and contact area in nanoindenter scratching

Nanostructures are widely used in various industries. Nanoscratching is an important technique for fabricating nanostructures. The cutting depth in nanoscratching is a crucial parameter that is closely related to the normal force, material properties, and tip geometry. Current prediction models are only suitable for some specific processing conditions. To extend the scope of application of prediction model, a comprehensive model is proposed. In the developed model, the indenter tip is divided into three parts: a spherical crown, transition part, and pyramid base. Accordingly, a comprehensive contact model considering elastic recovery is developed in the edge-forward, face-forward and side-forward directions based on the indenter tip geometry. The computational results indicate that face-forward nanoscratching with a conventional cube-corner indenter has the smallest contact area compared to edge-forward and side-forward nanoscratching. It is noted that the established model can reduce the prediction error by more than 10% compared with the current models when the cutting depth is lower than the tip radius. The influence of the indenter geometry is analysed based on this model. The geometric shape of the indenter has a significant influence on the contact area, and the face angle of the pyramid is the key factor. The proposed model is validated by numerous nanoscratching experiments.

Face Turning of Single Crystal (111)Ge: Cutting Mechanics and Surface/Subsurface Characteristics

Abstract Single crystal Ge is a semiconductor that has broad applications, especially in manipulation of infrared light. Diamond machining enables the efficient production of surfaces with tolerances required by the optical industry. During machining of anisotropic single crystals, the cutting direction with respect to the in-plane lattice orientation plays a fundamental role in the final quality of the surface and subsurface. In this study, on-axis face turning experiments were performed on an undoped (111)Ge wafer to investigate the effects of crystal anisotropy and feedrate on the surface and subsurface conditions. Atomic force microscopy and scanning white light interferometry were used to characterize the presence of brittle fracture on the machined surfaces and to evaluate the resultant surface roughness. Raman spectroscopy was performed to evaluate the residual stresses and lattice disorder induced by the tool during machining. Nanoindentation with Berkovich and cube corner indenter tips was performed to evaluate elastic modulus, hardness, and fracture toughness of the machined surfaces and to study their variations with feedrate and cutting direction. Post-indentation studies of selected indentations were also performed to characterize the corresponding quasi-plasticity mechanisms. It was found that an increase of feedrate produced a rotation of the resultant force imparted by the tool indicating a shift from indentation-dominant to cutting-dominant behavior. Fracture increased with the feedrate and showed a higher propensity when the cutting direction belonged to the <112¯> family.

Development of TaC-based transition metal carbide superlattices via compound target magnetron sputtering

Transition metal carbides belong to ultra-high temperature ceramics and are particularly valued for their high thermal and mechanical stability as well as melting points of even above 4000 °C. However, a considerable limitation of these materials is their high inherent brittleness. Inspired by the success of nanolayered superlattice architecture—shown to enhance both hardness and toughness of transition metal (TM) nitrides—we developed superlattice films with TM carbides. Among these, density functional theory calculations suggest TaC/HfC and TiC/TaC to have a similar shear modulus mismatch of 23 and 19 GPa, but a different lattice parameter mismatch of 4.2 and 2.4%, respectively. Detailed transmission electron microscopy and X-ray diffraction show a pronounced superlattice structure for TiC/TaC with nominal bilayer periods Λnom of 2, 6, and 10 nm. Contrary, the TaC/HfC showed a more solid solution like characteristic for Λnom = 2 nm, and a clear superlattice structure for Λnom = 6 and 10 nmjap. While the hardness of the TaC/HfC coatings is between those of their constituents TaC (33.3 ± 1.9 GPa) and HfC (37.4 ± 3.2 GPa), the TiC/TaC superlattices outperform their constituents and clearly show a superlattice-effect with a peak of 44.1 ± 3.4 GPa at Λnom = 2 nm (TiC has 37.6 ± 3.1 GPa). Also the qualitative fracture behavior investigation with 450-mN-loaded cube corner indentation yield the TiC/TaC superlattices to be superior to the TaC/HfC as well as the monolithically prepared TiC, TaC, and HfC coatings.

Discrepancies in Nanoindentation Hardness and Modulus with a Berkovich, a Cube-corner, and a Conical Tip in a Cu(In,Ga)Se2 Light-Absorption Layer

In this study, we tried to understand the difference in the mechanical properties (elastic modulus, E & hardness, H) values of CIGS compound semiconductors measured using the Berkovich indenter and the sharper cube corner and conical indenter. Adopted continuous stiffness measurement technique to characterize it along with the indentation depth. The depth was up to 1000 nm, and E and H values w ere obtained according to the depth. The projected contact area of the cube edge and the conical indenter was calculated assuming the two indenters had an ideal shape. In the case of the Berkovich indenter, which is the subject of comparison, both calculated values assuming an ideal shape and experimental values were used. Cube-corner and conical tip showed lower load at the same depth of 1000 nm compared to Berkovich indenter. This means that the same depth of indentation was achieved even at a low load, which could affect the value of the mechanical properties of the thin film. The cube-corner tip and the conical tip have a sharp shape with a projected contact area about 6 times smaller than that of the Berkovich tip. It was observed that not only the effect of grain boundaries of the microstructure of the CIGS thin film, but also the effect of reflecting the characteristics of the Mo substrate had a significant effect on the mechanical properties of the CIGS thin film.

Role of indenter geometry on the deformation behavior in a Pd-Si based metallic and nanoglass

Nanoindentation experiments are performed on a binary Pd-Si metallic glass (MG) and nanoglass (NG) using Berkovich and cube-corner indenters to investigate the effect of indenter geometry on the deformation behavior. A large number of pop-ins in the load vs. displacement curves and a higher pile-up of material around the indenter are observed for sharper cube-corner indenter compared to the Berkovich indenter. In case of both the indenters, NG displays lower hardness than the MG due to the presence of higher free volume and lack of any clusters in the glassy grains or interfaces. Further, the hardness is observed to decrease with indentation load signifying the indentation size effect (ISE) in hardness. The discrete plasticity ratio, Ψ defined as the ratio of pop-in displacement, ∆hdis to the total displacement, htot is used to estimate the influence of serrations on total plastic deformation and characterize the nature of the plastic flow. The Ψ indicates that the deformation mode is independent of indenter geometry for both the glasses.

Identification of a soft matrix-hard inclusion material by indentation

A new procedure for identifying the mechanical behavior of individual phases within a bi-material (matrix-particles) is presented. The case of AlSi10Mg (large globularized Si-rich particles surrounded by an α-Al phase) processed by additive manufacturing and post-treated is taken as a typical example. Grids of nano-indentation tests are performed at different locations on the nanocomposite using a Berkovich indenter and show an impact of the hard inclusions on the experimental curves. The elastoplastic properties of the matrix are identified based on the lowest load–indentation depth curves. Several representative finite element (FE) models demonstrate the influence of the particles on the nano-indentation response. The capacity of the FE model to predict the indentation curve of a cube corner indenter experiment and the Berkovich grid result scattering was checked. A representative volume element (RVE) based on a scanning electron microscope (SEM) image is defined. The identified material parameters of the α-Al phase and Si phase, it allows the prediction of the stress-strain curve of a macroscopic experimental tensile test.

Crack Propagation Behavior of Fused Silica during Cyclic Indentation under Incremental Loads

Fused silica is an important optical material with important applications, where the surface must be precisely machined without subsurface damage. In this study, multi-cyclic indentations under incremental loads were performed on fused silica using two kinds of indenters to clarify the mechanisms of crack generation and propagation induced by precision grinding. It was found that incremental loading cyclic nanoindentation induced various patterns of subsurface cracking and surface spalling. Four kinds of surface spalling were identified at different locations around an indent, the temporal formation mechanisms of which were clarified by microscopic observation and topographical measurement. Load–displacement curve analysis demonstrated that incremental propagation of lateral cracks during early indentation cycles caused large-scale brittle fractures during later cycles. Compared with a Berkovich indenter, a cube-corner indenter caused more significant brittle fractures and surface spalling. The findings in this study will deepen the understanding of subsurface damaging mechanism of fused silica and other brittle solids caused by cyclic tool-workpiece interactions in grinding and other mechanical machining processes.

Heavy-element-alloying for toughness enhancement of hard nitrides on the example Ti-W-N

The low intrinsic fracture toughness of transition metal nitride thin films critically restrains their applicability as protective coatings. We therefore investigate the Ti1-xWxNy system to provide detailed theoretical and experimental insight into simultaneous hardening and toughening effects induced by heavy-element-alloying via an enhanced metallic bonding character. The combination of structural and chemical analyses – supported by density functional theory (DFT) calculations – demonstrates that the addition of W progressively increases the concentration of nitrogen vacancies in rocksalt (rs) structured Ti1-xWxNy. With increasing W content, the hardness H initially increases from 25.4±0.5 GPa (for TiN) to 31.1±0.8 GPa (for Ti0.55W0.45Ny) and then slightly decreases to 30.4±0.5 GPa (for Ti0.42W0.58Ny) – beautifully following classical solid solution hardening principles. Cube corner indentations yield a continuous increase in resistance against crack propagation and formation with increasing W content. The highest W containing coating studied here, Ti0.42W0.58Ny, even yields no radial crack formation but pile-up formation at the corners of the imprint – being an unambiguous sign for plastic flow. Although Ti0.62W0.38Ny exhibits the same growth morphology and columnar grain size (∼10 nm wide and 100 nm long) as Ti0.42W0.58Ny – with a similar hardness of 31.0±0.6 GPa – this coating still exhibits (short) radial cracks (without pile-up formation). DFT-calculated charge density maps suggest that the superior toughness-related performance of Ti1-xWxNy (with respect to TiN, which showed a pronounced radial crack formation) is linked to a metallisation of the interatomic bonds, being most pronounced for balanced W and Ti contents and N vacancies.

Nanoscratching on surfaces: the relationships between lateral force, normal force and normal displacement

Abstract The relationship between lateral force, normal force and normal displacement has been investigated. Surfaces of diverse materials were nanoscratched at constant rate. Nanoindents with cube corner, Berkovich or cono-spherical indenter indicate proportionality of (normal force) ~ (normal displacement)3/2 up to considerable forces, sometimes approaching the 10 mN range, but phase transformations under pressure may change the slope. This differs from the varying Meyer exponents reported at forces higher by two to three magnitudes when applied to Vickers indenters. Nanoscratching on diverse materials consistently reveals proportionality of (lateral force) ~ (normal force)3/2. This relationship is valid for amorphous (fused quartz) and crystalline materials such as silicon, silica, strontium titanate and the polar molecular crystals of thiohydantoin and nin-hydrin with hydrogen bonds, or pure van-der-Waals crystals of tetraphenylethylene. Anisotropies of the crystals and the type of destruction (breaking covalent bonds, or hydrogen bonds, or van-der-Waals interactions; abrasion, or molecular movements) do not affect the obviously universal relationship but only the proportionality factor with the dimension μN–0.5 which describes materials response to the scratching action for the particular crystal face and anisotropic direction. The new quantitative relationship is usable for the calculation of scratch work and of other quantities related to the lateral force on the basis of the new empirical constants. Both new relationships from nanoindents and nanoscratches are unified in the (lateral force) ~ (normal displacement)9/4 relationship and experimentally verified.

Investigation of the effect of Berkovich and Cube Corner indentations on the mechanical behavior of fused silica using molecular dynamics and finite element simulation

In this study, elastic modulus and hardness of fused silica were evaluated and then simulated by molecular dynamics (MD) and finite element analysis (FEA). The reduced modulus, hardness of the surfaces, and elastic modulus caused by the process along the depth of the indentation on the surfaces are evaluated by the nanoindentation method on the fused silica. The obtained results indicate that applying different indenters such as Berkovich and Cube-Corner reduces the amount and size of surface microcracks. The load-displacement of various indenters such as Berkovich and Cube-Corner with similar load at about 50 mN for the Berkovich shows a 400 nm displacement and a 1600 nm for the Cube-Corner indenter. In this study, the MD was used to describe the mechanical behavior of fused silica structures with atomic nanostructure as simulated at T0 = 300 K and P0 = 1 bar as the initial condition. The mechanical constants such as hardness (with Berkovich tip), elastic modulus (with Berkovich tip), and fracture toughness (with Cube Corner tip) of fused silica nanostructure can be calculated from this MD simulation in which the hardness of the atomic matrix is obtained at 8.84 GPa.

Mechanical properties and nanostructure of monolithic zeolitic imidazolate frameworks: a nanoindentation, nanospectroscopy, and finite element study

The synthesis of metal-organic frameworks (MOFs) in a monolithic morphology is a promising way to achieve the transition of this class of materials from academia to industrial applications. The sol-gel process has been widely used to produce MOF monoliths. It is relatively cheap and simple compared with other techniques (e.g. mechanical densification), and moreover, it allows to produce ‘pure’ monoliths, that is, without the need of using binders or templates that could affect the functional properties of the MOF. Understanding the mechanical properties of these monoliths is crucial for their transit to practical applications. We studied the mechanical behavior of two zeolitic imidazolate frameworks (ZIF-8 and ZIF-71) by means of instrumented nanoindentation and atomic force microscopy (AFM). Tip force microscopy (TFM), an extension of AFM, was used to reveal the surface nanostructure of the monoliths. We used finite element (FE) simulations alongside the experiments, to establish a suitable constitutive model and determine an improved estimate of the yield stress (σY) of ZIF monoliths. Nano-Fourier-transform infrared (nano-FTIR) spectroscopy was subsequently used to pinpoint local structural alteration of the framework in the contact area. The combination of TFM, FE simulations, and nano-FTIR enabled us to identify the mechanical deformation mechanisms in monolithic ZIF materials: grain boundary sliding is dominating at low stresses, then breakage of chemical bonds and a partial failure of the framework occur, eventually leading to a densification of porous framework at the contact zone. Finally, we measured the fracture toughness using a cube corner indenter to study the resistance of monoliths against cracking failure.

Phase formation and mechanical properties of reactively and non-reactively sputtered Ti-B-N hard coatings

In the field of hard protective coatings, nano-crystalline Ti-B-N films are of great importance due to the adjustable microstructure and mechanical properties through their B content. Here, we systematically study this influence of B on Ti-B-N during reactive as well as non-reactive DC magnetron sputtering. The different deposition routes allow for an additional, very effective key parameter to modify bond characteristics and microstructure. Plasma analysis by mass spectroscopy reveals that for comparable amounts of Ti + , Ti 2+ , Ar + , and Ar 2+ ions, the count of N + ions is about 2 orders of magnitude lower during non-reactive sputtering. But for the latter, the N + /N 2 + ratio is close to 1, whereas during reactive sputtering this ratio is only 0.1. This may explain why during reactive deposition of Ti-B-N, the B N bonds dominate (as suggested by X-ray photoelectron spectroscopy), whereas the B B and Ti B bonds dominate for non-reactively prepared Ti-B-N. Chemically, reactively versus non-reactively sputtered Ti-B-N coatings follow the TiN-BN versus TiN-TiB 2 tie line, respectively. Detailed X-ray diffraction and transmission electron microscopy studies reveal, that up to 10 at.% B can be dissolved in the fcc-TiN lattice when prepared by non-reactive sputtering, whereas already for a B content of 4 at.% a BN-rich boundary phase forms when reactively sputtered. Thus, we could not only observe a higher hardness (35 GPa instead of 25 GPa) as well as a higher indentation modulus (480 GPa instead of 260 GPa), but also a higher fracture energy (0.016 instead of 0.009 J/m during cube-corner indentations) for Ti-B-N coatings with 10 at.% B, when prepared non-reactively. • Major differences in plasma species between reactive and non-reactive sputtering • The elemental composition also varies with the deposition route. • Significant differences in mechanical properties at higher boron contents

Revealing the relation between microstructural heterogeneities and local mechanical properties of complex-phase steel by correlative electron microscopy and nanoindentation characterization

Compositional and microstructural heterogeneity are characteristics of modern multiphase steels. However, the quantitative characterization of these heterogeneities is rarely considered in scientific publications. We characterized the compositional and microstructural heterogeneity of a commercial complex-phase steel (CP800) by combining various electron microscopy techniques and nanoindentation. Compositional gradients of C and Mn were characterized qualitatively and quantitatively through electron probe microanalysis (EPMA). Electron backscatter diffraction (EBSD) results were utilized to identify and segment the microstructural constituents. A novel nanoindentation approach was used to obtain hardness maps. Cube-corner indenter and micro-newton load were applied to limit the indent depth and spacing between adjacent indents to the nanometer scale. A high-resolution hardness map was obtained and successfully overlapped with EPMA and EBSD results, based on which the correlation between compositional heterogeneity and hardness variation in complex-phase microstructure was successfully established.

Volume, Side-Area, and Force Direction of Berkovich and Cubecorner Indenters, Novel Important Insights

The iteration-free physical description of pyramidal indentations with closed mathematical equations is comprehensively described and extended for creating new insights in this important field of research and applications. All calculations are easily repeatable and should be programmed by instrument builders for even easier general use. Formulas for the volumes and side-areas of Berkovich and cubecorner as a function of depth are deduced and provided, as are the resulting forces and force directions. All of these allow for the detailed comparison of the different indenters on the mathematical reality. The pyramidal values differ remarkably from the ones of so-called “equivalent cones”. The worldwide use of such pseudo-cones is in severe error. The earlier claimed and used 3 times higher displaced volume with cube corner than with Berkovich is disproved. Both displace the same amount at the same applied force. The unprecedented mathematical results are experimentally confirmed for the physical indentation hardness and for the sharp-onset phase-transi- tions with calculated transition energy. The comparison of both indenters provides novel basic insights. Isotropic materials exhibit the same phase transition onset force, but the transition energy is larger with the cube corner, due to higher force and flatter force direction. This qualifies the cube corner for fracture toughness studies. Pile-up is not from the claimed “friction with the indenter”. Anisotropic materials with cleavage planes and channels undergo sliding along these under pressure, both to the surface and internally. Their volumes add to the depression volume. These volumes are essential for the exemplified pile-up management. Phase-transitions produce polymorph interfaces that are nucleation sites for cracks. Technical materials must be developed with onset forces higher than the highest thinkable stresses (at airliners, bridges, etc.). This requires urgent revision of ISO 14577-ASTM standards.

New evidences for understanding the serrated flow and shear band behavior in nanoindentation of metallic glasses

Nanoindentation of a Zr-based metallic glass was performed under various loading rates by using a cube-corner indenter. Experimental results showed that increasing the loading rate from 2 to 20 mN/s, the size of serrated flow was greatly weakened, but the number of serrated flow kept very stable, together with very similar shear band features around the residual indents. These results challenge the current understanding derived from the results obtained by using the Berkovich indenter, and can be well explained by the shear-band propagation dynamics model, i.e., loading rate impeded the propagation of shear band rather than its nucleation.

Cathodoluminescence Studies of Nanoindented CdZnTe Single Crystal Substrates for Analysis of Residual Stresses and Deformation Behaviour

Nanoindentation-induced residual stresses were analysed on (111) Te face CdZnTe single-crystal substrates in this study. CdZnTe substrates were subjected to nanoindentation using cube corner indenter geometry with a peak load of 10 mN. Loading rates of 1 mN/s and 5 mN/s were used in the experiments, with a holding time of 10 s at peak load. Residual stresses on the indented region were analysed from load-displacement curves and explained using dislocation generation and elastic recovery mechanisms. Residual stresses were found to be of compressive type, just on the indented surface. The slip lines along the slip directions of this material were clearly visible in the FE-SEM images of the indents. Indents and surrounding surfaces were characterized using the Cathodoluminescence (CL) technique. CL mapping of the indented surface revealed the dislocation generation and their propagation behaviour just beneath the indenter as well as in the surrounding surfaces. The dislocations act as non-radiative recombination centres and quench the CL intensity locally. Dark lines were explained as the presence of dislocations in the material. CL mapping analysis shows that both the rosette glide and tetrahedral glide of dislocations are the primary deformation mechanisms present in CdZnTe. A rosette structure was observed in the CL mapping. CL spectra at 300 K of un-deformed CdZnTe show a peak at 810 nm wavelength, which corresponds to near-band-edge emission. After indentation, the CL spectra show the peak intensity at 814 nm and 823 nm wavelengths at the edge of the indents created with a loading rate of 1 mN/s and 5 mN/s, respectively. These peak shifts from 810 nm were attributed to the tensile residual stresses present in the indented material.