Indenter Tip Radius Research Articles

Cutting speed dependence of material removal mechanism for monocrystal silicon

In advanced semiconductor packaging, silicon wafers are typically thinned to tens of microns in thickness using ultra-precision grinding techniques, and the cutting speed greatly determines their surface integrity. However, an in-depth understanding of fundamental material removal mechanism considering the strain rate effect has not been revealed yet. This paper systematically explores the impact of cutting speed on the penetration depth, subsurface damage characteristics and scratch-induced stress field for monocrystal silicon material. First, nanoscratch tests in varied-load and constant-load modes are performed under different scratch speeds on the silicon specimen surface. The surface morphology of generated groove is observed to identify its brittle and plastic features. Next, the geometric relationship and contact pressure between the indenter and workpiece during the scratching process are analyzed. A theoretical penetration depth model is developed considering scratch speed, indenter tip radius and elastic recovery. The corresponding parameters are solved via the particle swarm optimization algorithm and agree very well with the experimental data. Then, the subsurface damage under different scratch speeds is measured by a transmission electron microscope. The atomic scale lattice defects are presented, involving the amorphous layer, stacking faults and phase transformation. Finally, a scratch-induced stress field model is established to interpret the distortion degree variation in damaged regions with scratch speed. The distribution of stress components in the scratch region is presented.

Inconsistent nanoindentation test hardness using different Berkovich indenters

When testing the nanoindentation hardness of the same sample with different Berkovich indenters, inconsistencies arise even when the frame stiffness and indenter tip area functions are regularly calibrated. This phenomenon has not been fully understood, making it challenging to accurately test and compare material hardness data from different laboratories. To address this issue, incremental test hardness caused by indenter tip defects and indentation size effects (ISE) is quantified. The ISE correction method proposed in this study is based on the Nix-Gao model for nanoindentation load-indentation depth (P-h) curves, and an area function equivalent modeling method is used to reproduce the geometry of Berkovich indenters in finite element (FE) analysis. Although the test hardness using different Berkovich indenters is inconsistent, their intrinsic hardness remains consistent. The proposed ISE correction method is validated by FE simulation results for A508-3 and 316 L steel that match perfectly with the ISE-corrected experimental P-h curves. The analysis of load increments shows that tip defects affect the test result through statistically stored dislocation (SSD) and geometrically necessary dislocation (GND). Indenter tip defects mainly affect the nanoindentation test results through GND. The smaller the indenter tip radius, the higher the GNDs, and the higher the test hardness. The different effects of indenter tip defects on GND lead to inconsistent hardness measurements using different Berkovich indenters.

Nanoindentation test of a DLC coated high-speed steel substrate using a two-dimensional axisymmetric finite element method

Diamond-Like Carbon is a thin coating that has high hardness, chemical inertia and low coefficient of friction characteristics that can improve the performance of cutting tools and mechanical components. To identify the characteristics of this film it is important to carry out mechanical tests, such as nanoindentation, which can provide important information in understanding and improving coating techniques and, when combined with the finite element method, leads to more detailed results of material behavior during testing. Considering this, the present work aimed to study and apply a nanoindentation test simulation of a Diamond-Like Carbon coated high-speed steel specimen. The results of the indenter penetration versus load were compared with experimental data seeking correlation of the model. A great proximity was observed between the experimental results and the results obtained in the simulation. When comparing the final indentation force, a proximity of 93.9 % and 95.5 % was found for the model with only one indentation and with partial indentations, respectively, thus validating the created model. The impact of modifying the indenter tip radius for the partial indentation method was also evaluated. The tip radius variation did not have a significant impact on the results of final indentation force and material hardness. The material hardness was also obtained in the simulation, which was equal to the experimental: 9.25 GPa.

Indentation of small format Lithium-ion pouch cells: Experiments and modeling

Lithium-ion pouch cells are widely used in applications such as cell phones and electric vehicle battery packs. Here, a series of indentation experiments is performed on 4Ah pouch cells. The experimental program includes hemispherical indentation with six different indenter tip radii as well as indentation with cylindrical indenters with three rod diameters. Aside from varying the shape and size of the indenters, the location and direction of loading is varied including out-of-plane and in-plane loading of the rectangular-prismatic pouch cells. It is found that the force–displacement curves obtained for hemispherical indenters scale linearly with the indenter tip radius, while a scaling with the square root of the radius is observed for the experiments with cylindrical indenters. Finite element simulations are performed of all experiments using an enhanced Deshpande-Fleck plasticity model with two stage hardening. Despite the orthotropic nature of the jelly-stack, it is found that the simulations with an isotropic plasticity model provide reasonable predictions of the force–displacement curves for all experimental configurations. This surprising result is explained through the exceptionally high slenderness of the metallic current collector foils comprised in a pouch cell that respond through early buckling failure instead of contributing to the in-plane compressive load carrying capacity.

Scratch test in boride layers: Influence of indenter tip radius on failure mechanisms

In this work, the influence of indenter tip radius (ITR) on scratch tests in boride layers was studied. The thermochemical treatment of boriding was performed on an AISI H13 steel at 1000 °C for 1 h. Depth sensing indentation test was developed to estimate both, hardness, and elastic modulus of the boride-layer/substrate system. Indenter radius of 200, 100, 50 and 20 μm were used for the scratch tests on borided steel. Failure mechanisms were analyzed by scanning electron microscopy (SEM). Predominant failure mechanisms were lateral cracking, chipping, and gross chipping. ITR of 20 μm developed more severe damage on the borided AISI H13 surface and the more severe substrate plastic deformation was obtained by ITR of 200 μm.

Mechanical properties of α-quartz using nanoindentation tests and molecular dynamics simulations

Understanding the mechanical properties of α-quartz is of vital importance to rock engineering because α-quartz is the main component of igneous, metamorphic and sedimentary rocks. Molecular dynamics simulations (MDs) of nanoindentation tests on α-quartz were performed to investigate the effects of indenter tip radius and penetration depth on the mechanical properties of α-quartz. Indentation load-penetration depth (P-h) curves were plotted, from which Reduced Young’s modulus ( E r ) , hardness ( H ) were obtained and these mechanical parameters were then compared with the laboratory nanoindentation results. The mechanical results obtained from MDs are in good agreement with the experimental values. It can be found that E r and H increase with indentation depth at shallow contact depth while they decrease with indenter tip size. To the authors’ knowledge, this is the first MDs of nanoindentation test of hard rock-forming minerals reported and we believe that this study can shed light on the precise measurement of the mechanical properties of rock minerals at micro- and nano-scales.

Novel approach to characterize the deformation under Berkovich and spherical indentations: Study on magnesium single crystals

In this work, we have developed a mathematical framework to investigate the deformation response under Berkovich and spherical indenters. Nanoindentation experiments are carried out on two single-crystal magnesium (Mg) samples oriented for basal slip and tensile twinning. The indentation load vs penetration depth curves are then analyzed to explain the pop-in events with the help of Schmid factor analysis and to identify the favorable deformation modes directly beneath and around the indentation. These results explain why there is only a small difference in the values of hardness between the two orientations despite having a significant difference in their crystallographic orientations. In addition to this, the role of indenter tip radius on the formation of extension twins when indented along the crystallographic $c$ axis is analyzed with the help of a simple analytical model.

Effect of indenter tip radius on indentation hardness by finite element analysis

In this study, the indentation hardness test is performed by elastic-plastic finite element (FE) analysis. In order to investigate the effect of the wear of indenter tip on the load-penetration depth curve ([Formula: see text] curve), indentation simulation is made by changing the indenter tip radius. The [Formula: see text] curve obtained by finite element method (FEM) is in good agreement with the experimental results. The calculation shows that the indentation plastic work [Formula: see text] corresponding to the area in the [Formula: see text] curve is hardly affected by the indenter tip radius.

Nanoindentation pop‐in in oxides at room temperature: Dislocation activation or crack formation?

AbstractMost oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation‐based plasticity prior to crack propagation. Here, we demonstrate the size‐dependent brittle to ductile transition in SrTiO3 at room temperature using nanoindentation pop‐in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop‐in event in SrTiO3 at room temperature, below a critical indenter tip radius, is dominated by dislocation‐mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop‐in event. Beyond the experimental examination and theoretical justification presented on SrTiO3 as a model system, further validation on α‐Al2O3, BaTiO3, and TiO2 are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation‐based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano‐/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation‐based mechanics and functionalities study in these materials.

Generalized approach of scratch adhesion testing and failure classification for hard coatings using the concept of relative area of delamination and properly scaled indenters

Failure characteristics and adhesion evaluation of hydrogen-free amorphous carbon coatings (a-C and ta-C) were examined by scratch testing using different indenter tip radii. Based on previous work of some of the authors, this article provides an extended description of main failure modes occurring for brittle coatings, with respect to the ratio of indenter radius R to coating thickness h. For best control over expected coating failure, it is shown that the failure mode of the coating can be reliably predicted and adjusted by the choice of the indenter radius. Failure modes of interest are predominant spallations (failure mode II) and predominant bending cracks (failure mode II). Same failure modes were typically found within certain ranges of R/h: Failure mode II occurred for 20 < R/h < 40 and failure mode III for 100 < R/h < 200.For an enhanced adhesion evaluation, the concept of adhesion assessment by comparing the relative size of delaminated area was expanded and generalized for variable indenter sizes and failure mechanisms. Thus, this approach enables direct comparison of scratch results in case of similar R/h, especially allowing adhesion comparison for a wide range of coating thicknesses.

Single-point scratch testing for understanding particle engagement in abrasion of multiphase materials

The current research explores the influence of multi-asperity abrasive particles engagement on multiphase materials. WC-Co (WC-15.6% Co) and NbC-cermet (NbC-12% Ni–10% Mo2C) hard materials were tested using a scale down single point scratch tester. Multi-asperity scratch patterns were produced by implying multiple scratches on hardmetal surface by parallel and repeated sliding. Superimposition of interactions has been implemented to study the damage evaluation of close-up parallel scratches. The abrasive particle characteristics such as size and apex angle were replicated by the diamond indenter and their influence with different applied loads [1–20 N] and sliding speeds [0.2–5 mm/s] were studied. NbC-cermet and WC-Co show a decrease in friction coefficient by 20–46% and 11–30% respectively, while the indenter tip radius changes from 200 μm to 25 μm under the same operating conditions. The wear micro-mechanism mainly changes from plastic deformation to fracture when the load and tip radius is increased. An extensive comparative study shows NbC-cermet prematurely experiences fracture dominated failure than its reference WC-Co. Moreover, tip size defect from indenter curvature geometry greatly affects the mean apex angle.

An investigation on the friction, wear and deformation of potassium dihydrogen phosphate

This paper investigates the friction, wear and deformation of potassium dihydrogen phosphate (KDP) using the nano-scratching technique with both Berkovich and conical indenters. It was found that the indenter tip radius significantly affected the tribological properties of the material. Under a smaller tip radius (Berkovich indenter), the pill-ups were higher at the end of the wear/scratching tracks and friction fluctuation during nano-scratching was greater. The ploughing and brittle deformation dominated the wear mode under a larger tip radius (conical indenter). The KDP deformed in a ductile, ploughing or ploughing and brittle mode depending on the magnitude of the scratching load. The variation in friction coefficient was related to the wear mode and brittle deformation brought about a greater friction fluctuation. The crystal orientation (plane) also affected the behaviour of friction and wear of the material. The softer plane of KDP experienced more brittle deformation under both indenter types. The indenter tip radius had a significant influence on the surface morphology of KDP.

Effect of spherical indenter radius and loading rate on the kinetic nanoindentation creep behavior of La-based metallic glasses

Although the effect of the deformation field size on the mechanical strength of metallic glasses (MGs) has been investigated thoroughly, a few studies have investigated the effect of the deformation field size on the kinetic creep deformation behavior for these materials. This issue is addressed in the current work by investigating the nanoindentation creep kinetics of La-based MGs under the application of spherical indenters with two different tip radii and three different loading rates. The experimental data are fit to a viscoelastic model to extract the activation volume and relaxation time characteristics of the kinetic nanoindentation creep deformation of the samples. The results demonstrate that the nanoindentation creep kinetics are not only strongly dependent on the loading rate, but also vary significantly with the indenter tip radius. The deformation dynamics is interpreted by the stretched exponent β, indicating its relatively small value at a large loading rate along with a large indenter tip radius. Furthermore, the observed effect of the deformation field size can be attributed to an interplay between the deformation field under the spherical indenter and flow defects associated with the excess free volume, shear transition zone, or shear band embryo with an evolution that is essentially dependent on the loading rate. The current findings contribute to a fundamental understanding of the mechanism of shear softening during creep deformation in MGs.

Nanoscale characterization of Titanium-based coatings plastic properties by dimensional analysis, FEA and Infimum resultant error criterion

Working with continuously harder materials and higher cutting speeds requires novel mechanical properties for cutting tools. The application of titanium-based coatings deposited by PVD is experienced as one of the most effective solutions. To assure achievement of the required characteristics in the metal cutting process, which mainly includes turning, milling, drilling and some other methods, extracting the plastic properties has been the main challenge for a long time. In this paper, a hybrid method emerging the modified dimensional analysis method (MDAM) and experimental data with novel algorithm named as minimum resultant error method is proposed. By using this algorithm, yield stress, strain hardening exponent and strain hardening coefficient are extracted as unique measures via using a single indenter nanoindentation result. An existing experimental output data and numerical solution of TiN thin film nanoindentation test are used to verify the proposed approach. The same procedure is implemented to calculate the plastic properties of TiAlN coating. Some of the results for TiAlN are among the rarely investigated matters. The effects of mesh refinement, friction coefficient and indenter tip radius are elucidated. According to the results attained from the new approach, there is an excellent agreement between MDAM and the combined algorithm results (4% for yield stress and 7% for strain hardening exponent). The resultant error is calculated in the range of 0.47–4.1% for optimized deviation. To provide another criterion of the adaptability of the results, the elastic modulus and hardness are calculated within less than 5% and 9% errors, respectively.

Understanding the response of aluminosilicate and aluminoborate glasses to sharp contact loading using molecular dynamics simulation

Experimental studies have shown that glass systems with high boron content exhibit superior crack resistance under sharp contact loading. However, the underlying mechanism is still not fully understood. In this context, we carried out classical molecular dynamics simulations on sodium aluminosilicate and sodium aluminoborate systems to investigate the effect of boron on the response of glass to nanoindentation. A rigid V-shaped indenter is used to indent the glass sample with a fixed loading rate, during which the indenter interacts with the glass via a repulsive force field. The indenter angle and tip radius are varied to study the effect of indenter sharpness, as what has been done in experiments. These simulated nanoindentation tests reveal how the stress/strain field and the glass structure evolve with deformation underneath the indenter. It was found that a large number of boron atoms in the plastic zone change from three- to fourfold coordination during the loading process, and most of them revert back to the threefold coordination state during the unloading process. Our study shows that this “reversible” boron coordination change plays a critical role in increasing the damage resistance of glass.

Implementation of the new minimum resultant error approach to extract elastic-plastic properties of titanium nitride thin film by nanoindentation, finite element analysis, and modified dimensional analysis

Obtaining the plastic properties of thin film coatings has been the main challenge for decades. Implementing the hybrid methods seems to be an applicable way to address this issue. Unfortunately, limitations of nonunique answers together with the need for enormous amount of calculations are counted as the main challenges. To overcome such difficulties, a modified dimensional analysis method is proposed, which is able to reduce the number of dimensionless parameters. Another novel algorithm named “minimum resultant error method” is developed to provide proper criteria to investigate the compliance of the analytical results with empirical data. With this algorithm, yield stress, strain hardening exponent, and strain hardening coefficient are extracted as unique values by using a single indenter nanoindentation results. The simulation results are processed with combined modified dimensional analysis method and minimum resultant error method algorithms. The effects of interlayer, friction coefficient, and indenter tip radius are investigated. Error analysis to the modulus of elasticity is undertaken and the results show less than 2% error for the infimum point, while the individual dimensionless functions errors are below 3.4%. According to the results, this new approach is well-coped with the earlier studies.

Nanoindentation-induced deformation, microfracture, and phase transformation in crystalline materials investigated in situ by acoustic emission

Abstract

A Microscopic Experimental Method Transversely Loading on Single High-Performance Fibers

We developed a microscopic experimental method that transversely loads and images single high-performance fibers. The experimental set-up was inside the chamber of a scanning electron microscope (SEM). Force and displacement histories were recorded by the loading device. The SEM enabled in-situ observation of the fiber’s initial contact with the transverse indenter and subsequent deformation, crack initiation and propagation until the final failure. Within the loading device, fiber gauge length, indenter tip radius and loading direction can be varied as desired. To demonstrate the new experimental capability, initial results for a razor blade transversely cutting a Dyneema® SK76 fiber are presented in this paper. To avoid the effect from the conductive coating on the mechanical behavior of the fiber, a low vacuum detector was adopted to capture the deformation and failure of an uncoated fiber. These experiments revealed the damage and failure processes of single fibers with high-resolution micrographs.

Modeling of Osteoprobe indentation on bone

Osteoprobe (ActiveLife, Santa Barbara, CA) is a novel handheld microindentation instrument designed to test bone in vivo by measuring a Bone Material Strength index (BMSi). In this paper, the Osteoprobe indentation on a cortical bone is modeled computationally to gain insights into the physical interpretation of the BMSi output. The analysis is conducted using an axisymmetric finite element model with an isotropic viscoelastic-plastic constitutive law with continuum damage. The computational model is validated by comparing it with experimental data from the literature. Experimental factors (indenter tip radius and friction coefficient between the indenter and the bone) and four mechanical properties of bone (Young's modulus, compressive yield stress, and damage and viscosity constants) are varied to study their influence on the BMSi.We find that varying the friction coefficient can proportionally change the BMSi up to 3%. The indenter tip radius is proportional to the BMSi, with a more pronounced proportional relation when it is greater than 30 µm. Young's modulus has a proportional relation with the BMSi, where decreasing it by 73% reduces the BMSi by 41%. The damage constant has an inversely proportional relation to the BMSi, where increasing it from 0.5 to 0.96 reduces the BMSi by 29%. The compressive yield stress and the viscosity constant have a close proportional relation to the BMSi, where increasing the compressive yield stress from 50 MPa to 200 MPa increases the Osteoprobe BMSi by 21%.In summary, the friction coefficient and the indenter tip radius (when smaller than 30 µm) have a small effect on BMSi. Young's modulus and damage have stronger relations with the BMSi than compressive yield stress and viscosity constant. This fundamental study provides new insights into the BMSi measurement and serves as a basis for further computational and experimental investigations on the Osteoprobe technique. Such research is needed to facilitate the embrace of this technique by the clinical community.

Tip radius variation with elastic indentation depth

The reduced elastic modulus of a material is measured with a nanoindenter probe that is operated in the tapping mode. The resonant frequency of a freely oscillating cantilever is reduced when contact is made between the indenter tip and surface under investigation. It’s shown using elasticity theory that the elastic deformation is a function of the indenter tip radius. A deeper penetration within the elastic range can change the tip radius, and introduce an error of 10% in calculating the reduced elastic modulus.