Indenter Tip Geometry Research Articles

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.

Direct calibration of indenter tip geometry by optical surface topography measuring instruments

Instrumented indentation test (IIT) is a depth-sensing hardness test allowing nano- to macro-mechanical characterisation of surface mechanical properties. Indenter tip geometry calibration allows nano-scale characterisation, overcoming the limits of conventional hardness tests. Calibration is critical to ensure IIT traceability and applicability for quality verification in manufacturing processes. The accuracy and precision of IIT are mainly affected by the indenter tip geometry calibration. State-of-the-art indenter tip geometry calibration reports either direct calibration by AFM, which is highly expensive and unpractical for industry, or indirect calibration methods, which are less accurate, precise and robust. This work proposes a practical, direct calibration method for IIT indenter tip geometry by optical surface topography measuring instruments. The methodology is complemented by uncertainty evaluation. The proposed approach is applied to Berkovich and Vickers indenters and its advantages are proven in terms of accuracy and precision of mechanical characterisation on metallic and ceramic material.Graphical abstract

Synthesis and characterization of metal carbides for nanoindentation tip applications

Instrumented indentation experiments at elevated temperatures require careful attention to a myriad of experimental details. Not the least of these is the choice of the indenter tip material. Traditional room-temperature indenters, e.g., diamond and sapphire, can break down, react, and wear excessively at elevated temperatures. In this work, rf-induction heating float-zone and high-temperature solution single-crystal growth techniques have been used to prepare a suite of bulk refractory carbide specimens (i.e., ZrC, VC0.86, NbC, TiC0.95, WC). These potential indenter tip materials were subsequently characterized using nanoindentation testing techniques to determine their single-crystal elastic modulus, hardness, and fracture toughness in order to evaluate their potential for use as elevated-temperature nanoindentation tips. Additionally, subject carbide crystal characteristics were compared to those of single-crystal sapphire and polycrystalline WC-Co. The cumulative results show that single-crystal WC is a promising candidate for indenter tip material based on a combination of its high elastic modulus, hardness, and resistance to cracking—in addition to being crystallographically favorable for fabrication in the frequently used three-sided pyramidal indenter tip geometries.

Artificial intelligence based analysis of nanoindentation load–displacement data using a genetic algorithm

We developed an automated tool, Nanoindentation Neo package for the analysis of nanoindentation load–displacement curves using a Genetic Algorithm (GA) applied to the Oliver-Pharr method (Oliver et al.,1992). For some materials, such as polycrystalline isotropic graphites, Least Squares Fitting (LSF) of the unload curve can produce unrealistic fit parameters. These graphites exhibit sharply peaked unloading curves not easily fit using the LSF, which tends to overestimate the indenter tip geometry parameter. To tackle this problem, we extended our general materials characterization tool Neo for EXAFS analysis (Terry et al., 2021) to fit nanoindentation data. Nanoindentation Neo automatically processes and analyzes nanoindentation data with minimal user input while producing meaningful fit parameters. GA, a robust metaheuristic method, begins with a population of temporary solutions using model parameters called chromosomes; from these we evaluate a fitness value for each solution, and select the best solutions to mix with random solutions producing the next generation. A mutation operator then modifies existing solutions by random perturbations, and the optimal solution is selected. We tested the GA method using Silica and Al reference standards. We fit samples of graphite and a high entropy alloy (HEA) consisting of BCC and FCC phases.

Quantitative evaluation of nanoindents: Do we need more reliable mechanical parameters for the characterization of materials?

Abstract Various sources of errors in the standard procedure according to the ISO 14577 draft for the iteration of elastic modulus and hardness of solid materials, with reference to fused quartz with its particular and unique indentation response, are pointed out on the basis of practical examples. Similar objections exist towards the use of the S 2 F N – 1 parameter, where S is the stiffness and F N is the normal force. It is suggested to use unambiguous mechanic characterization (at least additionally) by quantitative analysis of the loading curves in nanoindentations. These exhibit a general dependence between normal force and (displacement)3/2, the proportionality constant k being a non-iterated nanoindentation coefficient with dimension [force/length3/2] and unit [μN/nm3/2] that depends on the indenter tip geometry (pyramidal or conospherical) and is a characteristic material’s property. The validity has been demonstrated for virtually all types of materials (metals, semimetals, oxides, salts, organic molecular crystals, polymers) independent of their different bonding states. Pressure-induced phase transitions are detected by kinks in the linear plots for the loading curves well in the nanoindentation region. Crystalline materials, such as strontium titanate, exhibit far-reaching anisotropic effects along lattice axes that would strongly forbid the reference to an amorphous standard. The nanoindentation coefficient characterizes the different polymorphs and the face anisotropies. Another unambiguous mechanical characterization is given by the full work of indentation (as differentiated from the less secure plastic work of indentation). It also characterizes the face anisotropies with high precision for a given indenter as it is found proportional to (normal force)3/2, which allows for useful extrapolations.

Impact failure in two silicates revealed by ultrafast, in situ, synchrotron X-ray microscopy

To travel safely behind screens that can protect us from stones and hail, we must understand the response of glass to impact. However, without a means to observe the mechanisms that fail different silicate architectures, engineering has relied on external sensors, post-impact examination and best-guess to glaze our vehicles. We have used single and multi-bunch, X-ray imaging to differentiate distinct phases of failure in two silicates. We identified distinct micromechanisms, operating in tandem and leading to failure in borosilicate glass and Z-cut quartz. A surface zone in the amorphous glass densifies before bulk fracture occurs and then fails the block, whilst in quartz, fast cracks, driven down cleavage planes, fails the bulk. Varying the rate at which ejecta escapes by using different indenter tip geometries controls the failed target’s bulk strength. This opens the way to more physically based constitutive descriptions for the glasses allowing design of safer, composite panels by controlling the impulses felt by protective screens.

Mechanical properties of Al2O3 inverse opals by means of nanoindentation

In order to understand the mechanical behaviour of Al2O3 inverse opals, nanoindentation techniques have been implemented in material layers with three different microstructures, in terms of hollow or polystyrene spheres, with Al2O3 shells of distinct wall thickness. Different indenter tip geometries as well as contact loading conditions have been used, in order to induce different stress field and fracture events to the layers. Field emission scanning electron microscopy and focused ion beam have been employed to understand accommodation of plastic deformation induced during the indentation process. Results show that materials with polystyrene spheres exhibit higher hardness and modulus under sharp indentation, and cracking resistance under spherical indentation. Furthermore, deformation is discerned to be mainly governed by the rotation of the microspheres. In the case of the inverse opals made of hollow spheres, the main deformation mechanisms activated under indentation are the rearrangement and densification of them.

Indenter geometrical effects on sub-micro/nano indentation and scratch behaviors of polymeric surfaces

In this work, we study the indenter geometrical effects on the nanoindentation and scratch behaviors of polymers (epoxy resin and its based nanocomposites) through both experimental and numerical approaches. Two different types of indenter commonly used in nanoindentation tests, Berkovich (i.e., three-sided pyramid-shaped) and conical-shaped, are studied. An indenter (tip) geometry reconstruction procedure is presented and the results are input into finite element models to better understand the mechanisms of the geometrical effects on nanoindentation. The effect of indenter geometry on nanoscratch behavior is also investigated experimentally. Overall, our results show that the corrected Oliver and Pharr's method is applicable to nanoindentation of polymeric surfaces and the indenter geometry plays significant roles in both the nanoindentation and nanoscratch tests. The conical-shaped indenter provides slightly overestimated mechanical parameters for the polymers tested due to the material pile-up. Therefore, for nanoindentation and scratch tests, the type of indenter should always be mentioned and comparisons between tests using different types of indenter should be taken with caution.

Understanding the effects of ion irradiation using nanoindentation techniques

The effects of ion irradiation in materials for research are usually limited to a shallow surface layer of the order of one micrometre in depth. Determining the mechanical properties of such irradiated materials requires techniques with high spatial resolution. Nanoindentation is a relatively simple method for investigating these shallow layers with the advantage that statistically rich data sets for elastic and plastic property values can be generated. However, interpretation of the results requires and understanding of the material response, including the extent of the plastic zone with respect to the irradiated layer, pile-up or sink-in of material around the indentation site that affect the calculated contact area and hence derived mechanical property values. An Fe+ self-irradiated Fe12%Cr alloy was investigated with three different indenter tip geometries, a cube corner, Berkovich and 10μm radius indenter. Sharp indenters provide sufficiently small plastic zones to be contained within the irradiated layer but pop-in events and pile-up need to be taken into account for correct interpretation of the mechanical properties of the irradiated material.

Annealing-induced indentation recovery in thin film metallic glasses: Effects of indenter tip geometry, film thickness and film composition

Annealing-induced indentation recovery behaviours of sputtered Zr50Cu28Al14Ni8, Cu48Zr42Al6Ti4, Hf46Cu45Al6Ti3, and Fe65Ti13Co8Ni7B6Nb1 (in at. %) thin film metallic glasses (TFMGs) on silicon substrate are examined. Influences of indenter tip geometry, film thickness and film composition on indentation recovery of TFMGs have been studied. Nanoindentations are performed at room temperature with two three-sided pyramidal indenters (Berkovich and cube-corner), followed by annealing performed within the supercooled liquid temperatures. The results reveal that the extent of recovery of indentation by Berkovich indenter is higher than that of cube-corner owing to higher compressive stress underneath the Berkovich tip and larger radius of curvature of the indent left behind after Berkovich indentation. The numerical modelling of depth profile of Zr-based TFMG shows the blunter the indenter tip is the higher the recovery. The thicker film also shows larger recovery. In addition, because of the difference in bonding force among constituent elements, Zr-based TFMG exhibits larger recovery than Cu-, Hf- and Fe-based TFMGs.

계장화 압입시험의 하중-변위 곡선에 미치는 선단 형상 및 푸아송비의 영향

마이크로/나노 압입시험에 사용되는 각뿔 혹은 원뿔형 압입자의 선단 형상은 제작한계 및 사용 중 마모 등으로 인해 필수적으로 곡면 형태를 띄게 된다. 많은 압입시험 관련 연구에서 각뿔형 압입자의 선단 형상은 편의상 구형으로 가정한 후, 얕은 압입에 대한 구형압입 이론식을 적용하고 있다. 이러한 가정에는 근본적으로 두 가지 문제점이 있는데, 첫 번째로 이론해의 정확성은 재료 물성치 및 압입자 형상에 따라 변화한다는 점이며, 두 번째로 각뿔형 압입자의 실제 선단 형상은 이상적인 구형이 아니라는 점이다. 본 연구에서는 유한요소해석에 기반하여 압입시험에 미치는 이 두 요소의 영향을 분석한다. 먼저 탄성 구형 압입시험에 대해 푸아송비와 하중-변위 곡선의 상관관계를 살펴보고, 이를 기반으로 수정된 구형 탄성 압입 관계식을 제시한다. 이어 가정된 Berkovich 선단 형상의 3차원 유한요소해석으로부터 압입깊이에 따른 하중-변위 곡선의 특성을 분석한다.

Contact damage and fracture micromechanisms of multilayered TiN/CrN coatings at micro- and nano-length scales

In this study, systematic nanomechanical and micromechanical studies have been conducted in three multilayer TiN/CrN systems with different bilayer periods (8, 19 and 25nm). Additionally, experimental work has been performed on corresponding TiN and CrN single layers, for comparison purposes. The investigation includes the use of different indenter tip geometries as well as contact loading conditions (i.e. indentation/scratch) such to induce different stress field and damage scenarios within the films. The surface and subsurface damage under the different indentation imprints and scratch tracks have been observed by atomic force microscopy, field emission scanning electron microscopy and focused ion beam. Multilayer TiN/CrN coated systems are found to exhibit higher adhesion strength (under sliding contact load) and cracking resistance (under spherical indentation) than those coated with reference TiN and CrN monolayers. The main reason behind these findings is the effective development of microstructurally-driven deformation and cracking resistant micromechanisms: rotation of columnar grains (and associated distortion of bilayer period) and crack deflection of interlayer thickness length scale, respectively.

Characterization of Rockwell hardness indenter Tip using image processing and optical profiler and evaluation of measurement uncertainty

Hardness is a measure of the resistance of a material to be penetrated and eroded by sharp projections of other materials such as diamond. The process of creating sharp projections on any test surface is known as indentation. Hardness measurement of any material is the result of a complex process of deformation during indentation. The indenter tip geometry, which includes radius of curvature at the tip and tip angle, affects the hardness measurement by influencing the nature of the penetration process on the test surface, because every indenter deforms the specimen surface with a different geometry. The controlled indenter geometry can improve the consistency of hardness measurement. In this paper we report the estimation of two important geometrical parameters, radius of curvature and tip angle of a Rockwell indenter by using a simple method of image processing and compare the results with those obtained with a traceable 3D optical profiler. Evaluation of uncertainty in measuremts is carried out as per ISO guidelines (ISO-GUM) and a detailed uncertainty budget is presented. The tip angle estimted is 119.95 degree. The radius of curvature is estimted to be 199.96 ± 0.80μm by image analysis which agrees well with the value estimated by using optical profiler i.e. 199.12 μm.

Novel Analysis on the Influence of Tip Radius and Shape of the Nanoindenter on the Hardness of Materials

Nanoindentation is a powerful technique used for assessing mechanical properties at nano/micro-scale. It is used for obtaining material parameters like elastic modulus, hardness, plastic or viscous parameters from experimental readings of indenter load and depth of penetration. Forces involved are usually in the milli or micronewton range and the depth in the order of nanometers. Different kinds of probes can be used for making an imprint into the material surface. Very small material volumes having the order of several tens of nanometers can be accessed with the tip of the nanoindenter and material properties can be evaluated for such a small piece of the materials. Nanoindentation finds application in extracting the elastic and plastic properties of the indented material surface. The effective knowledge of the indenter tip geometry is significant in nanoindentation experimental analysis. A small deviation from the ideal tip geometry affects the accuracy of the result during nanoindentation experiments. In the present investigation, we have studied the influence of tip radius of the indenter on the hardness of for different indenter shapes such as spherical, conical and Berkovich.

Analysis of indentation size effect in copper and its alloys

For describing the indentation size effect (ISE), numerous models, which relate the load or hardness to the indent dimensions, have been proposed. Unfortunately, it is still difficult to associate the different parameters involved in such relationships with physical or mechanical properties of the material. This is an unsolved problem since the ISE can be associated with various causes such as workhardening, roughness, piling-up, sinking-in, indenter tip geometry, surface energy, varying composition and crystal anisotropy. For interpreting the change in hardness with indent size, an original approach is proposed on the basis of composite hardness modelling together with the use of a simple model, which allows the determination of the hardness–depth profile. Applied to copper and copper alloys, it is shown that it is possible to determine the maximum hardness value reached at the outer surface of the material and the distance over which both the ISE and the workhardening take place.

Fast determination of parameters describing manufacturing imperfections and operation wear of nanoindenter tips

Nanoindentation is an effective technique for determining mechanical properties of bulk materials and thin films. Prevailing measurement uncertainties in nanoindentations by Vickers or Berkovich diamond pyramids are commonly caused by manufacturing imperfections of the indenter's side angles and tip sharpness. Moreover, the tip geometry changes over the indenter operation time, due to diamond wear.The paper presents a fast method for estimating diamond indenters' tip nano and micro geometry. This method is based on a combination of nanoindentations on Si(100), used as reference material, with FEM supported calculations of Martens hardness. The hardness calculations are conducted using an equivalent indenter tip geometry with geometrical characteristics, which may vary for a specific set of parameters, describing the real indenter with manufacturing imperfections. These parameters are varied in successive iterations until the calculated hardness converges with that of the reference material.For a quick determination of these parameters, the software package “TIDE” (TΙp Deviations Estimation) has been developed. “TIDE” is based on numerous FEM supported simulation results of nanoindentations, conducted on the reference material, varying the indenter tip geometry. By this software package, a quick prediction of nanoindenters' tip equivalent geometry is facilitated, also for anticipating changes due to wear of the diamond over time.

Mechanical behavior of 3Al2O3·2SiO2 films under nanoindentation

A complete and systematic nanoindentation study was conducted on a mullite (3Al2O3·2SiO2) coating ∼1μm thick, deposited by means of chemical vapor deposition on a silicon carbide (SiC) substrate. The investigation included using different indenter tip geometries (Berkovich, spherical and cube-corner), complemented with atomic force microscopy and three-dimensional focused ion beam tomography to characterize the indentation response, deformation and damage micromechanisms. The intrinsic mechanical properties of the 3Al2O3·2SiO2 film and the interfacial toughness of the coated (3Al2O3·2SiO2/SiC) system were critically evaluated to assess the influence of substrate and film residual stresses. Through appropriate implementation of specific indenter tip geometry, different length-scale mechanical properties in the materials studied were successfully determined: yield strength and fracture toughness for the film, together with energy of adhesion per unit area and interface fracture toughness for the coated system.

An alternative to the determination of the effective zero point in instrumented indentation: Use of the slope of the indentation curve at indentation load values

In instrumented indentation testing, especially in the nano and micro scales, low scale artefacts such as sensor sensitivity, surface roughness, imperfect indenter tip geometry and material heterogeneity can create significant deviations of the measured indentation load-depth curve from the ideal curve corresponding to the bulk material.This study assesses the influence of an offset of the measured penetration depth on the identified bulk mechanical parameter values when using a reverse analysis model based on spherical indentation. It is shown through numerical examples that significant errors arise if the identification procedure is based on the load values recorded at penetration depth values. In over to overcome this effect, an alternative exploitation of the reverse analysis model is proposed, which is based on the use of the slope of the indentation curve at indentation load values. In addition, it is proposed to neglect the data at low load values in order to avoid the effect of low scale artefacts on the shape of the indentation curve at low load values.The proposed approach is applied to the numerical examples, and then an experimental case of a blunted indenter tip is presented. In all cases, the proposed approach provides accurate identification results which are not affected by low scale artefacts. The proposed approach can be significantly useful when analysing indentation curves obtained in the nano and micro scales, as well as indentation curves obtained in industrial conditions.

Influences of spherical tip radius, contact depth, and contact area on nanoindentation properties of bone

Nanoindentation has been widely used as a means to measure the micro-mechanical properties of bone and to predict the macroscopic properties. The role of indent depth and indenter tip geometry in measuring the hierarchical properties of bone tissue was explored experimentally using a range of spherical indenter tips of R=5, 25, 65, and 200 μm. Nanoindentation arrays, not targeted to fall on specific structures or locations, enabled statistical sampling of osteons within PMMA-embedded, bovine, cortical bone on a single sample to a range of maximum displacements (minimum of 100 nm and maximum of 2000 nm). Elastic finite element models were then utilized to isolate the contributions of indenter tip radius, contact area, and position within the lamellar structure in comparison to the experimental results. For a small, R=5 μm indenter tip, indentation modulus consistently increased with contact depth and increased plastic deformation, resulting in an artificial increase in elastic properties. While larger radius tips ( R=25, 65, and 200 μm) did not enable evaluation of a high spatial resolution on the surface, they produced data that was representative of the lower load and contact depth measurements with the smaller tip. However the sensitivity to mechanical property variations across the 2-D surface of the material was lost with increase in indenter tip size. Correspondingly, measurement variance was also decreased as the volume contributing to the indent response represented an average of surface roughness, varying mineral content, defects, and underlying tissue type and structure.

Effects of mechanical properties, residual stress and indenter tip geometry on instrumented indentation data in thin films

In this work, an axisymmetric two-dimensional finite element model was developed to simulate instrumented indentation testing of thin ceramic films deposited onto hard steel substrates. The level of film residual stress ( σ r ), the film elastic modulus ( E) and the film work hardening exponent ( n) were varied to analyze their effects on indentation data. These numerical results were used to analyze experimental data that were obtained with titanium nitride coated specimens, in which the substrate bias applied during deposition was modified to obtain films with different levels of σ r . Good qualitative correlation was obtained when numerical and experimental results were compared, as long as all film properties are considered in the analyses, and not only σ r . The numerical analyses were also used to further understand the effect of σ r on the mechanical properties calculated based on instrumented indentation data. In this case, the hardness values obtained based on real or calculated contact areas are similar only when sink-in occurs, i.e. with high n or high ratio Y/E, where Y is the yield strength of the film. In an additional analysis, four ratios ( R/h max ) between indenter tip radius and maximum penetration depth were simulated to analyze the combined effects of R and σ r on the indentation load–displacement curves. In this case, σ r did not significantly affect the load curve exponent, which was affected only by the indenter tip radius. On the other hand, the proportional curvature coefficient was significantly affected by σ r and n.