Berkovich Indenter Research Articles

Enhancing the wear performance of Ti-6Al-4V against Al2O3 and WC-6Co via TiBn layer produced by boriding

Abstract In this study, mechanical and tribological properties of the borided dual-phase α + β type Ti6Al4V titanium alloy were examined. For this purpose, Ti6Al4V alloy samples were borided for 6 h at a temperature of 1100 °C by the powder-pack boriding process. As a result of boriding, a boride layer consisting of TiB2 with a thickness of max ∼25 µm and TiB phases with a thickness of max ∼10 µm was obtained on the Ti6Al4V sample surfaces. As a result of the boride layer’s nanoindentation tests carried out using the Berkovich indenter, it was found to have an elastic modulus of 534.255 GPa and a hardness of 36.537 GPa. Wear tests were carried out using the pin-on-disc method under a load of 10 N and with a sliding distance of 1000 m. Whereas the dominant type of wear in non-borided samples was abrasive wear, oxidative mild wear was generally observed in borided samples. In borided samples, as a result of becoming of surface smoother by hard asperities breaking and increasing the actual contact area, the friction coefficients increased. It was determined that with boriding, the wear performance of Ti6Al4V alloy improved ∼46.8 times against the Al2O3 counterpart and ∼4.57 times against WC-6Co counterpart.

Rate and Load Effects on Scratch Behavior of Thermoplastics by Berkovich Indenter

Rate and Load Effects on Scratch Behavior of Thermoplastics by Berkovich Indenter

Application of the spherical indenter for determination of the elastic modulus of coatings

In this work a study of nanoindentation of the surface of epoxypolyester-based powder coatings deposited on steel substrates was carried out. The effect of the test method on the identifiable mechanical properties is investigated. The measurement results obtained by using a spherical indenter and a Berkovich indenter are compared. Estimates of reduced modulus of elasticity, Young's modulus and rigidity of coatings are obtained. The experimental data obtained indicate a significant dependence of the determined mechanical properties of the paint and varnish coatings depending on the type of indenter used. In the case of Berkovich indenter, the Young's modulus of coatings (0.6 GPa) is understated in relation to coating properties known from macro experiments (3 GPa). Using a spherical indenter, Young's modulus is overestimated (6.3 GPa).

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.

The Influence of Tilt on Berkovich Indentation of a Steel Sample Using FEM Analysis and Nanoindentation

Abstract The main shape deviations of a Berkovich indenter are the indenter bluntness and indenter tilt. The influence of the Berkovich indenter tilt on the results of the FEM modelling of steel nanoindentation is evaluated in this paper. The indenter tilt has an impact on the indentation curves and contact area. The X5CrNiCuNb 16-4 steel nanoindentation was modelled by FEM and the indentation curves were obtained. The Berkovich indenter was blunted and the tilt of the indenter was changed to determine its influence on the indentation curves. The results showed that growing tilt shifts the indentation curves to higher values of indentation forces and makes unloading curves steeper which is in agreement with a larger contact area. The calculated indentation curves were compared with the experimental indentation curves and the impact of the indenter tilt to the indentation curves was determined.

Influence of poly(ethyleneimine) functionalized multi-walled carbon nanotubes on mechanical and tribological behavior of epoxy resins

Epoxy-based nanocomposites were prepared with the addition of poly(ethyleneimine) (PEI, an amine-riched polymer) functionalized multi-walled carbon nanotubes (MWCNTs), whose microstructure was characterized by TEM and FTIR spectra. Effects of PEI-functionalized MWCNTs (PEI-MWCNTs) on micromechanical properties of nanocomposites were characterized by instrumented indentation with Berkovich indenter and microscratch test with Rockwell C indenter. With the increase in the content of PEI-MWCNTs: both nanoindentation hardness and elastic modulus of nanocomposites increase; scratch normal hardness and elastic recovery rate decrease in an approximately linear way; fracture toughness obtained by scratch-based linear elastic fracture mechanics increase in an approximately linear way.

Material removal behavior analysis of ZnSe crystal during side-forward nanoscratching

Zinc selenide (ZnSe) crystal is difficult to cut due to its high brittleness. A better understanding of the material removal mechanism of ZnSe crystal is indispensable to help achieve a high-quality machined surface. In this paper, a theoretical model is first developed for analyzing the material removal behavior of brittle crystals during side-forward nanoscratching using the Berkovich indenter. The model correlates scratching parameters with scratch behavior parameters, morphology parameters, material removal modes, and material mechanical properties. To validate the model, the nanoindentation and side-forward nanoscratch tests of ZnSe crystal are carried out, and the effects of load and strain rate on the mechanical properties and scratch behavior of ZnSe crystal are investigated. The results show that the hardness decreases first and then stabilizes as the indentation load increases; the elastic modulus generally increases with the indentation load while it increases sharply at a very small strain rate. The results also show that with an increasing scratching normal load, the elastic recovery decreases first and then stabilizes while the friction coefficient increases slightly first and then stabilizes; with the increase of strain rate, the elastic recovery, scratching load, and friction coefficient decrease quickly at first and then increase by a similar power function. The model is proven to be applicable to determining the scratching load, friction coefficient, scratching depth, and elastic recovery with pile-up parameters, groove parameters, indenter orientation angle, and mechanical properties of ZnSe crystal, which has an average relative error of less than 14%. Furthermore, the effects of scratching direction on the scratching load and friction coefficient are discussed using the model. The results show that for side-forward scratching, the maximum normal load always occurs which is independent of the indenter orientation angle, while a relatively small friction coefficient exists. This research provides insights into the material removal behavior and mechanism in ultra-precision machining of ZnSe crystal.

Dimensionless Analysis to Determine Elastoplastic Properties of Thin Films by Indentation

By assuming the elastoplastic properties of thin-film materials, a reverse analysis method is proposed by deriving a dimensionless function for the indentation process. The substrate effect is taken into account by assuming a perfect interface between thin-film and substrate materials. In order to obtain the applied load–penetration depth (P-h) curves, the indentation process is numerically modeled as an axisymmetric problem with a rigid-body Berkovich indenter on the semi-infinite substrate when performing finite element (FE) simulations. As a typical soft film/hard substrate problem, the elastic substrate is assumed and the power–law model is used to describe the constitutive properties of thin-film materials. Varying elastic modulus (10–50 GPa), yield strength (60–300 MPa), and hardening exponent (0.1–0.5) characterize different elastoplastic mechanical properties of thin-film materials with film thickness of 10–30 μm. Owing to the good trending P-h curves with the maximum indentation depth up to the 2/3 film thickness for different elastoplastic thin-film materials, a dimensionless function is derived and validated based on the predictions by reliable FE simulations. The proposed dimensionless function elegantly elucidates the essential relationship between the elastoplastic mechanical properties of the thin-film material and indentation responses (e.g., loading and unloading variables). The elastoplastic constitutive curves predicted by the proposed reverse method are confirmed to be in good agreement with the stress-strain curves of materials by FE simulations with the randomly selected elastoplastic mechanical properties and film thicknesses. This study provides a theoretical guidance to understand the explicit relationship between elastoplastic mechanical properties of the thin-film material and indentation responses.

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.

Relationships in instrumented indentation by Berkovich indenter

Relationships in instrumented indentation by Berkovich indenter

Linear dependence of dislocation pattern size on the imprint width and scratch width on (0001) GaN

With the aim of developing a method of estimating the thickness of an affected layer on a wide-bandgap semiconductor wafer caused by scratching, we investigated the dependence of dislocation pattern size on the width of the imprint (or scratch) induced by the Berkovich indentation (or scratching) using a Berkovich indenter. We found that the penetration depth and width of the dislocation pattern induced on (0001) GaN by indentation are approx. 0.9 times and 30 times that of the imprint width and the imprint depth, respectively. Based on the linearity between the imprint width and the square root of load (SqL), the constant hardness is confirmed to be 0.1 mN or more. In comparison to laterally expanding dislocation generation, inclined dislocation generation has a lower threshold load. The cause of this threshold discrepancy is discussed based on the imperfection of the indenter tip. The scratch width linearly increased with the SqL in the range of 0.5–7 mN. The width and depth of the dislocation pattern induced by the scratch are approx. 11–13 and 0.75–1 times the scratch width, respectively. The width of the dislocation pattern of the [100] scratch is larger than that of the [110] scratch, however, the penetration depth of the dislocation pattern of [100] is smaller than that of [110]. These findings indicate that estimating the affected layer thickness induced by mechanical polishing or grinding is possible only by finding the widest scratch on a wafer.

Finite Element Analysis of Nanoindentation Responses in Bi2Se3 Thin Films

In this study, the nanoindentation responses of Bi2Se3 thin film were quantitatively analyzed and simulated by using the finite element method (FEM). The hardness and Young’s modulus of Bi2Se3 thin films were experimentally determined using the continuous contact stiffness measurements option built into a Berkovich nanoindenter. Concurrently, FEM was conducted to establish a model describing the contact mechanics at the film/substrate interface, which was then used to reproduce the nanoindentation load-depth and hardness-depth curves. As such, the appropriate material parameters were obtained by correlating the FEM results with the corresponding experimental load-displacement curves. Moreover, the detailed nanoindentation-induced stress distribution in the vicinity around the interface of Bi2Se3 thin film and c-plane sapphires was mapped by FEM simulation for three different indenters, namely, the Berkovich, spherical and flat punch indenters. The results indicated that the nanoindentation-induced stress distribution at the film/substrate interface is indeed strongly dependent on the indenter’s geometric shape.

Nanoindentation and Atomic Force Microscopy Derived Mechanical and Microgeometrical Properties of Tooth Root Cementum

In the present research, nanoindentation, atomic-force microscopy and optical microscopy were used to study the mechanical and microgeometrical parameters of tooth tissues. A nanoindentation test unit equipped with Berkovich indenter was used to determine the values of the reduced Young’s modulus and indentation hardness and both nanoindentation and atomic force microscopy using a diamond probe on a silicon cantilever were used to study microgeometrical parameters of human tooth root cementum. Three areas of cementum were studied: the cervical region near the dentine–enamel junction, the second third of the tooth root, and the apex of the tooth root. The interpretation of the results was carried out using the Oliver–Pharr method. It was established, that the mechanical properties of cementum increase from the cervical region to the central part of the root, then decrease again towards the apex of the tooth root. On the contrary, the microgeometrical characteristics of cementum practically do not demonstrate any change in the same direction. A decrease in the roughness parameters in the direction from cellular cementum to dentine was observed. Additionally, a decrease in the reduced Young’s modulus and indentation hardness of dentine in the cervical area compared to dentine in the crown part of the tooth was found using nanoindentation. The investigation of the dentine–cementum junction with high resolution revealed the interspaced collagen fiber bridges and epithelial rests of Malassez, whose sizes were studied. The parameters of the topographic features of the cementum in the vicinity of the lacunae of cementocytes were also established.

Crmnv and Crmntiv Heas Elastic Properties for Use in Beam Exit Windows for MW Irradiation Facilities

The choice of a material and the engineering design that is intended to lead to a beam exit window capable of sustaining mechanical and thermal loads in a high-radiation environment, while minimizing the beam loss and maximizing the window lifetime is discussed. Thin titanium windows have been typically used in industrial accelerators in the tens of kW beam power [1].The focus of this research is to conduct fundamental studies related to the choice of a material, from a material science point of view, for MW-class beam exit windows and an engineering design, including parameters such as the window size, thickness, and cooling scheme, suitable for industrial accelerators. CrMnV and CrMnTiV HEAs were selected for this study. According to Yang et al., [2], 1.1 and 6.6% should be expected as the criteria for forming high entropy stabilized solid solution phases. The two parameters of the CrMnV and CrMnTiV alloys are and respectively. Therefore, the two alloys are expected to be solid solution.The mechanical properties of CrMnV and CrMnTiV solid solution HEAs exit window prior to E-beam irradiation were measured using nanoindentation. The nanoindentation testing was carried out using XP Nanoindenter tester equipped with a three-sided diamond Berkovich indenter tip with maximum displacement of 2000 nm. The hardness is measured as 5.2 and 6.1 GPa for the bulk CrMnV and CrMnTiV solid solution HEAs at a depth of indentation of 900 nm respectively, Fig. 1. We also observe that both solid solution CrMnV and CrMnTiV HEAs depict indentation size effect. References Chmielewski A.G., Zimek, Z., Panta P., Drabik W., Radiat. Phys. Chem. 45 1029 (1995). Yang, X. and Y. Zhang, Prediction of high-entropy stabilized solid-solution in multi-component alloys. Materials Chemistry and Physics, 2012. 132(2-3): p. 233-238. Figure 1

Determine the unique constitutive properties of elastoplastic materials from their plastic zone evolution under nanoindentation

The evolution of the plastic zone underneath the indenter is challenging to be described during nanoindentation, which is recently known to be crucial to establish a constitutive model that features the plastic properties of the substrate materials based on their indentation responses. Using molecular dynamics and axisymmetric finite element (FE) simulations in this study, we show that the plastic zone shape in the elastoplastic materials is hemispherical in a broad range of length scales under a three-sided pyramid-shaped Berkovich indenter. By considering the critical factors of the applied load–penetration depth (P–h) curve, dimensional analysis is performed to derive dimensionless functions regarding the radius of the hemispherical plastic zone. For the loading and unloading stages in extensive FE simulations, a set of polynomial functions are proposed by associating the instantaneous and residual plastic zone radii with constitutive parameters. In addition to Young's modulus and the hardening exponent, the ratio of the representative stress to the reduced modulus is found to be crucial for predicting the plastic deformation. Lastly, the proposed dimensionless function reveals that the plastic zone radii are drastically different for three representative materials with identical P–h curves as confirmed by three independent methods. This result suggests that the proposed plastic zone radius in the dimensionless analysis helps to overcome the challenging uniqueness issue for decades to determine the unique elastoplastic properties of materials based on nanoindentation responses.

Micromechanical properties of Dy3+ ion-doped (LuxY1-x)3Al5O12 (x = 0, 1/3, 1/2) single crystals by indentation and scratch tests

Three kinds of Dy3+ ion-doped (LuxY1-x)3Al5O12 (x = 0, 1/3, 1/2) single crystals fabricated by the Czochralski method with 4 at.% Dy3+ ion doping were investigated by indentation and scratch techniques under Vickers, Knoop, Berkovich, and spherical indenters to understand the influence of Lu ion on micromechanical properties and fracture behavior of Y3Al5O12 (i.e. YAG for x = 0) single crystals. The largest (or smallest) values of hardness, elastic modulus, and fracture toughness were found for x = 1/3 (or 1/2). The indentation size effect was explained by four different models with the Hays-Kendall approach being the most suitable one to determine the true hardness. Fracture toughness values of YAG crystals obtained by the Vickers hardness method agreed with those obtained by scratching with a spherical indenter based on linear elastic fracture mechanics.

Spatial Resolution Limit for Nanoindentation Mapping on Metallic Glasses.

Spatial heterogeneity, as a crucial structural feature, has been intensively studied in metallic glasses (MGs) using various techniques, including two-dimensional nanoindentation mapping. However, the limiting spatial resolution of nanoindentation mapping on MGs remains unexplored. In this study, a comprehensive study on four representative MGs using nanoindentation mapping with a Berkovich indenter was carried out by considering the influence of a normalized indentation spacing d/h (indentation spacing/maximum indentation depth). It appeared to have no significant correlation with the measured hardness and elastic modulus when d/h > 10. The hardness and elastic modulus started to increase slightly (up to ~5%) when d/h < 10 and further started to decrease obviously when d/h < 5. The mechanism behind these phenomena was discussed based on a morphology analysis of residual indents using scanning electron microscopy and atomic force microscopy. It was found that the highest spatial resolution of ~200 nm could be achieved with d/h = 10 using a typical Berkovich indenter for nanoindentation mapping on MGs, which was roughly ten times the curvature radius of the Berkovich indenter tip (not an ideal triangular pyramid) used in this study. These results help to promote the heterogeneity studies of MGs using nanoindentation that are capable of covering a wide range of length scales with reliable and consistent results.

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.

Effects of sliding velocity on microscratch responses of thermoplastics by Berkovich indenter

Effects of sliding velocity on microscratch responses of thermoplastics by Berkovich indenter

An Investigation into the Densification-Affected Deformation and Fracture in Fused Silica under Contact Sliding.

Subsurface damage of fused silica optics is one of the major factors restricting the performance of optical systems. The densification-affected deformation and fracture in fused silica under a sliding contact are investigated in this study, via three-dimensional finite element analysis (FEA). The finite element models of scratching with 70.3° conical and Berkovich indenters are established. A refined elliptical constitutive model is used to consider the influence of densification. The finite element models are experimentally verified by elastic recovery, and theoretically verified by hardness ratio. Results of densification and plastic deformation distributions indicate that the accuracy of existent sliding stress field models may be improved if the spherical/cylindrical yield region is replaced by an ellipsoid/cylindroid, and the embedding of the yield region is considered. The initiation sequence, and the locations and stages of radial, median, and lateral cracks are discussed by analyzing the predicted sliding stress fields. Median and radial cracks along the sliding direction tend to be the first cracks that emerge in the sliding and unloading stages, respectively. They coalesce to form a big median–radial crack that penetrates through the entire yield region. The fracture behavior of fused silica revealed in this study is essential in the low-damage machining of fused silica optics.