Nanoindentation Hardness Research Articles

Understanding the crystallographic and nanomechanical properties of bryozoans

This study examines how microscale differences in skeletal ultrastructure affect the crystallographic and nanomechanical properties of two related bryozoan species: (i) Hornera currieae, which is found at relatively quiescent depths of c. 1000 m, and (ii) Hornera robusta, which lives at depths of 50–400 m where it is exposed to currents and storm waves. Microstructural and Electron Backscatter Diffraction (EBSD) observations show that in both species the secondary walls are composed of low-Mg calcite crystallites that grow with their c-axes perpendicular to the wall. Branches in H. currieae develop a strong preferred orientation of the calcite c-axes, while in H. robusta the c-axes are more scattered. Microstructural observations suggest that the degree of scattering is controlled by the underlying morphology of the skeletons: in H. currieae the laminated branch walls are smooth and relatively uninterrupted, whereas the wall architecture of H. robusta is modified by numerous deflections, forming pustules and ridges associated with microscopic tubules. Modelling of the Young’s modulus and measurements of nanoindentation hardness indicate that the observed scattering of the crystallite c-axes affects the elastic modulus and nanohardness of the branches, and therefore controls the mechanical properties of the skeletal walls. At relatively high pressure in deep waters, the anisotropic skeletal architecture of H. currieae is aimed at concentrating elasticity normal to the skeleton wall. In comparison, in the relatively shallow and active hydrographic regime of the continental shelf, the elastically isotropic skeleton of H. robusta is designed to increase protection from external predators and stronger omni-directional currents.

Structural, mechanical and electrochemical properties of spark plasma sintered Ti-30Ta alloys

Ti-Ta alloys are choice materials for bio-medical applications, but obtaining tailormade material properties through using spark plasma sintering (SPS) fabrication exhibits potential challenges. The effects of sintering temperature, pressure and holding time on the microstructural, crystallographic, mechanical and corrosion behaviour of spark plasma sintered Ti-30Ta alloys were investigated. Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry, microhardness and instrumented nanoindentation were used for the investigation. Microstructures obtained include martensite plates (alpha-Ti phases), beta-Ti phases, as well as significant volume of beta-Ta phases. Notable variation in crystal structure, mechanical properties and electrochemical behaviour were recorded. Generally, the materials exhibited high densification (>98%), improved micro-and nano-indentation hardness (>500 Hv), and elastic moduli (>40 GPa). Average Oxygen content of the sintered samples was 0.0106%. The measured properties of the sintered Ti-30Ta alloys suggest they can be efficient for applications in biomedical technologies.

SiC paste with high curing thickness for stereolithography

In this study, the method and mechanism of the improvement of the curing thickness of SiC by stereolithography (SLA) were investigated, the rheological properties of SiC paste were optimised, and the problem of cracking problem during debinding was solved. The best moulding process for preparing SiC ceramics with the Ceramaker 900 equipment was studied. Oxidation at 1180 °C for 1 h and hydroxylation with 0.6 mol/L H2O2 were the best modification processes for SiC powder. SiC paste with good rheological properties and high curing thickness was prepared using a resin system of BPA, HDDA, TPGDA, TMPTA, DPHA, and A-BPEF (mass ratio = 9:7:5:20:15:6). The best debinding process for SLA SiC was segmented debinding. The bulk density, total porosity, and room temperature bending strength of the SiC ceramics obtained are 2.13 g/cm3, 10.2%, 229 MPa, respectively. The nanoindentation elastic modulus and hardness of SLA SiC ceramics were found to be 18.7 and 1.66 GPa, respectively. Through this process, a lattice structure of SiC parts with good surface quality was prepared.

Properties of high entropy borides synthesized via microwave-induced plasma

Microwave-induced plasma was used to anneal precursor powders containing five metal oxides with carbon and boron carbide as reducing agents, resulting in high entropy boride ceramics. Measurements of hardness, phase structure, and oxidation resistance were investigated. Plasma annealing for 45 min in the range of 1500–2000 °C led to the formation of predominantly single-phase (Hf, Zr, Ti, Ta, Mo)B2 or (Hf, Zr, Nb, Ta, Mo)B2 hexagonal structures characteristic of high entropy borides. Oxidation resistance for these borides was improved by as much as a factor of ten when compared to conventional commercial diborides. Vickers and nanoindentation hardness measurements show the indentation size effect and were found to be as much as 50% higher than that reported for the same high entropy boride configuration made by other methods, with average values reaching up to 38 GPa (for the highest Vickers load of 200 gf). Density functional theory calculations with a partial occupation method showed that (Hf, Zr, Ti, Ta, Mo)B2 has a higher hardness but a lower entropy forming ability compared to (Hf, Zr, Nb, Ta, Mo)B2, which agrees with the experiments. Overall, these results indicate the strong potential of using microwave-induced plasma as a novel approach for synthesizing high entropy borides.

Remote laser welding of Zn coated IF steel and 1050 aluminium alloy: processing, microstructure and mechanical properties

The integrity of steel-aluminium dissimilar alloy joints is dependent on the intermetallic phases (IMCs) and the extent of the bonding area. The excessive growth of brittle AlxFex IMCs within the weld pool and interfaces is disadvantageous due to the initiation and propagation of hot and cold cracking during the solidification. The purpose of this work was to assess the development of Remote Laser Welded (RLW) joints of Zn coated interstitial free (IF) steel to 1050 aluminium alloy, which can be used in cooling circuits and electrical connectors in automotive applications. Welding experiments with variable RLW parameters (power, welding speed and focal offset) were performed to study the formation of IMCs and impact of joint integrity. Results showed that while in conduction mode (at power densities of 0.13–0.18 MW/cm2) three IMCs were identified through SEM/EDX and EBSD: η – Al5Fe2, κ – AlFe3 and θ – Al13Fe4 which possessed nano-hardness indentation values of approximately 12, 5 and 5 GPa, respectively; they formed in a non-continuous interfacial layer, the weld pool composition remained homogenous, and cracking was minimal. On the contrary, in keyhole mode (at power densities of 0.16–0.40 MW/cm2) welded samples produced a continuous and thick IMC layer, continuous and/or excessive cracking and an inhomogeneous weld pool composition due to the excessive mixing of steel and aluminium, of up to 10 wt.% of Al in the weld pool. The nominal lap shear strength for the sample produced in conduction mode was of 77%, with respect to the weakest joint material (Al). This work found a close link between the welding mode and weld pool chemistry which significantly determined the IMCs distribution and thickness, extent of cracking within the weld pool and mechanical properties.

Insights into hardening, plastically deformed zone and geometrically necessary dislocations of two ion-irradiated FeCrAl(Zr)-ODS ferritic steels: A combined experimental and simulation study

As one of promising candidate materials for fuel claddings and structural components in the Gen-IV fission reactors, FeCrAl(Zr)-ODS ferritic steels were studied to well understand the radiation hardening behavior. Nanoindentation (NI) hardness and plastically deformed zone (PDZ), geometrically necessary dislocations (GNDs) as well as microstructures were investigated for two FeCrAl(Zr)-ODS ferritic steels irradiated with 6.4 MeV Fe3+ at room temperature (RT) up to the nominal damages of 2, 10 and 50 dpa. Irradiation-induced hardening, which was estimated by using the Nix-Gao model regardless of the damage gradient effect (DGE), increased continuously with increasing the nominal displacement damage. When taking the DGE into account, the dependence of the irradiation hardening (in MPa) on a local damage level (dpa) obtained by finite element method (FEM) simulations was 153.65 × (dpa)0.26 and 158.35 × (dpa)0.25 for the non-Zr steel and the Zr-added one, respectively. The hardening caused by ion-irradiation was discussed in terms of the loss of oxide particles, the formation of dislocation loops and the solid solution hardening mainly by dissolved oxygen. The addition of Zr reduced the ion-irradiation hardening of steel to some extent mainly by suppressing the formation of dislocation loops. Meantime, as the FEM simulations revealed, the PDZ size underneath a conical indenter at the equivalent plastic strain εeq > 1.9% can reasonably estimate the density of GNDs. According to the strain gradient plasticity (SGP) theory, the densities of GNDs at an indentation depth of 200 – 300 nm were slightly higher in the case of the 50 dpa/nominal than the unirradiated, in spite of similarity for the two FeCrAl(Zr)-ODS steels.

Bio‐Inspired Macromolecular Ordering of Elastomers for Enhanced Contact Electrification and Triboelectric Energy Harvesting

AbstractTriboelectrification of polymers enables mechanical energy harvesting in triboelectric generators, droplet generators, and ferroelectrets. Herein, triboelectric polymers, inspired by the ordering in spider‐silk, with strongly enhanced contact electrification are presented. The ordering in polyether block amide (PEBA) is induced by the addition of inorganic goethite (α‐FeOOH) nanowires that form H‐bonds with the elastomeric matrix. The addition of as little as 0.1 vol% of α‐FeOOH into PEBA increases the surface charge by more than order of magnitude (from 0.069 to 0.93 nC cm–2). The H‐bonds between α‐FeOOH and PEBA promote the formation of inclusions with higher degree of macromolecular ordering, analogous to the structure of spider silk. The formation of these inclusions is proven via nanoindentation hardness measurements and correlated with H‐bond‐induced chemical changes by Fourier transform infrared spectroscopy and direct scanning calorimetry. Theoretical studies reveal that the irregularity in hardness provides stress accumulation on the polymer surface during contact‐separation. Subsequent molecular dynamic studies demonstrate that stress accumulation promotes the mass‐transfer mechanism of contact electrification. The proposed macromolecular structure design provides a new paradigm for developing materials for applications in mechanical energy harvesting.

Tuning the microstructure and mechanical properties in nanocrystalline Cr coatings by sputtering power

A significant sputtering power effect on the microstructure and mechanical properties was investigated in the nanocrystalline Cr coatings that were prepared by employing magnetron sputtering. Experimental results demonstrated that all the Cr coatings exhibited a columnar grain structure with preferred (110) out-of-plane orientation. However, with raising the sputtering power from 50 to 250 W, the surface morphology changed from the faceted pyramid to vermiform-like shape due to the anisotropy of growth rate along different crystallographic plane. Meanwhile, raising sputtering power also increased the grain size and coating thickness, between of which followed a power-law relationship, indicative of an evolutionary overgrowth mechanism. In addition, both the nanoindentation hardness and elastic modulus of Cr coatings exhibited a monotonic increment with reducing the grain size. This size-dependent strengthening behavior was rationally interpreted by the classical Hall-Petch theory, and a grain coalescence model for columnar grain morphology was developed to quantitatively describe the size effect on elastic modulus of nanocrystalline Cr coatings.

Evaluating the irradiation hardening of reactor pressure vessel steels by nanoindentation hardness test and micropillar compression test

ABSTRACT Ultra-small testing technologies (USTTs), such as nanoindentation hardness tests and micropillar compression tests, can be potentially used to measure the mechanical properties of irradiated materials. However, the hardness and yield strengths of USTTs are different from those of standardized methods on bulk samples. In addition, irradiation-induced defects can affect the size dependence on the mechanical properties. This study examined A533B reactor pressure vessel steels before and after 5 MeV electron irradiation using USTTs. The depth dependence of the nanoindentation hardness was analyzed using the Nix-Gao model to evaluate the bulk-equivalent nanoindentation hardness and confirm its good linear relationship with the Vickers hardness. The compression yield strength was evaluated with a truncated square pyramid shape micro-pillars where the edge length (d) of the top surface and the height (L) of the micropillars were made similar: (d, L) = (1,2), (2,4), (3,6), (4,8), and (8,16) in μm. The size dependence of the yield stress in the micropillars has a minimum at d = 2 µm, which remained unaffected by electron beam irradiation up to 22 mdpa. The average yield stress of the d = 4 and 8 µm specimens was similar to that of the bulk tensile specimens.

Practical method to determine the effective zero-point of indentation depth for continuous stiffness measurement nanoindentation test with Berkovich tip

The zero-point of indentation depth in nanoindentation or depth-sensing instrumented indentation tests should be precisely set to evaluate the indentation hardness and indentation elastic modulus of materials to be tested, especially at shallow depths. A critical contact stiffness value has been widely used to determine the zero-point in nanoindentation tests with a Berkovich tip using the continuous stiffness measurement (CSM) method. However, this criterion occasionally gives an inadequate zero-point owing to the surface roughness of materials, the vibration of the testing system, and the flaws of the CSM method at shallow depth. This study proposes a practical method to determine the effective zero-point of indentation depth, which was obtained linearly at the zero-point of contact stiffness and extrapolated from the depth-dependent contact stiffness values, except for those at initially unstable contact depths. The proposed method enables nanoindentation tests to obtain a constant indentation elastic modulus and low deviation of nanoindentation hardness of homogenously fused silica and metallic materials, which provides an efficient way to obtain more accurate test data.

Mesoscale model and X-ray computed micro-tomographic imaging of damage progression in ultra-high-performance concrete

Predicting the mechanical performance of concrete from composition and processing remains a grand challenge. Our work focuses on predicting damage evolution in ultrahigh-performance concrete (UHPC), where analysis is challenging due to a lack of separation in the length scales of heterogeneity and a limited availability of data to describe the strength and failure of individual phases. Cement-hydration modeling informs segmentation of CT images from mechanical tests, providing a highly resolved 3-D representation of microstructure and damage evolution. Mesoscale simulations of damage in UHPC reveal how the relative strength of cement phases affects patterns of intra- and inter-granular fracture. We find that the nano-indentation hardness of individual phases is not necessarily a predictor of the relative shear strength needed to match experimentally observed fracture patterns. The mesoscale model predicts complicated material responses as emergent phenomena from relatively simple models of individual phases - a path towards forward modeling UHPC constitutive response.

Deposition, microstructure and nanoindentation of multilayer Zr nitride and carbonitride nanostructured coatings

Nitrides, carbides, and carbonitrides of transition metal elements like Zr, W, Ti, etc. are generally employed to produce hard coatings. Zirconium-based hard coatings have shown useful applications in the areas of tribology, biomedicine and electrical due to their high thermal stability, hardness, biocompatibility, good erosion, wear, and corrosion resistance. In this study, we created homogeneous and tenacious nanostructured hard coatings based on Zr with good mechanical properties. The magnetron sputter deposition technique was utilized to coat stainless steel 316L substrates with multilayers of Zr/ZrN and ZrN/ZrCN with individual layer thicknesses of 250 and 500 nm for each coating composition. The deposition conditions were adjusted to create two different coating thicknesses of 2 and 3 µm. The thickness of the coating was confirmed using Calotest and the coatings’ morphology and elemental composition were determined utilizing the atomic force microscope and scanning electron microscope equipped with energy dispersive x-ray spectrometer. Coating thickness and adhesion were measured using cross-sectional samples and XRD was utilized to analyze the coatings structure. Nanoindenter was employed to determine the instrumental nanoindentation hardness and elastic modulus. The influence of coating thickness on tribological behavior was further investigated using the ratio of nanohardness-to-elastic modulus (H/E). No evidence of decohesion was observed at the substrate/coatings interface, and the grains of all the coatings were observed to show columnar growth which were homogeneous, compact and dense. The grains of the ZrN/ZrCN coatings were observed to be denser, finer and more compact compared to those of the Zr/ZrN coatings. Correspondingly, higher hardness, modulus and H/E values were exhibited by ZrN/ZrCN than Zr/ZrN coatings. This suggests that the ZrN/ZrCN coatings are capable of exhibiting better wear resistance and fracture toughness. The coatings developed in this investigation are anticipated to be suitable for applications in tribology due to their excellent hardness and H/E properties.

Influence of Si Doping on Dislocations and Mechanical Properties of GaAs Crystals Grown by Modified Vertical Bridgman Method

AbstractGaAs crystals are important III–V compound semiconductor materials and the bandgap and quantum efficiency can be optimized by doping. However, the doping may bring some problems to the crystal growth. In this paper, Si‐doped GaAs crystals are grown by the modified vertical Bridgman method and the influence of Si doping on dislocations and mechanical properties are discussed. It is found that a proper amount of Si doping significantly reduces the dislocation density of GaAs crystals. The mechanical properties of (100), (110), (111), and (511) planes are measured, and the results show that the mechanical properties of Si‐doped GaAs crystals have obvious anisotropy. The (111) plane has the strongest mechanical properties among them. The Vickers hardness, fracture toughness, nanoindentation hardness, and elastic modulus of the (111) plane are 6.05 GPa, 0.69 MPa m1/2, 10.82 GPa, 138.7 GPa, respectively. Moreover, Si doping can improve the mechanical properties of GaAs crystals.

Ultra-high-rate deposition of diamond-like carbon films using Ar/C2H2 plasma jet CVD in combination with substrate-stage discharge

Diamond-like carbon (DLC) films with excellent mechanical properties are used as functional surface protective films for cutting tools. The deposition rate of DLC films using conventional plasma chemical vapor deposition (CVD) methods is several hundred nm min−1. This study applied a negative DC pulsed voltage to a substrate stage irradiated with an Ar/C2H2 mixed plasma jet. The effect of the voltage applied to the stage on the fabricated DLC films was investigated based on the thicknesses and characteristics of the films. DLC films were formed on Si substrates using an Ar/C2H2 plasma jet CVD system. Ar plasma was ejected from a circular nozzle, and C2H2 gas was supplied as a carbon source gas from the center of the circular nozzle. DLC films with a nanoindentation hardness of 17 GPa were obtained by applying −500 V to the stage with a deposition rate of 2140 nm min−1.

Ion Release and Surface Changes of Nickel-Titanium Archwires Induced by Changes in the pH Value of the Saliva-Significance for Human Health Risk Assessment.

The aim of this study was to explore whether changes in the salivary pH influence mechanical properties, surface roughness, and ion release from NiTi archwires with various surface coatings, and discuss the clinical significance of the findings. The uncoated, rhodium-coated, and nitrified NiTi wires were immersed into artificial saliva of different pH values (4.8, 5.1, 5.5, and 6.6). Released nickel and titanium ions were measured with inductively coupled plasma-optical emission spectroscopy at the end of 28 days. Atomic force microscopy was used to measure the arithmetic average surface roughness Ra, the root-mean-square roughness Rq, and the maximum height of the asperities RZ. The nanoindentation hardness (HIT) and Young’s modulus (EIT) measurements were performed. The change in the pH of artificial saliva is inversely proportional to the release of titanium from both coated and uncoated wires, and the release of nickel from uncoated wires. The surface roughness parameters of both coated and uncoated wires are unaffected by the change in the pH of artificial saliva. The change in the pH of saliva has minor influence on the hardness and Young’s modulus of elasticity of both coated and uncoated wires. The concentration of released metal ions measured was below the recommended upper limit for daily intake; nevertheless, hypersensitivity effects cannot be excluded, even at lower concentrations and at low pH.

3D micro-structuring by CW direct laser writing on PbO-Bi2O3-Ga2O3 glass

Direct laser writing was successfully performed into high refractive-index glasses with the composition of (PbO)0.75-x(Bi2O3)x(Ga2O3)0.25for x = 0–0.3, using focused continuous-wave laser beam emitting at 447 nm. The local changes in the material dimensions were induced by the illumination. Due to local overheating of the illuminated area microlenses and microcraters were formed. The overheating magnitude was calculated employing COMSOL-SWfor illumination time 0.5 s and directly measured for the steady-state conditions.The microlens and microcrater formations with potential applications in optics were studied and the role of Bi2O3content on their formation was investigated. The glasses with different Bi2O3content had similar optical (penetration depth of laser), physical (density) and thermal (coefficient of thermal expansion) properties. On the contrary, the threshold power densities of the microlenses formationand microlines or their heights were significantly affected by the Bi2O3presence. No changes in the chemical compositionand structural arrangement were observed between non-illuminated materials and the objects (microlenses, microlines) formed by direct laser writing.However, the nanoindentation hardness of the objects was significantly lower compared to non-illuminated glass. The threshold power density of microcraters formationdoes not depend on the chemical composition due to the similar residual roughness of the surfaces.

Nanoindentation Hardness and Corrosion Studies of Additively Manufactured 316L Stainless Steel

Nanoindentation Hardness and Corrosion Studies of Additively Manufactured 316L Stainless Steel

Using multiple regression analysis to predict directionally solidified TiAl mechanical property

The mechanical properties of TiAl alloy prepared by directional solidification were predicted through a machine learning algorithm model. The composition, input power, and pulling speed were designated as input variables as representative factors influencing mechanical properties, and multiple linear regression analysis was conducted by collecting data obtained from the literature. In this study, the R2 value of the tensile strength prediction result was 0.7159, elongation was 0.8459, nanoindentation hardness was 0.7573, and interlamellar spacing was 0.9674. As the R2 value of the elongation obtained through the analysis was higher than the R2 value of the tensile strength, it was confirmed that the elongation had a closer relationship with the input variables (composition, input power, pulling speed) than the tensile strength. By adding the elongation to the tensile strength as an input variable, it was observed that the R2 value was further increased. The tensile test prediction results were divided into four groups: The group with the lowest residual value (predicted value-actual value) was designated as group A, and the group with the largest residual value was designated as group D. When comparing the values of group A and group D, more overpredictions occurred in group A, while more underpredictions occurred in group D. Using the residuals and R2 values, the cause of the well-prediction was studied, and through this, the relationship between the mechanical properties and the microstructure was quantitatively investigated.

Особенности получения танталосодержащих покрытий на титане методом магнетронного напыления

Tantalum-containing coatings deposited on titanium in vacuum were studied. For deposition of films, a DC magnetron with a balanced magnetic system was used. High purity (99.99 %) tantalum sheet was used as a target. The current density of the glow discharge during the etching of the target was 20.4 A / m2. Plasma-forming gases were argon or a mixture of argon and oxygen. Three types of coatings of tantalum on titanium were obtained: the first one was tantalum oxide on titanium, the second — tantalum on titanium, and the third — tantalum on titanium with a tantalum oxide sublayer. The effect of a pre-deposited sublayer of tantalum oxide on the hardness and morphology of the “base-coating” system was studied. It was found that of the greatest practical interest is an oxygen-saturated tantalum coating with the thickness of 800 nm deposited on a tantalum oxide sublayer with the thickness of 75 – 80 nm. Nanoindentation of samples with a tantalum-containing coating without a tantalum oxide sublayer revealed an increase in hardness up to 39 GPa and in elastic modulus up to 194 GPa. In case of the deposited tantalum oxide sublayer, the nanoindentation hardness reached 60 GPa, and the elastic modulus was 230 GPa. This superhard two-layer structure had a bimodal hardness distribution and contained a Ta2O phase with a cubic crystal lattice. In this case, the proportion of measurements related to superhard inclusions was at least 43 %. The coating had a heterogeneous structure consisting of agglomerates with a size of 0.4 – 0.5 µm. The chemical composition of the surface layer was characterized by an oxygen content of 17.46 at.%, titanium — within 2.00 at.%, and tantalum — 80.54 at.%. An increase in the proportion of coating agglomerates with a size of 0.2 – 0.3 µm was observed from 53.13 to 68.25 % when using a tantalum oxide sublayer. The results make it possible to consider the developed process of obtaining coatings promising for the application of functional layers on titanium medical devices.

Machine learning prediction of the mechanical properties of γ-TiAl alloys produced using random forest regression model

The mechanical properties of a directionally solidified (DS) TiAl alloy were predicted through a random forest regression (RFR) machine learning algorithm. The prediction results were evaluated using the R2 value. As a result, the R2 values of prediction for the tensile strength, elongation, nanoindentation hardness, and interlamellar space were 0.9336, 0.9902, 0.8104, and 0.9810, respectively. To observe the correlation between the microstructure and mechanical properties, RFR prediction was conducted with a double input variable. This yielded a R2 value of tensile strength of 0.9856, which was higher than the tensile strength derived with a single input variable. The R2 value of nanoindentation hardness increased to 0.9902, which was higher than the nanoindentation hardness value with a single input variable. Through the use of the double input variables, the relationships among tensile strength and elongation, nanoindentation hardness, and interlamellar space were observed. Using feature importance, which could not be obtained in a previous study using the MLR algorithm, it was possible to determine which input variable had the most efficiency with respect to the output variable. Based on these research results, the speed and accuracy of new alloy development specifically in the design and processing, can be increased. In addition, metallurgical research on the relationship between the interlamellar space and mechanical properties was conducted, and the relationship was verified through the results of machine learning training.