Nanoscale Hardness Research Articles

Changes in the nanomechanical properties of the constituent minerals in the ductile fauske marble and the brittle kuru granite during progressive failure

The nanoscale elastic moduli and hardness of the constituent minerals of the Class II Kuru granite and the Class I Fauske marble were experimentally investigated. The aims were to correlate the microcrack patterns with the nanomechanical properties of the minerals, and to help understand the important roles of the nanomechanical properties of the minerals in brittle and ductile behaviors. Cylindrical rock specimens were uniaxially loaded to various stress levels in both the pre- and post-peak stages. The specimens were then unloaded to zero, and two thin sections –– one parallel with and the other perpendicular to the loading direction –– were prepared from each specimen. Nano-indentation tests were conducted on the thin sections to measure the elastic moduli and hardness of the major constituent minerals in the rocks. The test results showed that both the elastic moduli and hardness of the minerals abruptly decreased when the applied stress was above 80 % of the uniaxial compressive strength of the rock in the pre-peak stage and also in the entire post-peak stage. At the same time, the values of the two properties became more scattered with increasing damage to the minerals. The number of intragranular cracks was significantly less in the harder quartz and microcline than in the softer calcite. The abundant intragranular cracks in the calcite dissipated most of the strain energy in the Class I marble, such that the rock was not burstable after failure. A small number of intragranular cracks were created in the quartz and microcline in the Class II granite, such that most of the strain energy in the minerals was released to eject rock after failure. Intragranular cracking is thus a key factor in determining whether a rock is burst-prone or not.

Investigating the nanoscale hardness/strength properties of high-entropy alloy particles using the nanoindentation technique

Particulate feedstock constitutes the building block in modern day additive manufacturing (AM) era. Cold spray (CS) is a leading process technology to adhere to the AM principle. Therefore, meeting feedstock qualities is of utmost interest to ensure the conformability and competitiveness of the developed industrial modules, including coatings, architectured components, and additively repaired devices. This research advances the understanding of nanoscale hardness/strength properties of particulate matters, specifically of an emerging material class, - high-entropy alloys (HEAs). The feasibility of determining the hardness of mechanically alloyed AlCoCrFeNix (x = 0, 1, 2.1) HEA particles was studied employing the nanoindentation technique. Mechanical properties of milled AlCoCrFeNix particles with varying Ni atomic ratio (x = 0, 1, 2.1) were investigated over different milling times ranging between 4 and 24 h. The study analyzed the impact of mounting resin, pre-determined maximum load, and indentation depth on hardness/strength properties. Results reveal that the hot mounted samples yielded greater accuracy and higher hardness values than compared to those of the cold mounted samples. Additionally, although the low-load sensitivity of AlCoCrFeNix provided consistent nano-scale hardness values across selected loads, their hardness values were found to be depth-dependent. Overall, the study concludes with a methodology for the nano-scale hardness/strength measurement of HEA particles that must account for particle size, sample preparation technique, and nanoindentation test parameters.

Prediction of steel nanohardness by using graph neural networks on surface polycrystallinity maps

Nanoscale hardness in polycrystalline metals is strongly dependent on microstructural features that are believed to be influenced from polycrystallinity — namely, grain orientations and neighboring grain properties. We train a graph neural networks (GNN) model, with grain centers as graph nodes, to assess the predictability of micromechanical responses of nano-indented 310S steel surfaces, based on surface polycrystallinity, captured by electron backscatter diffraction maps. The grain size distribution ranges between 1–100 μm, with mean size at 18μm. The GNN model is trained on nanomechanical load-displacement curves to make predictions of nano-hardness, with sole input being the grain locations and orientations. We explore model performance and its dependence on various structural/topological grain-level descriptors (e.g. grain size and number of neighbors). Analogous GNN-based frameworks may be utilized for quick, inexpensive hardness estimates, for guidance to detailed nanoindentation experiments, akin to cartography tool developments in the world exploration era.

Deep learning virtual indenter maps nanoscale hardness rapidly and non-destructively, revealing mechanism and enhancing bioinspired design

Deep learning virtual indenter maps nanoscale hardness rapidly and non-destructively, revealing mechanism and enhancing bioinspired design

Functional Surfaces via Laser Processing in Nickel Acetate Solution.

This study presents a novel laser processing technique in a liquid media to enhance the surface mechanical properties of a material, by thermal impact and micro-alloying at the subsurface level. An aqueous solution of nickel acetate (15% wt.) was used as liquid media for laser processing of C45E steel. A pulsed laser TRUMPH Truepulse 556 coupled to a PRECITEC 200 mm focal length optical system, manipulated by a robotic arm, was employed for the under-liquid micro-processing. The study's novelty lies in the diffusion of nickel in the C45E steel samples, resulting from the addition of nickel acetate to the liquid media. Micro-alloying and phase transformation were achieved up to a 30 µm depth from the surface. The laser micro-processed surface morphology was analysed using optical and scanning electron microscopy. Energy dispersive spectroscopy and X-ray diffraction were used to determine the chemical composition and structural development, respectively. The microstructure refinement was observed, along with the development of nickel-rich compounds at the subsurface level, contributing to an improvement of the micro and nanoscale hardness and elastic modulus (230 GPa). The laser-treated surface exhibited an enhancement of microhardness from 250 to 660 HV0.03 and an improvement of more than 50% in corrosion rate.

Effect of Pre-deformation on Nanoscale Precipitation and Hardness of a Maraging Stainless Steel

Effect of Pre-deformation on Nanoscale Precipitation and Hardness of a Maraging Stainless Steel

Effect of heat treatment on nano-mechanical behaviour of matrix and carbide phases of Fe–13Cr–1C hardfaced alloy coating

Fe–Cr–C hardfaced coatings are applied over components used in mining, earth moving, ash and coal handling systems. The performance of these coatings depend on microstructural phases present in the deposit post-solidification and/or heat treatment. To prevent the failure of a coating, understanding the mechanical behaviour of the existing phases is one of the key areas of focus. In the current investigation, the study was limited to understand the influence of heat treatment process on nano-scale hardness and reduced modulus properties of phases of Fe–13%Cr–1%C hardfaced alloy coating by accelerated property mapping (XPM) technique. Colour variation in the property maps showed the relative deformation nature of the material. The hardness and reduced modulus values for carbide phases were found to be higher in all conditions. From Weibull statistical analysis, the Weibull modulus values reduced drastically for the carbide phase after heat treatment, revealing higher variability of mechanical properties. The above trends were observed mainly due to %C and %Cr difference across phases and carbide phase morphology transformation happened due to heat treatment.

Improving Mechanical Properties of Mg–Sc Alloy by Surface AZ31 Layer

Building a gradient structure inside the Mg alloy structure can be expected to greatly improve its comprehensive mechanical properties. In this study, AZ31/Mg–Sc laminated composites with gradient grain structure were prepared by hot extrusion. The microstructure and mechanical properties of the Mg–1Sc alloy with different extrusion temperatures and surface AZ31 fine-grain layers were investigated. The alloy has a more obvious gradient microstructure when extruded at 350 °C. The nanoscale hardness value of Mg–1Sc alloy was improved through fine-grain strengthening and solution strengthening of the surface AZ31 fine-grain layer. The strength of Mg–1Sc alloy was improved due to the fine-grain strengthening and dislocation strengthening of the surface AZ31 fine-grain layer, and the elongation of Mg–1Sc alloy was increased by improving the distribution of the microstructure.

Mechanisms of elastoplastic deformation and their effect on hardness of nanogranular Ni-Fe coatings

This article contains the study of correlation between the microstructure, mechanical properties and mechanisms of elastoplastic deformation of Ni-Fe coatings that were grown in five electrodeposition modes and had fundamentally different microstructures. A nonlinear change in hardness was detected using nanoindentation. Explanation of the abnormal change in hardness was found in the nature of the relaxation method of elastoplastic energy under load. It is shown that the deformation of coatings with a grain size of 100 nm or more occurs due to dislocation slip. A decrease in grain size leads to the predominance of deformation due to rotations and sliding of grains, as well as surface and grain boundary diffusion. The effect of deformation mechanisms on the nanoscale hardness of Ni-Fe coatings was established. Full hardening of the coatings (both in the bulk and on the surface) was achieved while maintaining the balance of three mechanisms of elastoplastic deformation in the sample. Unique coatings consisting of two fractions of grains (70% of nano-grains and 30% of their agglomerates) demonstrate high crack resistance and full-depth hardening up to H = 7.4 GPa due to the release of deformation energy for amorphization and agglomeration of nanograins.

Understanding imprint formation, plastic instabilities and hardness evolutions in FCC, BCC and HCP metal surfaces

Nanoindentation experiments in metal surfaces are characterized by the onset of plastic instabilities along with the development of permanent nanoimprints and dense defect networks. This investigation concerns massive molecular dynamics simulations of nanoindentation experiments in FCC, BCC and HCP metals using blunted (spherical) tips of realistic size, and the detailed comparison of the results with experimental measurements. Our findings shed light on the defect processes which dictate the contact resistance to plastic deformation, the development of a transitional stage with abrupt plastic instabilities, and the evolution towards a self-similar steady-state characterized by the plateauing hardness p p at constant dislocation density ρ p . The onset of permanent nanoimprints is governed by stacking fault and nanotwin interlocking, the buildup of nanostructured regions and crystallites throughout the imprint, the cross-slip and cross-kinking of surfaced screw dislocations, and the occurrence of defect remobilization events within the plastic zone. As a result of these mechanisms, the ratio between the hardness p p and the Young's modulus E becomes higher in BCC Ta and Fe, followed by FCC Al, HCP Mg and large stacking fault width FCC Ni and Cu. Finally, when nanoimprint formation is correlated with the uniaxial response of the indented minuscule material volume, the hardness to yield strength ratio, p p / σ ys , varies from ≈ 7 to ≈ 10, which largely exceeds the continuum plasticity bound of ≈ 2.8. Our results have general implications to the understanding of indentation size-effects, where the onset of extreme nanoscale hardness values is associated with the occurrence of unique imprint-forming processes under large strain gradients.

Effects of Y2O3/Ti/Zr addition on microstructure and hardness of ODS-CoCrFeNi HEAs produced by mechanical alloying and spark plasma sintering

Oxide dispersion strengthened (ODS) high entropy alloys (HEAs) are potential structural materials for advanced nuclear reactor application due to their excellent radiation tolerance and high-temperature mechanical properties. ODS-CoCrFeNi HEAs with different type and amount Y2O3/Ti/Zr addition were synthesized by mechanical alloying (MA) and spark plasma sintering (SPS) to reveal the effects of Y2O3/Ti/Zr addition on the types, size, and number density of nanoscale oxides and hardness. The microstructure was characterized by XRD, XPS, EBSD and HRTEM, and the micro-hardness was tested. The results showed that ODS-CoCrFeNi HEAs mainly consist of face-centered cubic structural CoCrFeNi matrix, high-density nanoscale oxides together with few coarse carbides/oxides. The alloys exhibit the bimodal grain size distribution, and the addition of Y2O3/Ti/Zr reduce the average grain size. The type of nanoscale oxides in the ODS-HEAs is strongly related to the type of oxide-forming elements added. The cubic or monoclinic Y2O3 oxides are identified in the ODS-HEAs with the addition of only Y2O3. The nanoscale oxides, orthorhombic Y2TiO5 and orthorhombic YTiO3 or cubic Y2Ti2O7, are observed in the HEAs with the addition of both Y2O3 and Ti. Hexagonal Y4Zr3O12 are found in the HEAs with both Y2O3 and Zr. The number density and average size of nanoscale oxides depend on both the number and type of Y2O3/Ti/Zr addition. In ODS-HEAs with 3 wt% Y2O3 and 3 wt% Zr, the number density of nanoscale oxides is the highest, which is ∼3.14 × 1022/m3, and the hardness is up to 676 HV. This demonstrates that the joint addition of Y2O3 and Zr has the most obvious influence on microstructure and hardness compared to the addition of Y2O3 or Y2O3+Ti.

SiCxNyOz Coatings Enhance Endothelialization and Bactericidal activity and Reduce Blood Cell Activation.

For biomedical applications, a number of ceramic coatings have been investigated, but the interactions with the components of living system remain unexplored for oxycarbonitride coatings. While addressing this aspect, the present study aims to provide an understanding of the biocompatibility of novel SiCxNyOz coatings that could validate the hypothesis that such coatings may not only enhance the cell-material interaction by re-endothelialization but also can help to reduce bacterial adhesion and activation of blood cells. This work reports the physicochemical properties, hemocompatibility, endothelialization, and antibacterial properties of novel amorphous SiCxNyOz coatings deposited on commercial pure titanium (Ti) by radiofrequency (RF) magnetron sputtering at varied nitrogen (N2) flow rates. A comparison is made with diamond-like carbon (DLC) coatings, which are clinically used. The surface roughness, surface wettability, nanoscale hardness, and surface energy of SiCxNyOz coatings were found to be dependent on the nitrogen (N2) flow rate. Importantly, the as-deposited SiCxNyOz coatings exhibited much better nanoscale hardness and scratch resistance than DLC coatings. Furthermore, Raman spectroscopy analysis of the SiCxNyOz coating deposited on Ti showed a change in the graphitic/disordered carbon content. Cytocompatibility and hemocompatibility properties of the as-deposited SiCxNyOz coating were evaluated using the Mus musculus lymphoid endothelial cell line (SVEC4-10) and rabbit blood in vitro. WST-1 assay analysis showed that these coatings, when compared to DLC, exhibited a better proliferation of endothelial cells, which can potentially result in improved surface endothelialization. Furthermore, qualitative and quantitative analyses of immunofluorescence images revealed a dense cellular layer of SVEC4-10 on SiCxNyOz coatings, deposited at 15 and 30 sccm nitrogen flow rates. As far as compatibility with rabbit blood is concerned, the hemolysis of the SiCxNyOz coatings was less than 4%, with slightly lower values for coatings deposited without N2 flow. The SiCxNyOz coatings support less platelet adhesion and aggregation, with no signature of morphological deformation, as compared to the uncoated titanium substrate or DLC coatings. Furthermore, SiCxNyOz coatings were also found to be effectively extending the blood coagulation time for a period of 60 min. The antimicrobial study of as-deposited SiCxNyOz coatings on E. coli and S. aureus bacteria revealed the effective inhibition of bacterial proliferation after 24 h of culture. An attempt has been made to explain the cyto- and hemocompatibility properties with antimicrobial efficacy of coatings in terms of the variation in the coating composition and surface energy. Taken together, we conclude that SiC1.3N0.76O0.87 coating having a roughness of 17 nm and a surface free energy of 54.0 ± 0.7 mN/m can exhibit the best combination of hardness, elastic modulus, scratch resistance, cytocompatibility, hemocompatibility, and bactericidal properties.

Study of plasma-hardened wheel steel using nanoindentation

The necessity and possibility of using nanoindentation in studying the physical and mechanical properties of plasma-hardened wheel steel are considered. The goal of the study is demonstration and substantiation of significant differences in the mechanical properties and behavior of the materials in nanoscale tests from those determined in traditional macroscopic tests. The method was implemented using a NanoHardnessTecter nanohardness tester. The electric field formed in the nanoscale hardness tester pressed on the indenter and the diamond tip of the indenter is immersed in the surface layer of the material under study. The characteristics of the surface layer are determined using the developed software. Knowledge of the physicomechanical characteristics of the material (hardness, Young’s modulus, elastic recovery, etc.) which affect the wear resistance of the surface layers, allows one to evaluate and select the optimal surface modification technology using plasma hardening. The credibility of determination depends on the parameters of measuring equipment and compliance with the requirements to the depth of the imprint depending on the thickness of the hardened layer. The studies were carried out on the samples cut from the rim and crest of a railway wheel subjected to surface plasma hardening on a UPNN-170 installation (Russia). It is shown that the hardness (according to VickersHVandH) of the rim is greater, and Young’s modulus, on the contrary, is less than the corresponding characteristics of the crest. Moreover, the wear resistance of hardened structural steel increases after nanostructural friction treatment.

Properties of silicon carbide fibers obtained by silicification of carbon fabric with SiO vapours

The method of siliconizing carbon fabric with SiO vapours yields a textile SiC material that preserves the structure and integrity of the fibers of the original fabric, as well as the average diameter of the monofilament. According to X-ray phase analysis, it was found that SiC fibres obtained by siliconizing silicon fabric with SiO vapor consist of a mixture of two modifications of 3C–SiC and 6H–SiC. According to infrared absorption, the oxygen content in the composition of silicon carbide fibers does not exceed 2.1 wt%. The mechanical properties of the obtained fibers were investigations: the mechanical tensile strength of silicon carbide fibers is σp = 1350 ± 120 MPa, the nanoscale hardness is 10 ± 0.5 GPa, and the elastic modulus is 100 ± 10 GPa.

The effect of nitrogen ion implantation on nano-scale hardness and elastic modulus of WC-Co indexable knives for wood materials machining

The effect of nitrogen ion implantation on nano-scale hardness and elastic modulus of WC-Co indexable knives for wood materials machining. The paper presents the results of a study investigating the effects of nitrogen ion implantation into the surface layer of WC-Co blades, used for machining wood materials, on their hardness and modulus of elasticity at the nano-scale. The modified blades were analyzed in six variants of implantation process parameters, and compared with control blades (virgin, unmodified). Three energies of accelerating nitrogen ions were used in the implantation process (5, 50 and 500 keV) and two doses of implanted ions (1e17 and 5e17 cm-2). The nano-hardness and elastic modulus of all blades were measured using an Anton Paar TriTec (UNHT) hardness tester.

Tailoring microstructure and mechanical performance of the graphite-Ni based superalloy brazed combination used for molten salt reactors through thermal exposure

The work investigated the effect of high- and medium-temperature thermal exposure on the microstructure and mechanical performance of the graphite/Au/Hastelloy N alloy brazed joint. The microstructure in the joint was studied with the aid of scanning electron microscope coupled with transmission electron microscope analysis. The nano-indentation was used to probe the nano-scale elastic modulus and hardness of reaction phases in the joint. The joint bond strength was evaluated by a shear test. Results indicate that: three zones (zone 1, 2 and 3) were observed in the joint with the zone 1 close to graphite while the zone 3 adjacent to Hastelloy N alloy. The precipitates in each zone were characterized and their formation mechanism was proposed. High-temperature thermal exposure was performed at 1333 K for 1–90 min. A longer soaking time facilitated the carbon diffusion and then produced a hierarchical structure with a more smooth transition of coefficient of thermal expansion, being favorable for the enhancement of the joint strength. Among the soaking time under investigation, the highest joint bond strength obtained was 34.1 MPa. Medium-temperature thermal exposure was carried out at 873–1073 K for 240 h. A high-quality joint was maintained when the joint was aged below 973 K. Over 973 K, a valid bonding was not achieved at the graphite/filler interface due to the precipitation of extensive carbon segregation in the zone 1 of the joint. The work performed will provide basic design principle for the graphite/Hastelloy N alloy brazed combinations used in molten salt reactors.

Microstructural Evolution and Mechanical Evaluation of a Laser-Induced Composite Coating on a Ni-Based Superalloy during Thermal Exposure.

A Ni–17Mo–7Cr-based superalloy was laser surface-modified to improve its tribological properties. Si particles were employed as coating materials. Si melted on the surface of the alloy during the process, triggering the formation of Mo6Ni6C carbides and Ni–Si intermetallics. A defect-free coating obtained was mostly made up of primary Mo6Ni6C and γ-Ni31Si12, as well as a eutectic structure of β1-Ni3Si and α-Ni-based solid solution (α-Ni (s.s)). The volume fraction of hard reinforcements (Mo6Ni6C, γ-Ni31Si12, and β1-Ni3Si) reached up to 85% in the coating. High-temperature microstructural stability of the coating was investigated by aging the coating at 1073 K for 240–480 h, to reveal its microstructural evolution. In addition, the mechanical performance of the coating was investigated. The nanoscale elastic modulus and hardness of Mo6Ni6C, γ-Ni31Si12, and α-Ni (s.s) were characterized using the nanoindentation tests. The nanoscratch tests were performed to measure the local wear resistance of the coating. Lastly, the Vickers hardness distribution across the cross-section of the coating before and after thermal exposure was compared. The work performed provides basic information understanding the microstructural evolution and mechanical performance of laser-induced coatings on Ni-based superalloys.

Preparation of silica–poly(methyl methacrylate) composite with a nanoscale dual-network structure and hardness comparable to human enamel

ObjectiveThis study aims to prepare an organic–inorganic composite with a nanoscale dual-network structure composed of a ceramic skeleton and infiltrated resin to mimic the mechanical properties of human enamel. MethodsA porous silica block was obtained by sintering a green body composed of SiO2 nanoparticles and poly(vinyl alcohol) organic binder. Methyl methacrylate monomers were infiltrated into the porous silica block and thermally polymerized to form poly(methyl methacrylate) (PMMA). A monolithic SiO2–PMMA composite was obtained, and its nanoscale structure was investigated. Its mechanical properties were characterized by Vickers hardness, elastic modulus, and flexural strength tests. ResultsThe SiO2–PMMA composite had a nanoscale dual-network structure composed of a silica–ceramic skeleton with PMMA-filled continuous 10–20 nm sized pores. The mechanical properties of the composite depended on the SiO2 content, which could be adjusted by modifying sintering time of the porous silica block. The mechanical properties of the composite exhibited wide variations with Vickers hardness values of 54–756, elastic moduli of 7–54 GPa, and flexural strengths of 75–120 MPa. SignificanceThe preparation of a SiO2–PMMA composite with a dual-network structure at the nanoscale was demonstrated, and the composite was characterized with respect to its hardness compatibility with human enamel.

Nano-scale hardness and elastic modulus of WC-Co composites and their relationship to the tools life during particleboard milling

Nano-scale hardness and elastic modulus of WC-Co composites and their relationship to the tool life during particleboards milling. The paper summarizes the results of the technique of hardness and elastic modulus determination using a load and displacement sensing indentation experiments. During the tests these properties were measured in nano-scale for different types of WC-Co composites using the Anton Paar TriTec Ultra Nano Hardness Tester (UNHT). In addition, durability examination of WC-Co tools during milling of particleboard was carried out. In the final stage, the correlation of the studied properties with the lifetime of tools was analyzed. The studies have revealed a relationship between micro-hardness and the total cutting length of the WC-Co tools.

Effect of Si addition on the microstructure and mechanical property of nanostructured oxide dispersion strengthened ferritic steel synthesized via mechanical alloying and spark plasma sintering

Nanostructured oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steel powders of two different nominal compositions, Fe-14Cr-2W-0.3Ti-0.3Y2O3 and Fe-14Cr-2W-0.3Ti-1Si-0.3Y2O3, wt.%, were synthesized by mechanical alloying and consolidated via spark plasma (SPS) sintering at different sintering temperatures (900, 1000 and 1050 °C). The effect of Si addition on the sinterability, phase composition, microstructure, and mechanical properties viz. microhardness, nanoscale hardness, and elastic modulus were investigated. The addition of 1 wt.% Si caused reduction in milling time and resulted in finer (5 ± 1.2 μm) and uniform particles. The addition of Si also led to faster reduction in crystallite size as compared to the Si-free sample. TEM analysis revealed formation of Y2Ti2O7 and Cr2O3 nano-sized particles in the Si-free ODS steel. However, formation of Cr2TiO4 and SiO2 along with Y2Ti2O7 particles were observed in Si-containing ODS steel. Hardness and Elastic modulus of Si-containing ODS steel sample sintered at 900 °C was higher than that of the samples sintered at higher sintering temperature because of fine microstructure and absence of α-Fe to γ-Fe phase transformation in 900 °C sintered sample.