Indentation Hardness Research Articles

Deposition mechanism of alumina particles in aerosol deposition based on the kinetic energy of particles

In this study, the aerosol deposition process was used to deposit the α-Al2O3 coating on Mo substrate under various conditions, i.e., particle size, type of carrier gas, gas flow rate and a nozzle–substrate distance. The formation behaviors of the α-Al2O3 coating in terms of deposition rate, microstructure and texture were studied in a correlation with the kinetic energy of the particles forming the coating. The fully dense and crystalline α-Al2O3 coatings were observed with the average grain size of 20 nm, significantly smaller than the particle sizes of 0.14 and 1.0 μm. The coating layers under all conditions were examined with a fiber texture with the (0001) plane tilted about 15° away from the coating plane. The microstructure and texture formation were resulted by fragmentation and plastic deformation of the particles during the deposition. The deposition formation of the particle collisions with the coating was simulated by the finite element analysis with the fragmentation model. The model suggested that the particles fracture at the boundary of the maximum shear strain generated by the particle impact. The deposit is formed by the lower part of the fracture particle. The strain energy in the deposited area of retained particles is considered to be equivalent to the kinetic energy, which includes the effects of the particle characteristics and physical properties. The result indicated that the changes of the deposition rate and texture formation can be well explained as a function of the strain energy. Regardless of the strain energy, the density of the α-Al2O3 coatings was almost the same as that of the bulk α-Al2O3 material. It was found that the high strain energy can lead to both high deposition rate and high indentation hardness.

Conductivity Enhancement of Fractured Carbonates through High-Temperature Diammonium Hydrogen Phosphate Consolidation: A Preliminary Study

SummaryIn well stimulation operations, the ability to sustain long-term conductivity of hydraulic/acid fractures defines an efficient and effective hydrocarbon production operation. However, it is challenging to keep the fracture conductive in the soft and weak carbonate formations due to many challenges. For example, the plastic deformation of rocks causes proppant embedment or asperities failure, resulting in fracture conductivity reduction. Consolidating chemicals, particularly diammonium hydrogen phosphate (DAP), have shown to be effective in rock consolidation and could reduce the decline in fracture conductivity if applied to carbonate formations. The previous research tested DAP at ambient conditions, whereas this work involves studying the hardening properties of DAP at reservoir conditions. The solutions with two initial concentrations (1 and 0.8 M) were tested at 77°F (ambient), 122°F, and 176°F. Furthermore, a post-treatment analysis was conducted to compare the performance of the chemical under different conditions. The analysis included understanding the changes in carbonate rocks’ (limestone and chalk) hardness (impulse hammer test and indentation test), porosity (helium porosimeter), permeability (steady-state and unsteady state nitrogen injection), and mineralogy [X-ray diffraction (XRD) and scanning electron microscopy (SEM)]. Results demonstrated that both rock lithologies reacted efficiently with the DAP solution, presented in terms of the noticeable improvements in their hardness. The elevated temperatures positively affected rock hardness, leading to a more than 100% increase in hardness for most samples. After obtaining successful results from experiments at various temperatures, the pilot American Petroleum Institute (API) conductivity experiments were conducted, testing the conductivity sustenance through the rock hardening concept. Preliminary API conductivity experiments have demonstrated that treated rock samples with DAP provided higher conductivity values than the untreated samples at high stresses. The results shown in this study provide a good foundation for further studies on the implementation of DAP in actual acid/hydraulic fracturing field operations.

The effect of delignification ratio on the PMMA occupation in poplar wood cell wall by the macro and micro comparative study

The polymer/wood functional products may not be true nanocomposites due to the poor permeability of non-polar monomers into the hydrophilic wood cell wall. In this paper, methyl methacrylate (MMA) chosen as the representative non-polar monomer was used to impregnate wood with different lignin removal and then polymerized in situ in delignified wood to obtain polymethyl methacrylate/delignified wood (PMMA/DW). The larger 10 nm mesopores reduction in PMMA/DW-29.9 and the disappearance of the smaller 3 nm mesopores of PMMA/DW-51.7 indicated that the removal of lignin was beneficial for the penetration of MMA in the wood cell wall. When the lignin removal reached between 29.9 and 51.7%, the dimensional stability of PMMA/DW was improved, and it could be speculated that the resin began to enter the wood cell wall at this stage. In addition, the indentation modulus and hardness of the PMMA/DW cell wall were significantly increased when the lignin removal reached 29.9%. This result was consistent with the conclusion of the pore size analysis, which further confirmed that the nanopores of the cell wall were filled with PMMA when the lignin removal was greater than 29.9%. The results of this paper indeed provide a basis for the design of biomass functional nanocomposites.

Hardness of nano- and microcrystalline lonsdaleite

Lonsdaleite is a hexagonal allotrope of carbon found in nature in meteorites and at meteorite impact sites. It has been predicted to have an indentation hardness greater than cubic diamond by first principles calculations. However, this has not been demonstrated experimentally. Here, nanoindentation was used to measure the hardness of two different lonsdaleite samples. One contains nanocrystalline lonsdaleite synthesized by high pressure compression of glassy carbon. The other is from a ureilite meteorite that contains lonsdaleite crystals up to ∼1 μm. The hardness of these two samples was determined using both the Oliver–Pharr and Meyer methods. Our results show that the hardness of the lonsdaleite samples is similar to that of diamond; therefore, there is no evidence that these forms of polycrystalline lonsdaleite are significantly harder than similar forms of diamond.

Using vacancies to tune mechanical and elastic properties in La3−xTe4, Nd3−xTe4, and Pr3−xTe4 rare earth telluride thermoelectric materials

Elastic and mechanical properties in advanced RE3−xTe4 (RE = La, Pr, Nd) thermoelectric materials are found to depend considerably on cation vacancy concentration x. Increasing x, which simultaneously reduces charge carrier concentration from metal-like to semiconductor-like, leads to significant stiffening of elastic constants due to charge carrier effects. The coefficient of thermal expansion in La3−xTe4 determined by high temperature X-ray diffraction correspondingly decreases with x, indicating that thermal expansion may be tuned by x in RE3−xTe4 materials systems. Vickers indentation hardness and fracture toughness tests show similarly significant effects of x on hardness and mode I fracture toughness, both of which decrease with increasing x. The mechanical property trends are counter-intuitive and merit further investigation, but demonstrate overall that higher x in RE3−xTe4 leads to more brittle behavior. The combined results show the importance of intrinsic defects in RE3−xTe4 and the potential to tune the mechanical performance of RE3−xTe4 for practical implementation in next-generation thermoelectric devices.

Experimental Verification of the Boundary Element Method for Adhesive Contacts of a Coated Elastic Half-Space

We consider analytical, numerical, and experimental approaches developed to describe the mechanical contact between a rigid indenter and an elastic half-space coated with an elastic layer. Numerical simulations of the indentation process were performed using the recently generalized boundary element method (BEM). Analytical approximation of the dependence of contact stiffness on the indenter diameter was used to verify the results of BEM simulations. Adhesive contacts of hard indenters of different shapes with soft rubber layers have been experimentally studied using specially designed laboratory equipment. The comparison of the results from all three implemented methods shows good agreement of the obtained data, thus supporting the generalized BEM simulation technique developed for the JKR limit of very small range of action of adhesive forces. It was shown that the half-space approximation is asymptotical at high ratios of layer thickness h to cylindrical indenter diameter D; however, it is very slowly. Thus, at the ratio h/D = 3.22, the half-space approximation leads to 20% lower contact stiffness compared with that obtained for finite thickness using both an experiment and simulation.

Superior oxidation resistance of the chemically complex but structurally simple Ti-Al-Ta-Ce-Si-La-B-nitride

Alloying (Ti,Al)N with Ta, CeSi2 or LaB6 is beneficial for both hardness and thermal stability. Here we show that their different mechanisms allow for a cumulative improvement when alloyed together, which is especially pronounced for the oxidation resistance. During isothermal oxidation treatments in ambient air at 900 °C (for up to 25 h), Ti0.44Al0.44Ta0.12N allows for a parabolic scale growth rate constant kp of 6.039 × 10-5 µm2/s. This is reduced to 2.074 × 10-5 and even 0.399 × 10-5 µm2/s when alloying with 2 mol% CeSi2 respectively CeSi2 + LaB6 (1 mol% each). The oxide scale growth kinetics for the latter can be even better described by a logarithmic or cubic law. In the as-deposited state the CeSi2 and CeSi2 + LaB6 alloyed (Ti,Al,Ta)N are single-phase fcc structured providing an indentation hardness of 32.6 ± 1.5 and 37.8 ± 1.5 GPa, combined with an indentation modulus of 496 ± 22 and 496 ± 14 GPa, respectively. After vacuum-annealing at 1000 °C, their hardness is still 33.0 ± 1.6 and 34.8 ± 1.1 GPa, and noticeable formation of hexagonal AlN and TaNx phases can only be detected by X-ray diffraction when annealed at temperatures above 1200 °C.Using CeSi2 and LaB6 instead of their elemental form is furthermore beneficial for the target production itself, as Ce and La are highly reactive.

The effect of kink-like defects on the twin boundaries of nanotwinned Ta under nanoindentation

To figure out the effect of kink-like defects on twin boundaries, BCC Ta with three different kinds of microstructures: single crystal (SC), perfect twin boundaries (PTB) and defective twin boundaries (DTB), are studied under nanoindentation. Both indenter load and hardness in PTB are enhanced by twin boundaries but reduced in DTB due to intrinsic kink-like defects. According to atomic surface morphology, the relative sink-in depth in DTB is lower than that in PTB but higher than that in SC. By comparing atomic images of prismatic loops in three different stages, it can be found that kink-like defects in DTB perform two opposite functions: acceleration and delay. In initial plastic stage, defective twin boundaries can accelerate pinching-off event and nucleation. In transmission stage, dislocation backward emission is advanced by defective twin boundaries. In obstruction stage, the symmetry of coherent twin boundaries will be broken and asymmetrical shear loops are formed, which will delay prismatic loops moving across twin boundaries. Dislocations of 12〈111〉 are the main factor of nanoindentation in [1¯1¯2] direction. Kink-like defects will lead to less drops in DTB on dislocation densities than that in PTB. These findings are helpful to reveal the influence of intrinsic kink-like defects in BCC nanotwinned materials.

Tailoring Variations in the Microstructures, Linear/Nonlinear Optical, and Mechanical Properties of Dysprosium-Oxide-Reinforced Borate Glasses

Hybrid dysprosium-doped borate glassy samples [B-Gly/Dy]HDG (Borate Glass/Dysprosium)Hybrid Doped Glass were prepared in this study via the melt-quenching method. Its linear/nonlinear optical, photoluminescence, hardness indentation, and micro-creep properties were analyzed. The amorphous structure for all the prepared samples was confirmed from the XRD patterns. In addition, density functional theory (DFT), optimized by TD-DFT and Crystal Sleuth, was used to study the structure and crystallinity of the [B-Gly/Dy]HDG as isolated molecules and agreed with the peaks of experimental XRD patterns. Additionally, theoretical lattice types were studied using Polymorph, a content studio software, and orthorhombic Pc21b (29) and triclinic P-1 (2) structures were provided. Both mechanical and optical properties were responses to different concentrations of Dy2O3 in the glassy borate system. It was found that the length of indentation increases by increasing the load time, and the hardness decreases by increasing the load time. The stress exponent value also increased from 4.1 to 6.3. The indentation strain increases by increasing the load time. The direct optical band gap was evaluated using the Davis–Mott relation. Urbach energy and its connection to the disorder degree in materials were studied depending on the Dy2O3 concentration. The acquired optical parameters were also analyzed to determine the nonlinear refractive index as well as the linear and third-order nonlinear optical susceptibility of the investigated glass samples. The photoluminescence emission spectra were recorded, and their attributed transitions were studied. The mechanical studies showed that the hardness values increased by increasing Dy2O3 concentrations from 4160.54 to 5631.58 Mpa. The stress exponent value also increased from 4.1 to 6.3. Therefore, the higher value of stress exponent (S) is more resistant to indentation creep.

Microstructure, mechanical properties, and oxidation behavior of arc-evaporated Cr–Al–O–N coatings with various Cr/Al ratios

Cr–Al-based oxynitride materials have attracted significant attention as hard protective coatings for decades. However, knowledge of the influence of the constituents on oxidation behavior is limited. Here, Cr–Al–O–N coatings with various Cr/Al ratios prepared using cathodic arc evaporation were studied with respect to their microstructure, mechanical properties, and oxidation behavior. With a decrease in the Cr/Al ratio, the coatings yielded a phase evolution from face-centered cubic CrN to rock salt-type cubic (Cr, Al)2O3 to a wurtzite-type hexagonal AlN structure. The cubic structured coatings showed a comparable indentation hardness, much higher than that of the Cr-free Al–O–N coating with a wurtzite structure. Thermogravimetric together with differential scanning calorimetric (TG-DSC) analysis revealed that the ternary Cr–O–N and Al–O–N coatings were more susceptible to oxidation than the quaternary Cr–Al–O–N coatings. Moreover, isothermal oxidation experiments indicated that the addition of 66 at.% Al within the metallic species gives rise to the growth of an Al-rich oxide scale on top of the Cr–Al–O–N coating. However, this oxide scale containing substantial voids cannot prevent the underlying coating from oxidation. Oxidation kinetics study illustrates that the oxidation activation energies of (CrxAl1−x)–O–N coatings with x = 1.00, 0.76, 0.58, 0.33, and 0 are 252.3, 305.2, 370.7, 303.8, and 297.7 kJ/mol, respectively. The best oxidation resistance was obtained by the (Cr0.58Al0.42)–O–N coating, whereas the Al-containing (Cr0.33Al0.67)–O–N coating showed inferior oxidation resistance owing to its high intrinsic oxygen fraction.

Effect of hardeners on the mechanical properties of epoxy coatings based on ED-20 resin

The aim of this study is to investigate the mechanical properties of coatings based on ED-20 epoxy resin, manufactured with polyethylenepolyamine or polyamidepolyamine used as hardeners. Instrumented indentation with a Berkovich triangular pyramid is used to determine the mechanical properties. Indentation hardness, reduced elastic modulus, and creep at a given holding time are used as the characteristic parameters. The results testify that the mechanical properties of the epoxy coatings made with different hardeners differ significantly from each other and demonstrate different behaviors.

Nanoindentation characteristics of nanocrystalline tungsten via atomistic simulation

ABSTRACT Molecular dynamics simulations are performed to explore nanoindentation characteristics of tungsten, and the influences of grain size, indenter velocity, indenter size, and temperature are discussed. The results illustrate that the hardness reduces as the grain size (5.00 ∼ 24.62 nm) decreases. There is no phase change observed during the whole deformation process. For monocrystalline W, the dislocation nucleation and propagation dominate the deformation mechanisms. Differently, the primary deformation mode of nanocrystalline W is the grain split and motion of GBs. Dislocations primarily nucleate below the contact surface of the indenter and substrate and then glide in the grain core. The monocrystalline W has better pattern-forming ability than nanocrystalline. Besides, the pattern-forming ability of nanocrystalline W is negatively correlated with the average grain size (5.00 ∼ 24.62 nm). The von Mises stress is mainly concentrated in the interface between the indenter and substrate, the dislocation area for monocrystalline, and grain boundaries for nanocrystalline. The indentation force and hardness are positively correlated with indenter radius size (30 ∼ 80 Å), negatively correlated with temperature (10 ∼ 1500 K), and insensitive to the indenter velocity when velocity is lower than 3.0 Å /ps (300 m/s).

Influence of Deposition Parameters on Hardness Properties of InconelTM 718 Processed by Laser Powder Bed Fusion for Space Applications

InconelTM 718 is widely used for commercial application in aerospace industry and additive manufacturing process allows for versatile design and manufacturing opportunities. In the present research, the results of a wide experimental campaign run on additive manufactured InconelTM 718 specimens obtained with different processing parameters are presented. In particular, the influence of process parameters (for both vertical and horizontal planes with respect to the building direction) on the hardness properties are investigated. A further investigation is performed on the optimal hardness testing procedure for additive manufacturing. The research is extended to as-built and heat-treated specimens. The new insight gained is that the orientation of the printing direction with respect to indentation direction can be responsible for scattering in hardness measurements and indentation size effect. As-built specimens show a strong anisotropy for in-plane and growth directions and an increment of hardness with respect to increasing energy density. The difference between hardness value with respect to the energy density and the measurements scattering are reduced by the heat treatment. A careful handling of hardness data is required when dealing with additive manufactured materials.

Mechanical Properties of Structural Components in Hastelloy X Joints Brazed with Ni-Pd-Cr-B-Si Alloy.

The brazing of structural high-temperature-resistant nickel alloys is a predominant method in manufacturing jet engines in the aircraft industry. Ni-Cr-base brazing filler metals (BFMs) containing B and Si as the melting point depressants are used for this purpose. The presence of the latter can lead to the formation of brittle constituents in the joints, decreasing their strength, toughness and creep resistance. The structures of Hastelloy X nickel superalloy joints brazed with Palnicro 36M BFM are presented in this paper along with the mechanical properties of their particular phases as a function of brazing time. Indentation hardness, Martens hardness, reduced modulus and creep coefficient were measured using the instrumented indentation method. The elastic part of the indentation work was also calculated. Pd forms an unlimited solution with Ni, but its high content in BFM does not fundamentally change the general joint structure known from other Ni-superalloy-Ni-BFM systems. However, new Pd-containing phases are emerging. The hardest components were Ni-B and Cr-B boride phases and Pd-Ni-Si phase in MZ and the boundary of DAZ and BM. MZ reduces the plasticity of a joint to the highest extent. The hardness of particular parts in the joints and the elastic portion of the indentation work decreased with the increase in brazing time, while the reduced modulus of the indentation contact and indentation creep increased. The results of indentation creep measurements indicate that all structural components of the joints were less susceptible to creep than the parent material at room temperature.

Hardness and Mechanical Properties of Wurtzite B–C–N Compounds

Diamond, cubic BN (c-BN), and cubic B–C–N compounds, i.e., c-BCXN, are well-known ultrahard materials. While cubic phases of these materials are relatively stable and have been widely studied, recent experimental and theoretical studies have reported evidence that indentation hardness can be significantly enhanced in wurtzite phases of BN (w-BN) and diamond, i.e., lonsdaleite. However, the mechanical properties and hardness of wurtzite B–C–N compounds have been less explored. In this study, we systemically investigated wurtzite B–C–N compounds (w-BCXN), such as wurtzite BCN (w-BCN), BC2N (w-BC2N), and BC4N (w-BC4N), and compared their properties with those of c- and w-BN, diamond, and lonsdaleite. Although w-BCXN shows relatively high formation energies compared with the others, configurational entropy can assist the compounds to be stabilized at elevated growth temperatures (over 2700 K). In addition, w-BCXN exhibits a relatively superior hardness, which increases with the C ratio. Our results provide a basic understanding of w-BCXN as a possible family of superhard materials.

OptIFnet: A Capacitive Antenna Dipole Indention-Flexure Predictive Model Optimized Using Hybrid Lichtenberg Algorithm and Neural Network

In performing underground imaging surveying, applying a coating in the antenna dipole plates with robust and durable material to stay protected against rough road features is vital to consider. By doing this, the mechanical properties of the metallic antenna dipole can be improved and be shielded from deterioration. With that, this study has developed an indentation-flexure algorithm optimized using a hybrid Lichtenberg algorithm (LA) and artificial neural network (ANN) that can predict the indentation-flexure as a function of the coating material’s elastic modulus, Poisson ratio, and thickness as well as the load antenna weight. Acrylic, epoxy, nylon 101, high-density polyethylene, and polyvinyl chloride were chosen as the top five most popular coating materials. A 120° titanium cone indenter with a 0.5-inch-diameter, slightly rounded point, and a constant compressive force of 200 N in the center was employed to plot and use a nonlinear mechanical finite element analysis on an antenna dipole plate using SolidWorks. Nature-inspired and evolutionary metaheuristics such as African vultures, Lichtenberg, and gorilla troop optimization algorithm including genetic algorithm (GA) were employed as optimized models for the hardness indentation for capacitively coupled antenna dipoles. Based on the results, the hybrid LA-ANN solution with a hidden neurons of 3000 and a sigmoid activation function is the best performing model as it acquired a MSE score of 0.0061 in validation and 0.1478 in testing compare to the other model with 0.1610 for GA with 100 hidden neurons with sigmoid activation function. Thus, LA-ANN model is considered as the optIFnet as it exhibited the best prediction performance and fastest convergence among all optimizers used.

Nanomechanical characterization of 3D printed cement pastes

Cement-based 3D printing (additive manufacturing) has drawn significant attention in recent years as an emerging construction technology because of its potential environmental and economic benefits over the traditional cast-in-place concrete construction. Most research to date has focused on the macroscale properties of the printed structure. However, the performance of the printed materials depends on the properties of the individual filaments. In this study, grid nanoindentation coupled with scanning electron microscopy and energy dispersive X-ray spectroscopy was used to determine the effects of the printing process through extrusion on the local elastic indentation modulus and hardness of filaments in 3D printed cement paste structures. Dynamic changes in the water-to-cement ratio during the extrusion process combined with stress-induced dissolution of the cement particles led to variation in the median modulus of the printed filaments, with filaments having values greater than 23 GPa or lower than 20 GPa. Extrusion through a small diameter nozzle affected the mesoscale assemblage of the primary hydrate phases and led to printed filaments having a more uniform mesoscale packing of calcium silicate hydrates (C–S–H) with the disappearance of loosely packed C–S–H compared to their traditionally cast counterparts.

Influence of processing on the microstructural evolution and multiscale hardness in titanium carbonitrides (TiCN) produced via field assisted sintering technology

Titanium carbonitride (TiCN) is an advanced, high-performance hard ceramic of great commercial importance that has been widely developed and employed. Nonetheless, it has only been in recent years that binderless titanium carbonitride bulk ceramics have been successfully fabricated using field-assisted sintering technology (FAST). However, the underlying structure-processing-property-performance relationships have yet to be fully evaluated, especially concerning indentation hardness of these materials across a broad range of loads and deformation length scales. In this work we aim to address these fundamental relationships and characterize the multiscale hardness phenomena in detail. It was found that the effects of soak temperature and time directly impacted the sintered microstructure and were reflected in the observed mechanical properties over various loads. Valuable insight into the load-dependence of hardness distributions, sensitivity/correlation with elastoplastic parameters, and multiscale parameterization were developed using micro-/nanoindentation. Particularly, the load-dependent hardness sensitivity and resolvability demonstrate a fundamental tradeoff with respect to the manifested mechanical response influenced by the presence of underlying heterogeneities. These new insights relating the interplay of compositional/microstructural evolution with FAST processing parameters and multiscale hardness are an important step in advancing next-generation hard ceramics.

Gradient characterization of steel-concrete interface at early ages

Steel-Concrete Interface (SCI) refers to the porous weak area at the interface between steel bar and cement matrix. This study proposes sophisticated methods for quantifying gradient properties and their evolution of SCI using back-scattered electron (BSE) imaging and nano-indentation. The gradient of SCI is identified through a robust statistical analysis. Distinct stratification structure of SCI is discovered, which can be demonstrated from the grayscale of BSE as well as the indentation modulus and hardness. The thickness of SCI increases with age and the increasing rates roughly decline with the increase of w/c. SCI can be divided into highly porous layer I and transition layer II according to the hierarchically porosity. The layer II is subdivided into II(a) and II(b) based on the gradient of mechanical properties, which is mainly caused by the spatial distribution of cement particles within SCI.

Comparative Evaluation of the Tribological Properties of Polymer Materials with Similar Shore Hardness Working in Metal-Polymer Friction Systems.

This article presents comparative tests of contact strength and tribological wear resistance of polymer sliding materials of the polyamide group. The aim of this work was to study Shore hardness, indentation hardness, modulus, creep, relaxation, Martens hardness and sliding wear resistance of two commercial materials. One of these materials was produced with the recycling process in mind. Abrasion tests were performed against a stainless-steel ball (100CRr6) on a normal load of 5 N for 23,830 friction cycles. The samples were tested under dry friction conditions and taking into account the hydrothermal factor, the presence of which was assumed in the anticipated operating conditions. It was distilled water at a temperature of 50 °C. The volumetric wear of the samples under various environmental conditions was assessed and related to the mechanical properties, in particular, Shore hardness. This mechanical size, which characterizes the surface, was considered the most frequently used by engineers selecting polymeric materials for tribological applications in industry. The Shore hardness of both materials was similar, which may indicate similar tribological performance properties. However, research and analysis indicate the need to use measures that directly correspond to tribological wear. The friction and wear of both materials varied. The coefficient of friction in hydrothermal conditions was lower and the wear was higher than in the dry friction test. It seems that it was not hardness that determined the suitability in the anticipated operating conditions, but the ability to form a sliding layer on the friction surface. The properties of the material that has been envisaged as a replacement may be appropriate for the intended uses.