Vickers Hardness Indentation Research Articles

Influence of Addition of Different Nanoparticles on the Surface Properties of Poly(methylmethacrylate) Denture Base Material.

To evaluate and compare the surface properties (roughness and hardness) of poly(methylmethacrylate) denture base material modified with zirconium dioxide (ZNPs), silicon dioxide (SNPs), and diamond (DNPs) nanoparticles. Two hundred sixty heat-polymerized acrylic resin disks (15 × 2 mm) were prepared. ZNPs, SNPs, and DNPs were added in concentrations of 0%, 0.5%, 1.0%, 2.5%, and 5.0% by weight of acrylic powder. This yielded a total of 13 groups for each test according to filler type and concentration (n = 10/group). The control group was made of pure acrylic. A mechanical polisher was used to standardize specimens' surfaces before testing. A profilometer and Vickers hardness indenter were used to test the surface roughness and hardness, respectively. ANOVA and Tukey post hoc tests were used for data analysis (α = 0.05). In comparison to control, results showed a nonsignificant increase in surface roughness (Ra ) of acrylic material after the addition of 0.5% nanoparticles (ZNPs p = 0.168, SNPs p = 0.166, and DNPs p = 0.177), while a significant increase was seen with all other concentrations (p ˂ 0.05). Ra values of ZNP and DNP groups were significantly higher than those of the SNPs group (p < 0.001). The addition of any of the fillers to acrylic denture base materials significantly increased the hardness (p ˂ 0.05), with ZNPs and DNPs having values lower than those of the SNPs group (p < 0.001). Although nanofiller addition increased the hardness of denture base material, Ra was adversely affected when the concentration exceeded 0.5%. Therefore, 0.5% is suggested to be the most appropriate ratio to improve hardness with acceptable Ra .

Biomineralization and osteogenic differentiation modulated by substrate stiffness

It is well known that extracellular matrix stiffness can affect cell proliferation and differentiation. However, when substrates of different stiffness are transferred into organisms, they affect cell behavior, and at the same time, the substrates themselves also undergo biomineralization owing to the extracellular matrix, this process of biomineralization during osteogenic differentiation adjusted by substrate stiffness has seldom been investigated. In this paper, we copolymerized 2-vinyl-terephthalic acid bis-[4-(2-carboxy-ethyl)-phenyl] ester (LCPE) as rigid chains and butyl acrylate (BA) as flexible chains to prepare a series of polymer materials. Films based on these copolymers are prepared by dip-coating method with controllable stiffness. Vickers indentation hardness tester was used to verify the stiffness of the films (199.9–5.3 kPa) with different ratio of LCPE and BA. Polymer coated substrates with different stiffness on biomimetic mineralization demonstrated that a moderate stiffness substrate (14.9 kPa) can induce the best biomimetic mineralized hydroxyapatite (HA), and further promote the proliferation and differentiation behavior of osteoblasts.

Vickers hardness indentation size effect in selective laser melted MS1 maraging steel

In this paper, selective laser melting fabricated specimens in non-heat-treated and heat-treated conditions were subjected to Vickers microhardness testing, by using a full range of loadings: 10, 25, 50, 100, 200, 300, 500, and 1000 g. Microhardness of longitudinal sections and cross-sections were correlated and the obtained values were plotted against loadings and indentation size effect was studied, in order to find the optimal loading range, that gives the material true microhardness, or load-independent hardness. The load dependence of the measured Vickers hardness values was described quantitatively through the application of the Meyer’s law, proportional specimen resistance, and the modified proportional specimen resistance model. It was found that the microhardness rises as the loading is higher, causing a reversed indentation size effect, clearly indicating the range of true hardnesses of the tested material. Also, proportional specimen resistance and modified proportional specimen resistance models were found to have the highest correlation factors indicating their higher adequacy compared to Meyer’s prediction model.

Size‐induced grain boundary energy increase may cause softening of nanocrystalline yttria‐stabilized zirconia

AbstractAn increase in hardness with reducing grain sizes is commonly observed in oxide ceramics in particular for grain sizes below 100 nm. The inverse behavior, meaning a decrease in hardness below a critically small grain size, may also exist consistently with observations in metal alloys, but the causing mechanisms in ceramics are still under debate. Here we report direct thermodynamic data on grain boundary energies as a function of grain size that suggest that the inverse relation is intimately related to a size‐induced increase in the excess energies. Microcalorimetry combined with nano and microstructural analyses reveal an increase in grain boundary excess energy in yttria‐stabilized zirconia (10YSZ) when grain sizes are below 36 nm. The onset of the energy increase coincides with the observed decrease in Vickers indentation hardness. Since grain boundary energy is an excess energy related to boundary strength/stability, the results suggest that softening is driven by the activation of grain boundary mediated processes facilitated by the relatively weakened boundaries at the ultra‐fine nanoscale which ultimately induce the formation of an energy dissipating subsurface crack network during indentation.

Effects of Six-fold Coordinated Silicon on Structure and Properties of BaO-SiO2-P2O5 Glasses

We studied the local structure and properties of six-fold coordinated silicon (Si[6]) in BaO-SiO2-P2O5 glasses. Nuclear magnetic resonance (NMR) and Raman spectroscopy revealed the existence of six-fold coordinated silicon species and network former units (NFUs) in the BaO-SiO2-P2O5 glasses. The glass transition temperature (Tg), which was measured by differential scanning calorimetry, increased rapidly along with the increase of SiO2 from 0 to 10 mol%, then declined and finally increased again, which showed a “Z” trend along with the increase of SiO2 while the density of the glasses showed the opposite trend. When the addition of SiO2 is 16 mol%, Tg decreased to an extremely low value (807.9 K). Besides, the Vickers indentation hardness (Hv) had been significantly enhanced from 4.66 to 6.63 GPa by adding 16 mol% SiO2. Furthermore, the liquid fragility index (m) of the glasses declined slowly firstly and then increased rapidly when the amount of SiO2 is greater than 13 mol%.

Strength and Fracture Behaviour of Dual Phase Steel Dp450 in Static and Dynamic Conditions

In this work, strength and plastic deformation effect of the dual phase steel are analysed in the static and dynamic conditions. Since the dual phase steel is extensively used in the outer body parts of the automotive vehicles, its dynamic strength and plastic strain energy absorption during the crash are essential. Dynamic strength of the dual phase steel is examined using the pendulum impact hammer tester machine. Spread of the plastic strain during the crash is an important factor for the energy absorption to passive safety, which is examined using the local hardness measurement using the Vickers hardness and local indentation yield strength is calculated using cylindrical indenter and obtained force-depth results are analysed using the Hencky theory for the plane strain indentation. Further, tested samples are observed using scanning electron microscopy for the fracture response after the static and dynamic tests.

The Effect of Thermocycling on Surface Layer Properties of Light Cured Polymer Matrix Ceramic Composites (PMCCs) Used in Sliding Friction Pair.

This paper discusses the problem of thermocycling effect of light-curing polymer–ceramic composites. Cyclic thermal shocks were simulated in laboratory conditions. As a rule, these loads were supposed to reproduce the actual conditions of biomaterials exploitation. Periodically variable stresses occurring in dental restorations are associated with the wear of cold and hot foods and beverages. They lead to changes in the properties of composites, including the properties of the surface layer. The aim of the work was to assess the impact of cyclic hydrothermal interactions on the properties of the surface layer of composites relevant to the operational quality. Two commercial materials manufactured by the world’s leading producer (3M ESPE)—Filtek Z550, Filtek Flow and two experimental, micro-hybrid and flow type composites marked Ex-mhyb(P) and Ex-flow(P), respectively. All tests were carried out before and after hydro-thermal cycles (flowing water thermocycling). Micro-hardness test using the Vickers method, indentation hardness, and resistance to tribological wear in a ball–disc system in sliding friction conditions were performed. In addition, observations of the surface layer of composites on the SEM (scanning electron microscope) were carried out. It was noticed that semi-liquid composites, containing a smaller amount of filler, retain higher stability of mechanical and tribological properties of the surface layer under cyclic hydro-thermal loads. Coefficient of friction of samples after hydro-thermal cycles increased for micro-hybrid materials and Filtek Flow (FFlow) composite. In the case of Ex-flow(P) material, the coefficient of friction decreased. The microhardness of composites also changed, the variability of this size depended on the type of material. Composites with a higher content of filler particles were characterized by greater variability of microhardness under the influence of thermocycles. The resistance to tribological wear also changed in a similar way. Composites containing higher volume fraction of inorganic filler showed higher tribological wear after thermocycling. The wear resistance of flow composites changed to a lesser extent, after thermocycling increased. The paper also showed that, in real kinematic nodes, the surface layer of light-curing ceramic–polymer composites is exposed to significant non-tribological (erosive, thermal, and chemical) defects that synergize with tribological ones. In slip pairs loaded dynamically, under mixed friction conditions, tribological wear of PMCCs (polymer matrix ceramic composites) is manifested by spalling (spalling of the material flakes, in particular the polymer phase) and pitting (crushing wear caused by wear products, in particular large filler particles or clusters, previously adhesively extracted).

Growth, Optical and Microhardness Studies of 2-Aminothiazole- 3, 5-Dinitrobenzoic Acid Complex

Single crystals of 2-Aminothiazole 3,5-Dinitrobenzoic acid has been synthesized and good quality optical crystals were grown by slow evaporation technique at room temperature. The crystallinity nature of the grown crystal was confirmed from X-ray diffraction technique. An optical transmittance study was also carried out by UV – Vis spectra. FTIR spectra confirm the presence of functional groups in the grown crystal. The dielectric measurements were carried out in the range of 50Hz to 2MHz. The dielectric constant was seen to increase exponentially at lower frequencies. The microhardness studies were carried out using Vickers hardness indenter. Photoluminescence study shows that maximum emission occurs at 435nm.

Predicting subsurface damage in silicon nitride ceramics subjected to rotary ultrasonic assisted face grinding

Silicon nitride is an advanced ceramic used in high performance applications. One of the main problems in machining of brittle materials such as silicon nitride is subsurface damage (SSD). On the other hand, rotary ultrasonic assisted face grinding (RUAFG) is considered as state of the art machining process for brittle and hard to machining materials such as ceramics and optical glasses. In this research, a new study on SSD generation in RUAFG by establishing both ductile deformation and brittle fracture conducted. To achieve this goal, initially single diamond grit cutting force based on Vickers hardness correlation and indentation fracture mechanics established and placed in crack propagation formulas to anticipate SSD. Verification tests performed and average 8% error detected. Moreover, RUAFG depicted up to 30% SSD reduction in comparing to conventional face grinding (CFG). Besides, scanning electron microscope utilized to investigate cracks morphology.

Verification of Vickers indenter geometry by means of three-dimensional coordinate measurement

The paper describes an accurate but practical method of the verification of a Vickers hardness indenter geometry. Three-dimensional coordinates of selected points on the surface of four faces of a Vickers indenter are measured with the laser probe 3D profile measurement instrument. The measurement is made with respect to the datum of the indenter so that the misalignment of the axis of pyramid will not interfere to the verification results of geometry. The directions of pyramid faces are analyzed with equations of the best-fit planes to data points estimated by the least-squares algorithm. The flatness of faces is also evaluated as the range of orthogonal distances of data points from the fitted plane. The results show that the geometry of a Vickers indenter is successfully verified with proposed method and the resolution and repeatability of the method are good enough to verify calibration-machine-grade indenters.

Hot-pressed sintered Ca-α-Sialon ceramics with grains from short prismatic to elongated morphology synthesized via carbothermal reduction and nitridation

Ca-α-Sialon powders was initially synthesized by carbothermal reduction-nitridation (CRN) of SiO2, AlN, CaF2 and carbon black at 1700 °C, subsequently was used as the raw material to prepare Ca-α-Sialon ceramic by hot-pressed (HP) sintering at 1900 °C. The main intermediate nitridated products were Si2N2O and O-Sialon formed at 1400 °C–1600 °C. The resultant Ca-α-Sialon just had hexagonally short prismatic structure at 1700 °C. In order to obtain its elongated crystals, α-Sialon seeding was introduced during CRN process. The results revealed that the seeding facilitated crystal refinement of Ca-α-Sialon and the increase in its aspect ratios from 2 to 5.45. The resultant HP-sintered Ca-α-Sialon ceramic with seeding at 1900 °C had compact structure with fine and elongated grains, forming a highly interlocked microstructure. They had a Vickers indentation hardness of ∼21 GPa independent of the microstructure. The flexural strength and fracture toughness of the Ca-α-Sialon ceramics drastically increased with increasing the amounts of seeds, which was in accordance with that in grains aspect ratio of α-Sialon crystals synthesized by CRN as function of amounts of seeds. The improved flexural strength and fracture toughness should be ascribed to the development of elongated α-Sialon grains, which could enhance crack deflection and grain pullout.

Effect of Carbon Content on the Microstructure and Mechanical Properties of NbC-Ni Based Cermets

The aim of this work was to correlate the overall carbon content in NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo starting powders with the resulting microstructure, hardness, and fracture toughness of Ni-bonded NbC cermets. A series of NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo cermets with different carbon content were prepared by conventional liquid phase sintering for 1 h at 1420 °C in vacuum. Microstructural analysis of the fully densified cermets was performed by electron probe microanalysis (EPMA) to assess the effect of carbon and VC or Mo additions on the NbC grain growth and morphology. A decreased carbon content in the starting powder mixtures resulted in increased dissolution of Nb, V, and Mo in the Ni binder and a decreased C/Nb ratio in the NbC based carbide phase. The Vickers hardness (HV30) and Palmqvist indentation toughness were found to decrease significantly with an increasing carbon content in the Mo-free cermets, whereas an antagonistic correlation between hardness and toughness was obtained as a function of the Mo-content in Mo-modified NbC cermets. To obtain optimized mechanical properties, methods to control the total carbon content of NbC-Ni mixtures were proposed and the prepared cermets were investigated in detail.

Improving sintering behavior of MWCNT/BaTiO3 ceramic nanocomposite with Bi2O3-B2O3 addition

The present research systematically investigated the novel low-temperature fabrication of a multi-walled carbon nanotube (MWCNT)/barium titanate nanocomposite using a two-step mixing technique. The synthesis was conducted using different amounts of MWCNT (0.25%, 0.5%, 1%, 2%, 4%, and 8% wt) with different compositions of (Bi2O3 + B2O3) as a sintering aid. Scanning and transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, three-point bending strength, Vickers hardness indentation and Archimedean technique were used to characterize the as-synthesized specimens. It was found that the appropriate content of sintering aid (Bi2O3+B2O3) strongly decreased the sintering temperature from 1200°C to 950°C. The results also revealed that any sintering aid with the optimum composition that included 30% (mol) Bi2O3 was optimal for a sintering aid content of 6% (wt). Consequently, the highest values of the flexural strength and fracture toughness were achieved by applying the optimal amounts of MWCNT (1% wt) and sintering aid (6% wt).

Indentation and bending behavior of electroless Ni-P-Ti composite coatings on pipeline steel

Electroless Ni-P coatings have been adopted in many industrial applications due to their excellent wear and corrosion resistance. The unique properties and autocatalytic nature suggest a potential usage as a pipeline inner coating in oil and gas industries. However, low toughness and erosion resistance limit the suitability of electroless Ni-P coatings as pipeline coatings. To improve the toughness of the Ni-P coating, nano-sized titanium particles were used to reinforce Ni-P coating in this study. The effect of titanium particles on Ni-P coatings and the effect of annealing on the structure and mechanical properties were studied. The morphology and structure of Ni-P-Ti coating were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Vickers hardness, three-point bending and Hertzian indentation tests were employed to characterize the mechanical properties of Ni-P-Ti coating. It is found that adding titanium did not change the semi-amorphous microstructure of as-deposited Ni-P coating. The micro-hardness of as-deposited and annealed Ni-P-Ti coating was found to be higher than that of Ni-P coating. Furthermore, the addition of titanium particles increases toughness of the as-deposited coating. Also, it is found that toughness increases with increasing annealing temperature. The annealing also has a significant effect on the indentation behavior of the coatings.

Crack-healing behavior of Al2O3-TiB2-TiSi2 ceramic material

Al2O3-TiB2-TiSi2 ceramic material was fabricated by vacuum hot pressing technique and the crack healing behavior was investigated by means of high-temperature oxidation. The Vickers hardness indenter was used to precrack with a standard crack length of 300µm. According to the recovery of flexural strength and the microstructure of crack appearance, the effects of crack healing temperature, healing time and crack length on crack-healing were studied. At the healing temperature of 800°C for 90min, the strength of crack-healing specimen was recovered completely and the recovery percentage of flexural strength reached up to 107.25%, compared with the flexural strength of the smooth specimen. The strength of crack-healing specimens with a crack length of 150µm and 300µm were fully recovered, but incomplete recovery appeared at the crack length of 500µm. The crack-healing mechanism was attributed to the crack-filling with liquid phases of SiO2 and TiO2 obtained by X-ray diffraction. The crack surface of Al2O3-TiB2-TiSi2 ceramic material was observed by Scanning Electron Microscopy and Energy-dispersive Spectrometry.

Spatial variation in mandibular bone elastic modulus and its effect on structural bending stiffness: A test case using the Taï Forest monkeys.

We investigated how heterogeneity in material stiffness affects structural stiffness in the cercopithecid mandibular cortical bone. We assessed (1) whether this effect changes the interpretation of interspecific structural stiffness variation across four primate species, (2) whether the heterogeneity is random, and (3) whether heterogeneity mitigates bending stress in the jaw associated with food processing. The sample consisted of Taï Forest, Cote d'Ivoire, monkeys: Cercocebus atys, Piliocolobus badius, Colobus polykomos, and Cercopithecus diana. Vickers indentation hardness samples estimated elastic moduli throughout the cortical bone area of each coronal section of postcanine corpus. For each section, we calculated maximum area moment of inertia, Imax (structural mechanical property), under three models of material heterogeneity, as well as spatial autocorrelation statistics (Moran's I, IMORAN ). When the model considered material stiffness variation and spatial patterning, Imax decreased and individual ranks based on structural stiffness changed. Rank changes were not significant across models. All specimens showed positive (nonrandom) spatial autocorrelation. Differences in IMORAN were not significant among species, and there were no discernable patterns of autocorrelation within species. Across species, significant local IMORAN was often attributed to proximity of low moduli in the alveolar process and high moduli in the basal process. While our sample did not demonstrate species differences in the degree of spatial autocorrelation of elastic moduli, there may be mechanical effects of heterogeneity (relative strength and rigidity) that do distinguish at the species or subfamilial level (i.e., colobines vs. cercopithecines). The potential connections of heterogeneity to diet and/or taxonomy remain to be discovered.

Crystallographic Analysis of Nucleation at Hardness Indentations in High-Purity Aluminum

Nucleation at Vickers hardness indentations has been studied in high-purity aluminum cold-rolled 12 pct. Electron channeling contrast was used to measure the size of the indentations and to detect nuclei, while electron backscattering diffraction was used to determine crystallographic orientations. It is found that indentations are preferential nucleation sites. The crystallographic orientations of the deformed grains affect the hardness and the nucleation potentials at the indentations. Higher hardness gives increased nucleation probabilities. Orientation relationships between nuclei developed at different indentations within one original grain are analyzed and it is found that the orientation distribution of the nuclei is far from random. It is suggested that it relates to the orientations present near the indentation tips which in turn depend on the orientation of the selected grain in which they form. Finally, possible nucleation mechanisms are briefly discussed.

Rate‐Dependent Mechanical Behavior and Amorphization of Ultrafine‐Grained Boron Carbide

An investigation into mechanical properties and amorphization behavior of ultrafine‐grained (0.3 μm) boron carbide (B4C) is conducted and compared to a baseline coarse‐grained (10 μm) boron carbide. Static and dynamic uniaxial compressive strength, and static and dynamic Vickers indentation hardness were determined, and Raman spectroscopy was then conducted on indented regions to quantify and compare the intensity of amorphization. In relation to coarse‐grained B4C the ultrafine‐grained material exhibited, on average, a 33% higher static compressive strength, 20% higher dynamic compressive strength, 10% higher static Vickers hardness, and 23% higher dynamic Vickers hardness. In addition, there was an 18% reduction in indentation‐induced radial crack length in ultrafine‐grained B4C, which corresponded to an increase in estimated fracture toughness. Although traditional coarse‐grained B4C exhibits an 8.6% decrease in hardness from the static to dynamic regimes, ultrafine‐grained B4C showed only negligible change under similar conditions, suggesting a reduced propensity for amorphization. Raman spectroscopic analysis confirmed this result by revealing significantly lower amorphization intensity in ultrafine‐B4C compared to coarse‐grained B4C. These results may have significant positive implications in the implementation of ultrafine‐grained boron carbide as a material for improved performance in impact and other high‐pressure applications.

Effect of optimal aging treatment on magnetic performance and mechanical properties of sintered Nd-Fe-B permanent magnets

The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A new method of Vickers hardness indentation combined with acoustic emission was used to test the brittleness of the magnets.The results show that the magnetic properties of the magnets could be improved through aging treatment, especially the intrinsic coercive force. But it is accompanied by a decrease of strength and fracture toughness. Theoretical calculation confirms that acoustic emission energy accumulated count value could be used to characterize the material brittleness. The bending fracture morphologies of the as-sintered and the optimal aged NdFeB magnets were investigated with the emphasis on the relationship between mechanical properties and microstructure using a field emission scanning electron microscopy (FE-SEM). The research results indicate that the intergranular fracture is the primary fracture mechanism for both as-sintered and optimal aged NdFeB magnets. Aging treatment changes the morphology and distribution of the Nd-rich phases, reducing the sliding resistance between Nd2Fe14B main crystal grains and lowers the grain boundary strength, which is the main reason for the strength and fracture toughness decrease of the aged Nd-Fe-B magnets.

Brittleness and fracture mechanism of sintered Dy-doped NdFeB magnets

The brittleness and fracture behaviors of the sintered and the two-stage aged Dy-doped NdFeB magnets were studied by a unique method of acoustic emission testing and Vickers hardness indentation method in this paper. A detailed analysis on the crack propagation mechanism along the grain boundary of the main grain phase (Nd, Dy)2Fe14B was done. By comparing the acoustic emission energy count value (En) with the Vickers hardness indentation load (P), it is shown that there is a linear relationship between En and P for both the sintered and the two-stage aged Dy-doped NdFeB magnets. According to the slope of En versus P linear lines, it can be found that the two-stage aged Dy-doped NdFeB magnet is more brittle than the sintered one. It is due to that the Nd-rich grain boundary phase of the two-stage aged Dy-doped NdFeB magnet is formed as thin film and uniformly distributes around the main grain phase, which plays a significant role in increasing the intrinsic coercive force of the magnet, but decreasing its interface binding strength. Therefore, the resistance of crack propagation along the grain boundary decreases and the brittleness increases.