Vickers Indentation Tests Research Articles

Electrical and Mechanical Properties of ZrO2-Y2O3-Al2O3 Composite Solid Electrolytes

Strategic priorities in the field of hydrogen energy include the design of intermediate-temperature solid oxide fuel cells capable of highly efficient operation in the temperature range of 573–973 K. Consequently, attempts are being made to replace the widely applied cubic zirconia electrolyte with an electrolyte consisting of tetragonal zirconia. The rationale for this approach is that 3Y-TZP exhibits higher mechanical strength and higher electrical conductivity at temperatures below 973 K. The addition of Al2O3 in an amount that exceeds its solubility limit in 3Y-TZP has been found to result in increased electrical conductivity and improved mechanical properties. The aim of the study was to synthesize 3-YSZ powder via co-precipitation and use it to obtain composites with a 3Y-TZP matrix and 0.5 mol.% or 1.0 mol.% of Al2O3 inclusions. The correlation between these samples' electrical conductivity and resistance to brittle fracture and their phase composition and microstructure was investigated by means of X-ray diffractometry, scanning electron microscopy, electrochemical impedance spectroscopy and Vickers indentation tests. For comparison, the properties of composites with an 8-YSZ matrix and Al2O3 inclusions were also investigated. It was determined that the composite based on the 3Y-TZP matrix and containing 0.5 mol.% of Al2O3 inclusions can be considered a viable alternative for 8-YSZ electrolytes in IT-SOFC applications.

Aqueous tape casting of super-hard B4C laminates with rGO-enriched reinforcing interlayers

Superhard B4C parts with microarchitectures constituted by ceramic layers and evenly-spaced rGO-enriched reinforcing interlayers were fabricated for the first time. To this end, a concentrated slurry of B4C with its Ti-Al sintering additive was first prepared by aqueous colloidal processing, optimizing its total solids loading and content of both binder and plasticizer to obtain, by tape casting, handleable and flexible green tapes. A semi-dilute aqueous suspension of B4C with Ti-Al and abundant GO was also prepared to dip-coat those green tapes with a GO-enriched layer, optimizing the withdrawal rate and the dipping time. The bare and GO-coated B4C+Ti-Al tapes were then sequentially laminated, thus yielding green multilayered laminates that finally were appropriately debinded and densified by spark plasma sintering. Vickers indentation tests demonstrated that these multilayered laminates are superhard (∼31 GPa), and that their rGO-enriched reinforcing interlayers are effective in arresting crack propagation.

Evaluation of surface hardness of NiCr coating using Finite Elements Analysis

Introduction: To enhance resistance to surface damage of materials due to mechanical actions, there have been created many procedures that allow its modification for different needs. This leads to researches conducted to determine the changes achieved in the properties due to said procedures. One method commonly applied is, for example, physical means of vapor deposition of thin films on a surface. In recent years, many rational and empirical models have been proposed for the study of said properties. One of these models is computational analysis, which allows determining a great number of properties while avoiding applying destructive tests, achieving to reduce experimental time spent and costs of manufacture of test tubes as well as the test itself. In this research, the hardness of a surface coating of Nichrome (NiCr 80-20) was determined with an indentation test modeled in Ansys, based on the finite elements' method. Objective: To design a computational model that allows determining the surface hardness of material with coating Method: The realization of this project was made with the software for engineering analysis ANSYS, and the model was made based on the Vickers Indentation Test regulation given by the ASTM, which states that the test must be done with a pyramidal diamond indenter, applying forces greater than 1 kgf. Results: By running the respective numerical analysis for both the substrate and the coating, a surface hardness of 197.5073 VH was obtained for NiCr coating and surface hardness of 160.5809 VH for the S235 Steel (hardness of the interface). Conclusions: It was determined that the model proposed is correct seeing as the values obtained for the Vickers' Hardness is approximately the same as the experimental value with an error of 0.7501% for the coating layer and 0.2605% for the substrate. It was also concluded that it is possible to use this same procedure to obtain the surface hardness for different materials than those treated in this article by using this tool. In this research the hardness of a surface coating of Nichrome (NiCr 80-20) was determined with an indentation test modeled in Ansys, based on the finite elements’ method [1]. Objective: To design a computational model that allows to determine the surface hardness of a material with coating Method: The realization of this project was made with the software for engineering analysis ANSYS, and the model was made based on the Vickers Indentation Test regulation given by the ASTM [2], which states that the test must be done with a pyramidal diamond indenter, applying forces greater than 1 kgf. Results: By running the respective numerical analysis for both the substratum and the coating, a surface hardness of 197.5073 VH was obtained for the S235 Steel (hardness of the interface) and a surface hardness of 160.5809 VH for the NiCr coating. Conclusions: It was determined that the model proposed is correct seeing as the values obtained for the Vickers’ Hardness is approximately the same as the experimental value with an error or 0.7501% for the substratum and 0.2605% for the coating layer. It was also concluded that it is possible to use this same procedure to obtain the surface hardness for different materials than those treated in this article by using this tool.

Spark plasma sintering and dry sliding-wear of ZrC-16.7 vol.% Co cemented carbides

The densifiability by spark plasma sintering (SPS) and the dry sliding-wear behaviour of novel cemented carbides based on micrometre-sized ZrC with 16.7 vol.% Co binder (ZrC–Co), compositionally equivalent to the typical WC–10 wt%Co but with ZrC in place of WC, were investigated. Firstly, detailed analysis of both the densification and the shrinkage-rate curves registered during SPS (at 50 MPa) showed that ~1275 °C is the onset SPS temperature for liquid-phase sintering, and ~1600 °C that of full densification. Hardness measurements by Vickers indentation tests confirmed the gradual densification with increasing SPS temperature up to 1600 °C, a condition yielding an extra-coarse-grained (~7–8 μm grain size), ultrahard (~18.2 ± 0.3 GPa) ZrC–Co cemented carbide that is also sufficiently tough (~6.1 ± 0.2 MPa m1/2). And secondly, pin-on-disk tribological tests (at both 20 N for 1000 m and 40 N for 2000 m) and subsequent characterization of the worn surfaces indicated that, under sliding contact, these ZrC–Co cemented carbides wear essentially by two-body abrasion dominated by plastic deformation. Wear increases with increasing severity of the contact conditions, but is nonetheless mild due to the high hardness of these ZrC–Co cemented carbides and to the formation of discontinuous oxide tribolayers.

Microstructures and Mechanical Properties of Al-Zn-Sn Bearing Alloys for High Performance Applications

The mechanical behavior and indentation creep of Al-20 wt% Zn bearing alloy has been modified with adding 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt% Sn. These bearing alloys were prepared by melt spinning technique. The scanning electron microscopy (SEM) was used to study the morphology of the melt spun alloys and x-ray diffractometer (XRD) for the identification of the phases pre- sent in these melt-spun bearing alloys. The results show that the structure of Al80-x-Zn20-SnX (X = 0.2%, 0.5%, 1% and 1.5%) bearing alloys is characterized by the presence of α-Al of FCC structure and SnZn intermetallic compound of anorthic structure. The Al-20Zn-1.5Sn has a smaller crystallite size and grain size as indicated from X-ray and SEM analysis respectively, which leading to the enhancement of the mechanical properties. The mechanical properties and indentation creep of these bearing alloys were studied by tensile test machine and vickers indentation testing at room temperature, respectively. The Al-20Zn-1.5Sn has higher hardness value and creep resistance than other alloys. This was attributed to the strengthen effect of Sn as a strong solid solution element in Al-matrix. The stress exponent values in the range 2.4 - 4.2 indicate that the grain boundary sliding is the possible mechanism during room temperature creep deformation of melt-spun Al-Zn-Sn bearing alloys.

Orientation Dependence of Plastic Deformation Behavior and Fracture Energy Absorption Mechanism around Vickers Indentation of Textured Ti<sub>3</sub>SiC<sub>2</sub> Sintered Body

In order to clarify plastic deformation behavior and mechanism of fracture energy absorption of Ti3SiC2, Vickers indentation tests were conducted for Ti3SiC2 sintered bodies with various textured orientations. Textured Ti3SiC2 sintered bodies were fabricated by slip casting in a strong magnetic field and spark plasma sintering (SPS), and their orientation distribution were analyzed by SEM/EBSD. It was found that for the textured Ti3SiC2, the plastic deformation behavior around Vickers indents such as an indent shape and a grain pile-up were strongly affected by basal slip and kink deformation. Furthermore, the fracture energy absorption mechanism around the indents also depended on the texture orientations. From our results, it is concluded that the most effective factor for suppressing the crack propagation was the grain pile-up, and the second one was crack deflections.

Subcritical crack growth parameters in glass as a function of environmental conditions

In the present work, subcritical crack growth in soda–lime silicate glass is investigated under different environmental conditions. Crack growth parameters as a function of temperature and humidity were determined by dynamic fatigue tests, which has been verified by using the in-situ method of filming crack growth during experiments. The specimens were pre-damaged for constant initial crack lengths in all specimens using the Vickers indentation test. The determined parameters were compared with those from literature in order to discuss existing deviations of sub-critical crack growth parameters in literature. These deviations may be caused by environmental conditions and different chemical compositions of the glass. Arrest lines were used to determine the ratio of crack width to crack depth in Vickers indented specimens. For the initial crack depth, images of fracture surfaces were taken using an scanning electron microscope. Furthermore, the influence of humidity and temperature on the failure stress of unindented specimens with a constant initial crack length was simulated.

Effects of temperature and loads on hardness and surface failure modes of cemented carbide

Cemented carbide is a common cutting material with a hardness that significantly affects its usability. A Vickers indentation test was performed to analyse changes in the hardness of cemented carbide cutters with temperature and loads to understand its variation law. Moreover, indentation-induced surface damage was observed, and its elements were analysed. Crack distributions on the indentation surface were detected and analysed through an etching method. The results demonstrate that the hardness of cemented carbide decreases with greater temperatures and loads. At room temperature, the hardness of cemented carbide decreased from 1321 to 996 MPa when the loads increased from 300 to 800 N. When the external load was fixed at 500 N, the hardness of the cemented carbide decreased from 1113 to 939 MPa as the temperature increased from 25 to 350 °C. Moreover, the density of the indentation-induced surface damages increased with a reduction of the Vickers hardness. In addition, the mean free path of the binding phase for the cemented carbide with large grain sizes was relatively high. Therefore, it is difficult to generate diagonal cracks under large loads and high temperatures, which are beneficial to prevent cutter flaking.

Mechanical Strengthening in S235JR Steel Sheets through Vibration-Assisted Ball Burnishing

The superficial effect of hardening caused after vibration-assisted ball burnishing and its consequences in the tensile behavior of a carbon steel material are studied in this paper. As ball burnishing affects the material to hundredths of micrometers in depth through plastic deformation, the overall macro effect of this modification was studied. Different levels of preload and vibration amplitude were studied to address the described issue. The study was done in two phases. First of all, the depth to which ball burnishing affects the material was studied by performing Vickers indentation tests with different loads. It was proven that the effects of ball burnishing are best represented when a 0.05 kg load is used, as higher loads include more volume of core material in the measurement, hence hiding the effect of ball burnishing. In a second phase, the ball burnished specimens were subjected to tensile tests. It was proven that an increase of burnishing preload diminishes the ductile behavior of the material and increases its strength representative values, although the proportion of affected material in the cross-section of the specimen is reduced with regard to the whole surface. Additionally, as the preload increases, the effects of assistance through vibrations is reduced, and the effect of the static preload acquires more relevance in modifying the macroscopic mechanical properties of the steel alloy. Experiments using different amplitudes and new forces are encouraged to obtain more information about how the material can be modified optimally through vibration-assisted ball burnishing.

Investigation the effect of weathering on chemically strengthened flat glasses

Present work discusses weathering behavior of chemically strengthened flat glasses. With this aim, different soda-lime silicate and sodium aluminosilicate glasses were subjected to weathering tests before and after chemical strengthening to simulate possible scenarios that toughened glass products face and effect of weathering on topographical, optical, structural and mechanical properties were investigated. Topographical evaluations were made through roughness measurements and topography images using white light interferometery and atomic force microscopy techniques. Depth profiling was accomplished by time of flight secondary ion mass spectroscopy. Optical transmittance spectra were recorded with ultraviolet-visible-near infrared spectrophotometer. Structural properties were analzyed by Fourier-transform infrared spectroscopy. Mechanical testing was realized by applying biaxial bending and Vickers indentation tests. Experimental results revealed that soda-lime silicate glasses are more prone to corrosion when weathering takes place after chemical strengthening due to formation of alteration layers. This behavior can be altered by increasing alumina content in the glass composition.

Sıcak Presleme Ve Yüksek Sıcaklık Sinterleme Kombinasyonu İle Β Tipi Biyomedikal Ti74Nb26 Alaşımının Üretimi

Titanium (Ti)-Niobium (Nb) alloys are generally produced by casting methods. Since themelting temperatures of pure Ti and Nb are quite high, their fabrication by casting techniques is costly.On the other hand, it is possible to produce these alloys economically at much lower temperatures (lessthan melting temperature of Ti), completely in solid state using powder metallurgy. In the present study,Ti74Nb26 alloys were produced using pure Ti and pure Nb powders by combination of hot pressing andhigh temperature sintering for the first time. The influences of processing temperature and time ondensity, microstructure, and mechanical behavior were investigated. Density measurements showed thathot pressing at 800 °C provided full density. XRD and SEM investigations revealed that amount of β phaseformed increased with increasing sintering time. In addition to main phase β, little amount of α phase anda very small amount of pure Nb were observed in the microstructure. Mechanical properties weremeasured by means of uniaxial compression and micro Vickers indentation tests. The results indicatedthat 4 h of sintering at 1200 °C exhibited the highest value of hardness (336 HV), elastic modulus (44 GPa),yield strength (894 MPa), and compressive strength (1178 MPa).

Influence of acid leaching surface treatment on indentation cracking of soda lime silicate glass

Past work has shown that water or acid soaking treatments can increase the mechanical strength of soda lime silicate (SLS) glasses. In this work, we show that acid leaching treatments result in an increase in the apparent crack resistance of the acid-leached surface of SLS glass during indentation. Vickers indentation tests in controlled environments show a humidity dependence of radial cracking, suggesting that the transport of water through the leached layer plays a critical role in the propagation of cracks to the glass surface. Molecular dynamics simulations with reactive force fields indicate that the leached surface layer can undergo pressure-induced mechanochemical reactions during indentation, which increases the bridging oxygen connectivity in the silica network of the leached layer. Such structural changes can hinder transport of water molecules from the environment to the subsurface crack tip. Based on experimental observations and simulation results, a new hypothesis is proposed that mechanochemical restructuring in the leached layer in response to the applied load may lower the transport kinetics of molecular water to critical flaws, resulting in an apparent enhancement in the crack resistance of the acid-leached surface of SLS glass.

Mechanical characterization of the AISI 316L alloy exposed to boriding process

In this study, the powder-pack boriding process on low-carbon stainless steel was carried out at 1273 K for 4 h of exposure to obtain a layer around ~57 μm conformed by FeB, Fe2B, and others alloying elements. Firstly, the presence of iron borides formed on the surface of borided AISI 316L alloy was confirmed by optical microscopy combined with the X-ray diffraction analysis. After, the sensed Vickers indentation test was performed on the iron boride layer to estimate the behavior of hardness and Young’s modulus. Sliding wear tests on the borided AISI 316L alloy were performed according to the ASTM G133-05 standard procedure, with the following conditions: distances of 50 and 150 m, normal loads of 5 and 20 N, and a sliding speed of 30 mm/s. Finally, the results showed that the presence of FeB-Fe2B improves the resistance to wear around 41 times compared to the untreated material.

Effects of density on the mechanical properties of spark plasma sintered β-SiC

The influence of density on the hardness value of β-SiC samples was studied based on Knoop and Vickers indentation tests. Hardness measurements were performed on additive-free spark plasma sintered SiC samples in the [80%–95%] density range and on highly dense samples (>99%) sintered with very low content of sintering aids. Results revealed that the density has a strong influence on the hardness value, which increases of about 7 GPa between samples presenting densities of 80% and 95% and even reaches 21 GPa under 2 kg with Knoop indenter for the densest samples sintered with very low content of sintering aids. These results allowed us to give a comprehensive model-supported analysis of the mechanical properties of spark plasma sintered β-SiC with controlled porosity that currently does not exist in the literature. The calculation of Young modulus and toughness further resulted in encouraging properties for our samples with regards to mechanical and ballistic performances.

Effect of crystallinity and microstructure on mechanical properties of CaO-Al2O3-SiO2 glass toughened by precipitation of hexagonal CaAl2Si2O8 crystals

In order to identify the most effective level of crystallinity and microstructure to increase the toughness of CaO–Al2O3–SiO2 glass with precipitated hexagonal-CaAl2Si2O8 crystals, we measured the fracture toughness and investigated the microcracking behavior of samples containing different amounts of the crystalline phase. The glass-ceramics were prepared in the range of 10–48 wt% crystallinity by changing the parent glass composition. Five glass compositions, xCaO–yAl2O3–zSiO2 wt% (x= = 25.6–22.7, y= = 18.0–28.1, z= = 56.4–49.2), were examined by Single Edge V-Notched Beam (SEVNB) method for fracture toughness measurement, and Vickers indentation tests for hardness measurement. Although the fracture toughness increased for a crystal content of up to 21 wt%, it remained constant at 21–40 wt%, and then started to decrease at 48 wt%. The Vickers hardness showed a minimum in the range of 21–35 wt% crystallinity. Microcrack formation around indentations was clearly observed in the same range of crystallinity. Also, non-elastic behavior was found at the same levels of crystallinity during bending tests for measurement of fracture toughness, with more fractured surface area. The microstructure of these glass-ceramics was characterized as a “house-of-cards” structure, suggesting that this microstructure was most effective at decreasing the brittleness of the glass by microcrack toughening.

Vickers indentation tests on olivine: size effects

We conducted Vickers indentation tests on Fe-free (Mg2SiO4) and Fe-bearing (Mg1.8Fe0.2SiO4) olivine single crystals and high-density polycrystalline material with average grain sizes ranging from 170 to 890 nm. The Vickers microhardness ($$H_{{\text{v}}}$$) of the Fe-free polycrystalline material with the finest grain size is ~ 17 GPa at a load of 0.1 N, while that of the Fe-bearing single crystal is ~ 8 GPa at the largest load applied. Overall, $$H_{{\text{v}}}$$ decreases with increasing grain size, load (indentation depth), and the presence of Fe. For each grain size, $$H_{{\text{v}}}$$ is well characterized by a power law of the form $$H_{{\text{v}}} /H_{{\text{v}}}^{0} \propto l^{ - x}$$, where $$H_{{\text{v}}}^{0}$$ is the depth-independent value of $$H_{{\text{v}}}$$, $$l$$ represents either grain size or indentation depth, and x is 0.09. Despite the small exponent value for each size effect, the nonlinear interaction of the two size effects results in large variations of $$H_{{\text{v}}}$$ in our samples. We show that our semi-empirically derived relationship as a function of grain size and indentation depth explains the $$H_{{\text{v}}}$$ of both polycrystalline and single-crystal olivine at any indentation conditions. Indentation fracture toughness of the finest-grained material is 0.8 $${\text{MPa}}\;{\text{m}}^{1/2}$$, which increases slightly to 1.1 $${\text{MPa}}\;{\text{m}}^{1/2}$$ with increasing grain size, while the toughness of the single crystals varies from 0.5 to 0.8 $${\text{MPa}}\;{\text{m}}^{1/2}$$ depending on the crystallographic orientation of the fracture planes.

Shape memory alloy reinforced magnesium matrix composite fabricated via friction stir processing

Shape memory alloys (SMAs) are the new generation functional material and being recognized as a smart or intelligent material. In this research, a novel Ni-rich NiTip shape memory alloy (SMA) reinforced magnesium matrix composites were prepared using a recent solid-state friction stir processing (FSP) technique. High speed steel was selected as tool material. A flat shouldered plain cylindrical tool pin profile was selected for experiment. The FSP was performed on a fixed value of 560 tool rpm, 100 mm/min traversing speed and 3° tool tilt. The particle distribution in processed zone was analyzed using optical micrography while micro-hardness were evaluated by Vickers indentation test. The results revealed that the FSP was successful in fabrication of surface composite on magnesium matrix. The processed zone indicates good bonding of reinforcement particles with the substrate. However, some accumulation of reinforcement was observed in the processed region. The micro-hardness of the reinforced zone shows significant improvement.

Hardness and Indentation Fracture Toughness of Slip Cast Alumina and Alumina-Zirconia Ceramics.

Alumina (Al2O3) and zirconia (ZrO2) have good overall properties and thus are widely used oxide technical ceramics. The biggest drawback of Al2O3 is its low fracture toughness. In contrast, ZrO2 is relatively tough, but is also much more expensive. In order to improve the alumina toughness, composite ceramics are being developed. Slip casting technology has economic advantages over the conventional hot isostatic pressure technology, but problems may arise when preparing stable highly-concentrated suspensions (slip) for filling the mold. The purpose of this study is to prepare aqueous suspensions using 70 wt. % α-Al2O3, with 0, 1, 5 and 10 wt. % of added t-ZrO2. Suspensions were electrosterically stabilized using the ammonium salt of polymethylacrylic acid, an alkali-free anionic polyelectrolyte dispersant. Also, magnesium oxide in form of magnesium aluminate spinel (MgAl2O4) was used to inhibit the abnormal alumina grain growth during the sintering process. Minimum viscosities were used as stability estimators, where an increase in ZrO2 content required adding more dispersant. After sintering, the Vickers indentation test was used to determine the hardness and the indentation fracture toughness from the measurement of the crack length. Also, the brittleness index (Bi, μm−1/2) was calculated from values of Vickers hardness and the Vickers indentation fracture toughness. It was found that with increasing ZrO2 content the fracture toughness increased, while the hardness as well as the brittleness index decreased. Zirconia loading reduces the crystallite sizes of alumina, as confirmed by the X-ray diffraction analysis. SEM/EDS analysis showed that ZrO2 grains are distributed in the Al2O3 matrix, forming some agglomerates of ZrO2 and some pores, with ZrO2 having a smaller grain size than Al2O3.

Ferroelastic domain switching and R‐curve behavior in lead zirconate titanate (Zr/Ti = 52/48)‐based ferroelectric ceramics

AbstractIn this work, ferroelastic domain switching and R‐curve behavior in lead zirconate titanate (Nb/Ce co‐doped Pb(Zr0.52Ti0.48)O3, ab. PZT‐NC)‐based ferroelectric ceramics were investigated, using the indentation‐strength‐in‐bending (ISB) method. Firstly, Vickers indentation test examined the notable fracture anisotropy of PZT‐NC ceramics between the poling direction and its perpendicular direction, and the crack open displacement (COD) profiles in the two directions were also theoretically calculated from the indentation fracture mechanics. And then two kinds of ferroelastic domain switching modes (in‐plane and out‐of‐plane) were used for explaining such anisotropic propagation behavior of indentation cracks. The subsequent three‐point bending test illustrated the dependence of fracture strength on indentation load and the rising crack growth resistance curves (R‐curves) in two directions. The resulted R‐curves were fitted by the Hill's type Growth Function successfully, giving the reasonable values of crack extension exponential (n), plateau fracture toughness (Kmax), and initial fracture toughness (Kini). The in‐plane ferroelastic domain switching was identified as a more significant toughening mechanism for PZT‐NC ceramics than the out‐of‐plane switching due to more switchable domains.

Understanding the elastic and thermal response in TiC-based ceramic-metal composite systems: First-principles and mechanical studies

First-principles and experimental studies of fundamental mechanical (elastic moduli, Poisson ratio and hardness) and thermal (expansion coefficient) properties were compared to assess the responses in titanium carbide (TiC) based ceramic-metal (cermet) composite systems, and evaluate the potential for predictive modelling of cermet behaviour. The TiC cermets were prepared with 30 vol-% of stoichiometric nickel aluminide (Ni3Al) binder using a liquid phase sintering process, performed at 1500 °C for 60 min. Densities greater than 99% of theoretical were achieved under these conditions. The experimental elastic moduli were determined using a pulse-echo method, while hardness was assessed using the Vickers indentation test. The volumetric thermal expansion of the sample was studied using dilatometry.