Vickers Indentation Method Research Articles

Alloying effects in Mo-5X (X=Zr, Ti,V) – Microstructural modifications and mechanical properties

The microstructures and mechanical properties of three different cast Mo-5X (X = Zr, Ti, V) alloys were investigated. The alloys Mo-5Ti and Mo-5V show a single-phase solid solution microstructure, whereas the Mo-5Zr alloy exhibits polycrystalline Mo2Zr phases embedded in the Mo(Zr) solid solution matrix. Microhardness measurements were carried out by the Vickers indentation method. Compared to the single-phase solid solution alloys the Mo2Zr precipitations in Mo-5Zr result in the highest microhardness. Based on a well-known solid solution model it was shown that Zr, Ti and V are effective solid solution strengtheners. Additionally, constant displacement tests in the compressive mode between room temperature and 1100 °C confirm these findings. However, the homogeneously distributed Mo2Zr phases offer an extraordinary potential to improve the high temperature strength of Mo-based alloys.

The Influence of Ni Addition on the Microstructures and Mechanical Properties of Al2O3–TiN–TiC Ceramic Materials

Al2O3–TiN–TiC ceramic materials with different Ni content were fabricated by hot-pressing technique. Mechanical properties such as flexural strength, Vickers hardness and fracture toughness were obtained by three-point-bending test and Vickers indentation method. The microstructures of the sintered body were observed by scanning electron microscopy. The effects of Ni content on the microstructures and the mechanical properties of Al2O3–TiN–TiC ceramic materials were investigated. The results indicated that the addition of Ni could change the topography of the microstructures which displayed various core–shell structures. Moreover, the fracture mode changed with the increment of Ni content. When the addition of Ni was 3 vol%, the flexural strength and fracture toughness were the greatest and the improvement could be explained by the unique microstructures of sintered bodies.

Electrical and mechanical properties of Na2.8Ca0.1Al2Ga0.5P2.7O12 glass based electrolyte materials: Influence of Ag+ ion-exchange

Sodium super ionic conductor (NASICON) based glass is emerging as solid electrolyte material for Na-ion batteries. In the present study, we report the influence of Ag+ → Na+ ion-exchange process on the electrical, optical, structural and mechanical properties of NASICON type glass with a chemical formula of Na2.8Ca0.1Al2Ga0.5P2.7O12 (NCAGP). Ag+ ion exchange process was carried out by dipping NCAGP glass in AgNO3 molten salt at 300 °C for 15 min (IE15min) and 30 min (IE30min). The diffusion depth of Ag+ ions was measured to be about ~7 μm and ~25 μm for IE15min and IE30min samples, respectively. The dc conductivity values were obtained from base (NCAGP), IE15min and IE30min bulk glass samples through the complex impedance plots at a temperature range of 75 °C–200 °C. With the increase in ion-exchange time, the dc conductivity slightly diminished on account of marginally increase in activation energy (Ea) values. Optical absorption spectra for 30 min ion-exchanged glass revealed the localized surface plasmon resonance (LSPR) band, confirming the reduction of Ag+ ion to Ag0 metal with an increase in ion-exchange time from 15 min to 30 min. Presence of Raman vibrational peak at 233 cm−1 has also confirmed the formation of AgO bonds. The mechanical hardness values obtained through Vickers indentation method reveal enhanced hardness and crack resistance of bulk glasses with the ion-exchange treatment by causing compressive stress on the surface of NCAGP glass. The threshold load for the crack generation is increased from 0.5 kgf (4.9 N) to 2 kgf (19.6 N) after the ion-exchange treatment. Overall, improved mechanical and good electrical properties reveal the applicability of IE15min NCAGP glass as an electrolyte material for Na-ion batteries.

Toughening mechanisms of SiC-bonded CNT bulk nanocomposites prepared by spark plasma sintering

In this work, silicon carbide (SiC) was utilized as a binding agent to fuse carbon nanotubes (CNTs) into highly tough dense CNT bulk nanocomposites through spark plasma sintering (SPS) method. Phase studies were performed using x-ray diffraction analysis (XRD) and field-emission scanning electron microscopy (FESEM) and obtained results were verified by the microstructural evolution. Also, the optimum processing temperature was determined as 1600°C at which the undesired allotropic phase transformation of SiC (β)→SiC (α) was avoided and single-walled CNTs (SWCNTs) were structurally preserved. Fracture toughness of the nanocomposite synthesized at optimum processing conditions was determined by Vickers indentation method equal to 13.3MP·m1/2. Toughening mechanisms were directly observed throughout the microstructure among which crack-wake bridging by SWCNTs and crack deflection by SiC particles were the most dominant.

Effect of powder morphology on sintering kinetics, microstructure and mechanical properties of monazite ceramics

This work focuses on the effect of precursor morphology on the microstructural evolution of monazite-type lanthanum-europium phosphate ceramics during sintering, including grain growth rate, as well as correlations between microstructure, texture effects and their mechanical properties. Sintering kinetics of La0.5Eu0.5PO4 powders with two different grain morphologies (needle-shaped and spherical) was studied by an in situ HT-ESEM method at 1340°C. La0.5Eu0.5PO4 pellets with high density (99% of the theoretical density) were obtained for both precursor powders by hot pressing. Analysis of XRD data collected for the hot pressed pellets obtained from needle-shaped precursors revealed preferential orientation of the grains towards the (100) direction. Mechanical properties of the hot pressed pellets were studied by the Vickers indentation method. The dependence of microhardness and fracture toughness on microstructure and texture was investigated.

Improvement in mechanical properties of titanium alloy (Ti-6Al-7Nb) subject to multiple laser shock peening

This paper is focused on laser shock peening (LSP) of titanium alloy (Ti-6Al-7Nb) for the first-time. This was to improve upon the artificial implant failures caused by destitute wear resistance of titanium alloys. As such, millions of patients are suffering from osteoarthritis pain, which costs billions of pounds annually to end users as they either have to undergo a complete replacement of the particular implants or a second surgery subject to implant failures. Therefore, the effect of multiple impacts on the mechanical properties and sliding wear behaviour of Ti-6Al-7Nb subjected to LSP were investigated. Ti-6Al-7Nb has the advantage of biocompatibility as the material can be applicable for orthopaedic implants. It is critical to improve the mechanical properties and wear resistance. LSP is one of the most effective methods to improve mechanical properties. Thus, in this study X-ray diffraction (XRD); Scanning Electron Microscope (SEM); surface roughness using 3-D profiling; microhardness using Vickers indentation method; and sliding wear with a tribometer were employed to measure the effect of Ti-6Al-7Nb alloy subjected LSP. It was found that the microhardness of Ti-6Al-7Nb alloy can be effectively improved from 290HV30 to 369HV30. In addition, the average the grain size was measured to be 10μm and showed a reduction of 67%. The surface roughness was increased after multiple LSP from 0.15μm to 0.52μm. However, the wear resistance was improved by 44% after multiple LSP. The findings from this work will contribute towards extending the services time of orthopaedic implants and help patients undergo reduced number of surgeries.

Determining the fracture resistance of B4C-NanoSiB6 nanocomposite by Vickers indentation method and exploring its mechanical properties

In this research, the effects of NanoSilicon hexaboride (NanoSiB6) additive, as a sintering aid, on mechanical properties and the sinterability of Boron Carbide (B4C) have been investigated. In addition, the results of several equations used for determining the Indentation fracture resistance (KIFR) by Vickers indentation test have been evaluated. For this purpose, 0, 2, 4, 6 and 8wt% NanoSiB6 additive have been added to B4C in order to improve its sinterability at temperatures 2050, 2150 and 2250°C. The findings indicate that by adding NanoSiB6, up to 4wt%, to B4C, its properties such as relative density, Young's modulus, microhardness and KIFR improve as the sintering temperature rises; however, these properties diminish with the further increase of the mentioned sintering aid. Also, a comparison between KIFR values shows the closeness of the results obtained by different equations and the satisfactory accuracy of the equation for determining KIFR by crack area method compared to the results of other equations; with a difference of <20% between the two results.

Microstructural development and electrical behavior during crystalization of iron-rich glass-ceramics obtained from mill scale

Abstract Mill scale is one of the most hazardous waste generated from the steelmaking industry. In 2014, around 16.4–32.8 million t of mill scale was generated all over the world. In this paper, we present recent results about the effect of the structure and microstructure of iron-rich glass-ceramics obtained from mill scale on their electrical behavior. Five iron-rich glass compositions were investigated. The crystalline phases of the crystallized (glass-ceramic) materials were identified by X-ray diffractometry, and phase content quantifications were performed by the Rietveld method. The crystallinity and porosity were also related to the electrical behavior of the glass-ceramics, which was determined by impedance spectroscopy, and the hardness, measured by the Vickers indentation method. Albite, andradite, anorthite, clinopyroxene, franklinite, nepheline, and spinel were shown to be the main crystalline phases present in the investigated compositions. The conductivity showed an increasing trend with the degree of crystallinity. This behavior was attributed to a decrease in porosity, an increase in the concentration of charge carriers in the glass phase (iron, Li+, and Na+), and an increase in the number of conduction paths through the glassy phase/crystalline phase interfaces. The relationship between hardness and crystallinity could not be verified due to the structural complexity of the glass-ceramics studied. However, a nearly linear relationship was found between the effect of porosity and hardness. The G2Z composition exhibited a hardness of 6.1 ± 0.5 GPa at 850 °C, which is a value in very good agreement with other iron-rich glass-ceramics studied.

Cyclic Loading of TiCN Coating by Vickers Indentation

Physical Vapour Deposited (PVD) coatings are used in wide range of industrial applications where requirements differ. For example, in cutting applications adhesive-abrasive wear along with high contact stresses prevail and PVD coating with thickness of ~2 μm are used. In forming applications adhesive wear usually dominates and relatively thick PVD coatings (~5 μm) are preferred. For both the applications coatings are subjected to cyclic stress and therefore it is a point of interest to learn the behaviour of PVD coatings with different thickness under cyclic loading. Cracking resistance and fatigue properties of gradient TiCN on hard metal substrate was evaluated by means of the cyclic Vickers indentation method. Hard metal was chosen as a substrate material to avoid pile-up effect and support the hard coating during indentation. The results of the single indentation Vickers test show that secondary radial and circumferential cracks appear in tested coatings already after the first indent. With increasing cycles the cracks grow up to a critical crack length after which the crack length doesn’t increase further. The tested coating thickness has no significant effect on cracking behaviour.

Investigation of Nano-Mechanical and- Tribological Properties of Hydrogenated Diamond Like Carbon (DLC) Coatings

AbstractHydrogenated diamond like Carbon (H-DLC) is a promising lubricious coating that attracted a great deal of interest in recent years mainly because of its outstanding tribological properties. In this study, the nano-mechanical and -tribological properties of a range of H-DLC films were investigated. Specifically, four kinds of H-DLC coatings were produced on Si substrates in pure acetylene, pure methane, 25% methane + 75% hydrogen, 50% methane + 50% hydrogen discharge plasmas using a plasma enhanced chemical vapour deposition (PECVD) system. Nano indentation was performed to measure the mechanical properties such as hardness and young's modulus and nanoscartching was performed to investigate the frictional behavior and wear mechanism of the H-DLC samples in open air. Moreover, Vickers indentation method was utilized to assess the fracture toughness of the samples. The results revealed that there is a strong correlation between the mechanical properties (hardness, young's modulus, fracture toughness) and the friction coefficient of DLC coatings and the source gas chemistry. Lower hydrogen to carbon ratio in source gas leads to higher hardness, young's modulus, fracture toughness and lower friction coefficient. Furthermore, lower wear volume of the coated materials was observed when the friction coefficient was lower. It was also confirmed that lower hydrogen content of the DLC coating leads to higher wear resistance under nanoscratch conditions.

Effect of BaO addition on the structural and mechanical properties of soda lime phosphate glasses

The phosphate glasses of composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x = 0,5,10,15 mol%) are prepared by melt-quenching technique. The variations in structural and mechanical properties are studied on glasses prepared at 1000, 1100 and 1200̊ C. The density of glasses increases with barium content for glasses prepared at different temperatures. The molar volume is nearly constant with compositional parameter. The amorphous nature of samples is confirmed by XRD. The calculated values of mass percentage of elements in the batch composition and EDS data are in a reasonable agreement. The FTIR spectra show that the main structural units in these glasses are Q1 and Q2 phosphate units. The frequency of the POP band remains constant with barium substitution. The microhardness is measured using Vickers indentation method by applying 0.98 N for 10 s. The hardness and fracture toughness are independent of composition. The nature of crack formations is examined by SEM. The brittleness and crack length are correlated with plastic flow in the material.

Effect of CO2 Exposure on the Chemical Stability and Mechanical Properties of BaZrO3‐Ceramics

The reactivity of BaZrO3 with CO2 has been addressed as one of the major challenges with BaZrO3‐based electrolytes in protonic ceramic fuel cells. Here, we present a study of the effect of CO2 exposure on BaZrO3‐materials at elevated temperatures. Dense BaZr1−xYxO3−x/2 (x = 0, 0.05, 0.1, 0.2) and BaCe0.2Zr0.7Y0.1O2.95 ceramics were prepared by sintering of powder prepared by spray pyrolysis. The Vickers indentation method was used to determine the hardness and estimate the fracture toughness of pristine materials as well as the corresponding materials exposed to CO2. Formation of BaCO3 on the surface of exposed ceramics was confirmed by X‐ray diffraction and electron microcopy. The reaction resulted in formation of Ba‐deficient perovskite at the exposed surface. The reaction with CO2 was most pronounced at 650°C compared to the other temperatures applied in the study. The reactivity was also shown to depend on the Y‐content and the grain size and was most pronounced for BaZr0.9Y0.1O2.95. The reaction with CO2 was observed to have a profound effect on the fracture toughness of the ceramics, demonstrating a depression of the mechanical stability of the materials. The results are discussed with respect to the chemical and mechanical stability of BaZrO3 materials, with particular emphasis on the composition and grain size.

Evaluation of Fracture Toughness of Tantalum Carbide Ceramic Layer: A Vickers Indentation Method

A tantalum carbide (TaC) ceramic layer was produced on gray cast iron matrix by in situ technique comprising a casting process and a subsequent heat treatment at 1135 °C for 45 min. Indentation fracture toughness in TaC ceramic layer was determined by the Vickers indentation test for various loads. A Niihara approach was chosen to assess the fracture toughness of TaC ceramic layer under condition of the Palmqvist mode in the experiment. The results reveal that K IC evaluation of TaC ceramic layer by the Vickers indentation method strongly depends on the selection of crack system and K IC equations. The critical indentation load for Vickers crack initiation in TaC ceramic layer lies between 1 and 2 N and the cracks show typical intergranular fracture characteristics. Indentation fracture toughness calculated by the indentation method is independent of the indentation load on the specimen. The fracture toughness of TaC ceramic layer is 6.63 ± 0.34 MPa m1/2, and the toughening mechanism is mainly crack deflection.

Vickers microhardness of K2Co(SO4)2 · 6H2O single crystals and fracture geometry around impressions of vickers, knoop, and spherical indenters

The microhardness on the (010) and (001) planes in K2Co(SO4)2 · 6H2O crystal has been measured by the Vickers indentation method. Its values are, respectively, 11500 and 1300 MPa. No microhardness anisotropy of the first kind is revealed on either plane. The fracture geometry under indentation by a spherical indenter and Vickers and Knoop indenters is studied. The crystal has lower brittleness than the isomorphic Cs2Ni(SO4)2 · 6H2O crystal.

High hardness-high toughness WC-20Co nanocomposites: Effect of VC variation and sintering temperature

WC-Co nanocomposites with variable VC content are synthesized by liquid phase sintering at two different temperatures. The as synthesized samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and optical microscope. The mechanical properties are obtained by Vickers indentation method. The high content of VC, lead to high porosity when sintering temperature is increased from 1350 to 1400°C. The relative density of all the samples is more than 95%. Microstructure reveals that agglomeration of W-Co-C and V-W-C increases at 1400°C, which generates layered interfaces in radial direction and hence the material inhomogeneity. XRD pattern shows that the formation of η phase increases at 1400°C, which is responsible to decrease the fracture toughness of the present samples. The average particle size of 102nm, highest hardness of 1870.6kgf/mm2 with fracture toughness of 14.4MN/mm3/2 is observed in sample having 7.5wt% VC, sintered at 1350°C for one minute. This combination shows the highest hardness and reasonably high toughness as compared to conventionally sintered materials reported so far.

Experimental and finite element study of residual thermal stresses in veneered Y-TZP structures

The main complications of zirconia-based laminated systems are chipping and delamination of veneering porcelain, which has been found to be directly associated with the development of residual thermal stresses in the porcelain layer. This study investigates the effects of cooling rate and specimen geometry on the residual stress states in porcelain-veneered zirconia structures. Bilayers of three different shapes (bars, semi-cylindrical shells, and arch-cubic structures) with 1.5mm and 0.7mm thickness of dentin porcelain and zirconia framework, respectively, were subjected to two cooling protocols: slow cooling (SC) at 32°C/min and extremely-slow cooling (XSC) at 2°C/min. The residual thermal stresses were determined using the Vickers indentation method and validated by finite element analysis. The residual stress profiles were similar among geometries in the same cooling protocol. XSC groups presented significantly higher tensile stresses (p=0.000), especially for curved interfaces. XSC is a time-consuming process that showed no beneficial effect regarding residual stresses compared to the manufacturer recommended slow cooling rate.

High-temperature crack-healing behaviour and strength recovery of (MoNb)Si2

(MoNb)Si2 materials were prepared using combustion synthesis and the vacuum hot-pressing technology. Cracks were introduced on the surface of polished materials using the Vickers indentation method. The crack-healing behaviour of (MoNb)Si2 materials were investigated with high-temperature oxidation in air. The results show that after annealing at 900°C, 1200°C and 1500°C for 1h, the crack-healing behaviour was observed in each case. The bending strength obviously decreased when the cracks were introduced, and the materials significantly recovered after the heat treatment. The crack-healed samples exhibited higher bending strengths than the original level after the 1200°C treatment, e.g. 479MPa versus 195MPa of pure MoSi2. MoSi2 micro alloyed with niobium shows a high bending strength at room temperature and excellent crack-healing properties at high temperatures.

Effect of Ti Content on the Microstructure and Properties of TiC/TiB&lt;sub&gt;2&lt;/sub&gt;-FeNiCr Composite Prepared by Thermite Reaction

TiC/TiB2-FeNiCr composite reinforced by TiC and TiB2 composite ceramic particles was successfully in-situ synthesized using thermite reaction. The effects of Ti content in the raw material on the microstructure and properties of the composite were studied. The microstructure was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The hardness, compressive strength and wear resistance were tested using the Vickers indentation method (HXZ-1000), mechanical testing machine (SANS5105) and the high temperature wear tester (HT-600), respectively. The results show that the composite is mainly consisted of TiC, TiB2, Cr7C3, α-FeNiCr and NiAl. The content of TiC and TiB2 is increased with the Ti content. The hardness and compressive strength of the composite is increased first and then decreased. They attain the maximum value at about 8.0wt%Ti. The hardness and the compressive strength of the composite are 1313.25HV and 2725.57MPa at 8.0% Ti. Also the wear resistance of the composite is good, and the weight wear loss at 8.0% Ti is nearly fifth of the mass loss of steel.

Effects of MgO addition on the phase, mechanical properties, and microstructure of zirconia-toughened alumina added with CeO2 (ZTA–CeO2) ceramic composite

The effects of MgO addition on properties such as density, firing shrinkage, microstructure, Vickers hardness, and fracture toughness of ZTA–CeO2 ceramics composites were investigated. The amount of CeO2 used in the experiment was fixed at 5.0wt% while the MgO addition was varied from 0wt% to 2.0wt%. Each composition was weighed, mixed, and pressed using hydraulic press under 300MPa into 13mm pellets. The pellets were sintered at 1600°C for 4h under pressureless condition. Vickers hardness and fracture toughness of the sintered samples were measured using the Vickers indentation method. Based on the SEM microstructures, elongated secondary phase, i.e. MgAl11CeO19, started to occur at 0.5wt% MgO. This elongated phase was responsible for the increase in fracture toughness of the ceramic composites. Similarly, the addition of more than 0.5wt% MgO produced another secondary phase (MgAl2O4), as detected by XRD. This phase was shown to have low intrinsic fracture toughness. Therefore, the sample with 0.5wt% MgO showed the optimum properties with the highest fracture toughness (9.14MPam) and Vickers hardness (1591HV) values.

Fatigue behavior of 3%Y2O3-doped ZrO2 ceramics

The objective of this work was to evaluate the cyclic fatigue strength of a commercial pre-sintered tetragonal zirconia ceramics for dental systems, and to determine the main mechanical properties. Samples were sintered in air at 1600°C for 120min with heating and cooling rate of 10°C/min. The sintered specimens were characterized by X-ray diffraction and scanning electron microscopy. Hardness and fracture toughness were determined using the Vicker's indentation method. The strength was determined by four-point bending tests. The cyclic fatigue tests were realized as four-point bending tests within a frequency of 25Hz and a stress ratio R of 0.1. The Weibull analysis was employed in order to perform failure probability calculations. Sintered specimens presented average values of hardness, fracture toughness and bending strength near to 13.5GPa, 8MPam1/2 and 900MPa, respectively. The fatigue tests results allow concluding that the fatigue strength limit over 5×106 stress cycles is about 550MPa or around 63% of the static strength of this material. The tetragonal–monoclinic (t–m) zirconia transformation observed by X-ray diffraction of fractured surfaces occurs during cyclic loading and the fracture of specimens. The 3Y-TZP samples clearly present a range of loading conditions where cyclic fatigue can be detected. The fatigue strength limit around 550MPa is appropriate for application in dental implant parts.