High Vickers Hardness Values Research Articles

Microstructural Evolution and Densification of Co-Based Alloy Powder by Spark Plasma Sintering for High-Hardness Applications

This work presents the densification of Co-based alloy powders by a spark plasma sintering process. The densification process was carried out at a temperature range of 800 °C to 1100 °C in order to obtain sintered coupons and study their microstructure and mechanical properties. The shrinkage behaviour of the sintered coupons was studied, and an optimal densification temperature was defined. The microstructural analysis showed a reduction in porosity with temperature increment along with the development of a fine microstructure comprised of cobalt-molybdenum-chromium-silicon-based intermetallic laves phases, which are dispersed in a softer cobalt-based alloy matrix. X-diffraction analysis showed that these crystalline phases were well-dispersed, with a lattice parameter corresponding to a hexagonal system. The obtained high Vickers hardness values were attributed to the preservation of a fine microstructure and to the precipitation of Co-Mo phases. Three-point bending tests were performed in order to identify the strain path concerning the densification of the sintered coupons.

Wear characteristics of resin-based luting agents used in the bonded CAD-CAM resin blocks.

This study aimed to investigate the wear and microhardness of luting agents and computer-aided design-computer-aided manufacturing (CAD-CAM) resin blocks, and to compare the wear characteristics of resin-based luting agents used in bonded specimens of CAD-CAM resin blocks. After three-body wear test, the amount of wear and Vickers hardness were measured and Pearson's correlation coefficient was calculated. The lowest amount of wear and the highest Vickers hardness values were obtained for Estecem II. Filler loss was observed in five composite resin cements. A strong negative correlation was observed in the luting agents between the amount of wear and Vickers hardness value (r=-0.874, p<0.0001). Additionally, a strong positive correlation was observed between the amount of wear of the bonded specimen and amount of luting agent used alone (r=0.943, p<0.0001). To conclude, the wear resistance of the luting agent used in the bonded specimen was significantly influenced by the bonding between the filler and matrix resin.

Synthesis of MgO Coating Gd2O3 Nanopowders for Consolidating Gd2O3-MgO Nanocomposite with Homogenous Phase Domain Distribution and High Mid-Infrared Transparency

Improved optical and mechanical properties are required for future infrared windows working in harsher mechanical and thermal environments than today. Ameliorating the homogeneity of the phase domain and reducing the size of the phase domain are effective approaches for enhancing the optical transmittance and mechanical hardness of a nanocomposite. In this work, we reported that the Gd2O3-MgO nanopowders were prepared by two different processes. The core–shell nanopowders synthesized by urea precipitation have a much lower agglomeration than the nanopowders prepared by sol–gel. Excellent transmittance (70.0%–84.1%) at 3–6 μm mid-infrared wave range and a high Vickers hardness value (10.3 ± 0.6 GPa) were maintained using the nanopowders synthesized by urea precipitation mainly due to its homogenous phase domain distribution.

Orthorhombic ScB3 and hexagonal ScB6 with high hardness

Transition metal borides (TMBs) have received great interest since these intriguing borides could be considered potential applications for designing exotic materials with distinguished properties such as superhardness. The search for TMBs regarding high hardness value remains urgent. Given that Sc is the lightest transition metal element that often exhibits unique properties, in this paper, we undertake a comprehensive investigation of the Sc-B system at high pressures using the state-of-the-art structure search method within the framework of first-principles electronic structure. As a result, our structure searches identified several stable Sc-B phases (i.e., ScB, ${\mathrm{ScB}}_{3}, {\mathrm{ScB}}_{4}$, and ${\mathrm{ScB}}_{5}$) as well as a metastable ${\mathrm{ScB}}_{6}$. Strikingly, among these scandium borides, $Pnma {\mathrm{ScB}}_{3}$ contains a boron framework with open channels, while ${\mathrm{ScB}}_{6}$ possesses interlinking boron trimer units. Remarkably, our simulations suggest the hard features of $Pnma {\mathrm{ScB}}_{3}$ and $P{6}_{3}mc {\mathrm{ScB}}_{6}$ with high simulated Vickers hardness values of 38.3 and 39.8 GPa, respectively, which are mainly attributed to their peculiar strong covalent boron network. The excellent stability and high hardness of ${\mathrm{ScB}}_{3}$ and ${\mathrm{ScB}}_{6}$ render them promising candidates for superhard materials. Additionally, an orthorhombic boron allotrope $o\text{\ensuremath{-}}{\mathrm{B}}_{12}$ is predicted by removing Sc from $Pnma {\mathrm{ScB}}_{3}$, where this structure exhibits an estimated hardness value of 24.9 GPa and superconducting critical temperature ${T}_{\mathrm{c}}$ of 2.9 K at 1 atm. In this paper, we advance the existing knowledge of TMBs as well as provide implications for the search for TMBs with unique properties.

Degradation of a mechanically recycled polylactide/halloysite nanocomposite in an ethanolic food simulant

&lt;p class="JARTEAbstract"&gt;This work aims to study the effect of immersion in a ethanolic food simulant in mechanically recycled poly(lactic acid) (PLAR) and its nanocomposites reinforced with halloysite nanotubes (HNT). PLAR was obtained by subjecting PLA to an accelerated ageing process, which includes photochemical, thermal and hydrothermal ageing steps, followed by a final demanding washing step. PLAR was further reinforced with 4 %wt. HNT to improve the properties of the PLAR films. The materials were melt compounded by melt extrusion and processed into films by compression molding. The resulting films were exposed to food simulant D1 (50 %vol. ethanol solution) for 10 days at 40 °C. The intrinsic viscosity, crystallization behavior, thermal stability as well as the mechanical performance were analyzed before and after the contact with the food simulant. The swelling, plasticizing and hydrolyzing effect of the food simulant led to an important decrease of the intrinsic viscosity of all the samples, along with a significant increase of the crystallinity. Thermal stability was negatively affected by the decrease of the molecular weight, while the high crystallinity values resulted in materials with higher Vickers hardness values after the immersion in the food simulant.&lt;/p&gt;

Shear and Hardness Properties Study of AA-6061 Aluminium Alloy Lap-Joints Produced by Friction Stir Spot Welding Process Using H13 Tool Steel

By virtue of high-strength verses weight ratio aluminium alloys are achieving attentions in automobile, marine, and aircraft industries as it reduces the fuel consumption for running the vehicles. But their main drawback is the destruction of their carefully engineered microstructures by high heat generated in traditional welding processes. Friction Stir Welding (FSW) minimizes excessive heat in the welding zone and does not influence the microstructural features. FSW is currently one of the recommended solutions for manufacturing aluminium alloy welded machine parts. In this study, AA6061 Al-alloy strips were lap joined using the improvised FSW setup tool clamping it on the spindle of a CNC milling machine with the speed rate varied from 1000 rpm to 3000 rpm, and three different feed rates 5, 15, and 25 mm/min. Shear strength experiments of these joints revealed that samples created with the speed rate of 1000 rpm and feed rate of 25 mm/min performed best showing the highest load carrying capacity of 8976 N with elongation of 1.04%. They also demonstrated highest Vickers hardness value of 31 at the centre of the weldment.

Mechanical and Microstructural Evolution of the Mg-B Powder/Nb/Cu Cladding Using Hydrostatic Extrusion and Subsequent Drawing Process.

The paper introduces the mechanical and microstructural evolution of Mg-B powders/Nb/Cu claddings fabricated using only drawing process and hydrostatic extrusion plus drawing process. We found that the Mg-B powder of the claddings during the latter process was more densified than that of the former process because of larger reduction rate in the process of hydrostatic extrusion. The claddings created by the latter process exhibited a little higher Vickers hardness values and lower grain size than those of the former process in Nb tubes. The refined microstructure of Nb tube by the latter process had higher image quality (IQ) value corresponding to lower dislocation density due to higher misorientation angles between grains than that of the former process, thereby demonstrating the broadly distributed (110) fiber texture.

Reactive hot pressing of super hard (Ti,Ta)(B,C)–(Ta,Ti)C composites

(Ti,Ta)(B,C)–(Ta,Ti)C composites were synthesized by reactive hot pressing using commercial TaB2 and TiC powders as starting materials. The reaction process and effects of TiC contents in the starting batches on the microstructure and mechanical properties of the resultant composites were reported. The microstructure of the composites was refined due to reaction and solid solution coupling effect. A core-rim structure was observed in the (Ti,Ta)(B,C) grains. Vickers hardness, flexural strength and fracture toughness of the composites increased with increasing the TiC content. The TaB2–70 mol.% TiC sample (starting batch composition) prepared by hot pressing at 2000 °C for 1 h had a super high Vickers hardness value of 30.5 GPa (indented under 9.8 N, 15 s) approaching that of B4C-based composites. Good flexural strength (714 MPa) and fracture toughness (5.4 MPa m1/2) were also found.

Structural, mechanical, and electronic properties of P21/m-Carbon✰

The structural, mechanical, and electronic properties of P21/m-carbon were comprehensively investigated by using first principles calculations. Our calculated structure parameters are in good agreement with the previous theoretical values. P21/m-carbon consists of 10 atoms in a unit cell and is made of an exclusively sp3 hybridized bonding network. The calculated phonon spectra and elastic constant verify that P21/m-carbon is dynamically and mechanically stable at ambient pressure. The analysis of the electronic band structure reveals that P21/m-carbon is an insulator with a band gap of 5.47 eV. It has a large bulk moduli of 398 GPa and a high shear moduli of 457 GPa. Further mechanical properties demonstrate that P21/m-carbon is prone to be ductile and possesses a high Vickers hardness value of 82.3 GPa. These values show that P21/m-carbon simultaneously possesses ultra-incompressible and the superhard property. Furthermore, the X-ray diffraction spectra is also theoretically simulated to provide more structure information for future experimental observations.

Physical, structural and optical properties of Sm3+ doped lithium zinc alumino borate glasses

Sm3+ doped lithium zinc alumino borate glasses with composition 15ZnF2–12Li2CO3–10BaO–8Al2O3–(55-x)B2O3–xSm2O3 where x = 0.1, 0.3, 0.5, 0.7 and 1.1 mol% were prepared by conventional melt quenching technique Their optical, physical, structural, mechanical and luminescence properties are investigated. UV–Vis-NIR absorption spectra showed all possible transitions of samarium ion in this glass matrix. Band gap values for all the glass samples were above 3 eV confirming the insulating nature for the glass. Densities, assessed using the Archimedes rule, were observed to be increasing with increasing samarium concentration. Increase in molar volume with addition of samarium content indicated that the extension of glass network is on account of the increase of number of Non-Bridging Oxygens created by network modifier samarium ions. Scanning Electron Microscopy (SEM) image showed a smooth surface for the synthezied glass. X-Ray Diffraction (XRD) technique was employed to verify the amorphous nature of the glasses. A Makishima and Mackenzie theoretical model gave acceptable approximation of elasticity constants viz. Young's modulus, shear modulus, bulk modulus and Poisson's ratio. The high Vickers hardness values evaluated with mechanical loads of 50, 100, 300, 500, 1000 g force, proved the stability of the glasses. Emission spectra showed a prominent transition 4G5/2 → 6H7/2 at 598 nm excited with 6H5/2 → 4P3/2 transition at 401 nm. Luminescence quenching effect was observed beyond 0.3 mol% Sm2O3 addition. The chromaticity coordinates (x, y) clustered in the orange-red region, making these Sm3+ doped lithium zinc alumino borate glasses suitable candidate for applications in LEDs and solid-state lasers.

Magnesiothermic Reduction Synthesis of Silicon Carbide with Varying Temperatures: Structural and Mechanical Features

The search for finding effective ways to produce high quality of nanostructured materials have always been the never-ending work of many scientists and engineers from time to time. Important issues to address are reducing fabrication expense and lowering energy utilization to complete the synthesis. A specific circumstance is an investigation of using relatively low temperature to fabricate pure silicon carbide (SiC), one of the most notable materials due to its excellent properties, from naturally appearing minerals. In this current study, silicon carbide was prepared by means of magnesiothermic approach at some adjusting temperatures using argon gas furnace. The source of silicon and carbon were respectively initiated from naturally purified silica and sucrose. The X-ray diffraction (XRD) assessment clearly uncovered the pure moissanite-3c phase of silicon carbide, having a cubic crystal structure. The disappearing of magnesium, otherwise in the form of magnesium oxide, was also validated by the X-ray fluorescence (XRF) test. Furthermore, the chemical functional groups were clarified by Fourier-transform infrared (FTIR) spectroscopy, and the silicon-carbide interaction was evidently detected from the FTIR spectrum. Besides, the SiC products exhibited high Vickers hardness values, nearly 150 MPa for the sample with temperature synthesis of 800 °C.

Microstructural evolution and mechanical properties of pure titanium powders processed by spark plasma sintering

In this study the effect of sintering pressure on the densification, microstructure and mechanical properties of commercial pure titanium (CP-Ti) powders with varying chemistry was investigated. The sintering was performed at a constant dwell time of 3 min at varying temperature and pressure in the range of 550–900 °C and 25-75 MPa in vacuum, respectively. Full densification with high Vickers hardness values of 340 HV and 262 HV was obtained at 25 MPa at 800 °C and 900 °C respectively for two commercial powders with different average particles sizes. Different microstructural transformations with respect to increasing temperature and pressure were observed on the sintered pellets. The results were discussed emphasizing the huge role of the interstitial elements, contained in the starting powders, on the properties (relative density, Vickers hardness and microstructure) of the dense samples. This paper shows that good mechanical properties can be obtained by SPS technique when CP-Ti powders are sintered at very low temperature during a short period in contrast to conventional fabrication techniques.

Low-temperature preparation of Al2O3-ZrO2 nanoceramics via pressureless sintering assisted by amorphous powders

In present work, Al2O3 nanoceramics toughened with 5 mol% ZrO2 and 10 mol% ZrO2 were prepared by pressureless sintering; polycrystalline ZrO2 powders and Al2O3-ZrO2 amorphous powders were used as dopants in conventional sintering and amorphous-phase-assisted sintering, respectively. In amorphous-phase-assisted sintering, the densification of Al2O3-ZrO2 nanoceramics was highly promoted, and nanoceramics with composition of Al2O3-5 mol% ZrO2 and Al2O3-10 mol% ZrO2 were almost fully densified at temperature as low as 1350 °C. The easy densification was attributed to the metastable state and phase transition of amorphous powders, which acted as sintering aids. The nanoceramics exhibited dense and homogenous mixture of Al2O3 and ZrO2 particles with fine grain size, and the microstructure refinement further contributed to superior mechanical properties with high Vickers hardness, bending strength and Weibull modulus values. This work may provide new guidance for low temperature fabrication of nanoceramics by employing amorphous powders as sintering aids.

EFFECT OF REINFORCEMEMT PARTICLES PREHEATING ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF AMC

An investigation into the effect of preheating the powder particles versus not preheating before mixing it with an aluminium slurry was carried out. This was seen as way of overcoming the challenge of wettability which often occurs when powder particles are added to a melted metal for the purpose of developing a metal matrix composite. In this study, non – preheated, 2 w.% preheated and 4 w.% preheated palm kernel shell ash powder was used to develop an aluminium matrix composite (AMC) via stir casting method. Mechanical properties revealed that AMC with 4 w.% pks ash inclusion has the highest Vickers Hardness value. Meanwhile, optical micrographs and scanning electron micrograph show that the pks ash both non – preheated and preheated are homogenously distributed into the matrix. This is further confirmed by the energy dispersive spectroscopy (EDS) mapping of the various samples. Although pks ash particles are only visible on the optical microscope micrographs, the elemental analysis of the various samples through EDS show a strong presence of carbon at various degree proving the presence of pks ash in the composite. Overall, preheating does not significantly affect the surface morphology of the AMCs based on the derived optical and scanning electron micrographs and AMC with higher content of pks ash particles seems to have better mechanical properties.

Effects of heat treatment temperature on microstructure and mechanical properties of lithium disilicate-based glass-ceramics

In this study, the mechanical properties and microstructure of lithium disilicate glass-ceramics in the Li2O-SiO2-P2O5-Al2O3-K2O glass ceramics was investigated for dental applications. The glass-ceramics were prepared from the casting glass melt into warmed mold. After that the samples were heat treatment at 650–850 °C for 2 h. The heat treatment temperatures were determined from the differential thermal analysis (DTA). The microstructure of the glass–ceramics were characterized by X-ray diffraction (XRD) technique and the scanning electron microscopy (SEM). Moreover, the mechanical properties were investigated by Vickers hardness testing. Results indicated that the samples confirmed the occurrence of Li2Si2O5, LiSi2O3 Li3PO4 and LiAlSi2O6 phases in prepared glass ceramics. Moreover, the lithium disilicate glass-ceramic exhibits a high Vickers hardness values in the range of 4.92–5.90 GPa.

Comparison of Plasma Transferred Arc and Submerged Arc Welded Abrasive Wear Resistant Composite Hardfacings

EComposite hardfacings produced by Plasma Transferred Arc Welding (PTAW) and Submerged Arc Welding (SAW) possess a good combination of hardness, wear resistance and fracture toughness, thus providing high wear resistance. Although they cannot substitute and be compared with conventional WC-Co based hardmetals, still they can be used in many applications where high wear resistance, hardness and toughness are in great demand. In this study two different hardfacing production technologies PTAW and SAW, were used to produce the hardfacings for abrasive wear conditions. In both cases hardfacings were welded on the top of low alloy steel using different proportions of disintegrator milled hardmetal WC-Co powder of different fractions as a reinforcement and self-fluxing alloy as a matrix. They were analysed in regard to Rockwell and Vickers hardness, wear behaviour, and microstructural analysis. SAW hardfacings were subjected to Rockwell hardness test after process and after two cycles of tempering; secondary hardness effect was detected as increment of hardness values from 39 HRC to 58 HRC after first cycle of tempering. High Vickers hardness values did not correlate with wear results, as it commonly shows hardness of hardmetal particles. Dissolution of hardmetal particles in the matrix was observed in both PTAW and SAW hardfacings with higher amount in the later. This amount correlated with heat input during welding process. Wear test results in abrasive emery wear (AEMW) and abrasive wheel wear test (AWW) showed almost analogous tendency, with slightly lower wear in later. Both types of hardfacings have shown promising results in intensive wear conditions. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.19121

First-principles study of mechanical and magnetic properties of transition metal (M) nitrides in the cubic M4N structure

We report results from systematic calculations performed by density functional theory on mechanical properties of twenty-eight 3 d, 4 d and 5 d transition metal (M) nitrides (TMNs) in metal-rich cubic M4N structure as novel candidates for hard coatings materials. We have computed lattice constants, elastic constants, derived moduli and ratios which characterize mechanical properties, and other properties like magnetic moments, formation energies, Debye temperature and Bader charge transfer. Our calculations indicate that all M4N-type metal nitrides except V4N, Nb4N, and Pt4N are mechanically stable. All Group 7 TMNs in the M4N structure are found to have high Vickers hardness values with the highest being 24.3 GPa for Re4N. Our computed lattice constants and magnetic dipole moments for Mn4N and Fe4N, the two compounds for which experimental measurements exist, are consistent with their measured values. Spin-polarized computations reduce the hardness of some magnetic compounds like Mn4N and Fe4N. The total density of states calculation reveals that all 28 M4N phases are metallic. The hybridization of metal d and nitrogen 2p orbitals is found to be the key factor in determining mechanical stability and hardness in these compounds. In contrast, ionicity, as computed by Bader charge transfer, does not correlate with hardness. Our comprehensive database for binary transition metal nitrides in M4N structure offers wide possibilities for experimental synthesis of such materials with desirable physical properties for the hard-coatings application.

Mechanical Properties and Microstructure of Li&lt;sub&gt;2&lt;/sub&gt;O-SiO&lt;sub&gt;2&lt;/sub&gt;-P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-K&lt;sub&gt;2&lt;/sub&gt;O-CaO Glass-Ceramics

In this study, the mechanical properties and microstructure of lithium disilicate glass–ceramics in the Li2O-SiO2-Al2O3-K2O-P2O5-ZrO2-CaO glass system were investigated. The glass-ceramics were prepared from the glass melt by casting into mold on hotplate. After that the glass was heat treated at 650-800 °C for 2 h. The heat treatment temperatures were determined from the differential thermal analysis (DTA). The phase formation and microstructure of the glass–ceramics were characterized by X-ray diffraction (XRD) technique and the scanning electron microscopy (SEM). Moreover, the mechanical properties was investigated by Vickers hardness testing. The results indicated that the samples confirmed the occurrence of Li2SiO3, Li2Si2O5, Li3PO4, and LiAlSi2O6 phases in the prepared glass ceramics. The optimum heat treatment temperature results in the physical properties with a high Vickers hardness values in the range of 5.4-5.8 GPa.

Microstructure and mechanical properties of rapidly solidified B2-type Zr–Co alloys containing a second phase of Zr2Co

Microstructure and mechanical properties of B2-type Zr–Co alloys containing a second phase (Zr2Co) were investigated. Results show that the as-cast Zr52Co48, Zr54Co46, and Zr56Co44 alloys are composed of a eutectic structure of B2 and Zr2Co phases. Relative amounts of Zr2Co phases increase with an increase in Zr content. Zr54Co46 exhibits high yield strength, high Vickers hardness, good ductility, and high toughness values, and thus, Zr54Co46 can be considered to be a novel engineering material. The increase in strength and decrease in plastic strain of the alloys are mainly attributed to the increase in high strength of the brittle Zr2Co phase and to grain refining of the B2 matrix phase.

Pengaruh Perlakuan Panas Quenching dan Tempering terhadap Laju Korosi pada Baja AISI 420

&lt;p&gt;Corrosion occurs in almost all metals. Even corrosion-resistant metals are corroded, but their corrosion rate is different from ordinary or non-corrosion resistant metals. This study examines the corrosion rate that occurs in stainless steel that is stainless steel. Stainless steel contains high enough chromium levels that can reduce the rate of corrosion that occurs. The metal material to be studied is the AISI 420 steel, which belongs to the Martensitic Stainless Steel class. This study examined the effect of heat treatment on corrosion rate and hardness level of AISI 420 steel. The heat treatment carried out was Quenching at 1020&lt;sup&gt;o&lt;/sup&gt;C with a holding time of 60minutes with an oil cooling medium. After quenching the subsequent heat treatment is tempering with temperature variations of temperature 200&lt;sup&gt;o&lt;/sup&gt;C and 300&lt;sup&gt;o&lt;/sup&gt;C with a resistance time of 45 minutes and air cooling media. The results of this study showed that the base material specimens had the highest corrosion rate of 0.569 mm/y. The lowest corrosion rate is in specimens with quenching process with a value of 0.267 mm/y. The highest Vickers hardness values were found in specimens with quenching process with a value of 551 kg/mm&lt;sup&gt;2&lt;/sup&gt;. The lowest hardness value is in the specimen with tempering process at 300&lt;sup&gt;o&lt;/sup&gt;C with 405 kg/mm&lt;sup&gt;2&lt;/sup&gt;.&lt;/p&gt;