Value Of Hv Research Articles

Microstructural evolution and mechanical properties of FeCrNiCuTix high entropy alloys

In this study, the microstructural evolution and mechanical properties of a series of FeCrNiCuTix (x = 0, 0.2, 0.4, 0.6, 0.8, and 1, in mole ratio) high entropy alloys (HEAs) were analyzed in detail to study the influence of Ti content on the HEAs. The microstructures of the alloys transformed from single-phase face-centered cubic (FCC) phase structure to FCC and body-centered cubic (BCC) diphase, finally to FCC, BCC and intermetallic compound (Fe2Ti) phase with the increase of Ti content. The addition of Ti element significantly refined the grain of the alloys. The hardness, strength and tribology tests of the alloys were also carried out. The results indicated that the Vickers hardness, yield strength, and fracture strength increased first and then decreased, the average friction coefficient variation law was just the opposite, and the plastic strain reduced monotonically, with the increase of x values for the alloys. At x = 0.4, the maximum yield strength and fracture strength of the alloy were 1646.89 MPa and 1947.09 MPa, respectively, and the average friction coefficient was a minimum of 0.47, with a hardness value of HV 489.68 and a plastic strain of 13.98%. The maximum hardness value of the alloy was HV 656.19 at x = 0.8. The fracture mechanism of the alloys was from ductile fracture to brittle fracture and the wear mechanism was form of abrasive wear. Accordingly, the FeCrNiCuTi0.4 alloy obtained the optimal mechanical properties overall. This research is of great significance for the development of engineering and structural materials with excellent mechanical properties.

Development and validation of a local thermal non-equilibrium model for high-temperature thermal energy storage in packed beds

High-temperature thermal energy storage (TES) in packed beds is gaining interest for industrial energy recovery. The wide range of temperature distributions causes significant variations in thermophysical properties of the fluid and solid phases, leading to inaccuracies of classical TES models and heat transfer correlations. The objective of this work is to develop and validate a detailed but pragmatic model accounting for high-temperature effects. Based on a literature survey spanning over several communities interested in high-temperature porous media, we propose a generic local thermal non-equilibrium model for granulate porous media accounting for conservation of mass, momentum and energy (two-equation temperature model). The effective parameters needed to inform the model are the effective thermal conductivities of the different phases and the heat transfer coefficient. An experimental-numerical inverse analysis method is employed to determine these parameters. A dedicated experimental facility has been designed and built to study a model granulate made of glass bead of 16 mm diameter. Experiments are conducted using the Transient Single-Blow Technique (TSBT) by passing hot air (ranging from 293 K to 630 K) through cold particles at various mass flow rates, covering a Reynolds number range of 58 to 252. The new model was implemented in the Porous material Analysis Toolbox based on OpenFoam (PATO) used to compute the transient temperature fields. Two optimization algorithms were employed to determine the parameters by minimizing the error between experimental and simulated temperatures: a Latin Hypercube Sampling (LHS) method, and a local optimization method Adaptive nonlinear least-squares algorithm (NL2SOL). The results indicate that the value of heat transfer coefficient hv in the two-equation model falls in the range of 1.0 × 104∼1.93× 104 W/(m3 K) under the given conditions. The axial dispersion gas thermal conductivity was found to be around 5.9 and 67.1 times higher than the gas thermal conductivity at Peclet numbers of around 55 and 165, respectively. Furthermore, two improved correlations of Nusselt number (Nu=2+1.54Re(T)0.6Pr(T)1/3) and of axial dispersion gas thermal conductivity (kdis,∥=0.00053Re(T)2.21Pr(T)⋅kg) are proposed and validated for a range of Reynolds number from 58 to 252. The overall approach is therefore validated for the model granulate of the study, opening new perspectives towards more precise design and monitoring of high-temperature TES systems.

Structure and cryogenic mechanical properties of severely deformed nonequiatomic alloys of Fe–Mn–Co–Cr system

The work is devoted to a study of the structure and mechanical properties of two nonequiatomic medium-entropy nanocrystalline alloys, in which in a coarse state additional mechanisms act during plastic deformation — twinning (TWIP) in the Fe40Mn40Co10Cr10 alloy and phase transformations (TRIP) in the Fe50Mn30Co10Cr10 alloy. The nanocrystalline state in these alloys is achieved by high-pressure torsion (HPT) at 300 K and 77 K after different numbers of revolutions n = 0.25 and 5. In the nanostructural state in the TWIP Fe40Mn40Co10Cr10 and the TRIP Fe50Mn30Co10Cr10 alloys, a basically complete phase transition from the fcc lattice to hcp is observed, the content of which does not depend very strongly on the HPT temperature and deformation. For both alloys in the nanostructured state, there is a significant decrease in differences in the phase composition and microhardness Hv by comparison with the coarse-grained state. A decrease in the HPT temperature and an increase in HPT deformation for all the cases studied lead to an increase in the value of Hv. The Fe40Mn40Co10Cr10 TWIP alloy remains ductile under active compression deformation at 300 and 77 K, while there is no macroscopic plasticity in the Fe50Mn30Co10Cr10 TRIP alloy under similar conditions. For the Fe40Mn40Co10Cr10 TWIP the thermally-activated character of plastic deformation is retained during the transition from the coarse-grained to the nanostructured state.

Experimental analysis of heat transfer characteristics of static water pool under low pressure vaporization

Low pressure vaporization (LPV) is considered a promising method for rapid cooling and a significant rate of water vaporization. This article presents an experimental investigation for the detailed heat and mass characterization of a static water pool exposed to low pressure conditions. An LPV experimental setup has been fabricated in the lab to investigate the effect of process parameters like initial temperature (Tw,0), initial vacuum tank pressure (Pv,0), and the water pool height (Hw,0) on the non-equilibrium fraction (NEF) and heat transfer coefficient (hv). Results shows that NEF initially increased to a high value and then tediously dropped. The final value of NEF decreased with decreasing the initial vacuum tank pressure and initial water pool height inside the flash chamber. A maximum value of the hv existed with the rise of the degree of superheat (ΔT) of liquid. It is found that with an increase of the degree of superheat by 13.44 °C, the value of hv is enhanced by 67%, and the NEF decreased by 46.7%, respectively.

Influences of Sc(NO3)3 on characteristics of micro-arc oxidation coatings

ABSTRACT Micro-arc oxidation (MAO) coatings were fabricated on 2195 aluminium-lithium alloy substrate, using a silicate and phosphate electrolyte with variable scandium nitrate (Sc(NO3)3) concentrations. The properties of the coatings were analysed by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical workstation. The comprehensive analysis demonstrates that adding proper amount of Sc(NO3)3 increased the oxidation voltage, which transformed the worm shape discharge micropores into round-hole shape, and the MAO coatings presented a double-layer structure. The primary phase composition of the coatings was γ-Al2O3, α-Al2O3, Sc2O3 and Al3Sc. The optimum concentration of Sc(NO3)3 was 0.6 g L−1. The hardness reached a maximum value of (1284 ± 43.5) HV, which was about 2.5 times higher than that without adding. The self-corrosion current density reduced from 138.00 × 10− 7 A cm−2 (substrate) to 3.65 × 10− 7 A cm−2, which was approximately two orders of magnitude lower, indicating that the corrosion resistance was improved.

Phase change materials as quenching media for heat treatment of 42CrMo4 steels

In the present work, paraffin phase change material is used as quenchant for the heat treatment of 42CrMo4 alloy and compared with water, air, and CuO doped paraffin. The samples were prepared based on ASTM E 8M-98 standard for tensile test and then heated up to 830 °C, kept for 4 h in an electric resistance furnace and then quenched in the mentioned media. Elastic modulus, yield strength, ultimate tensile strength, elongation, and modulus of toughness were determined according to the obtained stress-strain curves. Moreover, the hardness and microstructural evolution were investigated after the heat treatment at different media. The samples quenched in paraffin and CuO-doped paraffin are higher in ultimate tensile strength (1439 and 1306 MPa, respectively) than those quenched in water (1190 MPa) and air (1010 MPa). The highest hardness, with a value of HV 552, belonged to the sample quenched in CuO-doped paraffin. The microstructural studies revealed that the non-tempered steel had a ferrite/pearlite microstructure, while by quenching in water, paraffin and CuO-doped paraffin, ferrite/martensite microstructures were achieved. It is also observed that using the air as quenchant resulted in a three-phase bainite/martensite/ferrite microstructure.

A study on microstructure and mechanical properties of aluminium matrix composites with micro-sized iron fillers produced by powder metallurgy route

Aluminium matrix composites have become popular for new age applications mainly because of their light weight and high specific strength and find applications in the field of aerospace, automobile and defence. In the present study, aluminium matrix composites consisting of aluminium as the matrix and certain iron fillers added as reinforcement were prepared by powder metallurgy processing. The effect of iron addition on the microstructure and mechanical properties of aluminium matrix composites were studied. Aluminium powders (70 µm) and iron powders (60 µm) were mixed properly to prepare 5 wt%, 10 wt% and 15 wt% Fe-Al composites (weight fraction). Unlike Al-5 wt% and 10 wt%. Fe the addition of 15 wt% Fe on Al matrix composite showed the presence of Al13Fe4 intermetallic phase in XRD analysis, which was responsible for enhanced properties of the composite. The hardness was found to increase with increasing iron content and the highest value of HV 51.03 was found in Al-15 wt% Fe composites. The electrical conductivity decreased with increasing value of Fe content in the composite.

Effect of Tilt Angle and Pin Depth on Dissimilar Friction Stir Lap Welded Joints of Aluminum and Steel Alloys.

Automobile, aerospace, and shipbuilding industries are looking for lightweight materials for cost effective manufacturing which demands the welding of dissimilar alloy materials. In this study, the effect of tool rotational speed, welding speed, tilt angle, and pin depth on the weld joint were investigated. Aluminum 5052 and 304 stainless-steel alloys were joined by friction stir welding in a lap configuration. The design of the experiments was based on Taguchi’s orthogonal array for conducting the experiments with four factors and three levels for each factor. The microstructural analysis showed tunnel defects, micro voids, and cracks which formed with 0° and 1.5° tilt angles. The defects were eliminated when the tilt angle increased to 2.5° and a mixed stir zone was formed with intermetallic compounds. The presence of the intermetallic compounds increased with the increase in tilt angle and pin depth which further resulted in obtaining a defect-free weld. Hooks were formed on either side of the weld zone creating a mechanical link for the joint. A Vickers hardness value of HV 635.46 was achieved in the mixed stir zone with 1000 rpm, 20 mm/min, and 4.2 mm pin depth with a tilt angle of 2.5°, which increased by three times compared to the hardness of SS 304 steel. The maximum shear strength achieved with 800 rpm, 40 mm/min, and a 4.3 mm pin depth with a tilt angle of 2.5° was 3.18 kN.

Thermal Stability of the Structure and Microhardness of the Al–0.05 vol % Al2O3 Nanocomposite Fabricated by Accumulative Roll Bonding

The evolution of the microstructure and microhardness of the Al–0.05 vol % nAl2O3 nanocomposite (where nAl2O3 are aluminum nanoparticles) and aluminum without nanoparticles fabricated by accumulative roll bonding with annealing in a temperature range of 373–573 K is investigated. Ball-shaped Al2O3 nanoparticles with an average diameter of 50 nm are introduced between rolled plates of technically pure aluminum from the first to fourth rolling cycles, while the fifth to the tenth rolling cycles are performed without nanoparticles. The average grain size and aspect ratio of elements of the material grain–subgrain structure in the initial state and after annealing at 473 K are measured using transmission electron microscopy. It is shown that the nanocomposite microhardness is 5–13% higher than the corresponding value of HV for aluminum over the entire studied annealing temperature range. The main factor of the higher nanocomposite microhardness is precipitation hardening due to Al2O3 nanoparticles. The contribution of the substructural and grain-boundary hardening is identical in both materials. The thermal stability of the nanocomposite microhardness is only ~25 K higher than that of aluminum, which is caused by the nonuniform distribution of nanoparticles in the matrix and their low volume fraction. The high thermal stability of the fine-grain structure itself, formed by accumulative roll bonding, when compared with other methods of intense plastic deformation, also plays a role. It is established that most Al2O3 nanoparticles remain at the grain boundaries of nanocomposite after annealing at 473 K; therefore, the ability to fasten the boundary by Al2O3 nanoparticles under the conditions under study is retained at least to 473 K.

First-principles investigation into the effect of pressure on structural, electronic, elastic, elastic anisotropy, thermoelectric and thermodynamic properties of CaMgSi

In this work, the structure, electronic, elastic, elastic anisotropy, thermoelectric, and thermodynamic properties of CaMgSi under pressure are calculated via first-principles methods. The optimized structure and lattice parameters are in agreement with previously published experimental results, indicating the methods used in this work are feasible and reliable. The calculated results show that the values of bulk modulus, B, Young’s modulus, E, and shear modulus, G, increase with the pressure overall, while the values of G and Y decrease in special pressure regimes from 20 to 24 GPa. Analyses of Poisson’s ratio, v, and Pugh’s modulus ratio, B/G, imply that CaMgSi is prone to change from brittle to ductile with increasing pressure. The transition from brittleness to ductility occurs at a pressure of 16 GPa. The value of Hv decreases with the pressure overall, although it increases over the pressure ranges of 16–20 GPa and 24–28 GPa. Universal elastic anisotropy increases at pressures from 4 to 24 GPa, while it decreases over the pressure ranges from 0–4 and from 24–28 GPa. Moreover, the variation of elastic anisotropy for G and E is larger compared to that of B. In addition, the electrical conductivity and electronic thermal conductivity decrease with increasing pressure based on the total density of states for CaMgSi. In addition, the heat capacity decreases with increasing pressure, indicating the reduction of lattice thermal conductivity, which is beneficial for thermoelectric performance, especially at pressures from 8 to 16 GPa. Meanwhile, the structural stability can be enhanced at higher pressures, while the thermal stability of crystalline CaMgSi becomes weaker with increasing pressure. The investigation presented in this work offers a comprehensive understanding of the effects of pressure on the mechanical, thermoelectric, and thermodynamic properties of CaMgSi, which can provide guidance for further theoretical work and practical applications.

Effects of CeO<sub>2</sub> Addition on Slip - Cast Yttria Tetragonal Zirconia Polycrystals Toughened Alumina (ZTA)

Addition of CeO2 into ZTA and its effects on microstructure and mechanical properties were investigated. CeO2 was detected with significant amounts only above 10 wt%. Viscosity was measured for slurry preparartions and characterization of mechanical properties of ZTA. Additions of CeO2 of more than 10 wt% surpassed the solubility limit and formed Ce2Zr3O10. Ce2Zr3O10 increased the tetragonality factor, prevented excessive grain growth through a pinning effect, which is attributed to the segregation of Ce2Zr3O10 to the grain boundaries and showed a peak in fracture toughness with a value of 9.3 MPam1/2 with 10 wt% additions of CeO2. Further additions of CeO2 reduced ZTA’s mechanical strength. Maximum value of Hv was 17700 MPa with 10 wt% CeO2. Porosities have been attributed as the underlying reason as to why theoretical density were always higher than measured densities.

Electrochemically grown functionalized -Multi-walled carbon nanotubes/hydroxyapatite hybrids on surgical grade 316L SS with enhanced corrosion resistance and bioactivity.

Coatings using functionalized multi-walled carbon nanotubes (f-MWCNTs)/hydroxyapatite (HAP) on 316 L Stainless Steel by electrodeposition at the parameter of "-1.5 V" for 30 min. with three electrode set-up configuration and optimization of various concentrations of f-MWCNTs from 1 to 5% were done to improve the coating characteristics for future biomedical applications. The obtained coatings were characterized by Fourier Transformed-Infra Red spectroscopy (FT-IR) and X-ray diffractometer (XRD) to reveal the phase formation in the composites. With various additions of f-MWCNTs, the HAP phase was found to be retained. The growth of HAP on f-MWCNTs was analyzed by High-resolution Transmission Electron Microscope (HR-TEM) and the morphology of composite was found to be of the needle and flower-like particles. To understand the corrosion resistance effect of the developed HAP/f-MWCNTs composite in SBF, electrochemical investigations were carried out using Impedance and Tafel polarization analysis. From the results, it was observed that the coatings have enhanced corrosion resistance behavior and bioactivity. In addition, the Vickers Hardness study proved that the prepared HAP/fMWCNTs composite coating was found to have improved hardness value of (Hv) 390.2 ± 8.0. Thus, the electrodeposited composite coating on 316 L SS substrate can be effectively deployed for biomedical applications.

Synthesis and characterization of ferrimagnetic glass‐ceramic frit from waste

AbstractThe large amount of generated waste determines the importance of their valorization. Red mud is the residue of the Bayer process, which stored cumulative value raises 2.7 Bt. This paper describes an easy way to produce a ferrimagnetic glass‐ceramic frit, using bauxite residue, fly ash and glass cullet as raw materials. The synthesized frit consists of faceted and dendritic agglomerated crystals of magnetite and titanomagnetite embedded in a glass matrix, which exhibits a saturation magnetization (MS) of 6.3 emu/g, a remanent magnetization (MR) of 2.7 emu/g and a coercive field (HC) of 347 Oe. Furthermore, it presents Vickers hardness value of HV = 5.55 ± 0.16 GPa and fracture toughness value of KIC = 1.64 ± 0.34 MPa·m1/2.

Analysis of the Influence of Laser Power on the Microstructure and Properties of a Titanium Alloy-Reinforced Boron Carbide Matrix Composite (Ti6Al4V-B4C)

Laser Metal Deposition (LMD) process is a means of producing metal composites with the aid of a laser beam, ejected onto the substrate with the participating powder and fused together after solidification. In this research work, Ti6Al4V alloy is fused with 20 wt % of B4C in order to form metal matrix composites (MMCs). Using the Ytterbium Fibre Laser System powdered at 3000 W, the laser powers were varied between 800 W and 2400 W while all other supporting process parameters were kept constant. The deposited Ti6Al4V-B4C composites were characterized through the surfacing microstructure, microhardness and dry sliding wear. The microstructural properties of the deposited samples were profound, with a Widmanstatten structure of α-Ti, β-Ti and (α+β) Ti phases. The microhardness tests revealed that the composites deposited with a laser power of 2000 W exhibited the highest hardness value and standard deviation of HV 445 ± 61. Furthermore, characterisation revealed that the sample produced with the laser power of 800 W had the lowest wear loss and wear rate of 35.2 × 10–3 mm3 and 6.42 × 10-4 mm3/Nm. However, the motivation for this work is to improve the material properties of the Ti6Al4V alloy for surface engineering applications.

Development of processing windows for friction stir spot welding of aluminium Al5052 /copper C27200 dissimilar materials

Friction stir spot welding technique was used to join dissimilar combinations of aluminium alloy (Al5052) with copper alloy (C27200) and friction stir spot welding windows such as tool rotational speed–dwell time and tool rotational speed–plunge depth diagrams for effective joining of these materials were developed. Using a central composite design model, empirical relations were developed to predict the changes in tensile shear failure load values and interface hardness of the joints with three process parameters such as tool rotational speed, plunge depth and dwell time. The adequacy of the developed model was verified using ANOVA analysis at 95% confidence level. Response surface methodology was used to optimize the developed model to maximize tensile strength and minimize interface hardness. A high tensile shear failure load value of 3850 N and low interface hardness value of HV 81 was observed for joints made under optimum conditions, and validation experiments confirmed the high predictability of the developed model with error less than 2%. The operating windows developed shall act as reference maps for future design engineers in choosing appropriate friction stir spot welding process parameter values to obtain good joints.

Hardening and thermal stability of a nanocrystalline CoCrFeNiMnTi0.1 high-entropy alloy processed by high-pressure torsion

A CoCrFeNiMnTi0.1 high-entropy alloy (HEA) was subjected to high-pressure torsion (HPT) processing under 6.0 GPa pressure up to 10 turns. XRD results reveal that the initial and HPT-processed microstructures consist of a single fcc phase and there is no evidence for creating a new phase and the occurrence of a phase transformation during HPT processing. It is shown that there is a gradual evolution in hardness with increasing numbers of turns but full homogeneity is not achieved even after 10 turns. Microhardness measurements reveal that the material reaches a saturation hardness value of Hv ≈ 460 which is approximately three times higher than for the homogenized alloy. The nanostructured HEA was subjected to post-deformation annealing (PDA) at 473-1173 K and it is shown that the hardness increases slightly up to Hv ≈ 550 at 773 K due to a phase decomposition and the formation of new precipitates and then decreases to the hardness of the homogenized sample (Hv ≈ 140) at 1173 K due to a combination of recrystallization, grain growth and dissolution of the precipitates. The results reveal that an addition of only 2 at.% Ti will improve the hardness and thermal stability of the nanocrystalline CoCrFeNiMn HEA.

An investigation of age and yield of fresh fruit bunches of oil palm based on ALOS PALSAR 2

The objective on this study is to investigate age and yield of FFB of oil palms based on ALOS PALSAR 2. Study areas in oil palm plantations areas of Jerantut, Pahang Malaysia. Methodology consists collecting of ALOS PALSAR 2 and tabular data on the study area, processing of ALOS PALSAR 2 including of converting digital numbers to normalize radar cross sections (NRCS), topography correction and filtering, making of regions of interest according to areas of age and yield of FFB of oil palms and making of relationship analysis between backscatter value of HH, HV and age and yield of FFB of oil palm. The results have showed relationship between HH, HV and age of oil palm which R2 of 0.63 for HH and 0.42 for HV that indicated increasing of age of oil palm as increasing of HH and HV value. Also relationship between HH, HV and yield of FFB of oil palm which R2 of 0.26 for HH and 0.15 for HV, that indicated increasing of yield of FFB as decreasing of HH and HV value.

Absolute magnitudes and phase coefficients of trans-Neptunian objects

Context: Accurate measurements of diameters of trans-Neptunian objects are extremely complicated to obtain. Thermal modeling can provide good results, but accurate absolute magnitudes are needed to constrain the thermal models and derive diameters and geometric albedos. The absolute magnitude, Hv, is defined as the magnitude of the object reduced to unit helio- and geocentric distances and a zero solar phase angle and is determined using phase curves. Phase coefficients can also be obtained from phase curves. These are related to surface properties, yet not many are known. Aims: Our objective is to measure accurate V band absolute magnitudes and phase coefficients for a sample of trans-Neptunian objects, many of which have been observed, and modeled, within the 'TNOs are cool' program, one of Herschel Space Observatory key projects. Methods: We observed 56 objects using the V and R filters. These data, along with those available in the literature, were used to obtain phase curves and measure V band absolute magnitudes and phase coefficients by assuming a linear trend of the phase curves and considering magnitude variability due to rotational light-curve. Results: We obtained 237 new magnitudes for the 56 objects, six of them with no reported previous measurements. Including the data from the literature we report a total of 110 absolute magnitudes with their respective phase coefficients. The average value of Hv is 6.39, bracketed by a minimum of 14.60 and a maximum of -1.12. In the case of the phase coefficients we report 0.10 mag per degree as the median value and a very large dispersion, ranging from -0.88 up tp 1.35 mag per degree.

Biocompatible mechanical surface modification processing and mechanical properties of beta-type titanium alloys

Biocompatible mechanical surface modification processing and mechanical properties of beta-type titanium alloys

Developing superplasticity in an aluminum matrix composite processed by high-pressure torsion

An Al-7075 alloy reinforced with 10vol% Al2O3 particulates was processed by high-pressure torsion (HPT) at room temperature under a pressure of 6.0GPa through up to 20 turns. The metal matrix composite (MMC) showed significant grain refinement from an initial average grain size of ~8μm to ~300nm after processing by HPT through 20 turns. The Vickers microhardness also increased from an initial value of Hv≈167 to a saturation value after HPT processing of Hv≈260. Tensile testing at 623K demonstrated the potential for achieving true superplasticity in the HPT-processed MMC with a maximum elongation of ~670% when testing at a strain rate of 1.0×10−2s−1.