Increase In Vickers Hardness Research Articles

Microstructural and Mechanical Characterizations of a Ductile Metastable β Titanium Alloy Subjected to Low Temperature Annealing

Low temperature thermal treatments, between 423K and 573K, were performed to optimize the mechanical properties of a ductile beta metastable titanium alloy with TRIP and TWIP effects. A set of short-time heat-treatments (STT) were applied at 423K, 473K, 523K, and 573K for 60 and 600s, respectively. The results show that the tensile strength and Vickers hardness increase as the annealing temperature increasing. The sample annealed at 423K for 60s possessed a modest yielding strength (≈566MPa), Vickers hardness (≈327HV) and excellent elongation (≈53%); whereas the sample annealed at 573K for 600s shows a very high yielding strength (≈1256MPa), Vickers hardness (≈441HV) but a small ductility. It is worth noting that the sample annealed at 473K for 60s exhibited the best combination of high strength (close to 1200MPa of true stress) and a stable plastic zone of ɛ=0.4(true strain) with a significant strain hardening effect. It is clarified that both TRIP and TWIP deformation mechanisms are promoted after the heat treatment of 60s at 473K, resulting in good balance among the tensile strength, the ductility and the strain hardening behavior.

TRIP型ベイニティックフェライト鋼の表面残留応力に及ぼす微粒子ピーニングの影響

To apply a transformation-induced plasticity (TRIP)-aided steel consisting of bainitic ferrite structure matrix and metastable retained austenite of 10 vol% (TBF steel) to some precision gears, the effects of fine particle peening on the Vickers hardness and residual stress in a surface layer of the TBF steel were investigated. The peened surface layer showed much higher Vickers hardness and compressive residual stress than those of a quenched and tempered SNCM420 steel. The increased Vickers hardness was mainly caused by an increase in the strain-induced transformed martensite fraction. The compressive residual stress was increased by the increases in size and gravity of shot material and arc-height. The higher compressive residual stress was principally associated with (1) plastic strain due to severe plastic deformation and (2) expansion strain due to the strain-induced transformation of metastable retained austenite. Contribution of the (2) was approximately 30% of total residual stress.

Enhancement of the wear resistance and microhardness of aluminum alloy by Nd:YaG laser treatment.

Influence of laser treatment on mechanical properties, wear resistance, and Vickers hardness of aluminum alloy was studied. The specimens were treated by using Nd:YaG laser of energy 780 mj, wavelength 512 nm, and duration time 8 ns. The wear behavior of the specimens was studied for all specimens before and after treatment by Nd:YaG laser and the dry wear experiments were carried out by sing pinon-disc technique. The specimens were machined as a disk with diameter of 25 mm and circular groove in depth of 3 mm. All specimens were conducted by scanning electron microscopy (SEM), energy-dispersive X-ray florescence analysis (EDS), optical microscopy, and Vickers hardness. The results showed that the dry wear rate was decreased after laser hardening and increased Vickers hardness values by ratio of 2.4 : 1. The results showed that the values of wear rate for samples having circular grooves are less than samples without grooves after laser treatment.

Effect of sintering temperature and nanotube concentration on microstructure and properties of carbon nanotube/alumina nanocomposites

Multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites were prepared by simple wet mixing of MWCNT and Al2O3 powder followed by pressureless sintering in static Argon. X-ray diffraction (XRD) line broadening analyses using Williamson–Hall (W–H) technique revealed a polynomial dependence of crystallite size (DV) on sintering temperature (Tsin) and volume percent CNT added (VCNT) as DV≈[0.9(Tsin)−770]+[−1.1(Tsin)+1489](VCNT)+[0.4(Tsin)−547](VCNT)2. While the highest increase (~14%) in Vickers hardness (HV) over pure Al2O3 was offered by 0.15vol% MWCNT/Al2O3 specimen, the highest fracture toughness (KIC~5MPam0.5) and flexural strength (σFS~260MPa) were obtained for nanocomposite containing 0.3vol% MWCNT which were ~26% and ~16% higher, respectively, than those of pure Al2O3. The 0.15vol% MWCNT/Al2O3 specimen also offered maximum increase (~22%) in thermal conductivity over unreinforced Al2O3 (~39W/mK). Electrical percolation in nanocomposites was observed between 0.6 and 1.2vol% CNT loading.

E-modulus of the alkali–silica-reaction product determined by micro-indentation

The effects of expansion on concrete structures induced by alkali–silica reaction (ASR) are complex. Numerous attempts have been made to model them. Some of these models assume an E-modulus for the ASR product, as no experimental data exist up to now.In this study, Vickers hardness, indentation and E-modulus are determined by micro-indentation tests on undried, polished concrete samples taken from a structure damaged by ASR. Both the indentation tests and the chemical analysis by EDX performed on the ASR product in different aggregates indicate that it is relatively homogenous. Vickers hardness ranges between 10 and 19 and E-modulus between 7 and 9GPa. Towards the edge of the aggregates the ASR product takes up calcium and the values for Vickers hardness and E-modulus increase.

Physical Characterization and Recovery of Corroded Fingerprint Impressions from Postblast Copper Pipe Bomb Fragments

Pipe bombs made from 1mm thick copper pipe were detonated with a low explosive power powder. Analysis of the physical characteristics of fragments revealed that the copper had undergone work hardening with an increased Vickers Hardness of 107HV1 compared with 80HV1 for unexploded copper pipe. Mean plastic strain prior to fracture was calculated at 0.28 showing evidence of both plastic deformation and wall thinning. An examination of the external surface showed microfractures running parallel with the length of the pipe at approximately 100μm intervals and 1-2μm in width. Many larger fragments had folded "inside out" making the original outside surface inaccessible and difficult to fold back through work hardening. A visual examination for fingerprint corrosion revealed ridge details on several fragments that were enhanced by selective digital mapping of colors reflected from the surface of the copper. One of these fingerprints was identified partially to the original donor.

Oxygen diffusion hardening of tantalum coatings on cp-titanium for biomedical applications

Protective tantalum coatings on titanium substrates were produced using a two step process. At first, substrates were coated with Ta layers of 5μm thickness by physical vapor deposition (PVD). In a second step, the coated samples were hardened by oxygen diffusion for up to 3h. During this process the samples were exposed to oxygen for 1–2h at a pressure of 6.7·10−3mbar at 350–450°C, followed by 1–2h annealing in oxygen-free atmosphere at the same temperature. X-ray diffraction (XRD) analysis demonstrated a shift of peaks for oxygen diffusion treated samples, which was attributed to the diffusion of atomic oxygen into the Ta-layer. The hereby caused mechanical stress in the crystal lattice led to an increase in Vickers hardness of the Ta layers from 570HV to over 900HV. In order to compare the adhesion of untreated samples with oxygen diffusion treated samples, the coatings were investigated using Rockwell measurements. These tests demonstrated an increase of critical force for coating delamination from 12N for untreated samples up to 25N for diffusion treated samples.

Statistical analysis of mechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Mechanical properties of pressureless sintered 0.15–1.2 vol.% multiwalled carbon nanotube reinforced alumina matrix nanocomposites have been analyzed using the 2-parameter Weibull statistics. Electron microscopy and phase analysis of nanocomposites sintered at 1700 °C for 2 h in Argon revealed existence of interpenetrating network of nanotubes in alumina, formation of thin interface resembling stoichiometric aluminum monoxycarbide and matrix grain refinement by nanotubes. Statistical analyses indicated that with increasing Vickers hardness testing load (4.9–19.6 N) and flexural strength measurement temperature (room temperature to 1100 °C), Weibull modulus of nanocomposites increased significantly suggesting improved consistency at higher load and temperature. The highest Weibull moduli were obtained for nanocomposites containing either 0.15 or 0.3 vol.% nanotube which were ∼40% and ∼15% higher than single phase alumina for hardness and strength, respectively, supporting the specimen size effect on reliability of present brittle ceramic matrix nanocomposites. Superior mechanical reliability of nanocomposites over pure alumina was primarily attributed to the presence of structurally intact nanotubes forming effective interface region to ensure proper load sharing, matrix grain refinement, and especially, at higher testing load and temperature, overall averaging effect of flaws to yield higher Weibull moduli.

Effects of sintering temperature and graphite addition on the mechanical properties of aluminum

The effects of different sintering temperatures, namely 400, 500 and 600°C, on the mechanical properties of four aluminum–graphite alloys were reported. Different percentages of exfoliated graphite nanoplatelets particles (xGnP) were added to pure aluminum by using the powder metallurgy technique to produce Al-0wt.%xGnP, Al-1wt.%xGnP, Al-3wt.%xGnP, and Al-5wt.%xGnP. The density, fracture surface, compression, and hardness measurements were carried out to report the mechanical properties of the different aluminum–xGnP alloys. Combined data indicated that the Vickers hardness and compressive strength increase, on the other hand, the density decreases with increasing the graphite content in the Al alloys.

Densification and mechanical properties of TiC by SPS-effects of holding time, sintering temperature and pressure condition

Abstract The influence of sintering temperature, holding time and pressure condition on densification and mechanical properties of bulk titanium carbide (TiC) fabricated by SPS sintering has been systematically investigated. Experimental data demonstrated that relative density and Vickers hardness ( H V ) increase with sintering temperature and holding time, but fracture toughness ( K IC ) was not significantly influenced by sintering parameters. The H V and relative density of samples consolidated by SPS technique at 1600 °C for 5 min under 50 MPa pressure (applied entire sintering cycle) reached 30.31 ± 2.23 GPa and 99.90%, respectively. H V values of ∼24–30 GPa and K IC of ∼3.7–5 MPa m 1/2 were obtained in all bulk samples with relative densities of 95.61–99.90% when fabricated under various conditions presented above, without abnormal grain growth. More pronounced effects of pressure condition on grain growth (promoted by grain-boundary diffusion) than on densification were observed. The relationship of fracture toughness and fracture mode is also discussed.

Effect of SiC nano-whisker addition on TiCN-based cermets prepared by spark plasma sintering

TiCN-based cermets with different amounts of SiC nano-whisker were prepared by spark plasma sintering at 1350°C with an initial pressure of 30MPa and a holding time of 8min. The microstructural and mechanical properties of the as-prepared samples were investigated. The addition of SiC nano-whisker has a significant effect on the cermets, resulting in 6% increase in Vickers hardness and 63% increase in flexural strength, respectively, when 2.5wt.% of SiC nano-whisker was added, as compared with its counterpart without whisker. X-ray diffraction analysis revealed that no SiC peaks were detected but some peaks of new hard phases due to the reactions of SiC with the cermet matrix. The resultant hard phases were present normally in the grain boundary in the cermets on the basis of observation by transmission electron microscopy, and they are responsible for the hardness increase of the as-obtained cermets. The observation by scanning electron microscopy on the microstructure indicated that the fracture mechanism of the as-obtained cermets was mainly inter-granular of TiCN grains.

Synthesis and characterization of dense and fine nickel ferrite ceramics through two-step sintering

Two-step sintering (TSS) has been employed in the current study to suppress the accelerated grain growth of NiFe2O4 nanopowder compacts in the final sintering stage. Experiments are conducted to determine the appropriate temperatures for each step. The temperature range from 1200°C to 1300°C is effective for the first-step sintering (T1) due to its highest densification rate. The second-step sintering temperature (T2) should be within the kinetic window, where grain boundary diffusion is maintained but grain boundary migration is suppressed. The grain sizes of high density (≥98% theoretical density) NiFe2O4 compacts produced by TSS are smaller than 700nm, while that of those formed by CS are over 2.5μm. The evidence indicates that the saturation magnetization of nearly full NiFe2O4 ceramics is independent of grain size and likewise high, with the corresponding values of approximately 54emu/g. The Vickers hardness and fracture toughness both increase with the decrease of grain size and porosity.

Fabrication of exfoliated graphite nanoplatelets-reinforced aluminum composites and evaluating their mechanical properties and corrosion behavior

Aluminum composites with different amounts of exfoliated graphite nanoplatelets particles were fabricated by powder metallurgy method. The mixture powders were consolidated at 520 MPa for 5 min and followed by pressureless sintering at 600 °C for 6 h. The mechanical properties of composites were evaluated by compression and hardness tests. The corrosion behavior in 3.5% NaCl solution was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements. The mechanical testing results showed that the maximum strength and Vickers hardness increase as a function of exfoliated graphite nanoplatelets content. Corrosion data indicated that the presence of exfoliated graphite nanoplatelets and the increase of its concentration raise the corrosion rate and reduce the polarization resistance of Al. SEM/EDX investigations revealed that the presence of exfoliated graphite nanoplatelets activates the corrosion of Al due to the occurrence of galvanic corrosion. SEM/EDX investigations confirmed the electrochemical measurements showing that the increase of exfoliated graphite nanoplatelets content increases the corrosion of Al.

Effect of Metal Oxides Addition on the Superconducting Properties of YBaCuO

The superconducting properties of YBCO superconductor with ZrO2 addition prepared by different contents were prepared by a unique method so called thermal pyrolysis process to study the effect of the zirconium oxide on the electromagnetic properties and superconducting mechanism of the superconductor. The critical temperature of YBCO superconductor was not predominately dependent upon the zirconium oxide. The maximum magnetism was observed by adding 2% zirconium oxide. The addition of zirconium oxide forming a pinning center of magnetic flux due to ZrO2 phase which was related to the change of electromagnetic properties of the YBCO superconductor. The result indicates that magnetization is proportional to the number of magnetic flux lines passing through the sample. The added ZrO2 appear to contribute the increasing Vickers hardness.

Multiple strengthening mechanisms of cold-sprayed cBNp/NiCrAl composite coating

The cBNp/NiCrAl composite coating with 40 vol.% cBN was deposited by cold spray using a mechanically alloyed composite powder. The microstructure of the as-sprayed coating was characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that cBN particles in the size ranges of both nanometers and submicrometers were uniformly dispersed in NiCrAl alloy matrix. The XRD and TEM results revealed that the phase and nanocrystalline structures of the NiCrAl matrix were completely retained from the powder to coating during cold spraying. The hardness test results show that the dense composite coating exhibited an increased Vickers hardness of 1175 Hv compared with 280 Hv of the annealed NiCrAl matrix phase. The high hardness of the composite coating is attributed to the strengthening effects of particle dispersion, work hardening and crystal refinement. The contributions of the individual strengthening mechanisms, including particles dispersion, work hardening and crystal refinement, to hardness were theoretically estimated. The estimated hardness of the composite coating agreed well with the tested value. The work hardening strengthening is the most significant mechanism followed by crystal refinement effect and dispersion strengthening.

Elastic properties and Vickers hardness of optically transparent glass–ceramics with fresnoite Ba 2TiSi 2O 8 nanocrystals

Optically transparent glass–ceramics (40BaO–20TiO 2–40SiO 2 (mol%)) consisting of nonlinear optical fresnoite Ba 2TiSi 2O 8 (BTS) nanocrystals (diameter: 100–200 nm) are fabricated, and their elastic properties and deformation behavior are examined as a function of the volume fraction ( f) of BTS nanocrystals using cube resonance and Vickers indentation techniques. The elastic properties such as Young's modulus ( E) increases linearly with increasing the volume fraction of nanocrystals, e.g., E = 84 GPa for f = 0% (glass) to E = 107 GPa for f = 54.5%. The Vickers hardness ( H v) and indentation fracture toughness ( K c) increase from 5.0 to 6.0 GPa for H v and 0.48 to 1.05 MPa m −1/2 for K c with increasing the volume fraction (from f = 0% to f = 54.5%), but they do not change linearly against the volume fraction of nanocrystals. It is suggested that BTS nanocrystals themselves induce a high resistance against deformation during Vickers indenter loadings.

Microstructure and mechanical property evolution of 99.1% recycled aluminum during equal Channel Angular Extrusion

A 99.1% recycled aluminum was severely deformed by equal channel angular extrusion (ECAE) using two different processing routes BC and C, to study the evolution of the microstructure and associated changes of mechanical properties.The analysis of microstructure before and after ECAE for three orthogonal planes X, Y and Z, showed a significant variation of grain shape, which depend on the plane type and processing route. The analysis of X-ray diffraction peaks showed a significant broadening after ECAE. This is due to grain refinement and lattice distortions. A shift of the peaks is also observed, which was related to residual compressive stress caused by the ECAE. An important decrease of the lattice parameter was observed after the first passage, then it increases for subsequent numbers of passages; the increase is however, more important in the specimens extruded via route C. This is due to a high density of dislocations introduced by deformation via this route what generates a dynamic recovery during ECAE process. Changes in mechanical behavior are observed after ECAE. The yield stress and Vickers hardness increase with the number of passes. This is due to strain hardening.

A new reverse analysis to determine the constitutive response of plastically graded case hardened bearing steels

A new reverse analysis is presented that determines the plastic response of both nongraded and plastically graded materials (PGMs) without the need for traditional tension or compression tests. The method utilizes the concepts of expanding cavity model for strain hardening materials, Tabor’s rule of converting Vickers hardness to flow stress, representative plastic strain induced by indentation, and finite element modeling of the macro indentation process. A unique flow curve is determined when the experimentally measured increase in micro Vickers hardness matches that predicted by the proposed method within the plastic zone of a macro Vickers indent. The method is validated for a nongraded stainless steel first and then extended to determine the gradient in flow curves of plastically graded, case-hardened M50 NiL material, a widely used bearing steel. Such knowledge of the plastic response of the case hardened region will help optimize the design of case hardened bearings with longer rolling contact fatigue life and higher thrust load capabilities.

Phase Constitution and Mechanical Properties of Carbides in the Ta–C System

Carbides in the Ta–C system were prepared by hot‐pressing mixed powders of TaC and Ta in C/Ta atomic ratios of 1.0, 0.9, 0.8, 0.7, and 0.6 at 1800°C for 2 h. The compositions, 1.0, 0.9, and 0.8, produced single face‐centered‐cubic (fcc) TaCy phase with C/Ta ratios essentially the same as the starting compositions and densities exceeding 96.5% of theoretical. Grain size decreased with increasing carbon deficiency with a corresponding increase in Vickers hardness from 13.5 to 20 GPa. The flexural strength, however, decreased from 650 to 500 MPa due to a decrease in fracture toughness from 5.3 to 3.8 MPa√m. The compositions 0.7 and 0.6 produced two carbide phases, fcc TaCy and rhombohedral ζ‐Ta4C3−x phase in the 0.7 composition and ζ‐Ta4C3−x and hexagonal‐close‐packed (hcp) α‐Ta2C phase in the 0.6 composition. Fracture toughness measured by single‐edge‐precracked‐beam technique was exceptionally high (12.7±0.7 MPa√m) for the 0.6 composition with a high weight percent of the ζ‐Ta4C3−x phase (∼83 wt%). The fracture surface was highly faceted with multiple cleavage crack planes and steps.

Effect of Nanodiamond Particles Incorporation in Hydroxyapatite Coatings

Nanodiamond particles (ND, 4-6 nm in size) were added to a simulated body fluid (SBF) and electrodeposition (ED) at biological conditions (370C, pH 7.4) was performed on Ti surfaces. The novelty in this work was the addition of the ND particles to the SBF solution used as the electrolyte for the ED of biomimetic HA. The results from Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), coupled with energy dispersive X-ray (EDX) spectroscopy revealed that the Ti surface was covered by white, dense and homogeneous HA layer. X-ray photoelectron spectra (XPS) confirmed the formation of calcium phosphate, calcium carbonate, calcium oxide and hydrated surface layer. The ND particles incorporation yielded increased Vickers hardness of the HA. No cracks were observed in the SEM images of the HA-ND layer, which testifies for its ductility and good residual stress.