Hardness Increment Research Articles

Structural Changes in Human Teeth after Heating up to 1200°C in Argon Atmosphere

The phase transformation of hydroxyapatite (HAP, Ca10(PO4)6(OH)2) to the beta tricalcium phosphate phase (β-TCP, β-Ca3(PO4)2) at 1100°C is well known. However, in the case of human tooth, the HAP phase transformation is still an open area. For example, the CaO phase has sometimes been reported in the set of phases that make up the teeth. In this study, physical changes of human teeth when subjected to heat treatment in inert atmosphere (argon) were studied. The results were compared with those obtained in air atmosphere, from room temperature (25°C) up to 1200°C. Morphological changes were analyzed by light and scanning electron microscopy (SEM). The HAP to β-TCP phase transformation was followed in powder samples by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Heating of teeth results in the removal of organic material and structural water before the HAP to β-TCP phase transformation, the increment in hardness and the induced crystal growth. The percentage of the phases, crystal growth and lattice parameter variations as a function of temperature was quantified by Rietveld analysis. The black color was observed in dentin heated under argon atmosphere. Differences in expansivity produce fractures in dentin at 300°C in argon and at 400°C in air. In dentin, the coexistence of the HAP and β-TCP phases was observed after 800°C in argon and after 600°C in air; in enamel it was observed at 600°C in argon compared with 400°C in air. In general, the role played by the argon atmosphere during the thermal treatment of the teeth is to retard the processes observed in air.

Randomization of Ferrite/austenite Orientation Relationship and Resultant Hardness Increment by Nitrogen Addition in Vanadium-microalloyed Low Carbon Steels Strengthened by Interphase Precipitation

Randomization of Ferrite/austenite Orientation Relationship and Resultant Hardness Increment by Nitrogen Addition in Vanadium-microalloyed Low Carbon Steels Strengthened by Interphase Precipitation

An Experimental Evaluation of Electron Beam Welded Thixoformed 7075 Aluminum Alloy Plate Material

Two plates of thixoformed 7075 aluminum alloy were joined using Electron Beam Welding (EBW). A post-welding-heat treatment (PWHT) was performed within the semi-solid temperature range of this alloy at three temperatures, 610, 617 and 628 °C, for 3 min. The microstructural evolution and mechanical properties of EB welded plates, as well as the heat-treated specimens, were investigated in the Base Metal (BM), Heat Affected Zone (HAZ), and Fusion Zone (FZ), using optical microscopy, Scanning Electron Microscopy (SEM), EDX (Energy Dispersive X-ray Analysis), and Vickers hardness test. Results indicated that after EBW, the grain size substantially decreased from 67 µm in both BM and HAZ to 7 µm in the FZ, and a hardness increment was observed in the FZ as compared to the BM and HAZ. Furthermore, the PWHT led to grain coarsening throughout the material, along with a further increase in hardness in the FZ.

Microstructural evolution and hardening of GH3535 alloy under energetic Xe ion irradiation at room temperature and 650 °C

The GH3535 alloy was irradiated with 7 MeV Xe26+ ions to a dose of 10 dpa at room temperature (RT) and 650 °C, and subsequently examined using Transmission Electron Microscopy (TEM) and nanoindentation. High numbers of nano-sized black dots, identified as dislocation loops were observed in both irradiated samples. The dislocation loops detected at the high temperature irradiated sample (size/number density: 9.5 nm/1.9 × 1021 m−3) were found to be larger in size but less in amount as compared to that of the case of RT irradiation (6.9 nm/18.7 × 1021 m−3). In addition, the large-sized Mo-Cr rich precipitates (16.4 nm/3.7 × 1021 m−3) were observed in the sample irradiated at 650 °C. Moreover, the Xe bubbles, with smaller size (2.9 nm) but higher number density (77.8 × 1021 m−3) among the irradiated induced defects, were also detected in the case of high temperature irradiated sample via the diffusion and aggregation of Xe atoms. Nanoindentaion measurements showed a hardening phenomenon for the irradiated sample, and the hardness increment is higher in the case of high temperature irradiated sample. Dispersed barrier-hardening (DBH) model was applied to predict the hardening produced from the irradiation induced defects. The yield strength increment calculated based on TEM observations and the nanohardness increment measured using nanoindentation are in excellent agreement.

Different aging behaviors at surface layer and central region of a die-casting A380 alloy during heat treatment

Microstructural and hardness evolutions of a vacuum-assistant die-cast A380 (Al-8.67wt.%Si-3.27wt.%Cu) alloy during heat treatment were investigated. Isothermal DSC test at 200 °C revealed that the precipitation reaction in the surface layer was faster than that in the central region. This corresponded with the hardness evolution that the surface layer hardened faster. The hardness increment in the surface layer was higher than that in the central region. Further experimental evidences indicated that the differences were due to the different amounts of heterogeneous nucleation sites for precipitation in the two parts. The influence of the characteristic as-cast microstructure on the artificial aging process is analyzed and discussed in detail.

Effect of re-vibration on the compressive strength and surface hardness of concrete

This paper reports the results of experimental investigations carried out on the effect of re-vibration on the compressive strength and surface hardness of normal weight concrete. Five different concrete mixes with varying water cement ratio ranging from 0.35 to 0.7 were prepared. The compacted concrete was subjected to re-vibration during the initial setting time period. During the initial setting time, the compacted concrete was re-vibrated at the time of 30 minutes up to 150 minutes of an interval of 30 minutes. The compressive strength and surface hardness of re-vibrated concrete were tested at the age of 35 days. The experimental results showed a significant increment of compressive strength and surface hardness in all re-vibrated concrete. In general, the maximum gain in compressive strength and surface hardness was when the re-vibration occurred at the initial setting time of 2 hours. The average increasing of the compressive strength of concrete by re-vibration is ranging from 3.5% to 21.8%.

Characteristic of Mechanical and Morphological Properties of Heat Rolled Laterite Steel with Variety of Size Reduction

Indonesia has the most laterite ore reserves in the world. The element originated from the laterite ore is one of the materials in the steel industry. Despite its plentiful of reserves, laterite steel ore has not been used to its maximum potential. This research aims to overview reduction effect on mechanical properties of laterite steel as a result of heated rolling process with various reduction. The reduction variety used in this research were 30%, 40%, 50%, and 60%. Also, the temperature was 980oC. As a result of this research, the increment of reduction followed by the increment of hardness and firmness level of laterite steel. It is proofed by hardness and tensile test. Firmness of the material increased as the reduction increases. The most optimized mechanical properties obtained by 50% reduction, the hardness number was 280.03 HB, tensile strength 620 MPa, elongation 32%, yield 493.33 MPa. Micro structures which formed in this process are ferrite and pearlite phase with very fine pellet size and even pearlite distribution. Fracture types are brittle and ductile fracture with very fine pellet size.

Theoretical hardness analysis and experimental verification for composite ceramic tool materials

Abstract High hardness is the most important requirement for the property of cutting tool materials. Based on the assumption that the solid hardness is proportional to the resistance of the chemical bonds within indentation area, the theoretical hardness prediction model of the multiphase composite ceramic tool material was established combining with the hardness theory of multicomponent systems. In order to verify the applicability and accuracy of the theoretical model, validation experiment has been designed from the point of different dimensions and scales of raw materials, including TiC micron particles, SiC whiskers, TiC nanoparticles and SiC nanoparticles. The results showed that the experimental hardness of the materials with whiskers and micron particles addition were in good agreement with theoretical value with the error margin of −0.15 to +0.97%. By comparison, the experimental hardness of the material with nanoparticles addition was about +1.97–3.21% higher than theoretical counterpart. By analyzing experimental results and SEM micrographs, it was concluded that the experimental hardness of composite ceramic materials was scarcely influenced by the grain size of the matrix. And it was inferred that the intragranular and intergranular microstructure in nanocomposite ceramic materials might be the main factor that caused additional increment in experimental hardness.

The mechanism for the different effects of texture on yield strength and hardness of Mg alloys

A study regarding the effect of texture on tensile yield strength and hardness of an extruded Mg-15Gd-0.5Zr rod was performed, with a great emphasis laid on the relevant mechanisms. A 7% pre-tension along the extrusion direction (ED) in the solid solution condition was used to transform the texture from a broad distribution of basal poles with a peak approximately 45° with respect to the ED into a texture with basal poles largely perpendicular to the ED. This texture variation enhances the yield strength of peak aged sample by approximately 103 MPa, while hardly increases the peak hardness. The analysis about the ratio of the critical resolved shear stress (CRSS) to Schmid factor shows that this texture variation results in a larger fraction of grains favoring prismatic slip with a higher activation stress under tension along the ED. In contrast, the complex stress state during hardness test initiates multiple deformation modes, which renders the value of hardness insensitive to the texture variation. This different dependence of deformation modes on texture mainly accounts for the different increments in hardness and tensile yield strength.

Microstructural evolutions of low carbon Nb/Mo-containing bainitic steels during high-temperature tempering

In this work, the effects of tempering at three high temperatures (660, 680 and 700°C) for different holding times (5min to 16h) on the secondary hardening in Nb-bearing and Nb-Mo-bearing bainitic steel strips were investigated. It was found that with 0.3wt% Mo addition in Nb-Mo-bearing bainitic steel strip, the peak hardening occurred with a significant increment in hardness (up to 40HV) after approximately 10min of tempering at all temperatures (660, 680 and 700°C). In contrast, for the Nb-bearing steel strip, the corresponding increment in hardness was small (about 15HV). The microstructural evolutions of Nb-bearing and Nb-Mo-bearing steel strips during tempering at 700°C were investigated with scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy. It was found that during tempering, bainitic ferrite platelets in Nb-Mo-bearing steel strips remained much more stable and had a higher dislocation density than those in Nb-bearing steel strips. High-resolution transmission electron microscopy provided strong evidence that the Mo addition had significant effects on suppressing the annihilation rate of dislocations and retarding the coarsening rate of nanometer-sized carbides at higher temperatures, leading to a remarkable resistance to softening after secondary hardening.

Effect of quench-induced precipitation on microstructure and mechanical properties of 7085 aluminum alloy

The effects of quench-induced precipitation on microstructure and mechanical properties of 7085 aluminum alloy were investigated by means of hardness test, tensile test, optical microscopy, conventional and high resolution transmission electron microscopy and scanning transmission electron microscopy. Apart from quench-induced η phase, a plate-like Y phase appears with the decrease of cooling rate from 240K/s to 3.2K/s after solution heat treatment. η phase exists primarily in recrystallized grains and has little strengthening effect. Y phase mainly exists in subgrains with a high density of dislocations, it has a high aspect ratio and therefore gives rise to higher hardness and strength for the slowly-cooled specimens after natural aging. After further artificial aging, the aspect ratio of the Y phase decreases and its strengthening effect becomes smaller; moreover, the presence of η and Y phases reduces the quantity of metastable η′ strengthening precipitates and therefore leads to a smaller increment in hardness and strength for the slowly-cooled specimens; consequently, the rapidly-cooled specimens have higher hardness and strength than the slowly-cooled ones.

Structure Stability and Mechanical Property of Y<sub>2</sub>O<sub>3</sub> Thin Films Deposited by Reactive Magnetron Sputtering

Y2O3 has a great application potential at reaction barrier coating of high-temperature composites due to its high thermodynamic stability and high melting point, and the phase structure stability at high temperature and structure dependent mechanical property are key parameters for this application. Y2O3 thin films were deposited on silicon (100) wafers by DC magnetron sputtering with various oxygen partial pressure and substrate bias, and then vacuum annealing at 1000°C was performed to investigate the phase structure stability. The microstructure, stress and hardness of as-deposited and annealed Y2O3 thin films were explored by X-ray diffraction, transmission electron microscope, and nanoindenter. The result showed that as-60 bias voltage was applied to substrate, cubic-c phase formed regardless of variation of oxygen partial pressure, and the cubic-c phase remains stability and crystallinity became better after annealing at 1000 °C.In addition, the hardness and modulus also just had minor changes as a function of oxygen partial pressure. As oxygen partial pressure was kept at 0.043 Pa, phase transition from cubic-c to monoclinic-b phase took place with increasing substrate bias, accompanying by the increment of hardness and modulus, and 1000 °Chigh-temperature annealing resulted in that as-deposited monoclinic-b phase transforms to cubic-c phase.

Effect of Yttrium Addition on Microstructure and Hardness of Cast EV31A Magnesium Alloy

The effect of the rare earth (RE) element Y on the microstructure and hardness of (Mg–0.5Zn–0.5Zr–2.8Nd –1.5Gd) wt% Mg alloy investigated. 1 wt. % Y was added and compared with the base alloy. The microstructure results show the refinement of the grain by the addition of Y and the grains became smaller about 31.8 % and the volume fraction was increases 11.1% %, which led to the increment of hardness from 48.33 HV (as-cast EV31A) to 53.71 HV (as-cast EV31A +1 Y). Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) results showed that the base alloy mainly contained α-Mg matrix and Mg-(Nd, Gd) as a second phase crystallized along the grain boundaries and addition of (Y) yttrium resulted in the formation of the new phase, Mg-Zn-Y-phase was found as a new ternary phase, where Y combined with the original second phase.

Magnetic non-destructive evaluation of hardening of cold rolled reactor pressure vessel steel

Non-destructive test (NDT) of reactor pressure vessel (RPV) steel is urgently required due to the life extension program of nuclear power plant. Here magnetic NDT of cold rolled RPV steel is studied. The strength, hardness and coercivity increase with the increasing deformation, and a good linear correlation between the increment of coercivity, hardness and yield strength is found, which may be helpful to develop magnetic NDT of degradation of RPV steel. It is also found that besides dislocation density, the distribution of dislocations may affect coercivity as well.

Enhancement of high-temperature strength of Ni-based films by addition of nano-multilayers and incorporation of W

Nanocrystalline Ni thin film exhibits poor thermo-mechanical properties due to its unstable microstructure at elevated temperature. Here, the paper endows a new approach to solve above issue via addition of nano-multilayers and incorporation of W for nanocrystalline Ni-based films, to provide novel Ni/Ni3Al-W nano-composite multilayered structure with high hardness and good thermal stability. The thermal evolution of microstructure and mechanical properties was investigated to reveal nanocrystalline stability and strengthening mechanisms for co-sputtered Ni/Ni3Al-W multilayers with varied W concentrations and annealing temperature. The lamellar structure and nonequilibrium phases are well maintained in 600 °C annealed multilayers, while nano-grains are further refined with increasing W addition. Annealing at 800 °C results in the appearance of elemental redistribution and phase separation in multilayers, leading to the layered structure dissolved and globular W-related particles precipitated. Annealing hardening is founded in most of annealed Ni/Ni3Al-W multilayers. Based upon microstructure observation, grain boundary relaxation and W-related phase precipitation are mainly responsible for the hardness enhancement of multilayers at 600 °C and 800 °C, respectively. Notably, the best hardness is achieved at the value of 15.6 GPa for 800 °C annealed 12.5 at% W doped Ni/Ni3Al-W multilayer, which shows the residual layer interfaces with larger precipitations in microstructure. This hardness increment for annealed Ni-based multilayers can be attributed that the high degree of strengthening is provided by a combination of hardening precipitation and survived lamellar structure via the Orowan mechanisms, offering a feasible insight to develop nano-metallic coatings for further increasing thermo-mechanical properties.

Influence of Fe addition on annealing behaviors of a phosphorus containing brass

Abstract Effect of Fe addition on annealing behaviors of cold rolled Cu-30Zn-0.1P brass was investigated in terms of hardness behavior, microstructure development and microtexture evolution. A maximum increase of about 20% in hardness was observed with the addition of Fe before and after annealing. Fe2P particles were found dispersed in Cu-30Zn-0.1P-0.5Fe alloy before and after annealing and they showed great pinning effects and resulted in inhibited recrystallization, grains refinement and thermal stability enhancement. It is also indicated by kernel average misorientation (KAM) maps that a higher dislocation density and energy were stored in the sample with the addition of Fe. As a result, the second phase strengthening and grain boundary strengthening were found to be responsible for the hardness increment for the alloy with the Fe addition. Besides, a higher fraction of Brass texture was found at the beginning of annealing in Cu-30Zn-0.1P-0.5Fe alloy. The results also showed that Brass texture then translate into Brass-R and (55;30;0) textures during annealing, resulting in high fractions of Brass-R and (55;30;0) textures in Cu-30Zn-0.1P alloy with the addition of Fe after annealing.

Concurrent strengthening of ultrafine-grained age-hardenable Al-Mg alloy by means of high-pressure torsion and spinodal decomposition

In this study, the age-hardening behavior and precipitate microstructures of severely-deformed and then artificially-aged Al-13.4 wt%Mg alloy has been investigated by Vickers hardness test, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and atom probe tomography (APT). The combined processing of high-pressure torsion (HPT) and aging treatment at a temperature below spinodal lines results in a higher attained hardness of ∼HV296 with an age-hardenability (i.e ΔHV31 ± 2) comparable to that of the undeformed specimen without HPT (i.e. ΔHV33 ± 2). The corresponding TEM microstructures consist of modulated structures associated with spinodal decomposition, and quantitative estimation of the amplitude, as well as the wavelength, of Mg fluctuations was successfully conducted by APT for the first time for this alloy system. The linear relationship between the increment of Vickers hardness and the estimated amplitude of the undeformed specimen supposed that Kato's spinodal-hardening mechanism works even in the HPTed specimen with a high number density of grain boundaries. Therefore, our proposed strategy; i.e. taking advantage of spinodal decomposition, is regarded as a convincing approach to achieving concurrent strengthening by ultrafine-grained and precipitation hardenings for the alloys that decompose via spinodal decomposition.

Helium irradiation induced hardening in MNHS steels

A recently developed reduced activation martensitic MNHS steel was irradiated with 200keV helium (He) ions to a fluence of 1.0×1020ions/m2 at 300°C and 1.0×1021ions/m2 at 300°C and 450°C. After irradiation, transmission electron microscopy (TEM) and nano-indentation measurements were used to investigate the hardness change and defects induced by He irradiation. Two kinds of defects including He bubbles and dislocation loops are observed by TEM. Irradiation induces hardening of MNHS steels and peak hardness values occur in all irradiated samples. Hardness increments induced by He bubbles and dislocation loops are predicted and fitted with the experimental peak hardness increment, based on the dispersed barrier-hardening (DBH) model and the size and number density of the two defects. A good agreement is got between the predicted and experimental hardness increment and the obstacle strength factor of He bubbles is a little stronger than the obstacle strength of dislocation loops. Other possible contributions to irradiation induced hardening are also discussed.

Nanoprecipitates and Their Strengthening Behavior in Al-Mg-Si Alloy During the Aging Process

The different nanoprecipitates formed in a 6061 aluminum alloy during aging at 453 K (180 °C), with or without 168 hours of pre-natural aging (NA), and the age-hardening response of the alloy were investigated by atom probe tomography (APT) and hardness testing. A hardness plateau developed between 2 and 8 hours in both the artificial aging (AA) and artificial aging with pre-natural aging (NAAA) samples. The hardness of NAAA samples was lower than that of AA samples when artificially aged for the same time. A 168-hour NA led to the formation of solute atom clusters in the matrix. The NA accelerated the precipitation kinetics of the following AA. The solute atom clusters gave the highest hardness increment per unit volume fraction. The β″ precipitates were dominant in the samples at the hardness plateau. The average normalized Mg:Si ratios of the solute atom clusters and GP zones were near 1. The average Mg:Si ratio of β″ precipitates increased from 1.3 to 1.5 upon aging for 2 hours. The microstructural evolution of samples with or without NA and its influence on the strengthening effects are discussed based on the experimental results.

Improvement of interfacial bonding and mechanical properties of Cu-Al2O3 composite by Cr-nanoparticle-induced interfacial modification

The strength and ductility of copper matrix composites are usually limited due to the interfacial debonding between the reinforcement and matrix. Interfacial debonding is mainly caused by the interfacial stress induced by the differences in elastic modulus and thermal expansion coefficient (CTE) between the reinforcement and matrix. Cu-Cr-Al2O3 composite with Cr nanoparticles precipitated at the interface of Cu and Al2O3 was fabricated. It was found that the hardness of Cu-1 wt% Cr-4 wt% Al2O3 composite is higher than that of Cu-5 wt% Al2O3 composite over the temperature range from 25 °C to 1000 °C. Notably, the hardness increment reached 133% at 1000 °C. In addition, the compressibility increased 36% for Cu-1 wt% Cr-4 wt% Al2O3 composite compared with Cu-5 wt% Al2O3. The finite element simulation results confirmed that the interfacial residual stress in Cu-Al2O3 composite decreased by adding Cr, resulting in the improvement in mechanical properties.