Variation Of Hardness Values Research Articles

Influence of Aging Condition on the Characteristics of Continuous Precipitates of AZ80 Magnesium Alloy

The aim of this work is to evaluate the characteristics of continuous precipitates (CP) developed within the grain and grain boundary precipitates through statistical analysis of the number density and size (i.e., length and width) at varying aging conditions of AZ80 Mg alloy. Scanning electron microscopy illustrates the characteristics and features of precipitates, distinctively. The results reveal an increment of number density, whereas the reduction in the size of precipitates with decrease in the aging temperature for the varying aging times. The variation in hardness values at different aging conditions has been ascribed to this.

Thermal post-treatment and material characterization of laser powder bed fusion additively manufactured Ti-6Al-4V

Laser powder bed fusion of Ti-6Al-4V (PBF-LB/Ti-6Al-4V) alloy results in the formation of non-equilibrium microstructures due to very high cooling rates, causing them to be unfit for direct applications; therefore, post-heat-treatment operations are required. This paper investigates the effects of different heat treatment operations on the microstructure, hardness and phase composition of as-built PBF-LB/Ti-6Al-4V samples. Six sets of heat-treatment operations have been designed in which samples have been first subjected to either above or below the beta (β) transus zone of 980 °C, then subjected to air cooling or water quenching followed by ageing at 510 °C. The novelty of this article is performing double quenching on as-built Ti-6Al-4V parts. Optical microscopy, Vickers microhardness testing, and XRD analysis have been performed on heat-treated samples for material characterization. Microstructural studies have revealed that depending upon the cooling medium and subjected temperature during heat treatment, the extent of dissolution of martensitic (α′) needle-like phases present in as-built samples into α-β phase varies, resulting in variation of hardness values. XRD analysis confirmed the presence of β-phase along with the α-phase in the matrix in air-cooled heat-treated samples. Maximum hardness was obtained in the case when the sample was solutionized at 1050 °C, followed by water quenching and ageing due to the formation of intermetallic precipitates.

Irradiation hardening of WK-based PFM exposed to 14 MeV protons

W-based alloys are perceived as one of the most promising plasma-facing materials (PFMs). During the service of fusion reactors, W-based PFMs will be exposed to 14 MeV fusion neutrons, causing significant displacement damage and transmutation, consequently, the irradiation-induced defects will seriously deteriorate its service performance. The irradiation effect is always a critical issue in fusion reactors and concerns the performance and reliability of W-based PFMs. In this work, WK-0.05Ti alloy was irradiated under 14MeV protons, and notable irradiation hardening was observed using microhardness and nanoindentation characterization. Then, the mechanism of W-Re precipitate formation induced by K-bubble was revealed using transmission electron microscopy. Finally, the variation of hardness values at different irradiation depths was explained based on theoretical calculations and experimental data. The present work elucidates the effect of K-bubbles on the evolution of irradiation defects in WK-based PFMs during irradiation and reveals the underlying mechanisms contributing to the irradiation hardening at different depths. Moreover, it is expected to provide additional insights into the R&D of robust plasma facing components based on WK-based materials.

Numerical prediction and experimental investigation of aerospace-grade dissimilar aluminium alloy by friction stir welding

In a global scenario, the high strength lightweight dissimilar aluminium alloy 7075 and 2014 joining delivers a new opportunity to reduce weight in aerospace vehicles. The dissimilar aluminium alloy joining faces a technical challenge during fusion welding, due to the difference in thermo-mechanical properties. In this present work, the temperature distribution and grain size effects on dissimilar friction stir welded aerospace-grade aluminium alloy 7075 and 2014 was studied numerically and verified experimentally. The 3D integrated multiphysics model, coupled with a moving coordinate system, was simulated with the frictional effects of tool shoulder, pin to the workpiece and stick-slip mechanism. The dissimilar numerical model predicts the temperature and grain size changes across the weld zone. To verify the numerical model, two experiments T9 and T11 welded with a specimen size of 200 × 100 × 3 mm by the FSW-3T-CNC machine. The high-temperature computerized compact DAQ® 9212 and Lab VIEW© software interfaced with K-type thermocouple to measure the temperature. The measured temperature and grain size across the weld are in good agreement with simulated values. Optical microstructure and SEM micrographs illustrate T9 and T11 dissimilar joint with a clear onion pattern in the stir zone, which ensures the proper mixing of material with dynamically recrystallized fine equiaxed grains. The variation in hardness value observed from stir zone to base metal region and the average hardness in stir zone as 139 HV and 133 HV for T9 and T11 specimen, respectively.

Synthesis, microstructure and hardness of Al 7075/B4C/Fly-ash composite using stir casting method

Stir-casting is the appropriate and economical technique for HAMCs synthesis as it produces uniformly reinforcement distributed composite retaining finer grains. In the present work, Al 7075/x%wt.B4C/2%wt. fly-ash HAMCs were fabricated via stir casting route, where x is weight percentage of boron carbide (x = 2, 4, 6 and 8 wt%). Incorporation and distribution of reinforcement particles in HAMCs were analysed using scanning electron microscope (SEM) and optical micrographs. Also, Micro-hardness tests were conducted at seven locals points in hardness specimen to see the variation of hardness values. The coefficient of variation was calculated to ensure uniform hardness values, which further confirm the uniform distribution of reinforcements in the prepared composite. Moreover, mathematical modelling was done to obtain the empirical relation of micro-hardness of composite with respect to fly-ash and boron carbide content, which shows the correlation between the micro-hardness and reinforcements contents in the HAMC. The synthesized HAMCs may be suitable in automobile and aerospace application where low cost, lightweight, high temperature resistant and high wear resistant composite are required.

Bedrock hardness values and morphological zonation of a shore platform in South Africa

Shore platforms found along rock coasts worldwide are often interpreted as wave abrasion acting on uniform bedrock surfaces. Whilst this viewpoint may apply at the macroscale, there are complex feedbacks among bedrock properties (rock type, mineralogy, rock structures), weathering and erosion processes and rates, and microtopography at the meso- to microscale. In turn, these influence wave runup, backwash processes, and the extent of wave-splash and physical, chemical, and biological weathering processes that result. This study investigates the relationships among bedrock hardness properties, microtopography, and shore platform denudation processes from a site on the Indian Ocean-facing coast of South Africa. Three shore-normal transects (45–57 m in length) were surveyed across the sandstone platform using a differential global positioning system (GPS). These data were integrated with rock surface hardness measurements along the transects taken using a Proceq Equotip instrument. Results show that platform morphology and hardness values vary considerably, corresponding to the most dominant denudation processes found at different positions in the tidal frame. The lowest hardness values (most extensive rock weathering) are found on the landward third of the platform but away from the land margin. The highest and greatest variability of hardness values are found on bedrock highs immediately above the highest astronomical tide level, in the lower third of the profile. This position suggests a dominant role of wave-splash and wetting/drying. Variations in hardness values and microtopography through the transects were used to develop an evolutionary model linking rock hardness values to specific weathering and erosion processes of the rocky shore platform.

Microstructural characterization of cellular AlSi10Mg alloy fabricated by selective laser melting

In order to understand the microstructural characteristics of cellular (porous) AlSi10Mg alloy fabricated via selective laser melting (SLM), we designed SLM-fabricated AlSi10Mg alloy samples with various box-shaped structures containing interior X-shaped shelves as a representative model of porous aluminum. All fabricated samples exhibited characteristic microstructural morphologies comprising melt pools with columnar α-Al phases surrounded by fine eutectic Si particles. Several columnar α-Al phases exhibited 〈001〉 orientations along the elongation direction, resulting in a {001} texture. In the shelf wall regions of fabricated samples, the elongation direction of the columnar α-Al phases varied depending on the incline angle between the inclined wall plane and the laser irradiation direction (θ), reducing the formation of {001} texture in samples with high incline angles. In the regions wherein the X-shaped shelves intersect, the microstructure varied in different sections: the α-Al phases observed in the lower portion appeared coarser and more equiaxed compared with those in the upper portion. The microstructural difference was more significant in samples with higher incline angles, which contributes to the observed variations in hardness values. Based on the results obtained, we discuss the dominant factor leading to the observed inhomogeneity of the microstructure of cellular AlSi10Mg alloy fabricated via SLM.

Effects of long term thermal exposure on microstructure and mechanical property evolution of a new wrought Ni–Fe based superalloy

A new wrought Ni-Fe based superalloy was designed for advanced ultra-supercritical boiler tubes beyond 700°C. In this study, the recrystallization treatment of the alloy following cold rolling and the microstructural evolution following 500h, 1000h and 3000h at 750°C were studied. The optimization of heat treatment was performed by thermodynamic calculation and the optimum combination was determined, i.e. annealing treatment at 1150°C for 45min, followed by a two-step aging treatment, at 810°C for 1h and at 770°C for 16h. Following this process, the M(C,N) precipitates and Cr-rich M23C6 carbides were formed at grain boundaries. Following 3000h thermal exposure at 750°C, the coarsening rate of the spherical γʹ precipitates was consistent with the LSW model and similar to that of the IN 740H alloy, while the variation in hardness values was relatively low, as the exposure time was increased. The α-Cr phase was observed after 1000h at 750°C and during the long term thermal exposure the coarsening of α-Cr phase occurred. The formation of α-Cr phase enhanced the intragranular yield strength and hardness values at room temperature and the stability of the mechanical properties was partially improved.

Precipitation Hardening and Statistical Modeling of the Aging Parameters and Alloy Compositions in Al-Cu-Mg-Ag Alloys

The addition of Ag to Al-Cu-Mg systems has been proposed to replace the existing high-strength 2xxx and 7xxx Al alloys. The aged Al-Cu-Mg-Ag alloys exhibited promising properties, due to special type of precipitates named Ω, which cooperate with other precipitates to enhance the mechanical properties significantly. In the present investigation, the effect of changing percentages of alloying elements, aging time, and aging temperature on the hardness values was studied based on a factorial design. According to this design of experiments (DOE)—23 factorial design, eight alloys were cast and hot rolled, where (Cu, Mg, and Ag) were added to aluminum with two different levels for each alloying element. These alloys were aged at different temperatures (160, 190, and 220 °C) over a wide range of time intervals from 10 min. to 64 h. The resulting hardness data were used as an input for Minitab software to model and relate the process variables with hardness through a regression analysis. Modifying the alloying elements’ weight percentages to the high level enhanced the hardness of the alloy with about 40% as compared to the alloy containing the low level of all alloying elements. Through analysis of variance (ANOVA), it was figured out that altering the fraction of Cu had the greatest effect on the hardness values with a contribution of about 49%. Also, second-level interaction terms had about 21% of impact on the hardness values. Aging time, quadratic terms, and third-level interaction terms had almost the same level of influence on hardness values (about 10% contribution). Furthermore, the results have shown that small addition of Mg and Ag was enough to improve the mechanical properties of the alloy significantly. The statistical model formulated interpreted about 80% of the variation in hardness values.

Mechanical properties by instrumented indentation of solution precursor plasma sprayed hydroxyapatite coatings: Analysis of microstructural effect

The mechanical properties of solution precursor plasma sprayed hydroxyapatite (SPPS-HA) coatings were investigated by instrumented indentation test in relation to their microstructural characteristics. The morphology of the coatings using solution that is more concentrated shows cauliflower-like surface with fine particles and agglomerated fragmented shells while dome-like formations with spherical particles around were observed for coatings from less concentrated solution. The coatings had elastic modulus and hardness values in the range of 5.0 to 22.0 GPa and 0.04 to 0.17 GPa, respectively. The strong disparities in elastic modulus and hardness values were attributed mainly to the morphology and crystallinity of the coatings. The coatings prepared from more concentrated solution precursors had average elastic modulus and hardness nearly two times greater than the coatings prepared from solution of low concentration. Variation of hardness values was due to the densification of the coating material upon indentation. Models employed enabled to describe the hardness and elastic modulus of coatings as a function of crystallinity volume fraction. Moreover, for the HA coatings to exhibit bone-like microstructure, it was found that the crystallinity volume fraction should be within 0.56–0.86.

Process and progress of sintering behavior of Cu-Al2O3 composites

The sintering temperature plays a major role in determining the microstructural as well as mechanical properties of composite materials. Apart from temperature, there are many factors, such as reinforcement particle geometry and morphology, which directly affect the sintering behavior of the composites. This study emphasizes the role of reinforcement particle geometry in the differential sintering response of copper-alumina composite. The copper and alumina powders were blended, compacted and then sintered conventionally at various temperatures such as 900, 950 and 1000°C. The formation of an interfacial phase has been characterized by X-ray diffraction and scanning electron microscopy. The variations in hardness values were recorded with the variation of sintering temperature, and these have been correlated with the formation of the intermediate compound. The formation of an intermediate phase at 950°C, and the variation in the properties of the composite sketches the profile of interfacial kinetics of the copper-alumina interface when alumina is present as particulate. The decrease in hardness at 950°C indicates the formative stage of CuAlO2, and then an increase in hardness at 1000°C indicates the strengthening effect of the interfacial compound.

Studies on Dissimilar Welding of AA5083 and AA6061 Alloys by Laser Beam Welding

Dissimilar welds were prepared between 4 mm thick AA5083 and AA6061 sheets using Nd-YAG laser welding with different laser power, beam spot sizes and welding speeds. The results show that the temperature gradient and cooling rates play a major role in resultant microstructures of the weldments. Room temperature hardness and tensile properties of the weldments in the as-welded condition were studied and correlated with the microstructure. The microhardness examination showed that there was significant variation in hardness values at AA6061 side when compared with AA5083 side due to steeper temperature gradient. It has been observed that welds prepared with 3.5kW laser power, 3.5 m/min welding speed and 180 µm beam spot size exhibited highest tensile strength of 241 MPa.

Effect of constraint on fracture behavior of welded 17mn4 and aisi304 steels

In this study, 17Mn4 (P295GH) pressure vessels steel and AISI304 stainless steel were welded with ER309L austenitic consumable. In experimental part of the study, tensile tests were conducted on welded plates and variation of hardness values along specimen was measured. J-integral fracture toughness values were investigated for different crack locations. In order to determine the regions where plastic deformation did not take place due to constraint, uni-axial tensile test was performed on welded tensile specimen after attaching strain gauges. In numerical part of the study, finite element (FE) analyses were conducted by fixing 2-D models precracked on different locations by using ANSYS software. In these models, stress triaxiality and plastic deformation characteristics around crack tip were determined for each crack locations after stress — strain analyses. The limitation on the extension of plastic deformation at diffusion line causes extra increase in stress triaxiality at crack tip.

Growth Orientation Dependent Hardness for Epitaxial Wurtzite InN Films

We report the hardness of wurtzite InN thin film grown with different crystalline orientations of heteroepitaxial s-plane (1101) and a-plane (1120) on r-plane (1102) Al2O3, and homoepitaxial film on c-plane (0001) Al2O3. Hardness values along with elastic properties are studied using nanoindentation technique. Maximum hardness is reported for c-plane (approximately 8 GPa), which is followed by s-plane (approximately 5.5 GPa) and then a-plane (approximately 4 GPa) oriented InN Films. Peierls force in the slip system of different crystalline orientations for wurtzite sample is calculated for explaining the systematic variations in hardness values of these films grown with different crystalline orientations.

The Effects of Hardness Variation on a CMP Model of Copper thin Films

AbstractWith the rapid change of materials systems and decreased feature size, thin film microstructure and mechanical properties have become critical parameters for microelectronics reliability. An example of a major driver of this new technology is the data storage community who is pushing for 1 Terabit/square inch on its magnetic disk hard drives. This requires inherent knowledge of the mechanical properties of materials and in depth understanding of the tribological phenomena involved in the manufacturing process. Chemical mechanical polishing (CMP) is a semi-conductor manufacturing process used to remove or planarize ultra-thin metallic, dielectric, or barrier films (copper) on silicon wafers. The material removal rate (MRR), which ultimately effects the surface topography, corresponding to CMP is given by the standard Preston Equation, which contains the load applied, the velocity of the pad, the Preston coefficient which includes chemical dependencies, and the hardness of the material. Typically the hardness, a bulk material constant, is taken as a constant throughout the wafer and thereby included in the Preston coefficient. Through metallurgy studies, on the micro and nano scale, it has been proven that the hardness is dependent upon grain size and orientation. This research served to first relate the crystallographic orientation to a specific hardness value and secondly use the hardness variation in the previously developed particle augmented mixed-lubrication (PAML) model to simulate the surface topography and MRR during CMP. Recent test and results show that currently there is no empirical formula to relate the crystallographic orientation and thereby a critically resolved shear stress (CRSS) to a specific hardness value. The second part of this investigation utilized the variation in hardness values from the initial study and incorporated these results into the PAML numerical model that incorporates all the physics of chemical mechanical polishing (CMP). Incorporation of the variation of hardness resulted in a surface topography with a difference in roughness (Ra) from the bulk constant hardness value of 60 nm. The material removal rate (MRR) of the process differs by 2.17 μm3/s.

Micromechanical properties and structural characterization of modern inarticulated brachiopod shells

We investigated micromechanical properties and ultrastructure of the shells of the modern brachiopod species Lingula anatina, Discinisca laevis, and Discradisca stella with scanning electron microscopy (SEM, EDX), transmission electron microscopy (TEM) and Vickers microhardness indentation analyses. The shells are composed of two distinct layers, an outer primary layer and an inner secondary layer. Except for the primary layer in Lingula anatina, which is composed entirely of organic matter, all other shell layers are laminated organic/inorganic composites. The organic matter is built of chitin fibers, which provide the matrix for the incorporation of calcium phosphate. Amorphous calcium phosphate in the outer, primary layer and crystalline apatite is deposited into the inner, secondary layer of the shell. Apatite crystallite sizes in the umbonal region of the shell are about 50 × 50 nm, while within the valves crystallite sizes are significantly smaller, averanging 10 × 25 nm. There is great variation in hardness values between shell layers and between the investigated brachiopod species. The microhardness of the investigated shells is significantly lower than that of inorganic hydroxyapatite. This is caused by the predominantly organic material component that in these shells is either developed as purely organic layers or as an organic fibrous matrix reinforced by crystallites. Our results show that this particular fiber composite material is very efficient for the protection and the support of the soft animal tissue. It lowers the probability of crack formation and effectively impedes crack propagation perpendicular to the shell by crack‐deviation mechanisms. The high degree of mechanical stability and toughness is achieved by two design features. First, there is the fiber composite material which overcomes some detrimental and enhances some advantageous properties of the single constituents, that is the softness and flexibility of chitin and the hardness and brittleness of apatite. Second, there is a hierarchical structuring from the nanometer to a micrometer level. We could identify at least seven levels of hierarchy within the shells.

Analysis of the Size Effect in Low-Load Hardness Testing of Metals

Abstract Recent accounts of Vickers hardness tests in which the variation of hardness values with indentation size was suppressed by lubrication are re-examined to elucidate the nature of the size effect. It is shown that a simple constant error in either the measured indentation size or the force actually exerted would not explain the effect. A good description of the effect is obtained by reference to an indentation-size-dependent load error which is sensitive to both friction conditions and the plastic properties of the test material.

The Kentron microhardness tester, a quantitative tool in opaque mineral identification

The Kentron Microhardness Tester combines pin-point placement of the indenter to one micron, with reproducible hardness values (within variable limits) on minute opaque mineral grains as small as 10 microns in diameter. The hardness range, in Knoop values, is from 5 to 1,500 for the opaque minerals examined. The hardness values and limits of hardness for 48 opaque minerals are given. Anisotropic minerals show variations in hardness with respect to orientation. Variable loads on the indenter result in variations in hardness values which are not fully explained. The instrument should be especially useful in the field of polished surface studies of the opaque ore minerals.