Microhardness Measurements Research Articles

Microstructure Development of Powder-Based Cu Composite During High Shear Strain Processing

Commercially pure Cu features excellent electric conductivity but low mechanical properties. In order to improve the mechanical properties of Cu, strengthening elements can be added to prepare alloys or composites featuring enhanced performances. This study focuses on the detailed characterization of the microstructure of a Cu composite strengthened with Al2O3 particles during high shear strain processing. The Cu-Al2O3 mixture was prepared by powder metallurgy and directly consolidated by the intensive plastic deformation method of hot rotary swaging. Samples cut from the consolidated piece were further processed by the severe plastic deformation method of high pressure torsion (HPT). The primary aim was to investigate the effects of varying degrees of the imposed shear strain, i.e., the number of HPT revolutions, microstructure development (grain size and morphology, texture, grain misorientations, etc.) of the consolidated composite; the microstructure observations were supplemented with measurements of Vickers microhardness. The results showed that the added oxide particles effectively hindered the movement of dislocations and aggravated grain fragmentation, which also led to the relatively high presence of grain misorientations pointing to the occurrence of residual stress within the microstructure. The high shear strain imposed into (the peripheral region of) the sample subjected to four HPT revolutions imparted equiaxed ultra-fine grains and an average Vickers microhardness of more than 130 HV0.1.

Archaeometallurgical investigation of the Nebra Sky Disc

The world heritage object Nebra Sky Disc is one of the best investigated archaeological objects. The origin of the raw materials it is made of is well known. However, its manufacturing process was not completely clear. Investigations were made in order to clarify the steps of manufacturing from the initial casting to the finished disc using the latest metallographic techniques. Therefore, a small piece from the outer part of the disc was investigated and compared with a replica. Both were prepared regarding the metallographic procedure. Microstructural analysis was made by optical microscopy on a colour etched surface, EDS and electron backscatter diffraction. For the investigation of mechanical properties microhardness measurements were made. It could be found that the Nebra Sky Disc was manufactured from a flat cast followed by hot forging process. During the forging process the disc was heated and forged for approximately 10 times.

CORROSION RESISTANCE OF BRAKE DISCS AFTER NITRIDING

The article presents the work carried out to create a surface layer, ultimately on cast iron brake discs, by theZeroFlow method using regulated gas nitriding. The presented research is aimed at creating a nitrided layerwith corrosive wear resistance maintained at the stage of brake disc manufacture, waiting for sale of a newvehicle, and even during further exploitation. Examples of nitriding parameters enabling such treatment ofbrake discs made of flake cast iron are presented. The research also includes measurements of the roughnessof the working areas of brake discs before and after nitriding. The properties of the nitrided layers producedare assessed following microscopic observations and microhardness measurements using the Vickers method.The impact of nitrided layers on corrosive wear is also analyzed by observing the behavior of the surfaces ofthe tested discs in a corrosive environment in the so-called “corrosion experiment.”

Microstructure and Texture Evolution of X85MnAl29-9 Steel During Aging.

The research presented in this paper is part of a larger project concerning high-manganese alloys with different chemical compositions (mainly in manganese content from 21 to 31 wt.%). The presented examination results concern the analysis of the microstructure and textures in high-manganese X85MnAl29-9 steel, an age-hardenable steel, during aging at 550 °C for various times. X85MnAl29-9 steel was first hot rolled and subsequently cold rolled up to a 30% reduction. The samples were aged after deformation at 550 °C for various times in an argon atmosphere and cooled in air. The studies include X-ray phase analysis, texture measurement and observation of the microstructure by light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), as well as microhardness measurement. Research using scanning and transmission electron microscopy identified carbides in the analyzed samples. The results indicate that, when aging takes place, precipitation of κ'-carbide in an austenitic matrix and carbide κ at grain boundaries occurs. The appearance of satellites on diffraction patterns suggests that (Fe, Mn)3AlC nano-carbides are formed within the austenite matrix by a spinodal decomposition mechanism after the alloy is subjected to long-term aging, which is a key element for structure analysis in the design of safety systems. The use of shorter aging times (up to 24 h) leads to an increase in hardness caused by the precipitation of small κ'-carbide particles in the matrix. However, long aging times (100 h) lead to an increase in the precipitation of the carbide phase (κ and κ'), i.e., the steel becomes overage, which results in a decrease in hardness.

Mechanical and surface characterisation of additively manufactured polyetheretherketone for the tribo test

Purpose The additive manufacturing process, such as fused filament fabrication based on material extrusion, fabricates the samples layer-by-layer. The various parameters in the process significantly affect the dimensions, structure and mechanical properties of the fabricated parts. The purpose of this paper is to investigate the surface and mechanical properties that can affect the contact characteristics with other materials during tribological tests. Design/methodology/approach The investigation of 3D-printed Polyetheretherketone (PEEK) includes the measurement of dimensions, microhardness, surface roughness, surface energy and tensile strength to define material characteristics. The crystallinity is measured using an X-ray diffractometer to understand the hardness behaviour. Findings The printing parameters affect its surface roughness, hardness and crystallinity. This change in parameters such as layer thickness and infill density impacts mechanical properties such as hardness and surface roughness, which will influence the contact mechanism with the counter body during any tribological test. The change in a single parameter during the sample fabrication and the change in the surface and mechanical properties are observed. Research limitations/implications The material cost plays an important role in conducting numerous destructive tests, which is a major limitation to conducting parameter optimisation by varying more parameters. The study is limited to the as-fabricated samples rather than finished samples and without any heat treatment. Achieving optimal parameters is integral to the success of additive manufacturing, ensuring the production of components with consistent performance. Practical implications The study aims at the application of 3D-printed PEEK for bush or journal bearings that can be directly used in practice. The mechanical properties discussed in this paper can fill the gap between theory and practice. Social implications The research provides all fundamental properties, including the printing parameters and their effect on the dimensions and surface structure, which are required to understand the material and its use. The results are consistent as at least four samples were tested for tribological behaviour. The conclusion is updated as per suggestions. Originality/value The study outlines the relationship between the change in layer thickness and infill density with changes in surface energy, surface roughness, hardness and tensile strength. The deformation and adhesion during the friction test depend on these properties.

Evaluation of Structural Transition Joints Cu-Al-AlMg3 Used in Galvanizer Hangers

The paper deals with the evaluation of the quality of Cu-Al-AlMg3 structural transition joints (STJ) made by explosion welding proposed for the renovation of galvanizer hangers. The three-layer joint consisted of electrolytic copper with a thickness of 25 mm, 2 mm of aluminium represented by the AW1050 alloy, and 25 mm of the EN AW 575 aluminium alloy. Light microscopy analysis confirmed the wavy pattern of both interfaces of the welded joint and significant plastic deformation in close proximity to the waves. Microhardness measurement revealed a partial strain hardening of the AW5754 copper-aluminium alloy near the interface and a significant increase in microhardness in the vortex zone of waves, reaching a value of up to 863 HV 0.025. Microcracks were also observed in these places. The intermetallic phase Al2Cu was identified in the vortex zones by XRD analysis. As a continuous layer of intermetallic phase was not observed in the interface of the welded joint, it is possible to consider the used welding parameters as appropriate. A semi-quantitative EDX analysis revealed a diversity of chemical composition in the vortex zones, which does not correspond to the phase composition based on the equilibrium binary Al-Cu diagram due to non-equilibrium conditions in the formation of the welded joint interface. The bond strength of three-layer welded joint evaluated by the strength test ranged from 151 to 171 MPa, which represented approximately a two-fold increase in comparison to the ultimate tensile strength of alloy AW1050, while the failure occurred in all samples at the AW1050-AW5754 alloy interface.

Evaluation of Different Blending Methods to Obtain Copper Composites with Graphene Oxide

This study evaluated mixing methods for producing graphene oxide-reinforced copper matrix composites aiming for a better dispersion of graphene oxide in the composite, using powder metallurgy techniques. The compacted specimens were prepared by four different mixing processes that employed either a mechanical stirrer, rotary evaporator, tip ultrasound, or ultrasound process followed by mechanical stirring. Characterizations were performed using optical microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, compression tests, Vickers microhardness, and electrical conductivity measurements. The results indicate that the combined method yields a more homogeneous microstructure and superior mechanical properties, while electrical conductivity was maintained at a level higher than that achieved by the other methods.

Effect of Temperature Control and Rotational and Traverse Speeds on the Mechanical Properties of Friction Stir-Welded Polypropylene Plates.

In the present study, the effects of temperature and rotational and traverse speeds on the mechanical properties of polypropylene joints that are welded by friction stir welding using a non-rotational shoulder and a heat-assisted welding process is investigated. Tensile properties, microhardness measurements, microscopy observations, and thermal analysis are carried out in the present research to evaluate the effect of the welding parameters on the mechanical properties of welded joints. The experiments are conducted and analyzed by means of a central composite design using an analysis of variance (ANOVA). Variations in pre-heating temperature from 60 °C to 80 °C, rotational speed from 800 to 1500 rpm, and traverse speed from 20 mm/min to 100 mm/min are made for observations. A remarkable joint efficiency of 94% is achieved with joints that are free of discontinuities and defects. The fractured surfaces are observed to identify ductile and brittle zones. The crystallinity is measured, and a correlation between crystallinity and joint strength is discussed. The sample with highest efficiency shows 65% crystallinity and a ratio of 37.9% of ductile zone-total fractured area.

Synergic effect of nano sized ceramic powder of titanium dioxide and silver on AZ91D composites fabricated by friction stir processing

This study aims to observe the synergic effects of AgNPs/TiO2 on AZ91D hybrid composite fabricated via friction stir process. Nano-sized particles of titanium-di-oxide (TiO2) and silver (AgNPs) in powder form were utilized as reinforcement materials for fabricating mono and hybrid composites. The average size of the reinforcements was 80 nm. Friction stir processing (FSP) technique was done at constant parametric settings. Investigating the microstructure of the composites by optical microscope(OM) analysis showed a homogenous distribution of the incorporated particles in the AZ91D matrix. Scanning electron microscopy (SEM) analysis was done for fractography, which indicates ductile facture in all the specimens despite having any composition of reinforcements. However, rate of ductile fracture decreased with weight fraction of TiO2. Tensile strength and Micro-hardness measurements revealed enhancement in tensile properties i.e. ultimate tensile strength (UTS), yield strength(YS), percentage elongation(EL) and microhardness in all samples. The contribution of various strengthening mechanisms, i.e. Hall-patch, Orowan strengthening and thermal mismatch, were calculated for all samples and compared with actual values. Among strengthening mechanisms, Orowan strengthening is the most dominant. The modified Clyne method estimates the collective effect of various strengthening mechanisms to evaluate the theoretical YS for all samples. The maximum value of Yield strength (YS) is 175.612 MPa obtained for T-50-A-50. The maximum value for microhardness is obtained as 140.08 HV on Vickers scale for T-100-A-0 attributed to uniform dispersion of hard ceramic (TiO2) particles.

Effects of Different Austenitizing Times on the Microstructure and Properties of Cr‐Ni‐Mo‐V Series High‐Strength Steels

Herein, the effects of varying austenitizing times on the microstructure and mechanical properties of Cr‐Ni‐Mo‐V series high‐strength steel are investigated, discussing the mechanisms that enhance strength and toughness. By controlling the austenitizing duration, the microstructure during subsequent heat treatments is improved, leading to enhanced overall mechanical properties. The experimental steel undergoes treatments at different austenitizing times, and the microstructure is characterized using optical microscopy, energy‐dispersive spectroscopy, field emission scanning electron microscopy, and X‐ray diffraction. Mechanical properties are assessed through tensile testing, impact testing, and microhardness measurements. The results indicate that, when comparing an austenitizing time of 1 to 1 h and 15 min, the ultimate tensile strength decreases by 10%, microhardness reduces by 78.2 HV, elongation increases by 1.39 times, and toughness improves by 80%. The enhancement in toughness is primarily attributed to the synergistic effect of tempered martensite and bainite within the microstructure. Fracture morphology analysis reveals that variations in austenitizing time affect carbide distribution, accelerate carbide dissolution, decrease the crack growth zone, and enhance toughness. This study provides valuable insights for designing Cr‐Ni‐Mo‐V series high‐strength steels with optimal strength‐toughness synergies.

Effects of glutathione and potassium iodide on silver diamine fluoride application on remineralisation and colour change in dentine caries of primary teeth: an in vitro study.

The aim of this study is to compare the effect of GSH (reduced glutathione) and KI (potassium iodide) on SDF (silver diamine fluoride) discolouration and dentine remineralisation. Sixteen primary molars were utilised, yielding 4 dentine specimens each. Three specimens per tooth were allocated: one as a control and the others to experimental groups. Initial microhardness measurements were taken from one remaining dentine specimen per tooth. Subsequently, all groups underwent exposure to a demineralisation solution. Colorimetry assessed specimen colour, and post-second microhardness measurements on demineralised specimens, treatments were administered as follows: group 1 (control, n = 16): 38% SDF, group 2 (n = 16): 38% SDF followed by KI, group 3 (n = 16): 38% SDF with 5% GSH added by weight. Following pH cycling across all groups, colorimetry reassessed 48 dentine specimens. Final microhardness measurements ensued, followed by statistical analysis. Normality was checked via Shapiro-Wilk, and homogeneity via Levene's test. Independent samples t test compared normally distributed groups; Mann-Whitney U compared non-normally distributed groups. ANOVA compared means of normally distributed groups, and Kruskal-Wallis for non-normally distributed ones. Repeated measures ANOVA compared dependent groups with normal distribution, and Friedman test for non-normal. Post hoc Bonferroni analyses identified significant differences. IBM SPSS 25 was used to conduct analyses. The mean ΔE* values for SDF and SDF + GSH groups were significantly higher than those of the SDF + KI group (p < 0.05). Significant differences in L* values during final colour measurement were noted between the SDF + KI group and both SDF and SDF + GSH groups (p < 0.05). Although mean remineralisation microhardness measurements were higher than mean demineralisation microhardness measurements in all groups, statistical significance was observed only in the SDF and SDF + KI groups (p < 0.05). The study found that the addition of 5% GSH by weight to SDF does not significantly affect discolouration. Moreover, the addition of 5% GSH to the SDF solution may have a minor impact on the remineralisation potential of SDF. The application of KI after SDF reduces discolouration and does not affect the expected remineralisation process.

Correlation dependences between hardening in terms of yield strength and microhardness for austenitic and ferritic-martensitic steels

Instrumental measurements of microhardness were carried out using a Vickers indenter at a constant strain rate. The yield strength values were determined for austenitic chromium-nickel steels 08Kh18N10Т, 10Kh18N9 and 08Kh16N20M2Т in the initial (non-irradiated) state, after neutron irradiation at various regimes, as well as after plastic prestrain. Similar measurements were carried out for chromium stainless steels of the ferritic-martensitic class 07Kh12NMFB and 16Kh12MVSFBR (EP-823) in the initial (non-irradiated) state and after heat treatment, leading to hardening of the material and also after neutron irradiation. The relationships between microhardness and yield strength were determined for all studied states of all steels studied. A unified correlation has been established between hardening in terms of the yield strength and hardening in terms of Vickers micro-hardness, independently of the nature of the strengthening factor and the class of steel.

Effect of high pressure-low plasticity burnishing on the mechanical and microstructural behaviour of copper foil interlayered FSW aluminium alloys

Abstract This study delves into the impact of high pressure-low plasticity burnishing (HP-LPB) on the mechanical and microstructural behaviour of friction stir welding (FSW) joints, specifically involving AA5052 and AA6082 aluminium alloys. Notably, copper foil (CF) is introduced as a novel element in the HP-LPB process to enhance the weld strength. The experiments were conducted with the tool rotational speeds (TRS) of 1000, 1100, and 1200 RPM, each paired with the welding speeds (WS) of 20, 25, and 30 mm min−1, and tool tilt angle (TTA) of 0°, 1°, and 2°. Mechanical behaviour is assessed through tensile testing along with microhardness measurements, revealing the advantages of HP-LPB with CF in enhancing joint strength and toughness. The microstructural analysis reveals the dissolution of precipitates, highlighting the influential role of copper foil in the improvement of joint efficiency. From the weld without a CF interlayer, a maximum tensile strength of 188 MPa was achieved at a TRS of 1200 RPM, WS of 25 mm min−1 and TTA of 2°. The post-processed FSW sample interlayered with copper foil, exhibited an improvement in joint efficiency by 87% at the optimum process parameter. This research demonstrates that the use of copper foil interlayers combined with HP-LPB treatment can substantially enhance the mechanical properties and structural integrity of FSW aluminum alloys, offering a valuable solution for advanced industrial applications.

Bismorpholin-4-ium tetrabromo-cadmium metal-organic single crystal delivering Crystal structure, physicochemical properties and Characterizations for Optoelectronic Applications

For the development of nonlinear optical (NLO) materials, compositions of cadmium chloride (CC) and Morpholinium bromide (MB) molecules were utilized to form metal-organic materials. Morpholinium bromide was incorporated with cadmium metal to have electron charge transfer by constructing acentric structures that take advantage of strong third-order nonlinear optical properties. Bis Morpholinium cadmium bromide (BMCB) crystals were synthesized by a slow evaporation method (SEST). The BMCB crystal belongs to monoclinic P21/c space group with four molecules in the unit cell (a = 6.7607(4) Å, b = 16.5811(2) Å, c = 14.9744(2) Å, β=94.136(3) ° and Z = 4). The grown BMCB crystal phase purity and crystallinity were further investigated using powder X-ray diffraction (PXRD) analysis. Using Fourier transform infrared (FTIR) spectroscopy, the functional groups and their vibrational states were evaluated. From the results obtained from UV–vis-NIR spectral analysis, it is clear that the title compound is transparent in the visible range with the lower cut-off wavelength of 254 nm. The TG-DTA measurement has been used to evaluate thermal stability. Microhardness measurements were carried out to evaluate the mechanical stability of the grown crystal. The third-order nonlinear optical (NLO) characteristics were studied using Z-scan technique. The grown crystal exhibits outstanding third-order NLO response and wide laser damage threshold (LDT), which are crucial characteristics for developing practical NLO devices. The findings consequently open a novel path for the logical design of enormous, thermally stable and NLO-active metal-organic complexes for NLO applications.

Process optimization of refill friction spot stir of AA6061-T6 aluminum alloy for thick plate

To investigate the process parameters of refillable friction stir spot welding for AA6061-T6 aluminum alloy with a 3 mm plate thickness, and to extend the applicability of this technology, experiments were conducted using custom-made tools under varying rotational and penetration speeds. This study aimed to produce well-formed welds and analyze the metallurgical structure, tensile shear strength, and microhardness of the welded joints. The experiments were performed at rotational speeds of 1000, 1200, 1400, and 1600 rpm and penetration speeds of 20, 30, 40, and 50 mm/min. These conditions were found to facilitate effective refillable friction stir spot welding. The results indicated that at lower rotational speeds, the joints failed at the interface, while at higher speeds, failure occurred through the plug. Optimal tensile shear strength was achieved at a rotational speed of 1400 rpm and a penetration speed of 30 mm/min, with a peak force of 9.27 kN and a joint surface fracture mode. Microstructural examination revealed a significant refinement of grains in the weld zone compared to the base metal. Microhardness measurements showed a concentric ring pattern on the upper surface with higher hardness at the center, decreasing toward the edges. The cross-sectional hardness demonstrated a vertical gradient, being higher at the top and decreasing toward the bottom. Notably, the welded area exhibited signs of annealing with a reduced hardness compared to the base metal, where the maximum value was recorded as HV79.

Crystal growth, linear optical, thermal, mechanical and third-order nonlinear optical properties of 1,3-diphenyl prop‑2-en-1-one single crystals

This work brings out the viability of the chalcone derivative (E)-1,3-diphenyl-2-propen-1-one (DPP) for industrial applications in nonlinear optical technology and device fabrication, through investigations on its crystal structure and nonlinear optical properties. The unit cell features of the DPP single crystals grown by slow evaporation solution growth method have been determined and hkl values indexed. The optical transparency of DPP in the near infrared and visible range is found to be admirable and an optical bandgap of 3.42 eV is revealed in the UV–Vis-NIR analysis. The work hardening coefficient (n) of DPP, determined as 2 from Vickers microhardness measurement, shows the moderate mechanical strength of the crystal. The Laser Damage Threshold value of 3.9 GW/cm2 sheds light on the high tolerance of DPP to optical damage and suggests its suitability in device fabrication. The potential of DPP crystal in nonlinear optical applications is suggested from its superior value of 1.16×10−7 esu for third order susceptibility and appealing values of other nonlinear optical parameters.

Impact of Ultrasonic Welding Parameters on Weldability and Sustainability of Solid Copper Wires with and without Varnish.

This article contains an advanced analysis of the properties of solid wire electrical contacts produced by ultrasonic welding, both with and without varnish. The main disadvantage of ultrasonic welding of thin wires is the inability to achieve acceptable peel force and tensile strength, which is mainly due to the deformation and thinning of the wires. This study deals with ultrasonic welding using a ring of thin solid copper wires that minimises the deformation and thinning of the wires. The influence of welding parameters such as energy, pressure and amplitude were systematically analysed. Based on these parameters, the optimum welding programme and control method was determined to weld unvarnished and varnished wires. The investigations included electrical resistance tests, optical microscopy, micro-hardness measurements, peel tests and tensile tests, and the measurement of energy consumption. The results showed no significant differences in microstructure and hardness between varnished and unvarnished joints. Ultrasonic joints of varnished wires achieved lower electrical conductivity (by 38%), lower tensile strength (by 3%) and higher peel strength (by 7%), while the welding process was more sustainable in terms of energy (by 6.6%) and time consumption (without preprocessing).

Corrosion failure analysis of steel tubes operating in mining installations: Metallurgical, chemical and mechanical investigations

AbstractCorrosion of steel tubes represents a major challenge for various industries, leading to significant economic and environmental impacts, such as material losses, operational interruptions and safety risks. This study focuses on the metallurgical, chemical and mechanical characterization of corroded steel tubes operating in mining installations using metallographic analysis, X-ray diffraction (XRD), SEM-EDS studies, chemical analysis and micro-hardness measurements. The results reveal the existence of a considerable extent of corrosion, of which, the main corrosion products are magnetite – 72% and goethite – 18.1 associated with corrosion. The corroded tubes measured 0.128% carbon, against 0.23% in new tubes, indicating a loss in weight and mechanical strength properties. The observed tensile strength for the new tubes was 481 MPa while the same for the corroded tubes was to a large extent lower. Furthermore, metallographic examination indicates that indeed the structure is ferrite pearlite as to the composition. This study indicates that 304 L or 316 L stainless steels may be utilized which have better corrosion-protecting coatings thus prolonging service life and reducing maintenance activities.

Boron-modified super duplex stainless steels: microstructure, hardness, and industrial applications

In this work was investigated the boron modified super duplex stainless steel processed by spray-forming, to characterize the workpiece using different techniques, among them, optical microscopy, SEM-FEG, X-ray diffraction, Rama spectroscopy and Vickers hardness (VH) and Thermo-Calc software. As result, in this research was verified that in the ferrite phase the Cr element predominates, but in the austenite phase the Fe and Ni elements prevail by the EDS technique. As well as XRD spectra showed different meta-stable phases and (FeCr)2B phase. Besides, the Vickers microhardness measurement was around 460 HV, being much taller than the duplex stainless steel. This alloy can be successfully used in the chemical, oil and gas industries, petrochemical process plants, the pulp and paper industry, pollution control equipment, transportation and for general engineering thanks to their outstanding corrosion resistance and mechanical properties.

Hardness and corrosion resistance of Zn coatings on mild steel obtained by electrodeposition and hot-dip galvanization

The purpose of this work is a comparative study of the characteristics of the layers of Zn on a substrate of mild steel from two different processes (electrodeposition and galvanizing), and to review the progress that has been made in understanding the intermetallics phases’ effect on the corrosion behavior. The obtained Zn-containing film was investigated using diverse instrumental methodologies such as microhardness, X-ray diffraction, and potentiodynamic polarization measurements. This study allows the conclusion that the layers of Zn developed have: a homogeneous structure and good hardness. The corrosion test results showed an improvement in corrosion resistance for electrodeposition coatings compared with galvanizing coatings. XRD results identify that the electrodeposition and the galvanizing coatings have similar phases and the maximum hardness is obtained for the galvanizing process. Intermetallic phases were found to influence the corrosion behavior of mild steel. The results show that the size of Fe–Zn particles gradually decreases with the immersion time.