Results Of Microhardness Measurements Research Articles

CORROSION RESISTANCE OF LASER WELDED SHEETS OF STAINLESS STEEL 316L

The autogenous laser welding with a disk laser was used for producing butt joins of 2.0 mm thick sheets of AISI 316L stainless steel. The influence of basic laser welding parameters on the shape, microhardness distribution, microstructure and corrosion resistance of the joints was determined. The tests of corrosion resistance were conducted in a salt chamber under artificial NaCl environment conditions. The corrosion tests were conducted in accordance with the PN EN ISO 9227 standard. The produced test joints of 2.0 mm thick stainless steel were characterized by high quality, homogeneous and low-grained microstructure, and very narrow heat affected zone. The results of microhardness measurements indicated that the fusion zone was slightly hardened comparing to the 2.0 mm thick stainless steel sheet AISI 316L. The obtained results of corrosion test under artificial NaCl environment conditions showed that the tested butt joints are resistant for corrosion under the test conditions.

Сравнение подходов, основанных на методе Вильямсона–Холла, для анализа структуры высокоэнтропийного сплава Al0,3CoCrFeNi после холодной пластической деформации

Introduction. High-entropy alloys (HEAs) belong to a new and promising class of materials that are attracting the attention of both scientists and engineers from all over the world. Among all alloys of the AlxCoCrFeNi system, HEAs with x ≤ 0.3 attract special attention. Materials with this composition are characterized by the presence of only one phase with a face-centered cubic lattice (FCC). Such alloys have high ductility, excellent corrosion resistance and phase stability at high temperatures. The purpose of this work is to compare several methods of profile analysis on the example of plastically deformed ingots of a high-entropy Al0.3CoCrFeNi alloy. The methods of investigation. Using several methods of profile analysis of X-ray diffraction patterns, the structures of the cold-worked high-entropy alloy Al0.3CoCrFeNi are studied. In addition to the classical Williamson-Hall method, the analysis was carried out using a modified one, as well as a method that takes into account the anisotropy of the elastic properties of the crystal lattice. Research material. Ingots of the high-entropy Al0.3CoCrFeNi alloy deformed by cold rolling with a maximum reduction ratio of 80% were used as the object of the study. Samples were cut from the obtained blanks, which were studied by the method of synchrotron radiation diffraction according to the “transmission” scheme along two (longitudinal (RD) and transverse (TD)) directions of rolled products. Results and discussion. It is shown that the use of the classical Williamson-Hall method leads to a significant error in the approximation of experimental results. The modified Williamson-Hall method has the smallest approximation error and can be recommended for studying the Al0.3CoCrFeNi alloy. An analysis of deformed samples using this method made it possible to reveal several features of the formation of defects in the crystalline structure, which are in good agreement with the classical concepts of the mechanisms of plastic deformation. First, an increase in the degree of deformation of the high-entropy Al0.3CoCrFeNi alloy leads to an almost uniform increase in the number of twins and stacking faults. Secondly, with an increase in the degree of reduction, there is a decrease in the fraction of edge dislocations and an increase in the fraction of screw dislocations in the material. The results obtained correlate well with the results of microhardness measurements.

Исследование выделений вторых фаз в наноструктурном технически чистом титане

The results of studies on the process of precipitation of dispersed second phases in commercially pure titanium Grade 4 and the effect of secondary precipitates on its structure and mechanical properties in two states, coarse-grained and nanostructured ones, are presented. The nanostructured state was obtained by high-pressure torsion (HPT) under a pressure of 6 GPa up to N =10 revolutions at room temperature. A particular consideration is given to the study of changes in the phase composition and microstructure of titanium subjected to deformation processing after annealing at an elevated temperature of 700°C for 30 minutes. In this work, by means of studies in a transmission electron microscope, it was shown that at a temperature of 700°C and higher, in the structure of the samples, nanoparticles of the second phases which differ in size and morphology are precipitated in both states. The nature of the observed particles was studied in SEM, by indexing the electron diffraction patterns taken from the particles, and by carrying out X-ray phase analysis by the “transmission” method. Particles of the second phases are modifications of the high-temperature β-phase of titanium. The HPT treatment of the alloy, according to the XRD data, leads to an increase in the volume fraction of precipitated particles after annealing and, as a result, to an increase in the microhardness of the states under study. The results of microhardness measurements at varying regimes of deformation and annealing are presented. Combination of HPT up to N = 5 revolutions and annealing at 700°C for 30 minutes followed by additional torsion straining also up to N = 5 revolutions provides the highest microhardness values in commercially pure titanium, which reaches 423 HV.

Possibilities of the Utilization of Ferritic Nitrocarburizing on Case-Hardening Steels.

This paper is devoted to the possibilities of the utilization of chosen chemical heat treatment technologies on steels used for manufacturing highly stressed components of military vehicles and weapons systems. The technologies chosen for this research are plasma ferritic nitrocarburizing and ferritic nitrocarburizing in a gaseous atmosphere. These technologies were applied on a steel equivalent 1.5752 (i.e., CSN 41 6426), which is suitable for carburizing. Chemical composition of the steel was verified by optical emission spectrometry. An observation of a microstructure and an assessment of the parameters of obtained white layers were performed by optical microscopy. Morphology and porosity of the surface were observed by electron microscopy. The depth of diffusion layers was evaluated in accordance with ISO 18203:2016(E) from the results of microhardness measurements. A friction coefficient was obtained as a result of measurements in accordance with a linearly reciprocating ball-on-flat sliding wear method. Wear resistance was assessed by employing the scratch test method and a profilometry. The profilometry was also utilized for surface roughness assessment. It was proved that both tested chemical heat treatment technologies are suitable for surface treatment of the selected steel. Both technologies, ferritic nitrocarburizing in plasma and a gaseous atmosphere, are beneficial for the improvement of surface properties and could lead to a suppression of geometrical deformation in comparison with frequently utilized carburizing. Moreover, the paper presents a procedure that creates a white layer-less ferritic nitrocarburized surface by utilizing an appropriate modification of chemical heat treatment parameters, thus subsequent machining is no longer required.

ВЫБОР МАТЕРИАЛА НАНОРАЗМЕРНОЙ ФАЗЫ И УСТАНОВЛЕНИЕ РЕЖИМОВ НАНЕСЕНИЯ НАНОКОМПОЗИЦИОННЫХ ГАЛЬВАНИЧЕСКИХ ПОКРЫТИЙ НА ОСНОВЕ ХРОМА

The article presents the results of research on the establishment of an effective nanoscale phase and modes of applying nanocomposite electroplating coatings based on chromium. As a result of the conducted studies, it was found that it is advisable to use a nanodispersed aluminum oxide powder as a nanoscale phase. The method of mathematical planning of the experiment was used to determine the optimal modes of coating and the concentration of nanoscale particles in the electrolyte. The microhardness of the obtained coatings was chosen as an optimization parameter, since it significantly affects their wear resistance. The highest microhardness of a nanocomposite electrolytic coating based on chromium is achieved when the electrolyte is heated to a temperature of 50 °C, a current density of 59 A/dm2 and a concentration of nanoscale phase particles in the electrolyte of 3.2 g/l, which ultimately corresponds to an increase in microhardness to 14.32 GPa. It is also established that nanocomposition coatings have a positive microhardness gradient in thickness, which allows leveling the difference in the values of the microhardness of the coatings and the base metal and will help to increase the adhesion strength of the coatings to the base on the one hand and their wear resistance on the other. Based on the microhardness measurements of chromium-based nanocomposition coatings, statistical series were formed. 30 samples were subjected to measurements. According to the results of microhardness measurements, the average square deviation of the values of nanocomposition coatings based on chromium was 0.05 (coefficient of variation 0.283). To equalize the obtained experimental microhardness information, the law of normal distribution is chosen, since the coefficient of variation, according to which the greatest probability of microhardness values of nanocomposite coatings based on chromium is observed in the range of 14.32–14.37 GPa.

Friction stir spot welding of TiO2 nanoparticle-reinforced interstitial free steel

The purpose of the current study was to investigate the effect of different content of TiO2 nanoparticles and FSSW parameter such as tool rotational speed on microstructure and mechanical properties of IF steel FSSW joints. FSSW joints were realized by adding 0.45, 1.14, 2 wt% of TiO2nanoparticles to IF steel. Optical microscopy and scanning electron microscopy and energy dispersive spectroscopy studied along with the results of microhardness measurements and tensile shear analyses. The obtained results showed that the optimal welding conditions were a tool rotational speed of 1120 rpm and a dwell time of 9 s. Microstructural observations demonstrated a good dispersion of TiO2 reinforcements in the steel matrix. TiO2 nanoparticles addition led to a remarkable increase in the mechanical properties of the produced welds. This was attributed to the fine grain size obtained thanks to the ceramic particles addition. The hardness and ultimate load of joints produced by TiO2 amount of 1.14 wt% are optimum welding conditions for fabrication of the best quality of welds which have attributed to the uniform dispersion of TiO2 nanoparticles in the weld regions. For higher than 1.14 wt% content of TiO2, nanoparticles agglomeration occurred, this resulted in the decrease in strength and ductility.

Graphite Surface Microhardening with Femtosecond Laser Pulses

The effects of direct femtosecond laser processing of a polycrystalline graphite surface are experimentally investigated. The functional graphite surfaces are fabricated at laser intensity of ~1017 W/cm2 in vacuum and then thoroughly analyzed by means of Raman spectroscopy and nanoindentation test. The measured Raman spectra at 257 nm show presence of an amorphous carbon phase containing sp3 hybridized carbon atoms and a discontinuous nanocrystalline diamond film, while the results of microhardness measurements demonstrate a sixteen-fold increase in microhardness as compared to the unirradiated graphite surface. The modulus of elasticity is found to increase nearly by 3.4 times.

Numerical Investigation by the Finite Difference Method of the Laser Hardening Process Applied to AISI-4340

This paper presents a numerical and experimental analysis study of the temperature distribution in a cylindrical specimen heat treated by laser and quenched in ambient temperature. The cylinder studied is made of AISI-4340 steel and has a diameter of 14.5-mm and a length of 50-mm. The temperature distribution is discretized by using a three-dimensional numerical finite difference method. The temperature gradient of the transformation of the microstructure is generated by a laser source Nd-YAG 3.0-kW manipulated using a robotic arm programmed to control the movements of the laser source in space and in time. The experimental measurement of surface temperature and air temperature in the vicinity of the specimen allows us to determine the values of the absorption coefficient and the coefficient of heat transfer by convection, which are essential data for a precise numerical prediction of the case depth. Despite an unsteady dynamic regime at the level of convective and radiation heat losses, the analysis of the averaged results of the temperature sensors shows a consistency with the results of microhardness measurements. The feasibility and effectiveness of the proposed approach lead to an accurate and reliable mathematical model able to predict the temperature distribution in a cylindrical workpiece heat treated by laser.

Structure and properties of titanium produced by a new method of chip recycling

The paper proposes a new technique of recycling metallic chips and presents the results of examination of the products thus obtained. The aim of the experiments was to recycle commercial purity (cp) titanium Grade 2 chips obtained by turning, and to produce a solid bulk material. The recycling was realized using a plastic working process. The titanium chips were first subjected to preliminary consolidation and then directly extruded using the KOBO process. The properties of the recycling final product were examined and compared with those of the as-received, solid cp-titanium Grade 2 (reference material).The recycling process yielded a well consolidated solid titanium rod with a diameter of 8mm. The consolidation effect was high which was confirmed by the fact that only a small number of voids and discontinuities distributed randomly were observed. The final material had a homogeneous grained structure. The equiaxial grains observed on the transverse and longitudinal sections had similar sizes. The mechanical properties of the recycled material (estimated based on the results of microhardness measurements and uniaxial compression tests) were comparable with those of solid cp-titanium Grade 2.

Structural characteristics of a mechanically alloyed Al–Fe powder composite

The published data on the use of functional composite materials on the basis of Al–Fe intermetallic compounds are presented. Advantages of the solid-phase technology of aluminide production (mechanical alloying + thermal synthesis) when compared to the liquid-phase technology, namely, lower energy consumption and better control over the structure and phase composition of the material, are noted. The distribution of Al and Fe in the powder composite is determined using metallographic methods. It is shown that the use of the fraction of Al powder of 60–80 μm and the fraction of Fe powder of 20–40 μm is reasonable for production of composite materials with a more uniform distribution of the Fe component. It follows from the results of microhardness measurements that significant strain hardening of Al and Fe particles occurs during mechanical alloying.

Surface microstructure and properties of Cu-C powder metallurgical alloy induced by high-current pulsed electron beam

This paper investigates the microstructure and properties of Cu-6C powder metallurgy (PM) alloys irradiated by high-current pulse electron beam (HCPEB). After 20-pulsed HCPEB irradiation, the surface was melted completely and the remelted layer was formed in 2–3 μm thickness, which consisting of ultrafine Cu grains. Within the near irradiated surface, high-density dislocations and vacancy clusters were observed which provide a large amount of paths for carbon atoms to diffuse into Cu matrix, and it leads to the formation of the supersaturated solid solution, causing Cu lattice parameter expansion. In addition, the extreme rapid cycle generated the ultrafine carbon particles at the surface of Cu-6C metallic matrix. The results of microhardness measurements and sliding wear resistance testing indicated that the irradiated sample exhibited better properties than the initial one. The ultrafine carbon particles played an important role in the antifriction properties, which was attributed to the formation of carbonic tribolayer on the hard surface.

Production of superhard corundum under spark-plasma sintering of aluminum oxide nanopowders

In the process of optimization of the conditions of spark-plasma sintering of aluminum oxide powders, the repeated nonuniform distribution of microhardness over the surface of the sintered pellets is ascertained. The microhardness in the volume of the pellets was significantly higher (up to 35 GPa) than that on its surface. SEM microstructure investigations on the cleaved surface of the compact show the presence of zones with an unusual structure in the central regions of the sample. The structure of these zones is composed of randomly oriented flat crystals with the longitudinal size of up to 40 μm. Cavities between the long crystals are filled with small grains of 0.3–0.8 μm in size. The results of microhardness measurements indicate that the zones with anomalous structure have superhigh microhardness values.

Microstructural evolution of a CoCrFeMnNi high-entropy alloy after swaging and annealing

The processing parameters which govern the evolution of microstructure and texture during rotary swaging and subsequent heat treatments were studied in an equiatomic single-phase CoCrFeMnNi high-entropy alloy. After vacuum induction melting and casting, the diameter of the 40 mm cast ingot was reduced at room temperature to a final diameter of 16.5 mm by rotary swaging (diameter reduction of 60%/area reduction of 80%) and the alloy was then annealed at different temperatures for 1 h. The resulting microstructures were analyzed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction and correlated with results of microhardness measurements. It was found that the microhardness first increases slightly upon annealing below the recrystallization temperature but then drops steeply at higher annealing temperatures due to the onset of recrystallization. Special emphasis was placed on how the microstructure evolves with respect to the radial and longitudinal position in the rod. Finally, a combination of swaging and heat treatment parameters were identified that can produce CoCrFeMnNi high-entropy alloys with a homogeneous composition and grain size and almost no texture.

Microstructure and mechanical properties of ultrafinegrained Mg-Zn-Ca alloy

In this paper the influence of high pressure torsion (HPT) on the structure of Mg-Zn- Ca alloy is studied. The microstructure before and after HPT and after additional annealing has been studied by the scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results of microhardness measurements and tensile tests of HPT samples are discussed.

Microstructure evolution and mechanical properties of a Ti–35Nb–3Zr–2Ta biomedical alloy processed by equal channel angular pressing (ECAP)

In this paper, an equal channel angular pressing method is employed to refine grains and enhance mechanical properties of a new β Ti–35Nb–3Zr–2Ta biomedical alloy. After the 4th pass, the ultrafine equiaxed grains of approximately 300nm and 600nm are obtained at pressing temperatures of 500 and 600°C respectively. The SEM images of billets pressed at 500°C reveal the evolution of shear bands and finally at the 4th pass intersectant networks of shear bands, involving initial band propagation and new band broadening, are formed with the purpose of accommodating large plastic strain. Furthermore, a unique herringbone microstructure of twinned martensitic variants is observed in TEM images. The results of microhardness measurements and uniaxial tensile tests show a significant improvement in microhardness and tensile strength from 534MPa to 765MPa, while keeping a good level of ductility (~16%) and low elastic modulus (~59GPa). The maximum superelastic strain of 1.4% and maximum recovered strain of 2.7% are obtained in the billets pressed at 500°C via the 4th pass, which exhibits an excellent superelastic behavior. Meanwhile, the effects of different accumulative deformations and pressing temperatures on superelasticity of the ECAP-processed alloys are investigated.

The effect of homogenization treatment on microstructure and properties of ZnAl15 solder

The effect of homogenization treatment before extrusion process on microstructure and properties of ZnAl15 solders was investigated. The results of observing microstructure shown that homogenization treatment increased the structural homogeneity and stability of ZnAl15 solder. The results of microhardness measurements and reverse bend test indicated that the homogenized ZnAl15 solder resulted in lower microhardness and much higher ductility. Corrosion behavior of non-homogenized and homogenized ZnAl15 solders was studied in 3.5wt.% NaCl solution using immersion test and Tafel plots and resulted in higher corrosion resistance of the homogenized ZnAl15 solder.

Effect of Mg Content on the Characteristics of Al/SiC Nanocomposite Powders Produced via <i>In Situ</i> Powder Metallurgy Method

In the present study the effect of Mg addition on the characteristics of Al/SiC nanocomposite powder particles produced via a relatively new method called in situ powder metallurgy (IPM) is investigated. Commercially pure Al and Al-Mg alloy melts containing different amounts of Mg were used as the matrix alloy. Nano-sized SiC particles with the average size of 60 nm were used as the reinforcing material. The effect of Mg content on the fluidity of the melt as an influencing factor affecting both the process yield and wettability of SiC with molten metal was investigated. The size distribution of produced powders was characterized using a laser particle size analyzer. Scanning electron microscopy was utilized to investigate the possibility of embedding of SiC nanoparticles within the metallic matrix. Results of microhardness measurements together with SEM micrographs and EDS analysis showed that nano-sized SiC particles could be embedded in the relatively coarse Al-Mg powders containing at least 1 wt.% Mg.

Homogeneity of Bulk Nanostructured Titanium Obtained by Hydrostatic Extrusion

The aim of this study was to investigate the homogeneity of the bulk nanocrystalline titanium rods obtained by Hydrostatic Extrusion (HE). The investigated material was commercially pure titanium grade 2. The final products of extrusion were nanocrystalline rods with diameters of 7 and 10 mm and lengths of about 250 mm. The size and shape of the grains were examined on transverse sections using transmission electron microscopy (TEM). The grain size was determined by the average grain equivalent diameter d2. The grain size diversity was quantified in terms of the equivalent diameter coefficient of variation CV (d2). The samples for the microscopic analyses were cut from various regions of the rods i.e. top, end, centre, and from surface of the rods. In all the samples, the average grain size determined on transverse sections was about 70 nm and the nano-grains in the various regions of the rods were similar in the shape. The examinations demonstrated that the nanostructure of the extruded rods was homogeneous. This observation was confirmed by the results of microhardness measurements.

Structure and mechanical properties of an aluminum alloy 1570 subjected to severe plastic deformation by high-pressure torsion

The effect of an ultrafine-grained (UFG) structure formed in an aluminum alloy 1570 using severe plastic deformation by high-pressure torsion (HPT) at room temperature and at temperatures of 100 and 200°C on the mechanical properties (strength and plasticity) has been investigated. The specific features of the UFG states obtained have been studied by transmission electron microscopy and X-ray diffraction analysis. The main regularities of changes in the structure characteristics of the alloy (the average grain size, size of coherent domains, magnitudes of microdeformations of the crystal lattice, dislocation density, and the lattice parameter) have been established depending on the temperature of the HPT treatment. The mechanical properties of the alloy after HPT have been estimated from the results of microhardness measurements and mechanical tests for tension. It has been established that after HPT performed at room temperature, the UFG alloy demonstrates an ultimately high level of strength (the microhardness, offset yield strength, and ultimate strength reach 2300, 905, and 950 MPa, respectively) and a marked plasticity (the relative elongation at fracture was 4.7%). The HPT treatment performed at higher temperatures insignificantly reduces the strength characteristics of the UFG material but leads to a substantial drop in its plasticity. This unusual mechanical behavior of the UFG alloy is discussed based on an analysis of the results of structural investigations.

Synthesis and coating of micro-metal-matrix composite by combined laser sol–gel processing

Of the many methods of laser treatment for improving materials surface properties that have been reported, very few have addressed laser-assisted chemical reaction. In this work laser deposition of metal-matrix composites is reported, using chromium oxide and silicon carbide powders mixed in silica sol–gel mixtures, on EN43 mild steel substrates. Very fine SiC particles ≤ 1 μm and M 7C 3 carbides were synthesised in situ and dispersed in ferrite matrix by this process. A diode laser at different powers and scanning speeds was applied to specimens coated with slurries of different chemical compositions. The effect of solution composition and bath depths were examined in order to achieve optimum experimental parameters. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscopy (SEM) and field emission gun scanning electron microscope (FEG-SEM). Chemical composition was determined by energy dispersive X-ray analysis (EDX). The different phases were identified by X-ray diffraction (XRD). Results of microhardness measurements and wear properties of the coatings are also reported. Thermodynamic analysis of the reactions taking place is also given.