Microhardness Increment Research Articles

Effect of Machining-Induced Deformation and Grain Refinement on Microstructure Evolution in Hybrid Wire-Arc Directed Energy Deposition

Abstract Wire-Arc Directed Energy Deposition (DED) offers promise for large-scale metal component production, yet challenges persist in achieving a consistent microstructure and mechanical properties. This paper investigates the effect of machining-induced deformation and grain refinement on microstructure evolution in mild steel structures printed using Hybrid Wire-Arc Directed Energy Deposition (DED), which integrates interlayer machining steps into the Wire-Arc DED process. The study demonstrates that machining with radiused-edge cutting tools induces fragmentation of ferritic/bainitic grains, leading to dispersed and refined grain colonies, that, when subjected to reheating and remelting cycles during subsequent layer depositions, lead to a more refined overall microstructure compared to the Wire-Arc DED process. Comparative analyses revealed a statistically significant 19.5% mean reduction in grain size and 8.5% increment in microhardness of the resulting Hybrid Wire-Arc DED structure. The work points to interlayer machining as a promising strategy for in-situ enhancement of the microstructure and mechanical properties in DED processes.

Microstructural and nanoindentation study of spark plasma sintered high entropy alloy reinforced aluminium matrix composites

In this study, Spark Plasma Sintering (SPS) also known as a field-assisted technique was employed in the fabrication of high entropy alloy (HEA) reinforced aluminium matrix composites (using 5, 7 and 10 wt% HEA as the reinforcement in the composites); and conventional methods were employed to determine the relative density and microhardness; while nanoindentation technique was employed to determine the nanohardness, modulus of elasticity and nanoindentation depth of the sintered samples. Calculation Phase Diagram (CALPHAD) software, Thermocalc was employed in the prediction of the phases present in the HEA, while XRD was used in the confirmation of the phases. The phase analysis showed that BCC, FCC, and laves are the phases present in the fabricated HEA while the microstructural analysis showed that interdiffusion layers were formed; and atomic precipitation that resulted in the formation of new phases occurred during sintering. The microhardness, nanohardness, and modulus of elasticity of the sintered HEA-reinforced Al matrix composites increase with an increase in the wt% of HEA such that as little as 5 wt% HEA addition resulted in a 102.8 % increment in microhardness, while the densification and indentation depth were discovered to decrease with an increase in the wt% of HEA.”

Influence of silicon carbides on the structure and properties of composite nickel-phosphorus coating

The authors studied the structure, properties and corrosion resistance in various acids of nickel-phosphorus coatings with dispersed silicon carbides after crystallization annealing under various modes. Temperatures of the beginning of crystallization after heating at speeds of 1, 5, 20 °С/min and the percentage of crystalline phases formed under isothermal conditions (nickel phosphide Ni3P and nickel) were determined. High microhardness of more than 1000 HV is achieved in a composite nickel-phosphorus coating with dispersed particles of silicon carbides during prolonged low-tempera­ture annealing, accompanied by crystallization with formation of already insignificant (10 %) amounts of Ni3P. The revealed dispersed Ni3P located both in the body and along boundaries of the grain, make the main contribution to the increment of microhardness. The yield strength and ultimate strength of coatings increase during crystallization annealing by only 12 – 15 MPa, and the elongation drops to zero, which is due to the formation of brittle Ni3P compounds. Annealing with short soaking at crystallization temperatures leads to the fact that silicon carbides exhibit a barrier effect, reducing the intensity of formation of crystalline Ni3P and corrosion resistance, while long soaking at lower crystallization temperatures forms about 70 % Ni3P, contributing to consistently high hardness and improved corrosion resistance. Corrosion resistance of composite coatings Ni-P + silicon carbides, regardless of the heat treatment modes, is maximum in acetic and orthophosphoric acids at 70 % nickel phosphide and minimum in nitric acid and its mixtures with other acids.

Surface Integrity of additively manufactured Inconel-718 by peening approaches

ABSTRACT In this study, laser powder bed fused (LPBF) Inconel 718 alloy coupons are exposed to laser shock peening and shot peening to evaluate the post-treatment effect on mechanical performance. The coupons are analyzed under different conditions, such as As-built, heat-treated, shot-peened, and Laser shock peening (LSP) with overlapping percentages of 60, 70, and 80. The micrograph of the As-built IN718 sample surface shows the presence of unfused powder and tiny pores with precipitation, the laser-peened sample exhibits the refinement of the grains, while the shot-peened sample exhibits defect-free surface with waviness where the X-ray Diffraction (XRD) peaks ensure the quantitative agreement in each stage of the peening process. The microhardness was increased by 102.87% after LSP with 80% overlap, and by 71.96% after shot peening. The compressive residual stress was enhanced 2.39 times after shot peening and 1.78 times after LSP-80% when compared to the as-built coupon. This study has shown the elimination of the tensile residual stress, increment of microhardness, improvement of surface morphology in Laser powder bed fused material through LSP, and shot peening of IN718 alloy.

Microstructure and micromechanical properties evolution pattern of metamorphic layer subjected to turning process of carbon steel

Turning process results in microstructure alteration and forms a metamorphic layer beneath the machined surface, which influence micromechanical properties. The metamorphic layer induced by turning was divided into severe deformation layer (SDL) and moderate deformation layer (MDL) through grain size distribution, and the microstructure was observed and characterized by electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The model to predict the depth of SDL (hSDL) based on dynamic recrystallization and specific shear energy (US) in the cutting process was established, and the results showed that ΔUS had a linear relationship with hSDL (R2 = 0.8799). The micromechanical properties of SDL, MDL, and bulk material were characterized by micro-hardness and micropillar compression tests. The increment of micro-hardness in SDL (increased by 66.4 % on the bulk material) is mainly due to the Hall-Petch effect caused by nanocrystals formed through dynamic recrystallization, and the micro-hardness in MDL (increased by 24.1 % on the bulk material) is affected by the superposition of the Hall-Petch effect and Taylor strengthening caused by the gradient distribution of grain size and dislocation density. The yield stress (σy) obtained from the micropillar compression test decreased successively in SDL, MDL, and bulk material (from 1072 MPa to 604 MPa). The influence mechanism of the critical resolved shear stress (τCRSS) and Schmidt factor (SF) on SDL, MDL, and bulk material were illustrated.

Effect of Cr Content on the Microstructure of Casting Infiltration Layers: Simulations and Experiments

High chromium cast irons are commonly used as casting infiltration layers in the applications of wear resistance. The formation mechanism of the casting infiltration layer is essential to better develop the surface wear resistance materials using the casting infiltration method. In the present work, casting infiltration layers with various Cr contents were fabricated in situ on the surface of parent ZG45 steel. CALPHAD-type calculations using Thermo-Calc software, SEM, EDS and microhardness tests were performed to study the effect of Cr on the microstructure and hardness of casting infiltration layers. All the microstructures of casting infiltration layers were composed of pearlite matrix and eutectic M7C3 carbide. With the increase in Cr content from 7.01 wt.% to 17.20 wt.%, the amount of M7C3 carbide increased from 5.05 vol.% to 13.12 vol.%, resulting in the increment of microhardness. With the aid of simulations, the solidification behavior and formation mechanism of casting infiltration layers were revealed.

Effect of heat treatment on microhardness of electroless Ni-YSZ cermet coating

The paper discussed the effect of heat treatment on electroless nickel-yttria-stabilised zirconia (Ni-YSZ) cermet coating. Ni-YSZ cermet coating has potential applications such as cutting tools, thermal barriers, solid oxide fuel anode, and various others. The compatibility of ceramic YSZ and metallic nickel in terms of the mechanical properties such as hardness by varying the heating temperature, time and ceramic particle size is highlighted. Ni-YSZ cermet coating was deposited onto a high-speed steel substrate using the electroless nickel co-deposition method. The temperature and time were varied in a range of 300-400°C and 1-2 hours, respectively. The microhardness measurements were carried out using a Vickers microhardness tester (Shimadzu) according to ISO 6507-4. The surface characterisation of the cermet coating was carried out using JOEL Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray (EDX) JSM 7800F. The crystallographic structure of materials was analysed by X-ray diffraction (XRD) Bruker D8 Advance instrument. It was found that the microhardness of Ni-YSZ cermet coating with the ratio of 70:30, respectively, is directly proportional to the heating temperature and time. Heating the Ni-YSZ cermet coating at 300°C from room temperature (rtp) to 1 hour shows a 12% microhardness increment, while from 1 to 2 hours gives a 19% increment. Compared to heating at 350°C and 400°C, the increment is more significant at 33% and 49% for rtp to 1 hour and 8% and 16% for 1 to 2 hours, respectively. In addition, the effect of varying YSZ particle size in the Ni-YSZ cermet gave response differently for heating temperature and heating time. The paper is only limited to the discussion of the heat treatment effect on Ni-YSZ cermet coating hardness property. The tribological effect will be in future work. The microhardness data may vary due to the Vickers microhardness force applied and the amount of ceramic particle incorporation and phosphorus content in the nickel matrix. The value of this work is the compatibility of the ceramic YSZ and metallic nickel matrix in terms of mechanical properties, such as hardness, upon heat treatment.

Electron beam welding of 7075 aluminum alloy: Microstructure and fracture properties

Aluminum alloys have widespread use due to their superior properties. However, it exhibits complex effects with its various intermetallic compounds formed by clustering of other elements in its welded joints. In this study, electron beam welding (EBW) of the 7075 aluminum alloys (Al-alloys) was examined. Two different welding current values ​​are used in the welding process (20 and 25 mA). The welded specimens were subjected to tensile testing to determine their mechanical properties. In addition, the fractured surfaces were examined. The microhardness, scanning electron microscopy (SEM) and energy-dispersive spectroscopy analysis (EDS), EDS line analysis and EDS mapping were conducted. The microstructural evolution of EB welded plates investigated in the base metal (BM), heat affected zone (HAZ), and fusion zone (FZ), using SEM. Results indicated that after EBW, microhardness increment was observed in the FZ as compared to the BM and HAZ. The lowest hardness was observed in HAZ. The intermetallic formations in the FZ, and the effects of the elements on fracture were tried to be identified. At parameters 20 mA and 25 mA, 7075 alloys weld joints were brittlely broken. It was observed that the amount of Cu element increased at a high rate in the fracture zones of 7075 alloys (25 mA), it was clumped and active in fracture. Furthermore, it is estimated that a new formation is observed in the FZ of the welded joint made at 20 mA current in this study. As a result of the literature review, it is predicted that a natural structure similar to the one found in our study was not encountered for 7075 alloys or other welded Al-alloys. This formation was named, and the theory was put forward about the formation. The size, shape, chemistry and how this new formation came about were analysed.

Enhancement of mechanical and bioactive characteristics of NiTiMD composite reinforced with waste marble dust

Abstract Several bioceramics are used to enhance the bioactivity of NiTi, but the porous structure of these bioceramics simultaneously degrades the mechanical characteristics of implants. Therefore, NiTiMD composites were successfully synthesised with 0–10 wt.% reinforcement of waste marble dust (MD). Further, the effects of marble dust reinforcement on the physical, mechanical, and bioactive properties of NiTiMD composites were analysed. Field emission scanning electron microscopy images and X-ray diffraction patterns revealed the development of the primary NiTi and few secondary (e.g., NiTi2, Ni4Ti3, and Ni3Ti) phases. The porosity of NiTiMD composites increased from 8.74 to 20.83 % with the increase of marble dust reinforcement. Mechanical characterisation exhibited a two times increment in micro-hardness and bone-like Young’s modulus (3.10–6.93 GPa) and compressive strength (77.57–94.36 MPa). It was observed that the marble dust reinforcement enhanced the bioactivity of NiTiMD composites, and a uniform calcium phosphate (Ca-P) layer was formed on the NiTiMD6 and NiTiMD10 composites. Hence, the NiTiMD6 composite with balanced mechanical characteristics and enhanced bioactivity can be used as a novel material for orthopaedic implants.

Selective surface modification of SS304 using hybrid powder-mixed EDC process

ABSTRACT The present study acclaims the influence of hybrid powders (MoS2 +W) mixed dielectric fluid on the surface properties of SS304 by the electro-discharge coating (or EDC) process. Hard, wear-resistant, and lubricating surfaces are produced using different blending ratios of the powders infused in the dielectric liquid. The combined effect of both powders on the substrate’s surface properties is studied. The process performance is evaluated in terms of wear analysis, surface roughness, coefficient of friction, micro-hardness, and compositional study at different peak current and duty factors. The experimental results show an aggregate increment of micro-hardness from 119.3% to 255.2% compared to substrate. The average surface roughness increases (2.69–4.32 μm) with an increase in tungsten content (from 5% to 50%) in the dielectric and decreases with MoS2 content. The wear test results reveal a substantial decrease in coefficient of friction (COF = 0.104) with maximum concentration of MoS2 and 0.274 for maximum tungsten.

Microstructure and tribological behavior of Ti3C2Tx MXene reinforced chemically bonded silicate ceramic coatings

MXenes – In recent decades, great attention has been paid to the fast-growing two-dimensional (2D) transition metal carbides and nitrides, in terms of their prominent mechanical and electrical properties. The tribological essence of MXene has not yet been entirely investigated, although researches on MXene were conducted in all aspects of its applications. Hence, a newly compound 2D MXene (Ti 3 C 2 T x ) is exploited to reinforce the wear resistance of the chemically bonded silicate ceramic coatings, which are utilized to protect component surfaces under severe conditions. The structural features, hardness, and tribological behaviors of the targeted coatings are investigated and analyzed. Results show that the micro-hardness of the coatings increases to 156.9 HV 0.5 when added 1.2 wt% MXene. The increment of microhardness extraordinarily reaches 33.3%, compared with the original. The coating with 1.2 wt% MXene also indicates a 31.6% decrement of the coefficient of friction (COF) and a 73% reduction of the wear rate respectively. Furthermore, fatigue is found to be the main reason of the wear mechanism, through exploring the surface morphologies of wear traces and counterpart balls.

Tribological behavior of HVOF based composite coatings for wear resistance applications

In this research work, the sustainable temperature-dependent coating was developed with the use of agriculture waste with the aid of HVOF technology. The various characterization and testing techniques such as Vickers micro-hardness tester, high-temperature tribometer, and FESEM-EDS are practiced for evaluating and examine the microstructures, surface morphology, wear, corrosion, and mechanical properties. The high-temperature tribometer was employed for evaluating the tribological performance of the developed coating and showed the range of value 0.28–0.43 of COF, whereas wear value was received in the range of 42–145 µm at the followings tested conditions of temperature varies from 5 to 200 °C, load (30–60 N) and sliding velocity (0.1–0.4 m/s) respectively. The result obtained from the tribological test shown increment in micro-hardness i.e. 75%, COF decreases 34.88%, and at a temperature of 200 °C, the value of wear is reduced to 71% during the wear test at a SV of 0.4 m/s and applied load of 60 N.

Microstructural and mechanical properties assessment of transient liquid phase bonding of CoCuFeMnNi high entropy alloy

The transient liquid phase (TLP) bonding of CoCuFeMnNi high entropy alloy (HEA) was studied. The TLP bonding was performed using AWS BNi-2 interlayer at 1050 °C with the TLP bonding time of 20, 60, 180 and 240 min. The effect of bonding time on the joint microstructure was characterized by SEM and EDS. Microstructural results confirmed that complete isothermal solidification occurred approximately at 240 min of bonding time. For samples bonded at 20, 60 and 180 min, athermal solidification zone was formed in the bonding area which included Cr-rich boride and Mn3Si intermetallic compound. For all samples, the γ solid solution was formed in the isothermal solidification zone of the bonding zone. To evaluate the effect of TLP bonding time on mechanical properties of joints, the shear strength and micro-hardness of joints were measured. The results indicated a decrement of micro-hardness in the bonding zone and an increment of micro-hardness in the adjacent zone of joints. The minimum and maximum values of shear strength were 100 and 180 MPa for joints with the bonding time of 20 and 240 min, respectively.

Effect of work-hardening capacity on the gradient layer properties of metallic materials processed by surface spinning strengthening

The gradient layer induced by surface mechanical strengthening attracts plenty of attention as it can effectively improve the service performance of metallic materials, but how to design a suitable gradient layer and evaluate gradient layer properties need to be investigated further. In this work, the 316 stainless steel and TC4 alloy processed by surface spinning strengthening (3S) were investigated, including the work-hardening capacity before the 3S treatment and gradient layer properties after the 3S treatment. Results show that 316 stainless steel has a higher work-hardening capacity compared to the TC4 alloy before the 3S treatment; the maximum microhardness increment ratio, thickness of gradient layer and surface strengthening energy are also higher, and surface strengthening exponent is lower in the 316 stainless steel compared to the TC4 alloy after the 3S treatment. In addition, the exponential relation between the maximum microhardness increment ratio and work-hardening exponent, the exponential relation between the thickness of gradient layer and work-hardening exponent, the power function relation between the surface strengthening exponent and work-hardening exponent, and the linear relation between the surface strengthening energy and surface strengthening exponent are studied, respectively. Based on the above results and analysis, the microhardness distributions of gradient layer were discussed based on the work-hardening capacity, and the effects of the work-hardening capacity of the as-received metallic materials on the gradient layer properties of the surface strengthened metallic materials were summarized.

Selected Properties of the Surface Layer of C45 Steel Parts Subjected to Laser Cutting and Ball Burnishing.

In this article, we report the results of experimental studies on the impact of ball burnishing parameters on the roughness, microstructure and microhardness of the surface layer of laser-cut C45 steel parts. We also analysed the distribution of residual stresses generated in the surface layer of these parts. Laser-cut parts often require finishing to improve the quality of their surface. The tests performed in this study were aimed at assessing whether ball burnishing could be used as a finishing operation for parts of this type. Ball burnishing tests were performed on an FV-580a vertical machining centre using a mechanically controlled burnishing tool. The following parameters were varied during the ball burnishing tests: burnishing force Fn, path interval fw and the diameter of the burnishing ball dn. Ball burnishing of laser-cut C45 steel parts reduced the surface roughness parameters Sa and Sz by up to 60% in relation to the values obtained after laser cutting. Finish machining also led to the reorganization of the geometric structure of the surface, resulting in an increase in the absolute value of skewness Ssk. This was accompanied by an increment in microhardness (maximum microhardness increment was ΔHV = 95 HV0.05, and the thickness of the hardened layer was gh = 40 µm) and formation of compressive residual stresses in the surface layer.

Effect of Pulse and Direct Current Electrodeposition on Microstructure, Surface, and Scratch Resistance Properties of Ni–W Alloy and Ni–W–SiC Composite Coatings

The present work aims to study the influence of direct current and pulse current techniques as well as embedded SiC nanoparticles on the mechanical properties of the electrodeposited Ni–W coating. The electrodeposited coatings were studied for morphological, microstructural, mechanical, and scratch resistance properties using the surface roughness tester, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Vickers microhardness, and scratch tester. Application of pulse current exhibited relatively homogeneous and smooth surface of the coatings. A remarkable increment of microhardness was observed in both Ni–W and Ni–W–SiC coatings prepared under pulse current as compared to the direct current technique. Similarly, the scratch test revealed a considerable improvement in the scratch resistance behavior of the Ni–W alloy and the composite coatings from the pulsed current condition. Hence, the application of pulse current not only improved the surface- and microstructure-related properties but also enhanced the Vickers microhardness and scratch resistance properties of the coatings. In addition, the reduction in micro-cracks revealed the improvement in scratch resistance properties of the coatings due to the incorporated SiC nanoparticles into the Ni–W alloy matrix.

Effect of Heat Treatment on Microstructure of Al4Cu-SiC Composites Consolidated by Powder Metallurgy Technique

Silicon carbide particles-reinforced Al4Cu composites containing 2.5, 5 and 7.5 wt.% of reinforcement were fabricated using powder metallurgy (PM) technique. The sintered Al4Cu-SiC composites were solution treated for 6 h at two different temperatures (495 and 530 °C) and then aged at 180 °C for various aging periods (4, 12 and 24 h). Effects of heat treatment on the microstructural changes and microhardness were investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction and microhardness tests. The results indicate the ceramic particles-reinforced Al4Cu matrix requires different heat treatment parameters compared to the unreinforced alloy. The applied solution temperature did not allow for thorough dissolution of alloy phases in the matrix material produced by PM route. However, in Al4Cu-SiC composites the main strengthening phase (Al2Cu) was uniformly distributed in the matrix. The solid-solution temperature increase affects the reduction in time to reach peak hardness. The highest increment in microhardness by aging treatment was observed for composite with the addition of 5 wt.% of SiC solution treated at 530 °C for 12 h (110 HV0.05).

Cutting Speed and Feed Influence on Surface Microhardness of Dry-Turned UNS A97075-T6 Alloy

In this work, an analysis of the cutting speed and feed influence on surface roughness and microhardness of UNS A97075-T6 alloy, turned under dry conditions, was carried out. The results were compared before and after a corrosion process. The influence of these cutting parameters on each of these variables was analyzed, as well as the possible interrelation between them. The microgeometrical deviations showed a general trend to increase with feed. However, no significant modifications were observed as a function of the cutting speed. This trend was softer after the corrosion process, due to the surface alterations produced by pitting corrosion, which resulted in higher dispersion of the experimental data. In addition, a surface microhardness increment was observed in all samples, after machining and before corrosion, regardless of the cutting parameter values. The experimental results revealed that the mechanical effects, produced by the feed, should not be neglected against the thermal effects, produced by the cutting speed, within the range of the tested cutting speed. Finally, the corrosion process negatively affected the microhardness, but it was not possible to establish a direct relationship between the cutting parameters, surface roughness, and microhardness after a corrosion process.

Electro-work hardening of metals induced by the athermal electromigration effect

Direct current stressing treatment has been proposed as an effective potential method to modify the microstructures and optimize the mechanical properties of metals. Two contributions that could give rise to variations in the microstructure and mechanical properties of metals are involved in the direct current stressing treatment: thermal effects from Joule heat generation and athermal effects from electron-lattice interaction. The present study, for the first time, provides direct evidence of the work hardening behavior of pure Sn metals induced by the athermal electromigration effect, which is referred to the “electro-work hardening.” The micro-hardness of the Sn strip increased for all of the current densities (4–7 × 103 A/cm2) and current stressing times (1 h and 6 h) that were investigated. The maximum micro-hardness increment achieved could be as high as 27.3% at 5 × 103 A/cm2 for 1 h as compared with the as-annealed Sn strip benchmark. The thermal benchmark experiment further evidences that the thermal Joule heating effect did not contribute to any variations in the micro-hardness, suggesting the predominant athermal effect of electromigration. The high-resolution transmission electron microscope lattice images further revealed a high volume of dislocations produced in the Sn matrix, which was responsible for the electro-work hardening behavior. The electro-work hardening mechanism incorporated in a direct current stressing treatment can be applied in metals without the need for macroscopic mechanical deformation pre-treatment, which is regarded as a non-deformation material treatment. This innovative method for inducing work hardening is considered to have great potential for applications in which products have already been shaped.

Study of the aging treatment on selective laser melted maraging 300 steel

The aim of this work was to evaluate the effects of aging treatments, in terms of microstructure and micro-hardness, on 18 Ni 300 Maraging steel samples processed by Selective Laser Melting (SLM) and to compare them with those of the same material made by casting. Optimized process parameters were used to build SLM parts in order to obtain almost full density (above 99%). For aging treatments, following the principles of the Design of Experiments, a full factorial plan with 4 levels of temperature and 6 levels of time was used. Before aging, the microstructure consisted of many overlapping fused/resolidified zones with a dendritic solidification morphology and epitaxial growth of the grains. After aging, the fused/resolidified zones disappeared and the hardening of the material was mainly governed by the mechanism of precipitation. The maximum value of hardness, on selective laser melted samples, was obtained, for a treatment temperature of 480 °C for 10 h: whereas, at the same temperature and after 10 h, on casting sample, it stabilized at 640 HV. Compared to samples produced by casting, SLM samples showed a lower increment in micro hardness at the aging temperature of 440 °C, while for 510 °C and 560 °C, trends were similar.