High Hardness Research Articles

Role of surface grain refinement in AZ31 Mg alloy by shot peening on surface energy, biomineralization and degradation behavior

Grain refinement of magnesium (Mg) alloys to improve their performance as potential candidates for degradable implant applications is a promising strategy in the field of materials engineering. Surface properties play an important role in promoting higher implant tissue interactions which dictate the healing rate of the fractured bone. In the present work, AZ31 Mg alloy was subjected to shot peening by using steel balls of 2 mm diameter. From the microstructural studies carried out at the cross section, fine grain structure was observed up to 50 μm depth from the surface. Grain refinement up to ∼1.5 μm was achieved at the surface of shot peened AZ31. X-ray diffraction analysis confirms the development of non-basal texture at the surface. Increased surface energy was measured by contact angle measurements for the shot peened AZ31. Higher hardness was measured from the surface in the thickness direction of the AZ31 after shot peening. Corrosion behavior assessed by potentiodynamic polarization tests indicated marginally increased corrosion resistance for shot peened AZ31. In vitro bioactivity studies carried out in simulated body fluids demonstrated higher mineral depositions and lower weight loss for the surface grain refined AZ31. The results demonstrate the potential of shot peening to promote higher biomineralization and to control the degradation in improving the performance of biodegradable AZ31 Mg alloy.

Quantitative trait locus mapping and OsFLOq12 identification for rice grain hardness: towards improved rice flour for wheat substitution.

Recent shifts in consumer dietary preferences have led to a significant decline in rice consumption in Korea, resulting in surplus rice production. To address this issue, rice flour has been proposed as a substitute for wheat flour. However, the physical, chemical and structural differences between rice and wheat, particularly in grain hardness, pose challenges in using rice flour as an alternative. Understanding the genetic factors that influence rice grain hardness is crucial for improving the milling process and producing high-quality rice flour suitable for wheat flour substitution. In this study, various grain traits, including length, width, thickness, length-to-width ratio and hardness, were measured in a population of brown and milled rice. Quantitative trait locus (QTL) analysis revealed a significant association between grain hardness and thickness, with QTLs for grain hardness mapped on chromosomes 1 and 12 for brown and milled rice, respectively. A total of 20 candidate genes related to grain hardness were identified through QTL analysis. Among them, OsFLOq12 (LOC_Os12g43550) was identified as a key gene influencing grain hardness, which encodes a Ras small GTPase. Phenotypic analysis showed differences in endosperm appearance and particle size between lines with low and high grain hardness. The genetic analysis of OsFLOq12 revealed a single nucleotide polymorphism associated with grain hardness. This study provides valuable insights into the genetic background of grain hardness, offering a foundation for breeding rice varieties optimized for flour production as a viable substitute for wheat flour. © 2024 Society of Chemical Industry.

Data-driven design of novel lightweight refractory high-entropy alloys with superb hardness and corrosion resistance

AbstractLightweight refractory high-entropy alloys (LW-RHEAs) hold significant potential in the fields of aviation, aerospace, and nuclear energy due to their low density, high strength, high hardness, and corrosion resistance. However, the enormous composition space has severely hindered the development of novel LW-RHEAs with excellent comprehensive performance. In this paper, an machine learning (ML)-based alloy design strategy combined with a multi-objective optimization method was proposed and applied for a rational design of Al-Nb-Ti-V-Zr-Cr-Mo-Hf LW-RHEAs. The quantitative relation of “composition-structure-property” was first established by ML modeling. Then, feature analysis reveals that Cr content greater than 12 at.% is a key criterion for alloys with high corrosion resistance. The phase structure, density, melting point, hardness and corrosion resistance of the alloys were screened layer by layer, and finally, three LW-RHEAs with superb hard and corrosion resistance were successfully designed. Key experimental validation indicates that three target alloys have densities around 6.5 g/cm3, and all alloys are disordered bcc_A2 single-phase with the highest hardness of 593 HV and the largest pitting potential of 2.5 VSCE, which far exceeds all the literature reports. The successful demonstration in this paper clearly demonstrates that the present design strategy driven by the ML technique should be generally applicable to other RHEA systems.

Application of Product of Vitrification of Asbestos-Cement Waste and CRT Glass Cullet as Reinforcing Phase in Surface Composites Produced by FSP Method

In this study, the vitrification of asbestos-cement waste (ACW) and glass cullet from cathode-ray tubes (CRTs) was performed. The resulting product of vitrification from the abovementioned waste was used as the reinforcing phase in a composite with the AA7075 alloy matrix. The composite was made by means of the FSP (friction stir processing) method. The main aim of this work was to determine whether the product of the vitrification can be utilized as the reinforcing phase in the composite. The tests show that introducing the vitrification product into the composite matrix increases both the hardness of the material and its wear resistance. The composite was characterized by a 39% higher hardness and 30.4% higher wear resistance compared to the initial AA7075 alloy. The changes in the properties were caused by strong refinement of the grains, but primarily by the presence of the hard particles of the reinforcing phase in the composite matrix. This research demonstrates that vitrified material, thanks to its properties, can constitute a full-value reinforcing material that can ultimately replace more expensive engineering materials in composites.

Development and Taguchi optimization of HVOF sprayed Al2O3 and ZrO2 blended aluminum coating on 316L SS

Abstract A significant number of gas turbines, aircraft engines, bearings, and automotive engines operating under a wide temperature range fail frequently due to fatigue and surface oxidation. Thus, a new coating formulation 40Al-35Al2O3-25ZrO2 was deposited on 316L SS substrate through the high velocity oxygen-fuel (HVOF) thermal spray coating method. The number of passes, spray distance and oxygen flow rate were varied by using Taguchi L9 array to achieve an optimized coating with higher hardness, less porosity, and roughness. The coating phase analysis, microstructure, elemental composition, microhardness and nano hardness were examined by X-Ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Vickers microhardness and nano indentation testing. The sample 5 prepared at spray distance of 20 cm and oxygen/acetylene ratio of 2 exhibited optimal hardness (1972 HV1), tensile strength (6.463 GPa), porosity (0.75%) and roughness (6.2 µm) due to α-Al2O3 andt-ZrO2 phases. Oxygen flowrate was the influential parameter contributing 48.71% to microhardness and 42.41% to roughness, while spray distance with contribution 51.62% was influential parameter for porosity.

Analysis of the Causes and Control of High Hardenability of Gear Steel 18CrNiMo7-6HL

Analysis of the Causes and Control of High Hardenability of Gear Steel 18CrNiMo7-6HL

Effect of Electrofriction Treatment on Microstructure, Corrosion Resistance and Wear Resistance of Cladding Coatings

In recent years, the issue of increasing the wear resistance of the working bodies of agricultural machinery designed for cutting and breaking the soil has received special attention. The surface layers of working bodies of agricultural machinery during operation are subjected to intensive abrasive wear, which leads to rapid wear of equipment and a reduction in its service life. The induction cladding method using materials such as Sormait-1 is widely used to increase the wear resistance of tool working surfaces. However, after coating, additional heat treatment is required to improve the physical and mechanical properties of the material and increase its durability. In electrofriction technology (EFT) hardening, the surfaces of the parts are subjected to melting under the influence of electric arcs. In this work, three types of surface treatment of L53 steel have been investigated: induction cladding using Sormait-1, electrofriction treatment, and a combination of induction cladding followed by electrofriction treatment. The microstructure was analyzed using optical microscopy and scanning electron microscopy. Erosion and abrasion tests were carried out in accordance with ASTM G65 and ASTM G76-04 international standards to evaluate the wear resistance of the materials under mechanical stress. A dendritic structure was formed after the induction cladding of the Sormait-1 material, but subsequent electrofriction treatment resulted in a reduction of this dendritic structure, which contributed to an increase in the hardness of the material. However, the highest hardness, reaching 965 HV, was recorded after electrofriction treatment of L53 steel. This is explained by needle martensite in the structure, which is formed as a result of quenching. Further, the influence of structural characteristics and hardness on erosion and abrasion wear resistance was examined. The analysis showed that the material microstructure and hardness have a decisive influence on the improvement of wear resistance, especially under conditions of intensive erosion and abrasive friction.

Stainless Steel Deposits on an Aluminum Support Used in the Construction of Packaging and Food Transport Containers

A series of chemical elements from the chemical composition of the packs of liquid food products migrate inside them or they combine with other chemical elements existing in the food, resulting in chemical compounds that worsen the quality of the food. In the present paper, layers of food stainless steel were deposited using thermal arc spraying on an aluminum alloy substrate to stop the migration of aluminum ions inside liquid food products. The physical-chemical and mechanical properties of the protection system: stainless steel layer used in the food industry (suggestively called: food-grade stainless steel)—aluminum substrate were investigated, and then the organoleptic properties of the food liquids that came into contact with the deposit were evaluated. It was found that food-gradestainless steel deposits have low porosity (3.8%) and relatively high adhesion and hardness, which allows complete isolation of the substrate material. The investigations carried out on the properties of food liquids that come into contact with the stainless steel deposit revealed the fact that it perfectly seals the aluminum start. The food-grade stainless steel coating (80T) was much better and safer for preserving dairy products maintaining a constant acidity up to 17 degrees Thorner, wines (with an average acidity of 3.5–4 degrees), juices (with natural pigments), and oils (with a good absorbance level correlated with clarity). This aspect suggests that the created system can be successfully used to manufacture containers for the transport of liquid products.

Investigation of Electrochemical Discharge Machining for Tungsten Carbide: Effects of Electrolyte Composition on Material Removal Rate and Surface Quality

Abstract Tungsten carbide (WC-Co) with a cobalt binder has been widely used in industrial application. Through their high wear resistance and hardness, which make it a challenge to machine. Electrochemical discharge machining (ECDM) is a newly developed hybrid technique used to machine conductive and nonconductive materials. Tungsten carbide machining is an area that needs more investigation. In this study, different types of electrolytes have been tested in the electrochemical machining of tungsten carbide. It has been concluded that tungsten carbide was successfully machined with electrolytes that were either neutral salts or a combination of neutral salts and hydroxides, the highest material removal rate achieved was (0.09250 g/min), and the average surface roughness achieved in this work was measured at (Ra 0.9275 µm). However, deposition took place on the surface of machined tungsten carbide when the samples were treated with sodium hydroxide and potassium hydroxide. EDX analysis of successfully machined tungsten carbide samples reveal the presence of carbon (C) due to diffusion from the base material and oxygen (O), most likely due to oxidation brought on by the high temperatures utilized. Scanning electron microscopy confirmed that the machined surfaces had craters, pores, restricted microcracks, and re-deposited melt particles, among other things.

Influence of Cu and Co addition on metallurgical and wear characteristics of AlCrFeNi high entropy alloy

The creation of new alloys with improved qualities has become essential in modern industries for high-performance materials. This work’s main objective is to use vacuum arc melting (VAM) to synthesize two different high-entropy alloys (HEAs): AlCrFeNiCu and AlCrFeNiCo. The mechanical properties, phase composition, grain boundaries, and alloy composition of the HEAs were studied. The predominant crystal structure, the Body-Centred Cubic (BCC) phase was obtained for both alloys. Significantly, the Co-containing HEA showed a smaller particle size than the Cu-containing HEA, which led to a 14.21% increase in microhardness. It indicates that the Co-based HEA will likely perform better than the Cu-based HEA in applications prone to abrasion, and indentation, and requiring high hardness levels based on the observed microstructure and hardness parameters. According to wear surface morphology studies, main effects analysis and ANOVA show that increasing loads and sliding distances increase wear rate, whereas sliding velocity has less effect. The best wear rate-reducing parameters are 10 N, 0.5 m/s, and 500 m for Cu-containing HEAs, and the same can be predicted using regression analysis. The study categorizes the intricate worn surface structure by describing different surface properties and wear mechanisms, such as grooves, delamination, adhesive wear, and pitting.

Scratch-Induced Wear Behavior of Multi-Component Ultra-High-Temperature Ceramics

Multi-component ultra-high-temperature ceramics (MC-UHTCs) are promising for high-temperature applications due to exceptional thermo-mechanical properties, yet their wear characteristics remain unexplored. Herein, the wear behavior of binary (Ta, Nb)C, ternary (Ta, Nb, Hf)C, and quaternary (Ta, Nb, Hf, Ti)C UHTCs synthesized via spark plasma sintering (SPS) is investigated. Gradual addition of equimolar UHTC components improves the wear resistance of MC-UHTCs, respectively, by ~29% in ternary UHTCs and ~49% in quaternary UHTCs when compared to binary UHTCs. Similarly, the penetration depth decreased from 115.14 mm in binary UHTCs to 73.48 mm in ternary UHTCs and 44.41 mm in quaternary UHTCs. This has been attributed to the complete solid solutioning, near-full densification and higher hardness (~up to 30%) in quaternary UHTCs. Analysis of the worn-out surface suggests pull-out, radial, and edge micro-cracking and delamination as the dominant wear mechanisms in binary and ternary UHTCs. However, grain deformation and minor delamination are the dominant wear mechanisms in quaternary UHTCs. This study underscores the potential of MC-UHTCs for tribological applications where material experiences removal and inelastic deformation under high mechanical loading.

Structure and properties of the boride layer of steel using the plasma alloying method

Boration is one of the promising methods for increasing surface hardness and wear resistance, resistance to oxidation and corrosion of mechanical engineering parts. The diffusion saturation process is characterized by a long duration, as well as a shallow depth of the hardened layer. The use of concentrated heating sources can solve these problems. Among the methods of high-energy exposure, the technology of plasma surface alloying should be highlighted. In this paper, the study of the microstructure and properties of the boride layer obtained on steel by plasma alloying is carried out. It is noted that the boron-doped layer has a heterogeneous structure and high hardness. It is noted that the layer obtained after alloying with a current of 120 A has the highest microhardness value and amounts to 859–1265 HV. With an increase in current to 140 A, the microhardness of the alloyed layer decreases and amounts to 761–1048 HV. Increasing the current to 160 A leads to a significant decrease in the microhardness of the surface layer and it is 452–747 HV. It is known that the volume of iron boride fractions determines the degree of hardening of the steel surface. An increase in the plasma arc current leads to a decrease in the proportion of primary borides in the surface layer after alloying, and therefore leads to a decrease in microhardness. The alloyed layer has characteristic zones: hypereutectic, eutectic and hypoeutectic. An increase in current leads to a significant change in the microstructure of the surface layer and a decrease in the microhardness of the alloyed layer. The surface layer after plasma alloying with a current of 120 A has the highest microhardness (1265 HV). It has been established that it is possible to obtain a boride layer using the technology of plasma surface doping with boron. After processing, the alloyed layer is characterized by a heterogeneous structure and has high hardness.

Structural nature of pyroelectric effect revisited: Experimental and theoretical studies of synthetic Ni,Al - rich tourmaline

Tourmaline, the first pyroelectric material discovered, is also a promising borosilicate material with non-linear optical and luminescence properties, high thermal stability, high hardness and variable chemical composition. The structural nature of pyroelectricity in tourmaline is a subject of scientific debate since it requires precise structural studies and measurements at elevated temperatures. Here, an in situ high temperature single-crystal and powder X-ray diffraction studies (up to ∼1000 °C) and the direct pyroelectric measurements (up to ∼200 °C) of synthetic Ni, Al-rich tourmaline were performed. The pyroelectric coefficient was calculated from the structural data. The results demonstrate that polyhedra XO9, YO6 and ZO6 exert the greatest influence on the pyroelectric effect. The pyroelectric coefficient of tourmaline is practically independent of boron-oxygen triangles and silicon-oxygen tetrahedra. The primary pyroelectric coefficient of tourmalines could be calculated from single crystal structural data. This study contributes to the synthesis of tourmalines with the required pyroelectric properties and may be used for the study of the nature and properties of other pyroelectric materials.

Formation of requirements for impact resistance and wear resistance of grinding balls

The article presents the results of a study of the operation processes of steel grinding balls in semi-autogenous grinding mills (SAG). It was determined that the balls experience both abrasive and impact loads. The properties of steel grinding balls with the same production technology are determined by the chemical composition and the formed microstructure over the entire cross-section of the ball. Balls made using 3 different technologies were studied. The balls of sets 1 and 2 show high hardness values at the surface, sufficient to ensure good resistance to wear during operation, and a sharp decrease in hardness at a distance of ~(15–20) mm from the surface as the volume of pearlite structures increases. At the same time, the balls of the 1st and 2nd sets showed low values of impact strength and insufficient resistance to impact. The lowest hardness values from the surface to the center were observed for set 3. Also, the highest mass loss during the abrasive wear test was recorded for set 3, which is explained by the lowest hardness values. The balls of set 3 showed higher values of impact strength and no splitting during the ball-on-ball test, which is explained by the soft ferrite-pearlite structure both on the surface and across the cross section of the ball, due to the reduced carbon content and the presence of nickel in the chemical composition. At the same time, the balls from set 3 showed the worst result in terms of abrasive wear. In the course of the conducted research, it was established that for successful operation in SAG, steel grinding balls must have a surface with high hardness due to the martensitic structure and a viscous core with a ferrite-pearlite structure. A promising direction in the development of technology for the production of steel grinding balls will be to obtain a steel ball microstructure that decreases uniformly from the surface to the center, which will allow maintaining high wear resistance and increasing the resistance to ball splitting

Development of significantly hard hypereutectoid plain carbon steel through incomplete austenitization based cyclic quenching treatment

AbstractIn this investigation hot rolled steel bars of 1.24 weight % carbon steel are subjected to incomplete austenitization based cyclic quenching treatment. Each cycle consists of inserting the specimen in an electric resistance furnace at a temperature of 894 °C and holding for a short duration (6 minutes), followed by oil quenching to the room temperature. Such a typical thermal cycling results in the evolution of a novel microstructure that comprises of large clusters and blocks of cementite in a matrix of martensite after 3 and 4 cycles. Accordingly, a significantly high hardness (7.13 GPa) is achieved on execution of 3 cycles which envisages a new pathway of incomplete austenitization based cyclic quenching treatment for development of new‐generation plain carbon hypereutectoid tool steel.

Measuring the radiation hardness of terahertz devices for space applications

The application of terahertz technology in space is frontier for the development of 6G technologies. Terahertz transceiver devices based on gallium arsenide Schottky barrier diodes (GaAs SBDs) have the characteristics of small size, light weight and low power consumption, making them suitable for application on spacecraft. However, there is currently a lack of experimental assessments on their space adaptability. Here, we study the radiation hardness of terahertz devices to determine their adaptability in complex space environments. We exposed GaAs SBDs and terahertz multipliers as typical terahertz devices to gamma rays and protons. The experimental results showed that the terahertz devices exhibited good tolerance to protons, but prolonged exposure to gamma rays could significantly increase the leakage current of the GaAs SBDs and alter its C-V characteristics, leading to the failure of the terahertz multiplier. Nevertheless, the terahertz devices maintained a good level of radiation hardness, making them highly suitable for use in Low Earth Orbit (LEO) satellites. The comparison between the results of proton and gamma ray tests indicated that the terahertz devices exhibited high inherent radiation hardness against displacement damage but were more sensitive to ionization damage, requiring higher shielding requirements.

A Parametric Study on the Stability, Geometry and Hardness of AISI 308LSi WAAM-GMAW

Wire arc additive manufacturing (WAAM) has been established to be an efficient and cost-effective additive manufacturing technique for fabricating functional metallic parts from scratch. However, there is need to determine optimal processing condition for each material system to produce high-quality parts. In this work, a parametric study of WAAM of AISI 308LSi was performed to determine the processing condition(s) at which single tracks of high dimensional accuracy, excellent geometry, no visible crack and pore, and high hardness required for high-quality multi-track deposition can be achieved. The track geometries were investigated using a combination of optical microscopy and image processing software. The microstructure and hardness of the deposited single tracks were examined using optical microscopy and Vickers hardness tester respectively. A process map predicting the process stability of WAAM of AISI 308LSi was developed within a process window. Continuous single tracks of high dimensional accuracy were produced from a stable deposition process. The process becomes unstable whenever the wire deposition volume per unit length of track is in excess of the available heat energy per unit length of track. The wire feed rate and traverse speed significantly influence the stability and geometry of the single tracks. The processing conditions at which single tracks of low wetting angle (<90◦), high aspect ratio (>1.5), high surface quality, and high hardness (close to the as-received material) can be deposited were determined. These processing conditions were considered suitable for the fabrication, surface modification and repair of functional engineering parts made of 308LSi stainless steel.

Material characterization of forged bronzes from ancient China (c. 11th-2nd century BCE) reveals development of the non-mainstream metalworking technique in Chinese bronze production

Although ceramic piece-mould casting was the dominant metalworking technique in the Chinese Bronze Age (c. 2100-221 BCE), the forging technique was also employed by craftsmen to pursue lightweight bronzes with thin walls and high hardness. However, compared to the ceramic piece-mould casting technique, research on forging technology is relatively limited. In this research, 48 sheet metal fragments of Chinese bronzes from different regions and periods (from the Zhou to Han dynasties) across China were analyzed by metallography, SEM-EDS, and hardness testing. The results show that craftsmen had a profound understanding of copper alloy properties and were able to produce thin-walled, functional artifacts by forging cast blanks with appropriate alloy compositions. With the development of forging technology and political changes, the types of forged thin-walled bronzes became more diverse, and their consumers expanded from the elite to civilians. This study not only reveals the material characterization of forged bronzes, but also elucidates the historical trajectories of forging technology and the multifaceted interplay between cultural influence, aesthetic pursuits and technological advancement in the development of forging techniques in ancient China.

Analysis of the influence of different drying processes on the quality attributes of orange peel

The present research aimed to assess the effect of different drying processes on kinetics, antioxidant content and activity, texture, colour, morphology, and β-carotene content of orange peel (OP). The utilization of microwave drying resulted in a notable increase in the rate of evaporation of water present in the orange peel. This process facilitated the release of bound polyphenols. The OP dried at 600 W exhibited the highest total phenolic compound (24.65 mg GAE/g) and total flavonoid compound (11.73 mg QE/g), as observed in the recorded data. The total antioxidant value exhibited a decrease at both elevated and reduced levels of microwave power compared to raw OP. The study found that the drying model proposed by the Weibull model exhibited the most optimal fit, as evidenced by a low SSerror (1.6 × 10−3-16.12 × 10−3), RMSE (0.02–0.05) and high R2 (0.99–1.00). Among dried products, high hardness (30.92 ± 1.26 N), fracturability (28.31 ± 1.22 N), and lightness (74.01 ± 0.38) were observed in freeze-dried (FD) OP. The browning index was high in microwave drying at 180 W (MWD 180 W), and tray drying (TD) which also produced more vibrant colours, as observed in their high chroma value. The high performance liquid chromatography (HPLC) showed that the retention of β-carotene was observed highest in FD (0.057 ± 0.003 mg/g) and lowest in TD (0.032 ± 0.002 mg/g). The morphological study revealed small-sized particles in high-temperature drying methods (MWD 900 W and TD). Large pores and frequent cracking were observed in microwave drying compared to FD. Four clusters are formed in Principal component analysis (PCA) loading of Fourier transform infrared (FTIR) spectra based on their similar characteristics as found in FTIR. Antioxidant content and texture are closely related to the chemical moieties, as observed in PCA.

Surface defect detection model of laser cutting polycrystalline cubic boron nitride tool based on asymptotic fusion strategy

Due to the polycrystalline cubic boron nitride tool has the characteristics of high hardness, brittleness, etc., it is easy to break the tool or produce defects in the laser cutting process, which affects the cutting performance of the tool. Traditional defect detection methods can no longer meet the needs of modern manufacturing. Aiming at the problems of low accuracy and poor real-time detection of surface defects on laser-cutting polycrystalline cubic boron nitride tools, this study proposes the surface defect detection model of laser cutting polycrystalline cubic boron nitride tool based on asymptotic fusion strategy, which fills the gap in the field. In the backbone network, the C3SE module is constructed by modeling the correlation between feature channels to improve the model’s focus on key features in order to enhance the feature extraction and processing capability of the backbone network; In the neck network, adaptive spatial fusion operation and direct interaction of non-adjacent layers are utilized for multi-scale information fusion, and the asymptotic feature pyramid network for object detection (AFPN) is used instead of the FPN structure to improve the detection performance; In the head network, a soft suppression mechanism is introduced to reduce the overlapping frame score using a decay function, thus improving the detection accuracy. The experimental results based on the self-constructed laser-cutting polycrystalline cubic boron nitride tool surface defects dataset show that the average accuracy of the AFFS-YOLO model is improved by 5.6% compared with that of the YOLOv5 model, reaching 86.1%, and the detection effect is better than that of the original network and other classical target detection networks.