High Hardness Research Articles

Study on fabrication of multi-phase reinforcement coatings on Ti6Al4V by laser cladding for enhanced tribological performance

In order to improve the wear resistance, the multi-phase reinforcements coating with high hardness were fabricated on the surface of Ti6Al4V by laser cladding. In this study, Cr3C2 and Ti6Al4V powders, along with continuous fiber laser cladding in a protective gas of N2 atmosphere, were used to prepare a stepwise-solidifying-point multiphase composite coating (TiC, TiN, and CrN) on the surface of Ti6Al4V. The results showed that the crack-free coating with a coating depth of 1.24 mm and a maximum hardness of 1155.52 HV can be prepared on laser power of 900 W. As the laser power increases from 900 W to 1400 W, the combined effect of the soft α-Ti phase and the in-situ synthesized hard TiN phase on hardness results in a decrease in the maximum surface hardness at 1400 `W. And the surface hardness of Ti6Al4V after laser cladding increased by 2.80–2.68 times, and the wear rate decreased by 0.74–0.86 times. Due to the soft phase α-Ti and in-situ synthesized TiC-TiN secondary dendrites serve as the hard phase, which also serve as the supporting skeleton of the oxide film, and the coatings is enriched with TiO2 oxide film. Additionally, the wear mechanisms of Ti6Al4V include abrasive wear, adhesive wear, and oxidation wear. In contrast, the coatings primarily exhibit abrasive wear and oxidation wear.

ANALYSIS OF THE QUALITY OF THE RESTORED GEAR TOOTH OF LARGE-MODULE GEARS

This study examines the quality of a gear tooth surface fragment restored through electric arc welding. Visual inspection revealed a defect-free, dense surface. Macrostructure examination displayed uniformity and absence of cracks in the metal sample. The high hardness (HRC-36.61) of the weld deposit is crucial for wear resistance, while the base metal, with lower hardness (HRC-29.09), ensures ductility and impact toughness. Martensitic and residual austenitic structures in the weld deposit indicate deformation-resistant properties, with austenite providing good ductility and martensite contributing to high hardness and strength, making the material resistant to wear and deformation under dynamic loads. Thin lens-like martensitic plates and a reed-like structure suggest unique formation characteristics during electroslag welding’s oxidizing-reducing reactions. Microstructure analysis revealed a finer structure in the weld deposit compared to the base metal. The base metal exhibited a ferrite-pearlite structure typical of many steels, unchanged after welding. The weld deposit showed elevated carbon (0.70 %) and manganese (1.38 %) concentrations, typical for weld deposits, influencing mechanical properties. Elements like manganese and molybdenum enhance wear resistance, while the presence of chromium (0.42 %) and nickel (0.12 %) improves corrosion resistance, crucial in aggressive environments. Keywords: large-module gears, tooth wear, electro slag surfacing, hardness, analysis

Microstructure and mechanical properties of butt-welded Ti/steel bimetallic sheet using various multi-principal filler wires

Ti/steel bimetallic sheets have attracted significant attention in various engineering fields. However, achieving high-quality welded joints of Ti/steel bimetallic sheet presents difficulties because of poor metallurgical compatibility and different thermal expansion coefficients between titanium and steel. In this study, four types of multi-principal filler wires with varying contents of Cu, Ni, and Ti elements were designed and manufactured to finish the welding of TA2/Q235 bimetallic sheets. The study investigated the effects of various filler wires on the hardness, tensile strength, corrosion resistance, and microstructure of the welded joints. An interesting finding is that the highest tensile strength of 327±6 MPa was achieved in the welded joint using FeCoNi2Ti0.5 filler wire, with a joint coefficient of ∼79.1 %. The highest hardness in the weld zones was achieved by using FeCoNiTi0.5 filler wire, while the lowest hardness was achieved using FeCoNiCu0.5 filler wire. Dendrite (DR), interdendritic (ID), and eutectic structures were consistently observed in these weld zones. The phases of the DR and ID were identified as Fe2Ti and FCC structures based on EBSD data. A high content of Ni in filler wires could reduce the size and content of the Fe2Ti phase in the weld zones of Ti/steel bimetallic sheets.

SYNTHESIZING OF AN ALUMINUM ALLOY RICH IN IRON AND SILICON BY SURFACING WITH A CONSUMABLE ELECTRODE

Developing lightweight, high-strength materials is an important technological problem of the present decade. However, alloying with expensive elements is mainly used to increase the strength of structural materials. In contrast, aluminum alloys with a specific ratio of silicon and iron show very high mechanical properties. This work aims to develop a technology for synthesizing an aluminium-based alloy with a high content of iron and silicon, consisting mainly of intermetallic phases and having high strength and hardness. The additive technology method of surfacing with a consumable electrode produced the alloy. The ratio of the initial components, meticulously determined, led to the precise chemical composition of the alloy. As a result of the synthesis, an ingot with a uniform microstructure and insignificant porosity, a testament to the careful process, was obtained. At room temperature, the alloy has a phase composition of 42.6% β-phase, 43.4% θ-phase and 13.5% FCC-phase. Phases β and θ are large particles between which the FCC aluminum phase is located. The hardness of the intermetallic β/θ is 450.8±5 HV1, FCC aluminum has a hardness of 92.5 HV1. This research has the potential to inspire further developments in materials science and engineering.

COMPARATIVE EVALUATION OF HARDNESS AND SURFACE ROUGHNESS AFTER DIFFERENT COOLING PROCEDURES OF HEAT CURE DENTURE BASE MATERIALS

Aim: To evaluate the influence of different cooling procedures on mechanical properties of DPI & LUCITONE heat cure poly methyl methacrylate denturebase materials before andafter 1year of brushing simulation. Materials And Methods: A total of 100 specimens were prepared using two heat cure denture base materials i.e, DPI and LUCITONE. The specimens in each group were subdivided into five groups (n=10 ) based on the cooling procedure followed: A: Flask remains in water bath till room temperature B: Remove flask from water bath, bench cool for 30min and then cool under running water for 15min C: Remove flask from water bath, bench cool for 10min and then cool under running water for 15min D: Remove flask from water bath and bench cool till room temperature E: Remove the flask from water bath and cool under running water for 15 minutes.After finishing and polishing, samples were placed in a brushing machine to simulate one year of mechanical cleansing. The specimens were tested for surface roughness with profilometer and hardness with Vickers hardness tester before and after brushing. Results were statistically analysed by two and one- way Analysis of variance (ANOVA) plus Tukey post hoc tests. Results: Specimens with type C(Remove flask from water bath, bench cool for 10min and then cool under running water for 15min)cooling procedures have high hardness values, among whichLucitone showed better properties. Surface roughness did not show significant changes among different groups. Brushing did not significantly affect surface roughness and hardness of denture base materials. Conclusion: Two of the treatments tested, Treatment C: bench-cooling for 10 min and cooling under running water for 15min and Treatment A: cooling in water-bath till room temperature provided the highest hardness values.

Material removal and damage formation mechanisms induced by periodic indentation during ultrasonic vibration-assisted scratching of SiCf/SiC composites

Fiber-reinforced ceramic matrix composites (CMCs) exhibit high hardness, brittleness, heterogeneity, and anisotropy. This study explores the material removal and damage formation mechanisms during ultrasonic vibration-assisted scratching of SiCf/SiC composites through experimental and micro-finite element simulations. The research reveals that high-frequency periodic indentation-separation of abrasive grain influences stress transfer and crack propagation, which are affected by the interfacial layer and fiber orientation. Crack deflection plays a crucial role in material removal and determines the amplitude of normal scratching force. Stress transfer interference primarily governs damage formation, with more severe damage occurring along the longitudinal and transverse fiber directions due to secondary stress concentration and crack deflection. In contrast, scratching along the perpendicular fiber direction requires higher normal forces due to residual adjacent phase materials, but results in more controlled material removal and less damage. The study provides insights into optimizing the ultrasonic vibration-assisted machining of CMCs to minimize damage.

Piezoelectric Ultrasonic Local Resonant Ultra-Precision Grinding for Hard-Brittle Materials.

Hard-brittle materials are widely used in the optics, electronics, and aviation industries, but their high hardness and brittleness make it challenging for traditional processing methods to achieve high efficiency and superior surface quality. This study aims to investigate the application of ultrasonic local resonant grinding to sapphire to improve the efficiency and meet the requirements for the optical window in the surface roughness of the material. The resonant frequency of a piezoelectric ultrasonic vibration system and the vibration amplitude of a grinding head's working face were simulated and tested, respectively. The results of ultrasonic grinding experiments showed that the local resonant system reduced the surface roughness parameter (Ra) of sapphire to 14 nm and improved its surface flatness to 44.2 nm, thus meeting the requirements for the ultra-precision grinding of sapphire. Compared with a conventional resonant system, the surface roughness of the sapphire ground with the local resonant system was reduced by 90.79%, its surface flatness was improved by 81.58%, and the material removal rate was increased by 31.35%. These experimental results showed that ultrasonic local resonant grinding has better effects than those of conventional ultrasonic grinding in improving surface quality and increasing the material removal rate.

Hardness and Corrosion Behavior of CrMnFeCoNi Alloy Fabricated by Ball Milling and Spark Plasma Sintering.

The mechanical properties and electrochemical stability of high-entropy alloys are substantially affected by their composition distribution and crystal structure. However, the details concerning the conditions of milling and sintering for sintered alloys have rarely been reported. In this work, a series of CrMnFeCoNi alloys were fabricated by ball milling and spark plasm sintering for different periods. Their crystal structure, density, hardness, and corrosion resistance were investigated. As a result, a partial alloying of Cr, Mn, Fe, Co, and Ni was achieved by ball milling. However, Cr-rich particles, including Mn, were formed in the milled powders. The sintered alloys inherited the Cr-rich particles to form Cr-rich zones. The formation and change of chromium carbide were also confirmed in sintered alloys. Extended milling or sintering to 12 h achieved high hardness and corrosion resistance for the sintered alloys. The Cr-rich zones showed high hardness and Kelvin potential, which affect both the hardness and the corrosion resistance.

An investigation of Ti addition to optimize the tribological properties of TiCrNbTaW refractory high-entropy alloy

Many refractory high-entropy alloys (RHEAs) with high melting points suffer from severe wear-fracture failures due to compositional segregation, which is a key factor limiting their widespread application as structural parts. In this work, two novel TixCrNbTaW (x = 1 and 1.5) RHEAs were prepared using composition modulation and liquid phase assisted sintering strategies. The results showed that the further addition of Ti enhanced the strength, toughness and microstructural homogeneity of the RHEAs, which effectively suppressed the wear-fracture behavior. In addition, the dense oxidized amorphous layer formed in-situ has higher hardness than the matrix, which can provide additional load-bearing capacity. The synergistic effect of the above factors promotes the wear rate of Ti1.5 alloy to be as low as 2.9 × 10−5 mm3/(N·m). The present work provides some insights into the design of high anti-wear RHEAs.

Rapid carburizing of low-alloy steel by atmospheric-controlled induction-heating fine-particle peening and investigation of its fatigue properties

Atmospheric-controlled induction-heating fine-particle peening (AIH-FPP) was applied to low-alloy, low-carbon steel AISI 4120 to achieve rapid carburizing within minutes and enhance fatigue strength. The shot particles used during AIH-FPP were specifically created by mechanically milling a mixture of steel particles and carbon powders. The specimens were analyzed using laser microscopy, optical microscopy, X-ray diffraction for residual stress measurement, a micro-Vickers hardness tester, and an electron probe micro-analyzer. Axial fatigue tests and fracture surface analyses via scanning electron microscopy and energy-dispersive X-ray spectroscopy were also conducted. AIH-FPP effectively transferred carbon to the treated surface and facilitated its diffusion in a short period, creating a martensite layer with high hardness and compressive residual stress, which resulted in increased fatigue strength. The fatigue strength of the AIH-FPP-treated specimens was influenced by the conditions of reheating and quenching, which altered the prior austenitic grain size and stress concentration at the specimen surface. Notably, specimens treated with AIH-FPP followed by reheating and water-injection quenching exhibited fatigue strength comparable to that of conventional gas-carburized specimens, owing to the formation of a carburized layer with a small prior austenite grain size.

Grinding of C/SiC ceramic matrix composites: Influence of grinding parameters on tool wear

C/SiC Ceramic Matrix Composites (CMCs) have been identified as a key material for improving high-speed braking systems and aerospace components as they offer low density, and high specific strength at high temperatures. Grinding is often used for the machining stage due to the high hardness, heterogeneity, and brittle nature of CMSs. Previous studies have explored the effect of grinding parameters, but most of them do not indicate whether they have used the same grinding wheel for all tests. In fact, there is limited understanding of how wear impacts process performance over the grinding wheel's lifespan. In this work, the effect of grinding wheel wear on cutting forces is addressed and grinding wheel topography is analyzed with the objective of identifying a parameter that allows to quantify grinding wheel wear in a non-destructive way. Results have shown that, after a short conditioning stage, cutting forces increase approximately linearly with the machined length. For the machining conditions analyzed, normal forces increase 200 % in the first machined meter (first stage), then rise 17 % per meter thereafter (second stage). Tangential forces rise 300 % in first meter and then climb 27 % per meter subsequently. In this second stage, force ratio approaches a constant value and the generation of flat surfaces on the diamond grains is the dominating wear mechanism. Under such conditions, 3D surface roughness parameters Sa, Sq, Spk and Sku have been proven to be useful for monitoring wheel wear.

Mechanism of high content Mn & Ni synchronous stable solidification in Fe-spinel glass-ceramics from battery slag

New-energy industry produce large amount of emerging high-speed battery jarosite slag, containing Mn and Ni, which is large in quantity and harmful. Harmless treatment is in urgent need. We research on the curing mechanism of heavy metals migration and transformation during phase via iron clusters transformation in glass-ceramics. Based on first-principles and density functional theory, regulating electronic structure of Mn2+ and Ni2+ by Cr3+. After clarifying the interaction among curing compatibility, capacity and stability, the structure-activity relationship among electronic & molecular structure and leaching concentration of heavy metals was established. The results show that CaNiSi2O6 is difficult to cure Ni2+, the formation of iron clusters promotes the conversion of multiphase to Fe-Spinel A; Mn2+, Ni2+ went into the octahedron in Fe-Spinel A cannot be stabilized; Cr3+ promotes migration of Mn2+, Ni2+ into the tetrahedral, turning Fe-Spinel A into Fe-Spinel B, improves curing compatibility of Mn2+, Ni2+; Cr3+ also adjust the bond structure, which enhances solid solution attraction to Mn2+ and Ni2+, and capacity of Mn2+ and Ni2+ increases from 19%, 30%–147%, 195%; improving compatibility and capacity of Fe-Spinel reduces leaching concentration of Mn2+ and Ni2+ from 1.32, 0.51 mg/L to 0.48, 0.03 mg/L. This work realizes the harmless disposal of recycling Mn- and Ni-rich battery slag. The solidified body can also be reused as eco-friendly resource.

Developing novel Ti-Nb-Zr-Mo-Sn-O biomedical titanium alloys with high strength and low modulus through high-throughput experiments

Biomedical titanium alloys have been widely used as surgical implant materials, but traditional biomedical titanium alloys no longer meet practical needs, and there is an urgent need to develop new biomedical titanium alloys. In this study, the composition, microstructure, and mechanical properties of novel Ti-xNb-yZr-5Mo-6Sn-0.6O biomedical titanium alloys were investigated based on diffusion multiple high-throughput experiments. The results showed that although the microstructure of the alloys transitioned from β + α″ to β phase with the increase of Nb and Zr content, the β-stabilizing effect of Zr is weaker. The microhardness and elastic modulus of the alloys varied in the range of 2.7∼7.8GPa and 74.3∼130.2GPa, and depended strongly on the Nb content. In the Ti-xNb-yZr-5Mo-6Sn-0.6O system alloy, the Ti-7.8Nb-1.7Zr-5Mo-6Sn-0.6O alloy with the high hardness of 5.5 GPa and low elastic modulus of 74.3 GPa is a promising candidate for orthopedic implants. Moreover, this work indicates that high-throughput experiments are an effective method for rapidly developing high-performance biomedical titanium alloys.

Electrodialysis reversal (EDR) technology: a viable solution for addressing water quality challenges in the dry zone, Sri Lanka

ABSTRACT Chronic Kidney Disease of Unknown Etiology (CKDu) affects rural Sri Lankan agricultural populations, with poor-quality ground and surface water suspected as the root cause. Hence, we conducted this study to explore the effectiveness of Electrodialysis Reversal (EDR) technology in treating water quality issues related to CKDu in dry zone of Sri Lanka. The EDR plant in Kahatagasdigiliya, Anuradhapura district, managed by the National Water Supply and Drainage Board (NWS&DB) was selected. We measured both physical (colour, turbidity, pH) and chemical (electrical conductivity, total dissolved solids, chloride, alkalinity, hardness, nitrate, nitrite, sulfate, fluoride, total phosphate, iron, manganese) parameters of the EDR process. The parameters of the permeate stage of the EDR plant were validated by comparison with data from SLS 614:2013, and removal efficiencies were assessed. The results revealed that all parameters consistently fell within the permissible limits in the permeate stage of the EDR plant. Turbidity (62.65%), sulfate and manganese (50%), colour (47.37%), fluoride (44.19%), and hardness (35.71%) showed high removal efficiencies in the EDR process. The study demonstrated the effectiveness of EDR technology in addressing water quality challenges, validating its potential for groundwater treatment and this contributes to the improvement of groundwater quality in CKDu-prevalent areas.

Pengaruh Variasi Bahan Aditif Pada Base Quench Medium dan Holding Time Tempering Terhadap Sifat Mekanik Material Roda Gigi

Gears are one of the most important components in various machine systems, and in their use, the gears rub and press against each other with other components, so they often experience wear on their surfaces. Therefore, to overcome these problems, the gear material is given a hardening and tempering heat treatment to improve its mechanical properties. The purpose of this study was to determine the effect of variations in cooling media in the quenching process and tempering holding time on the hardness value and impact strength of S45C steel. The method used is S45C steel heated at 950°C for 35 minutes, then cooled using water + 0.12% activated carbon, a 5% NaCl solution, and SAE 15 W 40 oil + 0.12% activated carbon. After that, it was tempered at 260 °C for 15 minutes, 25 minutes, and 35 minutes. Then a hardness test was carried out to determine the hardness value, and an impact test was carried out to determine the toughness value. From the results of the study, it was found that the optimum parameters for overcoming wear problems on gears were using water + 0.12% activated carbon cooling media and a tempering holding time of 15 minutes. From these optimum parameters, it produces a high hardness value of 36.3 HRC and an impact price of 0.23 J/mm².

Development of Robust Steel Alloys for Laser-Directed Energy Deposition via Analysis of Mechanical Property Sensitivities

To ensure consistent performance of additively manufactured metal parts, it is advantageous to identify alloys that are robust to process variations. This paper investigates the effect of steel alloy composition on mechanical property robustness in laser-directed energy deposition (L-DED). In situ blending of ultra-high-strength low-alloy steel (UHSLA) and pure iron powders produced 10 compositions containing 10–100 wt% UHSLA. Samples were deposited using a novel configuration that enabled rapid collection of hardness data. The Vickers hardness sensitivity of each alloy was evaluated with respect to laser power and interlayer delay time. Yield strength (YS) and ultimate tensile strength (UTS) sensitivities of five select alloys were investigated in a subsequent experiment. Microstructure analysis revealed that cooling rate-driven phase fluctuations between lath martensite and upper bainite were a key factor leading to high hardness sensitivity. By keeping the UHSLA content ≤20% or ≥70%, the microstructure transformed primarily to ferrite or martensite, respectively, which generally corresponded to improved robustness. Above 70% UHSLA, the YS sensitivity remained low while the UTS sensitivity increased. This finding, coupled with the observation of auto-tempered martensite at lower cooling rates, may suggest a strong response of the work hardening capability to auto-tempering at higher alloy contents. This work demonstrates a methodology for incorporating robust design into the development of alloys for additive manufacturing.

Enhancing NiCrBSi coating by the spatial selectivity of in-situ shock wave assisted laser cladding

The composite energy field laser cladding (LC) can improve the mechanical properties of coatings. Based on the spatial selectivity of laser shock, in-situ shock wave assisted LC (in-situ SWALC) was proposed to fabricate NiCrBSi coatings. Firstly, based on the self-developed in-situ SWALC system, four NiCrBSi coatings were prepared on the 16Mn substrate by changing the centre-to-centre distance (CTCD) of two laser spots. Then, the differences of microstructure and element content between LC coating and in-situ SWALC coatings were analyzed. Vickers hardness tester and wear tester were used to compare the influence of CTCD. Finally, based on the theoretical calculation and propagation characteristics of the shock wave, combined with real-time monitoring of the molten pool during the in-situ SWALC process using high-speed imaging, the strengthening mechanism of the in-situ SWALC coatings was revealed. When the CTCD was 0.9 mm, the NiCrBSi coating had the highest hardness and wear properties, which was attributed to the effects of shock wave on the molten pool flow and solidification process. Therefore, the spatial selectivity of in-situ SWALC will play a important role in improving coating performance and energy efficiency, which contributes to the UN Sustainable Development Goal 9 (UN SDG 9).

Hard Copper Boride with Exceptional Conductivity.

Copper and boron seldom engage in reaction at ambient pressure. The few reports on copper-doped boron compounds that exist in the literature often lack definitive stoichiometry. Here, we report successful synthesis of Cu_{2-δ}B_{25} single crystals (δ∼0.03, indicating Cu understoichiometry) via a high-pressure melting method using copper and β-rhombohedral boron as precursors. Crystals thus synthesized are characterized by a tetragonal boron sublattice, within which Cu atoms are either partially or fully situated at different interstices between B_{12} icosahedra. The crystals possess a high Vickers hardness of 26.5GPa and an unusually high electrical conductivity of 1.19×10^{5} S/m-the highest conductivity among the icosahedron-based borides. Hall measurements reveal a notable p-n conduction type transition around 30GPa. This transition, alongside the remarkable conductivity, is potentially modulated by the copper content and its valence states within the structure. The synthesis of Cu_{2-δ}B_{25} not only broadens the spectrum of hard materials but also opens new avenues for innovative modulation of electronic properties in boron-rich compounds, with promising technological implications.

Superconductivity in ZrB12 under High Pressure

Transition metal borides have emerged as pivotal players in various fields. In addition to their exceptional properties such as high hardness, a high melting point, and corrosion resistance, certain compounds exhibit remarkable characteristics including superconductivity, magnetism, electrical conductivity, and catalytic activity. Among these compounds, ZrB12 has garnered significant attention due to its unique physicochemical properties. However, previous research on ZrB12 has predominantly focused on its mechanical behavior while overlooking the electron-electron interactions of the superconducting state. In this paper, resistance characterization of ZrB12 under high-pressure conditions was conducted to further investigate its superconductivity. Our research findings indicate that ZrB12 maintains its superconductivity within a pressure range of 0 to 1.5 GPa and is classified as a type 2 superconductor. Additionally, the results confirm the anisotropic nature of ZrB12’s superconductivity. As the pressure increases, the superconducting transition temperature undergoes a gradual decrease. Remarkably, ZrB12 exhibits metallic behavior under pressures up to 31.4 GPa. The observed decline in superconductivity in ZrB12 can be ascribed to the intensified influence of Zr’s movement on phonon dispersion, ultimately leading to a reduction in carrier concentration.

Sustainable engineering polymer composites fabricated using delignified bamboo fiber as reinforcement and walnut shell powder as filler

Developing sustainable engineering materials using renewable resources and agro-wastes represents an effective method for reducing carbon emissions and environmental pollution. In this study, a novel approach to fabricating high-performance biomass-based polymer composites was presented. Specifically, partially delignified bamboo fiber (DBF) and walnut shell powder (WSP) were incorporated into the matrix, namely melamine-hexamethylenediamine-urea (MHU) resin which was previously known for its excellent interfacial compatibility. Mechanical property investigations show that the DBF, acting as the reinforcement, provided the hybrid composites with high flexural and tensile strength up to 220 and 120 MPa, respectively, greatly surpassing those of commercial wood-plastic composites, wood-based composites, and natural wood, making them promising structural materials. As the filler, walnut shell powder endowed the composites with high hardness (Shore D > 90) and an appealing mirror-like surface gloss. Owing to the protection provided by the MHU matrix, the composite containing 38 % MHU exhibited outstanding flame retardancy (UL 94-V0 grade), which was further supported by cone calorimeter test (CCT) results. An unexpected and intriguing finding is that the composites exhibited fluorescence under UV irradiation. The rare silvery-grey fluorescence color imparted self-anticounterfeiting property to the composites. This study demonstrated the significant potential of bamboo fiber and walnut shell in the development of sustainable engineering materials.