Papers by Keyword: Hardness

Abstract: This study aims to predict the hardness of electrodeposited Ni-W alloy coatings by combining machine learning methods based on a small dataset, with the goal of streamlining the trial-and-error process and reducing experimental costs. In this study, 11 features comprised of electrolyte compositions and process parameters (including current density, pH value, bath temperature, and agitation) were utilized as input parameters, with coating hardness serving as the target value. Two machine learning models (KNN and Elastic-Net) were employed to predict coating hardness, and hyperparameters were tuned using Randomized-Search CV (CV=5). The results demonstrate that the KNN model exhibits the highest predictive accuracy, with R²=0.942 and RMSE=0.0658. The SHAP method was used to analyze the importance of features and their impact on hardness. It is found that bath temperature, current density, and ammonium chloride concentration have the most significant influence on coating hardness. This study demonstrates how machine learning can enhance electrodeposition to predict coating hardness, offering insights for improving Ni-W alloy coatings in mechanical applications.

Abstract: Advanced high-strength steels (AHSS) have their current applications directed mainly to the automotive industry, where they use modern metallurgical techniques to develop microstructures with retained austenite, which leads to an improvement in the combination of strength and ductility through transformation-induced-plasticity (TRIP). The main priority of the research work will be a detailed examination and optimization of the heat treatment parameters of medium-manganese steels, specifically by the Quenching and Partitioning (Q&P) method and the expansion of experimental data related to the increase of wear resistance of these materials. The issue of the application of medium-manganese high-strength AHSS steels in the field of tribology is currently very relevant. Mid-manganese AHSS steels, which show significant wear resistance, have the potential to replace traditional Hadfield Mn steels that contain 10-14 wt. % manganese. With the help of specifically designed heating and cooling cycles, it is possible to improve their wear resistance through metastable retained austenite, which has significant potential in demanding industrial environments. This scientific study examines the possibilities of increasing the economic efficiency of the production and use of AHSS steels in various industrial areas and at the same time reducing costs compared to expensive wear-resistant steels. A key aspect of the research is the experimental evaluation of heat treatment optimization to maximize resistance to mechanical damage and extend the life of materials in various applications.

Abstract: The production of high-quality and long-lasting products requires the application of materials with specific properties in their production. Therefore, the share of application of materials with high hardness and strength has been increasing recently. This encourages many researchers to focus their development on materials with specific properties. These materials, which are characterized by specific properties, include sintered carbides. Therefore, research was conducted with the aim of obtaining relevant dependencies of the influence of the chemical composition of sintered carbides with a Co binder on their selected mechanical properties. As part of the research, significant dependencies of the influence of the percentage of the Co bonding element in the sintered carbide as well as the grain size on its hardness, flexural strength and fracture toughness were obtained. It was found that with an increasing proportion of the Co bonding element, hardness decreases and at the same time flexural strength and fracture toughness increase. At the same time, with increasing grain size, hardness and flexural strength decrease, while fracture toughness increases. The obtained data also provide suitable data for optimizing the mechanical properties of sintered carbides and drawing complex conclusions in several important contexts.

Abstract: This study investigates the effectiveness of carbon nanotubes (CNTs) in enhancing the surface hardness of mild steel through carburization. CNTs were synthesized via chemical vapor deposition at 700°C using iron nitrate and cobalt nitrate as precursors on CaCO₃ support. Acetylene was used as the carbon source and nitrogen as the inert gas. The as-synthesized CNTs were purified using a one-step nitric acid treatment. Characterization by SEM, TGA, and FTIR revealed CNT diameters of 42-52 nm and improved thermal stability after purification, with TGA showing mass losses of 78% for as-synthesized CNTs and 85% for purified CNTs. Low carbon steel (AISI 1018) samples were carburized with as-synthesized and purified CNTs at austenitic temperatures of 750°C and 800°C for period ranging from 10 to 50 minutes. The carburizing process involved heating at 10°C/minute, followed by a defined number of boost and diffusion steps. Surface hardness was evaluated using a Vickers FM 700 micro-hardness tester, and microstructure was checked with an Olympus SC50 optical microscope. Results show that the use of purified CNTs in the carburization displayed the highest surface hardness of 191.64 ± 4.16 GPa at 800°C for 50 minutes, representing a 32% increase over the untreated substrate (145.188 ± 2.66 GPa). As-synthesized CNTs yielded a hardness value of 177.88 ± 2.35 GPa under the same conditions. At 750°C, the percentage increase in hardness for as-synthesized CNTs and purified CNTs were 10.04% and 15.77%, respectively, compared to the untreated substrate. Higher carburization temperature and longer treatment time consistently increased the surface hardness. The use of purified CNTs resulted in an increase of 6.37% hardness when compared to that of the as-synthesized CNTs at 750°C. Microstructural changes in the steel samples confirmed improved surface hardness with both purified and unpurified CNTs, with purified CNTs showing superior performance. This study therefore provides a platform for the use of CNTs for enhancing surface hardness of steel for various industrial applications requiring enhanced mechanical properties and wear resistance in low carbon steels.

Abstract: This research investigated the magnesium (Mg), silicon (Si) content, and aging temperature's effect on the microstructure and hardness of Al-Mg-Si alloys using Response Surface Methodology (RSM). The study varied Mg content between 0.4% and 1%, Si content from 0.4% to 0.8%, and aging temperatures between 170 °C to 210 °C. The findings revealed that increasing the Mg content from 0.85% to 1% and optimizing aging temperatures between 180 °C and 195 °C significantly improved hardness, primarily due to the enhanced formation of magnesium silicide precipitates (Mg₂Si). In contrast, lower Mg levels of 0.4%, Si content below 0.42%, or aging temperatures lower than 170 °C or higher than 200 °C resulted in reduced hardness. This reduction in hardness is linked to the limited precipitation of Mg₂Si, which diminishes the obstacles to dislocation movement.

Abstract: Sterling silver commonly uses copper as its primary alloying element, which enhances hardness. However, the presence of copper can cause a fire stain—a red spot microstructure—leading to tarnishing issues. This research focuses on reducing the copper content and developing suitable processes to enhance hardness through the use of three different alloy compositions within the AgCu and AgCuZnNi systems: Alloy SA (92.5 wt% Ag - 7.5 wt% Cu), Alloy A (93.5 wt% Ag - 5.01 wt% Cu - 0.79 wt% Zn - 0.70 wt% Ni), and Alloy B (94.5 wt% Ag - 4.24 wt% Cu - 0.63 wt% Zn - 0.63 wt% Ni). Precipitation hardening was measured at temperatures of 250 °C, 350 °C, and 450 °C for various durations ranging from 15 to 180 minutes. The results demonstrated an improvement in hardness, increasing from 60-70 HV to 120-160 HV after the heat treatment, with optimal results achieved for Alloy B at a temperature of 350 °C for one hour. This refined alloy composition presents a viable alternative, offering reduced copper content while maintaining enhanced mechanical strength and long-term durability post-heat treatment. Furthermore, the CIELAB test confirmed that Alloy B exhibits superior tarnish resistance. The composition and optimized process outlined in this research can serve as a guideline for producing sterling silver for commercial applications.

Abstract: The microstructure and growth kinetic of alumina (Al₂O₃)-modified aluminide coating were investigated at 650°C, 680°C, and 700°C for various durations (4, 6, 8, and 10 hours) using the slurry aluminizing process. The heat-treated samples were analyzed through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) to assess microstructural evolution, elemental composition, and phases of the coating. SEM observations revealed a two-layer aluminide coating, comprising an Al-rich intermetallic (FeAl₃) and a Fe-rich intermetallic (FeAl). Microhardness tests showed that FeAl₃ had hardness values ranging from 880 to 990 HV, while FeAl, with values between 610 and 700 HV. The growth kinetics indicated that the thickness of the aluminide layers increased with both the aluminizing temperature and time, following a parabolic growth law. The activation energy for the growth of FeAl was 343.15 kJ/mol.

Abstract: This study investigates the enhancement of hardness and mechanical properties of PPG-based polyurethane elastomers for wheel dolly applications through the incorporationof carbon black and the use of Plast 002 as a dispersing agent. The challenge addressed is the inherent lower mechanical performance of cost-effective PPG-based polyurethane compared to traditional polyester-based alternatives. Three dispersion methods were explored: the impactof Plast 002 on carbon black distribution, varying carbon black content (1, 3 and 5 phr), and comparing high-speed agitation with ultrasonic dispersion. The results indicate that without Plast 002, carbon black tends to agglomerate, leading to significant differences in hardness between the top and bottom of samples, particularly at higher carbon black contents. The addition of Plast 002 significantly improved dispersion, resulting in uniform hardness. Ultrasonic dispersion had more effective than high-speed agitation, delivering higher and consistent hardness values across the sample. Optimal mechanical performance was observed at 1 and 2 phr of carbon black, where tensile strength and modulus improved. The optimized carbon black content and ultrasonic dispersion can significantly enhance the performance of PPG-based polyurethane, offering a more economical alternative to polyester-based polyurethanes for wheel dolly applications.

Abstract: The use of silica sand tailings without leaching as a reinforcement in the development of composites remains a material class known for outstanding properties. However, owing to the availability, least expensive, and physical properties of silica beach sand, this study investigates the effect of non-leached silica (SiO₂) beach sand particulates on the mechanical and tribological characteristics of aluminium (Al) alloy matrix composites. In the study, an AA6061 alloy matrix was reinforced with varying content of SiO₂ beach sand (0, 20, 30, and 40 wt%) using the stir casting process. The SEM results revealed uniform dispersion of the beach sand particulates in the resultant composites with minimal agglomerations up to 30 wt% loading. Thus, the hardness and elastic modulus of the SiO₂/AA6061 alloy composites were improved by 326.7% and 90.9%, respectively, at 30 wt% SiO₂ particle addition. In addition, with the introduction of the SiO₂ particles in the alloy matrix, a reduction in the coefficient of friction by 24.5% and wear rate by 40.79% was recorded compared to the pure Al alloy. These findings indicate the substantial potentiality of silica beach sand particulates reinforced Al alloy matrix composite material as a promising candidate for mechanical load bearing, frictional components, and high-performance engineering applications including construction, automotive component, airframe, marine and rail transport.

Abstract: Ferritic 439 stainless steels, known as iron–chromium alloys with chromium content between 11% and 30%, have been extensively used worldwide due to their good corrosion resistance, good formability, high-temperature oxidation resistance, and lower cost compared to austenitic stainless steels. Conventional production processes for these steels, such as melting, casting, and rolling, are predominantly employed due to the material's difficult formability and machinability, especially when producing complex shapes. However, additive manufacturing (AM) offers new processing opportunities. AM technology, specifically Selective Laser Melting (SLM), fuses metallic powders using a precisely focused and controlled laser beam, enabling the production of highly complex parts with high precision. In this work, we present a comparison of ferritic 439 stainless steel manufactured using SLM technology with conventionally manufactured one, focusing on their microstructure, phase, and mechanical properties. The results reveal that SLM significantly increases material strength and hardness due to notable differences in microstructure fineness and phase composition. The rapid solidification during the SLM process results in a microstructure for the as-printed ferritic 439 stainless steel that significantly differs from that of conventionally manufactured ferritic 439 stainless steel. This distinctive microstructure in the additively manufactured product is likely responsible for various other differences in material behavior.