Papers by Keyword: Hardness

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.

Abstract: This study investigated the evolution of microstructure, hardness, and toughness in nodular cast iron following quenching and tempering at 450°C. The research explored how the heat treatment process impacts these mechanical properties, to identify an optimal balance between hardness and toughness. Untreated nodular cast iron displayed a microstructure comprising ferrite, pearlite, and spheroidal graphite, resulting in moderate hardness (24.33 HRC) and toughness (0.082 J/mm²). Quenching at 850°C, followed by rapid cooling in water, induced the formation of martensite, a hard and brittle phase, which significantly increased hardness to 56.73 HRC but decreased toughness to 0.068 J/mm². Tempering at 450°C transformed the martensite into tempered martensite, reducing hardness to 41.37 HRC while improving toughness to 0.11 J/mm². These findings highlighted the importance of tempering in achieving a better balance between hardness and toughness, making the material suitable for industrial applications requiring both wear resistance and impact durability. The results offered valuable insights for optimizing heat treatment procedures to enhance the performance and durability of nodular cast iron components in various industries.

Abstract: Post weld heat treatment is heating objects in the furnace to certain temperatures and times after the object has been welded. PWHT is expected to reduce residual stress on objects due to the welding process. In this case, we warm up annealing (holding in a furnace) at a temperature of 750 °C with a heating time of 40 minutes. We use MIG welding (metal inert gas) and a metal filler FS 705-6 with a diameter of 0.8 mm, with a total of 3 layers. First, the object will be formed according to the standard and welded in three layers with MIG welding. Then, the object will be cut and formed according to the tensile test standards, after which the tensile test and hardness test will test it to determine the mechanical characteristics of the object. From the testing that has been carried out, it is known that objects without PWHT have a higher stress and hardness value than objects with PWHT, with a stress value of 346.57 MPa and the highest hardness value of 93.5 HRB at the 3rd welding point. However, objects with PWHT have higher elasticity and strain values, with an elasticity value of 3.32 MPa, and the strain value of objects with PWHT is 13.1.

Abstract: Ni-based superalloys are commonly utilized in the production of hot-end components in the aerospace, energy, and other sectors. Due to the extreme environment, phase coarsening is prone to occur within the alloys, leading to degradation in the mechanical properties and thus posing a risk to equipment safety. To investigate the influences of volume fraction of precipitation particles and phase coarsening on hardness of materials, and explore the relationship between their microstructure and macroscopic hardness, based on the finite element method simulations, a two-dimensional Vickers hardness model is constructed for testing. Results show that hardness is closely linked to the particle shape, size, and distribution features; with the increase of the volume fraction of particles or the degree of phase coarsening, the hardness of alloys gradually weakens; and when the volume fraction of particles is larger, the decrease in the hardness is more obvious along with the degree of phase coarsening. Related research makes a good reference for the design of Ni-base superalloy structures as well as the evaluation or prediction of their mechanical properties during the service.

Abstract: The tool steel materials are expensive this is the reason why the lifetime increase is a goal of the production technology. The tool life is determined by the various complex mechanical, thermal, chemical, and tribological properties. Tools properties depend on the chemical composition and their microstructure. The microstructure depends on the chemical composition, the production process, the heat treatment and surface treatment technologies. The goal of this research was to increase the service lifetime of the casting mould tool. It was prepared and investigated four kinds of test specimens. The first kind of specimen was made from conventional steel (W302). It was made an austenitization (1020°C) and was cooled with 9 bar nitrogen gas to 40°C and kept for 6 minutes. The quenching was followed with three times tempering processes (570°C, 580°C, 560°C) in 2 bar N₂ gas. The second kind of test specimen was made from Unimax electro-slag remelted steel (ESR). It was made an austenitization (1020°C) and was cooled with 9 bar nitrogen gas to 40°C and kept for 6 minutes. After quenching the process continues with three times tempering (610°C, 620°C, 600°C). The third kind of test specimen Unimax a electro-slag remelted steel (ESR), to which firstly an austenitization (1020°C) was made, quenched in nitrogen gas with 9bar and then cooled in liquid nitrogen till minus 150°C. After cryogenic treatment, the process continues with three times tempering (610°C, 620°C, 600°C). The fourth kind of specimen was made by the same process as the second and after it a PVD coating process was made to coat the surface by a TiBN layer. It investigated the hardness and wear resistance of all heat-treated and surface-coated steel specimens. The comparative wear resistance testing was investigated by a ball cratering tester. The rank of the tested specimen was the next: the lowest wear resistance measured in the case of the heat-treated W302, the middle in the case of cryogenic heat-treated Unimax and the highest wear resistance earned in the case of the PVD-coated Unimax. The results of the investigations proved that the Unimax tool steel service lifetime can increase better than the conventional tool steel by heat treatment and surface treatment. The practice certified that the surface-treated Unimax tools' service lifetime is much longer than the conventional ones.