Materials Science Forum Vol. 1138

Abstract: Gray cast iron has been one of the most widely used engineering materials since a long time ago. However, the development of casting techniques and methods to produce various models of cast iron products for the domestic market is not followed by improvements in product quality. The intriguing aspect of gray iron products is the diverse morphologies that graphite can assume, leading to distinct variations in mechanical and physical properties. Quenching is a typical heat treatment procedure performed to improve the mechanical properties of a material that entails the rapid cooling of the material from a high temperature to a low temperature. The aim of this study is to investigate the effect of water quenching effects on microstructure, crystal structure, hardness, and wear of gray iron, which undergoes quenching from the austenitizing temperature. Gray cast iron was obtained from the local foundry industry, then thermally treated at 900°C, held for 15 minutes, and rapidly quenched by water. The quenching procedure induces a significant alteration in the overall microstructure, where transition of most dendrite arms to the eutectic phase microstructure is observed. Moreover, the quenching process is attributed to the reduction of crystal size and growth of carbon crystal. The average crystal size of the sample was reduced from 47.833 nm to 17.97 nm, hence improving the hardness from 16.375 HRC to 48.04 HRC, which in turn improved wear resistance under high loading condition from 0.014 g/sec to 0.00042 g/sec.

Abstract: This study examines the fatigue crack propagation behaviour of AISI 4140 steel subjected to multi-austempering heat treatments. Tensile test and fatigue crack propagation (FCP) specimens were prepared in accordance with ASTM E8 and ASTM E647, respectively. Multi-austempering was carried out by heating the specimen to an austenite temperature for 10 min using an induction heating coil. The specimen was then immersed in a salt bath for each isothermal transformation time of 60 min at three austempering temperature levels from 312°C to 412°C with a temperature increase of 50°C. Tensile and fatigue crack growth tests were performed on both annealed and multi-austempered specimens. It is observed that the multi-austempering heat treatment significantly improves the tensile properties and the FCP properties of AISI 4140 steel. Microstructural observations indicate that the bainitic phase and the retained austenite increase the tensile strength and reduce the fatigue crack propagation rate (da/dN). It is found that the bainitic structures are an effective barrier in reducing fatigue crack propagation as the fatigue loading cycle increases

Abstract: Aluminum casting using the stir casting method is a common practice in the industrial sector. This study aims to optimize the effect of stirring speed on the physical and mechanical properties of aluminum casting reinforced with alumina powder (Al2O3). The material used in this study is derived from discarded vehicle rim waste. The stir casting method was performed at varying speeds of 500, 600, and 700 rpm, with a mold temperature of 250°C and a pouring temperature of 700°C. Physical testing to examine the microstructure was conducted using optical metallography, hardness testing was performed using the Rockwell hardness scale B, and tensile strength was measured using a Universal Testing Machine. The microstructure observations showed that a stirring speed of 500 rpm yielded the best results, with minimal porosity. The highest hardness value recorded was 65 HRB at 500 rpm, consistent with the microstructure observations. The highest tensile strength was also recorded at 500 rpm, reaching 262 MPa.

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: 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: To alleviate the environmental problems caused by the excessive emission of CO₂, this study designed and synthesized a binary organocatalytic system based on urea-based hydrogen bond donors and polyether ionic liquids based on a cycloaddition reaction that converts CO₂ and small-molecule epoxides into cyclic carbonates with high industrial application value. The binary system is based on a polyether ionic liquid, introducing an organic base (to trap and activate CO₂), hydrogen bond donor (to activate the epoxide), and nucleophilic reagent unit (to help open the ring of epoxides), with a variety of active sites. In this paper, the effects of the hydrogen bond donor as well as polyether ionic liquids structure on the activity of the binary system were investigated, the optimal HBD/Lewis base binary catalytic system was established, and the cycle life of this binary system was tested.

Abstract: A new degreasing pretreatment technology for quick-drying towels has been developed to solve the environmental pollution caused by a large amount of waste gas during the degreasing process. The optimal deoiling rate of oil extracted from the microfiber surface in supercritical CO₂ fluid is 95.45% when the temperature is 100°C, the pressure is 14 MPa, the time is 60 min, and the CO₂ flow rate is 30 g/min. The implications of various treatment temperatures and times on the effectiveness of oil agent removal are addressed.

Abstract: In this study, cotton fabrics were dyed with extracts from Bougainvillea glabra (BG) flowers which are widely grown around the world, especially in Southeast Asia. The obtained results indicated the dyeability of dyed fabrics were influenced by BG concentration, exhaustion temperature, dyeing time, types and content of mordants, and the amount of alkali in the washing solution. By comparing color difference (DE) between standard sample and dyed sample, it is confirmed that dyeing efficiency was significantly improved with increased BG concentration and exhaustion temperature. All cotton fabrics should be dyed with BG extracts at reasonable temperature, ideally below 45°C. While the presence of metal mordants such as FeSO₄.7H₂O, CuSO₄.5H₂O and KAl(SO₄)₂.12H₂O increased the color fastness of the dyed fabric, they also caused seriously color change as compared to fabric dyed without mordants. To ensure color fastness during washing, dyed samples with BG extracts should be laundered with low alkalinity solution.

Abstract: In this study, the effects of cotton fiber characteristics, tested by Uster High VolumeInstruments (HVI) on the tenacity, elongation, unevenness, imperfection index (IPI) and hairiness values of the combed ring spinning yarns, were investigated in detail. Based on the experiments, it was found that an increase in fiber tensile strength and elongation leads to an increase in the specific tensile strength and elongation of the yarn; an increase in short fiber content and neps fiber materials leads to an increase in the unevenness, IPI of the yarn; an increase in the fiber length leads to a decrease the hairiness values of the yarn, etc. Information concerning the relative contribution of fiber characteristics to yarn properties is one of the important targets for the spinner to choose cottons that are best suited to the manufacture of specific end product.