Heat treatment of material particularly quenching requires a high thermal conductivity quench medium. Hardenability of material, dimension, and geometry of the component are considerate on choosing quench medium. The cooling rate of quenching affects the properties and microstructures by creating specific phase transformation to occur. Enhancing the quench medium by accelerating the cooling rate can be attained by the addition of nanoparticle which has higher thermal conductivity. This nanoparticle-added medium is commonly termed as nanofluid. Commercial and laboratory grade of TiO2 was used as the nanoparticle to distilled water as the nanofluid base to acquired higher conductivity on the heat treatment process. In this experiment, a top-down method was done to obtain TiO2 particles by grounding using a planetary ball mill for 15 hours at 500 rpm. Nanofluid quench medium was mixed with TiO2 in various concentration of 1%, 5% and 10% with a volume of 100 ml each. Samples of AISI 1045 or JIS S45C carbon steel were used to obtain different cooling rate on a different type of TiO2 particles. Samples were heat treated by austenizing at 1000°C for 1 hour, followed by rapid quenching in nanofluid quench medium with the addition of agitation as quenching variable. Observation of particle morphology and size, material composition, and the change of surface ere measured by Field-Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). Initial characterization showed that the TiO2 particle size was at 150 nm range, and roughly free from any impurities. Martensite microstructures have the most significant area and the amount at laboratory-grade TiO2 in 0.2 wt% composition, followed by commercial-grade at 0.3 wt% composition.
Recently, nanofluid is used to improve the thermal conductivity of the quench medium in the heat treatment industry. In this research, ball-milled micro-sized TiO2 powder and nano-sized TiO2 particle were used and compared for their cooling characteristic in a micro/nanofluid. The micro/nanofluids were produced by mixing 0.1%, 0.3%, and 0.5% volume of both micro- and nano-sized particle into 100 ml of distilled water. The planetary ball mill was used at 500 rpm for 15 hours to reduce the dimension of micron-sized TiO2. Composition characterization by Energy Dispersive Spectroscopy (EDS) showed that the powder used were free from impurities. Nanofluids were then used to quench S45C carbon steel samples, which heated at 1000°C for 1 hour. The hardness test result showed that the sample quenched with 0.5%addition of the nano-sized particle in nanofluid had the highest number up to 691 HV, almost 100HV increment from a water-quenched sample where the hardness was 598 HV, showing that the cooling rate in the nanofluid was much higher. The addition of micro-size particle in fluid generally had a lower cooling rate than the addition of nano-size particle.
Quenching is performed as part of steel heat-treatment to enhance mechanical properties, by rapid cooling. Factors that affect the selection of quench medium are hardenability of material, geometry, and dimensions of the component. In recent developments, nanofluids are used to improve heat transfer capacity. In this research, nanofluids were synthesized using the two-step method. Milling of particles was done using a high energy ball mill for 15 hours at 500 rpm. Observation of particle size, material composition, and morphology of particle, and surface changes of the particle were measured by Field-Emission Scanning Electron Microscope (FE- SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). Water-based nanofluids with a volume of 100ml were produced using the two-step method, with carbon concentrations of 0.1%, and 0.5% and Sodium Dodecylbenzene Sulfonate concentrations of 0%, 1%, 3%, and 5%. Samples of S45C steels were austenized at 1000°C for 60 minutes. Hardness testing results correspond to the severity of the quenching mediums, with peak hardness of 845 HV for 0.1% Carbon with 1% SDBS, and 878 HV for 0.5% carbon with 3% SDBS. Hardness testing results show a significant improvement over results without SDBS addition. Excess surfactant addition yields a lower hardness due to the re-agglomeration of particles.
The mechanical properties of a material depend on the quenching process. In this process, there is a rapid cooling from elevated to room temperature in a short time by using a quench medium. Therefore, the phase transformation from austenite to martensite occurs. The common medium used in the quenching process is water, oil, polymer, and gas. Nanofluids are started to be used as a quench medium because they offer better thermal conductivity compared with the conventional medium. Selection of carbon-based nanofluids as a quenching process medium aims to obtain high thermal conductivity values and controllable cooling rates. Thereby, the expected microstructure of the material could be relatively easier to form. In this paper, carbon particles were obtained using a top-down method with a planetary ball mill for 15 hours at 500 rpm. Based on the electron microscope and spectroscopy results, the particle dimension was average at 15 μm after milling, and the carbon purity of the powder used in this research was 99%. Carbon particles at 0.1%, 0.3%, and 0.5% with variation of non-ionic surfactant Polyethylene Glycol of 1%, 2%, 3%, 4% and 5% respectively was used in this research. AISI 1045 or JIS S45C carbon steel was used as a steel sample, and austenized at 1000°C for 1 hour and then quenched in the microfluid. The hardness obtained was up to 811 HV for the sample quenched in 0.5% carbon and 1% Polyethylene Glycol. The improvement was more than 100 HV, compared with the sample quenched in distilled water, which had a hardness only 666 HV.
Quenching takes an important part in the heat treatment process that controls the microstructure, thus enhance its mechanical properties. The heat treatment process starts with heating at an elevated temperature, holding time then rapid cooling to room temperature. It requires a medium with a good thermal conductivity that can be achieved by the addition of nanoparticles to the quench medium, referred to as nanofluids. In this research, carbon particles were prepared by the top-down method, where the reduction of carbon particle was done by planetary ball-mill for 15 hours at 500 rpm. Cetyl Trimethyl Ammonium Bromide is utilized as a cationic surfactant in order to reduce agglomeration at suspended particles thus increase quenching efficiency. Field-Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive X-Ray Spectroscopy (EDX) were used to observe the composition of material, particle size and particle morphology, and the change of the surface. Initial characterization by FE-SEM showed that the particle size after milling was averaged roughly at 15 µm, therefore, it was still not in the nanometer range. However, EDS result confirmed that the powder used in this research were 99% carbon. Carbon microparticles were added as the particle to distilled water as the microfluid base. Water-based carbon microfluid with a volume of 100 ml was produced by the two-step method, by mixing carbon microparticles at 0.1 wt%, and 0.5 wt% in various concentration of cationic surfactant of 1 wt%, 3 wt%, and 5wt % respectively. Samples of AISI 1045 or JIS S45C carbon steels were heat treated by austenizing at 1000°C in a heating furnace, followed by rapid quenching in microfluid as the medium quench resulting on cooling rate diagram. Mechanical properties and microstructures of the quenched samples will be observed by conducting hardness examination and metallography observation to analyze the effect of various carbon and surfactant concentration used in the water-based carbon microfluid quench medium.
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