Papers by Keyword: Si₃N₄

Abstract: The impact of heat treatment on the mechanical characteristics of aluminium metal matrix composite (MMC) was examined in this research work. Here the material chosen for matrix was Al7075-T6, which was aluminium alloy that was tempered with T6 configuration and the Al matrix was reinforced with Silicon nitride (Si₃N₄) powder. For the evaluation of mechanical properties totally two samples were fabricated, one was Al7075-T6 itself without any addition of any reinforcement and the other sample was composed of Al7075-T6 + 5% of Si₃N_4. These two samples were fabricated in necessary testing form with the help of stir casting technique. After fabrication and heat treatment of the samples the sample was mechanically tested to evaluate the tensile and impact strength of the samples prepared to find the changes in the mechanical properties due to the reinforcement of Si₃N₄ and due to the heat treatment process. The samples were subjected to heat treatment process at a temperature of around 500°C for 5 hours, after treating the samples with heat sudden quenching process was done by cooling with distilled water and artificial ageing process was conducted at 150°C for 24 hours. After all this process of fabrication and heat treatment the samples were analysed to find the mechanical properties.

Abstract: Investigating how two different ceramic additives affect the microstructure and nanomechanical characteristics of the Ti6Al4V matrix forms the goal of this work. Under 50 MPa pressure, 10 min dwell time, and 100 °C/min sintering rate at 950 °C, a pulsed electric current sintering process, or PECS, was used. An XRD spectrometer was used to examine the phases, and SEM-EDS was used to examine the bulk morphology of the starting powders and sintered composites. The fabricated Cs1, Cs2, and Cs3 composites attained theoretical densities of 99.74, 98.90, and 96.7%, respectively, above 96.22% of unreinforced Ti-alloy. The SEM analysis showed an even dispersion of the ceramic reinforcements in the matrix of Ti6Al4V, with the characteristics of porous craters in all the samples. Of the three composite samples, Cs1 showed the highest elastic modulus, micro, and nanohardness absolute values of 173 GPa, 796 MPa, and 8942 MPa, respectively, as compared to the unreinforced titanium alloy of 114 GPa, 589 MPa, and 6466 MPa. It was thought that the improved mechanical properties of the sintered composites were due to the production of intermediate phases of Ti₂N and SiO₂ during the sintering process. The materials improvement stands at approximately 30% of the unreinforced Ti-alloy.

Abstract: Wet etching of Si₃N₄ was conducted in superheated water at 160 °C with different additives type and concentration. In general, etching rate of Si₃N₄ increased with the pH of solution. However, it is difficult to fully explain the Si₃N₄ etching behavior just with the pH of solution. The OH^- concentration (or pH) in superheated water at 160 °C are different from the pH of solution at room temperature. Therefore, the OH^- concentrations in superheated water at 160 °C were calculated using van't Hoff equation, equilibrium constant equations, mass and charge balance equations. The calculated OH^- concentration at 160 °C showed better correlation with Si₃N₄ etching rate than that of initial pH of solution.

Abstract: This research examines the effect of ceramic particulate of Si₃N₄ on the hardness, tensile, corrosion, and microstructure of reinforced AA8011 composites. The composites were developed by two steps stir casting process where both the particulates and the alloy matrix were preheated and melted respectively before mixing. 0%, 5%, 10%, 15%, and 20% Si₃N₄ particulates compositions were varied to fabricate the composites. Vickers microhardness tester was employed to study the hardness, the universal testing machine was used to analyze the ultimate tensile strength, the tribological performances of the developed composites AA8011-Si₃N₄ were analyzed under dry sliding condition using Universal Tribometer. The results of the experiment clearly revealed the improvement in the mechanical properties of the composites compared to the primary Al-Fe-Si alloy with excellent strength mechanism recorded at 20% reinforcement. Composites with 20% Si₃N₄ was found to have a better wear resistance hence, lowest wear rate.

Abstract: Si₃N₄ film could be selectively removed by a special H₃PO₄-free etchant. In order to increase Si₃N₄ etching rate and Si₃N₄/SiO₂ etch selectivity, various additives were added to H₃PO₄-free etchant. The optimization of additives into H₃PO₄-free solution, a comparable Si₃N₄ etching rate with 50 times increased Si₃N₄/SiO₂ etch selectivity was obtained as compared to the conventional H₃PO₄ process.

Abstract: This paper discusses the relationship between torsion strength and bending strength of Al₂O₃ and Si₃N₄ ceramics. Measurement of the torsion strength was carried out by a simplified torsion test method proposed by Yasuda and Tsutsumi. In this experiment, the average torsion strength was approximately 2/3 of its average bending strength for both ceramics. By estimating the characteristic strength σ₀ in Weibull distribution from the strength data, σ₀ in torsion is almost the same as that in bending, which agrees to the basic discussion in mechanics of materials. The characteristic strength σ₀ is one of the normalized strength by eliminating the effects of specimen shape, dimensions and also its stress distribution, and therefore the apparent difference between torsion and bending strengths can be explained by the difference in effective surface area (Conversely, the measured torsion strength data by the simplified method must be reasonable). It reveals that biaxial fracture in tension/compression during torsion test is equivalent to uniaxial tensile fracture by this experiment.

Abstract: The effect of slip degassing on the microstructure and mechanical properties of slip cast and reaction bonded Si₃N₄ was studied. The slip was prepared by aqueous ball milling of silicon (Si) powder. Hydrogen bubbles, a result of Si oxidation during milling, were degassed from the slip using a combination of vacuum and heat. The slip was then cast into a plaster mould to obtain rectangular green bodies. The Si green samples were sintered in a nitrogen atmosphere at 1500°C to convert the Si to Si₃N₄. After that the nitrided samples were polished to dimensions of 3 x 4 x 30 mm. The density, porosity, flexural strength, phase content and microstructure of the sintered samples were studied. The results showed that the degassing process increased the slip density. After casting and subsequent nitridation, it was found that the average apparent density of the samples increased from 2.89 to 2.95 g/cm³, the porosity decreased from 52.9 to 49.5 %, and the flexural strength increased from 8.1 to 9.3 MPa, when the degassed slip was used. A microstructural examination showed that the pores in the samples were filled with whiskers, which most likely resulted from a vapor phase growth mechanism. The samples produced from the degassed slip tended to have fewer whiskers, due to the reduced pore size and volume. A comparison of the XRD patterns showed no phase differences between the samples. The appearance of Si₂N₂O, and SiC likely resulted from the reactions between O₂ and C impurities with Si₃N₄.

Abstract: Dependence of the mechanical properties of PM extruded titanium with the silicon nitride (Si₃N₄) on solid phase decomposition of Si₃N₄ was investigated. Si₃N₄ particles within Ti composite powder were decomposed during spark plasma sintering at 1223 K with 30 MPa pressure for 3.6 ks; and then, decomposition by-products of nitrogen and silicon atoms were defused into titanium matrix. The extruded Ti-1.0 mass% Si₃N₄ composite showed ultimate tensile strength (UTS) of 1139 MPa, and yield stress (0.2%YS) of 1065 MPa. UTS and 0.2%YS of P/M extruded Ti-1.0 mass% Si₃N₄ composite were 2 and 2.5 times compared to extruded pure Ti powder material, respectively. It was considered that the solid solution strengthening of both nitrogen and silicon originated from Si₃N₄ caused the high strength of PM extruded Ti-1.0 mass% Si₃N₄ composite.

Abstract: Silicon nitride (Si3N4) is one of the most important engineering materials. The developing trend of Si3N4 ceramic should be its composite with reinforce phase. However, due to its low self-diffusion coefficient at high temperature, the Si3N4 is very hard to be densified without sintering aids. In the present work, the Y2O3 and light rare-earth oxides of La series (La2O3, CeO2, Pr2O3, Sm2O3) and AlN, Al2O3, MgO, CaCO3 were chosen to be sintering aids. Their effect on the sintering of Si3N4 composite was studied. The results showed that the Y2O3 was the best sintering aid in all members, and the Y2O3-La2O3-AlN ternary composition was the best formula.

Abstract: Si₃N₄ is difficult to be machined due to its hard and brittle nature. In order to improve its machining quality, a new method of ultrasonic-assisted laser machining is proposed. The machining device is established including Nd: YAG pulsed laser, ultrasonic vibration stage and water flow system. Etching experiments of laser machining with and without sample vibration in anhydrous conditions and in water conditions are studied respectively. A VM-3030E two-dimensional image measuring instrument is applied to detect shape and measure dimension of the sample. Microstructure morphology of the sample is observed by a JSM-7500F scanning electron microscope. Experimental results show that there are fewer slags on inner surfaces of V-shaped grooves when laser machining with water flow. The surface quality and depth-to-width ratio of grooves machined by laser with vibration on sample are improved significantly in comparison with those without vibration. The depth-to-width ratio of groove machined by laser with 90.1W vibration power is near twice than that without vibration.