SYNTHESIS, CHARACTERIZATION AND MODELING STUDIES ON IN-SITU TiB2 REINFORCED ALUMINIUM MATRIX COMPOSITES

Abstract

The aim of the present research is to understand the suitability of mixed salt route using stir casting technique to fabricate in-situ Al-4.5%Cu-xTiB2 (x = 3, 6, 9 and 12 wt. %) composites. The mechanism behind titanium/boron-based phase evolution in Al-Cu alloy has been enlightened first time, particularly its strong influence over mechanical behaviour was examined. The in-situ TiB2 reinforcement particles were prepared by the exothermic reaction of K2TiF6 and KBF4 salts in melted aluminium copper alloy which improves the hardness, yield, and tensile strengths to the extent of ~89 VHN, ~236 MPa and ~295 MPa, respectively. Preliminary microstructural evolution was analyzed and discussed through optical microstructures and proposed mechanism. The composites were characterized carefully with the help of field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) to know the morphological details and TiB2 distribution in the aluminium matrix composite (AMC) microstructure. In support with electron microscopic observations, the X-ray diffraction (XRD) and Electron Probe Microscopic Analysis (EPMA) were also performed. To further enhance the mechanical properties, T6 heat treatment (HT) was done. During the HT process, the composites were solutionized at 540 ºC for two hours followed by water quenching. After that, artificial ageing was carried out at 170 ºC with varying durations of 5, 10, 15, 20, and 25 hours and post-ageing effect on the mechanical properties were recorded. Composites were thermally characterized through differential scanning calorimetry (DSC) to learn the precipitation kinetics and compared with alloy chosen. Further the variation of porosity present in cast composite with varying pouring temperature, pouring time and different types of gating systems were also analysed. The casting was found to be effective and economical for top gating system amongst rest of the gating design. The microstructural analysis of cast composite was carried out to determine the physical morphology and distribution of the TiB2 and Al2Cu phases in the matrix with the help of scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis of cast composite shows the formation of TiB2 particles in the absence of intermetallic, hard and brittle compound Al3Ti. Microstructural characterization was tandem with optical and high-resolution transmission electron microscopy (HR-TEM) results. These castings were checked for surface defects or sub-surface cracks using dye penetrant and ultrasound test. The amount of porosities present in all the castings was then determine precisely using Archimedes’ Principle of buoyancy. The experimental results thus found were validated with the simulation results obtained by AutoCAST simulation tool and improvements were incorporated by optimisation of gating systems using modelling and simulation technique.