MICROSTRUCTURE, PHASE TRANSFORMATIONS AND MECHANICAL PROPERTIES OF SOLUTION TREATED BI - MODAL ? TITANIUM ALLOY

The effect of heat treatment conditions on the microstructure, phase transformation and mechanical properties of Bi - modal ? titanium alloy was investigated. T he heat treatment process comprises of solution treated at various temperatures of 640, 680, 720 and 760 ? C for 30 min followed by water quenching and aged at 500 ? C for 30 min then air cooling. This study was carried out using X - ray diffraction analysis ( XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), differential thermal analysis (DTA), compression universal testing machine and Vickers hardness tester. The results show that the microstructure of investigated alloys consists of ? phase, as a matrix, primary ? phase, small precipitates of secondary ? phase in addition to orthorhombic martensite ( ? ”) phase found only in the solutionized samples at 720 and 760 ? C. Transus temperature for the ? phase found to be around 865 ? C at heating rate of 10 ? C/min. The ? / ? phase zone is ranging from 650 to 865 ? C at the same heating rate for all samples . The formation temperature of nanometer α phase and/or disappearing of ? iso phase are almost constant at 385 °C. The formation of prim ary α phase was detected at a temperature more than 400 ? C. Hardness measurements increased as the solution temperature increase. The highest ultimate compression strength, 2680 MPa, achieved with solution temperature of 680 °C. However the maximum yield s tress, 1725 MPa, obtained with 760 ? C solution temperature. The highest contraction was attained with the solutionized sample at 640 ? C for 30 min