Role of Ti3AlC2 MAX phase on characteristics of in-situ synthesized TiAl intermetallics. Part III: microstructure

Abstract

In this paper, the 3^rd part of a series of publications on the sinterability and characteristics of TiAl–Ti₃AlC₂ composites, the microstructure development during the synthesis and sintering processes was studied by scanning electron microscopy (SEM). Chemical evaluation of various phases in the developed microstructures was performed using energy-dispersive X-ray spectroscopy (EDS) in different ways such as point, line scan and two-dimensional elemental map analyses. For this purpose, five samples were fabricated with different percentages of Ti₃AlC₂ MAX phase additive (10, 15, 20, 25 and 30 wt%). Ball-milling and spark plasma sintering (SPS: 900 °C/7 min/40 MPa) of as-purchased Al and Ti powders with already-synthesized Ti₃AlC₂ additive were selected as composite making methodology. SEM/EDS analyses verified the in-situ manufacturing of TiAl/Ti₃Al intermetallics as the matrix during the SPS process and the presence of Ti₃AlC₂ as the ex-situ added secondary phase. Moreover, the in-situ synthesis of Ti₂AlC, another member of MAX phases in Ti-Al-C system, was also detected in titanium aluminide grain boundaries and attributed to a chemical reaction between TiC (an impurity in the initial Ti₃AlC₂ additive) and TiAl components.