Role of boron in TiAl alloy development: a review

Boron was found to be a unique grain refiner in cast TiAl alloys in the beginning of 1990s and has become an element in most of the TiAl alloys developed to date. Over the past 25 or so years, efforts to understand the role of boron in solidification, solid-phase transformation, thermal and thermomechanical processing and mechanical properties of TiAl alloys and the relevant mechanisms never ceased. As a result, abundant knowledge on boron in TiAl alloys has been accumulated but scattered in various research papers and conference proceedings. This review summarises the progress in understanding boron and its impacts on the TiAl alloy systems.