On the boron addition to beta-NiAl intermetallic obtained by microwaves ignited combustion synthesis

Aim of the present work is to accurately investigate the effect of Boron addition on the microstructure and mechanical properties of β-NiAl intermetallic phase obtained by microwave initiated and sustained combustion synthesis (CS). In this work the rapidness, selectivity and volumetric nature of microwaves (MWs) at the frequency of 2.45 GHz were exploited to ignite the combustion synthesis of precursor powder mixtures, leading to the preparation of free-standing β-NiAl intermetallic specimens presenting different boron amounts. Micro-alloying with B is known to contribute to improve the ductility and enhancing room temperature toughness of aluminides, while larger boron amounts significantly increase the yield strength and hardness. Since literature results are sometimes contradictory, particularly as far as the CS manufacturing process is concerned, an accurate investigation on the possible mechanisms which can be responsible for the above mentioned improvements, has been carried out, demonstrating that boron addition is effective in decreasing the intrinsic brittleness and improving the ductility of β-NiAl intermetallic phase, already starting form 50 ppm concentration.