Characterization of pack-borided last-generation TiAl intermetallics

In this work, Ti-46.6Al, Ti-45.2Al-7.2Nb and Ti-44.8Al-6.6Ta alloys were borided by a simple pack-boriding process. After boriding at 1150 °C for 12 h, thick and dense boride layers were obtained on the surfaces of the examined alloys. The layer deposited on the binary alloy exhibited a homogeneous structure and chemical composition. The layers on the Nb- and Ta-containing alloys were thicker than those on the binary alloy, and they were significantly more structurally and chemically heterogeneous. The mixed borides TiB2.NbB2 or TiB2.TaB2 were formed on the surfaces of these ternary alloys, and TiB whiskers were found at the boride/substrate interface. The surface hardness of the ternary alloys was observed to increase because of the presence of mixed borides and whiskers. The amount of mixed borides and TiB whiskers, as well as the consequent increase in the surface hardness, were significantly greater in the case of the Ta-containing alloy than in the case of the Nb-containing alloy. The wear resistances of the examined alloys were significantly improved through their boriding.

► Boride layers were created on the Ti-46.6Al, Ti-45.2Al-7.2Nb and Ti-44.8Al-6.6Ta alloys.
► The presence of Nb and Ta in the alloy increases the thickness of the boride layers.
► Nb and Ta increase the chemical heterogeneity of the obtained boride layers.
► Nb and Ta support the formation of TiB whiskers beneath the outer TiB2 layer.
► Nb and Ta increase the hardness of the boride layers which was up to 3500 HV 0.01.