Effect of Cr- and Y-implantation on oxidation behaviour of powder metallurgical Ni3 Al

Abstract

The effect of Cr- and Y-implantation on the isothermal and cyclic oxidation behaviour in air of a boron doped Ni3 Al alloy at 585 and 900°C for up to 200 h is discussed. Yttrium implantation proved to be detrimental, causing slightly higher oxidation rates at both temperatures, while the scale formed at 900°C on Y implanted Ni3 Al was prone to spallation. After 200 h at 585°C (isothermal or cyclic oxidation) the scale consisted of an outer NiO layer, an intermediate layer of pure Ni, and an internal oxidation zone. At 900°C the scale consisted of an outer NiO layer, an intermediate Ni and Al rich oxide zone, and an inner thin alumina layer. A similar scale pattern was observed for the non-implanted material, however, the oxide scale formed on the non- implanted material did not show any significant susceptibility to scale cracking and spallation. Chromium implantation on the other hand was beneficial in that it decreased the oxidation rates at both temperatures owing to the formation of a continuously healing alumina layer, induced by the presence of chromium. No spallation of the oxide scale occurred, even after 200 cycles at 900°C.