The nature of the dispersoids in INCONEL alloy M A6000

Analytical transmission electron microscopy has been used to examine the oxide dispersion in the mechanically alloyed, nickel-based, dispersion strengthened superalloy INCONEL alloy MA6000. Four mixed AI-Y oxides were identified in consolidated powder: Y₃Al₅O₁₂, yttrium aluminium garnet (YAG); YAIO₃, yttrium aluminium perovskite (YAP); Y₄Al₂O₉, yttrium aluminium monoclinic (YAM), and a previously unidentified YAlOI₃ polymorph. This new phase, designated yttrium aluminium hexagonal (YAH), has lattice parameters ofa = 2.206 ±0.035 nm andc = 3.219 ± 0.096 nm, a space group of P6₃mc and consists of 18 closepacked oxygen layers with the yttrium and aluminium cations in the resulting interstices. It is proposed that the high local stresses, strains and temperatures which occur during the mechanical alloying process facilitate the formation of the highly complex YAH phase. All four oxide types also contain significant amounts of zirconium (up to 13 cation at%) which randomly substitutes for both the yttrium and aluminium ions. This substitution was sufficient to have caused the removal of 75% of the zirconium from solution in the matrix.