Nanocrystalline NiAl intermetallic alloy with high hardness produced by mechanical alloying and hot-pressing consolidation

Abstract

An Ni-50% Al elemental powder mixture was mechanically alloyed in a SPEX ball mill. The powders after various milling times were investigated by X-ray diffraction and differential scanning calorimetry. A nanocrystalline NiAl intermetallic phase with the mean crystallite size of 13 nm was formed after 8 h of milling. The produced powder was consolidated by high-pressure hot-pressing at 800 °C under the pressure of 7.7 GPa. The consolidated material was characterised by structural investigations. Hardness, density and open porosity as well as heat resistance measurements were also conducted. The mean crystallite size of the NiAl intermetallic phase in the bulk material was 24 nm, which shows that the nanocrystalline structure was maintained during the consolidation process. The hardness and heat resistance of the produced nanocrystalline NiAl were compared with those of a reference microcrystalline NiAl. The hardness of the nanocrystalline NiAl intermetallic is 971 HV1 (9.53 GPa) and it significantly exceeds the hardness of the reference microcrystalline NiAl. The relative density of the consolidated sample is 100%. The produced nanocrystalline NiAl intermetallic exhibits very good oxidation resistance at 900 °C in air. For this material, the mass gain per area after 100 h of exposure is 1.4 × 10−4 g and is smaller than that for the reference microcrystalline NiAl sample. The quality of consolidation with preserving NiAl nanocrystalline structure is satisfactory and the hardness as well as the oxidation resistance of the produced material are relatively high.