EFFECTS OF B+ AND CR+ ION-IMPLANTATION ON THE OXIDATION OF NI3AL

Ni3Al samples were implanted with different doses of 150 keV B+ and Cr+ ions to modify the surface region and the high-temperature oxidation behaviour was tested. The surface layer structure was investigated by Auger electron spectroscopy, and transmission electron microscopy, secondary ion mass spectroscopy and optical microscopy before and after testing. The experimental results show that boron atoms exist in the form of interstitial atoms. No evidence was found that any new phase existed in boron implanted Ni3Al. Implanted Ni3Al alloy has better oxidation resistance than the unimplanted ones at 900-degrees-C. For B+-implanted Ni3Al, the oxide layer is basically composed of fine-grained NiO inner layer and an a-Al2O3 outer layer. Boron is oxidized into B2O3 of comparatively larger grain size. B2O3 particles are enriched at grain boundaries and defects. This curtails the short-circuit transportation of oxygen and improves the oxidation resistance of Ni3Al. Implantation with Cr+ and B+ combines the good effects of both elements and produces a remarkable improvement on the oxidation resistance. The effects of implanted elements and the possible reaction mechanisms are discussed.