Ni_3Al samples were implanted with different doses of Cr~+ and B~+ ions to modify the surface region. The high temperature oxidation behaviour and corrosion behaviour were tested. The surface layer structure was investigated by AES, SEM, TEM, XRD, EPMA before and after the tests. Effects of implanted elements and possible reaction mechanism were discussed. It was found that chromium atoms dissolve substitutionally in Ni_3Al, which turns ordered Ni_3Al to disordered Ni-Al-Cr alloy. Boron atoms exist, in the form of interstitial atoms. No evidence has been found that there is any new phase in boron implanted Ni_3Al. Implanted Ni_3Al alloy has better oxidation resistance than unimplanted one. For Cr-implanted Ni_3Al, the oxide layer is a multilayer, comprising a Cr_2O_3 inner layer, a spinel NiAl_2O_4 intermediate layer, and a-Al_2O_3 at the oxide/air interface. Both a-Al_2O_3 and Cr_2O_3 are healing and protective layers. For B-implanted Ni_3Al, oxide layer is basically composed of fine-grained NiO inner layer and a-Al_2O_3 outer layer. Boron is oxidized into B_2O_3 of comparatively boundaries and defects. This curtails the short circuit transportation of oxygen and improves the oxidation resistance of Ni_3Al. Implantation with Cr~+ and B~+ combines the good effects of both elements and makes remarkable improvement on oxidation resistance. Implanted elements also improve the corrosion resistance of Ni_3Al in aqueous solution. When the implanted dose is over 10~(17) ions/cm~2 and voltage E is 800 mV(SCE), in 0.25 mol NaCl + 0.25mol Na_2SO_4 (pH6) solution, current density i decreases 1 to 3 orders of magnitude. In 1mol NaCl (pH1) solution, the critical current density i decreases 1 to 3 orders of magnitude. Corrosion machanisms are also discussed in detail in the paper.
修改评论