Effects of Cr + ion implantation on the oxidation of Ni 3 Al
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C.X. Shi Laboratory of Fatigue and Fracture for Materials, Institute of Metal Research, Academia Sinica, Shenyang 110015, People's Republic of China (Received 7 September 1992; accepted 23 November 1992)
Ni3Al samples were implanted with different doses of 150 keV Cr + ions to modify the surface region. The high temperature oxidation behavior was tested. The surface layer structure was investigated by AES, TEM, XRD, and optical microscope before and after the test. The experimental results show that chromium ions turn a small amount of ordered superlattice Ni3Al phase into a disordered N i - A l - C r phase. Also there is a bec chromium phase in the implanted sample. Implanted Ni 3 Al alloy has better oxidation resistance than the unimplanted one at 900 °C. The oxide layer is of a multilayer structure after 50 h oxidation, composed of a NiO inner layer, Cr 2 O 3 , spinel NiAl 2 O 4 intermediate layers, and an a - A l 2 O 3 external layer at the oxide/air interface. The a - A l 2 O 3 and Cr 2 O 3 are independent scale-like layers. The two protective layers improve the oxidation resistance significantly. The effects of implanted elements and possible reaction mechanisms are discussed.
I. INTRODUCTION Ion implantation is regarded as an effective process in surface modification of materials. The surface-related properties, such as hardness, fatigue, friction, wear, and oxidation at high temperature can be significantly improved by this technique. Ion implantation is also a new and effective tool for studying the relationship among microstructure, composition, and properties of materials. Since Aoki and Izumi1 found an apparent solution to the brittleness of polycrystalline Ni 3 Al, much interest has been centered on Ni 3 Al. Scientists have achieved many results in various fields in the past ten years.2 Their investigation shows that this intermetallic compound has many excellent properties. No work concerning the high temperature oxidation behavior of implanted Ni3Al has been reported. It is useful to study the effects of ion implantation on the oxidation behavior of Ni3Al in order to give a more extensive understanding and increase in the knowledge concerning the practical value of the alloy. Chromium is a normal addition to superalloys. A large number of nickel-base superalloys rely on the formation of Cr 2 O 3 scales for better oxidation resistance. To overcome environment-related embrittlement, it has been necessary to alloy it with chromium.3 By implanting Cr + ions into Ni 3 Al, we prepare to investigate the microstructure of the implanted sample and the effects of 734 http://journals.cambridge.org
J. Mater. Res., Vol. 8, No. 4, Apr 1993 Downloaded: 16 Mar 2015
Cr + ion implantation on the oxidation behavior of Ni 3 Al. It is predicted that the implantation can improve the oxidation resistance of Ni3Al more obviously because the implanted alloy possesses the advantages of both ion implantation and chromium atoms. II. EXPERIMENTAL DETAILS A columnar crystalline Ni3Al rod was obtained by a directional growth t
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