Transmission electron microscopy of martensitic transformation in Xe-implanted austenitic 304 stainless steel
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Thin film specimens of austenitic 304 stainless steel implanted with 100 keV Xe ions at room temperature were investigated. Microstructural evolution and phase transformation were characterized and analyzed in situ with conventional and high-resolution transmission electron microscopy. The phase transformation in a sequence from austenitic ␥ face-centered cubic (fcc) to hexagonal close-packed (hcp), and then to a martensitic ␣ body-centered cubic (bcc) structure was observed in the implanted specimens. The fraction of the induced ␣(bcc) phase increased with increasing Xe ion fluence. Orientation relationships between the induced ␣(bcc) phase and austenitic ␥(fcc) matrix were determined to be (011¯)␣//(11¯1)␥ and [111]␣//[011]␥. The relationship was independent of the induced process of the martensitic phase transformation for austenitic 304 stainless steel specimen, in agreement with the Kurdjumov–Sachs (K-S) rule. It is suggested that the phase transformation is induced mainly by the formation of the highly pressurized Xe precipitates, which generate a large stress level in stainless steels.
I. INTRODUCTION
Ion implantation has been widely studied as a surface modification technique to improve the properties of metal surfaces in the last twenty years. The implantation of noble gases in metals has been found to induce some exciting phenomena, such as formation of precipitates containing solid gas,1–3 inducing solid/solid matrix phase transformations resulting in formation of new stable as well as metastable metallic phases,4–11 and so on. In stainless steels, ion implantation provides an alternative low-temperature process route for modification of the surface properties without changing the bulk properties. Ion implantation of stainless steels will not only introduce a new surface alloying element, but it may also promote various structural transformations in the implanted layer. The transformations, which usually occur under thermally diffusionless conditions, can lead to formation of martensitic phases. It has earlier been shown that transformations from an austenitic ␥ face-centered cubic (fcc) to a martensitic ␣ body-centered cubic (bcc) structure was induced in austenitic stainless steels implanted with phosphorus or antimony, irrespective of the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0218 J. Mater. Res., Vol. 20, No. 7, Jul 2005
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composition of the particular steels.12,13 Further investigations with transmission electron microscopy (TEM), glancing angle x-ray diffraction (GXRD), x-ray absorption spectroscopy (XAS), Rutherford backscattering (RBS), conversion electron Mossbauer spectroscopy (CEMS), etc., revealed that implantations with other energetic ions, such as metal ions (Au, Eu, Mo, Ti),5,14–17 noble gas ions (He, Ar, Kr and Xe),1–8,10,11,18 and the constituent element ions (Fe, Ni, and Cr) of the austenitic stainless steels,4,9,10 also induced the martensitic phase transformations.
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