Surface improvement and biocompatibility of TiAl 24 Nb 10 intermetallic alloy using rf plasma nitriding A.M. Abd El-Rahman a, * , M.F. Maitz b , M.A. Kassem c , F.M. El-Hossary a , F. Prokert b , H. Reuther b , M.T. Pham b , E. Richter b a Physics Department, Faculty of Science, Sohag University, Egypt b Institut fu ¨r Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden Rossendorf, Germany c Department of Materials & Metals Engineering, Faculty of Petroleum & Mining Engineering, Suez Canal University, Egypt Received 5 December 2006; received in revised form 10 May 2007; accepted 11 May 2007 Available online 18 May 2007 Abstract The present work describes the surface improvement and biocompatibility of TiAl 24 Nb 10 intermetallic alloy using rf plasma nitriding. The nitriding process was carried out at different plasma power from 400 W to 650 W where the other plasma conditions were fixed. Grazing incidence X-ray diffractometry (GIXRD), Auger electron spectroscopy (AES), tribometer and a nanohardness tester were employed to characterize the nitrided layer. Further potentiodynamic polarization method was used to describe the corrosion behavior of the un-nitrided and nitrided alloy. It has been found that the Vickers hardness (HV) and corrosion resistance values of the nitrided layers increase with increasing plasma power while the wear rates of the nitrided layers reduce by two orders of magnitude as compared to those of the un-nitrided layer. This improvement in surface properties of the intermetallic alloy is due to formation of a thin modified layer which is composed of titanium nitride in the alloy surface. Moreover, all modified layers were tested for their sustainability as a biocompatible material. Concerning the application area of biocompatibility, the present treated alloy show good surface properties especially for the nitrided alloy at low plasma power of 400 W. # 2007 Elsevier B.V. All rights reserved. Keywords: Radio frequency (rf) plasma power; Auger electron spectroscopy (AES); Surface hardness; Corrosion resistance; Wear rate; Biocompatibility 1. Introduction The high specific strength and low density of the TiAl intermetallic alloys gave their great importance in the application area of automobile, aerospace and gas turbine industries [1–4]. However, these alloys are suffering from the weak oxidation resistance at temperature above 800 8C due to formation of the nonprotective oxides TiO 2 based scale [5,6]. Therefore, an intensive research work has been concentrated on the improvement process of the oxidation resistance by adding another element to form a continuous Al 2 O 3 scale. Niobium is one of the most important elements to provide TiAl-based alloys with good oxidation resistance, creep resistance and room temperature toughness [7,8]. In particular the alloys which contain niobium as high as 10 at.% keep the preferred lamellar microstructure and provide a protective layer of alumina scale [9,10]. Furthermore, great efforts have been also made to improve the room temperature mechanical properties of TiAl based alloy [11–13]. It is well known that the Ti-based alloys are well established biomaterials where the biocompatibility and corrosion resistance of these alloys are high [14,15]. The good biomaterials are widely used for hard-tissue implants which are particularly important for load bearing application such as total joint replacement, bone cement accessories, orthopedic implants and instrumentation [15,16]. Different plasma techniques can be successfully used to improve the physical, chemical, and biomechanical properties of titanium and Ti-based alloys for various industrial applications. Glow discharge gas nitriding [17–20], ion beam processing [21], anodic plasma chemical treatment [22], and rf plasma nitriding [23,24] are typical examples. The focus of this paper is to improve the surface properties of TiAlNb alloy using rf plasma nitriding. Different character- ization techniques were used to investigate the modified layer, www.elsevier.com/locate/apsusc Applied Surface Science 253 (2007) 9067–9072 * Corresponding author. E-mail address: ahmedphys96@hotmail.com (A.M. Abd El-Rahman). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.05.021