 10 (2) ● February 2012 www.arpapress.com/Volumes/Vol10Issue2/IJRRAS_10_2_07.pdf                !" #$ %&!’( # ) *&+, -## Department of Mechanical Engineering, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria . Fractal analysis is used to numerically characterize the pores in AISI316L stainless steel to be able to study the shape, distribution and type of the pores. The fractal analysis uses two dimensionless parameters: fractal dimension D and Sphericity, β. The AISI316L stainless steel is widely used in medical field as an implant material due to its good corrosion resistance and biocompatibility. In this work AISI316L, stainless steel was implanted with two different ions: Oxygen and Helium separately at 100KeV with dose of 1×10 17 ions/cm 2 at room temperature. The crystallographic orientation and surface morphology were studied using x-ray diffraction analysis (XRD). The micro hardness was measured by Vickers method with varying load. The result indicated that the predominant pores in the virgin material are of spherical shapes with β< 0.3 and D>1. It was further observed that the pores are flake like type and clustered, thereby creating ease of linkage of the pores. The ion implantation showed a reduction in the pores, predominantly noodle-like types, (i.e. a shape change from spherical to round pores) and change in distribution from clustered to randomly spaced pores. The surface hardness is found to be 1202HV, 1020HV and 195HV for Helium, Oxygen and Virgin material respectively. There is a significant improvement in the shape, type, and distribution of the pores in AISI316L stainless steel implanted with Oxygen and Helium. The Vickers hardness test shows that the micro hardness of AISI316L stainless steel implanted with Oxygen and Helium is higher than that of the virgin material. -/0!+,1          #  The use of fractals to study surfaces of different materials has been done by different researchers and it is still receiving increasing attention. Scientists who study or try to describe natural phenomena have to consider the use of fractal geometry. From the theory of chaos to land surface description, from sea surface synthesis to stock market analysis, fractal concepts are used in more and more research fields (Giuseppe et.al. 2006). Chung-Kung (1998) used the fractal analysis and observed the effect of heat treatment on the well measured nitrogen isotherms on alumina and aluminum borate samples. He observed that heat treatment, for the two methods used may decrease fractal dimension,D of the four examined porous samples. From analysis carried out, fractured surfaces were discovered to be fractal in nature (Alexander, 1990). For alloys and composite materials containing regular microstructures a prediction of mechanical properties can be made by a quantitative measurement of features such as grain size, particle size, and spacing etc. This however is not the case where an irregular microstructure is involved because of difficulty in a numerical characterization of the structure. For each microstructure the application fractal geometry offers a method by which both the individual particle shapes and the mode of distribution of the particles can be fully described in numerical manner (Shu-Zu and Hellawell,1994). Durowoju (2007) used the fractal analysis to observe the size, shape, and distribution of pores in Al-V 2 O 5 alloyed composite. The analysis revealed that the pores are of irregular shapes, i.e Shrinkage pores, with β< 0.3.The graph of β against D shows that as β decreases the D values increases. Similarly, the sizes, shapes and distribution of the pores in samples of Al-20%wtMg heat-treated at 470 0 C for a soaking time of 30 minutes was done (Durowoju et. al., 2009). The results show that in the graph of β against D there exist critical values of fractal dimensions (1.0360 and 1.0510) above which any increase in the fractal dimension causes a decrease in the sphericity. Similarly, there exists minimum values of fractal dimension and sphericity (D= 1.048 and β= 0.0384), above which the tensile strength and hardness increases. AISI 316L stainless steel is being widely used as biomaterials and materials of construction. More specifically, AISI 316L SS is used in the medical field as an implant material due to its unique property of good corrosion resistance and biocompatibility.The success of implant in the human body depends on many factors such as bio safety, biocompatibility and biofunctionality in the environment wherein the implant are placed. But if the body environment is harsh, this might result in corrosion of implants (Liu Chenglong et al.,2005).Although AISI 316L stainless steel shows extremely good corrosion resistance, it is nevertheless prone to defects (pitting, pores, voids e.t.c) . Surface modification techniques have been applied to improve the corrosion resistance of AISI 316L stainless steel (Fossati et al.,2006). The use of implantation as a surface modification method has been done by different researchers.Nitrogen was implanted in