Implant Surface Treatment Research Articles

Ion implantation effects on friction and wear of joint prosthesis materials

The literature contains many results from in vitro friction and wear tests for simulating the behaviour of human joint prostheses. However, they are difficult to correlate, even when they are not contradictory. In friction tests, several friction-mechanisms occur when the Ti-6AI-4V titanium alloy rubs against the UHMWPE polyethylene. Corrosion effects which increase wear happen when the 316L stainless steel is used in Ringer's solution. Ion implantation surface treatments have been performed on these three materials. When the operating conditions were optimized, an important reduction of wear and corrosion was observed. The property improvements are due to structural modifications in a thin layer of the materials.

Medical application of ion implantation (Ionguard TM) for overall improvement of titanium alloys

Ion implantation is an emerging technology that allows for selective modification of the surface properties of materials. Properties such as hardness, corrosion resistance, friction and others can be improved without adversely affecting the bulk properties of the material. This paper concentrates on the discussion of the overall improvement of orthopaedic implants by the ion implantation (IONGUARD TM ) process. The unique capabilities, outstanding features and overall potential of the technology are described. Based on the very impressive improvement in wear, corrosion and fatigue resistance, the ion implantation process is expected to become the technology of choice not only for surface treatment of titanium orthopaedic implants but also in other medical applications such as titanium surgical scissors or dental implants. The technology is also expected to have an increasing contribution in a great variety of other applications such as the aerospace field.

Critical stress in silicon brittle fracture, and effect of ion implantation and other surface treatments

We introduce a method, which is free of specimen edge effect, for the determination of critical stress in material brittle fracture. Using this method, we have investigated the critical stress in silicon brittle fracture. Silicon wafers polished with silica gel showed an average fracture stress of 2.8 GPa, with a standard deviation of 1.2 GPa and a maximum observed value of 6.9 GPa. We have also investigated effects of various surface treatments on the critical stress. Mechanically lapped surfaces, with damage penetrating deeper than ∼3 μm, reduced the fracture strength to 0.3–0.4 GPa (damage surface placed in tension). Both polysilicon and quartz overlays reduced the silicon fracture strength only very slightly, while argon implantation (at 150 keV, with a dose of 1×1016 cm−2) did not show a detectable effect. However, anneal of the argon implanted samples at 900 °C in nitrogen for one hour significantly increased the silicon fracture strength, conceivably as a consequence of the removal of existing surface flaws by an epitaxial regrowth of the implantation-amorphized surface layer. The last finding is both of basic interest and of practical significance. Silicon wafers of (100) orientation showed a ∼50% higher fracture strength than wafers of (111) orientation.