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RESEARCHERS FROM US AND RUSSIA DEVELOP PROCESS FOR MAKING PURE TITANIUM MEDICAL IMPLANTS
The process, a combination of Equal Channel Angular Pressing, or ECAP, and cold rolling or cold extrusion, nearly triples the strength of pure titanium. This development could have worldwide impact on the use of titanium medical implants in health care. Typically, titanium alloys have been the materials of choice for medical implants. In particular, a titanium alloy called Ti-6Al-4V is used for most orthopedic implants. The Ti-6Al-4V alloy is generally considered chemically inert, compatible with human tissue and resistant to corrosion by human body fluids. However, the small percentages of vanadium and aluminum metals contained in the alloy are potentially toxic. Normal wear can lead to deterioration of the implant and the release of alloy elements into the body. Pure titanium is chemically and biologically more compatible with human fluids and tissue. But it is too weak for prostheses that must bear heavy loads, such as leg or hipbone implants. The strength of pure titanium is less than half the strength of Ti-6Al-4V alloy. Using a two-step process combining ECAP and cold rolling or cold extrusion, researchers increased the strength of pure titanium to levels even higher than that of Ti-6Al-4V alloy. In the first phase of the process, titanium billets 26 mm in diameter and 120 mm long (about the size of a hotdog) were passed through the ECAP die eight times; the billets were rotated between consecutive passes. The billets emerged having the original dimensions, but the process reduced the metal's grain size from 10 microns, or 10 millionths of a meter, to about 260 nanometers, or 260 billionths of a meter. This reduction in grain size increased the strength of pure titanium by 70 percent. In the second stage of the process, the billets were further deformed at room temperature by rolling, extrusion, or the combination of the two, with a 35-75 percent reduction in cross-section area. After this final processing, ultra-strong medical implants can be machined from the ultrafine-grained titanium. This new process creates medical implants that are strong enough to bear heavy loads without failure. The implant material is corrosion resistant and chemically compatible with body organs and fluids so it can remain in the body for years. This nanostructured pure titanium is more biocompatible and can attach to human tissue better than the Ti-6Al-4V alloy. It could replace the alloy for most medical implants and devices, including, but not limited to, hip implants, hearing aids, dental implants, heart valves, and even parts for pace makers. The Los Alamos researchers who collaborated to create this new material are Y. Theodore Zhu and Terry C. Lowe of the Materials Science and Technology Division. Their partners from the Institute of Physics of Advanced Materials, Ufa State Aviation Technical University in Russia are Vladimir V. Stolyarov and Ruslan Z. Valiev. Synmatix Corporation, of Southfield, Michigan, will co-develop and commercialize the new material as an industrial partner. This work was made possible through the Department of Energy's Newly Independent States Initiatives for Proliferation Prevention Program.
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