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JUL/AUG 2013  

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What’s old is new again

An engineering professor at the University of California, Riverside plans to use a century-old automotive manufacturing technique to enhance performance and reliability of new miniaturized medical devices, according to the university.

Masaru Rao recently received a 5-year, $400,000 Faculty Early Career Development award from the National Science Foundation, which, as one of its primary objectives, seeks to explore potential for strengthening miniaturized medical devices made from titanium.

Rao’s study will focus on developing techniques for strengthening tiny titanium-based medical devices, since this could lead to significant improvements in their performance and reliability, the university reports.

Masaru Rao

Masaru Rao, an assistant professor of mechanical engineering, works in a clean room.

While nearly all macro-scale metallic parts in use today rely on some form of strengthening, there has been minimal use of strengthening for micro- and nano-scale devices thus far. According to Rao, this is due, in large part, to limitations imposed by the micromachining techniques that must be used to access these reduced length scales.

For example, Rao’s technique only works with pure titanium, due to the highly chemical nature of the material removal mechanism upon which it is based. This, therefore, precludes opportunity for using it to micromachine other high strength biomedical alloys such as stainless steel, or even high strength titanium alloys, since all contain additional metallic elements that adversely affect the micromachining process.

To address these limitations, Rao will explore use of gas nitriding, a nearly century-old technique that is used widely for increasing the wear resistance of macro-scale metal parts for automotive and other applications such as with case hardened engine camshafts and rifle firing pins. In this technique, the surfaces of machined parts are strengthened by heating them in a nitrogen atmosphere, which causes nitrogen to diffuse into the metal.

When applied to titanium parts, the nitrogen atoms tend to squeeze into the spaces between the titanium atoms, thus forming a nitrogen-based titanium alloy. The presence of the nitrogen atoms makes it more difficult for the titanium atoms to rearrange themselves in response to mechanical loading, which leads to significant strengthening.

However, the relatively slow diffusion of nitrogen within the titanium means that strengthening is typically limited to the near-surface region (a few tens of micrometers at most), and the concentration of nitrogen decreases with depth.

Still, Rao thinks that this technique holds significant potential for miniaturized medical devices.

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