Shape memory alloys

Shape Memory Alloys (SMA) promise to become a vital part of future alloy compositions. The first shape memory alloy was discovered in USA around 1968, but it took it nearly two decades to become accepted in industry. The first major useful application was in rivets used to fasten thick steel girders on bridges. A rivet is like a nail, but with heads on both sides, and it holds things really tight.

Earlier, the workers would have to hang on the most dangerous 'outer' side and hammer the rivet heads into shape. With SMA rivets, the worker can do this without hanging outside. He just takes a portable soldering gun and heats the end of the rivet. In the factory, the rivet had been forged with a head, but was later the head was hammered down into a shape useful for passing through holes. When the worker heats the end of the rivet with his soldering gun, the rivet 'remembers' it had a head once, and promptly takes that shape. This takes a few seconds, and the rivet is fixed!

Here's a video* showing how fabulous these things can be:

These days SMAs are used in biomedical implants. Initially development of these alloys was slow due to the use of a nickel-titanium alloy called 'Nitinol' which was expensive and difficult to fabricate. Research in Japan led to about 160 alloys based on nickel with other, cheaper metals. The world is now looking afresh at this magical material.

More amazing titanium alloys

Titanium (Ti) is a lightweight metal which forms amazing alloys with aluminium, vanadium, tantalum, niobium etc. These alloys are hardy while being light. Initially, they were used in aerospace and aviation for making aircraft bodies. But now more applications are being found in automobile and general engineering. For example, the Tata Chemicals factory at Mithapur uses huge Ti-alloy vessels for processing caustic soda, which will otherwise corrode stainless steels in seconds.

Ti-alloys are difficult to weld and cut, hence they have not edged out steels. But they rule the roost in bio-medical implants. Ti alloys are now common in making jewellery, golf-clubs, expensive watches... there's a lot that can be done!

Powder Metallurgy alloys

Powder Metallurgy (P/M) is a shorter route for making alloys in just 2-3 steps. The traditional foundry route takes 11-12 steps and then requires a lot of cleaning, machining or grinding/polishing before the product can be used. P/M products are always 'near net shape' which means they are ready to use, without needing finishing operations. Metals that are difficult to melt and alloy, like tungsten, tantalum or molybdenum, can easily be handled. The modern automobile has a lot of crucial parts made with P/M methods.

Composites

These are odd combinations that are not really alloys. The most familiar and age-old example is that of Fibre Reinforced Plastics, better known as fibre glass which is used in sports cars. Composites today are made from any possible combination. MMCs or Metal Matrix Composites are metallic materials reinforced with carbon fibres or boron particles. Reinforced Cement Concret (RCC), which is used to make today's buildings, consists of cement-based concrete reinforced with steel rods. This makes them take great loads without breaking up.

Credits

The material for this article was contributed by Mr. M.A.K. Babi, eminent metallurgist and plasma technologist.

*video titled "RambI3r - January 23, 2009 - Titanium Nickle Alloy- when heated it returns to the shape it was originally molded to." sourced from www.YouTube.com