From turbine blades to wedding bells

What happens to nickel-based superalloy turbine blades when they are taken out of service?

Well, in this case, they get turned into tokens of love!

Because Dr William Newby’s fiancée, Claire Malpas, has spent most of her adult life working with gas turbine engines, Will thought it would be perfect if he could have their wedding rings made out of a recycled turbine blade, so he contacted the University of Sheffield to see if we could help.

Reprocessing this material proved to be no mean feat. Turbine blades are designed to withstand extreme temperatures, so melting the metal to ensure sufficient fluidity to fill particularly small casting cavities in specially designed sand moulds was quite a challenge.

Will, who works for Sandberg Consulting Engineers with Sheffield alumnus Dr Simeon Tulip, said, “I came up with this idea some time ago, and was determined to see it through.

“Sim shared my enthusiasm and, from his time at Sheffield, he knew that they had the expertise and equipment to do the job.”

Sim called in a favour from Neil Hind, Senior Engineering Technician, and Dr Lisa Hollands, Technical Engineering Team Leader in the Department of Materials Science and Engineering at the University of Sheffield to melt and cast the rings.

The process took its toll on the crucibleWill and Claire's wedding rings are made out of a turbine blade from the first stage of the high pressure turbine in an industrial engine. The high pressure turbine is the hottest and most highly stressed moving part in the whole engine. The blade operates at temperatures well in excess of its melting point, thanks to some advanced coatings and fancy cooling techniques.

There aren't many places in the country that can do this sort of thing; the melting temperature of this material is in excess of 1400 °C. Even lava, freshly spewed from a volcano wouldn't do it! But at Sheffield, we were able to help.

Using a furnace with a maximum temperature of 1650°C, it took nearly an hour and a half to melt the chunks of fan blade, during which time the crucible started to vitrify. Neil, the man with a wealth of experience with molten metal, grasped the glowing crucible with long tongs, punched through the chromium oxide slag layer, and poured the rings.

Sectioned turbine blade Removing the crucible from the furnace
Pouring the metal into the ring mould Taking the cast ring out of the mould

(All photos courtesy of Dr Will Newby)

All that was left to do now was to cut off the gate and runners, then grind, fettle, and polish them into the finished article. This was undertaken, with considerable skill, by technicians at Sandberg who managed to shape the inside and outside of the rings into a recognisable form, of the right size.

The unfinished rings The rings approaching completion

As you can see, the end product is stunning!

The advanced metallurgy does have a downside though: should the rings ever need to be removed in an emergency, it would take more than a pair of pliers or even a Dremel to do the job! But that's been taken care of too. Sort of.

Normally, one would apply a heat treatment to increase the strength of an alloy by 'trapping' certain phases in a favourable state. However, Will and Sim did the opposite. They tempered the rings in such a way as to decrease their strength by promoting the formation of the so-called sigma phase.

This causes the alloying elements to rearrange themselves in an uncooperative fashion, which reduces the toughness, ductility, and tensile strength of the alloy.

They also introduced a weak spot on the inside of each band, so it should be possible to break them without the fires of Mordor.

Nonetheless, this is all relative. The rings are still much stronger than typical gold, platinum, or even titanium wedding bands!

Will and Claire tie the knot on Saturday in Warwickshire, and we, in the Department of Materials Science and Engineering, wish them a lifetime of happiness together.