Metallurgists' models predict alloy applications

Impurities could make soft metals the next-generation materials for jet-engine and nuclear-power plant turbines, claim US scientists.

Dallas Trinkle and Christopher Woodward from the materials and manufacturing directorate at Wright Patterson Air Force base used theoretical chemistry models to investigate the observation that some metal additives soften rather than strengthen the resulting alloy. This contradiction has baffled metallurgists for years, say leading materials scientists.

Hard, strong metals can have what Trinkle describes as disastrous properties: low malleability and poor fracture resistance. Impurities - or solutes - soften the metal, and the fracture risk decreases. 

Trinkle and Woodward looked at molybdenum and other metals with body centre cubic structures. The metal is softened when so-called 5d solutes, rhenium or platinum are added. Softening is caused by chemical effects where crystal defects called dislocations have different bonding environments to the bulk metal. ’This difference is needed to correctly predict plastic behaviour,’ said Trinkle. ’Solute softening is a dramatic example of the importance of chemistry effects on deformation, or plasticity.’

Trinkle and Woodward’s theoretical models will be used to predict alloy properties, and new high-temperature alloys will be developed. Trinkle predicts applications for the alloys in jet-engine turbine blades, in nuclear power plants, or to replace the ceramic tiles that protect space vehicles when they re-enter the Earth’s atmosphere.

Metallurgy has suffered from a lack of predictability, said materials scientist Daryl Chrzan from the University of California. Trinkle and Woodward’s work is ’inspiring’ he told Chemistry World. ’They have used predictive theories that are normally the domain of chemists and solid-state physicists, to solve one of the outstanding puzzles of modern metallurgy - why impurities which should make a material stronger, sometimes make a material softer,’ said Chrzan.

Katharine Sanderson