A researcher at Western University has discovered never-before-seen deformation and stress levels in two materials – titanium and zirconium – both technologically important to the aerospace and nuclear industries.
Mechanical and Materials Engineering professor Hamid Abdolvand believes his work could lead to safer and longer lifespans for these materials, critical when considering the ways in which titanium and zirconium are used globally on a daily basis.
The study was published today by the journal Nature Communications.
Due to their unique mechanical properties, hexagonal closed-packed (HCP) polycrystals like titanium and zirconium are used extensively in many manufacturing and engineering sectors. But this industry-wide reliability is not without its concerns. For instance, the interaction and load sharing between the crystals, also known as grains, of titanium alloys can lead to a phenomenon known as cold dwell fatigue, which limits the life span of commercial aerospace components. Likewise, such interactions in zirconium alloys control the process of delayed hydride cracking in the key core components of nuclear reactors.
“If you have a strong grain, located in the middle of a lot of other stronger grains, the load in that middle grain relaxes because the other grains around it are now carrying the load. This simple concept can be used for tailoring and manufacturing stronger, and better engineering materials,” says Abdolvand.
Despite previous comprehensive analysis of HCP polycrystals, it has never been reported — until now — that grain-resolved stresses, along the loading direction, can drop while applied stress increases.
According to Abdolvand, the current assumption is that the load of each grain increases as tension is applied. But what Abdolvand found was, in 30 per cent of grains in zirconium and 20 per cent in titanium, that the effect is the opposite.
“It’s always been hard to determine how these grains in materials interact and we wanted to explain it. They share the load in a very specific way,” says Abdolvand. “But they have not been behaving in a way that we have been perceiving and thinking about for so long. This has become possible by developing new and advanced modeling and experimental toolboxes.”
Abdolvand, who joined Western’s Faculty of Engineering last year, conducted the study at the European Synchrotron Radiation Facility in France when he was a postdoctoral researcher at The University of Oxford’s Department of Materials.
The results of this research are open to the public and can be accessed at http://rdcu.be/EziA
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