New research shows defects in twin boundaries that strengthen materials

May 20, 2013

New research shows defects in twin boundaries that strengthen materials

Through experiments and simulations, a team of Lawrence Livermore National Laboratory scientists have found that twin boundaries (TBs) with good electrical conductivity and a strengthening mechanism in materials may not be so perfect after all.

Coherent twin boundaries (CTBs) have been studied for years and conventional wisdom dictates these interfaces are ideal for strengthening materials with very few defects.

However, the team, led by LLNL material scientist Morris Wang, found that when looking at CTBs in nanotwinned copper, they are inherently defective with kink-like steps and curvatures that consist of incoherent segments and partial dislocations.

Originally, scientists believed that CTBs in materials were much more reliable and stable than conventional grain boundaries, which are incoherently full of defects. But the new research shows they could both contain similar types of defects despite very different densities.

"Understanding these defective structures is the first step to take full use of these CTBs for strengthening and maintaining the ductility and electrical conductivity of many materials," Wang said. "To understand the behavior and mechanisms of these defects will help our engineering design of these materials for high-strength applications."

CTBs act as one of the major strengthening sources for a variety of materials and can maintain high conductivity. The defects have substantial impacts on the fundamental mechanical properties of materials, according to Wang.

Other LLNL researchers include Thomas LaGrange, Jaime Marian, Troy Barbee, Jr. and Alex Hamza. Collaborators from the University of Vermont and Ames Laboratory also contributed to the research. The research appears in the May 19 issue of the journal Nature Materials .