Microstructure and mechanical behavior of nanotwinned AlTi alloys with 9R phase

Nanotwinned metals have shown high strength and ductility. However, metals with high stacking fault energy, such as Al, typically do not contain high-density growth twins or stacking faults. Here we show that by using a small amount of Ti solutes, 0.15–5.1 at.%, fine grains with a large population of extended incoherent twin boundaries bounding broad 9R phase form in sputtered AlTi films. These nanotwinned AlTi films have hardness as high as 2 GPa. This study provides an alternative approach to design high-strength Al alloys by grain refinement and introducing high-density twin boundaries and 9R phase.