2, Empa, Swiss Federal Laboratories for Materials Science and Technology, Thun, , Switzerland
Nanolaminated metallic multilayers can show extreme strengths due to the ability to induce a strengthening mechanism, confined layer slip, which is only possible at length scales on the order of 10’s of nm’s. Similar performance can be found in materials which are formed in a metastable structure and then subsequently thermally treated to precipitate extremely fine arrays of second phase particles. This current study explores combining these two strengthening mechanisms to precipitate hard particles within a metallic multilayer. The relatively immiscible system of Cu/Cr was selected as the multilayer structure. Three systems were formed using sputter deposition: a Cu-5%Cr/Cr bilayer which was then subsequently heat treated to for Cr precipitates within the Cu layer, a Cu/Cr with W particles deposited on the interface between the FCC and BCC layer, and a Cu-W particle / Cr system where W particles were co-deposited during the Cu deposition. All layer thicknesses were 30 nm, and the particles ranged from 5 to 15 nm in size. All systems were then tested using nanoindentation to assess the hardness, and two different tips (Berkovich and cube corner) used to explore strain hardening behavior. The Cu-5%Cr system softened by approximately 5% when heat treated at 373K, but then increased in hardness by 10% when annealed at 573K. However, it was not possible to determine if the Cr precipitated at the Cu-Cr interface, or within the Cu layer itself. The W system was used to explore the difference in the impact of the effects of particles at the interface versus within the ductile FCC layer, and these results were compared to computational simulations using a combination of DFT and MD to explain the impact that intra-, rather than inter-layer deposition had on strength.