Tissue phase affected fracture toughness of nano-columnar TiB2+z thin films

Structural imperfections such as nano-columnar tissue phases constitute a morphological design feature in protective thin films. Especially in the rising group of PVD transition metal diborides, excess Boron is known to form nm-sized B-rich precipitations in-between nano-crystalline domains. Here, we focus on super-stoichiometric TiB2 + z thin films, varying the stoichiometry from TiB2.04 to TiB4.42 (B: 67-82 at.%). The tissue phase fraction and thickness is mainly governed by the B content and corresponding deposition conditions. A decreasing tissue phase width from approximate to 3-1 nm leads to an increasing critical stress intensity factor K-IC of approximate to 40%.

Automated summary

Structural imperfections, such as nano-columnar tissue phases, are an important feature in protective thin films. In PVD transition metal diborides, excess Boron results in nm-sized B-rich precipitations between nano-crystalline domains. This study focuses on super-stoichiometric TiB2 + z thin films, varying the stoichiometry from TiB2.04 to TiB4.42 (B: 67-82 at.%). The fraction and thickness of the tissue phase are mainly determined by the B content and deposition conditions. A decrease in tissue phase width from approximately 3-1 nm leads to an increase in critical stress intensity factor K-IC of approximately 40%.