Nano-Impact (Fatigue) Characterization of As-Deposited Amorphous Nitinol Thin Film

This paper presents nano-impact (low cycle fatigue) behavior of as-deposited amorphous nitinol (TiNi) thin film deposited on Si wafer. The nitinol film was 3.5 mu m thick and was deposited by the sputtering process. Nano-impact tests were conducted to comprehend the localized fatigue performance and failure modes of thin film using a calibrated nano-indenter NanoTest T, equipped with standard diamond Berkovich and conical indenter in the load range of 0.5 mN to 100 mN. Each nano-impact test was conducted for a total of 1000 fatigue cycles. Depth sensing approach was adapted to understand the mechanisms of film failure. Based on the depth-time data and surface observations of films using atomic force microscope, it is concluded that the shape of the indenter test probe is critical in inducing the localized indentation stress and film failure. The measurement technique proposed in this paper can be used to optimize the design of nitinol thin films.