Abstract
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 µm 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™, 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.
Highlights
Nitinol based shape memory alloys (SMAs) possess a unique combination of engineering properties such as shape memory and superplasticity and can be used in various applications [1,2]
Nitinol (TiNi) based thin film SMAs are considered as a core technology for actuation of some micro-electro-mechanical system (MEMS) devices, where large force and stroke are essential in condition of low duty cycles or intermittent operations, and in extreme environment, such as radioactive, space, biological and corrosive conditions [1,2]
These nitinol thin films may suffer from several forms of fatigue damage that range from component shape change to catastrophic failures [2,3]
Summary
Nitinol based shape memory alloys (SMAs) possess a unique combination of engineering properties such as shape memory and superplasticity and can be used in various applications [1,2]. Nitinol (TiNi) based thin film SMAs are considered as a core technology for actuation of some MEMS devices, where large force and stroke are essential in condition of low duty cycles or intermittent operations, and in extreme environment, such as radioactive, space, biological and corrosive conditions [1,2]. During applications, these nitinol thin films may suffer from several forms of fatigue damage that range from component shape change to catastrophic failures [2,3]. These films should have low residual stress to prevent deformation, precise deformation control, good adhesion to substrate, durable and reliable shape memory effects, and good resistance to wear [1].
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