Crack Spacing and the Flow Stress in NiTi Thin Films Deposited on Cu Substrate

Yong Hua Li; F.L. Meng; Chang Sheng Liu; Y.M. Wang

doi:10.4028/www.scientific.net/KEM.385-387.89

Paper Titles

Crack Development in Concrete, Part 2: Modelling of Fracture Process
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The Rationale of Adhesive Postinstalled Method to Estimate the Concrete Strength
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Cracking Cohesive Law Thermodynamically Equivalent to a Non-Local Damage Model
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Crushing Behaviour of CFRP Composite Structure
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Crack Spacing and the Flow Stress in NiTi Thin Films Deposited on Cu Substrate
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Crack Width of SRC Members Based on Fracture Mechanics
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Damage Analysis of the SRHSHPC Frame Columns under Low Cyclic Reversed Horizontal Loading
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Dynamic Growing Crack Tip Field in Visco-Elastic Compressible Material
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Dynamic Stress Intensity Problem of SH-Wave by Double Linear Cracks near a Circular Hole
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Crack Spacing and the Flow Stress in NiTi Thin Films Deposited on Cu Substrate

Abstract:

Ti-51.45at.%Ni thin films were deposited onto copper substrates by magnetron sputtering. The copper substrates were pre-punched into dog-bone specimens with 4.5mm×30mm(gauge portion) ×35µm( thickness). The substrate temperature was about 673K. The thin films were about 20µm thick. The as-deposited films were first solution treated at 1073K for 1h, and then aged at 773K for 30min. The grain size was estimated to be 1.5µm from scanning electron microscopy micrographs. Tensile tests were carried out on CSS-44100 electron universal test-machine. The strain rate was 1.1×10-4 s-1. The stress-strain curves of the free-standing film were obtained from the experimental stress-strain curves of copper substrate together with the thin film adherent to the substrate compared with the curves of copper substrate without film. The Hall-Patch coefficient was calculated, k=205Mpa.µm1/2. It seems that the Hall-Patch coefficient decreases with increasing film thickness. The experimental results showed that a series of parallel cracks grew in a concerted fashion across the thin film and the cracks were equally spaced. The cracks were more closely spaced if the film stress was increased. The fracture toughness of the film was estimated, c KΙ =0.96MPa·m1/2. Therefore, the minimum crack spacing is predicted by the film stress given.