Abstract
The multiscale analysis in the authors’ finite element code confirmed possibility of fracture, because of not sufficiently high level of compressive residual stress in the TiN deposited by physical deposition method and varied mechanical properties of the thin film and substrate. The residual stress cannot be identified by X‐ray technique for amorphous polymer and layer with domains of crystalline TiN. It is assumed that the buffer biocompatible thin film of Au in the TiN/Bionate II material system will alter the evolution of residual stress and, therefore, will allow to determine the residual stress in profilometry studies, and helps to improve toughness of the connection between TiN and Bionate II. The introduction of Au nanocoating in the material system results in bending of the sample and a compressive residual stress in the TiN coating. Results of finite element simulation show improvement of connection between the polymer and TiN, and an increase of compressive residual stress in the coating by introduction of Au nanointerlayer results in reduction of stress and strain in the substrate (close to the boundary between substrate and coating).
Highlights
The Polish pneumatic ventricular assist device (VAD) [1] is made of a thermoplastic polycarbonate-urethane Bionate II
A biocompatible thin film is recommended for surfaces of the VAD, so our construction has a TiN nanocoating deposited by a pulsed laser deposition (PLD) technique
For the PLD process, kinetic energies of ions and neutral species in an ablation plume can range from a few tenths to several hundred electron volts and are sufficient to modify a stress state of superficial layers through defect formation [14]
Summary
The Polish pneumatic ventricular assist device (VAD) [1] is made of a thermoplastic polycarbonate-urethane Bionate II. A biocompatible thin film is recommended for surfaces of the VAD, so our construction has a TiN nanocoating deposited by a pulsed laser deposition (PLD) technique Some disadvantages of this structure were presented elsewhere [11]. The PLD is a low temperature process allowing permanent modification of some properties only in a superficial layer of product, so it can be successfully applied on the polymer substrate This technique as the other physical vapour deposition (PVD) processes usually develops high values of residual stresses [12]. Experimental and numerical verifications of the effect of gold buffer on the residual stress in the TiN nanocoating deposited on the Bionate II polymer substrate and on the structure properties determined during a microtensile test are the practical goals of the present work. We hope that presented approach will be helpful to design the optimal structure of the VAD and provide methodology for construction of similar structures dedicated for other applications
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