Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties

Sneha Samal,Tomáš Chráska,Orsolya Molnárová,Ondřej Tyc,Petr Šittner,Zdeněk Weiss,Jaromír Kopeček,Jan Cizek,Jakub Klecka,Esther De Prado,František Lukáč,Luděk Heller

doi:10.3390/coatings11050610

Abstract

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for the characterization of functional shape memory properties of the thick coatings was developed. The coatings exhibited cubic to monoclinic martensitic transformation and shape memory effect. The presented results prove that NiTi coatings with functional thermomechanical properties can be easily produced on structural materials by RF-ICP. Further optimization will be needed to prepare NiTi coatings with better microstructural and chemical homogeneity.

Highlights

NiTi shape memory alloys (SMA) are functional materials offering unique thermomechanical functional properties, in particular the shape memory effect, superelasticity, high damping, or actuation capability in contrast to conventional metals and alloys [1,2,3]
Alternative production routes have been reported in the literature, including thin film growth by magnetron sputtering [5], 3D printing by lasers [6], spark plasma sintering (SPS) [7] or self-propagating high temperature synthesis (SHS) [8]
The three coatings possessed significantly different microstructures, ranging from fully remelted (Sample 1), to semi-remelted (Sample 2), to a layered pattern typical for thermally sprayed coatings (Sample 3). Such difference is linked to the different heat input experienced by the NiTi material in the spraying: the power of 15 kW, spraying onto a stationary substrate, and the low amount of material fed into the process (2.1 g/min) all resulted into excessive of heat that caused remelting of the deposited coating

Summary

Introduction

NiTi shape memory alloys (SMA) are functional materials offering unique thermomechanical functional properties, in particular the shape memory effect, superelasticity, high damping, or actuation capability in contrast to conventional metals and alloys [1,2,3]. Alternative production routes have been reported in the literature, including thin film growth by magnetron sputtering [5], 3D printing by lasers [6], spark plasma sintering (SPS) [7] or self-propagating high temperature synthesis (SHS) [8] Despite their successful use in the production of NiTi components for selected specific applications, none of these methods became widely commercialized yet

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