# Protection of N‑Type (Ni,Fe)TiSb Half-Heusler Materials against Static and Cyclic Oxidation Using a Si-Doped Cr Coating

## TL;DR

A Cr-Si coating was developed to protect thermoelectric materials from oxidation at high temperatures, significantly improving their durability.

## Contribution

A novel Cr–Si coating is shown to effectively protect N-type (Ni,Fe)TiSb materials from static and cyclic oxidation.

## Key findings

- Uncoated samples formed a TiO2 layer and NiSb-rich zone with cracking and delamination.
- Cr–Si coatings remained stable and resistant to oxidation under both static and cyclic conditions.
- Coated samples showed negligible mass gain and no mechanical damage after exposure.

## Abstract

In this study, Cr–Si coatings were deposited on
N-type (Ni,Fe)­TiSb
thermoelectric (TE) materials by using a closed-field unbalanced magnetron
sputtering PVD technique. Oxidation behavior was evaluated under both
isothermal (static) conditions (500 °C for 10 h and 600 °C
for 50 h) and thermal cycling regimens (500 and 600 °C for 10
or 50 1 h cycles). Mass gain, surface morphology, cross-sectional
microstructure, elemental distribution, and phase composition were
examined by using scanning electron microscopy (SEM), energy-dispersive
X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Regardless
of exposure mode, uncoated samples oxidized severely: a duplex scale
formed, consisting of an outer TiO2 layer and a subjacent
NiSb-rich zone, accompanied by extensive cracking and delamination.
In sharp contrast, the Cr–Si coatings remained thermally stable
and highly oxidation-resistant, maintaining the substrate’s
integrity during both static and cyclic tests. After exposure, coated
samples showed negligible mass gain, no discernible morphological
change, and no mechanical damage, confirming that the Cr–Si
layer markedly enhances thermal durability and prevents surface degradation.