A primary mode of failure of thin-film coatings is the mismatch in thermal expansion coefficients of the substrate and the coating, which results in accumulation of interfacial stresses and ultimately in film delamination. While much attention has been devoted to modulation of interfacial bonding to mitigate delamination, current strategies are constrained in their generalizability and have had limited success in imbuing resistance to prolonged thermal cycling. We demonstrate here the incorporation of rigid thermal expansion compensators within polymeric films as a generalizable strategy for minimizing thermal mismatch with the substrate. Nanostructures of the isotropic negative thermal expansion (NTE) material HfV2O7 have been prepared based on the reaction of nanoparticulate precursors. The NTE behavior, derived from transverse oxygen displacement within the cubic structure, has been examined using temperature-variant powder X-ray diffraction, Raman spectroscopy, electron microscopy, and selected-area electron diffraction measurements. HfV2O7 initially crystallizes in a 3 × 3 × 3 superlattice but undergoes phase transformations to stabilize a cubic structure that exhibits strong and isotropic NTE with a coefficient of thermal expansion (CTE) = -6.7 × 10-6 °C-1 across an extended temperature range of 130-700 °C. Incorporation of HfV2O7 in a high-temperature thermoset polybenzimidazole enables the reduction of compressive stress by 67.3% for a relatively small loading of 26.6 vol % HfV2O7. Based on a composite model, we demonstrate that HfV2O7 can reduce the thermal expansion coefficient of polymer nanocomposite films, even at low volume fractions, as a result of its substantially higher elastic modulus compared to the continuous polymer matrix. By changing the volume fraction of HfV2O7, the overall coefficients of thermal expansion of the film can be tuned to match a range of substrates, thereby mitigating thermal stresses and resolving a fundamental challenge for high-temperature composites and nanocomposite coatings.
|Number of pages
|ACS Applied Materials and Interfaces
|Published - Sep 22 2021
Bibliographical noteFunding Information:
The authors gratefully acknowledge support of this work from the National Science Foundation under DMR 1809866, DMR 1455154 (M.P.T. and B.S.G.), and OIA 1355438 (partial salary support for M.P.T.). Partial salary support was provided by NASA Kentucky under NASA award no.: NN15AK28A (M.P.T.). The in situ TEM data reported herein was collected at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
© 2021 American Chemical Society.
- hafnium pyrovanadate
- in situ TEM
- negative thermal expansion
- thermal stress
ASJC Scopus subject areas
- Materials Science (all)