Multifunctional ZrB2-rich Zr1-xCrxBy thin films with enhanced mechanical, oxidation, and corrosion properties

Babak Bakhit,Grzegorz Greczynski,Lars Hultman,Jun Lu,Agnieszka Kooijman,J.E Greene,Zhengtao Wu,Johannes M.C Mol,Ivan Petrov,Samira Dorri,Johanna Rosen

doi:10.1016/j.vacuum.2020.109990

Abstract

Abstract Refractory transition-metal (TM) diborides have high melting points, excellent hardness, and good chemical stability. However, these properties are not sufficient for applications involving extreme environments that require high mechanical strength as well as oxidation and corrosion resistance. Here, we study the effect of Cr addition on the properties of ZrB2-rich Zr1-xCrxBy thin films grown by hybrid high-power impulse and dc magnetron co-sputtering (Cr-HiPIMS/ZrB2-DCMS) with a 100-V Cr-metal-ion synchronized bias. Cr metal fraction, x = Cr/(Zr + Cr), is increased from 0.23 to 0.44 by decreasing the power P ZrB 2 applied to the DCMS ZrB2 target from 4000 to 2000 W, while the average power, pulse width, and frequency applied to the HiPIMS Cr target are maintained constant. In addition, y decreases from 2.18 to 1.11 as a function of P ZrB 2 , as a result of supplying Cr to the growing film and preferential B resputtering caused by the pulsed Cr-ion flux. ZrB2.18, Zr0·77Cr0·23B1.52, Zr0·71Cr0·29B1.42, and Zr0·68Cr0·32B1.38 films have hexagonal AlB2 crystal structure with a columnar nanostructure, while Zr0·64Cr0·36B1.30 and Zr0·56Cr0·44B1.11 are amorphous. All films show hardness above 30 GPa. Zr0.56Cr0.44B1.11 alloys exhibit much better toughness, wear, oxidation, and corrosion resistance than ZrB2.18. This combination of properties makes Zr0·56Cr0·44B1.11 ideal candidates for numerous strategic applications.

Highlights

Transition-metal (TM) nitride coatings have many industrial appli cations from mechanical components in aerospace industry to cutting tools [1,2,3,4]
The Cr metal fraction, Cr/(Zr + Cr), is increased from 0.23 to 0.44 by decreasing the power PZrB2 applied to the DCMS ZrB2 target from 4000 to 2000 W in 500-W increments, while the average power, pulse width, and frequency applied to the HiPIMS Cr target are maintained constant at 700 W, 50 μs, and 100 Hz, respectively
We demonstrate control of the composition, nanostructure, and properties of ZrB2-rich Zr1-xCrxBy films grown by hybrid Cr-HiPIMS/ ZrB2-DCMS co-sputtering

Summary

Introduction

Transition-metal (TM) nitride coatings have many industrial appli cations from mechanical components in aerospace industry to cutting tools [1,2,3,4]. Metastable NaCl-structure Ti1-xAlxN layers grown by magnetron sputtering are the most attractive group of TiN-based thin films, suitable as protective coatings for cutting tools, which show good hardness (typically ~30 GPa), high wear and oxidation resistance (depending on Al concentration), and self-hardening effects at elevated temperatures up to ~900 ◦C (resulting from spinodal decomposition) [3,4,5]. Zr1-xTaxBy alloys with x ≥ 0.2 exhibit a self-organized columnar core/shell nano structure in which crystalline Zr-rich stoichiometric Zr1-xTaxB2 cores are surrounded by narrow dense, disordered Ta-rich (B-deficient) shells that have the structural characteristics of metallic-glass thin films; both high strength and toughness [18] These layers show a high thermal stability in which their hardness increases as a function of annealing temperature up to 800 ◦C. Films with the highest Cr content, Zr0⋅56Cr0⋅44B1.11, exhibit a combination of enhanced properties

Experimental

Elemental compositions and microstructure

Mechanical properties

Oxidation properties

Corrosion properties

Conclusions