Multifunctional ZrB 2 -rich Zr 1-x Cr x B y thin films with enhanced mechanical, oxidation, and corrosion properties

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 ZrB 2 -rich Zr 1 - x Cr x B y thin films grown by hybrid high-power impulse and dc magnetron co-sputtering (Cr-HiPIMS/ZrB 2 -DCMS) with a 100-V Cr-metal-ion synchronized potential. Cr metal fraction, x = Cr/(Zr+Cr), is increased from 0.23 to 0.44 by decreasing the power P zrb2 applied to the DCMS ZrB 2 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 zrb2 , as a result of supplying Cr to the growing film and preferential B resputtering caused by the pulsed Cr-ion flux. ZrB 2.18 , Zr 0.77 Cr 0.23 B 1.52 , Zr 0.71 Cr 0.29 B 1.42 , and Zr 0.68 Cr 0.32 B 1.38 2 films have hexagonal AlB 2 crystal structure with a columnar nanostructure, while Zr 0.64 Cr 0.36 B 1.30 and Zr 0.56 Cr 0.44 B 1.11 are amorphous. All films show hardness above 30 GPa. Zr 0.56 Cr 0.44 B 1.11 alloys exhibit much better toughness, wear, oxidation, and corrosion resistance than ZrB 2.18 . This combination of properties makes Zr 0.56 Cr 0.44 B 1.11 ideal candidates for numerous strategic applications.