Age hardening in superhard ZrB2-rich Zr1-xTaxBy thin films [Elektronisk resurs]

• We recently showed that sputter-deposited Zr 1-x Ta x B y  thin films have hexagonal AlB 2 -type columnar nanostructure in which column boundaries are B-rich for x < 0.2, while Ta-rich for x ≥ 0.2. As-deposited layers with x ≥ 0.2 exhibit higher hardness and, simultaneously, enhanced toughness. Here, we study the mechanical properties of ZrB 2.4 , Zr 0.8 Ta 0.2 B 1.8 , and Zr 0.7 Ta 0.3 B 1.5  films annealed in Ar atmosphere as a function of annealing temperature  T a  up to 1200 °C. In-situ and ex-situ nanoindentation analyses reveal that all films undergo age hardening up to  T a  = 800 °C, with the highest hardness achieved for Zr 0.8 Ta 0.2 B 1.8  (45.5±1.0 GPa). The age hardening, which occurs without any phase separation or decomposition, can be explained by point-defect recovery that enhances chemical bond density. Although hardness decreases at  T a  > 800 °C due mainly to recrystallization, column coarsening, and planar defect annihilation, all layers show hardness values above 34 GPa over the entire  T a  range. 

Ämnesord

Natural Sciences  (hsv)

Physical Sciences  (hsv)

Naturvetenskap  (hsv)

Fysik  (hsv)

Genre

government publication  (marcgt)

Indexterm och SAB-rubrik

Thin films; Transition-metal (TM) diboridesAge hardening; Thermal stability; Hardness and elastic modulus