Effects of Mo target power on the structure and tribological properties of AlB₂ Ta_1-xMo_xB films by magnetron sputtering

In this paper, magnetron sputtering from TaB2 and Mo stoichiometric targets is used to prepare AlB2 ternary Ta1xMoxB films. The films with various Mo contents were obtained by adjusting the Mo target powers. It was discovered that the contents of Mo have an obvious impact on the crystallinity and phase structure stability of Ta1-xMoxB films. When x = 0.43, the (001) and (002) orientation is improved, while stabler AlB2 structure is maintained simultaneously. While increasing x to 0.59, the films show amorphous structure. Meanwhile, as Mo contents rise, the hardness of films first decreases and then increases, eventually drops a lot. The Ta1-xMoxB films with x = 0.44 exhibit the superhardness (H = 49.9 +/- 1.5 GPa) and elastic modulus (E = 520 +/- 4.7 GPa), which benefit from the structure of Transition-metal diboride (TMB2) and solid solution strengthening effect. Alloying Mo can increase the Valence electron concentration (VEC) of films and therefore enhanced films toughness, higher fracture toughness (KIC = 1.13 MPa & sdot;m1/2) and elasticity (85.805%) were achieved when x = 0.44, the films showed better ability to resist plastic deformation even in 500 gf load. In addition, the Ta0.56Mo0.44B films obtain higher wear resistance (4.5 x 10-7 mm3/Nm) in air, but excess Mo atoms lead to deterioration of mechanical properties (H = 25.0 GPa,E = 240.0 Gpa for Mo90). Ta1-xMoxB ternary films with appropriate Mo content show a good potential as a hard protective coating.