LAUSR

Abstract A series of (TixAl1-x)B2+y coatings with compositions in the range of x = 0.01–0.94 and y = 1.70–2.92 has been synthesized using magnetron sputtering from a segmented TiB2/AlB2 target. The coatings are amorphous at x ≤ 0.05 while a (TixAl1-x)B2+y solid solution forms for x > 0.05. As a consequence of the sputtering process, the B/(Ti + Al) atomic ratio varied with the metal content resulting in the formation of under-stoichiometric coatings at x   0.35. Surplus Al segregates to grain boundaries of the under-stoichiometric coatings whereas the over-stoichiometric coatings have a tissue phase containing mainly B and some Al. The B-rich tissue phase restrains grain growth in the in-plane direction while an increase in Ti content promotes the growth of columnar structured coatings with a pronounced (001) texture up to x = 0.84. The combination of such preferred orientation and tissue phase results in the highest hardness of 39 GPa for the (Ti0.79Al0.21)B2.70 coating. The Young's modulus, on the other hand, increases continuously from 262 GPa for the most Al-rich coating to 478 GPa for the most Ti-rich coating. Comparing to calculated values of Young's modulus, good agreement is observed for the close to stoichiometric coatings (x = 0.40–0.50). For the off-stoichiometric coatings, the experimental values are lower due to the existence of the tissue phase.