Influence of the Al concentration in Ti-Al-B coatings on microstructure and mechanical properties using combinatorial sputtering from a segmented TiB2/AlB2 target

摘要

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 and over-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)B-2.70 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.