Impact of the B/C-doping ratio on the microstructure, mechanical properties, and cutting performance of AlTiN-based coatings

Certain element doping is a facile and powerful vehicle for tailoring the organization and properties of hard coatings. This research fabricated AlTiBCN coatings with various B/C doping ratios (the boron-carbon incor-poration totaled 10 at.%) and explored the effect law of varying B/C ratios on the coatings' microstructure, mechanical properties, tribological, and cutting performances. All coatings exhibited a mixed structure of cubic and fibrous zincite phases, with the major phase being w-Al(Ti)N and the minor phases being c-Al(Ti)N and c-Ti (C, N). Besides, along with the increase in C-doping proportion, the coating organization shifted from a featureless glassy pattern to a fine-grained columnar crystal morphology. Boron was mainly found as-BN in the coatings, while carbon was mostly found as c-Ti(C, N) replacement solid solution (B/C ratio <= 2.5:1, 0:10) and amorphous C (B/C ratio <= 1:2.5, 0:10). According to the properties results, (1) AlTiBCN coating with a B/C ratio of 1:1 had the optimal mechanical, tribological, and cutting performance; (2) AlTiBCN coating with a B/C ratio >= 2.5:1 and 10:0 had higher hardness but poorer coating brittleness and tribological properties due to excessive alpha-BN; (3) At B/C ratios <= 1:2.5 and 0:10, the mechanical properties of its coatings dropped sharply, which means the coating's hardness, toughness, and wear resistance are aggravated by the strong softening effect of alpha-C.