Improved high temperature stability and enhanced high-speed dry cutting performance of AlCrBN coatings by alloying with B

Abstract

Boron (B)-containing AlCrBN coatings are promising protective coatings for high-speed dry cutting application. In this work, AlCrBN coatings with various B contents (0 at.%, 2.9 at.%, and 4.8 at.% namely B0, B1, and B2) were synthesized, and their high-temperature and high-speed dry cutting performance were evaluated by the high-temperature vacuum annealing and high-speed dry cutting experiment. Comparing with B0 coating (AlCrN coating without B), B1 and B2 coatings delayed/suppressed the phase decomposition from fcc-(AlCr)N into h-AlN and Cr₂N, and also suppressed the diffusion of Co from the substrate into the coating surface at an annealing temperature of 1000 °C. This also contributed to the high annealed hardness of 3400 HK_0.05 at 1000 °C for B1 and B2 coatings. High-speed dry turning result showed that B1 coated insert exhibited a longer cutting time (13 min), required less cutting force, and had a lower coefficient of friction during the whole cutting process. The wear mechanisms are abrasive, adhesive, and oxidative on both rake faces and flank faces for all coated inserts, however, addition of B reduced its wear of a B1-coated insert. TEM results from the worn rake face of a B1-coated insert revealed that an oxide tribo-film composed of w-AlN and Al₂O₃ emerged upon the unaffected AlCrBN coating, further confirming the structural stability of the AlCrBN coating under high-speed dry cutting.