Temperature dependent tribooxidation of Ti–B–N coatings studied by Raman spectroscopy

In this work, tribological wear tracks formed on moderate temperature chemical vapor deposited (MTCVD) TiB1.66N0.34 coatings were characterized by Raman spectroscopy and compared to those obtained on TiN. Therefore, ball-on-disk sliding tests against Al2O3 as well as 100Cr6 bearing steel were performed at room and elevated temperatures (25–700 °C). Raman microspectroscopy was found to be essential to identify different oxide and borate phases on the wear tracks, which originate from tribochemical reactions and tribooxidation. Furthermore, it was shown that the temperature dependence of tribological reactions at the interface can successfully be studied by combining exceptional short sliding distances with post-annealing experiments at different temperatures and durations. A good correlation between the detected compounds on the wear tracks and the observed friction coefficient was achieved.In addition to the ball-on-disk tests, turning tests with Ti–B–N coated inserts were performed at various turning speeds. The detection of several oxide phases by means of Raman spectroscopy on the rake face allowed an estimation of contact temperatures and wear behavior. It was found, that the temperature of the inserts is highly affected by the cutting speed. At moderate cutting speeds of vc ≤ 180 m/min the temperature was estimated to be ≤500 °C. On the other hand, the temperature was assumed to reach values of T ≥ 785 °C at increased cutting speeds of vc = 200 m/min, due to the detection of TiBO3 by Raman spectroscopy.

► Investigation of tribological behavior of Ti–B–N CVD coating by Raman spectroscopy.
► Good correlation between Raman results and friction coefficients.
► Study of tribochemical reactions as a function of temperature.
► Identification of boric acid, which may act as a self-lubricant.
► Estimation of contact temperature in machining by Raman spectroscopy.