Thermal degradation of TiN and TiAlN coatings during rapid laser treatment

Abstract

In this research, a fundamental study was conducted on damage behavior of cathodic arc evaporated TiN and Ti 0.44 Al 0.56 N coatings, in terms of oxidation and cracking/spallation, when they were exposed to single-pulse laser treatment in a temperature range of 1200–2100 °C. Moreover, a multiple-pulse laser treatment was designed to apply thermo-mechanical loads on the coatings in order to evaluate their thermal degradation during rapid heating/cooling cycles between 200 and 1200 °C. Single-pulse treatment of TiN up to 1500 °C led to the intercolumnar cracking and formation of ultrafine TiO grains. An increase in temperature up to 2100 °C resulted in a notable bulging of the surface, and formation of TiO 2 of various morphologies such as grainy structure, dense molten and re-solidified structure, droplets from melt expulsion and, more interestingly, nanofibers. Multiple-pulse treatment of TiN was accompanied by a severe cracking and spallation , which divided the surface into two layers: a heavily cracked top layer composed of dense TiO 2 grains, and a bottom layer having porous TiO 2 grains indicating incomplete oxidation. Conversely, Ti 0.44 Al 0.56 N did not show any visible cracking and oxidation after single-pulse treatment. Multiple-pulse treatment did not also yield cracking and spallation for Ti 0.44 Al 0.56 N, and its ablated region consisted of TiO 2 grains combined with thin Al 2 O 3 platelets . An excellent combination of properties including higher oxidation resistance and greater fracture toughness at high temperatures led to a higher thermal damage resistance for Ti 0.44 Al 0.56 N coating compared to TiN when undergoing single- and multiple-pulse laser treatments. • TiN coating suffered from severe oxidation and cracking during the laser treatments. • Single pulse laser of TiN at ≤1500 °C led to the ultrafine TiO grains formation. • Single pulse at ≥1800 °C and multiple pulse laser of TiN formed TiO 2 and microcracks. • TiAlN exhibited a superior thermal damage resistance than TiN upon laser treatments. • Higher crack resistance of TiAlN is due to greater oxidation resistance and K IC .