Influence of Yttrium on the Thermal Stability of Ti-Al-N Thin Films
Ti 1-x Al x N coated tools are commonly used in high-speed machining, where the cutting edge of an end-mill or insert is exposed to temperatures up to 1100 °C. Here, we investigate the effect of Yttrium addition on the thermal stability of Ti 1-x Al x N coatings. Reactive DC magnetron sputtering of powder metallurgically prepared Ti 0.50 Al 0.50 , Ti 0.49 Al 0.49 Y 0.02 , and Ti 0.46 Al 0.46 Y 0.08 targets result in the formation of single-phase cubic (c) Ti 0.45 Al 0.55 N, binary
... inary cubic/wurtzite c/w-Ti 0.41 Al 0.57 Y 0.02 N and singe-phase w-Ti 0.38 Al 0.54 Y 0.08 N coatings. Using pulsed DC reactive magnetron sputtering for the Ti 0.49 Al 0.49 Y 0.02 target allows preparing single-phase c-Ti 0.46 Al 0.52 Y 0.02 N coatings. By employing thermal analyses in combination with X-ray diffraction and transmission electron microscopy investigations of as deposited and annealed (in He atmosphere) samples, we revealed that Y effectively retards the decomposition of the Ti 1-x-y Al x Y y N solid-solution to higher temperatures and promotes the precipitation of c-TiN, c-YN, and w-AlN. Due to their different microstructure and morphology already in the as deposited state, the hardness of the coatings decreases from ~35 to 22 GPa with increasing Y-content and increasing wurtzite phase fraction. Highest peak hardness of ~38 GPa is obtained for the Y-free c-Ti 0.45 Al 0.55 N coating after annealing at T a = 950 °C, due to spinodal decomposition. After annealing above 1000 °C the highest hardness is obtained for the 2 mol % YN containing c-Ti 0.46 Al 0.52 Y 0.02 N coating with ~29 and 28 GPa for T a = 1150 and 1200 °C, respectively.