Structure and thermal stability of arc evaporated (Ti0.33Al0.67)(1-x)SixN thin films
(Ti0.33Al0.67)(1-x)SixN (0 <= x <= 0.29) thin solid films were deposited onto cemented carbide substrates by arc evaporation and analyzed using analytical electron microscopy, X-ray diffraction, nanoindentation, and density functional theory. As-deposited films with x <= 0.02 consisted mainly of a metastable c-(Ti,Al)N solid solution for which Si serves as a veritable grain refiner. Additional Si promoted growth of a hexagonal wurtzite (Al,Ti,Si)N solid solution, which dominated at 0.02= 0.17, the films were X-ray amorphous. Despite these widely different microstructures, all as-deposited films had nanoindentation hardness in the narrow range of 22-25 GPa. Isothermal annealing of the x=0.01 alloy film at a temperature of 900 degrees C, corresponding to that in turning operation, resulted in spinodal decomposition into c-AlN and TiN and precipitation of h-AlN. For x=0.09 films, annealing between 600 degrees C and 1000 degrees C yielded c-TiN precipitation from the h-(Al,Ti,Si)N phase. Furthermore, the x=0.01 and x=0.09 films exhibited substantial age hardening at 900 degrees C, to 34 GPa and 29 GPa due to spinodal decomposition and c-TiN precipitation, respectively. Films with a majority of c-(Ti,AI)N phase worked best in steel turning tests, while films with x>0.02 developed cracks during such operation. We propose that the cracks are due to tensile strain which is caused by a decrease in molar volume during the phase transformation from hexagonal wurtzite (Al,Ti,Si)N into cubic TiN phase, which results in degradation in machining performance. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: TiAlSiN ; Hardness ; Phase transitions ; Analytical transmission electron microscopy ; Si-N Coatings ; Initio Molecular-Dynamics ; Mechanical-Properties ; Nanocomposite ; Ti ; Microstructure ; Temperature ; Transition ; Deposition ; Hardness
Record created on 2010-11-30, modified on 2016-08-09