Tuning of mechanical properties of Ti1-xAlxN coatings through Ta alloying

The effect of alloying Ti1-x-yAlxTayN coatings with Ta on their structure and mechanical characteristics was studied by X-ray diffraction, nanoindentation and spherical indentation tests. The coatings with low Ta contents (y <= 0.2) were shown to demonstrate (111) texture in the growth direction, while a preferred orientation along (200) direction tended to form at high Ta contents (y > 0.35). It was revealed that the hardness and Young's modulus of the coatings exhibit overall decreasing trend with increasing the Ta content. However, the hardness breaks this trend at medium Ta contents and attains a peak value at y = 0.35. In contrast, the fracture toughness of the Ti1-x-yAlxTayN coatings extracted from the results of the spherical indentation exhibits an increasing trend with a local peak at the same Ta content (y = 0.35). This behavior of the hardness and fracture toughness is attributed to the changes in the character of interatomic bonding as well as to the evolution of the compressive residual stresses in the coatings, which are caused by Ta alloying.