High tensile strength of sputter-deposited ZrB2 ceramic thin films measured up to 1016 K

Abstract We report the results of tensile experiments on 900 nm sputter-deposited films of ZrB 2 , performed at temperatures ranging from ambient to 1016 K. The ZrB 2 samples were tested using micromachined sample frames with integrated micro-heaters. Transmission electron microscopy shows that both as-deposited films and films heated above 1000 K consist of two distinct layers, an amorphous layer and a crystalline layer with a very fine columnar structure. The ZrB 2 films have a room-temperature tensile strength in excess of 1.2 GPa, far exceeding the tensile strength of bulk ZrB 2 , but their stiffness is lower and decreases significantly with increasing temperature. The reduction in stiffness is attributed to the presence of the amorphous phase and the high density of transverse grain boundaries in the crystalline region. The fracture toughness of the ZrB 2 films was measured by introducing pre-cracks in the tensile specimens with a focused ion beam, and was found to be 2.57 ± 0.03 MPa√m, similar to values reported for bulk ZrB 2 .