Formation of a metallic amorphous layer during the sliding wear of Ti/TiN nanolaminates

This paper describes experimental studies of metallic/ceramic nanolaminate performance under sliding contact and identifies the formation of an amorphous layer between the nanolaminate and counterface. Nanolaminates used for this study had either 20- or 100-nm-thick alternating layers of Ti and TiN, resulting in a total thickness of ~1-μm films. The structure of the Ti and TiN layers was confirmed using X-ray diffraction [(111)_TiN and (002) _Ti], and compositions were determined using electron energy loss spectroscopy (EELS) - Ti and TiN_0.7. Variation of the individual layer thicknesses within Ti/TiN nanolaminates was shown to influence both the deformation observed through the nanolaminate thickness and also the friction coefficient between the nanolaminate and 440C steel counterface during linear reciprocating wear. During sliding, the 100-nm-layered nanolaminate had a lower coefficient of friction (0.25 ± 0.01) than the 20-nm-layered nanolaminate (0.56 ± 0.06). An amorphous titanium layer developed during sliding at the interface between the 100-nm nanolaminate and steel counterface. EELS confirmed that this layer did not contain any nitrogen and recrystallization occurred near the in-contact surface. While phase changes under compressive loading have been reported for other systems, this is the first report to indicate this response within a titanium layer.