The evolution of tribolayers during high temperature sliding wear

• High temperature wear of materials for valves and seat inserts is investigated.
• TEM investigations show the evolution of 4 distinct surface zones.
• The outer zone corresponds to a compacted oxide layer (glaze-layer).
• The glaze-layer shows a three times higher hardness as the Alloy 80A pin.
• We present detailed schematic illustrations of subsurface microstructure evolution.

High temperature reciprocating sliding wear experiments of a Ni-based superalloy pin against a cast iron disc were performed at 600 and 800 °C (load: 20 N, frequency: 20 Hz, stroke: 1 mm). The evolution of tribolayers was investigated using scanning and transmission electron microscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDX). Four distinct subsurface zones are identified and discussed in terms of plastic strain accumulation and microstructure evolution. The development of protective nanocrystalline oxide-layers (glaze-layers) on top of the wear surfaces leads to very low wear rates due to a suppression of the direct metal–metal contact between the pin and the disc. The nanohardness, microstructure and chemical composition of the glaze-layers are reported.