Repeated fast surface temperature transients can damage the materials and/or their surface treatments by
thermal fatigue. This happens in aluminium diecasting devices. One conducted thermal fatigue tests with
samples of hot work tool steel, respectively untreated, simply borided and protected by a multi-layer. In the
last case, top coat is yttria stabilised zirconia (YSZ), followed by a nickel superalloy and then a borided layer
(undercoat). The zirconia coating was applied with plasma spray. The multi-layer showed poor resistance
during the thermal fatigue tests. Better understanding these tests and the resulting thermal fatigue observed
on the treated materials was achieved by a lifetime model based on Cof
fin–Manson equations.