Investigation of Adhesion and Fracture Toughness of Thermally Grown Oxide Scales by Interface Indentation Test

HIGH TEMPERATURE ALLOYS rely on theformation of a dense layer against oxidation.Howeverthe crack,spallation and detachment of oxide layeunder growth stress and thermal stress fromtemperature difference cause the failure of theprotective layer.Therefore,high temperature materialsare required forming a good oxide scale with highstrength and high interface bonding strength.Anappropriate measuring method and evaluation fooxide/metal interfacial adhesion is of great importanceto understand …

Investigation of Adhesion and Fracture Toughness of Thermally Grown Oxide Scales by Interface Indentation Test

The adhesion and the fracture toughness of thermally grown oxide scales for pure nickel were investigated using Vickers indentation technique. The nickel samples were oxidised at 1200℃ for 100h-600h. The crack length induced by Vickers indentation test at NiO/Ni interface increases linearly with the incresing of the applied load in a logarithmic scale for each oxide thickness. There is a critical load Pc, when the applied load P＞Pc, the crack is produced at the oxide/metal interface. The critical load Pc decreases with the increasing of the oxide thickness. Therefore, the relation between the critical load Pc and the oxide thickness ho may be used as describing the adhesion of of thermally grown oxide scales. For pure nickel, the Pc-ho relation can be represented by the equation Pc = 761439e-0.0695h. The fracture toughness in oxide and at the interface decrease with the increasing of the oxide thickness in equation Ko = -1.0214Ln(ho) + 7.3382 (in oxide) and Ki = 529.71ho-0.9424 (at the interface). And there is a higher fracture toughness at the NiO/Ni interface. Therefore,for pure nickel, the oxide/metal interface is stronger than the oxide.