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°C for 100h-600h. The crack l...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°C 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"°’°695’1" The fracture toughness in oxide and at the interface decrease with the increasing of the oxide thickness in equation K0 —1.02l4Ln(h0) + 7.3382 (in oxide) and KJ = 529.7In,,"**424 (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.展开更多
Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20&...Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20°C to 600°C for the steel tempered 2h at 350 °C, 460 °C, 560 °C and 600 °C. The influence of temperature on cyclic behaviour was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. At 10"2 strain rate, amax,A(T/2 decrease with the test temperature for all hardness levels. They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or exceed tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300°C to 600°C, but the maximal softening intensity occurs at room temperature. The strain rate influences notably the cyclic behaviour when T>500°C. The time dependence of cyclic behaviour is closely related to test temperature and the tempering history of the steel.展开更多
文摘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°C 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"°’°695’1" The fracture toughness in oxide and at the interface decrease with the increasing of the oxide thickness in equation K0 —1.02l4Ln(h0) + 7.3382 (in oxide) and KJ = 529.7In,,"**424 (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.
文摘Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20°C to 600°C for the steel tempered 2h at 350 °C, 460 °C, 560 °C and 600 °C. The influence of temperature on cyclic behaviour was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. At 10"2 strain rate, amax,A(T/2 decrease with the test temperature for all hardness levels. They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or exceed tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300°C to 600°C, but the maximal softening intensity occurs at room temperature. The strain rate influences notably the cyclic behaviour when T>500°C. The time dependence of cyclic behaviour is closely related to test temperature and the tempering history of the steel.
