A New Method of Creep Ruptures Data Extrapolation Based on the Work
For structural and machine components in service at high temperature and pressure, such as those used in power generating and petrochemical plants, as well as aero-engines and metallurgical machineries, creep life assessment is a major concern because of safety and economic reasons. In this paper, a new model for creep life prediction is proposed based on energy processes. The work of making the material failure of applied loads is used to describe the creep processes respectively. By mathematical technique, the expression of the model is, where is Larson-Miller constant, and is also material constant at certain condition. This function Moreover, owing to its simple expression, it is very easy to use this model to predict the creep life. To check the validity of the new model proposed in this paper, the 250000h creep rupture strength estimates for 2.25Cr1.0Mo steel under stress control at 743~793K have been performed. The results are in a good agreement with the experimental data.
Creep life predictions in nickel-based superalloys
Abstract Creep life prediction techniques such as the Larson-Miller parameter, life trend diagrams, the Monkman-Grant relationship and the Dobes-Milicka relationship are critically reviewed. Problems associated with the scatter in creep life data and the inability of these relationships to accommodate for service-induced material degeneration are discussed. These effects are rationalized in terms of the erratic tertiary creep behaviour of complex engineering alloys. A new creep design relationship based on the sum of the primary creep life tp plus the secondary creep life ts, normalized by the sum of the primary creep strain ϵp plus the secondary creep strain ϵs, varying as a function of secondary creep rate ϵ has been proposed. The relationship is described by t p +t s ϵ p +ϵ s ϵ M =K where M and K are constants. The equation is accurate over a wide range of stresses (350–700 MPa) and temperatures (760–890°C) in IN-738LC. The method systematically reveals the creep degeneration effects with increasing service life. The relationship appears to be independent of any changes in the predominant deformation mechanism.
Creep resistance and high-temperature metallurgical stability of titanium alloys containing gallium
Tensile properties up to 1100°F and the creep resistance at 1000°F were correlated with composition for twelve complex developmental titanium alloys with additions of Al, Ga, Sn, Mo, Zr, and Si. Creep resistance for these alloys in the β heat-treated condition was found to be strongly dependent on the totalα stabilizer content and the silicon concentration. The creep activation energy for a Ti-4.5 Al-2 Sn-3 Zr-3 Ga-1 Mo-0.5 Si alloy, established over the 900° to 1100°F temperature range, was about 100 kcal per g-mole. This high creep activation energy is hypothesized to result from dispersion strengthening within theα matrix by the Ti3X(X = Al, Ga, Sn) phase and pinning of the interplatelet and priorβ grain boundaries by the Zr5Si3 phase. Both phases were identified by transmission electron microscopy in these respective locations. Metallurgical instability, as evidenced by decreased fracture toughness, is also shown to be relatable to the totalα stabilizer content. The activation energy for the embrittlement process is about 45 kcal per g-mole. which approximates that for interdiffusion of gallium inα titanium.