M. Eddahbi

Integral method from initial values to obtain the best fit of the Garofalo's creep equation

Abstract An integral computational method has been developed to provide initial values to a subsequent fitting of creep data based on non-linear and iterative methods. The fitting of the Garofalos equation, which describes creep data, utilizes a strong non-linear objective function. Various algorithms are developed which provide the solution for the fitting. An analysis is made of the significance of this solution in relation to the problem studied. The dispersion of the solution values is related to the final values provided by other non-linear and iterative methods. The method is applied to three types of steels and screens the experimental creep data with a statistical analysis that improves the fitting results.

Grain structure and microtexture after high temperature deformation of an Al-Li (8090) alloy

The dynamic recrystallization of an aluminum‐lithium (8090) alloy at high temperatures (380‐570°C) at a strain rate of 0.8 s 1 was studied. The microstructure of the annealed sample fragmented during deformation at high temperature to form new small recrystallized grains. The stress versus strain curves showed stress oscillations. The texture of the annealed material at 440°C is defined by a rotated cube component. This component rotates toward a cube component in the course of deformation at 440 and 550°C. Microtexture determinations revealed that the annealed sample as well as the deformed samples showed a high amount of low-S, coincident site lattice misorientations, particularly S1. Annealed samples are characterized by S1, 5, 7, 9, 13, 21 and 29 boundaries whereas S1, 3 and 13 boundaries are characteristic of the deformed samples.

Microstructural changes during high temperature deformation of an Al-Li(8090) alloy

In this work, the high temperature tensile behavior of an aluminum-lithium (8090) alloy is studied at various strain rates and temperatures. In particular, special attention was paid to the oscillations observed in the true stress versus strain curves at high strain rate, 0.8 s{sup {minus}1}, and high temperatures in excess of 380 C (> 0.57 T{sub m}, where T{sub m} is the melting temperature). The changes in the microstructure were analyzed and correlated to the flow curves of the deformed samples.

Elevated temperature creep behavior of three rapidly solidified Al-Fe-Si materials containing Cr, Mn, or Mo

Abstract Research on the high temperature creep behavior of three rapidly solidified Al-Fe-X-Si (where X = Cr, Mn or Mo) dispersion strengthened materials with three different alloying compositions has been conducted. Firstly, microstructural examinations have been carried out on the as-received, thermally treated and tested samples. The microstructure consists of a fine Al matrix embedding small round-shaped Al 12 (Fe,X) 3 Si and Al 13 (Fe,X) 4 dispersoids. Grain sizes ranging from 0.85 to 1.45 μm and dispersoid sizes ranging from 45 to 54 nm were observed. Secondly, tensile tests were performed at high temperature from 573 to 823 K at strain rates ranging from 2.5×10 −6 to 10 −2 s −1 . The experimental data exhibited high apparent stress exponent, n ap , and high activation energy, Q ap . The rnicrostructure remained stable and fine after testing. The results are analyzed by means of various models used in the literature.