Mines ParisTech

About: Mines ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Microstructure. The organization has 6564 authors who have published 11676 publications receiving 359898 citations. The organization is also known as: École nationale supérieure des mines de Paris & École des mines de Paris.

Morphology of y’ and y” precipitates and thermal stability of inconel 718 type alloys

Abstract: The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.

A physical model of the twinning-induced plasticity effect in a high manganese austenitic steel

Abstract: The steel Fe–22 wt.% Mn–0.6 wt.% C exhibits a low stacking fault energy (SFE) at room temperature. This rather low value promotes mechanical twinning along with strain which is in competition with dislocation gliding, the so called twinning-induced plasticity effect. The proposed modeling of the mechanical behavior introduces the formation of mechanical microtwins in a viscoplasticity framework based on dislocation glide at the mesoscopic scale in the case of a simple tensile test. The important parameter is the mean free path of the dislocations between twins, whose reduction explains the high hardening rate (by a dynamical Hall–Petch-like effect). It takes into account the typical organization of microtwins observed in electron microscopy (geometrical organization by using a twin-slip intersection matrix). To take into account the polycrystalline disorder, the macroscopic flow stress is calculated by assuming that the deformation work is equal in each grain for each strain step. This model gives an intermediate rule between Taylor and Sachs approximations and is simpler to compute than self-consistent methods. The parameters for gliding are first fitted on results at intermediate temperatures (without twinning), and the whole modeling is then correlated at room temperature. The simulated results (microstructure and mechanical properties) are in good agreement with experience.