Influence de la croissance de phase ω ainsi que de la composition en Mo sur les propriétés mécaniques et les propriétés de rupture de l’alliage Ti12Mo

Details

Supervisors

Jacques, Pascal

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux

Abstract

enOver the past several decades, interest in titanium has continued to grow due to its unique combination of physical, chemical and mechanical properties, including the best strength-to-density ratio among metals and excellent corrosion resistance. The Ti12Mo titanium alloy, composed of 12wt% molybdenum (Mo), belongs to a new family of interest because it combines very good mechanical properties except for low strength, which is being improved. Since the strength of a material is a property that depends on its microstructure, heat treatments are applied to Ti12Mo in order to make microstructural modifications. The heat treatments used in this paper are called ’Flash Treatments’ due to their very short duration in the furnace. A series of samples having undergone Flash Treatments ranging from 110°C to 385°C are analyzed by different characterization techniques. The main objective of this work is to observe the evolution of the mechanical properties and the evolution of the fracture properties in a Ti12Mo alloy by forming and magnifying a second phase inside the β matrix that composes it by applying Flash treatments. The other is to observe the evolution of the same properties, but this time, when the amount of Mo in the β titanium is modified (Ti10Mo, Ti15Mo and Ti30Mo). The evolution of the different mechanical and fracture properties in the Ti12Mo alloy by formation and growth of a second phase ω in the β matrix was obtained. For certain treatments with a sufficiently high temperature, the ω_iso phase is formed and significantly increases the resistance to deformation of Ti12Mo at the expense of part of its ductility. For the rest of the properties, the formation and growth of the ω_iso phase do not seem to have a major influence. The results indicate that there is a time-temperature equivalence for ω_iso phase formation. Future work focusing on this equivalence could lead to the boundary conditions for the heat treatments required to form the ω_iso phase. The failure mechanism of Ti12Mo is identified and appears to be similar to that of Ti10Mo and Ti15Mo as well as for all the Flash samples in this paper. The evolution of the ω phase does not seem to alter the Ti12Mo alloy fracture mechanism or to significantly change its fracture properties. The interest of the Flash treatments lies finally in the improvement of the elastic limit of Ti12Mo.