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Ghazal G.,CNRS Jean Lamour Institute | Chapelle P.,CNRS Jean Lamour Institute | Jardy A.,CNRS Jean Lamour Institute | Jourdan J.,CNRS Jean Lamour Institute | Millet Y.,TIMET Savoie
ISIJ International | Year: 2012

This paper deals with the presence of High Density Inclusions (HDI) in VAR melted titanium ingots. For performance and economical reasons, the elimination of these inclusions is of utmost importance for the titanium industry. However, very few studies have considered dissolution aspects of HDIs and accurate data on their dissolution rates still lack in the literature. In the present study, we investigate the mass transport driven dissolution of some HDIs (tungsten and molybdenum) in CPTi, Ti64 and Ti17 baths. This has been done by allowing the partial dissolution of cylindrical rods in molten titanium for various controlled periods of time. Dissolution rates have been determined by measuring the dimensions of these samples before and after the experiments. In some cases, the chemical composition of the solidified bath near the sample has also been measured by Scanning Electron Microscope. It has been evidenced that the dissolution kinetics depends highly on the liquid metal agitation and temperature. The results also revealed that the dissolution of both tungsten and molybdenum is higher in pure titanium than in the investigated alloys. A numerical model describing the mass transport driven dissolution was used to determine dissolution rates numerically and to compare them to experimental results. © 2012 ISIJ.

Brozek C.,Chimie Paristech | Sun F.,Chimie Paristech | Vermaut P.,Chimie Paristech | Vermaut P.,Paris-Sorbonne University | And 5 more authors.
Scripta Materialia | Year: 2016

In this paper, a new β-metastable titanium alloy, based on the Ti-Cr-Sn system, displaying both an extremely high work hardening rate and a uniform deformation larger than 0.35, was designed and successfully tested. The compositional design was guided through a stability mapping approach based on the "d-electron design method" and using an unexploited region of the Bo/Md map. Detailed analysis of deformation mechanisms shows combined transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects, resulting in a complex network of microstructural features and giving rise to marked kinematic hardening. © 2015 Elsevier Ltd. All rights reserved.

Semblanet M.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Semblanet M.,SNECMA | Montheillet F.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Piot D.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | And 3 more authors.
Ti 2011 - Proceedings of the 12th World Conference on Titanium | Year: 2012

The aim of this research is to simulate the forging step in the two phase α/β-range followed by recrystallization in the β field during which micro-structure evolves. This involves the following phenomena:grain deformation, recrystallization and grain growth for the β matrix and disorienta-tion/fragmentation for the α Widmanstatten platelets. More specifically, this work analyzes the effects of a deformation in the α/β field on the subsequent β grain growth during a heat treatment at higher temperatures for a Ti-17 titanium alloy. The experimental part is based on uniaxial compression tests in order to simulate the forging step. The complete thermomechanical treatment starts with a temperature homogenization step (10min) followed by uniaxial compression with a strain rate of 10 -2 s -1 in the aloha;/β-phase field and a water quenching; the samples are then subjected to a recrystallization / grain growth step at higher temperatures (in the β-phase domain). The evolution of grain structures and substructures were investigated by optical and scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD). The influence of strain and heat treatments time on the microstructure is described. The kinetics of recrystallization and grain growth in the alloy have been determined.

Lebrun E.,Ecole Nationale Superieure de Chimie de Paris | Svec P.,Slovak Academy of Sciences | Nowak S.,Laboratoire dInterfaces | Denand B.,CNRS Jean Lamour Institute | And 2 more authors.
Advanced Materials Research | Year: 2014

In this work, we have investigated the microstructural evolutions and the phase transformations of a new near-beta alloy with a nominal composition of Ti-5.5Al-5V-5Mo-2.4Cr-0.75Fe-0.15O (weight percent), the TIMETAL 18 [here after called Ti-18]. The complete microstructural state of the Ti-18 during heat treatments, from as quenched metastable state, has been first investigated. The phase transformations have been studied by combination of X-ray diffraction analysis, metallurgical observations and electrical resistivity measurements. From a series of isothermal treatments, the first complete TTT diagram has been then established displaying three C-curves corresponding to different precipitation domains for alpha phase. © (2014) Trans Tech Publications, Switzerland.

Chapelle P.,CNRS Jean Lamour Institute | Noel C.,CNRS Jean Lamour Institute | Risacher A.,CNRS Jean Lamour Institute | Jourdan J.,CNRS Jean Lamour Institute | And 2 more authors.
Journal of Materials Processing Technology | Year: 2014

High-speed camera imaging and optical emission spectroscopy have been used for investigating the structure of the electric arc and the transfer mechanisms of the liquid metal during vacuum arc remelting (VAR) of Ti alloys. The arc exhibited a similar operating regime to that described in the previous literature for the case of Inconel 718 and zirconium alloy electrodes. The arc behaved in a diffuse mode with many separate and rapidly moving cathode spots. Several parameters of the cathode spots, including their current, size and apparent velocity were evaluated. The application of an external axial magnetic field tended to encourage the cathode spots to locate themselves on the base of the electrode. A large density ratio of Ti+ ions and Ti atoms in the interelectrode plasma was evaluated, suggesting that the plasma was strongly ionized. The calculated excitation temperature of Ti+ ions (1-1.2 eV) was about 1.5-2 times greater than that obtained for Ti atoms. The transfer mechanisms of the drops of liquid metal might be classified into three main modes depending on the gap length: drop falling, drip short and drop erosion induced by the cathode spots. The importance of the influence of the arc on the metal transfer mechanisms was inversely related to the gap length. © 2014 Elsevier B.V.

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