{"id":12158,"date":"2023-07-04T10:55:32","date_gmt":"2023-07-04T08:55:32","guid":{"rendered":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/?p=12158"},"modified":"2023-07-04T15:29:44","modified_gmt":"2023-07-04T13:29:44","slug":"soutenance-de-these-28","status":"publish","type":"post","link":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/2023\/07\/04\/soutenance-de-these-28\/","title":{"rendered":"Soutenance de th\u00e8se"},"content":{"rendered":"

Title<\/strong> : Study of phase stability and point defects in the medium entropy system Ti-Zr-Nb centered cubic<\/b> at the atomic scale <\/b> <\/b><\/p>\n

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Abstract :<\/u><\/strong><\/div>\n

This study aims to better understand the stability of refractory high entropy alloys (RHEAs) having a bcc structure. This class of alloys are of great current interest because of their excellent mechanical properties retained up to elevated temperatures. Some of them also show some transformation-induced plasticity, a phenomenon closely related to their stability. Selecting the Ti-Zr-Nb system as a model alloy for group IV and V RHEAs mixing both hcp and bcc elements, ab initio calculations are performed on dilute to high concentration equiatomic alloys of this system. Vacancy calculations versus alloy composition are also considered, as important defects existing in materials responsible for diffusion processes, and possibly influencing phase stability. In the dilute limit, any substitutional contraction center (vacancy, solute) introduced in the bcc Ti or Zr matrix induces a phase transition towards a more compact hcp or \u03c9 phase. This is understood using local analysis of both electronic and atomic structures; the latter agrees well with diffraction experiments. Such point defects will thus introduce important heterophase fluctuations at finite temperature, which might explain the appearance of \u03c9 phase in some concentration domains of binary Ti-Nb, Zr-Nb and Ti-Zr alloys. For high concentration cases, phase stability is studied by considering both ordered and disordered alloys (generated as special quasi random structures). Random alloys are always more stable, and depending on alloy composition, several instabilities involving Burgers and Cook\u2019s mechanisms are observed. The bcc stability zone is identified as rather extended in alloy composition, due to very large local lattice distortions. Computation of the appropriate local order parameter shows that these bcc equiatomic alloys intrinsically comprise \u03c9 hetero-phase fluctuations, a behavior in close connection with the TRIP effect. Finally, vacancies are seen to enhance these phase fluctuations; an anomalous diffusion that is typical of bcc alloys is thus expected in such RHEAs.<\/p>\n

PhD committee:<\/u><\/p>\n

Mme Helena ZAPOLSKY, Laboratoire Groupe de Physique des Mat\u00e9riau (GPM), Universit\u00e9 de Rouen\u00a0 – Reviewer<\/div>\n
<\/div>\n
Mr Jean-Philippe COUZINIE \u00a0\u00a0\u00a0 Institut de Chimie et des Mat\u00e9riaux , Universit\u00e9 Paris-Est \u00a0 – Reviewer<\/div>\n
<\/div>\n
Mr Jean-Marc THEMLIN,\u00a0 Institut Mat\u00e9riaux Micro\u00e9lectronique Nanosciences de Provence,\u00a0 Universit\u00e9 Aix-Marseille\u00a0 President<\/div>\n
<\/div>\n
Mr Jean-Claude CRIVELLO , Institut de Chimie et des Mat\u00e9riaux,\u00a0 Universit\u00e9 Paris-Est – Examiner<\/div>\n
<\/div>\n
Mme Maeva COTTURA, Institut Jean Lamour, Universit\u00e9 de Lorraine \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Examiner<\/div>\n
<\/div>\n
Mr Hakim AMARA, ONERA, LEM, Universit\u00e9 Paris Saclay, Guest<\/div>\n
<\/div>\n
Mme C\u00e9line VARVENNE, CINaM, D\u00e9partement TSN, Universit\u00e9 Aix-Marseille \u00a0\u00a0\u00a0 PhD advisor<\/div>\n
<\/div>\n
Mr Guy TREGLIA , CINaM, D\u00e9partement TSN, Universit\u00e9 Aix-Marseille \u00a0\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 PhD advisor<\/div>\n
<\/div>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Sally Issa soutiendra le vendredi 7 Juillet \u00e0 10H00 dans la salle Raymond Kern au CINaM<\/p>\n","protected":false},"author":16,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/posts\/12158"}],"collection":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/users\/16"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/comments?post=12158"}],"version-history":[{"count":6,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/posts\/12158\/revisions"}],"predecessor-version":[{"id":12164,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/posts\/12158\/revisions\/12164"}],"wp:attachment":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/media?parent=12158"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/categories?post=12158"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/wp-json\/wp\/v2\/tags?post=12158"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}