Atomic scale imaging and analysis of T' precipitates in Al-Mg-Zn alloys

A Bigot (1) , P Auger (2) , Sylvain Chambreland (1) , D Blavette (1) , A Reeves (1)

1 GPM - Groupe de physique des matériaux
2 C-TEC - Constellium Technology Center

The inability to sustain attention has been proposed as a core deficit in schizophrenia. The Continuous Performance Task (AX-CPT) and the Rapid Visual Information Processing Task (RVP) are widely used neuropsychological tasks to measure sustained attention. The RVP displays numbers as stimuli, whereas the AX-CPT uses letters. Ten patients with chronic schizophrenia and 18 healthy control subjects were studied using four different versions of the RVP. The versions differed with regard to stimulus presentation time (600 vs. 1,200 ms) and the number of target sequences to be memorized: either one sequence (low cognitive load) or two sequences (high cognitive load). Schizophrenic patients showed a reduced number of hits only on the task version with 600 ms stimulus duration coupled with high cognitive load. The combination of high cognitive load and short stimulus duration created a critical performance breaking point for schizophrenic patients. This finding supports the hypothesis that patients have an impaired ability to coactivate different cognitive performances; thus the results favor the theory of impaired functional connectivity in schizophrenia.

La composition, la morphologie et la fraction volumique de la phase métastable $\rm T' $ formée par revenu d'un alliage industriel Al-4,91wt%Mg-3,20wt%Zn (24 heures à $\rm 140\ ^\circ C $ après mise en solution et trempe) ont été déterminées en sonde atomique tomographique. Les précipités $\rm T' $, de forme généralement globulaire et parfois allongée, sont rencontrés avec une densité numérique de $\rm 1{,}8 \times 10^{17}\ cm^{-3} $. La fraction volumique de la phase est proche de 4,5 %. La composition moyenne des précipités $\rm T' $ analysés est de 37,5 %at Mg, 36,5 %at Al et 26 %at Zn, ce qui correspond, aux incertitudes près, à la stoechiométrie $\rm Mg_{32}(Al,Zn)_{49} $ de la phase stable T.

Mots clés: T' precipitates; Al Mg Zn alloys; composition; morphology; volume fraction; tomographic atom probe; aged; solution heat treatment; water quenching; 24 h; 140 C; Al Mg Zn; ageing; aluminium alloys; atom probe field ion microscopy; crystal morphology; heat treatment; magnesium alloys; precipitation; zinc alloys; atomic scale imaging

Domaines: Physique [physics]

A Bigot, P Auger, Sylvain Chambreland, D Blavette, A Reeves. Atomic scale imaging and analysis of T' precipitates in Al-Mg-Zn alloys. Microscopy, Microanalysis, Microstructures, 1997, 8 (2), pp.103-113. ⟨10.1051/mmm:1997109⟩. ⟨hal-01928948⟩