• PDF / 469,306 Bytes
• 5 Pages / 612 x 792 pts (letter) Page_size
• 20 Downloads / 200 Views

DOWNLOAD

REPORT

---

0907-MM06-05.1

In-Situ Recrystallization Imaging of Polycrystalline Ni-S alloy using SEM Marilyne Cornen and René Le Gall Univ Nantes, Laboratoire Génie des Matériaux et Procédés Associés Polytech’Nantes, BP 50609, 44306 Nantes Cedex 03, France. ABSTRACT Impurity segregation at alloy grain boundaries (GB) depends on many parameters such as GB character and prior thermo-mechanical history. In this paper we describe an experimental set-up designed to record the individual behaviour of GB during recrystallization of a nickelsulfur alloy in order to correlate segregation level with mobility and disorientation of GB. Therefore a method allowing direct observation of the GB motion as well as disorientation mapping is needed. Studying grain growth and recrystallization of this particular alloy by Scanning Electron Microscopy is possible thanks to real time in-situ imaging. This requires a sensitive crystal orientation contrast and the ability to image hot evolving samples. To heat the samples, a special device designed for the SEM analysis chamber is used. This device is used at 455°C but is able to reach higher temperatures. In order to get the orientation contrast images, as well as to protect the Secondary Electron (SE) detector from heat and light, a channel plate converter has been designed. This experimental set-up, combined with the heating system, allow the observation of the sample during recrystallization and recording small videos providing information such as grain boundary displacement rate. Then, associated with an EBSD analysis we can get the disorientation map of the area of interest and eventually an electrochemical technique is performed to create preferential dissolution at GB. Geometry of the grooves resulting from an electrochemical etching gives an evaluation of the segregation level in GB. INTRODUCTION It has been known for a long time that impurity segregation at grain boundaries (GB) affects the physical properties of the metal in various ways and in various extents. Regarding the system nickel-sulfur, when segregated to GB sulfur makes nickel more brittle and less resistant to intergranular corrosion. This segregation depends on many parameters such as GB character (general GB or Sigma GB) [1] and prior thermo-mechanical treatments. A cold rolled and recrystallized sample will not behave the same way than equilibrium annealed one. The aim of our study is to correlate segregation level with mobility and disorientation of GB. Therefore a method allowing direct observation of the GB motion as well as disorientation mapping is needed. In this paper, we describe an experimental set-up designed to record individual behaviour of GB during in-situ recrystallization annealing of a Ni-S alloy. SAMPLES DESCRIPTION The alloy used for this study is a Ni-S alloy containing 1 atomic ppm of S (270 Wiggings Alloy). In order to promote dynamic segregation, due to solute drag effect during recrystallization, small pieces of this alloy are cold rolled to different stress levels. These different levels will give diff