Analysis of Phase Transformation in Nickel-Base Alloy after Ageing

Abstract

The aim of the performed tests was to analyse the precipitation processes in the 23Cr-45Ni-6W-Nb-Ti-B (HR6W) alloy based on nickel. The examined material was subjected to the process of long-term isothermal annealing at 700 • C, for various time periods of up to 10000 h. The scope of the tests included: structural tests using scanning electron microscopy, the analysis of the precipitation processes with the use of X-ray phase analysis and electron diffraction with transmission electron microscopy. The tests showed that only MX-type precipitates occurred in the analysed alloy in the as-received condition, whereas the long-term annealing contributed to the precipitation of secondary phases of M23C6 carbides and the Laves phase.

Effects of Long‐Term Ageing at High Temperatures on Oxide Scale Development and Evolution of Austenitic Steels Microstructure

“…Aging of supersaturated alloys leads to the changes in their microstructure, mainly due to the precipitation processes. The predominant secondary particles phases in austenitic alloys precipitated during ageing are MX carbonitrides, M 23 C 6 carbides, Z phase, Laves phase, Cu precipitates, and σ phase . In HR3C steel (Figure and A,B), apart from Nb‐rich precipitates and Cr‐rich precipitates are observed as shown in Figure , Cr–Si‐rich precipitates were observed in Figure B.…”

“…The presence of a strong carbide forming elements in chemical composition results a high number of precipitates in as‐received state (Figure and ). Both HR3C and Sanicro 25 steels, in as‐received conditions, formulate NbC primary carbides and primary Z phase according to the studies provided by Golański et al and Yan et al In the case of HR6W, two morphologies of the primary precipitations are observed: Nb‐rich precipitates with a globular shape and rectangular shape of TiX precipitates . Due to their micrometric dimensions, those precipitates accomplish the role of the binding precipitates that bind C and/or N atoms in the tested materials, to prevent the precipitation of chromium‐rich carbides at the grain boundaries.…”

“…In contrast to the previous findings, no Cr‐rich precipitates within the microstructure were observed (Figure C–F). According to the work performed by Yan et al and Merda et al, HR6W and Sanicro 25 are prone to develop a W‐rich phase called Laves phase with tetrahedral close‐packed structure. However, Zurek et al reported that W‐rich phase belongs to μ phase.…”