title: Kinetics and Mechanisms of γ' Reprecipitation in a Ni-based Superalloy.
abstract: The reprecipitation mechanisms and kinetics of γ' particles during cooling from supersolvus and subsolvus temperatures were studied in AD730(TM) Ni-based superalloy using Differential Thermal Analysis (DTA). The evolution in the morphology and distribution of reprecipitated γ' particles was investigated using Field Emission Gun Scanning Electron Microscopy (FEG-SEM). Depending on the cooling rate, γ' particles showed multi or monomodal distribution. The irregularity growth characteristics observed at lower cooling rates were analyzed in the context of Mullins and Sekerka theory, and allowed the determination of a critical size of γ' particles above which morphological instability appears. Precipitation kinetics parameters were determined using a non-isothermal JMA model and DTA data. The Avrami exponent was determined to be in the 1.5-2.3 range, suggesting spherical or irregular growth. A methodology was developed to take into account the temperature dependence of the rate coefficient k(T) in the non-isothermal JMA equation. In that regard, a function for k(T) was developed. Based on the results obtained, reprecipitation kinetics models for low and high cooling rates are proposed to quantify and predict the volume fraction of reprecipitated γ' particles during the cooling process.
authors.affiliation: Department of Mechanical Engineering, École de Technologie Supérieure (ETS), H3C 1K3, Montreal, QC, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Masoumi
authors.affiliation: Department of Mechanical Engineering, École de Technologie Supérieure (ETS), H3C 1K3, Montreal, QC, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Shahriari
authors.affiliation: Department of Mechanical Engineering, École de Technologie Supérieure (ETS), H3C 1K3, Montreal, QC, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Jahazi
authors.affiliation: Institute Pprime, UPR CNRS 3346, Physics and Mechanics of Materials Department, ISAE- ENSMA, BP 40109, Futuroscope- Chasseneuil Cedex 86961, France.
authors.forename: J
authors.initials: J
authors.lastname: Cormier
authors.affiliation: Aubert &Duval, Site des Ancizes, BP1, 63770 Les Ancizes Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Devaux