JMA analysis of the transformation kinetics from the amorphous to the nanocrystalline state. [Ni-P alloy]
Journal Article
·
· Scripta Metallurgica et Materialia; (United States)
- Inst. fuer Werkstoffwissenschaft, Stuttgart (Germany)
- Inst. of Metal Research, Shenyang (China)
In the theory of solid state phase transformation, the Johnson-Mehl-Avrami (JMA) equation is widely used in modeling the isothermal phase transformation mechanism. The JMA equation relates the transformed volume fraction x at a constant annealing temperature T and time t. The Avrami exponent for crystallization of an amorphous Ni-P alloy has been studied by means of differential scanning calorimetry measurements. In this work, the transformation kinetics of the amorphous-to-NC process was studied in a Ni-P alloy system using a magnetothermal analysis method. The JMA analysis of the measured data for the transformation revealed some new phenomena which were not found previously. The JMA analysis of the data reveal that there are three stages in the transformation: (i) a surface crystallization with n = 1.3; (ii) a bulk transformation process of nucleation and growth of three-dimensional crystallites with n = 3.5; and (iii) a segregation of solute atoms to the grain boundaries with n = 0.7. The activation energies for the transformation process were obtained by use of the Arrhenius relation and the activation energy for the surface crystallization was found to be smaller than that of the bulk process. By comparison of the results from the MTA and DSC experiments, it seems the MTA method is more sensitive in detecting the formation of nanometer-sized crystallites.
- OSTI ID:
- 6519462
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 28:9; ISSN 0956-716X; ISSN SCRMEX
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
AMORPHOUS STATE
CALCULATION METHODS
CALORIMETRY
COMPARATIVE EVALUATIONS
CRYSTAL-PHASE TRANSFORMATIONS
CRYSTALLIZATION
DATA
EVALUATION
EXPERIMENTAL DATA
INFORMATION
KINETICS
NICKEL ALLOYS
NICKEL BASE ALLOYS
NUMERICAL DATA
PHASE TRANSFORMATIONS
PHOSPHORUS ADDITIONS
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
AMORPHOUS STATE
CALCULATION METHODS
CALORIMETRY
COMPARATIVE EVALUATIONS
CRYSTAL-PHASE TRANSFORMATIONS
CRYSTALLIZATION
DATA
EVALUATION
EXPERIMENTAL DATA
INFORMATION
KINETICS
NICKEL ALLOYS
NICKEL BASE ALLOYS
NUMERICAL DATA
PHASE TRANSFORMATIONS
PHOSPHORUS ADDITIONS