I. Kinetics of Coarsening of the Gamma-Prime Precipitate in Ni-Si Alloys. II. Rate of Crystallisation of an Amorphous Fe-P-C Alloy

Citation

Rastogi, Prabhat Kumar (1970) I. Kinetics of Coarsening of the Gamma-Prime Precipitate in Ni-Si Alloys. II. Rate of Crystallisation of an Amorphous Fe-P-C Alloy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/NQW7-SH65. https://resolver.caltech.edu/CaltechTHESIS:07182014-131630839

Abstract

The coarsening kinetics of Ni₃ Si(γ') precipitate in a binary Ni-Si alloy containing 6.5 wt. % silicon was studied by magnetic techniques and transmission electronmicroscopy. A calibration curve was established to determine the concentration of silicon in the matrix. The variation of the Si content of the Ni-rich matrix as a function of time follows Lifshitz and Wagner theory for diffusion controlled coarsening phenomena. The estimated values of equilibrium solubility of silicon in the matrix represent the true coherent equilibrium solubilities.

The experimental particle-size distributions and average particle size were determined from dark field electron micrographs. The average particle size varies linearly with t^-1/3 as suggested by Lifshitz and Wagner. The experimental distributions of particle sizes differ slightly from the theoretical curve at the early stages of aging, but the agreement is satisfactory at the later stages. The values of diffusion coefficient of silicon, interfacial free energy and activation energy were calculated from the results of coarsening kinetics. The experimental value of effective diffusion coefficient is in satisfactory agreement with the value predicted by the application of irreversible the rmodynamics to the process of volume constrained growth of coherent precipitate during coarsening. The coherent γ' particles in Ni-Sialloy unlike those in Ni-Al and Ni-Ti seem to lose coherency at high temperature. A mechanism for the formation of semi-coherent precipitate is suggested.

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