info:eu-repo/semantics/conferenceProceedings
COARSENING OF ` PRECIPITATES IN NIRICH NI-TI ALLOYS
Autor
HECTOR JAVIER DORANTES ROSALES
IVANOVICH ESTRADA GUEL
Institución
Resumen
The Ni-rich Ni-Ti system has been studied by many researchers using many different
techniques. The mentioned studies have concluded that cuboidal-type γ´ precipitates are
the cause of hardening, but these precipitates coarsen at high-temperature and prolonged
service time causing loss of coherency and eventually affect the mechanical properties.
Coarsening is theoretically described by the model proposed by Lifshitz-Slyozov and
Wagner (LSW theory) [1, 2] which predicts precipitates dispersed in a fluid matrix that
coarsen according to the relationship, r3 = krt. A different behavior of kr during the
coarsening has been reported for Ni-based alloys with elastic strains, where kr decreases
in function of increasing fv, which is known as anomalous coarsening [3, 4]. A more realistic
model, where coarsening is independent fv, has been developed by Ardell and Ozolins [5]
and Ardell [6] and is called trans-interface diffusion-controlled (TIDC) theory. A rate law of
type <r>n ≈ kIt is predicted by the TIDC theory. On the other hand, Miyazaki [7] proposed a
novel microstructural characterization method to study the precipitation process in binary
alloys, called the macroscopic concentration gradient (MCG) method. It is based on the
microstructural observation of different composition alloys formed by a continuous
composition gradient. The purpose of this work is to analyze the coarsening of γ´ precipitates
in Ni-rich Ni-Ti alloys using a composition gradient generated by diffusion couples in order
to determine which model, LSW or TICD, fits better.
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