ABSTRACT
Ostwald ripening
, according to which, the
mean size
of
equiaxed
precipitates,
d
,
changes with time,
t
, at a constant temperature and a small volume fraction of
precipitates
, as follows:
d
–
d
=
k
(
t
–
t
)
The subscript 0 in the equation relates to the initial magnitudes of
d
and
t
, and the constant,
k
, is directly proportional to the energy of the
interface
between precipitates and the
matrix
,
σ
. In addition,
k
is proportional to the
diffusion coefficient
of
solutes
in the matrix, as well as to their
solubility limit
. The equation is usually referred to as
t
dependence and is characteristic of
diffusion-controlled
growth. Since
coherent
and
partially coherent interfaces
are characterized by low
σ
,
coherent precipitates
coarsen slower than do
incoherent
precipitates.
