L. Arnberg et al., DETERMINATION OF DENDRITIC COHERENCY IN SOLIDIFYING MELTS BY THEOLOGICAL MEASUREMENTS, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 173(1-2), 1993, pp. 101-103
The instant, during equiaxed solidification, when the dendrites start
to impinge and form a network is called the dendritic coherency point.
The paper presents a method for measuring the dendritic coherency poi
nt. The method utilizes the fact that the shear strength of the solidi
fying material increases sharply at the coherency point. A probe is sl
owly rotated in the melt during controlled solidification and the torq
ue and temperature are measured. The coherency point can be deduced fr
om the derivative of the torque/temperature curve. Coherency measureme
nts of solidifying aluminium alloys have shown that the coherency poin
t for a given alloy is reproducible for given cooling conditions, but
varies greatly with alloying composition, grain refinement and cooling
rate. It has been found that the fraction solid at which coherency oc
curs varies between less than 0.1 for poorly grain refined Al foundry
alloys and more than 0.5 for fine grained Al alloys.