Prakt. Met. Sonderband 38 (2006) 155 
e is mostly 
owledge of 2 EXPERIMENTAL 
jour of the 
allographic A small quantity of experimental Cu-Zr alloy was prepared by induction vacuum melting 
the case of using high purity copper (Cu — 99,999) and a Cu-Zr master alloy (51.430 wt.% Zr) as starting 
ry small in materials. The melt was cast into ingots 40 mm in diameter and 200 mm in height. The 
ration and zirconium content of the ingots was determined by wet chemical analysis to 1.01 wt.% , 
Jy which is which corresponds to 0.7 at.% Zr. Rapidly solidified ribbons were prepared by a Chill-Block 
rmation of Melt-Spinning (wheel diameter = 350 mm) under an Ar atmosphere using peripheral velocity 
1e samples of about 23 ms™. The nozzle diameter, injection overpressure, angle and the nozzle height 
> additional above the copper-beryllium substrate as well as the melt superheat were kept constant at 
es. Finally, 0.8 mm, 0.3 MPa, 6°, 8 mm and 50K, respectively. Continuous ribbons about 3 mm in width 
portion of and 60 to 90 um in thickness were produced. 
nerefore, a The solidification microstructure and the surface topology of the ribbons were investigated 
d scanning by light optical microscopy, scanning electron microscopy (Jeol JSM 840A) and FIB/SEM 
nd etching, system (FEI Quanta 200 3D) equipped with a gallium liquid ion source and a Pt-gas injection 
system. Specimens for optical and scanning electron microscopy were obtained as vertical 
the above and horizontal cross-sections, prepared with standard metallographic methods and 
electropolished in a mixture of 60 vol.% H3PO4 and 40 vol.% HO. FIB polishing, etching and 
am system cutting were performed on samples cleaned in ultrasound. 
ed particle 
ution of the 
rons drawn 3 RESULTS AND DISCUSION 
1 metal ion 
secondary The rapid solidification alters the nucleation and growth conditions of different phases in an 
ckscattered alloy by inducing a very large undercooling prior to the solidification process. This also 
ckscattered affects the evolution of the morphology of solidified products and leads to the formation of 
Indamental metastable phases. The solidification conditions are determined mainly by measuring the 
ed species most influencing parameters (interface growth rate, temperature gradient in the liquid ahead 
of the ion of the solid-liquid interface and cooling rate) but they can be estimated also by analysis of 
ised in the the microstructure. 
nnot easily The comparison of the results of our microstructural analysis obtained on the samples 
outer shell prepared by standard metallographic technique with those using a combination of FIB 
e sample's etching and 3D microscopy clearly shows that the solidification history can be best 
face region recognized in the transverse cross-sections of the standard prepared samples. In Fig. 1a it 
hed by the can be seen that the structure of rapidly solidified Cu-Zr ribbons consists of three different 
fon beam. morphological zones: a zone with fine columnar grains at the wheel side, coarse columnar 
tion of the grains in the transition region and a zone with equiaxed grains at the top side of the ribbons. 
anied by an Detailed examination of ribbons of different thickness revealed that the fraction of columnar 
capable of grains increases with decreasing thickness of the ribbons. Thinner parts contain a smaller 
m, its mass portion of heat energy which has to be extracted in the solidification process and therefore a 
sfer a large higher velocity of the solidification front is obtained. Since high velocity of the solidification 
igh enough front and steep temperature gradient favor directional solidification it is understandable that 
r sample x the size of the columnar zone is higher in thinner ribbons. 
1 system is The formation of the columnar zone at the substrate side can be explained on the basis of 
ging [9]. the high temperature gradients and growth velocities achieved in this area. Because the 
olidified Cu temperature gradient and growth velocity decrease from the wheel side to the free surface, 
repared by three different substructural regions - microsegregation-free, banded and cellular-dendritic - 
cussed ion formed from the bottom to the top of the ribbon