Prakt. Met. Sonderband 30 (1999) 207 
3 Ming . . . = . . . 
hy (Fig. 2 c). Note also traces of the prismatic {1010} and pyramidal facets. It is not possibly to 
determine the Miller-Bravais indices of these pyramidal planes only by inspection of deep-etched 
specimens, but it seems possible that their indices are {hk01} (h> 1; h = -k). 
18, 
trace of the 
(1120) plane 
© 7 trace of the CD SE SE SE SETS = 
o © 7 1 az U-a WU aU a 
8 - > I (1010) plane En SZ 
~ ’ 0 An 
3° En 
need Ti 9 ’ “0 ARR 
melted TB, — 00 —0 
Ls "ae oon 6GALA En 0g 
5 5 Yo BRT RRC 
0 2 A % o 
> > . - 3 ® 
0 > 2 2 0 
0 2 0 0 
oh viel: ® 88 9 2 © 
rr eel co ooo ® Ti (0001) 
nich diboride 0 Oo 0 
® ® 
O B 
Fig. 3. Arrangement of atoms in some planes of TiB,. In a) TiB; crystal is bound by traces of 
{1010} and {1121} planes (projection perpendicular to (0001) plane), in b) planar arrangement of 
titanium and boron atoms in (0001) plane is shown 
To explain the influence of Ti/B ratio on the observed morphology of the diboride particles we must 
take a closer look to the atomic arrangement in the following crystallographic planes {0001}, 
{1010}, {1120}, {1121} and {2201} In the {0001} planes, boron and titanium atoms form alternate 
planar layers (Fig. 3). Thus, the outer layer in the contact with the liquid phase could be occupied 
only by boron or only by titanium atoms. In the family of {1010} planes only titanium atoms are 
arranged in planar array, but the arrangement of boron atoms is not planar (Fig. 3 a). In both {1120} 
and {1121} families of planes it is not possible to get the planar outer layer occupied by only one 
kind of atoms, but always with both titanium and boron atoms (Fig. 3 a). On the other hand, boron 
1) 2 0010; atoms are arranged planarly only in the {0001} plane, therefore the facets of these plane dominate in 
the alloy A7-1 
; According to the results it is very probable that diboride particles in the alloys with an excess of 
sgy 15 not EC . . . = . . . . . 
ol TB, titanium are bound with {0001} and {1010} planes in which titanium atoms are arranged in a planar 
: ads array. Similarly in the alloys with an excess of boron {0001} facets dominate, because in these plane 
OO C . . . . . 
hes boron atoms form planar layers. On the other hand, in the alloy A6 with a near-stoichiometric 
: cets can = — . . . . 
oe i composition are getting more important also planes {1121} and {1120} which contain both titanium 
oy ATL 
Senate (Fg 
a) b)