206 Prakt. Met. Sonderband 30 (1999) 
(T — temperature in K). The results show (Table 2) that 4 — 7.2 % TiB, remain unmelted. Since the 
solubility product defined by the equation 3 is probably to high (11), the amount of unmelted TiB, 7 
might be slightly higher. . 
Alloy titanium "boron dissolved in estimated initial unmelted TiB, 
dissolved in the 1 the melt [wt. %] quantity of TiB, at 1600 °C 
melt [wt. %] | (wt. %] [wt. %] 
A8 $522 (042 00 2... 48 lc 
_A6 2.40 0.62 92 72 ne 
‚AT 0.53 132 S4 17 
A7-2 | 036 1.59 4.6 4 
Table 2: Concentration of titanium and boron in the liquid phase and the quantity of unmelted TiB> 
at 1600 °C calculated with the help of equation 3 
Morphology of diboride particles 
The size of the diboride particles in the initial state (after aluminothermic reduction) rarely exceeds 
I pm (9), but during annealing at 1600 °C very large hexagonal plates of the titanium rich diboride 
are formed. The height of the plates often exceeds 5 um and their edge 10 um (Fig. 2). 
1g 
Jann 
[oxi 
take a 
(1010) 
planar ¢ 
oo m rer 
— A= 
Fig. 2: Scanning electron micrograph of diboride particles in the investigated Al-Ti-B alloys after @ 
deep-etching: a) A8, b) A6 and c) A7-1 after 10 hours exposure at 1600 °C (1: (0001); 2: (1010); ) : 
3: (1120); 4: (1121); 5: (hkO1), h> 1, h=-k) 
All diboride particles are bound with very well defined crystal faces, but their morphology is not the Woe 
same in all investigated alloys. In the alloy A8 with an excess of Ti over that needed to form TiB; 
(Ti/B = 4.43), the diboride particles are only bound by basal {0001} and prismatic {1010} facets 
(Fig. 2 a). In the near-stoichiometric alloy A6 (Ti/B = 2,56) two additional types of facets can be v 
observed (Fig. 2 b). Namely, prismatic {1120} and pyramidal {1121} facets. In the alloy A7-1 with 
an excess of B over that needed to form TiB, (Ti/B = 1,34) the basal {0001} facet dominate (Fig