204 Prakt. Met. Sonderband 30 (1999) 
AIB, (Al, Ti)B, 1, Di 
m &: a = m &= ZZ m. er we 
SAE TT Tf i : ae i ET 
TT ( J - Tt Al den 
i Hl i i SE 
be @ ea ar 
| iH i 2 + ] we 
m & nn fh m == Dn m. . a 
I Ar € = large 
J large 
a = 0.30054 nm OA @Ti ®B a = 0.30303 nm m 
c =0.32527 nm c = 0.32295 nm ~- 
Fig. 1: Crystal structure of diborides in the system Al-Ti-B. This crystal structure possesses layered 
form with alternate sequence of planar hexagonal metal layers (m) and hexagonal boron layers (b) 
Experimental [he phu 
Annealing of alloys i ) 
In this investigation we use samples of Al-Ti-B alloys prepared by aluminothermic reduction of Ti range 
and B from K,TiFs in KBF,. Chemical compositions of the alloys are given in Table 1. Details of i 
the alloy preparation can be found elsewhere (9). Before annealing we put samples into small Lge es 
alumina crucibles situated inside a covered alumina vessel. The annealing took place in a high re 
temperature furnace ASTRO in an argon atmosphere. Heating and cooling rates were 60 °C/min, wh 
and specimens were held at 1600 °C for 10 hours. Ran we 
Alloy Ti [wt. %] B [wt. %] Ti/B weight Ti+Bin i 
ratio in an an alloy 
alloy [wt. %] 
AS | 8.55 1.93 243 | 1048 
A6 I 7.34 2.86 2.56 } 10.2 
TAT 373 277 34 6.5 
A7-2 314 "285 i 599 
Table 1: Composition of the investigated Al-Ti-B alloys prepared by an aluminothermic reduction 
of Ti and B from K,TiFs and KBF,. 
Metallographic preparation 
Samples for the light and scanning electron microscopy were prepared by standard metallographic 
techniques (10). Immediately before performing the EDS analysis we freshly polished samples to by 
remove eventual etching products and oxide layers on the investigated surface. [os 
Samples used for investigation of the morphology of the diboride particles were deeply etched [1] oa 
in a solution consisting of 50% HCI in water and [2]-in a methanol-iodine solution (30 ml nn ) 
methanol, 3 g tartaric acid and 1 g iodine). Satisfied results were obtained after 10 to 15 min etching - N 
in the HCI solution and after 1 to 2 hours etching in the methanol-iodine solution. In particular alloy te 
the morphology of the diboride particles was independent from the applied etchant indicating that 
etchants dissolve onlv aluminium matrix and do not attack diboride particles. 
I,