COST 507 - Repositório Aberto da Universidade do Porto
COST 507 - Repositório Aberto da Universidade do Porto
COST 507 - Repositório Aberto da Universidade do Porto
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3 Results and Discussion<br />
3.1 Measurement of density<br />
A pygnometer was used to determine the density of the fabricated alloys. The<br />
following tables show the various values in dependence on a constant Ti and Al<br />
proportion and a variable Cu and Ni content. The determined values of the alloys range<br />
roughly between 4 and 5 g/cm 3 compared with 4,5 g/cm 3 for CpTi.<br />
The results show for all TixxAl-base systems a constant increasing of the density after<br />
increasing the Cu- and/ or the Ni-proportion. Furthermore there is no connection<br />
between density and phase transition evident. Because of its higher Al-amount the<br />
TÌ20A1- and Ti25Al-based alloys have slightly smaller values than the TilOAl- and<br />
Til5Al-based alloys.<br />
3.2 Measurement of characteristic temperatures<br />
The problem is that especially the titanium will react with the A1 2 0 3 crucible, if there<br />
is a liquid phase. Therefore it is possible to measure phase transitions in solid state, but<br />
no temperatures after the reaction with the crucible because the chemical reaction<br />
changes the composition of the alloys. The plots of cooling- and reheating-cycle<br />
demonstrate that the composition of the alloys have changed, hence the measurement<br />
of characteristic temperatures after the reaction with the crucible is impossible.<br />
Table 5 shows the temperatures of phase transitions of the investigated alloys (heating<br />
rate: 20 K/min, atmosphere: Argon). Table 5 depicts the changing of characteristic<br />
temperatures determined for alloys in all base systems. Annealing the samples at<br />
800°C -12 hours cause no evident changing of the characteristic temperature.<br />
3.3 Oxi<strong>da</strong>tion behaviour<br />
The investigation of the oxi<strong>da</strong>tion behaviour indicates no significant increasing of<br />
weight after a heat treatment at 600°C for 15 hours in atmosphere. Alloys with solidus<br />
temperatures above 900°C show no systematic behaviour after heat treatment at 825°C<br />
for 15h in atmosphere. Furthermore it is obvious, that a higher Al-portion causes a less<br />
increasing of oxi<strong>da</strong>tion weight. The value of the oxi<strong>da</strong>tion mass of the annealed<br />
samples reaches ca. 50% of those, which were casted. It is determined that a phase<br />
system in an equilibrium state has a much better oxi<strong>da</strong>tion behaviour than a system in<br />
the casted state. The absolute oxi<strong>da</strong>tion values are shown in Table 6.<br />
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