Ti-Al type lightweight heat-resistant materials containing Nb, Cr and Si

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, reasons for the limitation of the content (% by weight) of each chemical component in the Ti-Al type lightweight heat-resistant material of the present invention will be explained.
Al: 32 to 36% Al is the essential element for forming the intermetallic compounds TiAl and Ti.
sub.
3 Al together with Ti.
If Al content is too low, the volume fraction of Ti.
sub.
3 Al becomes too high so that ductility is lowered and at the same time oxidation resistance becomes degraded.
To the contrary, if Al content is too high, a single phase of TiAl is formed or the volume fraction of Al.
sub.
3 Ti becomes too high, so that ductility is lowered.
In order to obtain a two-phase alloy of TiAl/Ti.
sub.
3 Al with excellent strength and ductility, it is necessary that the volume fraction of Ti.
sub.
3 Al in the TiAl/Ti.
sub.
3 Al two-phase alloy be 5 to 40%.
This is why Al content is limited to the range of from 32 to 36% w.
Si: 0.
1 to 2.
0% The above-mentioned TiAl/Ti.
sub.
3 Al two-phase alloy is more improved in oxidation resistance when Si is added to the alloy in combination with Nb than when only Si is added thereto.
It is from Si content of 0.
1% w that this effect of Si appears under coexistence with Nb.
However, if Si content exceeds 2.
0%, the ductility at ordinary temperature is lowered by formation of a large amount of Si compounds.
This is why Si content is limited to the range of from 0.
1 to 2.
0% w in the present invention.
A more preferable range is from 0.
2 to 1.
0% w.
Nb: 0.
1 to 5.
0% Also in the case of Nb, the above-mentioned oxidation resistance is more improved when Nb is added to the alloy in combination with Si than when only Nb is added.
It is from Nb content of 0.
1%w that this effect of Nb appears under coexistence with Si.
The oxidation resistance increases with increase of Nb content, but it becomes saturated substantially at Nb content of 5.
0%.
Therefore, the upper limit of Nb content is 5.
0% in the present invention.
If Nb content exceeds 5.
0%, because of high specific gravity of Nb, specific gravity of the Ti-Al type material becomes so high that the original feature of lightness of the Ti-Al type material is diminished