Samples were obtained in an electron beam furnace, cold rolled at a MDM duo reversible mill and 
heat-treated in a resistor vacuum furnace, water quenched (WQ) and aged. i 
We can explain the results sumarised in Table 1 as follows: iS 
Alloys containing Al and more than 3 % Nb exhibit good combination of room temperature Lm 
ductility anal high temperature properties. 
Nb which increases the number of slip systems, may be replaced by specific elements for [pews 
improvede strenghth (Mo, Ta) and oxidation resistnate (Ta, Mo, Si). 
The influence of Nb on structure and proprieties of Ti-Al-Mo-Nb-Si alloys 
[ne 
- Niobium forms with other elements (Ti,Al,Ta) - y phase that promote strengthening and 
additiontionally enhance oxidation resistance (fig. 2) 
- In Ti-Al-Nb alloys (2) containing more than 5 % Nb, a ductile ordered b.c.c. phase (B2) forms on on 
quenching from high temperatures, this also occurs in alloys containing other B stabilizing ro 
elements. 
- Additionally, an equilibrium ordered ortrombic phase is detected with an approximate Micros 
stoechiometry of Ti,AiNb 
- Nb reduces the slip length by refining microstructure and increasing the amount of the retrained 
ß phase Micros 
get 
. 1,400 ast: 
© 1,000 
400 : 9" 
5 ae A oe 
F : . 
ot 025 05 ors Nb. Al 
WEIGHT % SILICON 
Fig. 1 — The influence of Si content on Fig. 2 — Phase diagram 
creep properties of Ti-Al-Nb 
Ti-15Mo-5A1-5Nb-6,5Si alloy 
(creep tested at 500°C / 400 MPa) 
The influence of Al 
- Aluminiu have an important contribution to stability and strengthening of o phase Fie | 
- Increasing the Al level till 5 % and the amount of B stabilizers results in increased yield strength. To 
The yield strength of ß alloys after ageing can be expressed by the following empirical formula (3) all | 
Gooz=850+ 70d" [2] 
where AS 
540 
318