Studies and Researches Concerning the Influence of Heat Treatment 
on the Structure and Properties of Ti-AL-Mo-Nb-Si 
M. Dobrescu, C. Dumitrescu, S. Dumitriu, University Politehnica Bucharest (RO) 
Introduction 
The key factor in increasung maximum use temperature is enhanced oxidation resistance while 
maintaining strength performance (1). 
Metastable ß alloys from the system Ti-Al-Mo-Nb-Si exhibit exceptional oxidation resistance and 
elevated temperature strength (2). 
Strengthening of titanium alloys can be obtained by quenching from f field and ageing. The 
strenght of B alloys can be increased by homogenous and fine precipitation of the a phase and by 
grain refrinement, following the reaction: 
Bnand/ ora’ > a. + Be [1] 
where 
Bm = metastable 
ao’ = a - martensitic type 
Qe, Pe = equilibrum phases 
Eperimental reasearches 
We have analised several alloys with a composition near those of well — known B 21 S alloy 
(Ti-15Mo-2,7Nb-3A1-0,2 Si) as it can be seen in Table 1. 
Table 1 — Mechanical properties at 20°C and 450°C of titanium alloys from 
Ti-Al-Nb-Mo-Si system (with or without Ta) after and again 
‘Tensile properties I 
yl Tests at 20°C test at 540°C 
TS |YS |E E  Heat-treatment 
a . MPa) | (MPa) | (% {MPa) | (MPa) | (%) : Quenched 
| Ti-15 Mo-5 Nb- “1315 [1240 19 930 | 710 20 (845°C2WWQ) 
'5A°~ 058i | | _ and aged 
(Ti-15Mo-5Nb 1130 | 1040 {9 670 | 515 119 1 (540°C/8h) 
: -0,5 Si | 
sg after Ih for 1 Ti—-)5Mo-Nb-- | 1295 | 1165 7 : 895 1 670 | 22 
— | 1,5 Ta-3Al--0,25 Si | | od | LL 
a | Ti-15Mo-2Nb- | 1305 | 1230 | 5 | 900 | 670 | 23 
0 uo | 2A1-05 Si | | | ) 
Ts — tensile strengih; YS — yield strength; E — elongation; WQ — water quenched 
Ailoy 
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