添加稀土元素以改善Ti-40Al-15Nb鈦鋁介金屬合金之高溫機械性質研究
Date Issued
2003
Date
2003
Author(s)
顧鈞豪
DOI
912216E002024
Abstract
The effect of a slight increase in Nb content of
approximately 1 at% and the effect of adding a minor
Sc or La-rich misch metal (Mm) on the microstructure
and phases of Ti-40Al-15Nb alloy show that the
microstructures of the as-cast Ti-40Al-16Nb and the
as-cast Ti-40Al-15Nb alloy are the same, but slightly
differs from the homogenized Ti-40Al-15Nb alloy, in
which the B2 phase matrix of the Ti-40Al-16Nb alloy
is replaced by á2 phase and ó phase precipitates after
homogenization at 1100℃ for 72h. Microstructural
analysis and phase characterizations of the
Ti-40Al-16Nb alloy with 0.39 wt% Sc or La-rich
misch metal additions are summarized as follows: (i)
The as-cast Ti-40Al-16Nb-0.39wt%M (M= Sc or Mm)
alloys have an á2 matrix and contain á-Ti and B2
phase precipitates but few ã phase precipitates. The
Sc2O3 or partial oxidized (La,Al)1-xOx oxide
dispersoids, formed by internal oxidation, are
observed in this work; but Ti3(Al,Sc) presented in the
dual phases of γ-TiAl are not found. The solubility
of the partially oxidized Sc in á-Ti is higher than that
of Mm. (ii) Adding Sc and La-rich Misch metal
decreases the á-transus temperature of the TiAl-Nb
alloys, possibly stabilizing the á2 phase and inhibiting
the B2 or ã phase formation. (iii) After
homogenization, the ó phase and ã phase precipitate in
the á2 phase matrix, but the B2 phase is absent. The
partially oxidized Sc in á-Ti may be further oxidized
to Sc2O3 after homogenization. The distributed
morphology of the oxide dispersoids in the TiAl-Nb
alloy with added La-rich Mm is more uniform and
discontinuous than that in the TiAl-Nb alloy with
added Sc after the homogenization. Experimental
results about effects of a minor addition of Sc or
La-rich misch metal on the high-temperature
compressive properties and isothermal oxidation
behavior of a TiAl alloy with a high niobium content
indicate that the high-temperature mechanical
properties at temperatures from 900℃ to 1150℃ and
the oxidation resistance of the alloy at 800℃ as well
as 1000℃ are improved by alloying with a minor Sc
and La-rich misch metal. Adding a slight amount of
Sc or La-rich misch metal may significantly enhance
2
the high-temperature compressive peak stress of the
high niobium content TiAl alloy. The peak flow stress
increment measured from high temperature
compression testing at 900℃ is around 450MPa and
the high temperature strength at temperatures above
900℃ is also enhanced. The significant improvement
in high-temperature mechanical properties is
attributed to the precipitation of fine oxide particles
with high thermal stability in the alloys. These
particles form an effective barrier to the moving
dislocations. Furthermore, adding either a minor Sc
or La-rich Mm to the alloy reduces the oxidation rate,
increases the strength of adhesion between the oxide
layers and the alloys and changes the morphology of
the oxide layers formed in the TiAl alloy with a high
niobium content. The TiAl alloys with oxide
dispersoids strengthening may effectively increase the application temperature from intended temperature 700℃ to 900℃.
Subjects
Titanium aluminide alloy
Microstructure
Mechanical properties
Oxidation properties
Phase transformation
Dispersion strengthening
Rare earths
Publisher
臺北市：國立臺灣大學材料科學與工程學研究所
Type
report
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