钛铝金属间化合物

Traditional techniques
Manufacturing
[5]
Advanced techniques
• Direct rolling • Laser forming • Mechanical alloying Advantages: reducing post-processing steps. Drawbacks: scalability.
Ti-Al44-Nb4-Mo0.5-Cr1.5-B0.1-Y0.1(wt%)
• Effect of Al[11]
Conventional Alloys: Ti-48Al-2Cr-2Nb(by General Electric);
All contain a relatively high aluminum content compared to more modern alloys.
Effect of selected alloying elements on mechanical properties of Ti Al[5]
Effect of Nb
Effects of Nb and Al on the high temperature strength of alloys: (a) FL, (b) NL and (c) DFL.[8]
Background
high-temperature structural materials
Traditional materials[1]
Ti alloys Ni alloys
Highest used temperature Density
600℃ 4.5g.cm-3
1100℃ 8.3g.cm-3
Ways to increase ductility
• Add alloying element
• purify
By reducing of impurities such as oxygen and nitrogen, the ductility has been observed to increase significantly. For example, reduction of oxygen from 800 ppm to 370 ppm increased the ductility from 2% to 2.7%.
Phases of titanium aluminides
at >50% Al pure gamma phase exhibiting no ductility.
L10
Crystal structure forγTiAl
Phases of titanium aluminides
at<40% α2 (Ti3Al) phase better room temperature ductility Yet the ductility is unacceptable from an engineering stand point.
Ti-48Al-2Cr ; Ti-46Al-1Cr-0.2Si(developed by Frommeyer et al. ) γ-TAB (Ti-47Al-4(Nb, Cr, Mn, Si, B)) from GKSS Plansee -MET (Ti-46.5Al-4(Nb, Cr, Ta, B))
Ti-Al44-Nb4-Mo0.5-Cr1.5-B0.1-Y0.1(wt%)
• Effect of Al 49.4% [13]
44.6%
45-49%Al (peritectic alloys) Solidify via the hexagonal α-phase: L+β α (form columnar grains along the C axis[0001] growth direction with dendrite side arms along <1010>, not depend on the direction of β ) show anisotropic microstructures as well as significant texture and segregation.
Tuebo Charger(by casting) (Tetusi 2005)
Advantage of titanium aluminides
α-2Ti3Al ,γ2TiAl 基合金与常规Ti 基合金、Ni 基高温合金的性能比较[3]
Intermetallic and Alloys
Crystal structure forγTiAl(a) and α2Ti3Al(b)
DO19
Crystal structure for α2Ti3Al
Properties and microstructure [18]
FL: poor ductility, but they are superior to the duplex structures in other mechanical properties such as： fracture toughness; fatigue resistance; High temperature creep strength. DP: fine and homogeneous duplex structures have good ductility.
disadvantages micro porosity
limit the strength of the material
Challenge
Low room temperature ductility and fracture toughness.[5]
RT ductility of typical TiAl based alloys[7]
Advantage of titanium aluminides[2]
LPT Blades(by casting)
• Low density • Good corrosion,creep • High strength High stiffness and oxidation resistance
[1]
the and
porosity
Coarse columnar grains
Title
According to GfE– Metalle und Materialien GmbH (Germany) [9]
Powder Metallurgy
[6]
Powder Metallurgy
advantages Powder metallurgy can avoid the problems such as centerline porosity, chemical inhomogeneity, regions of varying density and microstructure. The yield is much high and also the powder metallurgy route has been found to be more cost- effective than IM.
Titanium Aluminides Intermetallics
R.J Song TongjiUniversity
Contents
• • • • • Introduction Basic information about TiAl ManufacturinFra Baidu bibliotek techniques Ways to improve the RT ductility Conclusion
The maximum in ductility was believed to be centered at Al concentrations around 48 at.%. The strength levels determined were rather low with yield stresses of 300 to 330 MPa and fracture stresses of 445 to 477 MPa being reported.
α2
α2+γ
γ
Alloy composition and microstructure [5]
FL
N L
DP NG
Of these phases, only the Ti3Al (α2), and TiAl (γ) phases have been found to be of any engineering significance.
Alloy development
• Ti45-52 -Al44-48 -X1-3 -Y2-5 –Z <1 • X:(Cr, Mn and V) increase the ductility of TiAl. • Y:( Nb, Ta, W and Mo)increase the oxidation and creep resistance at high temperatures in Ti Al. • Z:(B, C) refine the grain or increase the creep resistance
Ways to increase ductility
Refine grain sizes[7]
As the grain size decreases, the volume of defects such as grain boundaries increase, which in turn aids in the deformation mechanisms.
Effect of Nb
[5]
Increasing oxidation and creep resistance Four types: i. Ti–48Al–2Nb ii. Ti–(46–47)Al–(2–3)Nb iii. Ti–45Al–(5–10)Nb iv. Ti–45Al–(5–7)Nb–RM (refractory metals) increase the high temperature strength by solid solution strengthening.
Ways to increase ductility
• Controlling microstructure
At 45.0% Al, titanium aluminides exist in the pure gamma phase. The microstructure for this alloy composition is characterized by equiaxed gamma grains exhibiting no ductility.
Rocket Shroud
Aircraft Development of new structural materials used at high temperature is important and essential to take the first step in aerospace industry.
Ti-Al44-Nb4-Mo0.5-Cr1.5-B0.1-Y0.1(wt%)
• Effect of Al 49.4% [13]
44.6%
42-45%Al,solidify via the body-centered cubic β-phase: L L+β β β+α(the preferential directions of crystal growth are [1 0 0], [0 1 0] and [0 0 1] and the orientation relationship of β and α are: {110}β//(0001)α and <111>β//<1120>α) exhibit an isotropic, equiaxed and texture-free microstructure with modest micro-segregation.
Phases of titanium aluminides
Of the intermetallic compound phases identifed in Ti-Al alloys, Ti3Al(α2), TiAl(γ), Al2Ti and Al3Ti phases are stable at room temperature.[5]