CN104328311B - There is niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature - Google Patents
There is niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature Download PDFInfo
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Abstract
Had a niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature, be add moderate content niobium element in the titanium aluminum alloy of 48.29 ~ 48.4at.% at aluminium content, its solidification path was peritectic freezing.Cast structure of the present invention was peritectic freezing tissue, formed the globular α dendrite of not obvious differentiation; Peritectic freezing tissue is crossed without obvious peritectoid is dizzy, dentrite is not obvious, microsegregation is unconspicuous in α interdendritic, decreases the Hot Cracking containing niobium cast ti al alloy ingot casting and foundry goods; Add appropriate N, B element, cause Solidification Structure fine uniform, reduce the cracking between lamella group in material further.The present invention is the desirable cast ti al alloy manufacturing dense structure, reduced in segregation, good, the of good performance titanium aluminum alloy ingot casting of hot-cracking resistance and foundry goods, can be used for manufacturing engine and casts the heat resistant structure parts such as low-pressure turbine blade, charging turbine blade.
Description
Technical field
The present invention relates to high-temperature structural material field, is cast titanium aluminium (TiAl) alloy that a kind of hot-cracking resistance being applicable to lightweight thermal structure is good.
Technical background
Gamma-TiAl alloy has low density, high specific tenacity and compare Young's modulus, the advantages such as good anti-oxidant and creep-resistant property, become the material manufacturing the light heat-resisting structural part most competitive power such as high thrust-weight ratio advanced aircraft engine hpc blade, low-pressure turbine blade, automobile charging turbine.
From first-generation TiAl-base alloy (Ti-48Al-1V (at.%)) to s-generation TiAl-base alloy (Ti-48Al-2Nb-2Cr (at.%)), arrive third generation TiAl-base alloy (K5) again until the high temperature TiAl-base alloy of will be on active service in 800 – 900 DEG C future, TiAl alloy Composition and property is the focus that people pay close attention to always.But, owing to adding more β stabilizing element in existing TiAl alloy, cause its cast structure's segregation obvious, add the room temperature intrinsic fragility that TiAl alloy itself has, make its ingot casting and foundry goods in process of cooling, near tough crisp invert point, easily occur hot tearing, and hot tearing crackle is easy especially expands on the interface of segregation tissue, thus causes ingot casting and foundry goods cracking.Seriously constrain TiAl alloy ingot casting and foundry goods particularly large size ingot casting and foundry goods manufacture power.Now there are some researches show, solidification path and its alloying constituent of Peculiarities of Solidification Structure and alloy are closely related, and obtaining rational Peculiarities of Solidification Structure by allotment alloying constituent will contribute to reducing the cracking trend of ingot casting and foundry goods.
Peritectic Alloy is by solidification path, usually can be divided into: single-phase solidified superalloy, sub-peritectic freezing alloy and mistake peritectic freezing alloy (D.H.St.John, L.M.Hogan, ASimplePredictionoftheRateofthePeritecticTransformation, Acta, Metall, 35,1987:172).TiAl alloy is typical Peritectic Alloy, according to TiAl alloy binary phase diagram, current casting TiAl alloy also can be divided into: single β solidifies TiAl alloy, sub-peritectic freezing TiAl alloy and crosses peritectic freezing TiAl alloy, specifically: Aluminum in Alloy equivalent content is single beta phase alloy lower than the alloy of β phase maximum solid solution degree point 44.3at.%; Aluminum in Alloy equivalent content is sub-peritectic freezing alloy higher than 44.3at.% lower than the alloy of peritectic point aluminium content 47.3at.%; Aluminum in Alloy equivalent content is higher than the alloy of 47.3at.% and the alloy lower than α phase maximum solid solution degree point aluminium content 49.3at.% was peritectic freezing alloy.In addition, according to document: measuring at the alloy of 3 ~ 5at.% containing Nb is the middle niobium Ti Al alloy (THERMAL STABILITY [D] of Hu Wei .Ti-45Al-2Mn-2Nb-0.8vol%TiB2 and Ti-46Al-5Nb-0.5W-l.2B, Southwest Jiaotong University's master thesis, 2014:18), measuring at the alloy of 5 ~ 10at.% containing Nb is high niobium Ti Al alloy (FritzAppel, JonathanDavidHeatonPaul, MichaelOehring.GammaTitaniumAluminides2003, TMS, Warrendale, PA, P472).
TiAl alloy is solidified for single β, in its tissue, there is obvious β segregation, and the humidity province field width existed due to β phase in single phase region, easily retain B2 phase or the ω phase even D8 of fragility in room temperature texture
8-ω phase, ingot casting easily produces hot tearing.Sub-peritectic freezing TiAl alloy, its tissue signature is that β phase branch is first separated out and grows up, and crystallization range is wider, causes the mushy freezing feature of this kind of TiAl alloy more than Layer by layer solidification feature.And, for sub-Peritectic Alloy, due to Peritectic Reaction terminate after there is no remaining liquid phase, Peritectic Reaction is incomplete, causes β phase not eliminate completely, and nascent β phase dentrite tissue residue is in solidified structure, and formed on these nascent β dentrites significantly " α peritectoid is swooned " (accompanying drawing 1), make the solidified structure of such alloy there is obvious dendritic segregation and coagulation defect, thus cause alloy casting degradation, tearing tendency is larger.For crossing peritectic freezing TiAl alloy, its nascent β phase at the peritectoid phase α do not grown up or namely produced by Peritectic Reaction before breaking up surround, little owing to crossing peritectoid composition alloy β crystallization range, the nascent little peritectoid α phase size that causes of β phase size is little, and dendroid is not obvious.Because Peritectic Reaction is complete, its dendrite edge is without " α peritectoid is swooned ".Have remaining liquid phase after Peritectic Reaction, remaining liquid phase is finally with alpha-phase growth.When the peritectoid phase content generated after its Peritectic Reaction is complete and residual solution phase content are 1:1, α phase is not obvious is divided into dendritic morphology, and forms globular α dendrite, and in follow-up α process of setting, growing up of α phase still mainly keeps the feature of n on-dendritic.This alloy melt casting fluidity is good, and component segregation is little, and substantially reduce the probability of microsegregation and coagulation defect appearance, ingot casting not easily produces hot tearing; Nb element is for improving alloy strength and resistance of oxidation; Cr element is for improving the heat deformability of titanium aluminum alloy; B element can make Solidification Structure fine uniform; N element can refining alloy tissue, increases intensity and the lamella stability of lamella, thus suppresses the cracking of sheet interlayer.
Cross in peritectic freezing TiAl alloy, the alloy meeting above-mentioned feature is completely U.S.'s exploitation, famous Ti-48Al-2Nb-2Cr (at.%) alloy, is current uniquely a kind of TiAl alloy be applied in the large-scale Civil Passenger Plane Engine of Boeing787.But, because the service temperature of Ti-48Al-2Nb-2Cr (at.%) alloy only has 700 DEG C, the needs that alternate-engine low-pressure turbine blade service temperature brings up to 750 ~ 800 DEG C of scopes can not be met, in the urgent need to developing new casting TiAl alloy.Because Nb can significantly improve intensity and antioxidant property, therefore, people have developed various new height niobium and middle niobium Ti Al alloy by improving Nb content.But, because Nb element has strong β stabilization features in Ti alloy, cause in the current TiAl alloy containing niobium, as: K5, WMS alloy of U.S.'s exploitation; The 09C alloy (Ti-44Al-4Nb-2Cr-(0.2-0.4) (B, C) (at.%)) that the famous TNM alloy (Ti-43Al-4Nb-1Mo-0.1B (at.%)) of Germany's exploitation and American scholar Young-WonKim propose; Ti-48Al-7Nb-2.5V-1Cr (at.%) alloy of Beijing Iron and Steel Research Geueral Inst exploitation; Ti-45Al-8Nb-0.5 (B, W, Y) (at.%) alloy etc. of University of Science & Technology, Beijing's exploitation, is sub-peritectic freezing or single β phase solidified superalloy, non-over peritectic freezing alloy.The hot tearing trend of these alloy cast ingots and foundry goods is serious, easily produces cracking, has a strong impact on the production of TiAl alloy mother alloy ingot and foundry goods.
Summary of the invention
For overcome exist in prior art can not meet alternate-engine low-pressure turbine blade service temperature and hot tearing trend is serious, easily produce the deficiency of cracking, the present invention proposes and a kind of there is niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature.
Described had niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature, comprising: Ti, Al, Nb, Cr, B and N element, is characterized in that: be the content niobium element adding 3 ~ 5at.% in the titanium aluminum alloy of 48.29 ~ 48.4at.% at aluminium content; Wherein: Al is 48.29 ~ 48.4%, Nb is 3 ~ 5%; Cr is 1.9 ~ 2%; N is 0.6 ~ 0.8%; B is 0.1 ~ 0.3%; Remaining is Ti.The equal atomic percent of described per-cent.
The equivalent thickness of aluminium sum of the Al equivalent of described Al, Cr element and the niobium element of 3 ~ 5at.% should be in the peritectoid composition range excessively in TiAl alloy figure.
The described peritectoid phase content had in the thermal crack resistant type of peritectic freezing feature in niobium casting TiAl alloy: residual solution phase content=1:0.95 ~ 1, to ensure the mobility of alloy melt and to control peritectoid mutually not in dendritic growth.
The present invention is the moderate content niobium element adding 3 ~ 5at.% in the titanium aluminum alloy of 48.29 ~ 48.4at.% at aluminium content, cause the cast structure of alloy, be rendered as and cross peritectic freezing tissue without obvious peritectoid is dizzy, dentrite is not obvious, microsegregation is unconspicuous, decrease the Hot Cracking containing niobium cast ti al alloy ingot casting and foundry goods, can be used for for a kind of the desirable cast ti al alloy manufacturing dense structure, reduced in segregation, good, the of good performance titanium aluminum alloy ingot casting of hot-cracking resistance and foundry goods.The component atoms ratio of alloy of the present invention is: Al48.29 ~ 48.4%; Nb3 ~ 5%; Cr1.9 ~ 2%; N0.6 ~ 0.8%; B0.1 ~ 0.3%; Surplus is Ti.This alloy can mainly for the manufacture of heat resistant structure parts such as engine low-pressure turbine blade, charging turbine blades.
For obtaining dense structure's reduced in segregation, hot-cracking resistance is good, of good performance had niobium cast ti al alloy in peritectic freezing feature, the present invention meets following requirement: 1. adjust Al constituent content and solidify to cross peritectic freezing path with the alloy of content of niobium 3 ~ 5at% in ensureing, namely in alloy the Al equivalent of Al, Cr element and the equivalent thickness of aluminium sum of moderate content Nb should be in TiAl alloy figure peritectoid composition range; 2. the complete peritectoid phase content generated afterwards of alloy Peritectic Reaction must be ensured: residual solution phase content=1:0.95 ~ 1, to ensure the mobility of alloy melt and to control peritectoid mutually in dendritic growth; 3. add appropriate N, B element thinning microstructure, reduce segregation further, and strengthen matrix, improve alloy casting state performance.
For this reason, the present invention is based on the peritectic freezing characteristic Design excessively of Ti-48Al-2Nb-2Crat.% alloy, the scope of adjustment Al content and Nb content range, particularly will adjust Nb content, to ensure that the Al equivalent corresponding to it is unlikely to affect the Al equivalent of Integral alloy.
When determining scope and the Nb content range of described Al content:
1) by formula (1) and formula (2) by quad alloy TiAl-xNb-2Cr (x=1,2,3,4,5,6,7) ternary alloy TiAl-yNb (y=1.67,2.67,3.67,4.8 are changed into, 6,7.11,8.25) alloy, wherein:
y＝x+0.67(y≤3)(1)
y＝2*(1/((0.00643x
2-0.098x+0.54)*10))(y≤3)(2)
In formula (1) and (2): y is quad alloy TiAl-xNb-2Cr (x=1,2,3,4,5,6,7) ternary alloy TiAl-yNb (y=1.67,2.67,3.67 are changed into, 4.8,6,7.11,8.25) the Nb equivalent of alloy.
With document (DavidR.Johnson, HaruyukiInui, ShinjiMuto, YujiOmiya, TakamitsuYamanaka.Microstructuraldevelopmentduringdirect ionalsolidificationof α-seededTiAlalloys.ActaMaterialia54 (2006) .P1084.Tab. (2), Fig.10 (b)) in be standard about the Al equivalent value of Nb, Cr: Cr equivalent coefficient is 0.1, niobium equivalent coefficient changes in 0.16 ~ 0.3 according to Nb content, Nb content is higher, and Al equivalent coefficient is lower.
2) ternary TiAl alloy composition is changed into binary TiAl alloy composition by formula (3) and formula (4): Ti-zAl (z=49.03,49.44,49.84,50.30,50.79,51.24,51.70),
z＝b/(100-y)-0.3*y(y≤3)(3)
z＝b/(100-y)-(0.00643x
2-0.098x+0.54)*y(3<y≤7)(4)
(b＝48.21,48.23,48.39,48,41,48.35,48.32,48.25)
In formula (3) and (4): z is the Al content that ternary TiAl alloy composition changes binary TiAl alloy composition into; B be for the Peritectic Reaction of different N b content after remaining liquid phase and peritectoid Phase Proportion be the Al content of 1:1.
3) pass through with TiAl-8Nb alloy phase diagram (ChenGL, XuXJ, TengZK, WangYL, LinJP, MicrosegregationinhighNbcontainingTiAlalloyingotsbeyondl aboratoryscale.Intermetallics, 2007; 15:625-631.P628, Fig.4) be foundation, by the β maximum solid solution degree point C on the Peritectic Reaction line in TiAl-8Nb alloy phase diagram and binary TiAl alloy phasor
β, peritectic point C
pwith α maximum solid solution degree point C
αthree points connect, carry out decile according to different N b content, obtain the β maximum solid solution degree point C in the Ti-Al-xNb three-part system of following different N b content on Peritectic Reaction line
β, peritectic point C
pwith α maximum solid solution degree point C
α, the Al content value of these three important component points is in table 1.
4) adopt lever rule, the ratio of the peritectoid phase content that the desirable TiAl alloy obtaining different N b content generates after Peritectic Reaction terminates and residue liquid phase is in table 2.Actual alloy due to the melting loss of elements in fusion process inevitable, the degree close with nominal composition can only be maintained.Therefore, in design, applicant will the proportionlity of the Peritectic Reaction of the actual 4822 alloys peritectoid phase content and residue liquid phase that terminate rear generation as basis, in design, the actual TiAl alloy of content of niobium, the results are shown in Table 3.
Peritectic Reaction terminates the peritectoid phase content=C of rear generation
α-certain alloy A l equivalent/(C
α-C
p)
Residual solution phase content=1-Peritectic Reaction terminates the peritectoid phase content of rear generation
On table 1TiAl alloy peritectic line, three important component points are with the change of content of niobium
| Alloying constituent | Nb equivalent (at.%) | β point | Peritectic point | α point |
| TiAl | 0 | 44.80 | 47.30 | 49.40 |
| TiAl1Nb2Cr | 1.67 | 45.20 | 47.63 | 50.42 |
| 4822(TiAl.92Nb1.94Cr) | 2.57 | 45.41 | 47.81 | 50.97 |
| TiAl2Nb2Cr | 2.67 | 45.43 | 47.83 | 51.04 |
| TiAl3Nb2Cr | 3.67 | 45.67 | 48.03 | 51.65 |
| TiAl3.94Nb1.95Cr | 4.81 | 45.94 | 48.26 | 52.34 |
| TiAl4Nb2Cr | 4.80 | 45.94 | 48.26 | 52.34 |
| TiAl5Nb2Cr | 6.00 | 46.23 | 48.50 | 53.08 |
| TiAl6Nb2Cr | 7.11 | 46.49 | 48.72 | 53.75 |
| TiAl7Nb2Cr | 8.25 | 46.76 | 48.95 | 54.45 |
| TiAl8Nb2Cr | 9.25 | 47.00 | 49.15 | 55.07 |
The Peritectic Reaction of table 2 desirable TiAl alloy terminates the change with content of niobium of rear peritectoid phase and residual solution Phase Proportion
| Alloying constituent | Al equivalent at.% | α Phase Proportion | Liquid phase ratio | Liquid phase and α Phase Proportion |
| Ti48.04Al1Nb2Cr | 49.03 | 50.00 | 50.00 | 1 |
| Ti48.23Al2Nb2Cr | 49.44 | 49.99 | 50.01 | 1 |
| Ti48.39Al3Nb2Cr | 49.84 | 50.00 | 50.00 | 1 |
| Ti48.41Al4Nb2Cr | 50.30 | 50.00 | 50.00 | 1 |
| Ti48.35Al5Nb2Cr | 50.79 | 50.00 | 50.00 | 1 |
| Ti48.32Al6Nb2Cr | 51.24 | 50.00 | 50.00 | 1 |
| Ti48.25Al7Nb2Cr | 51.70 | 50.00 | 50.00 | 1 |
| Ti47.90Al8Nb2Cr | 51.74 | 50.00 | 50.00 | 1 |
The Peritectic Reaction of table 3 actual TiAl alloy terminates the change with content of niobium of rear peritectoid phase and residual solution Phase Proportion
| Alloying constituent | Al equivalent at.% | α Phase Proportion | Liquid phase ratio | Liquid phase and α Phase Proportion |
| 4822(Ti48.19Al1.92Nb1.94Cr) | 49.35 | 51.24 | 48.76 | 0.95 |
| Ti48.39Al2.94Nb1.95Cr | 49.80 | 51.25 | 48.75 | 0.95 |
| Ti48.40Al3.94Nb1.95Cr | 50.25 | 51.29 | 48.71 | 0.95 |
| Ti48.41Al4.94Nb1.95Cr | 50.73 | 51.26 | 48.74 | 0.95 |
According to the design result that table 1 shows, in the TiAl of different content of niobium, all reasonable to be thought of as point occurs, low content of niobium alloy middle ideal alloy is 4822 alloys, and when alloying constituent is middle niobium Ti-48.4Al-3.94Nb-1.95Cr and high niobium Ti-48.25Al-7Nb-2Cr (table 2,3), peritectoid phase content is 1:0.95 ~ 1 with the ratio of residue liquid phase, close with the ratio remaining liquid phase with the peritectoid phase content in the middle of 4822 alloys.But high niobium alloy was for realizing peritectic freezing, and alloy monolithic Al equivalent will reach 51.7at.%, solidifying γ phase content in rear tissue increased, and can increase the fragility of alloy, the Hot Cracking of alloy cast ingot and foundry goods is still very high, and hot-cracking resistance is poor.Therefore, middle content of niobium, the Ti-48.45Al-3.94Nb-1.95Cr alloy with peritectic freezing is more satisfactory cast ti al alloy, obtains the alloy cast ingot (accompanying drawing 2) without hot tearing crackle and full sheet layer solidified structure (accompanying drawing 3).
As everyone knows, crystal grain thinning can reduce microstructure segregation and component segregation further, and complete lamellar structure has best mechanical property.In order to obtain in final ingot casting and foundry goods crystal grain tiny, etc. the complete lamellar structure of axle, the present invention also adds the alloying elements such as appropriate N, B in the alloy, and to the ingot casting of this alloy production and foundry goods, carrying out temperature is in a vacuum furnace 1100 ~ 1200 DEG C, the isothermal annealing of 100h.
The present invention relates to a kind of middle niobium cast ti al alloy with peritectic freezing feature.Comprise: Ti, Al, Nb, Cr, B, N element, it is characterized in that: be the moderate content niobium element adding 3 ~ 5at.% in the titanium aluminum alloy of 48.29 ~ 48.4at.% at aluminium content, its solidification path was peritectic freezing, the peritectoid phase content generated after Peritectic Reaction is complete: residual solution phase content=1:0.95 ~ 1, its Solidification Characteristics is: the cast structure of alloy was peritectic freezing tissue, first separate out nascent β dentrite, through Peritectic Reaction, peritectoid α phase completely consumed β dentrite, nascent β phase is substantially consumed by peritectoid α phase and replaces, primary dendrite changes non-dendritic structure into, the globular α dendrite of the not obvious differentiation of final formation, peritectic freezing tissue is crossed without obvious peritectoid is dizzy, dentrite is not obvious, microsegregation is unconspicuous in α interdendritic, decreases the Hot Cracking containing niobium cast ti al alloy ingot casting and foundry goods, B element adds appropriate N, B element, causes Solidification Structure fine uniform, thus reduces the cracking in material between lamella group further.Determine that the component atoms ratio of alloy of the present invention is: Al is 48.29 ~ 48.4%; Nb is 3 ~ 5%; Cr is 1.9 ~ 2%; N is 0.6 ~ 0.8%; B is 0.1 ~ 0.3%; Surplus is Ti.The object of the invention, by the rational allocation to Al, Nb content in TiAl alloy, obtains the TiAl alloy containing moderate content niobium 3 ~ 5at.% that a kind of hot-cracking resistance is good.In sum, the object of the invention is by the rational allocation to Al, Nb content in TiAl alloy, in acquisition, niobium casting TiAl alloy had peritectic freezing feature, its alloy cast ingot and foundry goods are after being cast, solidify to cross peritectic freezing mode, obtain the solidified structure without obvious dentrite and segregation, ingot casting and casting thermal fragmentation tend to little, not easy to crack.This alloy is the desirable cast ti al alloy manufacturing dense structure, reduced in segregation, good, the of good performance titanium aluminum alloy ingot casting of hot-cracking resistance and foundry goods.This alloy can be used in manufacturing heat resistant structure parts such as engine casting low-pressure turbine blade, charging turbine blade etc.
Accompanying drawing explanation
Fig. 1 is sub-peritectoid TiAl Solidification Microstructure Morphology;
Fig. 2 is the alloy cast ingot without hot tearing crackle;
Fig. 3 was peritectoid TiAl Solidification Microstructure Morphology.
Embodiment
The present invention a kind ofly to have in the thermal crack resistant type of peritectic freezing feature niobium casting TiAl alloy, described in have niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature be that the niobium element adding 3 ~ 5at.% in the titanium aluminum alloy of 48.29 ~ 48.4at.% obtains at aluminium content.In described thermal crack resistant type, niobium casting TiAl alloy is made up of Al, Nb, Cr, B, N and Ti, wherein: Al is 48.29 ~ 48.4%, Nb is 3 ~ 5%; Cr is 1.9 ~ 2%; N is 0.6 ~ 0.8%; B is 0.1 ~ 0.3%; Remaining is Ti.Described per-cent is atomic ratio.
Described had in the thermal crack resistant type of peritectic freezing feature in niobium casting TiAl alloy, and the equivalent thickness of aluminium sum of the Al equivalent of Al, Cr element and the niobium element of 3 ~ 5at.% should be in the peritectoid composition range excessively in TiAl alloy figure.
The described peritectoid phase content had in the thermal crack resistant type of peritectic freezing feature in niobium casting TiAl alloy: residual solution phase content=1:0.95 ~ 1, to ensure the mobility of alloy melt and to control peritectoid mutually not in dendritic growth.
Propose 6 embodiments in the present invention, the component of each embodiment is as shown in table 4:
The component of each embodiment of table 4:
Described per-cent is atomic percent.
When there is described in preparation niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature, according to a conventional method batch mixing was carried out to the starting material of each element, be pressed into vacuum consumable arc-melting electrode.Described TiAl alloy adopts conventional vacuum consumable arc-melting cast, obtains TiAl alloy ingot casting.In order to make the TiAl alloy obtained have the tiny complete lamellar structure waiting axle of crystal grain, cooled TiAl alloy ingot casting is carried out in a vacuum furnace to the isothermal annealing of 100h, isothermal annealed temperature is 1100 ~ 1200 DEG C.The TiAl alloy ingot casting of final formation can be used in the production of TiAl alloy foundry goods, and it is 1100 ~ 1200 DEG C that cooled TiAl alloy ingot casting also carries out temperature in a vacuum furnace, the isothermal annealing of 100h.
Claims (1)
1. there is a niobium casting TiAl alloy in the thermal crack resistant type of peritectic freezing feature, comprising: Ti, Al, Nb, Cr, B and N element, is characterized in that: be the content niobium element adding 3 ~ 5at.% in the titanium aluminum alloy of 48.29 ~ 48.4at.% at aluminium content; Wherein: Al is 48.29 ~ 48.4%, Nb is 3 ~ 5%; Cr is 1.9 ~ 2%; N is 0.6 ~ 0.8%; B is 0.1 ~ 0.3%; Remaining is Ti; The equal atomic percent of described per-cent;
The equivalent thickness of aluminium sum of the Al equivalent of Al, Cr element and the niobium element of 3 ~ 5at.% should be in the peritectoid composition range excessively in TiAl alloy figure;
The described peritectoid phase content had in the thermal crack resistant type of peritectic freezing feature in niobium casting TiAl alloy: residual solution phase content=1:0.95 ~ 1, to ensure the mobility of alloy melt and to control peritectoid mutually not in dendritic growth.
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