本文選題：高Nb-TiAl合金 + 有序ω相��； 參考：《北京科技大學(xué)》2015年博士論文

【摘要】：高Nb-TiAl合金由于其優(yōu)異的高溫強(qiáng)度,高溫抗氧化性和蠕變性能,已經(jīng)成為一種先進(jìn)的輕質(zhì)高溫結(jié)構(gòu)材料。然而,在高Nb-TiAl合金凝固過(guò)程中產(chǎn)生的高溫β相經(jīng)有序化轉(zhuǎn)變?yōu)槭覝卮嘈韵郆2相。雖然B2相降低了高Nb-TiAl合金的室溫性能,然而近年來(lái)的研究發(fā)現(xiàn)無(wú)序的高溫β相可以有效改善合金的熱加工性能。另外,B2相在最近發(fā)展的Beta-GammaTiAl合金中的體積分?jǐn)?shù)非常高,因此關(guān)于B2相的研究顯得尤為重要；同時(shí)B2相中有序ω相的存在溫度區(qū)間與高Nb-TiAl合金可能的服役溫度區(qū)間重合,因此有序ω相的演變規(guī)律正逐步成為研究熱點(diǎn)。本文主要研究了高Nb-TiAl合金中B2相區(qū)域內(nèi)部有序ω相的相變規(guī)律,主要結(jié)論和創(chuàng)新點(diǎn)如下： 1、研究了高Nb-TiAl合金鑄態(tài)組織中有序ω相的演變規(guī)律。結(jié)果表明,高Nb-TiAl合金鑄態(tài)組織中的Nb偏析區(qū)一般會(huì)有有序ω相形成。衍射分析證明有序ω相存在B82-ωo相和ω”相的結(jié)構(gòu)差異。闡明了Nb偏析區(qū)在鑄錠冷卻過(guò)程中的成分與相結(jié)構(gòu)的演變機(jī)制,尺寸不同的有序ω相顆粒的出現(xiàn)是Nb和W的擴(kuò)散及ω。相的析出溫度高于ω”相造成的。 2、揭示了冷卻速度對(duì)有序ω相形核長(zhǎng)大的影響規(guī)律。不同的冷速導(dǎo)致不同結(jié)構(gòu)的有序ω相形成。水冷樣品中ω”相形核；空冷樣品中ω。相和ω”相共存；而爐冷樣品中ω。相長(zhǎng)大,其間為ω”和B2相的混合組織。高Nb-TiAl合金中有序ω相的形成難以避免。 3、研究了熱處理對(duì)有序ω相相變的影響規(guī)律。結(jié)果表明,中溫(850℃)保溫時(shí)ω。相大量析出,Nb偏析區(qū)實(shí)際上由ωo+γ相構(gòu)成,ω。相變體間的界面過(guò)渡平滑。闡明了α2相向ω。相的相變機(jī)制,并用“邊-邊”法計(jì)算表明了兩者只存在兩種位向關(guān)系,其中[1120]α2//[0001]ωo；(0002)a2//(1120)ωo更穩(wěn)定,與TEM觀察一致。高溫(950℃)短時(shí)保溫即可使有序ωo相快速消失。 4、研究了合金元素對(duì)有序ω相的影響規(guī)律。結(jié)果表明,ω。相在Ti-45Al-(7-10)Nb合金中是中溫平衡相。而添加少量合金元素即可有效控制有序ω相的數(shù)量和形貌：Mn可以強(qiáng)烈抑制有序ω相的生成；W、Cr的抑制作用稍弱；Ni則強(qiáng)烈促進(jìn)有序ω相的生成。合金元素通過(guò)改變有序ω相的析出溫度來(lái)控制其形核長(zhǎng)大。 5、研究了有序ω相對(duì)高Nb-TiAl合金力學(xué)性能的影響。結(jié)果表明,少量有序ω相對(duì)合金力學(xué)性能的影響較小。在高溫變形中,微米級(jí)ω。相難以強(qiáng)化合金；而以納米級(jí)尺寸細(xì)小彌散分布的有序ω相可提高合金強(qiáng)度,這可以通過(guò)中溫短時(shí)保溫來(lái)實(shí)現(xiàn)。 6、煉制了Ti-34Al-13Nb合金以研究有序ω相相變規(guī)律。此合金在中溫處于ωo+α2兩相區(qū),a2相由ωo。相中直接析出。α2相變體之間的界面可以自發(fā)調(diào)整至低能量狀態(tài),表現(xiàn)為共格界面或者類似孿晶的界面。 7、研究了B19相的相變規(guī)律。B19相在α2→ωo轉(zhuǎn)變中于二者界面處出現(xiàn),晶格常數(shù)為a=0.464nm、b=0.290nm、c=0.510nm。 HRTEM直接觀察到B19相可作為α2相到Y(jié)相轉(zhuǎn)變的過(guò)渡相,與同步輻射報(bào)道結(jié)果一致。B19相的析出溫度在650℃-750℃之間,而高溫短時(shí)保溫即可消失。高Nb-TiAl合金中快冷獲得α2相處于非平衡態(tài)。
[Abstract]:High Nb-TiAl alloy has become an advanced lightweight high temperature structural material because of its excellent high temperature strength, high temperature oxidation resistance and creep properties. However, the high temperature beta phase produced in the solidification process of high Nb-TiAl alloy is transformed into a brittle phase B2 phase at room temperature. Although B2 phase reduces the room temperature properties of high Nb-TiAl alloy, however, it is close to it. Recent studies have found that the disordered high temperature beta phase can effectively improve the thermal processing properties of the alloy. In addition, the volume fraction of the B2 phase in the recently developed Beta-GammaTiAl alloys is very high. Therefore, the study of the B2 phase is particularly important. At the same time, the existence of the temperature range of the ordered Omega phase in the B2 phase and the possible service temperature zone of the high Nb-TiAl alloy The evolution of ordered Omega phase is becoming a hot spot of research. This paper mainly studies the phase transition of ordered Omega phase in B2 phase in high Nb-TiAl alloy. The main conclusions and innovation points are as follows:
1, the evolution of ordered Omega phase in the cast microstructure of high Nb-TiAl alloy is studied. The results show that the ordered Omega phase in the Nb segregation region in the cast structure of high Nb-TiAl alloy is generally formed. The diffraction analysis shows that the structure difference between the B82- Omega o phase and the Omega phase exists in the ordered Omega phase. The composition and phase structure of the Nb segregation area in the cooling process of the cast ingot are clarified. The evolution mechanism is that the appearance of ordered Omega phase particles with different sizes is caused by the diffusion of Nb and W and the precipitation temperature of Omega phase.
2, the influence of cooling rate on the ordered Omega nucleation growth is revealed. Different cooling rates lead to the formation of ordered Omega phase of different structures. Omega phase nuclei in water cooled samples, Omega phase and Omega phase coexist in air cooled samples, and omega and B2 phase are mixed in cold samples. The ordered Omega phase in high Nb-TiAl alloy It's hard to avoid.
3, the effect of heat treatment on the ordered Omega phase transformation is studied. The results show that the phase of the Nb segregation is substantially precipitated at the medium temperature (850 degrees C). The phase transition between the phase transition and the phase transition is smooth. The phase transition mechanism of the phase transition between the phase transition and the phase transition is clarified, and there are only two potential relations between the two phases, which are calculated by the "side edge" method. Among them, [1120] alpha 2//[0001] Omega o; (0002) a2// (1120) Omega o is more stable, consistent with TEM observation. High temperature (950 degrees) can make the ordered Omega o phase disappear rapidly at short time.
4, the effect of alloying elements on the ordered Omega phase is studied. The results show that the phase in Ti-45Al- (7-10) Nb alloy is a medium temperature equilibrium phase, and the addition of a small amount of alloying elements can effectively control the number and morphology of the ordered Omega phase. Mn can strongly inhibit the formation of ordered Omega phase; W, Cr has a weak inhibition effect; Ni strongly promotes ordered Omega phase. Alloy elements control their nucleation and growth by changing the precipitation temperature of ordered Omega phase.
5, the influence of the mechanical properties of the ordered Omega relative high Nb-TiAl alloy was studied. The results showed that a small amount of ordered Omega has little influence on the mechanical properties of the alloy. In the high temperature deformation, the micrometer Omega is difficult to strengthen the alloy, and the ordered Omega phase with the nanometer size and dispersion can improve the strength of the alloy. This can be achieved through the medium temperature short time heat preservation. Now.
6, Ti-34Al-13Nb alloy is made to study the order of ordered Omega phase phase transition. The alloy is at Omega o+ alpha 2 phase and A2 phase precipitates directly from Omega O. phase. The interface between alpha 2 phase variants can be spontaneously adjusted to low energy state, showing a common interface or a similar twin interface.
7, the phase transition of B19 phase.B19 phase appears at the two interface in the transition of alpha 2 to omega o, the lattice constant is a=0.464nm, b=0.290nm, c=0.510nm. HRTEM can be observed directly as the transition phase of the alpha 2 phase to the Y phase transition, and the crystallization temperature of the.B19 phase is at 650 C -750, while the high temperature short time heat preservation is at the same time as the synchrotron radiation report. It can vanish. The fast cooling of high Nb-TiAl alloy obtains the alpha 2 and gets along with the nonequilibrium state.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG146.416

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本文編號(hào)：1822369