本文選題：高鈮TiAl合金 + 真空磁懸浮熔煉　； 參考：《北京科技大學(xué)》2015年博士論文

【摘要】：TiAl合金的潛在應(yīng)用領(lǐng)域主要為高溫和循環(huán)載荷下的結(jié)構(gòu)部件,比如航空發(fā)動(dòng)機(jī)低壓渦輪葉片、汽車增壓渦輪器等。隨著Ti-48Al-2Cr-2Nb(除特殊標(biāo)注外,全文都為原子分?jǐn)?shù))合金在美國波音787客機(jī)GenX發(fā)動(dòng)機(jī)的應(yīng)用,國內(nèi)外對(duì)于TiAl合金的研究和應(yīng)用又產(chǎn)生了新一輪的熱潮。無論是開發(fā)新型的鑄造TiAl合金還是變形TiAl合金,提高合金的潔凈度都有著重要意義。因此,本文的主要研究?jī)?nèi)容針對(duì)高潔凈度熔煉高鈮TiAl合金的真空磁懸浮熔煉過程進(jìn)行了系統(tǒng)的研究,包括制備工藝、成分-組織均勻性和力學(xué)性能；還借助于真空磁懸浮熔煉的電磁攪拌作用以攪拌-鑄造法制備了TiAl基納米復(fù)合材料,并研究了納米顆粒對(duì)TiAl合金組織和力學(xué)性能的影響。本文的主要結(jié)論和創(chuàng)新點(diǎn)如下：(1)在真空磁懸浮熔煉高鈮TiAl合金時(shí),不當(dāng)?shù)牟剂戏绞綍?huì)導(dǎo)致原料搭橋和熱爆損失,影響熔煉過程以及合金成分的準(zhǔn)確性。通過坩堝內(nèi)Al上Ti下的布料方式可以有效避免原料搭橋的產(chǎn)生。熱爆的產(chǎn)生是由于氣體和Al蒸氣的壓力大于原料靜壓力而導(dǎo)致的,通過減少坩堝內(nèi)海綿鈦的質(zhì)量和提高爐內(nèi)壓力可以有效抑制熱爆的產(chǎn)生。(2)通過優(yōu)化的真空磁懸浮兩次熔煉工藝,高鈮TiAl合金鑄錠的成分組織均勻。在第二次熔煉中采取了抽真空-熔化-充氬氣-熔煉的工藝制度使合金含O量降低到300ppm。(3)在真空熔煉高鈮TiAl合金時(shí),合金的燒損主要來源于海綿鈦的飛濺損失。盡管Al具有較高的蒸氣壓,但足通過充Ar使?fàn)t內(nèi)達(dá)到500Pa以上可以有效降低Al的揮發(fā)損失。(4)通過對(duì)錠型的優(yōu)化設(shè)計(jì),促進(jìn)了高鈮TiAl合金在錠型內(nèi)的順序凝吲。鑄錠中集中縮孔分布在冒口處,氣縮孔基本消除,有效地減小了分散縮孔的體積。通過鑄錠溫度溫度場(chǎng)的模擬設(shè)計(jì)出最佳的錠型尺寸為：錠型壁厚20mm、錠身斜度4.2。、錠身高徑比3.3、冒口斜度30。。(5)經(jīng)過真空懸浮熔煉并澆注的高鈮TiAl合金鑄錠,其組織為均勻的等軸近片層組織。降低Al含量和添加B元素都使片層團(tuán)尺寸減小。雖然B細(xì)化作用最為顯著,然而大量硼化物的析出損害了材料的室溫拉伸力學(xué)性能。(6)當(dāng)高鈮TiAl-B合金在α單相區(qū)進(jìn)行熱處理時(shí),鑄錠中出現(xiàn)了粗晶環(huán)。粗品環(huán)的形成與B的含量(0.5%)和鑄錠凝固時(shí)的冷卻速率有關(guān)。降低B含量和提高鑄錠的冷卻速率都會(huì)使粗品環(huán)的寬度增大。粗晶環(huán)的形成是因?yàn)锽含量大于某一臨界值時(shí)凝固前沿B導(dǎo)致的成分過冷和溫度過冷共同作用使整個(gè)鑄錠硼化物的分布密度不同,使得α單相區(qū)熱處理時(shí)硼化物對(duì)α晶粒的釘扎作用不同。并且高溫時(shí)彎曲板條狀的硼化物轉(zhuǎn)變?yōu)獒槧畹呐鸹?這種轉(zhuǎn)變也削弱了對(duì)α晶粒的釘扎作用,這兩種硼化物都富集了Nb元素并且都具有相同的B27正交結(jié)構(gòu)。(7)通過攪拌-鑄造法成功制備了TiAl基納米復(fù)合材料,試驗(yàn)的納米陶瓷顆粒有α-Al2O3、γ-Al2O3、TiO2、Y2O3、TiC,納米金屬顆粒有W和Mo。其中α-Al2O3、TiO2、TiC和W納米顆粒在經(jīng)過電磁攪拌后都可以在TiAl基體中實(shí)現(xiàn)均勻分散的分布,根據(jù)其分布判斷出這幾種顆粒的潤(rùn)濕性大小為：WTiO2TiCα-Al203。(8)納米顆粒在TiAl合金凝固中起到了異質(zhì)核心的作用,因此細(xì)化了初生β枝晶,然而納米氧化物陶瓷顆粒卻使片層團(tuán)組織粗化,其主要原因是O的溶解穩(wěn)定了高溫α相,促進(jìn)了α晶粒的快速生長(zhǎng),進(jìn)而轉(zhuǎn)變?yōu)榇执蟮钠瑢訄F(tuán)。當(dāng)納米TiC的添加量大于1wt.%時(shí),基體中有Ti2AlC的析出并細(xì)化了片層團(tuán)組織,同時(shí)C的溶解減小了7和a2片層間距。(9)納米顆粒的添加使TiAl合金的室溫和高溫維氏硬度都有一定提高,硬度提高最顯著的是納米TiC和納米W,然而TiC卻損害了材料的室溫?cái)嗔秧g性,只有納米W顆粒的添加即提高了基體的室溫和高溫硬度又提高了基體的斷裂韌性,達(dá)到40MPa/m1/2。
[Abstract]:The potential applications of TiAl alloys are the structural components under high temperature and cyclic loading, such as aero engine low pressure turbine blades, automotive turbocharger, and so on. The application of Ti-48Al-2Cr-2Nb (the full text for atomic fraction) alloy to the GenX engine of the Boeing 787 aircraft in the United States and the study of TiAl alloys at home and abroad. There is a new round of upsurge of application and application. It is of great significance to develop new cast TiAl alloy or deformed TiAl alloy to improve the cleanliness of the alloy. Therefore, the main research content of this paper is to systematically study the vacuum magnetic levitation process of Gao Jie's pure melting high niobium TiAl alloy, including the preparation process, The composition homogeneity and mechanical properties of TiAl based nanocomposites were also prepared by the stirring casting process in vacuum magnetic suspension melting. The effects of nanoparticles on the microstructure and mechanical properties of TiAl alloys were studied. The main conclusions and innovations of this paper were as follows: (1) high niobium TiAl in vacuum maglev smelting. In gold, improper material will lead to bridge and thermal explosion loss, influence melting process and the accuracy of alloy composition. Through the material under Al Ti in the crucible, the production of bridge can be avoided effectively. The thermal explosion is caused by the pressure of gas and Al steam greater than the static pressure of the raw material, by reducing the crucible inside the crucible. The quality of the titanium sponge and the increase of the pressure in the furnace can effectively suppress the thermal explosion. (2) the composition of the high niobium TiAl alloy ingot is homogeneous through the optimized two smelting process of vacuum magnetic levitation. In the second smelting process, the vacuum melting, argon filling and melting process system has been adopted to reduce the content of O to 300ppm. (3) in vacuum smelting. When high niobium TiAl alloy, the burning loss of the alloy is mainly due to the spatter loss of titanium sponge. Although Al has high vapor pressure, it can effectively reduce the volatilization loss of Al by filling up to 500Pa in the furnace by filling Ar. (4) through the optimum design of the ingot type, the sequential indation in the ingot type of high niobium TiAl gold is promoted. The concentrated shrinkage of the ingot is concentrated. In the riser, the air shrinkage cavity is basically eliminated and the volume of the dispersed shrinkage cavity is effectively reduced. The optimum ingot size is designed by the simulation of the temperature and temperature field of ingot. The ingot thickness 20mm, the ingot body slope 4.2., the ingot height ratio 3.3, the riser slope 30.. (5) through the vacuum suspension melting and pouring of the high niobium alloy ingot are uniform. The reduction of Al content and the addition of B elements reduce the size of the lamellar mass. Although the B refinement is the most significant, the precipitation of a large number of boride damages the tensile mechanical properties of the material at room temperature. (6) when the high niobium TiAl-B alloy has been heat-treated in the alpha single-phase region, the coarse ring is formed in the ingot. The formation of the coarse ring and B The content (0.5%) is related to the cooling rate of the ingot solidification. Reducing the B content and increasing the cooling rate of the ingot will increase the width of the ring. The formation of the roughing ring is due to the combination of the component overcooling and the temperature overcooling caused by the B content greater than a critical value in the solidification front B, which makes the distribution density of the boride in the whole ingot different. The boride has different pinning effects on the alpha grain during the heat treatment of the alpha single phase region. And at high temperature, the boride of the strip shape of the curved plate turns into a needle like boride, which also weakens the pinning effect on the alpha grain. These two borates have enriched the Nb elements and all have the same B27 orthogonal structure. (7) success by the agitation casting method. TiAl based nanocomposites have been prepared. The tested nano ceramic particles are alpha -Al2O3, gamma -Al2O3, TiO2, Y2O3, TiC. The nano particles have W and Mo. in which the alpha -Al2O3, TiO2, TiC and W nanoparticles can be distributed uniformly in the matrix after electromagnetic stirring, and the wettability of these particles is judged according to their distribution. WTiO2TiC alpha -Al203. (8) nanoparticles play the role of heterogeneous core in the solidification of TiAl alloy, thus refining the primary beta dendrites. However, the nano oxide ceramic particles make the lamellar tissue coarser. The main reason is that the dissolution of O has stabilized the high temperature alpha phase and promoted the rapid growth of the alpha grain, and then changed into a coarse lamellar mass. When the addition of nano TiC is greater than 1wt.%, the matrix is precipitated by Ti2AlC and the lamellar tissue is refined. At the same time, the dissolution of C is reduced by 7 and A2 layer spacing. (9) the addition of nano particles makes the hardness of the TiAl alloy at room temperature and high temperature Vivtorinox to a certain extent, and the most notable is the nano TiC and nano W. However, TiC has damaged the material. At room temperature fracture toughness, only nano W particles increased the hardness of the substrate at room temperature and high temperature, and increased the fracture toughness of the matrix, reaching 40MPa/m1/2.
【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)】：TG146.2;TB33

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