本文選題：冷坩堝 + 定向凝固�。� 參考：《哈爾濱工業(yè)大學》2017年碩士論文

【摘要】：Ti Al基合金因具有優(yōu)良的高溫性能和優(yōu)異的抗氧化性能,在過去的20年里,Ti Al基合金在航空航天領域的應用引起了非常廣泛的關注,因此對推動高溫結構材料的發(fā)展起到了極大的作用,然而Ti Al基合金的室溫塑性與斷裂韌性不足,是限制擴大其實際應用的主要障礙。本課題首先采用水冷銅坩堝真空感應熔煉爐(ISM)制備Ti45Al2Nb2Mn母合金錠,再利用電磁冷坩堝對Ti Al合金進行定向凝固實驗制備出表面質量和宏觀定向組織良好的Ti45Al2Nb2Mn合金鑄錠。對Ti-45Al-2Nb-2Mn合金經(jīng)冷坩堝定向凝固,通過控制不同的抽拉速度(凝固速率)制備出了具有良好定向效果的鑄錠;原始鑄態(tài)組織中有縮孔產(chǎn)生,而定向凝固后缺陷消失。合金在電磁冷坩堝定向凝固過程中,固液界面形貌隨著凝固速率的提高,呈枝狀-胞枝狀-胞狀變化,隨抽拉速度的增加,定向凝固區(qū)的晶粒減小。Nb屬于β穩(wěn)定元素,可以擴大β凝固區(qū)間,因此反應過程中β相始終為初生相,由于是二維照片,當先析出相為β時,部分α2/γ片層取向與生長方向并不嚴格呈45°或平行關系,進行XRD分析以及能譜分析發(fā)現(xiàn),其組織主要是α2+γ的雙相全片層組織,少量的B2相。相比于鑄態(tài)組織,定向凝固組織力學性能均得到明顯提高。Ti Al基合金在定向凝固后其壓縮強度最高達到1654MPa,而原始鑄態(tài)的合金壓縮強度僅僅達到899Mpa。鑄態(tài)合金在同等條件下的峰值應力僅為329MPa左右,而定向凝固后的合金峰值應力最高達到了479MPa左右,拉伸強度隨著抽拉速度增加而提高。合金的柱狀晶全片層組織斷裂韌性均超過20MPa·m1/2。定向凝固條件下的合金顯微硬度較原始鑄態(tài)的提高了40%-70%。壓縮斷口斷裂方式主要以撕裂斷裂為主,同時混有穿層斷裂;拉伸斷口出現(xiàn)了階梯狀斷裂形貌以及P型斷口形貌;斷裂韌性斷口形貌均為典型的脆性解理斷裂。
[Abstract]:Due to its excellent high temperature properties and excellent oxidation resistance, TiAl-based alloys have been widely used in aerospace industry in the past 20 years. Therefore, it plays an important role in promoting the development of high temperature structural materials. However, the lack of room temperature ductility and fracture toughness of Ti-Al-base alloys is the main obstacle to the expansion of their practical application. In this paper, Ti45Al2Nb2Mn master alloy ingot was prepared by water cooled copper crucible vacuum induction melting furnace (ISM), and Ti45Al2Nb2Mn alloy ingot with good surface quality and macroscopical directional structure was prepared by directional solidification experiment with electromagnetic cold crucible. Through directional solidification of Ti-45Al-2Nb-2Mn alloy by cold crucible, the ingot with good directional effect was prepared by controlling the different drawing speed (solidification rate), and the shrinkage holes were produced in the original cast structure, but the defects disappeared after directional solidification. During the directional solidification of the alloy in the electromagnetic cold crucible, the morphology of the solid-liquid interface changes as the solidification rate increases, and with the increase of the drawing speed, the grain size in the directional solidification zone decreases. NB is a 尾 stable element. The 尾 phase is always a primary phase in the reaction process. When the precipitated phase is 尾, the orientation of some 偽 2 / 緯 lamellae is not strictly 45 擄or parallel to the growth direction when the precipitated phase is 尾. The results of XRD analysis and energy spectrum analysis showed that the structure of 偽 2 緯 was mainly a two-phase full-lamellar structure with a small amount of B2 phase. Compared with the as-cast microstructure, the mechanical properties of the directionally solidified alloy were obviously improved. The compressive strength of the as-cast alloy reached 1654MPa after directional solidification, but the compressive strength of the as-cast alloy was only 899Mpa. The peak stress of the as-cast alloy is only about 329MPa under the same conditions, but the peak stress of the alloy after directional solidification reaches about 479MPa, and the tensile strength increases with the increase of the pulling speed. The fracture toughness of the columnar crystal layer of the alloy is higher than that of 20MPa m 1 / 2. The microhardness of the alloy under directional solidification is 40-70 higher than that of the as-cast alloy. The fracture mode of compression fracture is mainly tear fracture and mixed with penetrating layer fracture; the tensile fracture surface has ladder and P fracture morphology; the fracture toughness fracture surface morphology is typical brittle cleavage fracture.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.23;TG292
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本文編號：1950590