本文選題：定向凝固 + Fe-Al金屬間化合物��； 參考：《西安建筑科技大學(xué)》2017年碩士論文

【摘要】：金屬間化合物具有低密度、高熔點、高強度以及優(yōu)異的抗氧化腐蝕等特點,是一類極具潛力的新型中高溫結(jié)構(gòu)材料。金屬間化合物既優(yōu)于高溫合金的耐溫性,又優(yōu)于陶瓷材料的韌性與可熱加工性,受到材料研究者的廣泛關(guān)注。在備受關(guān)注的金屬間化合物種類中,Fe-Al系金屬間化合物以其較小的密度、低廉的價格以及優(yōu)越的性能,使其一度成為中高溫結(jié)構(gòu)材料研究的熱點。本文采用亞快速定向凝固技術(shù),通過向Fe-Al金屬間化合物中添加微量的Ta元素,制備出Fe-Al-Ta共晶自生復(fù)合材料。借助先進的分析設(shè)備和測試儀器,在較大范圍的凝固速率內(nèi)深入分析亞快速定向凝固的工藝參數(shù)對相成分、固液兩相界面形態(tài)以及凝固組織生長特征等的影響。同時也探討了Fe-Al-Ta共晶自生復(fù)合材料凝固組織與力學(xué)性能的關(guān)系,分析了共晶合金的表面顯微硬度、室溫拉伸斷口、三點彎曲斷口以及強化機制。通過EDS和XRD分析,真空感應(yīng)熔煉態(tài)(鑄態(tài))和定向凝固不同凝固速率下的Fe-Al-Ta共晶自生復(fù)合材料均由基體相Fe(Ta,Al)和增強相Fe2Ta(Al)兩相組成。在不同凝固速率下Fe-Al-Ta共晶自生復(fù)合材料的穩(wěn)態(tài)生長區(qū)橫截面宏觀組織形貌逐漸細(xì)化,出現(xiàn)均勻到非均勻的轉(zhuǎn)變。結(jié)合穩(wěn)態(tài)生長區(qū)的微觀縱截面和橫截面得出,合金凝固組織形態(tài)呈現(xiàn)出由棒狀→球狀→亂序短棒狀的演化規(guī)律。且在凝固速率R為90μm/s到600μm/s的范圍內(nèi),合金的增強相體積分?jǐn)?shù)出現(xiàn)先減后增的變化,當(dāng)凝固速率為R=150μm/s,合金增強相體積分?jǐn)?shù)最小為36.11%。合金組織的片層(棒狀)間距逐漸減小,其關(guān)系符合λ=75.99R-0.79,基本滿足J-H理論模型。Fe-Al-Ta共晶自生復(fù)合材料的固液界面受凝固速率影響較小,主要是胞枝狀界面。但隨著凝固速率的增大,胞枝狀組織分枝出現(xiàn)變化,由規(guī)則的一次分枝到多分枝再到不規(guī)則的多分枝演變。在不凝固速率下,合金的表面硬度差距較大,且有逐漸增大的趨勢。在室溫拉伸試驗時,真空感應(yīng)熔煉態(tài)Fe-Al-Ta共晶合金和亞快速定向凝固下Fe-Al-Ta共晶合金均表現(xiàn)為脆性斷裂。定向凝固Fe-Al-Ta合金中大的Laves強化相體積分?jǐn)?shù)逐漸減小的層片(棒狀)間距以及較高的過冷度均有利于共晶合金室溫抗拉強度的提高,使得其最大抗拉強度遠(yuǎn)遠(yuǎn)高于鑄態(tài)Fe-Al-Ta共晶合金。由三點彎曲試驗曲線以及宏觀斷口形貌分析,Fe-Al-Ta共晶合金屬于解理斷裂。但在高倍顯微鏡下對試樣分析發(fā)現(xiàn),定向凝固條件下Fe-Al-Ta共晶合金的斷口有少部分韌窩出現(xiàn),為Fe-Al-Ta共晶復(fù)合材料室溫斷裂韌性提高做出了貢獻。
[Abstract]:Intermetallic compounds have the characteristics of low density, high melting point, high strength and excellent oxidation resistance. Intermetallics are better than superalloys in temperature resistance, toughness and heat processability of ceramic materials, and have been paid more attention by material researchers. Among the most concerned intermetallic compounds, Fe-Al intermetallics have become a hot topic for their low density, low price and superior properties. In this paper, Fe-Al-Ta eutectic in-situ composites were prepared by adding a small amount of Ta to Fe-Al intermetallic compounds by subrapid directional solidification technique. With the help of advanced analysis equipment and testing instruments, the effects of technological parameters of sub-rapid directional solidification on phase composition, solid-liquid two-phase interface morphology and solidification microstructure growth characteristics were analyzed in a wide range of solidification rates. The relationship between solidification microstructure and mechanical properties of Fe-Al-Ta eutectic in-situ composites was also discussed. The surface microhardness, tensile fracture at room temperature, three-point bending fracture and strengthening mechanism of eutectic alloy were analyzed. By means of EDS and XRD analysis, the Fe-Al-Ta eutectic in-situ composites in vacuum induction melting (as-cast) and directionally solidified Fe-Al-Ta eutectic composites at different solidification rates are composed of two phases, the matrix phase (Fe _ (10) Ta-Al) and the reinforced phase (Fe _ (2) Tao _ (Al). At different solidification rates, the microstructure of the stable growth zone of Fe-Al-Ta eutectic in-situ composites was gradually refined and changed from uniform to non-uniform. Combined with the microcosmic longitudinal section and cross section of the steady growth zone, it is found that the solidification microstructure of the alloy shows the evolution law of the short rod shape from the rod-shaped orbicular order. In the range of solidification rate R from 90 渭 m / s to 600 渭 m / s, the volume fraction of the reinforcing phase of the alloy decreases first and then increases. When the solidification rate is 150 渭 m / s, the minimum volume fraction of the reinforcing phase is 36.11. The lamellar (rod) spacing of the alloy structure decreases gradually, and the relationship accords with 位 _ (75.99R) -0.79, which basically meets the J-H theoretical model. The solid-liquid interface of Fe-Al-Ta eutectic in-situ composites is less affected by solidification rate, mainly the dendritic interface. However, with the increase of solidification rate, the branching of cellular dendritic tissue changes, from regular primary branching to multi-branching to irregular multi-branching. At the unsolidification rate, the surface hardness of the alloy has a large gap and tends to increase gradually. In the tensile test at room temperature, both the vacuum induction melting Fe-Al-Ta eutectic alloy and the sub-rapid directionally solidified Fe-Al-Ta eutectic alloy exhibit brittle fracture. The large volume fraction of Laves strengthened phase in directionally solidified Fe-Al-Ta alloy decreases the lamellar (rod) spacing and the higher undercooling degree is beneficial to the increase of the room temperature tensile strength of the eutectic alloy. The maximum tensile strength of Fe-Al-Ta eutectic alloy is much higher than that of as-cast Fe-Al-Ta eutectic alloy. The fracture of Fe-Al-Ta eutectic alloy belongs to cleavage fracture by means of three-point bending test curve and macroscopic fracture morphology. However, the fracture surface of Fe-Al-Ta eutectic alloy under unidirectional solidification condition has a few dimples, which contributes to the improvement of fracture toughness of Fe-Al-Ta eutectic composites at room temperature.
【學(xué)位授予單位】：西安建筑科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG21

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