【摘要】：Ti-Al基合金可在較高的溫度下工作,且具有密度小、抗氧化、抗疲勞等性能。枝晶的形成對Ti-Al合金性能有很大影響,控制枝晶形貌對改善合金性能有著重要意義。枝晶凝固過程中受大量參數(shù)和復雜的邊界條件影響,實際實驗成本較高,使用計算機模擬可有效降低成本。本文首先對相場方法的發(fā)展及相關理論進行了論述。其次,以熵增加原理和熱力學定律為基礎,引入各項異性,構造了包括描述相場有序參數(shù)的方程,建立二元合金相場模型。再次,編寫數(shù)值模擬程序,利用建立好的程序模型對Ti-Al二元合金的枝晶生長進行模擬。最后,研究了均勻溫度場條件下各項異性系數(shù)、界面動力學系數(shù)以及界面能對枝晶的形貌和尖端生長速度的影響,初步研究了非均勻溫度場條件下枝晶的生長情況。得到如下結論:1.各向異性強度對枝晶形成的影響主要體現(xiàn)在枝晶的形貌及生長速度上,在各向異性強度系數(shù)較小時枝晶不明顯,當各向異性強度增大時枝晶也隨之變成較為明顯的樹枝形態(tài),并產(chǎn)生二次支臂,同時各向異性強度的增大還會加快枝晶的生長速度。2.界面能對枝晶形成的影響主要體現(xiàn)在枝晶的二次支臂上,當界面能較小時枝晶的形態(tài)無明顯變化,隨著界面能的增大,枝晶生長速度也加快,同時二次支臂的數(shù)量增多。3.各向異性強度系數(shù)對枝晶的影響同樣體現(xiàn)在二次支臂上,界面動力學系數(shù)增大枝晶的生長速度也增大,隨著運行時間的增大,枝晶受各項異性強度系數(shù)的影響也更為顯著。4.非均勻溫度場條件下,隨著溫度梯度的增大枝晶二次支臂的生長呈現(xiàn)明顯趨勢。
[Abstract]:Ti-Al-based alloy can work at high temperature and has low density, oxidation resistance, fatigue resistance and other properties. Dendrite formation has great influence on the properties of Ti-Al alloys, and controlling the dendrite morphology is of great significance to improve the properties of the alloys. The dendrite solidification process is affected by a large number of parameters and complex boundary conditions, and the actual experimental cost is high. Computer simulation can effectively reduce the cost. In this paper, the development of phase field method and related theories are discussed. Secondly, based on the principle of entropy increase and the law of thermodynamics, the equation including describing the ordered parameters of phase field is constructed, and the phase field model of binary alloy is established. Thirdly, a numerical simulation program is developed to simulate the dendritic growth of Ti-Al binary alloy. Finally, the effects of heterogeneity coefficient, interfacial kinetic coefficient and interfacial energy on the morphology and tip growth rate of dendrite under uniform temperature field were studied. The conclusions are as follows: 1. The effect of anisotropic strength on dendritic formation is mainly reflected in the morphology and growth rate of dendrite. When the anisotropic strength coefficient is small, the dendrite becomes a more obvious dendritic shape when the anisotropic strength increases. The secondary arm is produced, and the growth rate of dendrite is accelerated with the increase of anisotropic strength. The effect of interfacial energy on dendritic formation is mainly reflected on the secondary branch arm of dendrite. When the interfacial energy is small, the morphology of dendrite has no obvious change. With the increase of interfacial energy, the dendritic growth rate also accelerates, and the number of secondary branches increases. The effect of anisotropic strength coefficient on dendrite is also reflected on the secondary branch arm, and the growth rate of dendrite increases with the increase of interfacial kinetic coefficient. With the increase of running time, the dendrite is affected more obviously by the anisotropic strength coefficients. 4. Under the condition of inhomogeneous temperature field, the growth of secondary dendritic arms shows an obvious trend with the increase of temperature gradient.
【學位授予單位】：沈陽師范大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.23

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