【摘要】：TC4合金具有比重性好,比強度高以及抗氧化能力強等一系列優(yōu)點,因此被廣泛應用于航空航天、汽車制造及石油和化工等工業(yè)領(lǐng)域。激光快速成形技術(shù)可以控制熔池凝固過程中微觀組織的生長方向和形態(tài),有效提高鈦合金的力學性能和高溫性能。由于TC4鈦合金激光快速成形過程中,熔池凝固具有非平衡高溫瞬時性等特點,通過實驗探究觀察熔池微觀組織形態(tài)具有一定難度。本文運用宏觀與微觀相結(jié)合的方法,將有限元法與胞自動機法相耦合的Cellular Automata-Finite Element(CA-FE)模型對TC4鈦合金激光快速成形熔池凝固過程中的微觀組織進行動態(tài)模擬。FE法對熔池溫度場進行數(shù)值模擬,CA法模擬熔池凝固過程中的微觀組織�；跍囟葓鼋Y(jié)果進行插值計算,帶入微觀元胞中,通過編程實現(xiàn)TC4熔池凝固的動態(tài)過程。在運用CA法模擬微觀組織生長時,考慮晶粒形核的隨機性和生長的確定性。用連續(xù)形核模型描述熔池形核過程,建立晶粒生長的等軸晶和柱狀晶生長動力學模型。修正現(xiàn)有與元胞自動機模型相關(guān)的固相率和溶質(zhì)分配算法,對熔池在均勻溫度場下等軸晶生長以及柱狀晶生長進行模擬,模擬結(jié)果與晶粒生長動力學基本吻合,顯示晶粒生長指數(shù)接近理論值。將耦合的CA-FE模型帶入,模擬非均勻溫度場下熔池凝固過程中的晶粒生長。模擬結(jié)果顯示:在固液相界面有大量晶粒形核,且各晶粒間存在競爭生長,晶粒組織以粗大的柱狀晶為主。元胞網(wǎng)格越小,模擬晶粒形態(tài)越精確。與實驗條件下熔池金相組織進行對比,結(jié)果顯示熔池整體微觀組織模擬情況與實際熔池凝固組織形貌基本一致,表明數(shù)值模擬結(jié)果具有可信度。
[Abstract]:TC4 alloys have many advantages such as good specific gravity, high specific strength and strong oxidation resistance, so they are widely used in aerospace, automobile manufacturing, petroleum and chemical industry. Laser rapid prototyping technology can control the growth direction and morphology of microstructure during the solidification process of molten pool and effectively improve the mechanical and high temperature properties of titanium alloy. In the process of laser rapid prototyping of TC4 titanium alloy, the solidification of molten pool has the characteristics of non-equilibrium high temperature transient, so it is difficult to observe the microstructure of molten pool through experiments. In this paper, the method of combining macro and micro is used. The Cellular Automata-Finite Element (CA-FE) model coupled with the finite element method and the cellular automata method is used to simulate the microstructure during the solidification process of the laser rapid prototyping of TC4 titanium alloy. The temperature field of the molten pool is numerically simulated by FE method. The microstructure of molten pool during solidification was simulated by CA method. Based on the results of temperature field interpolation, the dynamic process of solidification in TC4 molten pool was realized by programming. In the simulation of microstructure growth by CA method, the randomness of grain nucleation and the certainty of growth are considered. The continuous nucleation model is used to describe the nucleation process of molten pool and the kinetic model of equiaxed and columnar grain growth is established. The solids rate and solute distribution algorithms related to cellular automata models are modified to simulate the equiaxed crystal growth and columnar crystal growth in the molten pool under uniform temperature field. The simulation results are in good agreement with the grain growth kinetics. The grain growth index is close to the theoretical value. The coupled CA-FE model was introduced to simulate the grain growth during the solidification process of the molten pool under the inhomogeneous temperature field. The simulation results show that there are a large number of nucleation grains at the solid-liquid interface, and there are competing growth among the grains, and the grain structure is dominated by coarse columnar crystals. The smaller the cell mesh is, the more accurate the simulated grain morphology is. Compared with the experimental results, the results show that the simulation of the whole microstructure of the molten pool is basically consistent with the morphology of the solidified microstructure of the actual molten pool, which indicates that the numerical simulation results are reliable.
【學位授予單位】：沈陽航空航天大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.23;TG665

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