本文選題：TC4合金粉末 + 激光熔覆沉積��； 參考：《石家莊鐵道大學》2017年碩士論文

【摘要】：鈦合金高的比強度、優(yōu)異的耐腐蝕性、良好的耐熱性使其廣泛應(yīng)用于航空、航天、船舶等領(lǐng)域。但是,鈦合金高溫下會與氧氣劇烈反應(yīng),需要為激光熔覆沉積成形過程提供惰性氣體保護。本文設(shè)計了一套適用于TC4合金粉末激光熔覆成形的真空系統(tǒng),基于此系統(tǒng)采用數(shù)值模擬與實驗相結(jié)合的方法研究了基板強制水冷對成形件組織的影響。首先,設(shè)計了一種低真空成形環(huán)境并完成系統(tǒng)搭建,開發(fā)了一款LCD成形軟件,實現(xiàn)三維平臺的自動化控制,為TC4合金粉末的激光熔覆沉積成形提供一套成形平臺。然后,分別采用正交實驗法、單因素變量成形實驗法對TC4合金粉末進行了激光單道、多道成形工藝實驗研究,得到優(yōu)化的工藝參數(shù)為:激光功率600 W,掃描速度5 mm/s,送粉速率4.3 g/min,搭接率為30%。利用最優(yōu)的工藝參數(shù),進行實體零件成形,并對其內(nèi)部氧含量及拉伸性能進行了檢測,檢測結(jié)果為:真空室內(nèi)成形件的內(nèi)部氧含量比惰性氣體保護下的成形件下降了48%;隨著成形件氧含量的增加,抗拉強度和屈服強度得到提高,而延伸率降低了59.3%;不同氣氛保護下的成形件抗拉強度相差不大,但均高出基體(910 MPa)35%左右,屈服強度均高出基體(850MPa)38%左右。說明實驗用真空系統(tǒng)對成形件內(nèi)部氧含量控制有效。最后,使用ANSYS有限元軟件模擬了基板不同對流換熱系數(shù)下TC4合金激光熔覆沉積過程中溫度場變化。得出:從熔池底部到熔池頂部,溫度梯度不斷降低;對基板設(shè)置高的對流換熱系數(shù)會增大熔池凝固時的溫度梯度,熔池底部尤為顯著,溫度梯度方向有向平行于沉積方向轉(zhuǎn)變的趨勢,成形件內(nèi)部的冷卻速率也會增大。利用優(yōu)化的工藝參數(shù)在真空系統(tǒng)中進行成形實驗,研究基板強制水冷對成形件組織的影響。得出:TC4激光熔覆沉積試樣組織為貫穿整個試樣呈外延生長的粗大柱狀晶。但對基板施加強制水冷后,成形件中沿垂直基板方向的β柱狀晶能獲得更大競爭優(yōu)勢而持續(xù)生長,因受到層間單道熔覆的影響,組織由魏氏組織變?yōu)榫W(wǎng)籃狀組織。實驗結(jié)果與模擬結(jié)果較為接近,為后續(xù)微觀組織“控性”研究打下了良好的基礎(chǔ)。
[Abstract]:Titanium alloy has high specific strength, excellent corrosion resistance and good heat resistance, which makes it widely used in aviation, aerospace, ship and other fields. However, titanium alloys react strongly with oxygen at high temperature, so it is necessary to provide inert gas protection for laser cladding deposition. A vacuum system suitable for laser cladding forming of TC4 alloy powder is designed in this paper. Based on this system, the effect of forced water cooling on the microstructure of forming parts is studied by means of numerical simulation and experiment. Firstly, a low vacuum forming environment is designed and the system is built. A LCD forming software is developed to realize the automatic control of 3D platform, which provides a forming platform for laser cladding deposition of TC4 alloy powder. Then, the single pass and multi-pass laser forming experiments of TC4 alloy powder were carried out by orthogonal experiment and single factor variable forming method, respectively. The optimized technological parameters are as follows: laser power 600 W, scanning speed 5 mm / s, powder feeding rate 4.3 g / min, lap ratio 30g / min. The optimum process parameters are used to form the solid parts, and the oxygen content and tensile properties of the parts are tested. The results are as follows: the oxygen content of the forming parts in the vacuum chamber is decreased by 48% than that of the formed parts under the protection of inert gas, and the tensile strength and yield strength are increased with the increase of the oxygen content of the formed parts. The tensile strength of the formed parts under different atmosphere protection is similar, but the tensile strength is about 35% higher than that of the matrix (910 MPA), and the yield strength is about 38% higher than that of the matrix. The results show that the vacuum system used in the experiment is effective in controlling the oxygen content in the forming parts. Finally, the variation of temperature field during laser cladding deposition of TC4 alloy under different convection heat transfer coefficients of substrate was simulated by ANSYS finite element software. From the bottom of the molten pool to the top of the pool, the temperature gradient decreases continuously, and the high convection heat transfer coefficient of the substrate increases the temperature gradient of the molten pool during solidification, especially at the bottom of the molten pool. The temperature gradient direction changes to the direction parallel to the deposition direction, and the cooling rate increases. The effect of forced water cooling on the microstructure of the formed parts was studied by using the optimized process parameters in the vacuum system. It is found that the microstructure of the sample deposited by the laser cladding of the W TC4 is a coarse columnar crystal with epitaxial growth through the whole sample. However, the 尾 columnar crystals along the vertical direction of the substrate can gain greater competitive advantage and continue to grow after forced water cooling on the substrate. Due to the influence of interlaminar single pass cladding, the microstructure changes from Weiss structure to netted structure. The experimental results are close to those of the simulation results, which lays a good foundation for the further study on the "controllability" of microstructures.
【學位授予單位】：石家莊鐵道大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG665;TG146.23

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