本文關(guān)鍵詞： 激光熔覆 鈷基合金 鈦合金 數(shù)值模擬 顯微組織　出處：《大連理工大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：隨著我國(guó)航空航天事業(yè)的發(fā)展,鈦及鈦合金因其密度小、比強(qiáng)度高等優(yōu)點(diǎn)得到了廣泛應(yīng)用,但硬度低、耐磨性差等自身缺陷又嚴(yán)重限制了鈦合金的應(yīng)用領(lǐng)域。近年來,材料表面改性領(lǐng)域研究的熱點(diǎn)之一——激光熔覆技術(shù),可以為改善鈦合金表面缺陷提供極具發(fā)展前景的途徑。利用激光熔覆技術(shù)可在鈦合金表面熔覆一層高硬度、耐磨損的復(fù)合涂層,在保證基體良好性能不變的同時(shí)有效改善其表面缺陷。在激光熔覆過程中,尺寸很小的熔池內(nèi)存在極其復(fù)雜且反應(yīng)迅速的傳熱現(xiàn)象和化學(xué)變化,這直接影響材料成形熔覆層的質(zhì)量和力學(xué)性能,因此對(duì)熔池內(nèi)溫度場(chǎng)的控制顯得尤為重要。利用計(jì)算機(jī)軟件對(duì)熔池內(nèi)溫度場(chǎng)進(jìn)行數(shù)值模擬,用以指導(dǎo)熔覆工藝參數(shù)的選擇及涂層質(zhì)量缺陷的預(yù)測(cè),從而達(dá)到改善熔覆層質(zhì)量的目的,這在實(shí)際應(yīng)用中具有重要的意義。本文利用激光熔覆技術(shù)在TC4鈦合金上制備了鈷基復(fù)合涂層。首先利用ANSYS有限元軟件對(duì)激光熔覆過程中熔池內(nèi)溫度場(chǎng)分布情況進(jìn)行了研究,并對(duì)激光功率參數(shù)進(jìn)行了優(yōu)化選擇。然后利用優(yōu)化的工藝參數(shù)進(jìn)行激光熔覆實(shí)驗(yàn),熔覆材料有兩種,純KF-Co50鈷基自熔性粉末和摻雜10%Zr02的混合粉末,并對(duì)兩組試樣熔覆層的顯微組織形貌和力學(xué)性能進(jìn)行了分析。具體研究?jī)?nèi)容如下：利用ANSYS有限元軟件建立了預(yù)置式激光熔覆幾何模型,并利用參數(shù)化設(shè)計(jì)語言APDL實(shí)現(xiàn)了移動(dòng)激光熱源的施加。溫度場(chǎng)模擬結(jié)果表明,激光熔覆熔池呈橢球形,熔池內(nèi)溫度等溫線呈勺狀,并且光斑前沿溫度梯度大(等溫線密集),而光斑后的熔覆層溫度梯度小(等溫線稀疏)。不同激光輸出功率下熔池內(nèi)溫度場(chǎng)分布的研究結(jié)果表明,隨著激光功率的增大,熔池內(nèi)最高溫度也逐漸增大,熔深增加,為保證熔覆層較小的稀釋率,激光功率選擇在1000W—1100W之間比較合適。利用Laserline LDF 4000-100型號(hào)半導(dǎo)體激光器在TC4合金上進(jìn)行預(yù)置式激光熔覆實(shí)驗(yàn),實(shí)驗(yàn)參數(shù)為：激光輸出功率P=1000W,掃描速度V=5mm/s,激光光斑直徑D=3mm。隨后利用XRD、EPMA、SEM等實(shí)驗(yàn)設(shè)備對(duì)熔覆層進(jìn)行形貌及相組成分析。分析結(jié)果表明,A1和A2(添加10%部分穩(wěn)定Zr02)兩組試樣的熔覆層物相大體相同,主要是在7-Co和少量β-Ti固溶體上分布著長(zhǎng)條或塊狀的TiB2和WB,原位生成的呈顆粒狀的TiC,以及CoTi、Cr23C6、CrB硬質(zhì)增強(qiáng)相等,A2試樣整個(gè)熔覆層內(nèi)彌散分布著大量細(xì)小的白色Zr02顆粒。采用型號(hào)為DHV-1000的維氏硬度計(jì)測(cè)量熔覆層的顯微硬度值。熔覆層橫截面顯微硬度分布曲線表明,鈷基復(fù)合涂層的顯微硬度值與鈦合金基體相比得到顯著提高,約為基體硬度的3倍,顯微硬度值由熔覆層表面至基體呈梯度平緩下降趨勢(shì)。橫向?qū)Ρ葍山M試樣的顯微硬度分布曲線可知,陶瓷顆粒氧化鋯的添加并沒有顯著提高熔覆層的硬度,主要是為了減少熔覆層內(nèi)裂紋的產(chǎn)生及擴(kuò)展,提高熔覆層的強(qiáng)度和韌性。
[Abstract]:With the development of aerospace industry in China, titanium and titanium alloys have been widely used because of their low density and high specific strength. However, their own defects, such as low hardness and poor wear resistance, have seriously restricted the application fields of titanium alloys. Laser cladding technology, one of the hot research topics in the field of material surface modification, can provide a promising way to improve the surface defects of titanium alloy. Laser cladding technology can be used to cladding a layer of high hardness on titanium alloy surface. The wear-resistant composite coating can effectively improve the surface defects while keeping the good performance of the substrate. In the laser cladding process, the heat transfer phenomena and chemical changes are extremely complex and react rapidly in the very small melting pool. This directly affects the quality and mechanical properties of the cladding layer, so it is very important to control the temperature field in the molten pool. It can be used to guide the selection of cladding process parameters and predict the quality defects of the coating, so as to improve the quality of the cladding layer. This is of great significance in practical application. In this paper, cobalt based composite coatings were prepared on TC4 titanium alloy by laser cladding technique. Firstly, the distribution of temperature field in the molten pool during laser cladding was studied by ANSYS finite element software. The laser power parameters were optimized, and the laser cladding experiments were carried out using the optimized process parameters. There were two kinds of cladding materials, pure KF-Co50 cobalt-based self-fluxing powder and mixed powder doped with 10Zr02. The microstructure and mechanical properties of the cladding layer of two groups of specimens are analyzed. The main contents are as follows: a prefabricated laser cladding geometry model is established by using ANSYS finite element software. The temperature field simulation results show that the laser cladding pool is ellipsoid, and the temperature isotherm in the molten pool is spoonlike. And the temperature gradient at the front of the spot is large (the isotherm is dense, but the temperature gradient of the cladding layer behind the spot is small (the isotherm is sparse). The results of the study on the temperature field distribution in the molten pool with different laser output power show that, with the increase of the laser power, The maximum temperature in the molten pool also increased gradually, and the penetration increased. In order to ensure the lower dilution rate of the cladding layer, the laser power was chosen in the range of 1000W-1100W. A preset laser cladding experiment was carried out on the TC4 alloy by using the Laserline LDF 4000-100 semiconductor laser. The experimental parameters are as follows: laser output power PQ 1000W, scanning speed V = 5mm / s, laser spot diameter DX 3mm. then the morphology and phase composition of the cladding layer are analyzed by means of XRDX EPMA-SEM. The results show that there are two groups of samples, I. e. A1 and A _ 2 (adding 10% partially stabilized Zr02). The cladding material of the sample is roughly the same. TiB2 and WB were mainly distributed on 7-Co and a small amount of 尾 -Ti solid solution, and in situ formed granular tic, and CoTiC23C6CrB hard reinforced A2-samples distributed a large number of fine white Zr02 particles in the whole cladding layer. The microhardness of the cladding layer is measured by Vickers hardness meter of model DHV-1000. The microhardness distribution curve of the cross section of the cladding layer shows that, The microhardness value of cobalt-based composite coating was significantly higher than that of titanium alloy substrate, which was about 3 times of that of the substrate. From the surface of the cladding layer to the substrate, the microhardness value decreased gradually. Comparing the microhardness distribution curves of the two groups of samples, it can be seen that the addition of ceramic particle zirconia does not significantly improve the hardness of the cladding layer. The main purpose is to reduce the generation and propagation of cracks in the cladding and to improve the strength and toughness of the cladding.
【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG174.4

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本文編號(hào)：1552056