【摘要】：目前的工業(yè)運(yùn)用中,經(jīng)熱處理后的45鋼存在著表面硬度低、耐磨性差、易氧化等不足而限制了它的進(jìn)一步廣泛應(yīng)用。通過(guò)采用高能激光束在被選定工件表面熔覆一層具有特殊性能的合金粉末,可以改善工件綜合性能,這種表面改性技術(shù)稱(chēng)為激光熔覆技術(shù)。因此,通過(guò)激光熔覆在45鋼表面制備出與基材成分接近、界面結(jié)合牢固、高硬耐磨且成本低廉的Fe-Cr-Si合金涂層便成為近年來(lái)材料科學(xué)和表面工程領(lǐng)域致力于研究的熱點(diǎn)。本實(shí)驗(yàn)在45鋼板材上進(jìn)行不同機(jī)械振動(dòng)參數(shù)輔助下,同步送粉法輸送激光熔覆鐵基自熔性粉末,獲得Fe-Cr-Si合金熔覆層。對(duì)比不同振動(dòng)參數(shù)下的實(shí)驗(yàn)試樣宏觀和微觀結(jié)構(gòu),研究分析不同機(jī)械振動(dòng)參數(shù)對(duì)熔覆層及結(jié)合界面性能差異。其中,通過(guò)OM分析涂層與基體材料的組織形貌,利用XRD、SEM等表征手段研究了熔覆層及熔覆層與基材間的結(jié)構(gòu)和顯微組織,同時(shí)借助EDS點(diǎn)掃描及線掃描手段,分析熔覆層與基材間相組成和元素分布,采用顯微硬度計(jì)測(cè)試研究了合金涂層中的顯微硬度分布,然后根據(jù)不同振動(dòng)參數(shù)下的熔覆層相貌特征確定激光熱源分布,進(jìn)行熔覆過(guò)程數(shù)值模擬分析。最后,針對(duì)不同振動(dòng)參數(shù)下結(jié)合界面處的元素分布規(guī)律,計(jì)算該元素的擴(kuò)散系數(shù)與濃度和距離的關(guān)系。結(jié)果表明：1、在合理的振動(dòng)參數(shù)范圍內(nèi),涂層可獲得良好的表面質(zhì)量,且熔覆層與基體的結(jié)合性能好,為冶金結(jié)合。但在機(jī)械振動(dòng)能量增加的情況下,涂層表面出現(xiàn)熔化瘤,且表面粗糙。2、機(jī)械振動(dòng)能量相近下,分別對(duì)振幅占優(yōu)和頻率占優(yōu)情況的激光熔覆過(guò)程進(jìn)行有限元模擬。結(jié)果表明,振幅占優(yōu)時(shí)激光熔池中心熱量更為集中,熔池熔深增加,熔寬減小,溫度梯度增加；頻率占優(yōu)時(shí)激光熔池產(chǎn)生均化現(xiàn)象,熔池熔深減小,熔寬增加。從不同振動(dòng)參數(shù)的熱循環(huán)曲線來(lái)看,振幅的作用是使溫度梯度增加,頻率的作用反之。根據(jù)冷卻后殘余應(yīng)力場(chǎng)分布圖和分布曲線可得：機(jī)械振動(dòng)對(duì)激光熔覆殘余應(yīng)力的分布位置影響較小,但振幅占優(yōu)和頻率占優(yōu)的激光熔覆試樣中,沿掃略方向殘余應(yīng)力壓應(yīng)力值有一定的減小,說(shuō)明機(jī)械振動(dòng)對(duì)激光熔覆殘余應(yīng)力有緩釋作用。3、Fe-Cr-Si合金粉末在激光熔覆過(guò)程中可形成以α-Fe或γ-Fe為基體的合金碳化物(Fe,Cr)7C3、(Fe, Cr)23C6和少量以Fe2B為代表的硼化物,這些碳化物和硼化物具有較高的強(qiáng)度和硬度。而根據(jù)機(jī)械振動(dòng)能量計(jì)算,可知振幅對(duì)激振能的變化影響比較明顯,頻率作用較小。4、激光熔覆微觀結(jié)構(gòu)中發(fā)現(xiàn),在熔覆層和基體間易形成2～3μm深色帶狀結(jié)構(gòu),為Cr、 Si等合金元素?cái)U(kuò)散速率不平衡導(dǎo)致的結(jié)果。本文測(cè)定界面處Fe-(Cr、Si)擴(kuò)散中Cr、Si元素濃度分布曲線并計(jì)算擴(kuò)散系數(shù),結(jié)果可得,機(jī)械振動(dòng)可使等濃度位置的擴(kuò)散系數(shù)下降,界面處Cr、Si元素?cái)U(kuò)散系數(shù)與溫度梯度和濃度有關(guān),且振動(dòng)參數(shù)中幅度對(duì)擴(kuò)散系數(shù)的影響大于頻率
[Abstract]:In the current industrial application, the low surface hardness, poor wear resistance and easy oxidation of 45 steel after heat treatment limit its further application. The comprehensive properties of the workpiece can be improved by cladding a layer of alloy powder with special properties on the surface of the selected workpiece by using a high energy laser beam. This surface modification technique is called laser cladding technology. Therefore, the preparation of Fe-Cr-Si alloy coating by laser cladding on the surface of 45 steel, which is close to the composition of substrate, strong interface bonding, high hardness and wear resistance, and low cost, has become the focus of research in material science and surface engineering field in recent years. In this experiment, the laser cladding iron-based self-fluxing powder was transferred by simultaneous powder feeding method under the aid of different mechanical vibration parameters on the 45 steel plate, and the Fe-Cr-Si alloy cladding layer was obtained. The macro-structure and microstructure of the experimental specimen under different vibration parameters were compared, and the difference of mechanical vibration parameters on the properties of cladding layer and bonding interface was studied and analyzed. The microstructure and morphology of the coating and the substrate were analyzed by OM, and the microstructure and microstructure of the cladding layer and substrate were studied by means of XRD,SEM. At the same time, by means of EDS point scanning and line scanning, the microstructure and microstructure of the cladding layer and the substrate were studied. The phase composition and element distribution between the cladding layer and the substrate are analyzed. The microhardness distribution in the alloy coating is studied by means of microhardness tester, and then the laser heat source distribution is determined according to the phase characteristics of the cladding layer under different vibration parameters. Numerical simulation analysis of cladding process was carried out. Finally, according to the distribution rule of elements at the interface under different vibration parameters, the relationship between the diffusion coefficient of the element and the concentration and distance of the element is calculated. The results show that: (1) in the range of reasonable vibration parameters, the coating can obtain good surface quality, and the bonding property between the cladding layer and the substrate is good, which is metallurgical bonding. However, with the increase of mechanical vibration energy, a melting tumor appears on the surface of the coating and the surface is rough. 2. When the mechanical vibration energy is similar, the laser cladding process with dominant amplitude and frequency is simulated by finite element method. The results show that the central heat of the laser pool is more concentrated when the amplitude is dominant, the penetration of the pool increases, the width of the pool decreases and the temperature gradient increases, and the homogenization of the laser pool occurs when the frequency is dominant, and the penetration of the pool decreases and the width of the molten pool increases. According to the thermal cycle curves of different vibration parameters, the effect of amplitude is to increase the temperature gradient, whereas the effect of frequency is vice versa. According to the distribution diagram and distribution curve of residual stress field after cooling, it can be concluded that mechanical vibration has little effect on the distribution position of residual stress in laser cladding, but in laser cladding sample with dominant amplitude and frequency, The residual stress and compressive stress along the sweep direction decrease to a certain extent, indicating that mechanical vibration can slow-release the residual stress of laser cladding. 3, During laser cladding, alloy carbides (Fe,Cr) 7C3and (Fe,Cr) 23C6 with 偽-Fe or 緯-Fe as matrix and a small amount of boride represented by Fe2B can be formed by laser cladding of Fe-Cr-Si alloy powder. These carbides and boride have high strength and hardness. According to the calculation of mechanical vibration energy, the influence of amplitude on excitation energy is obvious, and the effect of frequency is small. 4. In the microstructure of laser cladding, it is found that the dark band structure of 2 ~ 3 渭 m is easily formed between the cladding layer and the substrate, which is Cr,. The result of unbalanced diffusion rate of alloy elements such as Si. In this paper, the concentration distribution curve of Cr,Si element in Fe- (Cr,Si) diffusion at the interface is measured and the diffusion coefficient is calculated. The results show that mechanical vibration can decrease the diffusion coefficient at the equal concentration position and Cr, at the interface. The diffusion coefficient of Si element is related to temperature gradient and concentration, and the influence of amplitude on diffusion coefficient in vibration parameter is greater than that of frequency.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TG174.4

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