【摘要】：激光熔化沉積(laser melting deposition,LMD)在航空航天、醫(yī)療器械等領(lǐng)域具有廣泛的應(yīng)用前景。但由于該技術(shù)本身所固有的驟熱、驟冷特點(diǎn),沉積件內(nèi)部大多存在殘余應(yīng)力、氣孔等微觀缺陷,制約了零件的推廣和應(yīng)用。為此,本文提出電磁沖擊增強(qiáng)金屬激光熔化沉積技術(shù)方法,以期通過(guò)電磁力對(duì)熔池附近高溫沉積層施加沖擊,起到在線降低制件內(nèi)部殘余應(yīng)力、減少孔隙等缺陷的作用。本文以激光熔化沉積鐵基粉末、316L不銹鋼基板為例進(jìn)行該方法的研究,具體研究?jī)?nèi)容如下:(1)研究電磁沖擊增強(qiáng)激光熔化沉積的理論基礎(chǔ),包括對(duì)沉積層所受電磁力的推導(dǎo)分析,激光熔化沉積殘余應(yīng)力的產(chǎn)生及控制方法研究,以及電磁沖擊消減激光熔化沉積制件內(nèi)殘余應(yīng)力的機(jī)理的初步分析。(2)運(yùn)用有限元技術(shù)獲得了平面螺旋線圈作用下沉積層內(nèi)感應(yīng)電磁力的時(shí)間、空間分布特性以及不同電參數(shù)及幾何參數(shù)下內(nèi)電磁力的分布規(guī)律,確定線圈施力區(qū)域,提出集磁器線圈,并對(duì)其進(jìn)行優(yōu)化設(shè)計(jì)。從仿真結(jié)果得出,集磁器上表面半徑與勵(lì)磁線圈半徑相同,下表面與內(nèi)孔半徑較小時(shí)更適合電磁沖擊增強(qiáng)激光熔化沉積試驗(yàn)。此外,電流強(qiáng)度較高時(shí),電磁力更大,更有利于沖擊效果。(3)根據(jù)仿真參數(shù)搭建電磁沖擊增強(qiáng)激光熔化沉積裝置并完成不同勵(lì)磁電流下的單道、多層多道沉積件制作,并與常規(guī)制件進(jìn)行對(duì)比。(4)對(duì)制件微觀組織、孔隙、殘余應(yīng)力等方面進(jìn)行分析,結(jié)果表明:電磁場(chǎng)的施加有利于制件晶粒細(xì)化,顯微硬度增加、孔隙數(shù)量和平均尺寸的下降,沉積層顯微組織一次枝晶間距由5μm降低至3.2μm,內(nèi)部殘余應(yīng)力最大降低49%。
[Abstract]:Laser melt deposition (laser melting deposition,LMD) has been widely used in aerospace, medical equipment and other fields. However, due to the inherent characteristics of sudden heat and sudden cooling, the microcosmic defects such as residual stress, porosity and so on exist in the deposition parts, which restrict the popularization and application of the parts. In this paper, a method of electromagnetic shock enhanced laser melting deposition of metals is proposed in this paper. It is expected that the electromagnetic force will exert an impact on the high temperature deposit near the molten pool, which can reduce the internal residual stress of the parts and reduce the defects such as pores on line. In this paper, the method of laser melting deposition of iron-based powder and 316L stainless steel substrate is studied. The main contents are as follows: (1) the theoretical basis of electromagnetic shock enhanced laser melting deposition is studied. Including the derivation and analysis of electromagnetic force, the generation and control of residual stress in laser melt deposition. The mechanism of reducing residual stress in laser melted deposition parts by electromagnetic shock is analyzed. (2) the time of inductive electromagnetic force in the deposit layer under the action of planar spiral coil is obtained by using finite element technique. According to the spatial distribution characteristics and the distribution law of electromagnetic force in different electric and geometric parameters, the force region of the coil is determined, and the magnetic collector coil is proposed and optimized. From the simulation results, it is concluded that the upper surface radius of the collector is the same as that of the excitation coil, and the radius of the lower surface and the inner hole is more suitable for the electromagnetic shock enhanced laser melting deposition test. In addition, when the current intensity is high, the electromagnetic force is larger, which is more favorable to the impact effect. (3) according to the simulation parameters, the electromagnetic shock enhancement laser melting deposition device is built and the single channel, multi-layer and multi-channel deposition parts are made under different excitation current. And compared with the conventional parts. (4) the microstructure, pore and residual stress of the parts are analyzed. The results show that the application of electromagnetic field is beneficial to the grain refinement and the increase of microhardness of the parts. With the decrease of the number of pores and the average size, the primary dendritic spacing of the deposited layer decreases from 5 渭 m to 3.2 渭 m, and the internal residual stress decreases by 49%.
【學(xué)位授予單位】：南京航空航天大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG665

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