【摘要】：高熵合金是目前發(fā)展起來的含有五種以上主要元素且呈現(xiàn)出FCC和BCC結(jié)構(gòu)的固溶體相合金，其具有高硬度、高強度，較好的耐磨性、耐腐蝕性能以及優(yōu)異的抗氧化性能。激光表面改性技術(shù)可以實現(xiàn)在低成本的金屬材料表面，制備出高性能的涂層。本課題采用Nd:YAG固體脈沖激光器、半導體、CO2及光纖激光器分別在純銅表面進行系列激光高熵合金化層的制備，研究激光輻照工藝對高熵合金化層的成形質(zhì)量、顯微組織、性能的影響規(guī)律。利用金相顯微鏡、掃描電鏡、能譜儀、X-射線衍射儀、顯微硬度儀、納米壓痕儀及往復摩擦實驗機對合金化層組織形貌、成分、相結(jié)構(gòu)及性能進行系統(tǒng)研究。 試驗結(jié)果表明：激光快速成形四元FeCoCrAl合金是由BCC和兩種金屬間化合物組成，利用Nd:YAG激光輻照可使FeCoCrAl四元合金粉末在純Cu表面反應(yīng)合成制備FeCoCrAl/Cu五元高熵合金化層，合金化層具有簡單固溶體結(jié)構(gòu)。隨Nd:YAG激光器電流增大，合金化層組織由顆粒狀向胞狀轉(zhuǎn)變。熱力學分析表明，F(xiàn)eCoCrAl/Cu激光高熵合金化層滿足形成固溶體的條件。由于固溶強化和晶粒細化作用使高熵合金化層硬度明顯提高。 采用半導體、CO2及光纖激光合金化技術(shù)制備的FeCoCrAlNix/Cu（x=0，0.5，1，1.5）高熵合金化層，隨Ni元素的加入，合金化層的相組成由FCC+BCC逐漸轉(zhuǎn)變成單一FCC結(jié)構(gòu)，其硬度呈下降趨勢。分別加入Mo和Ti元素的合金化層除了含有簡單固溶體相外還出現(xiàn)其他相，而加入Si元素的合金化層仍為簡單固溶體，且成形性較好。 往復磨損試驗表明，F(xiàn)eCoCrAlNix/Cu（x=0，0.5，1，，1.5）激光合金化Ni含量變化時，耐磨性與硬度變化規(guī)律并不一致，F(xiàn)eCoCrAlNi/Cu合金化層由于經(jīng)絡(luò)狀組織的存在，耐磨性較好。此外，F(xiàn)eCoCrAlSi0.5/Cu合金化層磨損表面仍較平滑，無明顯的黏著，只出現(xiàn)少量黑色顆粒，磨損量較小。 由于激光功率密度以及材料對不同波長的激光吸收率的差異，不同的激光合金化層顯微組織各異，經(jīng)計算，Cu對不同波長激光吸收率及合金化過程中激光能量密度依次為：CO2激光＜光纖激光＜半導體激光。結(jié)合激光高熵合金化宏觀成形性、組織、性能及制備工藝，利用光纖激光在Cu基材表面實現(xiàn)高熵合金化為最優(yōu)方法。
[Abstract]:High entropy alloy is a kind of solid solution alloy which contains more than five main elements and presents the structure of FCC and BCC. It has high hardness, high strength, good wear resistance, corrosion resistance and excellent oxidation resistance. Laser surface modification technology can be used to fabricate high performance coatings on low cost metallic materials. In this paper, Nd:YAG solid-state pulse laser, semiconductor, CO2 and fiber laser were used to prepare series of laser high-entropy alloying layers on the surface of pure copper, and the forming quality and microstructure of high-entropy alloying layer by laser irradiation were studied. The influence law of performance. The microstructure, composition, phase structure and properties of alloyed layer were systematically studied by metallographic microscope, scanning electron microscope, energy spectrometer, X-ray diffractometer, microhardness tester, nano-indentation instrument and reciprocating friction tester. The experimental results show that the quaternary FeCoCrAl alloy is composed of BCC and two intermetallic compounds. The FeCoCrAl quaternary alloy powder can be synthesized by Nd:YAG laser irradiation on the surface of pure Cu to prepare FeCoCrAl/Cu quaternary high entropy alloying layer. The alloying layer has a simple solid solution structure. As the current of Nd:YAG laser increases, the alloying layer changes from granular to cellular. Thermodynamic analysis shows that the FeCoCrAl/Cu laser high entropy alloying layer meets the condition of forming solid solution. The hardness of high entropy alloying layer is improved obviously because of solid solution strengthening and grain refinement. The high entropy alloying (FeCoCrAlNix/Cu) layer prepared by semiconductor, CO2 and optical fiber laser alloying technology was used. With the addition of Ni element, the phase composition of the alloying layer gradually changed from FCC BCC to single FCC structure. Its hardness shows a downward trend. The alloying layer with Mo and Ti elements has other phases except simple solid solution phase, while the alloying layer with Si element is still simple solid solution, and the formability is good. The results of reciprocating wear test show that the wear resistance of FeCoCrAlNix/Cu (x0. 0. 5%) laser alloyed Ni is not consistent with the change of hardness. The wear resistance of FeCoCrAlNi/Cu alloying layer is better because of the existence of meridian structure. In addition, the wear surface of FeCoCrAlSi0.5/Cu alloying layer is still smooth, no obvious adhesion, only a small amount of black particles appear, and the amount of wear is small. Due to the difference of laser power density and the absorptivity of materials to different wavelengths, the microstructure of different laser alloying layers is different. The order of laser energy density in the process of laser absorption and alloying by Cu is as follows: CO2 laser < fiber laser < semiconductor laser. Combined with the macroscopic formability, microstructure, properties and preparation process of laser high entropy alloying, the optimal method of high entropy alloying on the surface of Cu substrate is achieved by using optical fiber laser.
【學位授予單位】：沈陽工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG174.4

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