【摘要】：激光熔覆技術是集激光加熱熔化、熔池中物質交互作用及快速凝固成形等多學科交叉的一門新技術,主要應用于表面改性與堆焊再制造。該課題在原有實驗的基礎上,利用脈沖式激光在不同激光功率下制備新型的Co基合金覆層。主要研究內容包括激光功率對Co基合金覆層的組織形貌、物相和稀釋率的影響,對Co基材料的非晶形成能力進行分析,借助模擬軟件對覆層的溫度場進行計算,結合熱力學與動力學對其微觀組織形成機制進行總結分析,最后研究了激光功率對Co基合金覆層的物理性能的影響。對覆層的上中下三部分的微觀組織特征進行分析,發(fā)現(xiàn)覆層的中上部以非晶相為主,非晶相中存在有帶狀分布的等軸晶,覆層熔合線區(qū)域以枝晶為主,生長方向垂直于熔合線指向覆層,激光功率為467W時,枝晶的高度最小為10μm。覆層內的Fe元素在結晶相區(qū)域發(fā)生聚集現(xiàn)象,通過XRD計算得出非晶相的含量,激光功率為467W時覆層的非晶相含量最大。隨著激光功率的增大,覆層的稀釋率增大。通過Inoue三原則和Yan參數(shù)法分別對新型合金覆層微觀組織形成機制進行理論分析,驗證該材料在激光熔覆的制備工藝下具有非晶形成能力。通過甩帶技術將覆層制備為純非晶,計算其臨界冷卻速率、約化溫度和ΔT_x,說明該覆層具有強的非晶形成能力和高的熱穩(wěn)定性。借助Marc模擬軟件對不同功率下的合金覆層的溫度場進行模擬計算,得出覆層的冷卻速率均大于臨界冷卻速率。結合熱力學與動力學理論對覆層進行分析,研究發(fā)現(xiàn)結晶相與非晶相混合的覆層的形成主要是極高的冷速、熔體的流動、溶質的擴散、Fe元素的聚集導致的異質形核共同作用的結果。研究了不同激光功率對Co基合金覆層硬度的影響,當激光功率為467W時,覆層的硬度達到了1192.5HV0.2,覆層中上部區(qū)域的硬度發(fā)生上下波動的現(xiàn)象,是因為非晶相與結晶相硬度相差較大,隨著距覆層表面的距離變大,覆層的硬度整體呈現(xiàn)下降趨勢。對不同功率下的覆層和基體的耐蝕性和耐磨性進行分析。在3.5wt.%Na Cl溶液和1mol/l HCl溶液中,激光功率為467W的覆層腐蝕電位最高,激光功率為583W的覆層腐蝕電流最小,在HCl溶液中467W的覆層優(yōu)先出現(xiàn)鈍化現(xiàn)象,在阻抗實驗中,激光功率為467W的覆層的阻抗半徑最大,說明其在這兩種腐蝕環(huán)境下的耐蝕性最強。溫度為20oC時,覆層的磨擦系數(shù)基本在0.15附近,激光功率為467W覆層的磨損量最小,磨痕深度最小,說明其耐磨性最大。覆層的磨損形式以磨粒磨損為主,同時伴有少量的黏著磨損,基體的磨損為大量的黏著磨損和磨粒磨損。
[Abstract]:Laser cladding technology is a new technology which combines laser heating and melting, material interaction in molten pool and rapid solidification forming. It is mainly used in surface modification and surfacing remanufacture. Based on the previous experiments, a new Co based alloy coating was prepared by pulse laser at different laser power. The main research contents include the influence of laser power on the microstructure, phase and dilution rate of Co based alloy coating. The amorphous forming ability of Co based material is analyzed, and the temperature field of the coating is calculated by means of simulation software. The mechanism of microstructure formation was summarized and analyzed by thermodynamics and kinetics. Finally, the effect of laser power on the physical properties of Co based alloy coating was studied. The microstructure of the upper, middle and lower parts of the coating is analyzed. It is found that the middle and upper part of the coating is dominated by amorphous phase, and there are banded equiaxed crystals in the amorphous phase, and dendrite dominates in the fusion line region of the coating. The growth direction is perpendicular to the fusion line, and the height of the dendrite is 10 渭 m when the laser power is 467 W. The content of amorphous phase was calculated by XRD. The content of amorphous phase was the largest when the laser power was 467 W. With the increase of laser power, the dilution rate of the coating increases. The formation mechanism of microstructure of the new alloy cladding was theoretically analyzed by Inoue three principles and Yan parameter method respectively. It was verified that the material had the ability of amorphous formation under the laser cladding process. The coating was prepared into pure amorphous by belt throwing technique, and the critical cooling rate, reduction temperature and 螖 T _ x were calculated, which indicated that the coating had strong amorphous forming ability and high thermal stability. The temperature field of the alloy coating under different power is simulated by Marc software. The results show that the cooling rate of the coating is higher than that of the critical cooling rate. Based on the thermodynamics and kinetics theory, it is found that the formation of the coating mixed with crystalline phase and amorphous phase is mainly due to the extremely high cooling rate, melt flow, solute diffusion, etc. The aggregation of Fe elements results in the coaction of heterogeneous nuclei. The effect of different laser power on the hardness of Co based alloy coating is studied. When the laser power is 467 W, the hardness of the coating reaches 1192.5 HV0.2, and the hardness of the upper and middle parts of the coating fluctuates up and down. Because the hardness of amorphous phase and crystalline phase is different, the hardness of the coating decreases with the increase of the distance from the surface of the coating. The corrosion resistance and wear resistance of coating and matrix under different power were analyzed. In 3.5wt.%Na Cl solution and 1mol/l HCl solution, the coating with 467W laser power has the highest corrosion potential, the coating with 583W laser power has the lowest corrosion current, and the coating with 467W in HCl solution preferentially passivates, and in the impedance experiment, the corrosion potential of the coating is the highest when the laser power is 467W. The maximum impedance radius of the coating is obtained when the laser power is 467 W, which indicates that the coating has the strongest corrosion resistance in these two corrosion environments. When the temperature is 20oC, the friction coefficient of the coating is about 0. 15, and the laser power of 467 W is the smallest, and the wear depth is the smallest, which indicates that the wear resistance of the coating is the greatest. The wear form of the coating is mainly abrasive wear, accompanied by a small amount of adhesive wear, the matrix wear is a large number of adhesive wear and abrasive wear.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG174.44

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