Al基复合材料选区激光熔化成形机理及摩擦磨损性能研究

发布时间：2018-08-17 16:46

【摘要】：本课题采用先进的选区激光熔化(Selective Laser Melting,SLM)工艺成形球磨均匀的Al_2O_3/Al和Al_2O_3/AlSi_(10)Mg混合粉末,从而成功制备了Al_2O_3/Al以及原位Al_2Si_4O_(10)/Al复合材料试样。研究了陶瓷颗粒增强Al基复合材料的SLM成形工艺,探讨了SLM工艺参数对AMCs试样物相、致密度、显微组织、硬度及摩擦磨损性能的影响。进而优化工艺参数,获得最佳性能的材料。在以上基础上,进一步调研了择优化参数下成形的Al_2Si_4O_(10)/Al复合材料试样的摩擦磨损性能。得出以下主要结论:针对Al_2O_3/Al复合材料的SLM成形,当激光线能量密度(η)较低时,SLM成形的Al_2O_3/Al试样冶金缺陷较多,致密度较低,断裂不连续的Al_2O_3增强相发生严重团聚现象,且与Al基体界面结合较弱,成形试样硬度及耐磨性较差。合理地增加η至236 J/m,试样表面光滑、致密,无明显冶金缺陷,长条状Al_2O_3增强相显著细化,分布均匀,且与Al基体具有良好的界面结合。此时成形试样性能优异,平均显微硬度值高达175 HV0.1,摩擦系数和磨损率分别低至0.33和9.78×10-5 mm3 N-1 m-1。针对原位Al_2Si_4O_(10)/Al复合材料的SLM成形,当η较低时,Al_2Si_4O_(10)增强相之间结合性较差,并呈现不均匀的分布,而当η较高为350 J/m时,晶粒发生严重粗化,以上都降低了成形试样的性能。择优化η为289 J/m时,在激光核心区,Al基体以胞状枝晶形态生长,环状Al_2Si_4O_(10)增强相之间结合良好,分散均匀,同时其晶粒显著细化。在激光重熔区内,Al基体呈现柱状枝晶形貌,环状Al_2Si_4O_(10)增强相略微粗化,同时Al基体上分散着大量细小的Al_2Si_4O_(10)增强颗粒,此时成形试样的纳米硬度和摩擦磨损特性得到显著提高。针对原位Al_2Si_4O_(10)/Al复合材料的摩擦磨损实验,载荷的增加使试样表面颗粒破损程度增大,进而导致了严重的三体磨粒磨损,加剧了试样表面的磨损。滑移速度越大,摩擦热效应及热量聚集越明显,表面温升越高,从而促进了硬质Al_2O_3的生成及Fe_2O_3的转移,提高了AMCs试样的摩擦磨损特性。长时间摩擦磨损中,摩擦系数值在0.65和0.55之间波动。磨损后期,摩擦热量发生积累,导致试样表面硬质Al_2O_3反应物和Fe_2O_3转移层的数量大大增加,因此降低了摩擦系数的波动程度。
[Abstract]:In this paper, the advanced selective laser melting (Selective Laser Meltings-SLM process was used to fabricate the Al_2O_3/Al and Als _ 2O _ 3 / AlSi _ (10) mg mixed powders, and the Al_2O_3/Al and Al _ 2SiS _ 4O _ (10) / Al composite samples were successfully prepared. The SLM forming process of ceramic particle reinforced Al matrix composites was studied. The effects of SLM process parameters on the phase, density, microstructure, hardness and friction and wear properties of AMCs samples were investigated. Then the process parameters are optimized and the material with the best performance is obtained. On the basis of the above, the friction and wear properties of Al _ 2Si _ 4O _ (10) / Al composite specimens formed under optimized parameters were investigated. The main conclusions are as follows: for the SLM forming of Al_2O_3/Al composites, when the laser energy density (畏) is low, there are more metallurgical defects, lower density and serious agglomeration of the Al_2O_3 reinforced phase with discontinuous fracture. The interface with Al matrix is weak and the hardness and wear resistance of the formed samples are poor. By increasing 畏 to 236J / m reasonably, the surface of the sample is smooth and compact, and there is no obvious metallurgical defect. The long strip Al_2O_3 reinforced phase is finer, more evenly distributed, and has a good interface with Al matrix. The average microhardness is 175HV0.1, and the friction coefficient and wear rate are as low as 0.33 and 9.78 脳 10 ~ (-5) mm3 N-1 ~ (-1) m ~ (-1), respectively. For the SLM forming of in situ Al2Si4O10 / Al composites, when 畏 is lower, the adhesion between Al2Si4O10 / Al2Si4O10 reinforcements is poor, and the distribution is uneven. When 畏 is higher than 350J / m, the grain size coarsens seriously, which reduces the properties of the formed specimens. When the optimized 畏 is 289 J / m, the Al matrix in the laser core region grows in cellular dendritic morphology, and the circular Al2Si4O10 reinforcement phase is well bonded and uniformly dispersed, and the grain size is significantly refined. In the laser remelting zone, the Al matrix presents a columnar dendritic morphology, the annular Al2Si4O10 reinforcement phase is slightly coarser, and a large number of fine AlStack-Si4O10 reinforced particles are dispersed on the Al matrix. The nano-hardness and friction and wear properties of the formed samples are greatly improved. According to the friction and wear experiments of Al _ 2Si _ 4O _ (10) / Al composites in situ, the wear degree of the surface particles increased with the increase of load, which led to serious wear of three-body abrasive particles and aggravated the wear of the specimen surface. The higher the slip rate, the more obvious the friction heat effect and heat accumulation, the higher the surface temperature rise, thus the formation of hard Al_2O_3 and the transfer of Fe_2O_3 are promoted, and the friction and wear characteristics of AMCs samples are improved. The friction coefficient fluctuates between 0.65 and 0.55 during long time friction and wear. At the later stage of wear, the friction heat accumulates, which results in a great increase in the number of hard Al_2O_3 reactants and Fe_2O_3 transfer layers on the surface of the specimen, thus reducing the fluctuation degree of friction coefficient.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB333

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