【作者】 吴晓娟；

【导师】 沈以赴；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2010， 硕士

【摘要】 利用行星高能球磨机设备,高能机械合金化微米级的W/Ni和W/Ni/Cu体系,成功制备了纳米W-Ni和W-Ni-Cu复合粉末,并研究了W-Ni和W-Ni-Cu纳米复合粉末压坯在激光高能作用下的显微组织演变及性能变化。利用XRD、SEM、EDS分析和检测手段,研究了纳米复合粉末及粉末压坯烧结样的物相、晶粒大小、颗粒形貌和显微组织,并阐明了纳米复合粉末的形成机理。球磨转速为400rpm下球磨W-10%Ni混合粉末,随球磨时间的延长,衍射峰逐渐宽化,晶格畸变严重。球磨至10h,即可产生金属间化合物Ni4W。球磨至20h后,粉末颗粒的粒度分布均匀,颗粒尺寸细化至~3μm。球磨转速为400rpm下球磨W-20%Ni混合粉末,随球磨时间的延长,衍射峰逐渐宽化,衍射强度逐渐下降。球磨至1h,粉末的粒径约为5μm。球磨至5h,即可产生金属间化合物Ni4W。复合粉末的衍射强度和晶粒粒径随着球磨时间的延长而降低。球磨转速为400rpm下球磨W-Ni-Cu混合粉末,随着球磨时间的延长,Ni峰逐渐消失,复合颗粒形貌由不规则发生扁平化,最终变为等轴状。当球磨至50h,颗粒尺寸细化至~5μm。球磨100h形成W/Ni金属间化合物Ni4W。在相同的激光参数条件下烧结W/Ni复合粉末压坯。W-10%Ni复合粉末激光烧结试样,由于液相与W晶粒之间接触程度低,润湿性较差,不能获得致密的烧结组织。W-30%Ni复合粉末激光烧结试样,液相增多,导致熔体过热,出现“球化”现象。Ni质量分数为20%能获得良好的表面形貌、烧结组织和致密度。在相同的激光参数条件激光烧结W/Ni/Cu复合粉末压坯。不同成分的W-Ni-Cu经激光烧结后的显微组织也有很大差异,20W-40Ni-40Cu获得连续柱状晶组织,40W-20Ni-40Cu获得枝晶组织。并对W-Ni-Cu复合粉末激光烧结凝固理论进行探讨。更多还原

【Abstract】 Nano-W/Ni and Nano-W/Ni/Cu composite powders were successfully obtained via high energy ball milling (HEBM), using the micrometric W/Ni and W/Ni/Cu powders as the raw materials. Meanwhile, the structural evolution and performance of laser sintering of W/Ni and W/Ni/Cu powders compacts were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) were used to investigate the phases, crystal size, morphological changes and microstructure of nanocomposite powders and laser sintering samples. The mechanism regarding the formation of nanocomposite powders is elucidated.W-10%Ni mixed powders were milled using the rotation speed of 400 rpm. With increasing the milling time, the X-ray diffraction peaks are broadening and lattice distortions are serious. After milling for 10h, the intermetallic compound Ni4W was found. After milling for 20h, the particulates were homogeneously distributed and the size changed to ~3μm. W-10%Ni mixed powders were milled using the rotation speed of 400 rpm. With increasing milling time, the X-ray diffraction intensity and grain size of the composite powders were reduced. After milling for 1h, the particulate size changed to ~5μm. After milling for 5h, the intermetallic compound Ni4W was found.W-Ni-Cu mixed powders were milled using the rotation speed of 400 rpm. With increasing milling time, the X-ray diffraction peaks of Ni disappeared and the starting irregular powders became flattened, eventually became equiaxed. After milling for 50h, the particulate size changed to ~5μm. After milling for 100h, the intermetallic compound Ni4W was found. W/Ni composite powder compacts were laser sintered using the same laser processing parameters. It shows that using W-10%Ni composite powders results in poor densification, due to a limited liquid phase and poor wettability. Poor densification with severe balling phenomena and a superheating of the melt is obtained at a high Ni content of 30wt.%, because of a excessive liquid formation. Using an optimal Ni content of 20 wt.% leads to a compatible interfacial microstructure, so as to obtain a favorable sintered density.W/Ni/Cu composite powders compacts were laser sintered using the same laser processing parameters.The scanning electron microscope(SEM) analyses show that mass fraction of W-Ni-Cu effects microstructure. It can be seen that columnar crystals were formed for 20W-40Ni-40Cu system and dendritic crystals for 40W-20Ni-40Cu system. Theories of metal solidification for laser sintering were discussed.更多还原