【作者】 王志刚；

【导师】 史玉升；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2011， 硕士

【摘要】 选择性激光熔化成形(Selective Laser Melting,SLM)技术作为一种新型的快速成形技术在缩短零件研发周期,直接制造高性能复杂零部件有很大的优势。国内外已经对其原理做了一定的研究,但是SLM制件仍存在诸多缺陷,性能不高,限制了其广泛应用。本文以镍及镍基高温合金GH4169、AISI316L不锈钢为代表材料,通过研究表面形貌,金相组织、显微硬度,相对密度等对SLM成形前的准备工作提高SLM成形质量、调整工艺参数以提高其制件性能、通过热等静压(hot isostatic pressing,HIP)对SLM制件后处理以提高其性能等方面进形了研究。研究结果表明:(1)选用合适的粉末、基板、保护气并对其进行前处理会提高SLM成形质量;(2)激光功率越高扫描线宽越大;扫描速度越低扫描线宽越大;铺粉层厚越大,扫描线球化趋势越明显,零件相对密度越低;保护气氛中氧含量越多,扫描球化现象越明显;扫描搭接率适中(40%~60%)时面扫描球化现象不明显,表面精度越好。(3)SLM制件经过HIP后,真空裂纹完全愈合,试样中不规则孔体积缩小,且形状变为球形或者近球形。对于层厚较小,层与层之间粘结紧密,相对密度较高的零件HIP后晶粒更粗大;层厚较大,层间存在少许粘结不良,但孔洞大部为闭合孔,HIP后晶粒细小且沿SLM加工层间分布。SLM制件经过HIP后,相对密度都有一定的提升,尤其是对于闭合孔较多的制件中相对密度提升很大;而对于大部为通孔的零件,高压气体可以进入到孔隙中,相对密度提升有限;HIP后样品中仍然存在机械性能的各向异性,显微硬度与材料距离表面的距离关系不大。通过本文的研究结果,可以对SLM成形前、成形中、成形后提升制件性能进行指导。更多还原

【Abstract】 Selective laser melting (SLM) is a novel rapid prototyping technology which has many advantages in shortening developing circle and fabricating metal parts with high quality and complicated shape directly. Researchers at home and abroad have studied its mechanism, but SLM parts have many problem resulting in poor property, which restricts their application.Taking Ni-based high-temperature alloy GH4169 and AISI316L stainless steel as the materials, preparation work, SLM parameters and hot isostatic pressing(HIP) post-treatment were investigated to improve the properties of SLM part by studying surface topography, fine texture, micro-hardness and relative density of parts.The results show that: (1) Selecting proper powder, base plate and protecting gas and pre-treating them properly can promote the property of SLM parts. (2) The higher laser power, the bigger of scanning track width; the thicker of layer, the more likely balling phenomenon appears, and the lower of the final part relative density; the more oxygen contented in the atmosphere, the more obvious balling phenomenon; when the scanning lap ratio is between 40%~60%, the balling phenomenon is less and surface accuracy is good. (3) After HIP the vacuum cracks in SLM parts heal completely, the volume of the anomalous holes inside the parts reduces, and the holes become spherical or near spherical. SLM parts with the small processing thickness, will be well bonded, and have high relative density, the crystal grains of which are big after HIP. But to the SLM parts with the big thickness, the bad cementation between each layers and closed holes inside which are post-processed by HIP, the crystal grains are tiny and distribute along the SLM processing layer. The relative density of HIP parts rise after HIP, especially for most of those holes are close holes; if most of the holes are through holes, highly pressed gas will go into the holes, then the relative density cannot be raised a lot; samples after HIP are still anisotropic in mechanical properties, and the micro-hardness is not related to the distance to sample surface.The achievement of this study can give advice to promote the property of SLM part before, in, and after SLM.更多还原