【作者】 龚艳丽；

【导师】 陈振华；

【作者基本信息】 湖南大学 ， 材料加工工程， 2007， 硕士

【摘要】 喷射沉积技术作为一种先进的材料制备新技术,已经被广泛应用于制备合金及金属基复合材料。然而喷射沉积坯料中通常存在一定量的孔隙,颗粒表面存在一定厚度的氧化膜,颗粒之间未能完全达到良好的冶金结合状态,因此需要进行后续致密化和塑性变形才能获得理想的组织和性能。本文通过对喷射沉积多孔材料的致密化和塑性变形规律的研究,以及对现有的喷射沉积多孔材料塑性加工工艺的分析比较,特别是根据准热等静压工艺特点提出了一种新型的轧制技术——陶粒轧制。本论文的主要研究内容和研究结果如下:(1)对喷射沉积8009Al/SiCp板坯陶粒轧制工艺进行了研究。分析了陶粒轧制的7种实验方案,研究了该工艺中的诸如钢压头形状、原始坯件的设计以及轧制方式等对多孔材料陶粒轧制变形行为的影响,在此基础上对工艺条件进行优化。在陶粒轧制过程中,钢压头的形状以及轧制方式对喷射沉积多孔材料板坯的轧制变形行为有很大的影响,特别是采用厚的平压头以及道次间采用180°转向轧制工艺,能够满足喷射沉积铝合金板坯轧制成形性能的要求。并且在陶粒轧制过程中喷射沉积板坯的致密化和轧制变形行为与用于传递压力的陶瓷颗粒介质特性有关。采用200目Al2O3进行陶粒轧制时,喷射沉积铝合金板坯的致密化效果和轧制成形性能最佳。(2)对在陶粒轧制工艺条件下喷射沉积5A06和8009/SiCP板坯的致密化规律和组织演变规律进行了研究。与常规轧制工艺比较,在陶粒轧制工艺中的裂纹形成阶段,由于陶瓷颗粒对材料纵向和横向变形的阻碍作用使多孔材料的延伸变形量明显小于常规轧制,从而减小了促使裂纹形成的拉应变,有利于材料的致密化进程,减小和避免表面裂纹的产生和扩展。并且在陶粒轧制过程中,轧件在三向大小不等的压应力作用下,轧件内部粉末颗粒表面的氧化膜发生剪切变形,粉末颗粒和氧化膜很容易破碎,有利于增强粉末颗粒粘结的完整性,获得更良好的冶金结合,故轧件通过陶粒轧制后的致密度相对通过常规轧制的致密度在同等变形程度下更高。(3)对在陶粒轧制工艺条件下喷射沉积5A06和8009/SiCP板坯的加工性能进行了研究。采用陶粒轧制工艺对喷射沉积法制备的5A06和8009/SiCP板坯进行轧制加工,板坯在变形量达到65%时仍不会形成表面裂纹,轧制后的板坯致密度、强度、延性均优于常规轧制,并且板坯在先陶粒轧制致密再轧制工艺下通过充分的变形,其室温力学性能也可超过传统轧制。采用陶粒轧制工艺对喷射沉积法制备的多孔材料板坯进行轧制加工,改善了喷射沉积5A06和8009/SiCP板坯轧制加工性能,轧制出了组织与性能优良的铝合金薄板。更多还原

【Abstract】 As an advanced material preparation technology, spray deposition has been widely used to produce alloys and metal matrix composites. In principle, the spray deposited preforms usually exhibit limited mechanical properties due to the porosity and a lack of sound metallurgical bond between the particles. Higher performance can be achieved by further densification and deformation. The densification and plastic deformation behaviors and fracture behaviors of the as-spray deposited porous performs were investigated in this thesis. The involved deformation process is rolling. A novel rolling methods named as“Ceramic Rolling”developed based on pseudo-HIP technology is applied.The main conclusions are as follows:(1) The effects of processing conditions during“Ceramic Rolling”technique were investigated.Seven kinds of“Ceramic Rolling”experiments have been experimentally verified to improve the formability of the porous 8009/SiCP alloy performs.The experimental results show that the shape of the pressure transfer medium and the rolling method has obvious effect on the deformation of the spray deposited performs. The densification and plastic deformation behaviors and the fracture behaviors of the as-spray deposited porous performs are related with the effects of particulate characteristics during“Ceramic Rolling”process. The ceramic particulates, especially the Al2O3 particle with the size of about 200 meshes, can serve as the medium for transferring pressure, thus to provide a more homogenous severe hydrostatic stress field to handicape the flowing of the metals in the longitudinal and transverse directions and to avoid cracking during the rolling process.(2) The influence of the processing conditions on the densification and deformation behaviors of the porous 5A06 and 8009/SiCp alloy perform during“Ceramic Rolling”process were investigated. The experimental results show that comparing with the fully dense materials, the deformation behavior of spray deposited preforms is very complicated and difficult because of the existence of porosity in the preforms and oxidation film on the surface of the alloy particles in the matrit. During the conventional rolling process, the porous preform is liable to cracking or tearing. During Ceramic Rolling, the ceramic particulates may serve the dual functions of a compactible pressure transfer medium and also as a medium for heat preservation in workpiece body, thus helps to maintain the necessary temperature levels for the deformation during rolling. It is obvious that the ceramic particles can retard the flowing of the metal in the longitudinal and the transverse during Ceramic Rolling when the thickness reduction is up to 25%-30%, which is important in avoiding the cracks. Since severe hydrostatic stress field benefits the formability, extrusion is widely adopted for the densification and deformation of the as-spray deposited preforms.(3) The processing parameters such as packing materials, ceramic particulate size and kind should be paid more attention in order to improve the densification effect to so as to and obtain large dimension sheet free of crack. The results show that the“Ceramic Rolling”technique is an effective method to speed up the densification and improve the formability of porous spray deposition alloy preforms, which is thought to be resulted from the severe hydrostatic and homogenous stress. As the immature manufacture technique to process spray deposited aluminum alloys, great efforts will be stimulated for further investigation, and significant progress is expected. Nevertheless, extrusion can not produce large dimension plates limited by the facility.更多还原