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Lost mold-rapid infiltration forming: Strength control in mesoscale 3Y-TZP ceramics.




The strength of nanoparticulate enabled microdevices and components is directly related to the interfacial control between particles and the flaws introduced as these particles come together to form the device or component. One new application for micro-scale or meso-scale (10's microm to 100's microm) devices is surgical instruments designed to enter the body, perform a host of surgeries within the body cavity, and be extracted with no external incisions to the patient. This new concept in surgery, called natural orifice transluminal endoscopic surgery (NOTES), requires smaller and more functional surgical tools. Conventional processing routes do not exist for making these instruments with the desired size, topology, precision, and strength. A process, called lost mold-rapid infiltration forming (LM-RIF), was developed to satisfy this need. A tetragonally stabilized zirconia polycrystalline material (3Y-TZP) is a candidate material for this process and application because of its high strength, chemical stability, high elastic modulus, and reasonably high toughness for a ceramic.Modern technical ceramics, like Y-TZP, are predicated on dense, fine grained microstructures and functional mesoscale devices must also adhere to this standard. Colloid and interfacial chemistry was used to disperse and concentrate the Y-TZP nanoparticles through a very steep, yet localized, potential energy barrier against the van der Waals attractive force. The interparticle interaction energies were modeled and compared to rheological data on the suspension. At high concentrations, the suspension was pseudoplastic, which is evidence that a structure was formed within the suspension that could be disrupted by a shearing force. The LM-RIF process exploits this rheological behavior to fill mold cavities created by photolithography. The premise of the LM-RIF process is to process the particulate material into a dense ceramic body while the unsintered mesoscale parts are supported en masse by a substrate. Numerous challenges were overcome that relate to the application of photoresist on a refractory substrate capable of withstanding the high temperatures needed to sinter the ceramic parts. Strength of approximately 1 GPa was achieved for the first parts produced, which demonstrated the feasibility of the LM-RIF process.Although respectable, a 1GPa strength is not as strong as would be predicted based on the small size (332 x 26 x 17 microm) of the parts. An effort to identify and eliminate the largest flaws in the specimen produced by the LM-RIF process was undertaken, which ultimately increased the average strength to 2.35 GPa. Geometric defects, previously unreported in ceramic microfabrication techniques, were degrading the strength of the early parts. An in-depth characterization of these defects by optical profilometry and then eliminating the underlying cause was the key to obtaining this high strength. One interesting phenomena discovered in this work was the role that the substrate plays in the sintering of the ceramic part through the enhanced diffusion pathways created by the more intimate contact of the mesoscale parts compared to macroscale analogs. Impurities of alumina and silica were found to adversely affect the sintering kinetics of mesoscale parts causing localized grain growth or exaggerated grain growth depending on the sintering conditions.The role that the microstructure, specifically the grain size, plays in determining the strength versus the role that the surface flaw population plays, as characterized by the surface roughness, was determined through isothermal sintering experiments. It was found that the strength of mesoscale ceramics lies in the transition region between the flaw-dominated stress intensity effect and the Hall-Petch microstructural effect. This proves that processing science and microstructural refinement about equally determine the strength of particulate based mesoscale materials.The hierarchical approach that was used to marry the development of the LM-RIF process to the mechanical design and optimization of surgical instruments is described. This approach used nested iteration loops to refine both the design and fabrication processes to create and test surgical instrument prototypes. These prototypes as well as some of the unique shapes possible with the LM-RIF process are presented.
机译:启用纳米颗粒的微型设备和组件的强度直接与颗粒之间的界面控制以及随着这些颗粒聚集在一起形成设备或组件而引入的缺陷有关。微型或中型(10微米至100微米)设备的一项新应用是外科手术器械,旨在进入人体,在体腔内进行一系列外科手术,并且无需对患者进行外部切口即可将其取出。这种新的外科手术概念称为自然孔腔内镜手术(NOTES),需要更小巧,功能更强大的手术工具。不存在用于使这些仪器具有期望的尺寸,拓扑,精度和强度的常规加工路线。为了满足这一需求,开发了一种称为快速脱模成型(LM-RIF)的工艺。四方稳定的氧化锆多晶材料(3Y-TZP)由于其高强度,化学稳定性,高弹性模量和相当高的陶瓷韧性而成为该工艺和应用的候选材料.Y-TZP等现代工业陶瓷,以致密的,细粒度的微结构为基础,并且功能中等的设备也必须遵守该标准。胶体和界面化学被用来分散和浓缩Y-TZP纳米粒子,通过非常陡峭但局部的势能垒来抵抗范德华力。对粒子间相互作用能进行建模,并与悬浮液的流变数据进行比较。在高浓度下,悬浮液是假塑性的,这表明悬浮液中形成的结构可能会被剪切力破坏。 LM-RIF工艺利用这种流变行为来填充由光刻产生的型腔。 LM-RIF工艺的前提是将颗粒材料加工成致密的陶瓷体,同时未烧结的中尺度零件由基材整体支撑。克服了许多挑战,这些挑战涉及将光致抗蚀剂施加到能够承受烧结陶瓷零件所需的高温的耐火基材上。最初生产的零件达到了约1 GPa的强度,这证明了LM-RIF工艺的可行性。虽然值得尊敬,但1GPa的强度却不如根据小尺寸(332 x 26 x 17微米)所预测的那样强)的部分。努力找出并消除了LM-RIF工艺所产生的试样中的最大缺陷,最终将平均强度提高到2.35 GPa。以前在陶瓷微细加工技术中未曾报道过的几何缺陷正在降低早期零件的强度。通过光学轮廓测定法对这些缺陷进行深入表征,然后消除根本原因,是获得这种高强度的关键。在这项工作中发现的一个有趣现象是,基体通过与中型部件相比,与中型部件更紧密接触而产生的增强的扩散途径,在陶瓷部件的烧结中发挥了作用。发现氧化铝和二氧化硅的杂质会对中尺度零件的烧结动力学产生不利影响,从而导致局部晶粒长大或晶粒长大(取决于烧结条件),微观结构(特别是晶粒尺寸)在确定强度方面所起的作用通过等温烧结实验确定了以表面粗糙度为特征的表面缺陷群体。已经发现,中尺度陶瓷的强度位于缺陷占主导的应力强度效应和霍尔-帕奇微结构效应之间的过渡区域。这证明了加工科学和微观结构的改进几乎平等地决定了基于颗粒的中尺度材料的强度。描述了用于将LM-RIF工艺的发展与手术器械的机械设计和优化相结合的分层方法。该方法使用嵌套的迭代循环来完善设计和制造过程,以创建和测试手术器械原型。介绍了这些原型以及LM-RIF工艺可能产生的一些独特形状。


  • 作者

    Antolino, Nicholas E.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Nanotechnology.Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 267 p.
  • 总页数 267
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词


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