Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA; GE Global Research, Niskayuna, NY 12309, USA.
Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA; School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA.
J Mech Behav Biomed Mater. 2019 Mar;91:99-108. doi: 10.1016/j.jmbbm.2018.12.001. Epub 2018 Dec 4.
Micro-surgical instruments are a new application for mesoscale ceramics formed using the lost mold-rapid infiltration forming (LM-RIF) process. Instrument strength and reliability are the foremost concerns for this sensitive application. It is hypothesized that increasing grain size can improve the damage tolerance of the parts associated with the transformation toughening in the 3Y-TZP material, while retaining high strength. In this work, mesoscale bend bars (314 × 22 × 18 µm) of 3Y-TZP fabricated using the LM-RIF process were heat treated at 1400 °C for 1 h, 8 h, or 16 h, respectively, to obtain samples with different grain sizes. Strength tests were performed under three-point bending and results were evaluated using Weibull statistics. Fractographic and confocal Raman spectroscopic analyses were carried out to interpret the data. Experimental findings showed that the characteristic strength decreased with increasing grain size contrary to the damage tolerance hypothesis. An Orowan-Petch model was recalled to correlate the strength with the flaw size to grain size ratio. At fine grain sizes the strength was controlled by the flaws introduced by the LM-RIF process, whereas at large grain sizes the strength become more grain size controlled. Although larger-grained samples did have a higher propensity to transform, and thus increase toughening, exaggerated grain growth in some of the specimens tested caused an additional flaw population which led to an overall lower strength. Finally, based on the experimental observations and fracture mechanics considerations, we believe that an upper bound of ∼2.5 GPa exists for the strength of mesoscale as-fabricated 3Y-TZP ceramic parts.
微外科器械是介观陶瓷的一种新应用，采用失模-快速浸渗成型（LM-RIF）工艺成型。对于这种敏感应用，仪器的强度和可靠性是首要关注点。据推测，增加晶粒尺寸可以提高与 3Y-TZP 材料相变增韧相关的部件的耐损伤性，同时保持高强度。在这项工作中，使用 LM-RIF 工艺制造的介观弯曲棒（314×22×18µm）分别在 1400°C 下热处理 1、8 或 16 小时，以获得具有不同晶粒尺寸的样品。在三点弯曲下进行强度测试，并使用威布尔统计数据进行评估。进行了断口形貌和共焦拉曼光谱分析，以解释数据。实验结果表明，特征强度随晶粒尺寸的增加而降低，这与耐损伤性假设相反。回忆起奥罗万-佩奇模型，将强度与缺陷尺寸与晶粒尺寸的比值相关联。在细晶粒尺寸下，强度受 LM-RIF 工艺引入的缺陷控制，而在大晶粒尺寸下，强度变得更受晶粒尺寸控制。尽管较大晶粒的样品确实有更高的转变倾向，从而提高了韧性，但在一些测试的样品中，晶粒过度生长导致了额外的缺陷群体，从而导致整体强度降低。最后，根据实验观察和断裂力学考虑，我们认为介观原始 3Y-TZP 陶瓷零件的强度存在约 2.5GPa 的上限。
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