Materials World Network: Annealing Twin Formation for Grain Boundary Engineering

材料世界网络：用于晶界工程的退火孪晶形成

• 批准号: 1107986
• 负责人: Anthony Rollett
• 金额: $ 39万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1107986&HistoricalAwards=false
• 关键词: Materials; World; Network; Annealing; Twin

A team of investigators from the Materials Science & Engineering Department at Carnegie Mellon University (CMU) and the Centre for Material Forming (CEMEF) at the Paris School of Mines in Sophia Antipolis, France, examines the mechanisms of annealing twin formation that enable Grain Boundary Engineering (GBE) of materials to be accomplished. GBE is being applied increasingly as a process that seeks to improve a wide range of properties such as corrosion resistance and fatigue life through control of the grain boundary content of the material. GBE typically involves repeated cycles of deformation and annealing but little research has been done on how these steps result in optimized microstructures. This research focuses on detailed characterization of the early stages of the recrystallization process as a function of initial grain size, annealing temperature, particle content and prior strain level in order to determine the mechanisms that give rise to high fractions of desirable boundaries but most especially the break-up of the network of general high angle boundaries by annealing twins. There is also good evidence that the desired increases in the twin fraction are easiest to obtain at low to moderate strains, which is strongly associated with the Strain Induced Boundary Migration (SIBM) mechanism. This research offers the opportunity to test the hypothesis that the GBE process depends on a combination of SIBM with twinning, and that the spatial and textural distributions of the locations where it takes place are key to understanding the process. CMU has the capability to zoom in on particular regions of interest and characterize them with in-situ serial sectioning by using a dual-beam FIB-SEM equipment. CMU will also partner with Integran USA to investigate microstructural evolution in both nanocrystalline nickel and pure Ni. The CEMEF group, supported by the French National Research Agency (ANR), has hot stage microscopy and advanced simulation tools for the entire deformation plus annealing process. Key new information to be gained includes data on twin formation during annealing and the topology of grain boundary networks, as opposed to only measuring fractions of "special boundaries".The hypothesis-based approach addresses the underlying mechanisms of twin formation that enable GBE to be accomplished. Most work so far has focused on before-and-after characterization, which has optimized properties but offers no understanding or control of the GBE process. The hypothesis, if verified, will also explain why large deformations do not promote GBE because other recrystallization mechanisms arise, such as abnormal coarsening of sub-grain networks. Successful delineation of the key mechanisms for GBE has the potential to expand the range of application of the process. Several parts of the industrial sector in the US make use of superalloys and will therefore be likely to be interested in the outcome of the work, such as Integran, Pratt & Whitney, and General Electric.

来自卡内基梅隆大学 (CMU) 材料科学与工程系和法国索菲亚安提波利斯巴黎矿业学院材料成型中心 (CEMEF) 的一组研究人员正在研究使晶界形成的退火孪晶形成机制要完成的材料工程（GBE）。 GBE 作为一种工艺得到越来越多的应用，旨在通过控制材料的晶界含量来提高各种性能，例如耐腐蚀性和疲劳寿命。 GBE 通常涉及变形和退火的重复循环，但关于这些步骤如何产生优化的微观结构的研究很少。这项研究的重点是再结晶过程的早期阶段作为初始晶粒尺寸、退火温度、颗粒含量和先前应变水平的函数的详细表征，以确定产生高比例理想晶界的机制，但最特别的是通过退火孪晶破坏一般高角度边界网络。还有充分的证据表明，在低至中等应变下最容易获得孪晶分数所需的增加，这与应变诱导边界迁移 (SIBM) 机制密切相关。这项研究提供了检验以下假设的机会：GBE 过程取决于 SIBM 与孪生的结合，并且其发生位置的空间和纹理分布是理解该过程的关键。 CMU 能够放大特定的感兴趣区域，并使用双束 FIB-SEM 设备通过原位连续切片来表征它们。卡耐基梅隆大学还将与 Integran USA 合作，研究纳米晶镍和纯镍的微观结构演变。 CEMEF 小组在法国国家研究机构 (ANR) 的支持下，拥有用于整个变形加退火过程的热台显微镜和先进的模拟工具。获得的关键新信息包括退火过程中孪晶形成的数据以及晶界网络的拓扑结构，而不是仅测量“特殊边界”的一部分。基于假设的方法解决了孪晶形成的基本机制，使GBE能够被完成了。迄今为止，大多数工作都集中在前后表征上，其具有优化的属性，但没有提供对 GBE 过程的理解或控制。如果这一假设得到验证，它还将解释为什么大变形不会促进GBE，因为会出现其他再结晶机制，例如亚晶网络的异常粗化。成功描述 GBE 的关键机制有可能扩大该过程的应用范围。美国工业部门的多个部门都使用高温合金，因此可能会对这项工作的成果感兴趣，例如 Integran、普惠公司和通用电气。