Efficient Determination of Intermediate Temperature Phase Diagrams Using Dual-Anneal Diffusion Multiples

技术摘要大多数合金在使用中的中温(铁基和镍基合金约为600°C至900°C)的实验相图数据在世界范围内严重短缺。这一不足导致热力学数据存在很大的不确定性，因此无法准确预测在此温度范围内材料加工和使用过程中的相稳定性和相变驱动力。这项研究将开发一种新的双退火扩散-多重方法，用于高效测定中温相图，并将该方法应用于Fe-Co-Cr-Mo-Ni系。扩散倍数的高温(例如1200℃)退火首先将产生广泛的固溶体和中间化合物的成分区域，这相当于同时制造许多合金成分。随后的中温(例如600℃)退火将诱导析出和形成平衡相，这相当于在相图测定所需的温度下对许多单独的合金进行热处理。这里将要开发的有效方法将对材料的设计和长期稳定性预测产生影响。这种方法的广泛应用将产生大量的相平衡数据，以便准确地评估吉布斯能量函数，从而能够在中温下进行高保真的热力学预测。高保真预测可以减少或消除目前需要的长期热暴露实验，以测试合金形成有害相的倾向或促进稳定的析出相以强化合金，从而减少合金设计迭代，提高新合金设计的速度。这项研究还将提供几个三元系的中温等温截面，这些三元系对沉淀强化不锈钢和镍基高温合金的发展非常重要。非技术性总结中温(钢和镍基合金约为600℃至900℃)相图在全球范围内严重短缺。由于缺乏相图(材料科学家设计合金时使用的相图)，导致无法准确预测在大多数合金使用的这一关键温度范围内的合金行为。这项研究将开发一种新的双退火扩散-多重方法，用于高效测定中温相图。有效的方法将对合金的设计和长期稳定性预测产生影响。这种方法的广泛应用将产生大量的相图，使高保真预测成为可能，这些相图可以用来消除现在需要进行的长期热暴露实验，以测试合金形成有害相的倾向，从而加快新合金设计的速度。高性能合金的及时设计和插入对美国工业的全球竞争力至关重要。这一NSF计划还将用先进的实验工具教育下一代材料科学家，使他们能够更好地为行业服务。

TECHNICAL SUMMARYThere is a significant worldwide shortage of experimental phase diagram data at intermediate temperatures (around 600ºC to 900ºC for Fe-based and Ni-based alloys) where most alloys are used in service. This shortage results in large uncertainty of thermodynamic data and thus inability to accurately predict phase stability and driving force for phase transformations during materials processing and usage at this temperature range. The proposed study will develop a novel dual-anneal diffusion-multiple approach for high-efficiency determination of intermediate temperature phase diagrams and will apply the methodology to the Fe-Co-Cr-Mo-Ni system. A high-temperature (e.g. 1200 ºC) anneal of diffusion multiples will first create wide composition regions of solid solutions and intermediate compounds, which is equivalent to making many alloy compositions simultaneously. A subsequent intermediate temperature (e.g. 600 ºC) anneal will induce precipitation and formation of equilibrium phases, which is equivalent to the heat treatment of many individual alloys at a temperature of interest for phase diagram determination. The effective methodology to be developed here will have an impact on the design and long-term stability prediction of materials. Wide application of this method will lead to large amounts of phase equilibrium data for accurate assessment of the Gibbs energy functions to enable high-fidelity thermodynamic predictions at intermediate temperatures. High-fidelity prediction can reduce or eliminate the long-term thermal exposure experiments that are required now to test an alloy's propensity to detrimental phase formation or to promote stable precipitate phases to strengthen alloys, thus reducing the alloy design iterations and increasing the speed of new alloy design. The proposed study will also provide intermediate temperature isothermal sections of several ternary systems that are very important for the development of precipitation-strengthened stainless steels and Ni-based superalloys. NON-TECHNICAL SUMMARYThere is a significant worldwide shortage of phase diagrams at intermediate temperatures (around 600ºC to 900ºC for steels and Ni-based alloys). This shortage of phase diagrams (which are maps for materials scientists to design alloys) leads to inability to accurately predict alloy behaviors at this critical temperature range where most alloys are used in service. The proposed study will develop a novel dual-anneal diffusion-multiple approach for high-efficiency determination of intermediate temperature phase diagrams. The effective methodology will have an impact on the design and long-term stability prediction of alloys. Wide application of this method will lead to large amounts of phase diagrams to enable high-fidelity prediction which can be used to eliminate the long-term thermal exposure experiments that are required now to test alloys' propensity to detrimental phase formation, thus increasing the speed of new alloy design. The timely design and insertion of high-performance alloys are critical to the global competitiveness of U.S. industries. This NSF program will also educate next-generation materials scientists with the advanced experimental tools so they can better serve the industry.