Understanding Transformation Superplasticity, High Temperature Deformation and Manufacturing of Entropy Stabilized Oxides

陶瓷材料固有的脆性通常使它们在制造过程中难以形成，限制了它们不需要复杂形状的应用。最近发现的一类陶瓷，熵稳定氧化物（ESOs），表现出独特的可逆相变行为，通过热处理提供了对性能的重要控制，从而允许有效的方法将这些材料制造成复杂的形状而不会断裂或失效。该奖项支持基础研究，以探索转化超塑性的机制，并发现制造eso的新方法。这些材料有望成为超级电容器、电池阴极、催化剂和电解质，对美国工业和经济产生影响。该项目探索先进制造和材料科学与工程领域，通过教育、培训和推广活动，为本科生、研究生和K-12学生，特别是那些来自代表性不足的少数民族的学生，提供跨学科主题的机会。熵稳定氧化物（ESOs）是一种结构无序的陶瓷材料，其中多个阳离子随机填充在亚晶格位置。当在特定的温度窗内热处理时，eso表现出可逆的相变行为。这种相变表现为一种可控的相非均质性，对ESOs的微观结构具有前所未有的控制能力。这种戏剧性的转变可以用来提高高温变形时的延展性，通过转变超塑性和循环变形实现高效成形。相变超塑性允许超过100%的机械变形，这是由于共存相之间的不匹配引起的内部应变，这可能在热循环过程中积累。研究内容包括：1)不同粒径的ESO块状试样的合成与固结；2)热处理以达到所期望的相态（二次相的数量和组成）；3)高温变形和超塑性成形；4)组织与性能评价。实验与理论模型相结合，分析了晶粒尺寸、外加应力、压力、应变速率和温度对扩散的影响，进而分析了变形机制和超塑性。本研究建立了初始微观结构与变形行为之间的关系，从而促进了对eso变形机制的理解，以及它们使用锻造和挤压等技术进行超塑性成形的潜力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The inherent brittleness of ceramic materials often makes them difficult to form during manufacturing, limiting them to applications that do not require complex shapes. The recently discovered class of ceramics, entropy stabilized oxides (ESOs), exhibit a unique reversible phase transformation behavior that provides significant control over the properties via heat treatment, thus allowing for an efficient means of manufacturing these materials into complex shapes without fracture or failure. This award supports fundamental research to explore the mechanisms underlying transformation superplasticity and uncover new methods of manufacturing ESOs. These materials show promise as supercapacitors, battery cathodes, catalysts, and electrolytes, which impacts U.S. industry and economy. The project explores the fields of advanced manufacturing and materials science and engineering, with educational, training and outreach activities that provide exposure to interdisciplinary topics for undergraduate, graduate and K-12 students, especially those from underrepresented minorities.Entropy stabilized oxides (ESOs) are ceramic materials in which configurational disorder is compositionally engineered into a single phase with multiple cations randomly populating sublattice locations. ESOs display a reversible phase transformation behavior when heat treated within a particular temperature window. This phase transformation manifests as a controllable phase heterogeneity, giving unprecedented control over the microstructure of ESOs. Such a dramatic transformation could be leveraged to enhance ductility during high temperature deformation, allowing for efficient forming through transformation superplasticity and cyclic deformation. Transformation superplasticity allows for mechanical deformation of more than 100% due to the internal strain that arises from the mismatch between co-existing phases, which can accumulate during thermal cycling. The research involves the following tasks: 1) synthesis and consolidation of bulk ESO samples with different grain sizes; 2) heat treatment to achieve the desired phase state (amount and composition of the secondary phase(s)); 3) high temperature deformation and superplastic forming; and 4) evaluation of microstructure and properties. Experiments are complemented with theoretical modeling to analyze the influence of grain size, applied stress, pressure, strain rate and temperature on diffusion, and consequently deformation mechanisms and superplasticity. This research establishes a relationship between starting microstructure and deformation behavior, thus advancing the understanding of deformation mechanisms in ESOs and their potential for superplastic forming using techniques such as forging and extrusion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.