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成形，从而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（ESO），表现出独特的可逆相变行为，通过热处理提供了对性能的显着控制，从而允许将这些材料制造成复杂形状而不断裂或失效的有效手段。该奖项支持基础研究，以探索相变超塑性的潜在机制，并发现制造ESO的新方法。这些材料显示出作为超级电容器、电池阴极、催化剂和电解质的前景，这将影响美国的工业和经济。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学生提供跨学科主题，特别是那些来自代表性不足的少数民族的人。是陶瓷材料，其中构型无序在组成上被设计成具有多个阳离子随机填充的单相子晶格位置。当在特定的温度窗口内热处理时，ESO显示可逆的相变行为。这种相变表现为可控的相不均匀性，对ESO的微观结构提供了前所未有的控制。这种剧烈的转变可以用来增强高温变形期间的延展性，从而允许通过转变超塑性和循环变形进行有效的成形。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失配引起的内部应变，其可以在热循环期间累积。该研究涉及以下任务：1）具有不同晶粒尺寸的块状ESO样品的合成和固结; 2）热处理以实现所需的相状态（第二相的量和组成）; 3）高温变形和超塑性成形;以及4）微观结构和性能的评估。实验与理论建模相结合，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，从而分析了变形机制和超塑性。这项研究建立了初始微观结构和变形行为之间的关系，从而推进了对ESO变形机制的理解，以及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NSF的法定使命，并通过使用基金会的智力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.