Design and mechanical properties of compositionally complex alloys from twinning-induced towards bidirectional transformation-induced plasticity (MULTI-TRIP CCAs)

利用从头算-实验相结合的方法，成功地将相变诱发塑性（TRIP）效应引入到界面合金面心立方（FCC） crconimnfe基HEAs中。从从头计算中选择了三个五元HEAs，并进行了实验制备和研究。原子计算使我们能够解释不同的观察到的变形模式，并强调了在第一个项目中开发的用于开发机械高性能、低sfe、间隙合金CCAs的耦合从头算-实验方法的高效率。进一步的机会在于探索这种接近零的SFE HEAs的热力学和性质。在这些合金中，由于共存相的能量等效，在相同的体组织的相邻区域，基体可能同时具有六方封闭堆积（HCP）和FCC结构。相位能的相似性可以导致双向TRIP效应，其中fcc结构的基体部分在载荷作用下转变为HCP区域，反之亦然，这取决于局部的微机械应力。这种效应可以导致极端的微观结构细化到纳米级，并增强机械性能。MULTI-TRIP cca项目建立在第一阶段项目成功的基础上，旨在通过将双向TRIP效应引入间隙合金cca，进一步显著提高五组分cca的强度-延性组合。这将通过结合最先进的从头计算和多种实验技术来实现，如快速合金原型（RAP）、数字图像相关（DIC）辅助拉伸测试、电子背散射衍射（EBSD）、x射线衍射（XRD）、透射电子显微镜（TEM）和原子探针断层扫描（APT）。从头计算将用于筛选一个大的成分HEA/CCA相空间，以获得有前途的低sfe候选合金。连接量子力学计算和实验的关键量是广义sfe和HCP、FCC和DHCP相能。通过微调间隙C、N和h的浓度，可以制备出sfe接近于零的非等原子五元CoCrFeMnNi合金，每个主元素的浓度在5 ~ 35 at之间。%，少量间隙合金元素（C、N、H）含量较低（小于1.5 at）。%)。与项目第一阶段相关，MULTI-TRIP CCA探索了更大的成分相空间，包括Cr和Co的变化。从头算模拟将使我们能够识别有前途的合金、设计规则和物理解释。上述先进的实验技术将通过微观和纳米尺度的微观结构研究来证明新材料优越的力学性能，并揭示其潜在的机制。

The transformation induced plasticity (TRIP) effect has been successfully introduced into interstitially alloyed face centered cubic (FCC) CrCoNiMnFe-based HEAs utilizing a combined ab initio-experimental approach. Three quinary HEAs have been selected from ab initio calculations, experimentally prepared and investigated. The atomistic calculations allowed us to interpret the different observed deformation modes and highlight the high efficiency of the developed coupled ab initio-experimental approach developed within the first project for developing mechanically high-performing, low-SFE, interstitially alloyed CCAs. Further opportunities lie in the exploration of thermodynamics and properties of such near-zero SFE HEAs. In these alloys, the matrix could possibly assume both the hexagonal closed packed (HCP) and FCC structure, in adjacent regions of the same bulk microstructure, owing to the energetic equivalence of the coexisting phases. The similarity in phase energy can lead to a bidirectional TRIP effect, in which FCC-structured matrix portions transform under load into HCP regions and vice versa, depending on the local, micromechanical stresses. This effect can lead to an extreme microstructure refinement down to the nanometer regime and enhanced mechanical properties.The project MULTI-TRIP CCAs builds on the successful first project phase and aims at further significantly enhancing the strength-ductility combination of quinary CCAs by introducing the bidirectional TRIP effect into interstitially alloyed CCAs. This will be achieved by combining state-of-the-art ab initio calculations and multiple experimental techniques such as rapid alloy prototyping (RAP), digital image correlation (DIC) assisted tensile testing, electron backscatter diffraction (EBSD), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atom probe tomography (APT). Ab initio calculations will be used to screen a large compositional HEA/CCA phase space for promising low-SFE candidate alloys. Key quantities linking the quantum-mechanical calculations and experiment are, e.g., the generalized SFEs and HCP, FCC, and DHCP phase energies. Non-equiatomic quinary CoCrFeMnNi alloys with near-zero SFEs will be developed by fine-tuning the concentrations including interstitial C, N and H. Each principal element will have a concentration between 5 and 35 at. %, and the content of minor interstitial alloying elements (C, N, H) will be low (less than 1.5 at. %). In relation to the first project phase MULTI-TRIP CCA explores a larger compositional phase space including also variations of Cr and Co. The ab initio simulations will allow us to identify promising alloys, design rules and physical interpretations. The above-mentioned advanced experimental techniques will be utilized to demonstrate the superior mechanical properties of the new materials and reveal the underlying mechanisms via micro- and nanoscale microstructural investigations.