Materials Development and Mechanical Properties of Single-Phase High Entropy Alloys

该项目的主要目标是研究具有fcc、bcc和hcp晶体结构的单相高熵合金(HEA)，重点是基本性质。作为面心立方固溶体的等原子CrMnFeCoNi、体心立方等原子TiZrNbHfTa和等原子YgdTbDyHo的基组分，将通过测定比热容和随后的温度积分来进行熵测量。这些测量将表明，与fcc、bcc和hcp HEA相比，热熵和构型熵对纯金属的影响是否不同。这里特别令人感兴趣的是Hcp YgdTbDyHo，因为稀土元素彼此非常相似。该项目将调查位错是否认为这些原子相同，从而导致没有净固溶体强化，或者机械性能是否也存在所谓的吉布斯悖论。作为机械强度的基本衡量标准的临界可分辨剪应力将被确定，并对所有三种HEA进行相互比较。在该项目中，将在拜罗伊特大学(UBT)和日立大学(FZJ)生产HEA合金样品。如果可能，样品将通过区熔法或布里奇曼铸造法制备成单晶。机械测试将使用专有设备对从低温到高温的微型样品进行。用超声共振光谱仪测量了小尺寸(4x5x6 mm^3)面心立方、体心立方和六方相HEA单晶样品的弹性性能随温度的变化，并用扫描和透射电子显微镜进行了微观结构分析和变形机制的研究。

The key objective of the project is to investigate single-phase high entropy alloys (HEA) with fcc, bcc and hcp crystal structures with focus on fundamental properties. As a base composition for fcc solid solutions equiatomic CrMnFeCoNi, for bcc equiatomic TiZrNbHfTa and for hcp equiatomic YgdTbDyHo are to be investigated.Entropy measurements will be carried out by determination of the specific heat capacity and subsequent integration over temperature. These measurements will indicate if thermal entropy in connection with configurational entropy have different influences for pure metals in comparison to fcc, bcc and hcp HEA. Of particular interest here is hcp YgdTbDyHo because the lanthanide elements are very similar to each other. The project will investigate whether dislocations consider these atoms identical hence resulting in no net solid solution strengthening or whether a so-called Gibbs paradox also exists for mechanical properties.The critical resolved shear stresses as basic measures of mechanical strength will be determined and compared to each other for all three mentioned HEAs. The impact of further elemental additions to these HEA base alloys onto the CRSS as well as the phenomenon of deformation localization will be addressed.Within the project, the HEA alloy samples will be produced at the University Bayreuth (UBT) and the Forschungszentrum Jülich (FZJ). If possible, samples will be prepared as single crystals by zone melting or Bridgman casting. Mechanical testing will be carried out with proprietary equipment on miniature specimens from cryogenic temperatures up to high temperatures. Elastic properties will be measured as a function of temperature on small (4x5x6 mm^3), single crystal fcc, bcc and hcp HEA samples by ultrasonic resonance spectroscopy.Microstructure analysis and investigation of deformation mechanisms are performed by scanning and transmission electron microscopy.