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），重点是基本性能。作为fcc固溶体的基本成分，等原子CrMnFeCoNi，bcc等原子TiZrNbHfTa和hcp等原子YgdTbDyHo将被研究。熵测量将通过确定比热容和随后的温度积分来进行。这些测量将表明，如果热熵与构型熵有不同的影响相比，fcc，bcc和hcp HEA纯金属。这里特别感兴趣的是hcp YgdTbDyHo，因为镧系元素彼此非常相似。该项目将研究位错是否认为这些原子是相同的，因此没有净固溶体强化，或者是否也存在所谓的吉布斯悖论的机械性能。临界分解剪切应力作为机械强度的基本措施将被确定，并相互比较所有三个提到的HEAs。在该项目中，将在拜罗伊特大学（UBT）和于利希研究中心（FZJ）生产HEA合金样品。如果可能，将通过区域熔化或Bridgman铸造将样品制备为单晶。将使用专有设备对微型试样进行从低温到高温的机械测试。采用超声波共振光谱法测量小尺寸（4 × 5 × 6 mm^3）、单晶fcc、bcc和hcp HEA样品的弹性性能随温度的变化，并采用扫描和透射电子显微镜进行微观结构分析和变形机制研究。

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.