Influence of ultrasound on the strain hardening behaviour of metallic materials

超声波被用来改善和优化许多制造过程的结果。目前的超声波应用通常是基于Blaha和Langenecker在20世纪60年代所做的工作的结果。他们表明，如果在拉伸试验中叠加超声波，金属材料的流动应力可以显著降低。此外，超声波在一些材料中的应用会导致暂时或永久硬化。从材料科学的角度来看，这种所谓的声学软化和硬化的原因仍然不完全清楚。虽然有几个出版物涉及声学软化并试图解释其基本机制，但只有少数几个出版物涉及声学硬化。在所有这些工作中，主要报道了六方(锌)或面心立方(铝)金属的声软化和硬化，尽管许多技术应用主要涉及超声支持的钢的制造过程。在当前的建议中，应进行系统的研究，以澄清铁素体、体心立方和奥氏体面心立方钢首次发生声软化和硬化的情况。因此，必须建立一个实验装置，以便在经典压缩测试过程中，在限定的时间内在限定的时刻叠加超声波脉冲。这些实验将对上述钢进行，以分析初始材料状态的变化，即初始位错密度的变化，以及超声脉冲功率和持续时间的变化对声学软化和硬化的影响。因此，必须在超声脉冲期间和之后测量机械材料的响应。此外，显微组织的变化必须用光学显微镜、电子显微镜和局部压痕实验来表征，最终要得到金属物理解释才能解释超声诱导的软化和硬化现象。这一声学效应的阐明是本项目的主要目标，并计划为声学软化和硬化在其他金属材料中的应用奠定基础。

Ultrasound is used to improve and optimize the results of many manufacturing processes. Current ultrasound applications are often based on the results of work done by Blaha and Langenecker in the 1960s. They showed that the flow stress of metallic materials can be reduced significantly if ultrasound is superimposed during a tensile test. Additionally, the application of ultrasound can in some materials lead to temporary or permanent hardening.The reason for this so-called acoustic softening and hardening is still not completely understood from a materials science point of view. While there are several publications dealing with acoustic softening and attempting to explain the underlying mechanisms there are just a few publications dealing with acoustic hardening. In all those works acoustic softening and hardening are reported mainly for hexagonal (zinc) or face-centred cubic (aluminium) metals, although many technical applications deal mostly with the ultrasonic supported manufacturing processes of steels.Within the current proposal systematic investigations shall be carried out to clarify the circumstances, at which acoustic softening and hardening occurs in ferritic, body-centred cubic and austenitic, face-centred cubic steels, for the first time. Therefore, an experimental setup has to be built up to superimpose ultrasonic pulses at a defined moment for a restricted time during a classical compression test. These experiments will be carried out with the above mentioned steels to analyse how variations of the initial materials state, namely the initial dislocation density, and variations of the power and the duration of the ultrasonic pulses will influence the acoustic softening and hardening. Thereby, the mechanical materials response has to be measured during and after the ultrasonic pulses. In addition, the microstructural changes have to be characterised by light optical microscopy, electron microscopy, and by local indentation experiments.It is envisaged to finally derive a metal physical explanation has to be derived to explain the ultrasonic induced softening and hardening phenomena. This clarification of the acoustic effect is the main goal of the project and is planned to serve as basis for the application of the acoustic softening and hardening also in other metallic materials.