Quasi-static and Impact Nanoindentation to Study Deformation Mechanisms in Metals

纳米压痕是一种有吸引力的技术，它允许以一种通用和经济的方式研究局部机械特性。戈登实验室的两个MML压头代表了当前的技术水平。已经开发出热阶段和冷阶段，允许在高达~800℃和低至-170℃的条件下工作，可以进行冲击压痕，从而产生（瞬态）局部应变率，范围可达约10^4 s^-1。两种系统中的一种可以在真空或可控气氛下运行，大大减少了高温下试样氧化和金刚石尖端侵蚀的发生率，也消除了低温下的冷凝。此外，还开发了一套FEM建模程序，允许从纳米压痕数据推断准静态材料本构关系和特定样品的残余应力水平，具有良好的可靠性和准确性。拟议的工作将涉及这些能力的发展，特别是与冲击模式压痕有关的能力。这将需要增强当前的建模套件，并全面表征压头运动的动力学。这应该允许提取应变率灵敏度信息，超过应变率范围，传统的测试提出了严重的困难。这些技术将应用于“参考”材料，如纯铜，也适用于特别感兴趣的合金。其中包括（贫）铀，将由AWE提供。这种合金在相对较低的应变下可以表现出明显的超弹性变形，并且将开发用于提取表征这种行为的参数的方法。老化对这些合金的影响也将进行研究，这将有助于在压头阶段（真空室内）就地进行热处理的能力。AWE将资助一名博士生，该博士生将特别针对这些合金以及超弹性变形在其整体机械行为中的作用。

Nanoindentation is an attractive technique, allowing study of local mechanical characteristics in a versatile and cost-effective manner. The two MML indenters in the Gordon Laboratory represent the current state of the art. Hot and cold stages have been developed, allowing operation at up to ~800 C and down to -170 C. Impact indentation can be carried out so as to generate (transient) local strain rates ranging up to about 10^4 s^-1. One of the two systems can be operated in vacuum or under controlled atmosphere, greatly reducing the incidence of specimen oxidation and diamond tip erosion at high temperature, and also eliminating condensation at low temperature. Furthermore, a suite of FEM modelling routines has been developed, allowing quasi-static material constitutive relations, and residual stress levels in particular specimens, to be inferred from nanoindentation data, with good degrees of reliability and accuracy.The proposed work will involve development of these capabilities, particularly relating to impact mode indentation. This will require enhancement of the current modelling suite, and comprehensive characterisation of the dynamics of indenter motion. This should allow the extraction of strain rate sensitivity information, over ranges of strain rate for which conventional testing presents severe difficulties. These techniques will be applied to "reference" materials, such as pure copper, and also to alloys of particular interest. These include (depleted) uranium, which will be supplied by AWE. Such alloys can exhibit pronounced superelastic deformation at relatively low strains and methodology will be developed for the extraction of parameters characterising such behaviour. The effect of ageing on these alloys will also be investigated, which will be facilitated by the capacity for heat treatments to be carried out in situ on the indenter stage (inside the vacuum chamber). AWE will fund a PhD studentship, which will be oriented particularly towards these alloys and the role of superelastic deformation in their overall mechanical behaviour.