Understanding the Deformation Mechanism of Face-centered Cubic Metals from High Strain Rate Nanoindentation
Abstract
Title: Understanding the Deformation Mechanism of Face-centered Cubic Metals from High Strain Rate Nanoindentation (Proposal submitted to Dr. Daniel Cole, Mechanical Behavior of Materials.) High strain rate plastic deformation mechanisms in metals are of fundamental interest to researchers studying and modeling dynamic loading. At bulk scales, high-rate deformation (~10^3 s^-1 strain rate) is usually studied by Kolsky bar testing. However, such studies are experimentally very demanding. In contrast, nanoindentation is a high-throughput technique that can be used to quantify and map local mechanical properties and has recently been adapted for high strain rate testing (> 10^4 s^-1). Since the high strain rate nanoindentation has only recently become available, the attendant mechanical behavior of materials remains largely unexplored. The overarching goal of the project is to understand the deformation mechanisms and microstructural evolution in face-centered cubic (FCC) metals indented under extreme rates (>10^4 s^-1) using high strain rate nanoindentation. The underpinning hypothesis is that higher strain rate nanoindentation leads to higher hardness values, which can be explained by the refined dislocation cell (or sub-grain) structure and high dislocation density within cell (or subgrain) interior in FCC metals. To achieve this goal, the following scientific objectives have been established: 1) to identify the effect of nanoindentation strain rate on hardness values, 2) to understand the effect of nanoindentation strain rate on dislocation activities, which is manifested by sub-grain boundary and free-standing dislocation characteristics, and 3) to establish the relationship between hardness strain rate sensitivity and dislocation-level microstructural information. The [001] single-crystal pure Ni is selected as the model system. Three research tasks will be undertaken: 1) nanoindentation testing at both low and high strain rates to measure hardness as a function of strain rate, 2) sub-grain characterization of the deformed volumes below the hardness impressions at both low and high strain rates, and 3) dislocation structure characterization in the deformed volumes below the hardness impressions at both low and high strain rates. The new knowledge gleaned from the high-rate responses and the resultant microstructure of the model system will provide direct experimental evidence correlating strain rate, mechanical properties, and deformation mechanisms in FCC metal crystals. The results will also serve as a benchmark for future studies on low stacking fault energy (SFE) FCC metals, body-centered cubic, and hexagonal closed-packed metals, where the SFE, Peierls barrier and twinning also play critical roles in accommodating plastic deformation. Moreover, the proposed effort enables the education and training opportunity for 1 Ph.D. student for 9 months in the areas of mechanical behavior of materials, nanoindentation, and electron microscopy.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 26, 2023
- Source ID
- W911NF2310119
Entities
People
- Kelvin Xie
Organizations
- Army Contracting Command
- Texas Engineering Experiment Station
- United States Army