Observation and analysis of defect cluster production and interactions with dislocations

Microstructure of Neutron-irradiated Iron Before and After Tensile Deformation

High softening resistance, high strength at elevated temperature and high conductivity is important performances for the high voltage breaker and vacuum interrupter contact materials. A novel nano-Al 2 O 3 –Cu composite was fabricated for them by using a modified internal oxidation method. The microstructure was investigated by means of a scanning electron microscope and a transmission electron microscopy. The softening temperature, tensile strength at elevated temperature and electrical conductivity of the composite were also determined. The grain size of the Cu–0.5 vol.% Al 2 O 3 composite is very fine and the annealing temperature greatly affects its microstructure. The electric conductivity reaches 93% IACS and the softening temperature is about 800 °C, while the yield strength reaches 169 MPa and the ultimate tensile strength reaches 172 MPa at the testing temperature of 600 °C. The main contributions of nano-alumina particles is to strengthen the composite, not by Orowan strengthening, but due to the strong pinning effects on the grain boundaries and sub-grain boundaries with high dislocation density to prevent the nuclei formation of recrystallization.

Microstructure and properties at elevated temperature of a nano-Al2O3 particles dispersion-strengthened copper base composite

Irradiation of materials by energetic particles (e.g., electrons, ions and neutrons) is associated with very high internal power dissipation, which can drive the underlying nano- and microstructure far from normal equilibrium conditions. One of the most unusual responses in this connection is the ability of the material's nano- and microstructure to self-assemble in well-organized, two- and three-dimensional periodic arrangements. We review and assess here experimental evidence and theoretical models pertaining to the physical understanding of nano- and microstructure self-organization under irradiation conditions. Experimental observations on the formation of self-organized defect clusters, dislocation loops, voids and bubbles are presented and critically assessed. Implantation of metals with energetic helium results in remarkable self-assembled bubble super-lattices with wavelengths (super-lattice parameters) in the range of 5–8 nm. Ion and neutron irradiation produce a wide variety of self-assembled 3-D defect walls and void lattices, with wavelengths that can be tailored in the range of 10's to 100's of nanometers. Theoretical models aimed at explaining these observations are introduced, and a consistent description of many features is outlined. The primary focus of the most recent modeling efforts, which are based on stability theory and concepts of non-linear dynamics, is to determine criteria for the evolution and spatial symmetry of self-organized microstructures. The correspondence between this theoretical framework and experimental observations is also examined, highlighting areas of agreement and pointing out unresolved questions.

/pdf/theory-and-experiment-of-nanostructure-self-organization-in-24h99kruzw.pdf

Theory and experiment of nanostructure self-organization in irradiated materials

S. Chen

Papers

Brazing of vanadium and carbon-carbon composites to stainless steel for fusion reactor applications

Low activation braze joint of dispersion-strengthened copper

Braze joints of dispersion strengthened copper

Effect of alumina strengthening particles on brazed joints of GlidCop Al-15 copper alloy

Special Metallurgical Welding Considerations for Refractory Metals