Effect of volume fraction of dispersed SiO₂ particles on intermediate-temperature embrittlement in Cu–SiO₂ polycrystals

Abstract

Several kinds of Cu polycrystals with dispersed SiO 2 particles of different volume fractions were tensile tested at high temperatures from 473 K to 1023 K. All of the alloys showed clear intermediate-temperature embrittlement (ITE). Although the temperature of minimum elongation was almost the same in all the alloys, temperature dependence of fracture strain depended strongly on the SiO 2 volume fraction: (1) At a fixed temperature, the fracture strain tended to first decrease with increase in SiO 2 volume fraction, showed minimum in an alloy with certain volume fraction, and increased again with increase in volume fraction.(2) With increase in SiO 2 volume fraction, the temperature range of ITE became narrower and sharper. These results were reasonably understood by considering the occurrence of stress concentration at grain-boundary particles induced by grain-boundary sliding (GBS) and occurrence of dynamic recrystallization and stress relaxation by Cu͞SiO 2 interfacial diffusion. 3100

Preferential Dynamic Nucleation at Triple Junction in Copper Tricrystal During High-Temperature Deformation

“…Numerous researches have been carried out about the roles of the grain boundary in mechanical behaviors at high temperatures, e.g. creep, 1,2) fracture strength, 3,4) fatigue 5) and so on. Sometimes, researches were carried out with usage of orientation controlled bicrystals to reveal clearly the effects of grain boundaries on the high-temperature mechanical behaviors.…”

Effects of Grain-Boundary Sliding and Plastic Deformation of Grains on the Formation of Grain-Boundary Cracks in a Double Cylindrical Bicrystal of a Cu-SiO<SUB>2</SUB> Alloy

“…This is understood since the occurrence of GBS is a major reason for intergranular brittle fracturing of polycrystalline materials, in particular, those which contain small grain-boundary particles. 7,8) However, formation of the grain-boundary cracks was preferential and no cracks were observed in the same specimen D2 at the other diagonal locations, about % =4 and 5=4, where similarly large GBS was observed. The large grain-boundary crack in specimen D3 shown in Fig.…”

“…The testing temperature of 800 K was selected since significant intermediate temperature embrittlement is expected to occur for Cu polycrystalline alloys containing small oxide particles. 7,8) Deformation of the specimens was interrupted at certain strains and microstructural observations of the specimens were made after the tensile tests. Figure 3 shows the nominal stress-plastic strain curves, the -" curves, of the Cu-SiO 2 bicrystal at 800 K under 2 Â 10 À4 s À1 .…”

“…The Cu-SiO 2 alloy was selected since brittle grain-boundary fractures are expected to occur in Cu alloys when they contain small grain-boundary particles. 7,8) Although deformation behavior at room temperature has been studied for a Cu double cylindrical bicrystal, 9) fracture behavior of the bicrystal at elevated temperatures has not been studied.…”

High temperature deformation and extended plasticity in Mg single crystals

“…In single crystals, the DRX behavior depends instead on orientation, with kink formation, DRX and twinning taking place when the crystal is oriented for multiple slip. In polycrystals, there is a loss of ductility when a metallic material is deformed under conditions where DRX is difficult, i.e., at intermediate temperatures [17]. However, the occurrence of DRX in Mg single crystals has the opposite effect, as shown above.…”