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Tensile and fatigue fracture of nanometric alumina reinforced copper with bimodal grain size distribution

Simchi, H ; Sharif University of Technology | 2009

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  1. Type of Document: Article
  2. DOI: 10.1016/j.msea.2009.01.037
  3. Publisher: 2009
  4. Abstract:
  5. Alumina dispersion-strengthened copper was produced by an internal oxidation process and hot powder extrusion method. The microstructure of the composite consisted of fine-grained region with an average grain size of 1.1 ± 0.1 μm, coarse-grained region with an average grain size of 5.6 ± 0.1 μm, nanometric alumina particles (γ-type) with an average diameter of 30 nm, and coarse alumina particles (350 nm) at the boundaries of the large grains. The tensile and fatigue fracture of the composite was studied in the extruded condition and after 11% cold working. The low cycle fatigue behavior was examined in strain control mode (ε = 0.5%) under fully reverse tension-compression cycle at 1 Hz up to 1000 cycles. High cycle fatigue was conducted using rotate-bending test up to 107 cycles. To reveal the role of alumina particles and the bimodal grain size structure, the tensile and fatigue fracture of extruded copper with normal grain structure was examined. It is shown that: (1) the strength and hardness of the nanocomposite are about three folders of the magnitude of the unreinforced copper; (2) fatigue strength of the nanocomposite at 107 cycles is about 40% higher than that of the copper; (3) both extruded copper and the nanocomposite exhibit cyclic hardening during the early stages of low cycle fatigue test which eventually approaches to a saturation stress; (4) dimple-type fracture is realized on the fracture surface of the tensile tests where dimple size decreases in the presence of the alumina particles; (5) the fatigue fracture mechanism is locally ductile deformation, microscopic void formation and coalescence. © 2009 Elsevier B.V. All rights reserved
  6. Keywords:
  7. Fracture ; Mechanical properties ; Nanocomposite ; Aluminum ; Coalescence ; Cold working ; Copper ; Cracks ; Fatigue of materials ; Fatigue testing ; Grain size and shape ; Internal oxidation ; Tensile strength ; Tensile testing ; Alumina dispersions ; Alumina particles ; Average diameters ; Average grain sizes ; Bimodal grain-size distributions ; Bimodal grains ; Coarse-grained ; Cu-Al2O3 ; Cyclic hardenings ; Ductile deformations ; Fatigue fracture mechanisms ; Fatigue fractures ; Fatigue strengths ; Fracture surfaces ; Grain structures ; High cycle fatigues ; Large grains ; Low cycle fatigue behaviors ; Low-cycle fatigue tests ; Microscopic voids ; Nanometric aluminas ; Powder extrusions ; Saturation stress ; Tensile tests ; Tension compressions ; Ductile fracture
  8. Source: Materials Science and Engineering A ; Volume 507, Issue 1-2 , 2009 , Pages 200-206 ; 09215093 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/abs/pii/S0921509309000598