TY - JOUR
T1 - Creep of magnesium strengthened with high volume fractions of yttria dispersoids
AU - Han, B. Q.
AU - Dunand, D. C.
N1 - Funding Information:
This work was supported by the National Science Foundation, under Grant No. DMR 9417636, with Dr B. McDonald as monitor.
PY - 2001/2/28
Y1 - 2001/2/28
N2 - Creep experiments were performed on dispersion-strengthened-cast magnesium (DSC-Mg), consisting of unalloyed magnesium with 1 μm grain size containing 30 vol.% of 0.33 μm yttria particles. Strain rates were measured for temperatures between 573 and 723 K at compressive stresses between 7 and 125 MPa. DSC-Mg exhibits outstanding creep strength as compared with other magnesium materials, but is less creep resistant than comparable DSC-Al and other dispersion-strengthened aluminum materials. Two separate creep regimes were observed in DSC-Mg, at low stresses (σ < 30 MPa), both the apparent stress exponent (napp ≈ 2) and the apparent activation energy (Qapp ≈ 48 kJ mol-1) are low, while at high stresses (σ > 34 MPa), these parameters are much higher (napp = 9 - 15 and Qapp = 230-325 kJ mol-1) and increase, respectively, with increasing temperature and stress. The low-stress regime can be explained by an existing model of grain-boundary sliding inhibited by dispersoids at grain-boundaries. The unexpectedly low activation energy (about half the activation energy of grain boundary diffusion in pure magnesium) is interpreted as interfacial diffusion at the Mg/Y2O3 interface. The high-stress regime can be described by dislocation creep with dispersion-strengthening from the interaction of the submicron particles with matrix dislocations. The origin of the threshold stress is discussed in the light of existing dislocation climb, detachment and pile-up models.
AB - Creep experiments were performed on dispersion-strengthened-cast magnesium (DSC-Mg), consisting of unalloyed magnesium with 1 μm grain size containing 30 vol.% of 0.33 μm yttria particles. Strain rates were measured for temperatures between 573 and 723 K at compressive stresses between 7 and 125 MPa. DSC-Mg exhibits outstanding creep strength as compared with other magnesium materials, but is less creep resistant than comparable DSC-Al and other dispersion-strengthened aluminum materials. Two separate creep regimes were observed in DSC-Mg, at low stresses (σ < 30 MPa), both the apparent stress exponent (napp ≈ 2) and the apparent activation energy (Qapp ≈ 48 kJ mol-1) are low, while at high stresses (σ > 34 MPa), these parameters are much higher (napp = 9 - 15 and Qapp = 230-325 kJ mol-1) and increase, respectively, with increasing temperature and stress. The low-stress regime can be explained by an existing model of grain-boundary sliding inhibited by dispersoids at grain-boundaries. The unexpectedly low activation energy (about half the activation energy of grain boundary diffusion in pure magnesium) is interpreted as interfacial diffusion at the Mg/Y2O3 interface. The high-stress regime can be described by dislocation creep with dispersion-strengthening from the interaction of the submicron particles with matrix dislocations. The origin of the threshold stress is discussed in the light of existing dislocation climb, detachment and pile-up models.
KW - Creep
KW - Magnesium
KW - Metal matrix composites
KW - Oxide-dispersion-strengthened materials
KW - Threshold stress
KW - Yttria
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U2 - 10.1016/S0921-5093(00)01781-0
DO - 10.1016/S0921-5093(00)01781-0
M3 - Article
AN - SCOPUS:0035961209
VL - 300
SP - 235
EP - 244
JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
SN - 0921-5093
IS - 1-2
ER -