The creep behavior of Al2O3.SiO2 fiber reinforced ZL109 composites has been investigated at four temperatures ranging from 553 to 623 K. The results show high stress exponent and high apparent creep activation energy....The creep behavior of Al2O3.SiO2 fiber reinforced ZL109 composites has been investigated at four temperatures ranging from 553 to 623 K. The results show high stress exponent and high apparent creep activation energy. A good correlation between the normalized creep rate and normalized effective stress means that the true stress exponent of minimum creep strain rate of the composite is very close to 5, and the minimum creep strain rate is matrix lattice diffusion controlled. The threshold stress decreases with increasing temperature linearly and disappears at a temperature close to 623 K. It is assumed that the long range internal back stresses generated in creep reduce the load transfer to fibers and the interaction between dislocations and strengthening precipitates decreases at high temperature. At a high temperature where the long range internal back stresses is very close to the applied stress, the threshold stress disappears.展开更多
Cyclic symmetrical tension-compression fatigue tests in an axial plastic strain range of 2.0×10-4 to 1.5×10-3 were performed on three copper tetracrystal specimens containing two grain boundary triple lines ...Cyclic symmetrical tension-compression fatigue tests in an axial plastic strain range of 2.0×10-4 to 1.5×10-3 were performed on three copper tetracrystal specimens containing two grain boundary triple lines as well as one copper tricrystal specimen employing a multiple step method. Experimental results show that the strengthening effect of triple junction (TJ) on axial saturation stress increased with increasing plastic strain amplitude. The strengthening effects owe much to the strain incompatibilities at TJ. The cyclic stress-strain (CSS) curves of tetracrystals are higher than that of tricrystal. At low strain amplitude, deformation at TJ is smaller than that near grain boundary (GB), which results in that the width of TJ effect zone is smaller than that near GB. Whether GB split or not is associated with the angle between GB and loading axis, activation of slip systems beside GB and the accommodation and annihilation of residual dislocations on GB planes.展开更多
文摘The creep behavior of Al2O3.SiO2 fiber reinforced ZL109 composites has been investigated at four temperatures ranging from 553 to 623 K. The results show high stress exponent and high apparent creep activation energy. A good correlation between the normalized creep rate and normalized effective stress means that the true stress exponent of minimum creep strain rate of the composite is very close to 5, and the minimum creep strain rate is matrix lattice diffusion controlled. The threshold stress decreases with increasing temperature linearly and disappears at a temperature close to 623 K. It is assumed that the long range internal back stresses generated in creep reduce the load transfer to fibers and the interaction between dislocations and strengthening precipitates decreases at high temperature. At a high temperature where the long range internal back stresses is very close to the applied stress, the threshold stress disappears.
文摘Cyclic symmetrical tension-compression fatigue tests in an axial plastic strain range of 2.0×10-4 to 1.5×10-3 were performed on three copper tetracrystal specimens containing two grain boundary triple lines as well as one copper tricrystal specimen employing a multiple step method. Experimental results show that the strengthening effect of triple junction (TJ) on axial saturation stress increased with increasing plastic strain amplitude. The strengthening effects owe much to the strain incompatibilities at TJ. The cyclic stress-strain (CSS) curves of tetracrystals are higher than that of tricrystal. At low strain amplitude, deformation at TJ is smaller than that near grain boundary (GB), which results in that the width of TJ effect zone is smaller than that near GB. Whether GB split or not is associated with the angle between GB and loading axis, activation of slip systems beside GB and the accommodation and annihilation of residual dislocations on GB planes.
