研究了蠕变温度与蠕变应力载荷对SiCp/Al复合材料高温蠕变行为的影响,分析了该复合材料的蠕变断裂机制,并计算得出了材料的应力指数与激活能。结果表明:蠕变速率随蠕变应力荷载的增大和蠕变温度的升高而增大,应力指数与变形激活能分别为...研究了蠕变温度与蠕变应力载荷对SiCp/Al复合材料高温蠕变行为的影响,分析了该复合材料的蠕变断裂机制,并计算得出了材料的应力指数与激活能。结果表明:蠕变速率随蠕变应力荷载的增大和蠕变温度的升高而增大,应力指数与变形激活能分别为n=9.8和Q=182 k J/mol。该复合材料的蠕变断裂机制为韧性断裂。通过对比得出,SiCp/Al复合材料的抗高温蠕变性能明显优于基体材料。展开更多
The empirically reported values of the critical current density (j<sub>c</sub>) of Bi-2212 as 2.4 × 10<sup>5</sup> (j<sub>c</sub><sub>1</sub>;Sample 1) and 1.0 ...The empirically reported values of the critical current density (j<sub>c</sub>) of Bi-2212 as 2.4 × 10<sup>5</sup> (j<sub>c</sub><sub>1</sub>;Sample 1) and 1.0 × 10<sup>6</sup> A/cm<sup>2</sup> (j<sub>c</sub><sub>2</sub>;Sample 2) are intriguing because both of them correspond to the same values of the temperature T = 4.2 K and the applied magnetic field H = 12 × 10<sup>4</sup> G. This difference is conventionally attributed to such factors—not all of which are quantifiable—as the geometry, dimensions and the nature of dopants and the manners of preparation of the samples which cause their granular structures, grain boundaries, alignment of the grains and so on to differ. Based on the premise that the chemical potential μ subsumes most of these features, given herein is a novel explanation of the said results in terms of the values of μ of the two samples. This paper revisits the problem that was originally addressed in [Malik G.P., Varma V.S. (2020) WJCMP, 10, 53-70] in the more accurate framework of a subsequent paper [Malik G.P., Varma V.S. (2021) JSNM, 34, 1551-1561]. Besides, it distinguishes between the contributions of the electro-electron (e-e) and the hole-hole (h-h) pairs to j<sub>c</sub>—a feature to which no heed was paid earlier. The essence of our findings is that the j<sub>c</sub>s of the two samples differ because they are characterized by different values of the primary variables μ<sub>i</sub><sub> </sub>and <img src="Edit_e1b831e9-dc51-4c3b-bd84-fa905e3e62b5.png" alt="" />, where <img src="Edit_1f775a80-30ab-447d-861f-afb4ba8fba6a.png" alt="" /> is the effective mass of a charge-carrier and m<sub>e</sub><sub> </sub>is the free-electron mass and i = 1 and 2 denote Sample 1 and Sample 2, respectively. In the scenario of the charge-carriers being predominantly h-h pairs, the values of these parameters are estimated to be: μ<sub>1</sub> ≈ 12.3 meV, η<sub>1</sub> ≈ 0.58;μ<sub>2</sub> ≈ 22.7 meV, η<sub>2</sub> ≈ 0.94. Following from these and similar estimates when the charge-carriers are e-e pairs, given below for each sample are the detailed results for the values of the secondary variables viz. the number density of the charge-carriers and their critical velocity, the number of occupied Landau levels and the magnetic interaction parameter.展开更多
文摘研究了蠕变温度与蠕变应力载荷对SiCp/Al复合材料高温蠕变行为的影响,分析了该复合材料的蠕变断裂机制,并计算得出了材料的应力指数与激活能。结果表明:蠕变速率随蠕变应力荷载的增大和蠕变温度的升高而增大,应力指数与变形激活能分别为n=9.8和Q=182 k J/mol。该复合材料的蠕变断裂机制为韧性断裂。通过对比得出,SiCp/Al复合材料的抗高温蠕变性能明显优于基体材料。
文摘The empirically reported values of the critical current density (j<sub>c</sub>) of Bi-2212 as 2.4 × 10<sup>5</sup> (j<sub>c</sub><sub>1</sub>;Sample 1) and 1.0 × 10<sup>6</sup> A/cm<sup>2</sup> (j<sub>c</sub><sub>2</sub>;Sample 2) are intriguing because both of them correspond to the same values of the temperature T = 4.2 K and the applied magnetic field H = 12 × 10<sup>4</sup> G. This difference is conventionally attributed to such factors—not all of which are quantifiable—as the geometry, dimensions and the nature of dopants and the manners of preparation of the samples which cause their granular structures, grain boundaries, alignment of the grains and so on to differ. Based on the premise that the chemical potential μ subsumes most of these features, given herein is a novel explanation of the said results in terms of the values of μ of the two samples. This paper revisits the problem that was originally addressed in [Malik G.P., Varma V.S. (2020) WJCMP, 10, 53-70] in the more accurate framework of a subsequent paper [Malik G.P., Varma V.S. (2021) JSNM, 34, 1551-1561]. Besides, it distinguishes between the contributions of the electro-electron (e-e) and the hole-hole (h-h) pairs to j<sub>c</sub>—a feature to which no heed was paid earlier. The essence of our findings is that the j<sub>c</sub>s of the two samples differ because they are characterized by different values of the primary variables μ<sub>i</sub><sub> </sub>and <img src="Edit_e1b831e9-dc51-4c3b-bd84-fa905e3e62b5.png" alt="" />, where <img src="Edit_1f775a80-30ab-447d-861f-afb4ba8fba6a.png" alt="" /> is the effective mass of a charge-carrier and m<sub>e</sub><sub> </sub>is the free-electron mass and i = 1 and 2 denote Sample 1 and Sample 2, respectively. In the scenario of the charge-carriers being predominantly h-h pairs, the values of these parameters are estimated to be: μ<sub>1</sub> ≈ 12.3 meV, η<sub>1</sub> ≈ 0.58;μ<sub>2</sub> ≈ 22.7 meV, η<sub>2</sub> ≈ 0.94. Following from these and similar estimates when the charge-carriers are e-e pairs, given below for each sample are the detailed results for the values of the secondary variables viz. the number density of the charge-carriers and their critical velocity, the number of occupied Landau levels and the magnetic interaction parameter.
