The correlation of chemical structure, crystalline morphology, and space charge distribution under a dc electrical field was investigated with three kinds of poly(propylene) (PP) with a different chemical structure, that is, homogeneous PP and block copolymer and random copolymer of PP. The space charge distribution of the samples was prominently affected by their chemical sequence structure and crystalline microstructure. Among samples of different PPs, all isothermally crystallized at 140°C, the sample of random coPP represents the most well proportional space charge distribution and the smallest number of space charges. The effect of thermal history on the space charge distribution was also investigated by the samples of block coPP. The sample thermally treated at 50°C clearly represents a better proportional distribution than that at higher temperature of 140 and 100°C. Subsequent experiments indicate that the better proportional distribution attributes to imperfect and fine sperulites with the fine distribution of the "amorphous" region. The imperfect and fine sperulites originate from the random incorporation of ethylene segments or units into PP chains or from the low annealing temperature, and play an important role in the formation of shallow traps and transportation of space charges.

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An Fe-34.5Mn-0.04C steel has been processed by cold rolling and annealing to prepare samples with a lamellar structure, a recrystallized grain structure and a composite structure of layers of recovered and recrystallized structures. For the recrystallized grain structure and the lamellar structure, the flow stress has been analyzed by applying Hall-Petch formulations. For the composite structure, the rule of mixture has been applied to calculate the flow stress, revealing an extra strengthening from a constraint effect. An excellent combination of strength and ductility has been found in a composite with 10% hard lamellae in a recrystallized grain structure.

At low temperatures most metals show reduced ductility and impact toughness. Here, we report a compositionally lean, fine-grained Fe-30Mn-0.11C austenitic steel that breaks this rule, exhibiting an increase in strength, elongation and Charpy impact toughness with decreasing temperature. A Charpy impact energy of 453 J is achieved at liquid nitrogen temperatures, which is about four to five times that of conventional cryogenic austenitic steels. The high toughness is attributed to manganese and carbon austenite stabilizing elements, coupled with a reduction in grain size to the near-micrometer scale. Under these conditions dislocation slip and deformation twinning are the main deformation mechanisms, while embrittlement by α′- and ε-martensite transformations are inhibited. This reduces local stress and strain concentration, thereby retarding crack nucleation and prolonging work-hardening. The alloy is low-cost and can be processed by conventional production processes, making it suitable for low-temperature applications in industry.

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