摘要:

Frank sessile dislocations surrounding a region of stacking fault are shown to be nucleation sites for &ggr;′ phase precipitation in aluminum‐silver alloys. The segregation of silver to these regions is explained in terms of extinction fringe contrast. Direct evidence for ``pipe'' diffusion along dislocations to a grain boundary is also presented.

ISSN:0021-8979    

DOI:10.1063/1.1728432

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The modulus and internal friction of polytetrafluoroethylene were measured with longitudinal waves at a frequency of 12 Mc between 248° and 548°K and the fluorine magnetic resonance was studied between 77° and 375°K. The samples covered a wide range of crystallinities and included a specimen which had not been sintered (as polymerized material which had not been heated above the melting temperature). The results resolve discrepancies which existed in the literature and introduce new information about the relaxations and first‐order transitions in polytetrafluoroethylene. In the ultrasonic work it is shown that the ``19°C'' and ``30°C'' diffuse first‐order crystalline transitions can be studied independently of the crystalline relaxation which occurs at 418°K at 12 Mc. The ``19°C'' transition is not observed but the ``30°C'' transition causes an appreciable decrease in the modulus. X‐ray data show that this accompanies a decrease in the rotational order of the lattice. This transition is found to occur over a wider temperature range in unsintered polymer (possibly because of a distribution of the lengths of the molecular segments in the ordered regions). An NMR absorption line from the crystalline regions is resolved and its narrowing above 280°K is attributed to rotational motions associated with the first‐order transitions. Comparison with published data shows that the narrowing occurs over a wider temperature range in unsintered polymer. Consideration of a distribution of relaxation times suggests that the narrowing above 190°K of an NMR absorption line from the amorphous regions results from the molecular motion which gives rise to a relaxation observed at 263°K in the ultrasonic measurements. Another amorphous relaxation is observed at 470°K in the ultrasonic measurements and the activation parameters are obtained. Examination of these parameters for the two relaxations suggests that the higher‐temperature relaxation should be assigned to the larger molecular segments. For all the relaxations, the parameters follow a relation which obtains for activated processes in inorganic solids.

ISSN:0021-8979    

DOI:10.1063/1.1728433

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The electrical resistance of evaporated, high purity tin films deposited at 88°K decreases rapidly in two temperature regions as determined by isothermal annealing studies. One pronounced annealing peak occurs at 110°K and has an activation energy of 0.34±0.06 ev. The second much less pronounced peak at 180°K has an activation energy of 0.74±0.10 ev.The annealing characteristics of five pure films varying in thickness from 960 A to 4100 A and a film deposited in a high partial pressure of N2are quite reproducible. The presence of O2during evaporation, however, drastically altered the annealing kinetics and increased the activation energy at any given temperature. The defect resistivity at the time of evaporation was the same for all five pure films and a film deposited in a high partial pressure of N2, but is about 75% higher for the film deposited in the presence of O2.

ISSN:0021-8979    

DOI:10.1063/1.1728434

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Diffusion of a high concentration of boron impurities into a shallow surface layer of silicon and subsequent etching reveals regular arrays of etched lines with crystalline symmetries. These patterns are interpreted as slip lines introduced by the stress from the nonuniformly distributed, undersized substitutional boron impurities in the silicon lattice.

ISSN:0021-8979    

DOI:10.1063/1.1728435

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Young's modulus at 21°C in quenched &agr; Cu‐Al alloys increases with time. This correlates with a decrease in resistivity which has been attributed to vacancy‐enhanced diffusion and short‐range ordering [M. S. Wechsler and R. H. Kernohan, Acta Met.7, 599 (1959); R. H. Kernohan and M. S. Wechsler, J. Phys. Chem. Solids18, 175 (1961)]. The total change in modulus during aging increases with Al content and quenching speed and is also a function of the quenching temperature. An effective activation energy of 0.69 ev was determined 38 min after quenching. This is an effective energy of motion for the point defects involved in the diffusion process at this point in the reaction.

ISSN:0021-8979    

DOI:10.1063/1.1728436

出版商:AIP    

年代:1961

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728438

出版商:AIP    

年代:1961

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728440

出版商:AIP    

年代:1961

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728442

出版商:AIP    

年代:1961

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728444

出版商:AIP    

年代:1961

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728445

出版商:AIP    

年代:1961

数据来源: AIP