摘要:

Zinc whiskers and platelets with a (0001) orientation and thin enough (≲ 1/2 μ) to be transparent to 100 kv electrons were deformed in tension inside the electron microscope and the motion of individual dislocations followed by the transmission technique. These observations were then related to the macroscopic properties as determined by stress–strain curves. The crystals, which were found to be initially free of dislocations, deformed mainly by twinning (which is not considered here) or by pyramidal glide on the (1122) [1123] system. Dislocations with three types of Burgers vectors were produced: long ⟨1120⟩ dislocations which were easily immobilized and contributed very little to the deformation; short ⟨1123⟩ screw dislocations which caused pyramidal glide and sometimes left behind long, narrow ⟨1123⟩ loops which then split up into circular loops with the same Burgers vector; and circular ⟨0001⟩ loops which were formed from ⟨1123⟩ loops by the reaction 1/3⟨1123⟩ → 1/3⟨1120⟩ +⟨0001⟩. Both types of loops were sessile but disappeared by climb at room temperature at a rate which agreed with the predicted rate. The loops impeded the motion of dislocations and were responsible for the propagation of glide as a Lüders band.

ISSN:0031-8086    

DOI:10.1080/14786436008238307

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The addition of impurities affects both the lattice and electronic thermal conductivities of a semiconductor. At high temperatures the lattice resistance is increased by an amount independent of temperature: for the small concentrations normally present in semiconductors the impurity resistance can be derived very simply from the variational principle. The electronic contribution is normally obtained from the electrical conductivity via a Lorentz number. For a degenerate electron gas assuming polar scattering dominates an approximate calculation shows that at high temperatures the Lorentz number can be considerably reduced below the standard' value g0= (π2/3)(k/e)2. These theoretical calculations do not completely agree with the observed conductivity of impure In As between 300 and 700°K (Stuckes 1960). The disagreement is attributed to the electronic contribution. To give agreement the Lorentz number would have to be reduced further but the precise amount is uncertain owing to experimental errors.

ISSN:0031-8086    

DOI:10.1080/14786436008238308

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The nuclear magnetic resonance lines from β brass at room temperature have been studied as a function of composition and deformation. A simple model is proposed to explain the variation of intensity with composition. The Knight shift is 0–14%, independent of composition. Filing at room temperature eliminates the line from most specimens but it can be restored by annealing. Changes in line shape occur before, during, and after recrystallization.

ISSN:0031-8086    

DOI:10.1080/14786436008238309

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Two properties of the Ising model are considered. Firstly, by extrapolating appropriate series expansions, the spontaneous magnetization of a ferromagnet for three-dimensional lattices is obtained. From the results accurate values for the critical temperature are found. Secondly, the high temperature susceptibility of an antiferromagnet is derived from the approximation of Kikuchi. The resulting susceptibility curves show that for loose-packed lattices a maximum value occurs at a temperature slightly above the critical point, while for the close-packed lattices no such effect is obtained.

ISSN:0031-8086    

DOI:10.1080/14786436008238310

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The stresses round a circular prismatic dislocation loop are determined and used to calculate the spacings between such loops in a row generated from a source of internal stress. The results are consistent with the available experimental observations.

ISSN:0031-8086    

DOI:10.1080/14786436008238311

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The longitudinal and shear wave velocities of 10 Mc/s ultrasonic waves have been measured in polycrystalline specimens of zirconium and tungsten at temperatures between 14° and 300°k and the elastic constants calculated from these measurements. The difference between the specific heats at constant pressure and at constant volume in these metals at various temperatures has been calculated by means of the thermodynamic relation involving the bulk modulus of the metal; this difference is used in the examination of a suggested method of obtaining the γ values, and hence the electronic specific heats of metals.

ISSN:0031-8086    

DOI:10.1080/14786436008238312

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Resoftening characteristics of quench-hardened gold were experimentally determined. Resoftening occurred above 600°c at a highly temperature-dependent rate with an activation energy of 4·7 ev. Various quench-hardening mechanisms are considered. The processes corresponding to the observed characteristics are for quench-hardening: formation of tetrahedral stacking faults; and for resoftening: the nucleation of a Shockley partial dislocation ring on any face of the tetrahedron.

ISSN:0031-8086    

DOI:10.1080/14786436008238313

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Interrupted tensile tests have been earned out on single crystals of super-purity aluminium and solid solutions of aluminium-zinc. Partial load removal during an interruption of the test is shown to have several effects on subsequent plastic flow. Unloading yield points are formed during tests on both alloy and aluminium specimens, while strain ageing yield points formed during tests on alloy specimens are shown to be either enhanced or diminished, depending on the sequence of prior ageing and unloading. Finally the relationship between unloading and room temperature recovery is examined and the results suggest that the trapping of glissile dislocations, as a result of unloading, leads to a partial suppression of recovery.

ISSN:0031-8086    

DOI:10.1080/14786436008238314

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The dynamical theory of electron diffraction including a term to take account of absorption has been applied to explain some contrast anomalies observed at extinction contours and stacking faults on transmission electron micrographs of metal foils. The theory is at present phenomenological because the detailed mechanism of the absorption process is not understood. This paper reports some preliminary results of the theory and compares them with observations.

ISSN:0031-8086    

DOI:10.1080/14786436008238315

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Heat and Thermodynamics. Fifth edition. By J. K. Roberts, revised by A. R. Miller. (Blackie, 1960.) [Pp. 619.] Price £2 5s.

ISSN:0031-8086    

DOI:10.1080/14786436008238316

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor