摘要:

The creep of a-brasses containing 10–35%Zn was studied in the range 350–650°c. The equilibrium creep rate satisfied the relation i=A0(T) exp (-H/kT) sinh (qσ/kT), but two sets of the parametersAe,Hand of the activation volumeqassociated with the tensile stress σ were required, one above and one below a critical stress σe1(T) above which Cottrell-Lomer locking appeared t o become a less effective impediment to slip than at lower stresses. A peak in the activation energyH' (below σc') close to the composition represented by Cu3Zn is interpreted in terms of local order near dislocation cores. This affects the migration of jogs and hence recovery by climb. Below σc',His equal to 1–6 times the activation energy for grain boundary self-diffusion. Two models are proposed in which the climb of dislocations over intragranular obstacles or within grain boundaries are rate determining, depending on whether σ<σc' or σ>c'. The temperature dependence ofAo',Ao,q' andqis explained on the basis of the assumption that the dimensions of the intragranular substructure developing during creep attain lower limiting values which, at any given temperature, depend only on σc'.

ISSN:0031-8086    

DOI:10.1080/14786436008235862

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The formation of dislocations by the collapsing vacancy disc mechanism is examined for aluminium, copper, silicon and germanium. It is shown that this mechanism can be important in the case of metals. In the case of silicon and germanium dislocation loops produced by the above mechanism, during usual crystal growth from the melt, will not roach sizes detectable by means of the optical microscope.

ISSN:0031-8086    

DOI:10.1080/14786436008235863

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Superficially conflicting evidence has been found concerning the direction and sense of the earth's magnetic field in carboniferous times. Various explanations of the results are considered here. We conclude that the discrepancies in direction occur because some sites underwent secondary rumagrietization during the Triassic period. If this hypothesis is correct, the mean direction for the Carboniferous period was 200[ddot] east of true north and 27[ddot] down; placing Britain 15[ddot] south of the equator. As regards the sense of the field we conclude that it probably underwent a rapid series of inversions in the early part of the Carboniferous period and then remained reversed for a considerable time.

ISSN:0031-8086    

DOI:10.1080/14786436008235864

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

For quenches inrtde, frorn 1000°c, 93% of the quenched-in resistivity anneals out in the vicinity of room temperature leaving 10% which subsequently recovers only at much higher temperatures. This remaining resistivity is associated with configurations which are formed from the quenched-in vacancies. Tho recovery of this remaining resistivity was studied. Two recovery regions were defined: The first region way found within a wide temperature range, 200°c to 600°c the second region was observed within a very narrow temperature rango about 630°c. Complete recovery occurred during this stage. The recovery in the temperature range 200°c to 600°c had no observable effect on the yield stress. However, the second step of the resistivity recovery observed in a narrow temperature range above 600°c corresponds to the resoftening of quench-hardening.

ISSN:0031-8086    

DOI:10.1080/14786436008235865

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

A theory is put forward in qualitative terms to account for the sharp nibs frequently observed at the long wavelength end of the spectral lines of ionic crystals, in which optical absorption by a cation has taken place. The broad band is primarily due to excitation of the vibrational modes of the crystal by the Franck-Condon strain; nibs are supposed to be caused by localized modes introduced in the crystal either by the differing mass or by a change in the force constants of the absorbing ion. Experimental evidence in rocksalt-type crystal indicates the presence ofT2g-modes of localized vibrations.

ISSN:0031-8086    

DOI:10.1080/14786436008235866

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Evidence on mechanisms of fracture in magnesium oxide single crystals subjected to tensile loading is given. As-cleaved crystals contain micro-cracks typically 10−4in. long and slip originating from near these cracks occurs during deformation. At a later stage the cracks grow gradually until they increase to a critical size when catastrophic propagation occurs. If the cracks are removed by polishing ductility is enhanced five to ten times Some crystals were reactor irradiated to doses in the range 1014-1019n.v t. (epithermal) and the effects of this testament on flow and fracture are described and discussed.

ISSN:0031-8086    

DOI:10.1080/14786436008235867

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The initiation of etch attack of strained aluminium has been studied by optical and electron microscopy. It is concluded that an important factor is rupture of the protective natural oxide film and its subsequent failure to repair completely in a short time. Slip, in a direction closely parallel to the specimen surface, or a deformation in compression appears to damage the oxide film more severely than deformation in tension. No correlation between etch pits and the end of dislocation lines has been found.

ISSN:0031-8086    

DOI:10.1080/14786436008235868

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The anhysteretic properties of magnetic tapes are discussed by introducing the idea of internal demagnetization spectra.

ISSN:0031-8086    

DOI:10.1080/14786436008235869

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

An electron spin resonance spectrum, due to the formation of cupric ions during illumination, has been observed in crystals of silver chloride containing 0–1 mol %, of cuprous chloride, which have been quenched to−183[ddot]c immediately following irradiation. The spectrum fades rapidly if the crystals are kept at any temperature above −140[ddot]c after the end of illumination. An interpretation of this behaviour is given which is based upon the Mitchell theory of the photochemical process in crystals of silver halides.

ISSN:0031-8086    

DOI:10.1080/14786436008235870

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The electron microscopic examination of thin foils of bismuth and antimony telluride, prepared by repeated cleavage, reveals the presence extended dislocation patterns. Since the c-plane is simultaneously glide and cleavage plane, the dislocation arrangements are preferentially situated in the plane of observation. This is a considerable advantage if one wishes study the configurations due to glide, since one might hope that the typical thin foil behaviour would not apply to the glide planes parallel to the foil. Sets of concontric dislocation lines are often observed, but they invariably originate in soma invisible source, outside the crystal.

ISSN:0031-8086    

DOI:10.1080/14786436008235871

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor