摘要:

The embrittlement of copper by small amounts of bismuth has been known for many years. Voce and Hallowes proposed recently that the agent responsible for embrittlement is bismuth present in the form of thin films at copper grain boundaries. In order to examine this picture from a different angle, internal friction and elastic modulus measurements were made on copper specimens free from and containing bismuth up to 0.01 percent with a frequency of transverse vibration of about 1000 cycles per second from −50°C to 550°C. It has been found that: (1) In the bismuth‐bearing copper heat‐treated to be brittle, there is no abrupt change in elastic modulus in passing through the melting point of bismuth (271°C). (2) The internal friction peak (around 500°C) associated with the stress relaxation across copper grain boundaries was reduced by the presence of bismuth, indicating that some bismuth did go to the grain boundaries. (3) Each bismuth‐bearing specimen gives an internal friction peak around 290°C and the height of this peak varies approximately linearly with the bismuth content. This ``bismuth peak'' is correlated to the embrittlement of copper. It was subsequently utilized in studying the effect of cold‐work, heat treatment and the rate of cooling upon the embrittlement of copper by bismuth. The effect of previous cold‐work was found only to speed up the precipitation of bismuth to the grain boundaries the rate of which is very slow at low temperatures.The data presented above corroborate the proposition that embrittlement of copper is caused by bismuth present at copper grain boundaries. However, it appears that the bismuth is distributed in a highly heterogeneous manner. Across most of the boundaries no appreciable amount of bismuth is precipitated, at least not enough to influence the grain boundary viscosity. It is these grain boundaries which give rise to that internal friction peak characteristic of pure copper. Across a few of the grain boundaries enough bismuth is precipitated to markedly decrease the grain boundary viscosity. Since no discontinuous behavior is observed as the temperature passes through the melting point of pure bismuth, it is concluded that the film of bismuth along these boundaries is not of sufficient thickness as to acquire the properties of crystalline bismuth.

ISSN:0021-8979    

DOI:10.1063/1.1698313

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

It has been shown that excessive error may be introduced in small angle x‐ray scattering by the use of an incident beam of finite cross section. To account for this error the usual procedure has required multiple integrations for rays reaching a single pointPon the film from all points within each slit. However, the common effect from both finite slit height and width is a range of scattering angle for rays reachingP. The integrations over each slit dimension are reduced to a single integration over scattering angle, which entails finding the limits of scattering angle.The assumption of a constant distribution of intensity throughout the range allows the range of scattering angle &dgr;&egr; to be taken as a measure of the collimation error. Minimization of &dgr;&egr; permits determination of optimum values of slit height‐width ratio. For two slit collimation, it further leads to determination of optimum slit spacing and optimum relative slit sizes.

ISSN:0021-8979    

DOI:10.1063/1.1698314

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A concrete containing only magnetite ore concentrate, cement, and water is found to have appreciably better shielding properties than ordinary concrete, and to possess good strength and ease of handling. Exceptionally high moisture content, although gradually lost by diffusion, decreases by only about 50 percent in thirty years in an eight‐foot thick wall. Its use is desirable under certain conditions because of space economy due to its high density.

ISSN:0021-8979    

DOI:10.1063/1.1698315

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A method has been devised by which the volume changes occurring during plastic flow in simple compression are directly measured in a dilatometer during the flow process. The great superiority of such a direct determination over an indirect determination from the alteration of dimensions is pointed out. Results are obtained for three rocks, quartz crystal, and a number of metals, including several grades of steel and iron. The volume change during plastic flow is not equal to the product of mean hydrostatic stress into the ordinary compressibility in the elastic range, but may vary in a much more complicated way. There are in the first place permanent changes of volume retained after release of stress; these have long been known and may be of either sign. In addition to the permanently retained changes there may be changes of volume during the action of stress which may be notably larger than the permanently retained part and which also may be of either sign. The most striking of these is a component of volumeincreaseunder increasing compressive stress which in the upper range of stress near the fracture point may be larger than the normal component of volume decrease, so that the total volume change is retrograde. This component is recoverable and reversible on release of stress. It would appear, therefore, that in at least some cases theirreversiblephenomenon of fracture is prepared for in the region immediately below the stress of fracture by the appearance of areversiblechange of volume of sign the opposite of that due to the elastic action of the stresses.

ISSN:0021-8979    

DOI:10.1063/1.1698316

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The relation of theQto the impedance of a resonant transmission line is clarified. Universal curves relatingQand resonant impedance of capacitively terminated transmission‐line and wave guide sections are presented and discussed. Their use in cavity resonator design and as a method for measuring resonator shunt resistance is considered.

ISSN:0021-8979    

DOI:10.1063/1.1698317

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698318

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698319

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698321

出版商:AIP    

年代:1949

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1698322

出版商:AIP    

年代:1949

数据来源: AIP