摘要:

Refractory metallic coatings of (W0.6Re0.4)76B24(WReB) have been deposited onto glass, quartz, and heat‐treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As‐deposited WReB films are amorphous, as shown by their diffuse x‐ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (∼ 1000 °C) crystallization temperature. Adhesion strength of these coatings on heat‐treated AISI 52100 steel is in excess of ∼20, 000 psi and they possess high microhardness (∼ 2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin‐on‐disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 &mgr;m thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel.

ISSN:0021-8979    

DOI:10.1063/1.336295

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new plate impact technique for studying the dynamic properties of shock‐damaged materials has been developed. The technique is based on impacting the specimen with two flyer plates which are separated by a small gap. Impact of the first plate causes spall in the target. Impact of the second plate closes the spall. The transmitted shock wave is monitored with a VISAR and/or manganin stress gauge. Analysis of the waves gives the properties of the damaged region. Preliminary results for copper and polycrystalline aluminum oxide have been obtained.

ISSN:0021-8979    

DOI:10.1063/1.335759

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Prolonged annealing of Czochralski silicon at 485°C leads to the formation of a number of defects which is accompanied by a reduction in the concentration of oxygen interstitials in the matrix. High‐resolution electron microscopy has been used to investigate the structure of these defects which are basically of three types: (1) ribbonlike, (2) looplike defects which result in local lattice strains and hence are also visible in conventional transmission electron microscopy, and (3) dark regions visible in high‐resolution micrographs with no lattice strains. Based on image characteristics and a comparison of the reduction in interstitial oxygen, from infrared spectroscopy, with the sizes of the ribbons, estimated from high‐resolution micrographs, it is proposed that the ribbonlike defects are, in fact, the coesite phase which forms at prolonged anneals of the same material at the higher temperatures of 630–650°C. Using a simple model for the diffusion of oxygen to ribbons, the diffusivity of oxygen in silicon is estimated to be enhanced by nearly four orders of magnitude at 485°C! It is proposed that the looplike defects are extrinsic Frank loops which act as sinks for the interstitial silicon ejected during the oxygen precipitation. The fading away of the dark regions under electron irradiation in the microscope suggests that they are agglomerates of point defects.

ISSN:0021-8979    

DOI:10.1063/1.335760

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Interdiffusion in the Ta‐W system, a continuous body‐centered‐cubic solid solution, has been investigated in the temperature range 1300–2100 °C with single‐phase diffusion couples prepared by chemical vapor deposition. Fine inclusions, presumably oxides or carbides, decorated the couple interfaces and served as Kirkendall markers. The diffusion annealing times ranged from 16 h to 220 days. The resulting concentration profiles were measured with the electron microprobe and analytical electron microscope. The chemical diffusion coefficient was determined by the classical Boltzmann–Matano technique. The intrinsic diffusivities were determined by the technique of Darken. In the composition range 20–80 at. % W, the activation energyQfor chemical diffusion was constant at 130.5±1.5 kcal/mole. The activation energies for the intrinsic diffusion coefficients at the composition of the Kirkendall marker plane, approximately 70 at. % W, wereQ(Ta)=132.3±0.5 kcal/mole andQ(W)=122.0±0.5 kcal/mole.

ISSN:0021-8979    

DOI:10.1063/1.335761

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An edge dislocation in a simple cubic crystal is considered as the basis for a model for vacancy‐induced transport. The Burgers vector for the dislocation is [01¯0], and a solute atom moves along the compressed region of the core by vacancy exchanges along the edge of the extra half plane of atoms. The length of the dislocation is carried to the limit of an infinite number of lattice sites. Consequently, when the vacancy is tightly bound to the dislocation, that limit of tight binding becomes exact. In the tight binding limit, the correlation factor goes to zero for self‐diffusion as expected. With vacancy solute tight binding, this result is not altered. Vacancy‐solute repulsion can override vacancy‐dislocation attraction and change the limit. In the case of dislocation and solute binding to the vacancy, the diffusivity becomes indefinitely large due to the abundance of defects increasing the jump frequency at a rate faster than the correlation factor decreases it. The mobility for electromigration also shows unusual limits. When the solute and dislocation both bind the vacancy, the ratio of the mobility to diffusivity becomes indefinitely large. So long as there is large dislocation vacancy binding, the ratio remains large even with solute vacancy repulsion.

ISSN:0021-8979    

DOI:10.1063/1.335762

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Molecular beam homoepitaxy of InSb on the nonpolar (110) face is reported for the first time. Growth conditions and substrate preparation techniques are discussed. With an In beam flux of 3×1014at./cm2 s a growth rate of 0.72 &mgr;m/h is obtained, hence the sticking coefficient of In on InSb (110) is one. Layers of good crystalline quality and of stoichiometric composition were grown at a substrate temperature of 380 °C and a flux ratio &Fgr;Sb/&Fgr;In=3. The &Fgr;Sb/&Fgr;InvsTsdiagram is given. Two surface reconstructions are reported: the well‐known (1×1) at highTsand a new reconstruction with (1×4) symmetry at lowerTs. The latter may be connected with InSb bond breaking or an In overlayer. The epilayers with thicknesses from 1 to 7.7 &mgr;m all shown‐type conductance with mobilities from 1.2 to 7.5 m2/V s at 77 K. By optimizing the growth conditions with respect to the electrical transport properties much higher values should be attainable.

ISSN:0021-8979    

DOI:10.1063/1.335763

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The reaction kinetics of Al with Ti22W78alloys has been investigated under vacuum annealing conditions. In particular, the effects of Cu in Al and venting during deposition of TiW were studied. It was observed that Cu did not play any significant role in the kinetics of the interdiffusion of Al and TiW. During the reaction process at temperatures around 500 °C, Ti accumulated on the surface of the samples with or without Cu in Al. The Ti accumulation is diffusion limited with an activation energy of 2.4 eV. Interface oxides are believed to be primarily responsible for the stability of Al/TiW metallization.

ISSN:0021-8979    

DOI:10.1063/1.335764

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Thin‐film reactions of Al/Ti22W78(∼10 wt. % Ti) with and without ∼2 at. % Cu in the Al were investigated by transmission electron microscopy for vacuum annealing in the temperature range 300–600 °C. The reactions are nonuniform and the presence of Cu has little effect on the reaction kinetics. Reactions are grain boundary dominated and start at 400 °C with the formation of WAl12.

ISSN:0021-8979    

DOI:10.1063/1.335765

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Dislocation and growth striation hereditability from liquid‐encapsulated Czochralski (LEC) grown GaAs substrates to molecular beam epitaxially (MBE) grown epilayers is studied for the different types of epilayer structures including homo‐, hetero‐, and superlattice. Also the correlation of surface defects in the epilayers with dislocations in the substrates is studied. It is found that growth striation in the substrate is not inherited into the epilayer, whereas dislocation propagation strongly depends on the epilayer structure. Dislocation distributions in GaAs epilayers for homo‐ (GaAs/GaAs substrate) and hetero‐ (GaAs/Al0.3Ga0.7As or AlAs/GaAs substrate) structures inherit the dislocation distribution maps for their substrates. On the other hand, dislocation propagation can be effectively prevented by introducing an AlAs/GaAs superlattice spacer between the GaAs epilayer and the substrate. As for surface defects, micron‐sized hillocks emerge when the superlattice structure is fabricated. Their morphological configurations are very similar to those of previously reported oval defects in MBE‐grown GaAs layers. However, these newly found surface defects are apt to be generated by the shutter operation and this close correlation with the dislocations in the substrate is quite different from the usual oval defects.

ISSN:0021-8979    

DOI:10.1063/1.335766

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

High‐resolution transmission electron microscope (TEM) observation is made on cross sections including the growth direction of MBE‐grown AlxGa1−xAs‐AlyGa1−yAs superlattice samples. Lattice images with contrast high enough to distinguish each of the constituent layers in superlattices are important for the study of heterointerfaces on an atomic scale, and two methods are developed in order to obtain them. One is to use superlattices with large difference &Dgr;x=y−xin Al composition. It is found that the degree of abruptness at the heterointerface is one or two monolayers and that the heterointerface of the ternary AlGaAs grown on the binary AlAs is smoother than that of the binary grown on the ternary. The other is to observe superlattices by using an electron beam incident along a [100] crystal axis. A theoretical consideration based on both kinematical and dynamical theory of diffraction is given, which suggests that, in obtaining lattice images with high contrast, an electron beam along a [100] crystal axis is more favorable than one incident along the [110] axis which is conventionally used. This is confirmed experimentally by using a GaAs‐AlGaAs superlattice sample.

ISSN:0021-8979    

DOI:10.1063/1.335767

出版商:AIP    

年代:1985

数据来源: AIP