摘要:

A computer code is described which permits investigation of the energy and structure of coincident‐site lattice (CSL) grain boundaries, stacking faults, and free surfaces in ionic crystals. The code uses computational techniques similar to those of Harwell's HADES code for the study of point defects in bulk ionic crystals. Two sets of short‐range potentials are used to determine the energy and structure of the free (001) surface and of (001) CSL twist boundaries in MgO with values of Γ, the inverse density of CSL sites, ranging between Γ= 5 and Γ= 65. From comparison of the results obtained by means of the different potentials it is concluded that the Van der Waals attraction between oxygen ions on opposite sides of the interface is mainly responsible for the rather weak cohesion predicted for such bicrystals, whereas Coulombic interactions are found to play only a minor role. It then follows that (i) the (001) plane is not a favored plane for the formation of grain boundaries in pure oxides with NaCl structure and (ii) similarities should exist between (001) twist boundaries in ionic crystals with NaCl structure and in fee metals. These similarities are investigated by comparing calculated boundary structures and energy‐vs‐misfit angle curves for MgO with recent results for aluminum, copper, silver, and gold, in which a broad spectrum of different interatomic potentials was used. It is suggested that the rather strong cohesion of the pressure‐sintered MgO bicrystals of Sun and Balluffi may be due to impurities which have migrated to the boundary duri

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19137.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

An organic chelation reagent, cupferron, was used to coprecipitate Ti4+andZr4+. After the materials were fired, they were mixed with PbO powder and fired again at high temperatures to obtain Pb(Zr,Ti)03(PZT). It was confirmed that this method is useful for the preparation of homogeneous PZT having no compositional fluctuations. No coexistence range of the tetragonal and rhombohedral phases was observed in the PZT compositions near the morphotropic phase boundary.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19153.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Compatibility relations of Al203in the quaternary system Zr02‐Al203‐Si02‐CaO were studied by firing and quenching followed by microscopy and energy‐dispersive X‐ray examination. A projection of the boundary surface of the primary crystallization volume of Al203was constructed in terms of the CaO, Si02, and Zr02contents of the mixtures recalculated to 100 wt%. Two invariant points, where four solids coexist with a liquid phase, are defined, and the positions of the isotherms were es

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19154.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Drop calorimetry measurements for four Na20‐Si02liquids indicate that, to within ±0.5%, the heat capacities are temperature‐independent between 900 and 1800 K and additive functions of composition for liquids containing from 50 to 100 mol% Si02. In this composition interval, the partial molar heat capacities of Si02and Na20 are 81.37 and 100.6 J /mole‐K, respec

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19155.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The internal friction of metaphosphate glasses was measured as a function of temperature by a free torsional vibration method. In the high‐temperature region metaphosphate glasses (MO/P2O5=l)for which M=Ca, Sr, or Ba exhibit high‐temperature peaks in plots of internal friction vs temperature, whereas for M =Mg or Zn this peak is miss

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19156.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Up to 3.3 wt% nitrogen can be incorporated into Na2O‐B2O3glass melts. The melting procedure is described, and structure models are given. In contrast to N‐containing silicate glasses, the borate glasses were transparent; however, micrographs of their fracture surfaces showed some crystallinity. Properties were determined as a function of the N and Na2O contents of the glasses. Compared with N‐containing silicate glasses, the properties of borate glasses are much less changed by the nitrogen intro

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19157.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The mechanical properties of chemically vapor‐deposited boron carbides (B4C) with varied B/C ratios were investigated as a function of composition. The maximum hardness, H, and fracture toughness, K1c, were observed at an almost stoichiometric composition. For nonstoichiometric B4C (B/C>4), H and K1cdecreased with increasing B content, suggesting that excess B diminishes the bond strength in the B4C structure. The decrease in H and K1Cat B /C<4 was attributed to free C in the microstructur

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19158.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Alumina thin‐walled tubes were fractured in axial tension, hoop tension, balanced biaxial tension, balanced tension‐compression, and pure torsion using an electrohydraulic mechanical testing apparatus. A slight anisotropy in the axial and hoop uniaxial strengths indicated that the predominant defects were axially oriented, and probably fabrication‐related as opposed to machining flaws. A 10% weakening was observed in balanced biaxial tension as compared to uniaxial tension, whereas strength was insensitive to a balanced tension‐compression stress state. The strength in pure torsion was 16% higher than the axial strength. Stress state results suggest a weakening due to in‐flaw plane tensile stresses and more complex fracture‐initiation phenomena for stresses not oriented perpendicular to the domin

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19138.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The method introduced by Evans and colleagues to calculate transformation toughening resulting from a dilatant transformation is extended, using the Eshelby “equivalent inclusion” approach, to treat the case of toughening resulting from microcrack

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19159.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The oxidation ofa‐SiC single crystals and sintered α‐ and β‐SiC polycrystals has been investigated at elevated temperatures. Bubble formation is commonly observed in oxide scales on polycrystalline SiC but is rarely found on single‐crystal scales; bubbles result from the preferential oxidation of C inclusions, which are abundant in SiC polycrystals. The absence of bubbles on single crystals in fact implies that diffusion of the gaseous species formed on oxidation, CO (or possibly SiO), controls the rate of oxidati

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1984.tb19160.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY