摘要:

Ce‐TZP is reported to exhibit cyclic transformation during machine grinding. Previous conclusions were based on the results obtained by grinding Ce‐TZP at a single speed and depth of cut. In the present work, grinding parameters were carefully chosen to induce varied stresses. Results show that Ce‐TZP exhibits cyclic transformation, not always, but only under certain favorable grinding conditions. Results are supported by XRD, optical microscopy, and dynamometric observations. Three stages of transformation, namely, a mechanical‐stress‐inducedttom, a frictional‐heat‐drivenmtot, and a thermal‐quenching‐stress‐inducedttom, in sequence, are

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05611.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

An analysis is presented to predict the strength of glass after subsurface cracking is produced by drawing a lightly loaded angular particle across the surface. It is shown that the presence of subsurface cracks combined with the residual stresses introduced by such scratches under very small loads greatly lowers the strength of glass. The predicted ranges of tensile strength for soda–lime glass in dry and moist environments are in agreement with typical values in the literatur

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05612.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The dielectric loss tangent at microwave frequencies for the complex perovskite Ba(Zn1/3Ta2/3)O3was calculated with respect to the degree of structural disorder on B sites. Starting out from the equations of ion motion, dielectric loss was expressed in terms of the pair‐correlation functions corresponding to the ordering of Zn and Ta ions on B sites. The characteristic length included in the pair‐correlation functions corresponds to the average size of the region containing disorder in ion arrangements on B sites; thus the relation between the structural disorder on the B site and the dielectric loss tangent at microwave frequencies was clarified theoretically. The numerical results show that the microwave loss tangent values change their power from – 3 to – 6 with increasing degree of order on the B site, which agrees well with the experimental observations. Results obtained here confirm the physical origin of the microwave loss of complex perovskite Ba(Zn1/3T

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05613.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The energetics of martensitic transformation in ZrO2is studied using a thermodynamic approach, with particular reference to Al2O3–ZrO2composites. The different characters of three types of transformation‐toughened ceramics are analyzed, and several factors affecting thet→mtransformation in Al2O3–ZrO2composites are discussed. The expression of transformation temperature dependence on particle size is derived and has good agreement with experimental results. The energetics concerned with nucleation of martensitic transformation is also di

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05614.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Stoichiometric quantities of AR‐grade chemicals, e.g., Ba(NO3)2, Sr(NO3)2, and Nb2O5, were used to synthesize Sr0.5Ba0.5Nb2O6(SBN:50) by the solid‐state reaction route. The reaction mixture was characterized by DTA/TG/DTG to locate the formation temperature of SBN:50. X‐ray diffrction was used to identify the major and any additional phases formed in the calcined as well as sintered materials. The materials were further characterized by electrical measurements, the temperature dependence of the dielectric constant (ɛ) and the loss (tan δ), FE hysteresis‐loop parameters (PsandEc), and room‐temperature dc resistivity. SBN:50 exhibited a broad maximum of ɛ in the temperature range 65° to 95°C. Moreover, the FE hysteresis loop persisted even at 130°C, which is much higher than the Curie range determined from an ɛ vsTplot. Microstructural photographs revealed varied grain‐size distribution between 5 and 20 μm. The presence of residual porosity (∼ 95% dense) result

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05615.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Surface strengthening of SiC by in situ surface nitridation during post‐hot isostatic pressing (post‐HIPing) in N2was investigated. The formation of a thin (5–15 μm) layer of submicrometer β‐Si3N4on the surface of SiC was obtained at 1850°C and 200 MPa. While SiC HIPed in Ar attained a mean bending strength of 660 MPa, a significant increase in strength (with a maximum fracture stress above 1000 MPa) was observed for the SiC/Si3N4‐layer composite material. Generation of residual compressive stresses on the surface layer caused by the differences in thermal expansion may account for the observed strengthening. Thus, in situ surface nitridation by post‐HIPing in N2may offer an attractive way to improve surface‐sensitive mechanical properties of complex‐sha

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05616.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

β‐BaB2O4(β‐BBO) powders and films were successfully synthesized by the sol–gel method using metal alkoxides. A homogeneous and stable solution was prepared by the reaction of barium metal with boron triethoxide in ethanol by addition of diethanolamine. The drip‐coated precursor films began to crystallize to β‐BBO on Pt substrates at 500°C and converted to β‐BBO films with preferred orientation to th

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05617.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Radial cracks for indented soda–lime glass aged in distilled water were highly elliptical because of truncation by lateral cracks. Indentation in silicone oil minimized radial/lateral crack interaction but still produced cracks having nominally constant ellipticity during bend testing. Analysis of applied stress/indentation crack length data using stress intensity factors based on half‐penny crack shape resulted in apparentR‐curve behavior and/or overestimation of the fracture toughness. Incorporation of elliptical shape factors eliminated theR‐curve behavior and reduced measured toughness to near the accepted value for soda–l

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05618.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Thermal decomposition of aluminumsec‐alkoxide in inert organic solvents at 300°C yielded a product composed of agglomerates of 4‐ to 20‐nm particles having the χ‐alumina structure. The χ‐alumina was stable and maintained a surface area above 100 m2/g until its transformation at 1150°C

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05619.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The relative frequencies of pore location on grain corners, edges, and surfaces in final stage sintering have been measured in both pure and MgO‐doped Al2O3. Both materials showed identical location frequencies, with an average of 58% of the pores on grain corners, 29% on grain edges, and 13% on grain surfaces, over a density range from 92% to>99% of full densit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05620.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY