Formation of secondary phases and microdiscs on flux-grown HoFeO3 crystals

Results of optical and scanning electron microscopic and EDAX studies, carried out on structures exhibited by HoFeO₃ crystals grown from the PbO-PbF₂-B₂O₃ flux system, are reported. Aluminium and silicon are present as impurities in the crystals studied. EDAX of certain structures indicate formation of magnetoplumbite (PbO · 6Fe₂O₃) during the flux growth of HoFeO₃. Crystallization of HoOF on the HoFeO₃ crystal surfaces is also indicated; the process taking place almost at the end of HoFeO₃ crystal growth. A variety of microdisc patterns on HoFeO₃ crystal surfaces are illustrated. Their formation is attributed to the covering process of impurity phases by the rapidly advancing growth fronts on the HoFeO₃ crystal surfaces. Experimental evidence in support of this is offered by exposing the impurity phase buried under the microdisc. Precipitation of the secondary phases during the flux growth of HoFeO₃ crystals and their influence on the latter is discussed.     

Microstructural,etching and hardness studies on flux-grown KNiF3 crystals

Surface structures on {100} faces of flux-grown KNiF₃ crystals are reported. Etching experiments establish HNO₃ to be a dislocation etchant for the crystals. The etching behaviour of the HNO₃-KNiF₃ surface system is investigated. The results obtained on the effect of etching time and etchant concentration on lateral extension and depth of dislocation etch pits are reported. It is observed that the etchant is rendered passive after some period of initial etching. Indentation-induced hardness testing studies suggest a Vickers microhardness value in the range of (2.93 to 3.50)×10² kg mm^–2, and the response of indentation to load is in accordance with Kick's Law.     

Characterization of flux-grown PZN-PT single crystals for high-performance piezo devices

Relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3-x)PbTiO(3) (PZN-PT) and Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3)(PMN-PT) single crystals are the potential candidates for future high-performance piezoelectric devices due to their exceptionally high dielectric and piezoelectric properties. Characterization on flux-grown PZN-PT single crystals of different orientations revealed that PZN-(6-7)%PT single crystals show good homogeneity in dielectric and electromechanical properties and composition. When poled in [001] direction, these crystals exhibit high longitudinal-mode properties with dielectric constant (K(T)) approximately equal to 7000, piezoelectric coefficients (d(33)) approximately equal to 2800 pC/N, and electromechanical coupling factors (k(33)) > or = 0.92. For [011]-cut crystals, optimally poled PZN-7%PT single crystal exhibits very high transverse-mode dielectric and piezoelectric properties with K(T) > or = 5000, d(32) approximately equal to -3800 pC/N and k(32) > or = 0.90. [011]- poled PZN 6%PT has d(32) approximately equal to -3000 pC/N and comparable k(32) and K(T) values. In comparison with melt-grown PMNPT single crystals, flux-grown PZN-PT single crystals show good compositional homogeneity, superior and consistent dielectric and electromechanical properties, and higher depolarization temperatures (TDP).     

Glow curves and the emission of flux-grown BaFCl:Na crystals

The thermoluminescence glow curves and the emission spectra of flux-grown BaFCl:Na crystals were recorded. An additional TL peak at 320 K, an optical absorption band at 570 nm and an emission peak at 490 nm have been seen in X/-irradiated crystals. Bleaching, room-temperature annealing and high-temperature emission results led us to conclude that the sodium impurity is responsible for the additional glow peak, optical absorption band and emission peak.     

Studies on microhardness of quenched mesolite crystals

Observations and results on studies of the microhardness of {1 0 1} and {1 0 ¯1} faces of natural mesolite crystals are illustrated and explained. Variations in Vickers hardness number (VHN) with temperature of quenching and also with the applied load are discussed.     

Environmental effect on sclerometric brittleness of ionic crystals

The conditions of plastic-to-brittle transition during microscratching with a Vickers diamond indentor of natural cleavage surfaces of lithium fluoride (LiF) single crystals (pure samples and those covered with octadecylamine films) in heptane, distilled water, and their saturated aqueous solution, were studied. Indentor loads varied in the range 3.2×10^–3-1.9×10^–1 N; indent or sliding velocity was 30 m s^–1. Quantitative characteristics of microplasticity and microbrittleness of near-surface layers in single crystals under appropriate test conditions were studied. The basic mechanisms of crack formation in non-uniform indentor-induced fields of stresses and deformations were revealed and the active media effect on the relative intensity of the functioning of these mechanisms was analysed.     

Optical and scanning electron microscopic and energy-dispersive X-ray analytical studies on some typical surface structures of flux-grown DyFeO3 crystals

The results of optical, scanning electron microscope and qualitative analysis studies conducted on surface structures displayed by flux-grown DyFeO₃ crystals are reported. The crystals were grown from PbO-PbF₂ B₂O₃ flux under various conditions. Magnetoplumbite (PbO · 6Fe₂O₃) is the most favoured secondary phase. Crystallization of DyOF and DyBO₃ on the DyFeO₃ crystal surfaces also takes place, almost at the end of DyFeO₃ crystal growth. Macro- and micro-disc patterns on DyFeO₃ and a rare observation of an elliptical disc of material containing lead are illustrated. Metallic platinum deposited on flux-grown DyFeO₃ is reported when the crystals were finally cooled in contact with the flux. Additional secondary phases (material containing lead, platinum, PbO · 6Fe₂O₃, DyBO₃) and other imperfections (inclusions, cavities, microcrystals) also occur. The addition of V₂O₅ to the flux leads to incorporation of traces of vanadium in the DyFeO₃ crystals and DYVO₄ as a secondary phase.     

Etching and microhardness studies on lead molybdate single crystals

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Typical hillocks and spirals on flux-grown DyFeO3 crystal surfaces

Multi-sided and almost rectangular growth hillocks on (1 1 0) faces of flux-grown DyFeO₃ crystals are illustrated. Some such hillocks exhibit spiral growth layers originating from the summits of hillocks. Spiral growth layers originating from more than one initiation centre interact, giving rise to closed loop, interlocked and interlaced or other complex growth formations. The origin of the multi-sided hillocks is attributed to preferential growth at the sites of screw dislocations in DyFeO₃ crystals. Defects other than screw dislocations also stimulate growth on (1 1 0) faces of DyFeO₃ crystals. An example of this is offered. The mechanism of independent growth on (1 1 0) faces of these crystals is discussed.     

Effect of the structural state on the cold brittleness and fracture toughness of low-alloyed molybdenum

We investigate the effects of the chemical and phase compositions of grain boundaries and the state of an excess phase on the fracture toughness, cold brittleness, and strength of low-alloyed molybdenum by the methods of scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy. The structural state of the material was changed without changing grain sizes by annealing in various modes at different temperatures. It was shown that the level of segregation of interstitials on grain boundaries is determined by both the annealing temperature and distinctive features of the evolution of excess phases. Embrittlement of grain boundaries results in a decrease in the strength and fracture toughness of the material and in an increase in its temperature of cold brittleness. In the case of transcrystalline fracture, the material exhibits better mechanical properties correlated with distinctive features of the evolution of excess phases inside the grains.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 5, pp. 34–44, September–October, 1994.     

Intermediate temperature brittleness and directional coarsening behavior of nickel-based single-crystal superalloy DD6

The microstructure of the nickel-based single-crystal superalloy DD6 after tensile deformation has been studied by transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscopy (EDS). The samples were strained to fracture at room temperature, 650 °C, 850 °C and 1020 °C along the [001] orientation. The results indicate that the yield strength at 650 °C is superior to that at room temperature (20 °C), 850 °C and 1020 °C, but low ductility was observed at 650 °C. It is demonstrated that the intermediate temperature brittleness (ITB) behavior was caused by the change of the deformation mechanism at intermediate temperature. At high temperature, the γ′ precipitates coarsening directionally along the direction perpendicular to the stress axis. This can be attributed to the directional diffusion of the chemical elements.     

Surface structural investigations on (100) and (110) faces of flux-grown lanthanum borate crystals

Results of topographical studies carried out on (100) and (110) faces of lanthanum borate crystals grown from the PbO-B₂O₃ flux system are illustrated and discussed. The habit faces display the formation of cavities, microcrystals, elliptical etch pits, elliptical hillocks, circular hillocks and irregular structures. Also described are a various number of elevated structures identified as impurity phases. Energy dispersive X-ray (EDAX) studies have confirmed that these impurity phases in the growth of lanthanum borate (LaBO₃) crystals are enriched by lead (Pb). The habit faces also exhibit some elevated regions which are reported to be more imperfect in comparison with others. It is inferred that independent growth on the habit faces has taken place during the last stage of crystal growth by a two-dimensional nucleation mechanism.     

Microhardness measurements on single crystals of flux-grown rare earth perovskites (orthoferrites,orthochromites and aluminates)

The results of indentation-induced microhardness testing studies of flux-grown single crystals of rare earth orthoferrites, RFeO₃ (R=Gd to Er and Yb), rare earth orthochromites RCrO₃ (R=La, Eu and Dy), and rare earth aluminates RAlO₃ (R=La, Sm, Gd, Eu and Ho) are presented. The variation in the value of microhardness with load is observed to be non-linear in the case of all these materials. It is found that the results are not in accordance with Kick's law. The results have been analysed and the applicability of the idea of materials resistance pressure in the modified law as proposed by Hays and Kendall [Metallography 6 (1973) 275] is discussed.     

Temperature dependence of vickers microhardness and creep of InBi single crystals

Variation of Vickers microhardness of InBi single crystals with temperature has been studied. Loading time dependence of the microhardness at different temperatures has been used for the creep study in the temperature range 30° – 85°C. The activation energy for creep has been evaluated and the results are discussed.