Knoop Hardness Anisotropy and Plastic Deformation in Mn-Zn Ferrite Single Crystals

The Knoop hardness anisotropy and plastic deformation markings around the DPH indentation were investigated for an Mn-Zn ferrite single crystal. Knoop hardness values, which depended primarily on the crystallographic direction, were represented on a standard stereographic triangle. The hardness was maximum in the <001> direction and minimum in the <111> and <011> directions. The patterns of the plastic deformation markings show that the ferrite deforms plastically at room temperature by {110} <110> and {111} <110> slip.     

Knoop Microhardness Anisotropy of Single-Crystal Rutile

Knoop microhardness profiles were determined for singlecrystal rutile on the (100), (001), (110), and (111) for test loads from 50 to 300 g. The profiles were related to the slip systems as they determine the corresponding effective resolved shear stress (ERSS) diagrams according to the concepts advanced by Brookes and co-workers. Several previously reported slip systems were confirmed while slip on the {11 1 } <101> was also suggested. Cleavage of rutile on the {110} and {100} was substantiated. The load dependence of the microhardness was addressed in terms of the classical Meyer's law, P = Adⁿ . The n values were between 1.53 and 1.77, varying with the crystallographic planes and directions. However, no obvious systematic variation was evident.     

Knoop Microhardness Anisotropy of Single-Crystal Aragonite

The Knoop microhardness was measured for indentation test loads from 25 to 200 g on the (100), (010), and (001) planes of single-crystal aragonite (nonbiogenic). Although the microhardness of this aragonite is quite anisotropic on the (100) and (010), it is nearly isotropic on the (001) plane. The microhardness profiles are discussed relative to the structure of aragonite, and the hardnesses are compared with those which have been determined for calcite on its cleavage plane. The indentation load/size effect (ISE) is addressed for aragonite and compared with that of calcite on its cleavage plane.     

Knoop Microhardness Anisotropy and the Indentation Size Effect on the Basal Plane of Single-Crystal Alumina (Sapphire)

The Knoop microhardness anisotropy profile was determined for the basal plane of a Czochralski grown alumina single crystal for indentation test loads from 100 through 1000 g. Microhardness maxima occur at low indentation test loads for the long axis of the Knoop indenter parallel to the 〈2[Onemacr][Onemacr]0〉. Minima exist for the long axis parallel to the 〈10[Onemacr]0〉. This low indentation test load profile is attributed to slip on the primary slip system, the (0001)〈[Onemacr][Onemacr]20〉, as previously noted by Brookes and co-workers. The degree of the microhardness anisotropy decreases for higher indentation test loads. This results from the activation of multiple slip systems to accommodate the greater amounts of plastic flow required by the larger indentation sizes. The microhardness profile becomes more uniform with increasing indentation test load until the Knoop microhardness approaches a test-load-independent, orientation-independent microhardness of 1167 ± 34 kg/mm². The indentation size effect (ISE) was further investigated through lubricated indentation hardness measurements. Lubrication of the test specimen surface significantly reduces the ISE. Results indicate that friction between the test specimen surface and the indenter facets is a major portion of the ISE.     

Knoop Microhardness Anisotropy of Single-Crystal Cassiterite (SnO2)

The Knoop microhardness anisotropy of single-crystal cassiterite (SnO₂) was measured on the (100), (110), (001), and (111). That anisotropy is depicted as the microhardness profiles for those planes. The results are addressed first in terms of the elastic anisotropy of SnO₂ and then on the basis of the effective resolved shear stress (ERSS), the latter an approach initially advanced by Brookes and co-workers. The load dependence of the Knoop microhardness is also evaluated in terms of the classical Meyer's law for which it is demonstrated that the Meyer's law coefficient and Meyer's law exponent are related.     

Effect of Nonstoichiometry on Fracture Toughness and Hardness of Yttrium Oxide Ceramics

This work deals with the changes in mechanical properties of yttrium oxide ceramics induced by nonstoichiometry. The maximum fracture toughness, K_lc, is observed at the stoichiometric composition. For an oxygendeficient ceramic, a decrease of K_lc is observed from 3.5 to 2.3 MPa.m^1/2. On the other hand, the Vickers hardness seems to be less dependent on stoichiometry. These results are discussed in the frame of the evolution of the Y-O bond with the stoichiometry. They set in particular the problem of the role of electrostatic energy stored in a brittle material containing charged defects in the energy balance controlling crack propagation.     

Nonstoichiometry and Its Effect on the Magnetic Properties of a Manganese-Zinc Ferrite

The effect of oxygen nonstoichometry on physical and magnetic properties of a Mn-Zn ferrite has been studied by using annealed samples under various oxygen pressures and temperaure. The dependence of oxygen nonstoichiometry7 on disaccommodation and Fe²⁺ content changed at the stoichiometric composition, and the lattice parameter became maximum at the stoichiometric composition. These results suggest that Mn-Zn ferrites have two different defect structures: cation vacancies in cation-deficient regons and oxygen vacancies in anion-deficient regions. Initial permeability was maximum and power loss was minimum at the stoichiometric composition, suggesting he importance of the number of point defects for the magnetic properties.     

Cracking and the Indentation Size Effect for Knoop Hardness of Glasses

The Knoop hardnesses of five glasses decreased with increasing load in accordance with the classic indentation size effect (ISE). At moderate loads, cracking dramatically altered the indentation sizes and the ISE trends in three of the five glasses. Cracked indentations were as much as 10 μm longer than uncracked indentations made under identical conditions. Diagonal length readings must be corrected for optical resolution limitations if low power lenses are used.     

Oxygen Self-Diffusion in Single-Crystal Mn-Zn Ferrite

Self-diffusion coefficients for the oxygen ion in single-crystal Mn-Zn ferrite were determined by the gas-solid isotope exchange technique. The oxygen volume diffusion coefficients can be expressed as D =6.70 × 10⁻⁴ exp (-330 (kJ /mol) /RT)m₂/s (>1350°C), D=3.94 × 10⁻¹⁰ exp (−137 (kJ/mol)/RT)m²/s (1100° to 1350°C), and D=7.82 × 10⁴ exp (−507 (kJ/mol)/RT)m²/s (<1100°C).     

Knoop Microhardness Anisotropy of Single-Crystal Stoichiometric MgAl2O4 Spinel

Microhardness anisotropy profiles for the (100) and (111) planes of single-crystal stoichiometric MgAl₂O., spinel were determined at room temperaturé. The (100) microhardness profile has ahardness maximum in tiie [001] and a minimum in the [O11], which supports the previous suggestion that the primary slip system is the {111}〈11¯0〉. The microhardness of the (111) plane is independent of indenter orientation, also consistent, with a {111}〈11¯0〉 primary slip system. It is concluded that these microhardness profiles are in accord with other experimental observations that the {111}〈11¯0〉 is the primary slip system in stoichiometric MgAl₂O₄ spinel.     

Mutual Indentation Hardness of Single-Crystal Magnesium Oxide at High Temperatures

The mechanical properties of single crystals of MgO were measured from 600° to 1700° C using the mutual indentation hardness technique. This method, which involves pressing together two similar crossed specimens, overcomes the problem of finding materials sufficiently rigid and chemically stable for use as indenters in conventional quasi-static methods of indentation hardness testing. By this means the hardness of the hardest materials can be measured at very high homologous temperatures. Yield strengths at known strains are obtained from the hardness measurements and are presented. The form of the hardness impression very well depicts changes in the mode of deformation of MgO over different temperature ranges. Creep processes affect the measurements; a creep analysis can be applied, and from this activation energies for the creep mechanism are obtained.     

Effect of Neutron Irradiation on Knoop Microhardness Anisotropy in MgO·3Al2O3 Single Crystals

MgO·3Al₂O₃ single crystals were irradiated with neutron fluences of 8.3 × 10²² n/m² at 100°C and 2.4 × 10²⁴ n/m² at 470°C ( E > 1.0 MeV) in the Japan Materials Testing Reactor. The Knoop microhardness of several orientations on the (100) plane of both the irradiated and unirradiated crystals were measured with different indentation loads. The change in hardness profile of the crystals was almost the same after the two irradiation conditions. The hardness increased by 4–15% because of the irradiations depending on the crystallographic orientation, the larger change being observed at orientations between the (001) and (011) directions. While both the {111}     and {110}     slip systems are simultaneously active in the unirradiated MgO·3Al₂O₃, the {111}     system may be the dominant slip system in the neutron-irradiated crystals. It is concluded that the restriction of the {110}     slip system is caused by irradiation-induced interstitial ions.     

Nd(NO_3)_3对Ni-Fe合金镀液及镀层性能的影响

研究了Nd(NO_3)_3对Ni-Fe合金镀液的阴极极化及Ni-Fe合金镀层的耐蚀性、硬度、高温抗氧化性和表面形貌的影响。结果表明:Nd(NO_3)_3可以增大Ni-Fe合金镀液的阴极极化,改善Ni-Fe合金镀层的结构,提高Ni-Fe合金镀层的耐蚀性、硬度和高温抗氧化性。     

Synthesis,Magnetic Anisotropy and Optical Properties of Preferred Oriented Zinc Ferrite Nanowire Arrays

Preferred oriented ZnFe₂O₄ nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe₂ nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe₂O₄ nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe₂O₄ nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.     

Effect of Crystal Orientation on Conductivity and Electron Mobility in Single-Crystal Alumina

The electrical conductivity of high-purity, single-crystal alumina is determined parallel to and perpendicular to the c -axis. The mean conductivity of four samples of each orientation is a factor 3.3 higher parallel to the c -axis than perpendicular to it. The conductivity as a function of temperature is attributed to extrinsic electron conduction at temperatures from 400° to 900°C and intrinsic semiconduction at temperatures from 900° to 1300°C. In the high-temperature regime, the slope on all eight specimens is 4.7 ± 0.1 eV. Hence, the thermal bandgap at 0 K is 9.4 ± 0.2 eV.     

Effect of Dopants on the Defect Structure of Single-Crystal Aluminum Oxide

Density and lattice parameter changes induced by dopants were studied in Czochralski rubies containing from 0.054 to 0.160 wt% Cr₂O₃, in Czochralski sapphires containing from 0.083 to 0.120 wt% TiO₂, and in verneuil crystals grown from powders containing 250 to 1000 ppm Ca, Mg, Si, and V. Densities were determined within at least ∼0.005% using a hydrostatic weighing technique; lattice parameter shifts were measured within a maximum of 0.25% using a step-scanning goniometer technique. Some crystals which appeared to be clear, transparent, and single-phase contained fine particles of a second phase. It is concluded that Si⁴⁺ and Ti⁴⁺ ions enter solution with the formation of cation vacancies to maintain charge neutrality, that verneuil crystals contain vanadium as V³⁺, that the solid solubility of Ca²⁺ is low (<340 ppm), and that MgO decomposes under verneuil growth conditions, resulting in formation of a second phase.     

稀土La对Ni-Fe合金镀层性能的影响

研究了La(NO_3)_3对Ni-Fe-La合金镀层的耐蚀性、高温抗氧化性、硬度、微观形貌和成分的影响。结果表明:随着La(NO_3)_3的质量浓度的增加,Ni-Fe-La合金镀层的耐蚀性、高温抗氧化性、硬度均得到明显提升,并且在La(NO_3)_3的质量浓度为0.4g/L时达到最优;Ni-Fe-La合金镀层结晶细致、结构紧密,其中含稀土La。     

Effect of Liquid Phase Chemistry on Single-Crystal Growth in PMN–35PT

This study investigated the liquid phase chemistry in Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ with excess PbO as previous studies suggested that the chemistry of the grain boundary phase may change {001} single-crystal growth. It has been shown that the chemistry of the liquid phase was dynamic as characterized in an analytical electron microscope. In fact, MgO was found to precipitate out of the system due to the saturation of MgO in the liquid, which in turn altered the liquid/solid surface energy. By changing the surface energy of the system, the matrix grains became more faceted, i.e. the frequency of {001} surfaces increased. This reduced the driving force for growth of the single crystal, which appears to be responsible for reducing the growth rate during annealing. Additional supporting evidence came from observing the effect of varying the PbTiO₃ content.     

Effect of Powder Parameters on Grain Growth in Manganese-Zinc Ferrite

The effect of calcination and ball milling on the grain growth in Mn-Zn ferrite is presented. Rates of grain growth and the effect of ball milling on the growth behavior were observed for ferrite powders calcined above and below the recrystallization temperature. It is shown that in addition to particle size and distribution, calcination temperature was a critical factor responsible for the growth behavior of ferrite.