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Showing papers on "Microstructure published in 1981"


Journal ArticleDOI
TL;DR: In this paper, the mechanism of formation of plasma-sprayed coatings was examined and related to the microstructure produced, and it was shown that the real area of contact between individual lamellae within the coating and between lamella and substrate is much less than the apparent area because of adsorbed and entrapped gas, oxide films or other contamination.

367 citations


Journal ArticleDOI
H.J.A. Van Dijk1, N. Hattu1, K. Prijs1
TL;DR: In this paper, the elastic properties, fracture toughness, strength and sub-critical crack growth of hydroxy apatite ceramic blocks were investigated, and it was shown that very serious slow crack growth is present.
Abstract: Hydroxy apatite ceramic blocks of varying density have been prepared from a commercial powder. The elastic properties, fracture toughness, strength and sub-critical crack growth of these materials have been investigated. Young's modulus for the nearly fully dense material is 112 GPa while the compressive strength is about 800 MPa. For the same material the strength and fracture toughness under dry conditions are 115 MPa and 1.0 MPa m1/2, respectively. Substantial slow crack growth was found under these conditions. Under wet conditions the values for strength and fracture toughness drop to about 75% of their “dry” values. In this case very serious slow crack growth is present.

287 citations


Journal ArticleDOI
TL;DR: In this article, the largest electrocaloric effect (26°K) was measured for coarse grain material in the PZST system, in the vicinity of the Curie point.
Abstract: When an electric field is applied to a dielectric material under adiabatic conditions there is a resultant change in temperature, a phenomenon known as the electrocaloric effect Compositions in the Pb(Zr,Sn,Ti)O3 system (PZST) have several phases of nearly equal free energy, allowing antiferroelectric (AFE) to ferroelectric (FE) and paraelectric (PE) to ferroelectric (FE) transitions to occur Data are presented for electrocaloric measurements on AFE materials in the vicinity of the Curie point The effect of microstructure is reported, and experimental values are related to dielectric properties through thermodynamic relations Culmination of this work resulted in the largest electrocaloric effect (26°K) measured to date for coarse grain material in the PZST system

237 citations


Journal ArticleDOI
TL;DR: In this paper, a two phase cellular morphology with a 2:17 phase surrounded by a 1:5 boundary phase was used to obtain the best hard magnetic properties of (BH) max = 33 MGOe and iHc = 13kOe.
Abstract: Alloys with compositions Co‐25.5 wt % Sm‐8 wt % Cu‐15 wt % Fe‐3 wt % Zr and Co‐Sm‐Cu‐Fe‐1.5 wt % Zr have been step aged to produce magnets with coercive force (iHc) in the range of 10–25kOe, much higher than those reported so far in the literature for the Zr alloys. The high coercive force magnets are typically aged at 800–850 °C for 10–30 hours following the solution treatment at 1150 °C. Subsequently, these are step aged to produce materials with high coercivity. The microstructure in all these alloys has a two phase cellular morphology with 2:17 phase surrounded by a 1:5 boundary phase. The long aging treatments at 800–850 °C lead to coarsening of the two phase structure. The subsequent step aging does not change the morphology, but only changes the chemical composition of the two phases. Best properties are obtained in materials with a coherent microstructure of optimum boundary phase thickness and optimum chemical composition. The highest values of iHc obtained so far are ∼26kOe and ∼16kOe for the 3% Zr and 1.5% Zr alloys respectively. The best hard magnetic properties of (BH) max = 33 MGOe and iHc = 13kOe are for a 25% Sm‐20%Fe‐4 Cu‐2% Zr alloy.

151 citations


Journal ArticleDOI
TL;DR: SiC-AIN alloys were prepared by the carbothermal reduction of silica and alumina, derived from an intimate mixture of silicon, aluminium chloride and starch, and the resulting single-phase SiC-ain powder was hot-pressed without additives to a high density.
Abstract: SiC-AIN alloys were prepared by the carbothermal reduction of silica and alumina, derived from an intimate mixture of silica, aluminium chloride and starch. The resulting single-phase SiC-AIN powder was hot-pressed without additives to a high density. The dense bodies had a fine-grained uniform microstructure. The Young's elastic modulus, microhardness, fracture toughness, thermal expansion and thermal conductivity were measured as functions of composition. The creep behaviour of the SiC-AIN alloy was compared with that of silicon carbide.

147 citations


Journal ArticleDOI
TL;DR: In this article, it was found that boron carbide can be sintered pressureless to ultrafine-grained bodies with densities of more than 95% of the theoretical density of B 4 C, if small additions of carbon are made to bors carbide powders of submicron particle size and if the compacts are heated in inert atmospheres to temperatures near 2150 °C.
Abstract: It was found that boron carbide can be sintered pressureless to ultrafine-grained bodies with densities of more than 95% of the theoretical density of B 4 C, if small additions of carbon are made to boron carbide powders of submicron particle size and if the compacts are heated in inert atmospheres to temperatures near 2150 °C. In particular the carbon acts as an inhibitor of surface-to-surface matter transport so that densification via grain boundary and/or lattice diffusion is enhanced at lower sintering temperatures. The mechanical properties of this new sintered material are summarized and compared with those of the commercial hot-pressed product.

142 citations


Journal ArticleDOI
TL;DR: In this article, a steady state processing conditions, characterized by equiaxed powder particles, a constant particle size distribution and a saturation hardness, was found to depend on the size distribution of the initial powders.
Abstract: Mechanical alloying of two aluminum alloy powders to form composite A1-A12O3 powders has been studied. Changes in powder microstructure with processing are reported and interpreted. Mechanical alloying proceeds by the continual cold welding and fracturing of the constituent powder particles when subjected to the large compressive forces of a high speed mill. A suitable organic surfactant must be added so that a balance between cold welding and fracturing is obtained. The organic surfactant is embedded and finely distributed in the powder particles during mechanical alloying and is converted to discrete A14C3 particles after hot pressing. The establishment of steady state processing conditions, characterized by equiaxed powder particles, a constant particle size distribution and a saturation hardness, is found to depend on the size distribution of the initial powders. The oxide particles formed and distributed during mechanical alloying are equiaxed, small (30 nm) and homogeneously distributed with a volumetric center to center distance of about 60 nm.

120 citations


Journal ArticleDOI
TL;DR: In this paper, dissolution of electrochromic (EC) films in aqueous media was studied and the results strongly suggest that EC films formed by evaporation are amorphous molecular solids consisting of trimeric molecules bound weakly to each other through water−bridge, hydrogen, and van der Waal's bonding.
Abstract: Despite much investigation of the electrochromic (EC) coloration process in films, such displays have not yet become commercially viable because of limited useful device life. Device degradation occurs by film dissolution on the shelf and erosion during cycling. Water plays a crucial role in both efficient coloring/bleaching and in film degradation. To better understand the degradation process and the role of water, dissolution of EC films in aqueous media was studied. The results strongly suggest that EC films formed by evaporation are amorphous molecular solids consisting of trimeric molecules bound weakly to each other through water‐bridge, hydrogen, and van der Waal's bonding. The nature of this microstructure is responsible for the high solubility. Films subjected to ion bombardment show decreased dissolution rates as well as decreased electrochromism and, while amorphous, are believed to have a random network rather than molecular microstructure.

119 citations


Journal ArticleDOI
TL;DR: In this article, the effect of both total gas pressure (Ar+H2) and partial pressure of H2 during the puttingtering of amorphous hydrogenated silicon films was investigated.
Abstract: The effect of both total gas pressure (Ar+H2) and partial pressure of H2 during the rf‐sputtering of amorphous hydrogenated silicon films was investigated. It is shown that decreasing the total gas pressure (PT) leads to a number of consistent and desirable film characteristics including no post‐deposition oxidation, essentially zero etch rate, no resolvable microstructure, predominant monohydride bonding, and low optical band gap. These lowest PT films contain ∼17 at. % H and 4 at. % Ar, have reasonable deposition rates (60–70 A/min) and are in a high state of compressive stress. The relations between the deposition variables and the more fundamental surface reaction processes are discussed. Specifically, we demonstrate that Ar ion bombardment effects, due to high negative substrate self‐biases, are dominant at low PT.

112 citations


Journal ArticleDOI
15 May 1981-Wear
TL;DR: The effects of the microstructure of two ductile steels on their behavior under solid particle erosion were determined in this article, where the steels chosen allowed microstructural changes to be made without drastically changing their hardness, which is reported to be a direct function of erosion resistance.

108 citations


Journal ArticleDOI
TL;DR: In this paper, a polysilicate-based coating is applied to polysilicon-based paints containing particles of the desired metals and the coating is sintered into a porous structure which is bonded firmly to the substrate.
Abstract: Electrodes for alkaline water electrolysis have been made by applying high specific surface area coatings of nickel or nickel‐iron alloy to steel or nickel substrates. The coatings are applied as polysilicate‐based paints containing particles of the desired metals. The coating is sintered into a porous structure which is bonded firmly to the substrate. The present electrode preparation method has been used to coat a variety of substrate forms, such as flat plates or wire screens, and is compatible with commercial alkaline electrolysis equipment. The resulting electrodes were found to be particularly effective as anodes for oxygen evolution. The efficiency of the electrodes was greatly influenced by coating microstructure. This microstructure, in turn, could be controlled by adjusting the sintering conditions. Electrochemical operating characteristics of the electrodes in at 80°C were determined. Comparable oxygen evolution efficiencies were obtained with coatings made from nickel powders, nickel flake, and nickel‐iron alloy powder.

Journal ArticleDOI
TL;DR: In this paper, a pyrolytic hydrogen reduction of MoO2Cl2 in the temperature range 550-710°C on both quartz and metal substrates is described.

Journal ArticleDOI
TL;DR: In this article, a uniform, equiaxed fine dispersion of oxygen-and carbon-based particles is obtained, and a very fine grain structure, pinned by the dispersoid, is generated.
Abstract: Mechanical alloying is a unique high energy milling process for producing metal powders with a controlled microstructure When applied to aluminum based alloys, a uniform, equiaxed fine dispersion of oxygen- and carbon-based particles is obtained In addition, a very fine grain structure, pinned by the dispersoid, is generated Relatively low volume loadings of dispersoid may be employed to achieve attractive combinations of properties including ambient temperature tensile strength, corrosion resistance and stress corrosion cracking resistance The development of a dispersion strengthened aluminum-4 pct magnesium alloy is discussed

Journal ArticleDOI
TL;DR: In this article, the optical properties of undoped and P-doped silicon prepared by low-pressure chemical vapor deposition were measured by spectroscopic ellipsometry over the energy range 3.0-6.0 eV.
Abstract: The optical properties of undoped and P‐doped silicon prepared by low‐pressure chemical vapor deposition were measured by spectroscopic ellipsometry over the energy range 3.0–6.0 eV. A marked effect of material microstructure is observed. Approximate values of the density deficit and of the volume fractions of crystalline and amorphous material are estimated as components of the microstructure by comparing measured spectra to those synthesized from constituent spectra in the Bruggeman effective‐medium approximation.

Journal ArticleDOI
TL;DR: In this paper, the effects of long-term thermal ageing on the microstructure of AlSl type 316 stainless steel are described, which is related to reported embrittlement of the steel.
Abstract: The effects of long-term thermal ageing on the microstructure of AlSl type 316 stainless steel are described. The microstructure of the aged steel is related to the reported embrittlement of the steel. The precipitation found is complex and the embrittlement appears to result, in part, from specimen preparation techniques interacting with the microstructure. The dominant creep deformation mechanism under service conditions appears to be diffusion creep.

Journal ArticleDOI
TL;DR: In this paper, the effects of compositional and microstructural variables and processing conditions on the room temperature thermal diffusivity of hot-pressed and reaction-sintered silicon nitride were determined.
Abstract: The effects of compositional and microstructural variables and processing conditions on the room temperature thermal diffusivity of hot-pressed and reaction-sintered silicon nitride were determined. The thermal diffusivity for hot-pressed silicon nitride increases withβ-content. Maximum thermal diffusivity is reached at about 3 wt % MgO. The higher thermal diffusivity of the β-phase is attributed to its higher purity level and the less distorted crystal structure compared to theα-phase. In reaction-sintered nitride the thermal diffusivity is strongly influenced by the relative amount and needle-like morphology of theα-phase. Correlations of the thermal diffusivity with mechanical properties are discussed.

Journal ArticleDOI
TL;DR: In this paper, the deformation behavior during upset forging has been determined for Ti-6242 in both the (α + β) and β starting microstructures, with an approximate transition temperature of 930 °C.
Abstract: The deformation behavior during upset forging has been determined for Ti-6242 in both the (α + β) and β starting microstructures. For (α + β), flow softening attributed to deformation heating was observed. Deformation heating accounted for only a fraction of the extensive flow softening of the β microstructure. The dependence of log σ on 1/T was linear for (α + β) and bilinear for the β microstructure, with an approximate transition temperature of 930 °C. The two temperature regimes for β corresponded to distinct deformed microstructures which were manifestations of different softening mechanisms, all promoting the flow-induced transformation of metastable β microstructure to the equilibrium (α + β) microstructure. Based on the experimental data, flow stress equations for both microstructures, and empirical equations describing the flow softening behavior of β have been developed. WithT and ġe as the only input variables, these equations can accurately predict the σ - e relationships for process modeling of this alloy.


Journal ArticleDOI
TL;DR: In this article, the properties of boride layers on steels alloyed with chromium, molybdenum or vanadium are investigated, and the results reveal that adhesion, abrasion, and surface fatigue are strongly influenced by the solution of the elements of the differently alloyed steels in the Boride layers, while tribooxidation is influenced to a minor extent.

Journal ArticleDOI
TL;DR: In this article, polycrystalline MgO and MgAl2O4 (spinel) samples were irradiated at 430 ±5 K in HFIR to a fast neutron fluence of 2.1 × 1026 n/m2, E > 0.2 MeV, and 4.6× 1026 thermal N 2.

Journal ArticleDOI
TL;DR: In this paper, the development of precipitation microstructure during stress-relief heat treatment of the bainitic heat-affected zone in 2.25Cr-1Mo steel has been studied using transmission electron microscopy, scanning transmission electron microscope, and energy-dispersive X-ray analysis techniques on carbon extraction replicas and thin foils.
Abstract: The development of precipitation microstructure during stress-relief heat treatment of the bainitic heat-affected zone in 2.25Cr-1Mo steel has been studied using transmission electron microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray analysis techniques on carbon extraction replicas and thin foils. Examinations have been made of four 2.25Cr-1Mo alloys (‘pure’, doped with 540 ppm phosphorous, doped with 500 ppm tin, and commercial purity) as part of an overall investigation into stress-relief cracking in 2.25Cr- 1Mo steel. The precipitation behaviour is discussed in terms of its relevance to fracto graphic observations and segregation characteristics which are reported in detail elsewhere.

Journal ArticleDOI
TL;DR: SiTiO3 capacitor material with indiffused Bi2O3 was studied using SEM, ESCA combined with Ar+ ion-etching, and TEM equipped with EDX.
Abstract: SiTiO3 capacitor material with indiffused Bi2O3 was studied using SEM, ESCA combined with Ar+ ion-etching, and TEM equipped with EDX. The apparent thickness of a second-phase layer observed with SEM was found to be influenced by in-depth effects. ESCA and TEM results show that only a 10- to 100-nm thick layer of second phase is present between the SrTiO3 grains. In addition, it was found with TEM that the outer part of each grain contained Bi (at most 2 at.%), representing a diffusion layer. These results have implications for the boundary-layer model proposed to explain the dielectric properties.

Journal ArticleDOI
TL;DR: In this paper, the microstructures of oxide scales on SiC single crystals, produced by oxidation at 1400°C for various lengths of time, were studied by light and transmission electron microscopy and by X-ray diffraction.
Abstract: Microstructures of oxide scales on SiC single crystals, produced by oxidation at 1400° C for various lengths of time, were studied by light and transmission electron microscopy and by X-ray diffraction. At short oxidation times the oxide films were amorphous; at longer times they consisted of spherulitic cristobalite. The cristobalite is thought to grow by devitrification of the amorphous phase. No significant difference in oxide scale thickness or structures was found between commercial purity and semiconductor grade crystals.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the effect of adding V and Nb to the 0.05C-10Cr-2Mo steels and their effects on the creep rupture strength and microstructure of the steels.
Abstract: The new ferritic heat-resisting steels of 0.05C-10Cr-2Mo-0.10V-0.05Nb (Cb) composition with high creep rupture strength and good ductility have already been reported. The optimum amounts of V and Nb that can be added to the 0.05C-10Cr-2Mo steels and their effects on the creep rupture strength and microstructure of the steels have been studied in this experiment. The optimum amounts of V and Nb are about 0.10 pct V and 0.05 pct Nb at 600 °C for 10,000 h, but shift to 0.18 pct V and 0.05 pct Nb at 650 °C. Nb-bearing steels are preferred to other grades on the short-time side, because NbC precipitation during initial tempering stages delays recovery of martensite. On the long-time side, however, V-bearing steels have higher creep rupture strength. By adding V to the steels, electron microscopic examination reveals a stable microstructure, retardation during creep of the softening of tempered martensite, fine and uniform distribution of precipitates, and promotion of the precipitation of Fe2Mo.

Journal ArticleDOI
TL;DR: In this paper, in situ observations of thin polycrystalline specimens of sodium nitrate (calcite structure) at temperatures between 20°C and 300°C (0.98 Tm) deformation twinning is observed.

Journal ArticleDOI
01 Jan 1981-Wear
TL;DR: In this article, the effects of both mechanical surface treatments and heat treatments on the erosion resistance of 6061 aluminum alloy were studied in order to gain a better understanding of material properties which affect erosion behavior.

Journal ArticleDOI
TL;DR: In this article, during neutron irradiation of an Al-2.2% Mg solid solution alloy in the High Flux Isotope Reactor to fast and thermal fluences μ1027neutrons(n)/m2 at 328 K (0.35 Tm) about seven percent insoluble, transmutant silicon was produced.

Journal ArticleDOI
TL;DR: In this paper, the d.c. resistance of amorphous red phosphorus has been measured up to pressures of 90 kbar and at 70 kbar, a transition to orthorhombic black phosphorus was observed.
Abstract: The d.c. resistance of amorphous red phosphorus has been measured up to pressures of 90 kbar. At 70 kbar, a transition to orthorhombic black phosphorus was observed. The effect of an initially inhomogeneous microstructure is discussed. At a fixed pressure, a time dependence of the resistance was observed, and this is considered to be due to a relaxation of the glass structure. The temperature dependence of the resistance at constant pressure suggests that variable-range hopping becomes the dominant conductivity mechanism as pressure is increased and an increase in the number of defect sites is responsible for the decrease of resistance. Comparison is made with the chalcogenide glasses, the tetrahedral amorphous materials and with preliminary data for phosphorus produced by chemical transport in a low-pressure hydrogen plasma.

Journal ArticleDOI
TL;DR: In this paper, a high power CW CO2 laser with an average power density of 13.4 MW cm-2 was used to produce metastable phases in three Ag-Cu alloys.
Abstract: A scanning high power CW CO2 laser with an average power density of 13.4 MW cm-2 was used to produce metastable phases in three Ag-Cu alloys; Cu 25 at pct Ag, Cu 50 at pct Ag, and Cu 75 at pct Ag. Scanning, at traverse rates of 10 to 115 cm s-1, was performed in an inert atmosphere to prevent oxidation. Inspection of the trails by scanning electron microscopy showed the microstructure to be either cellular dendritic or featureless. X-ray examination of the trails verified the presence of extended metastable solid solutions. After etching, the transverse section showed alternating light and dark bands perpendicular to the local growth direction. Through the use of energy dispersive X-ray analysis, it was shown that there was a significant increase in the Ag concentration in the light bands.

Journal ArticleDOI
TL;DR: In this article, a crack propagation model in a brittle composite containing “penetrable” particles was proposed to explain the Lange-Evans theory of fracture in brittle composites containing impenetrable particles.
Abstract: Flexural strength and fracture surface energy were determined for lead borate glasses whose compositions lie in the immiscible region of the PbO-B2O3 system. The microstructural characterization indicated that the glasses are typical particulate composites which consist of two immiscible phases. For the glasses whose microstructure consists of PbO-rich particles/B2O3-rich matrix (B2O3-rich side of the miscibility gap), the fracture surface energy was found to decrease with increasing second-phase particles. To explain this behaviour, a crack propagation model in a brittle composite containing “penetrable” particles was proposed. On the other hand, for the glasses whose microstructure consists of B2O3-rich particles/PbO-rich matrix (PbO-rich side of the miscibility gap), an increase in fracture surface energy with volume fraction of dispersed particles was observed. This phenomenon could be best explained by Lange-Evans theory of fracture in brittle composites containing “impenetrable” particles. It was concluded that, when the critical crack size in a non-dispersed host glass is much larger than the particle size, the crack size in particulate composites is invariant with microstructure and also that the variation of strength results entirely from the variation of fracture toughness.