Fracture toughness of steels with nickel content in respect of carbide morphology

Abstract

This paper is focused on the influence of Ni addition on the microstructure and fracture toughness of structural steels after tempering. Nickel is known to increase the resistance to cleavage fracture of steel and decrease a ductile–brittle transition temperature. The medium carbon, low alloy martensitic steels attain the best combination of properties in low tempered condition, with tempered martensite, retained austenite and transition carbides in the microstructure. In the present research, four model alloys of different Ni contents (from 0·35 to 4·00%) were used. All samples were in as quenched and tempered condition. Quenching was performed in oil at room temperature. After quenching, samples were tempered at 200°C for 2?h. An increase in nickel content in the investigated model structural steels causes a decrease in ε carbide volume fraction in their microstructure. Cementite nucleates independently in the boundaries of martensite laths and in the twin boundaries in the areas where the ε carbide has been dissolved. It was stated that stress intensity factor K_Ic significantly decreases in the case of the presence of dispersive elongated cementite precipitations at the boundaries of the prior austenite grains.     

Thermodynamic study and intrinsic type II superconductivity in the A-15 compound V3Si

The specific heat of a single crystal of the A-15-type compound V₃Si in the normal, mixed, and superconducting states has been measured from 4 to 30 K in magnetic fields up to 50 kOe. The analysis has been performed in a self-consistent way based on the second-order phase transition from the normal to the superconducting state. The thermodynamic critical field and then various physical parameters characterizing the superconducting and normal states are almost consistently derived from the thermodynamics and the microscopic BCS-GLAG theory. It is confirmed that V₃Si is an intrinsic type II superconductor with a high intrinsic GL parameter ₀.This work was partially supported by a Grant in Aid for Scientific Research (B) from the Ministry of Education.     

Information content of multiwavelength lidar data with respect to microphysical particle properties derived from eigenvalue analysis

The multiwavelength Raman lidar technique in combination with sophisticated inversion algorithms has been recognized as a new tool for deriving information about the microphysical properties of atmospheric aerosols. The input optical parameter sets, provided by respective aerosol Raman lidars, are at the theoretical lower limit at which these inversion algorithms work properly. For that reason there is ongoing intense discussion of the accuracy of these inversion methods and the possibility of simultaneous retrieval of the particle size distribution and the complex refractive index. We present results of the eigenvalue analysis, used to study the information content of multiwavelength lidar data with respect to microphysical particle properties. Such an analysis provides, on a rather mathematical basis, more insight into the limitations of these inversion algorithms regarding the accuracy of the retrieved parameters. We show that the effective radius may be retrieved to 50% accuracy and the real and imaginary part of the complex refractive index to +/- 0.05 and +/- 0.005i, if the imaginary part is < 0.02i. These results are in accordance with the classic approach of simulation studies with synthetic particle size distributions. Major difficulties are found with a particle effective radius of < 0.15 microm. In that case the complex refractive index may not be derived with sufficient accuracy. The eigenvalue analysis also shows that the accuracy of the derived parameters degrades if the imaginary part is > 0.02i. Furthermore it shows the importance of the simultaneous use of backscatter and extinction coefficients for the retrieval of microphysical parameters.     

Validation of the ORA spatial inversion algorithm with respect to the Stratospheric Aerosol and Gas Experiment II data

We present the results of a comparison of the total extinction altitude profiles measured at the same time and at same location by the ORA (Occultation Radiometer) and Stratospheric Aerosol and Gas Experiment II solar occultation experiments at three different wavelengths. A series of 25 events for which the grazing points of both experiments lie within a 2 degrees window has been analyzed. The mean relative differences observed over the altitude range 15-45 km are -8.4%, 1.6%, and 3% for the three channels (0.385, 0.6, and 1.02 mum). Some systematic degradation occurs below 20 km (as the result of signal saturation and possible cloud interference) and above 40 km (low absorption). The fair general agreement between the extinction profiles obtained by two different instruments enhances our confidence in the results of the ORA experiment and of the recently developed vertical inversion algorithm applied to real data.     

Effects of bacterial adhesion with respect to the type of material, structure and design of intraocular lenses

The properties of the biomaterials used to constitute lenses are important factors choosing a lens for human implantation because these can influence in posterior clinical evolutions of patients. In this study, different characteristics of intraocular lenses such as chemical composition, surface roughness and lens design have been investigated in terms of their influence into a pathological environment. Eight commercial lenses were tested by optical profiling, Infrared spectra with Fourier transformation (FTIR), water-material contact angle and scanning electron microscope (SEM) to know their chemical composition and structural characteristics. These lenses were then exposed to infectious conditions in order to evaluate their responses to the bacterial environment.     

Correlating changes in collagen secondary structure with aging and defective type II collagen by Raman spectroscopy

A novel application of Raman spectroscopy for monitoring damage to ocular collagen in wild-type mice and Del1 (+/-) transgenic mice, a murine animal model of osteoarthritis, is described. In order to understand the progression of diseases of collagen, it is necessary to use methods that can recognize alterations in affected tissue due to chemical and/or genetic modifications. The heterozygous Del1 (+/-) transgenic mouse is established as a model for early-onset osteoarthritis caused by modifications to the type II collagen gene (COL2A1) that result in a truncated collagen fiber. We expect that abnormal type II collagen is expressed in articular cartilage and eye tissue of the Del1 (+/-) mouse. Eyes excised from a subset of specimens from another study using Del1 (+/-) mice were examined by Raman spectroscopy for evidence of defective collagen. Spectral contributions from the collagen protein were readily observed. The amide III envelope (1220-1280 cm-1) was used to characterize changes in collagen secondary structure. Raman spectra of the sclera component of eyes taken from transgenic and older wild-type mice show an increased collagen disorder, as expected. These preliminary results suggest that Raman is capable of recognizing and measuring abnormality in eye collagen and may have potential as a diagnostic tool for ocular collagen damage.     

Reactions in the formation of Na3Zr2Si2PO12

Nasicon ceramics of formula Na₃Zr₂Si₂PO₁₂ were prepared from two systems, namely NH₄H₂PO₄-Na₂CO₃-SiO₂-ZrO₂ and Na₃PO₄-SiO₂-ZrO₂. The partial reactions and sequence of reactions was studied using differential thermal analysis and X-ray diffraction analysis. Kinetic restraints to completeness of reaction are indicated and sodium oxide volatilization is shown to occur. The rate-determining partial reaction involves zirconia and a sodium phosphosilicate intermediate.     

Positions of cations and molecules in zeolites with the mordenite-type framework II dehydrated hydrogen-ptilolite

A single crystal of natural ptilolite was ion-exchanged with NH₄⁺, heated to 320°C, sealed in a capillary at temperature, and the crystal structure was refined to R=0.048. Upon heating, NH₃ and H₂O were expelled and hydrogen condensed with framework oxygens. A strong correlation between T-O-T angle and the perturbation of T-O distances in adjacent tetrahedra is very similar to that in dehydrated-Ca-mordenite and is consistent with similar correlations in feldspar which were attributed to molecular-orbital effects. After adjustment for this correlation, mean T-O distances indicate slight Si, Al ordering. Remaining perturbations in T-O distances are small, and there is no convincing evidence for preferential attachment of protons to any particular framework oxygen. Some residual Na and K ions were located in site I at a twisted eight-ring. Two percent of the rings are not correctly stacked in Cmcm.     

Phenomenological approach to the coexistence of planar antiferromagnetism with high-t c type II superconductivity

A phenomenological study in d-spatial dimensions is presented for the coexistence of planar antiferromagnetism and type II superconductivity. In this approach critical temperatures in the range 30–100 K arise due to the proposed coupling of magnons and conduction electron pairs. We discuss some remarkable features of oxide ceramics, including a longer London penetration depth, shorter coherence length, lower H _c 1, higher H _c 2, large current densities, and large pinning force.     

29Si MAS n.m.r. studies of the distribution of Si and Al in the framework of zeolite LaHY

The distributions of Si and Al in the framework of LaHY zeolites were studied by ²⁹Si MAS n.m.r. and the ordering schemes of the distribution of Si and Al in the LaHY framework were obtained according to the results of ²⁹Si MAS n.m.r. It was found that the La ions can stabilize the Si (3Al) and Si (2Al) units of the framework of LaHY and can affect the coordination distribution of the next-nearest-neighbor Al atom (i-NNN) for the original Al atom. Thus, the concentration and the strength of Brönsted acid sites in LaHY zeolites can be modified by La ions.     

Transition from type I to type II behavior and the density of states in thin indium films

We have studied thin indium films in a perpendicular magnetic field by electron tunneling. From measurements of the density of states and critical field we conclude that the films undergo a transition from type I to type II behavior at a thickness of 2700 Å at 0.4 K. In thicker films the number of flux quanta in a bundle increases smoothly with thickness and we observe supercooling effects associated with type I. The thin films all have the same density of states and are reversible, indicating type II behavior. A comparison is made with other determinations of the critical thickness. The densities of states in type II lead, indium, and aluminum films are found to be different but show a consistent trend with transition temperature. Calculations only exist for bulk, dirty type II materials and are not applicable to these bulk type I materials.     

Experimental study of the copper thiosulfate system with respect to thin-film deposition

An experimental study of the copper-thiosulfate system in mild acidic (pH 5) aqueous solutions, with respect to thin-film formation, was undertaken. Thin films of Cu_xS (1 x 2) were deposited by a simple electroless technique on glass or transparent polyester films, at 50 °C. Thin films were deposited from chemical baths in which the ratios of copper to thiosulfate were varied from 1:1 to 1:10. Thin films of different compositions (Cu₂S, Cu_1.8S, Cu_1.4S and CuS) were prepared and then characterized for morphological, optical and electrical properties. The deposited films chemically close to Cu₂S were found to be amorphous, while the CuS films were a mixture of both amorphous and polycrystalline phases. The optical spectra of the Cu₂S films exhibited high transmission both in the visible region of the spectrum (beyond 600 nm) and throughout the near-infrared region (800 to 2500 nm), while CuS films were found to be highly absorptive throughout the near-infrared region, with peaked transmission in the visible region at about 560 nm. The sheet resistances of the films, determined by the standard four-probe measurements, were between 100 and 650 Ω/square.     

Developments in the synthesis of LiF:Mg,Cu,Na,Si TL material

A procedure for synthesis of the highly sensitive pellet-type LiF:Mg,Cu,Na,Si thermoluminescent (TL) detector has been newly developed. It was found that the optimum concentrations of dopants for a pellet-type LiF:Mg,Cu,Na,Si TL detector were found to be Mg: 0.2 mol %, Cu: 0.05 mol %, Na: 0.9 mol%, and Si: 0.9 mol%. The TL sensitivity of this new detector was about 30 times higher than that of the TLD-100 by light integration measurements. Reusability study of the detector was carried out for 10 cycles. The results show that the coefficients of variation for each detector separately did not exceed 0.016, and that for all 10 detectors collectively was 0.0054.     

Applicability and limitations of the Adam mathematical phantom with respect to radiological protection

Monte Carlo (MC) simulation of radiation transport is applied to an anthropomorphic mathematical (ADAM) or Zubal's voxel phantom, representing a male adult. The purpose is to compare absorbed energy in various organs (liver, kidneys, lungs, pancreas, spleen, adrenals and heart) in the simplified (mathematical) and more realistic (voxel) anatomy. A broad beam of monodirectional and monoenergetic photons (20 keV to 10 MeV), perpendicular to the longitudinal body axis, is incident on the front (AP) or the back (PA) of the phantom. Two MC codes, MCNP-4C and MCNPX-2.1.5, are used for the calculations. Specific absorbed fraction as a function of energy reflects the shielding of an organ by other organs. Comparison of the results for the two phantoms enables an evaluation of the applicability and the limitations of ADAM with respect to radiological protection. The cases studied indicate no urgent need to replace the (commonly used) mathematical phantom by a more sophisticated voxel phantom.     

On the performance of high‐order finite elements with respect to maximum principles and the nonnegative constraint for diffusion‐type equations

The main aim of this paper is to document the performance of p‐refinement with respect to maximum principles and the nonnegative constraint. The model problem is steady‐state anisotropic diffusion with decay (which is a second‐order elliptic partial differential equation). We consider the standard single‐field formulation based on the Galerkin formalism and two least squares‐based mixed formulations. We employ Lagrange polynomials with unequal‐spaced points, and polynomials of order p = 1 to p = 10 are used. It is shown that the violation of the nonnegative constraint cannot be overcome with p‐refinement alone for anisotropic diffusion. We shall illustrate the performance of p‐refinement by using several representative problems. The intended outcomes of the paper are twofold. First, this study will caution the users of high‐order approximations about their performance with respect to maximum principles and the nonnegative constraint. Second, this study will help researchers develop new methodologies for enforcing maximum principles and the nonnegative constraint under high‐order approximations. Copyright © 2012 John Wiley & Sons, Ltd.     

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain‐relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN‐on‐Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack‐free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10⁷ cm^?2 achieved to date in GaN‐on‐Si is demonstrated. With these advances, the first vertical GaN metal–insulator–semiconductor field‐effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost‐effective high power device paradigm on an Si CMOS platform are demonstrated