Effects of grinding process on residual stresses in nanostructured ceramic coatings

This paper investigates the depth profiles of residual stresses using the sin² method combined with grazing incident X-ray diffraction (GIXD) technique. It specifically focuses on the effects of grinding process on the residual stresses in the thermally sprayed nanostructured WC/12Co and Al₂O₃/13TiO₂ (n-WC/12Co and n-Al₂O₃/13TiO₂) coatings on low carbon steel substrates. The influence of grinding parameters, such as depth of cut (DOC), table feedrate, abrasive grit size and wheel bond type, on residual stresses is studied. The conditions and limitations of X-ray diffractometry for residual stress measurements are discussed. Discussed also is the difference between the average and actual depth profiles of residual stresses. The paper introduces a method for retrieving the actual depth profiles from the measured average depth profiles. Finally, the influence of peak broadening of grain size, anisotropy from different diffraction planes and surface finish of the samples on the measurement results is explored.     

Secondary ion mass spectrometry depth profiling and simultaneous electrical investigation of MOS structures

A comparative study of the electrical behaviour of MOS structures and the composition of the oxide layer was carried out by means of secondary ion mass spectrometry depth profiling and simultaneous electrical measurements. The width of the SiSiO₂ interface region was determined for wet, dry and HCl oxide layers using a special method for definition of the virtual SiSiO₂ interface of the depth profiles. A good correlation was found between the interface region width and the electrical parameters such as fixed oxide charge density and minimum surface state density for the samples analysed. The secondary ion intensity distributions of different contaminating species show a maximum at a distance of 20–80 Å from the interface. The incorporation of chlorine during HCl oxidation was monitored and a direct identification of migrating sodium ions in the HCl oxide layers was accomplished by comparing ²³Na⁺ depth profiles before and after positive bias- temperature stress.     

SIMS depth profiling of implanted helium in Al-Mn alloy using CsHe+ molecular ion detection

The use of Cs⁺ primary ions in conjunction with the detection of CsHe⁺ molecular ions is proposed for the analysis of helium in metals by secondary ion mass spectrometry (SIMS). Concentration depth profiles of helium implanted at 100keV in Al₆₀Mn₄₀ alloy have been measured. Helium concentrations down to about 100 ppm were measured at moderately low sputtering rate of 0·5nm/sec. The experimentally determined implantation profile of helium is compared with the theoretical profile obtained using the Monte Carlo Code TRIM.     

Depth profiles and concentration percentages of SiO2 and SiO x induced by ion bombardment of a silicon (100) target

Very thin-film of silicone oxide is of importance in many microelectronics device fabrication. A 9 keV Ar⁺ beam was applied to bombard a silicon (100) target ambient oxygen gas. The measurement was performed with a fixed time of bombardment but different oxygen pressure, beam intensity and temperature. An X-ray Photoelectron Spectroscopy (XPS) was employed to analyze the depth profiles and the concentration percentages of SiO₂ and SiO _x within the bombarded Si (100) samples. The percentage of SiO₂ in different depth of the sample is found to be proportional to the oxygen pressure. The thickness of SiO₂ film formed at room temperature is larger than the thickness at temperature 650 °C. The net percentages of SiO _x , except at the top layer of the surface, are varied in a small difference among different ion-bombardment conditions as the depth below 2 nm.     

Surface composition and near-surface hardness studies on high dose boron-implanted 304 stainless steel

The modification of boron-implanted near surface of 304 stainless steel having strained and strain-free surfaces was studied. The energy of the boron ion was 130 keV at a dose of 2·5×10¹⁷ ions cm⁻². Ion-implantation is known to modify the tribological properties of metals, however, it is not well-understood as to how such a shallow implanted layer can affect the microhardening. A full understanding of the process involved is yet to emerge. In the present work the ion implanted layer was characterized for boron depth profiles using AES and XPS. The implanted layer is observed to contain B₂O₃, Fe₂B, FeB and CrB₂ compounds with small fractions of chromium and iron oxides. The strain-free surface of 304 SS shows an increase in microhardness by ∼ 80% after boron ion implantation at 2 gf and the strained surface by ∼ 30% at the same load. The annealing effects on microhardness for mechanically polished and implanted samples were also investigated in the temperature range 100 to 400°C. The possible correlation of near-surface microhardness increase with boride formation is discussed.     

Electrical and optical characterisation of silicon and silicon/phosphorus implantsin InP doped with iron

Abstract

Silicon implantations into semi-insulating InP with a wide range of doses and energies have been carried out with the aim of obtaining n type layers suitable for device applications. The electrical activations obtained were typically about 70%, reaching 80% for Si/P co-implants with a dose of 10¹⁴ cm^?2, and the electrical depth profiles showed no redistribution of the implants during annealing. The mobilities obtained after all rapid thermal annealing cycles used were very high, indicating the good crystalline quality of the resulting layers. This was confirmed by Raman scattering measurements, which showed that even if the material is completely amorphised by the implantation, the annealing treatment restores the emissions found for as received unimplanted InP. After Si implantation, the photoluminescence spectrum of the samples showed the appearance of a band at 1·17 eV with high thermal stability, the origin of which was tentatively assigned to V_p–Si_p (P vacancy–Si on P lattice site) complexes.

MST/3423     

Corrosion behavior of copper T2 and brass H62 in simulated Nansha marine atmosphere

The accelerated corrosion behavior of copper T2 and brass H62 exposed in simulated Nansha marine atmosphere for different periods were investigated by weight loss method, SEM, XRD and potentiodynamic polarization measurements. The results indicate that copper T2 and brass H62 underwent severe corrosion, and the final corrosion rates at 32 days of exposure were 0.24 μm/d and 0.10 μm/d, respectively. Moreover, the overall corrosion type of copper T2 was uniform and the corrosion products Cu₂O and Cu₂Cl(OH)₃ played a vital role in the corrosion rate of copper. While the dezincification corrosion with zinc preferential dissolution was obvious in brass H62. The predominant phases were the zinc-rich compounds Zn₅(OH)₈Cl₂·H₂O, Zn₁₂(SO₄)₃Cl₃(OH)₁₅·5H₂O and NaZn₄(SO₄)Cl(OH)₆·6H₂O. There existed a large number of copper-rich holes with 20–50 μm depth beneath the corrosion product layer.     

Multiple implantation of29Si+ in semi-insulating GaAs and its characterisation

Formation of a uniformn-layer by multiple²⁹Si⁺ implantation on LEC grown semi-insulating GaAs 〈100〉 substrate and its characterisation by differential Hall measurement at room temperature is reported. The implantation energies are 60, 160 and 260 keV with corresponding doses of 1 × 10¹², 2·55 × 10¹² and 3 × 10¹² cm⁻². Asimplanted, uncapped substrates were furnace-annealed with face-to-face configuration in an N₂ ambient at 850°C with arsenic overpressure. After annealing, the samples were subjected to Hall measurements using Van der Pauw configuration. Experimental and theoretical (LSS) profiles are compared. Electrical activation of the dopant atoms was found to range from 65–90% with average mobility values lying between 2000–2300 cm² V⁻¹ s⁻¹. Uniform concentration of then-layer ∼ 10¹⁷ cm⁻³ up to a depth of 0·3 μm has been achieved. These layers are used for the fabrication of power MESFETs.     

Compositional depth profile investigation of plasma nitriding by multiple analyses techniques

Compositional depth profile in plasma nitriding is investigated by several experimental techniques including EDS, GDOES and SIMS as well as a calculated method. Plasma nitriding was carried out on high purity iron substrate at a temperature of 550 °C in an atmosphere of 75 vol.% H₂-25 vol.% N₂ for time periods of 1, 2, 5 and 10 h. SEM and XRD methods were used for microstructural evaluation and phase identification. According to EDS, GDOES and calculated data, composition of the compound layer reached nearly to Fe-8 wt% N and Fe-6 wt% N indicating ε-Fe_2-3N and γ′-Fe₄N nitrides were formed, respectively. Although nitrogen concentration was decreased to nearly zero close to the nitrided surface, calculated data and SIMS profiles show very smooth gradient in diffusion zone down to several hundreds of micrometers. The results of compositional depth profiling by EDS, GDOES and SIMS indicated good agreement between experimental findings and, thus, the techniques completed one another. It was found that EDS and GDOES are appropriate for analysis of Fe and N in the compound layer, but both have limitations for profiling of nitrogen in the diffusion zone. SIMS, on the other hand, was distinguished as a professional technique for accurate measurement of nitrogen within the diffusion zone. The experimental depth profiles indicated good consistency with calculated diffusion profiles for all treatment cycles.     

A cold model study of mass transfer in Q-BOP

At steel-making temperature, chemical kinetics can rarely be the rate-limiting step. Thus most of the reactions are limited by the rate of mass transfer to and from the reaction interface. The overall rate of mass transfer may be controlled by gas phase mass transfer or liquid phase mass transfer. Since in Q-BOP, the rate of reaction may be controlled by the rate of mass transfer in gas phase or in liquid phase, both were studied in a cold model. The different variables studied were tuyere diameter, jet direction, flow rate of gas and tuyere depth. The results of gas phase mass transfer indicate that the effect of tuyere diameter and jet direction is very small. For Reynolds number less than 9000 the effect of flow rate and tuyere depth is given by the equation,K _g A/L ₀ Q = 0·02d ₀ + 0·043, whereas for Reynolds number greater than 9000 the effect of flow rate and tuyere depth is given by the equation,K _g A/L ₀ Q=0·061d ₀+0·046. Similarly the liquid phase mass transfer coefficient is independent of the tuyere diameter and the shrouding gas, and is not much affected by the jet direction. The effect of gas flow rate and tuyere depth is given by the equation,K _L A=0·077 (Q)^0·75(L ₀)^0·61.     

Depth of Field Measurements Relevant to Single Photon Detection Using Image-intensified Microscopy

The problems of defining a depth of field d _p when individual photons emitted in a low-level luminescent process are recorded via an image-intensified microscope are discussed. Simulation studies of a self-luminous cylindrical volume source whose axis lies along the optical axis of the microscope were carried out by moving a uniformly-illuminated pinhole along the optical axis, and arranging for its in-focus image to fill exactly a circular light detector. The detector output plotted against pinhole position is approximately Gaussian in form for the objectives studied (from 10 2 /0·25 to 74 2 /0·65), and d _p is defined as the full width at half maximum. These values of d _p adequately fit the theoretical relation d _p = 2·45 R/tan sin^-1(NA/n), where NA is the numerical aperture of the objective and n is the refractive index of the immersion medium. With spherical, or near-spherical, volume sources d _p is usually significantly greater than the volume of the source. The problems of defining a depth of field p when individual photons emitted in a low-level luminescent process are recorded via an image-intensified microscope are discussed. Simulation studies of a self-luminous cylindrical volume source whose axis lies along the optical axis of the microscope were carried out by moving a uniformly-illuminated pinhole along the optical axis, and arranging for its in-focus image to fill exactly a circular light detector. The detector output plotted against pinhole position is approximately Gaussian in form for the objectives studied (from 10 2 /0·25 to 74 2 /0·65), and d _p is defined as the full width at half maximum. These values of d _p adequately fit the theoretical relation d _p = 2·45 R/tan sin^-1(NA/n), where NA is the numerical aperture of the objective and n is the refractive index of the immersion medium. With spherical, or near-spherical, volume sources d _p is usually significantly greater than the volume of the source.     

Crystallization and microstructure of a glass seal for rapid laser sealing in the system CaO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>

A glass with the composition 61 CaO·30 Al₂O₃·9 SiO₂ was studied with respect to its crystallization behavior and its suitability as a rapidly crystallizing material for laser sealing. The glass was studied by differential scanning calorimetry; from the profiles recorded, Avrami activation energies and Avrami coefficients were calculated. The latter are in the range between 0.99 and 1.55 which is supposedly attributed to sole surface crystallization. During thermal treatment as well as during laser sealing, Ca₁₂Al₁₄O₃₃, CaAl₂O₄ and Ca₃Al₂O₆ are formed. These phases were also observed in SEM micrographs as evidenced by electron backscatter diffraction from the attributed Kikuchi patterns. Transmission electron microscopy showed a crystallized CaO- and SiO₂-enriched interface which strongly adhered to the Al₂O₃ ceramic. The porosity of the crystallized seal was in the order of few percent. The studied glass proved suitable as crystallizing seal for rapid laser sealing.     

Ion probe technique for the study of gallium diffusion in silicon nitride films

The penetration of Ga in films of amorphous Si₃N₄ about 2000 Å thick on Si substrates has been studied. The films were produced by pyrolysis. Diffusion profiles were obtained by surface exposure to Ga vapor, and the implantation profiles by ion bombardment in an isotope separator. Evaluation of the profiles was effected by means of sputtering in a secondary ion microanalyzer. For depth calibration, ion yield profiles of ⁶⁹Ga⁺ of ⁷¹Ga⁺ were compared with the profiles of ³⁰Si⁺, ⁷⁰(Si₂N⁺, SiN⁺₃) and ⁷²Si₂O⁺. The integration of implantation peaks furnished a means of obtaining absolute values of Ga concentrations from the secondary ion intensities. Hence the surface concentration of vapor-deposited Ga at 1100°C was assessed to be of the order of 8 × 10²⁰ atoms cm^-3. The diffusion coefficient of Ga in Si₃N₄ at 1100°C was found to be about 5 × 10^-17 cm² s^-1. The method, which combines sputtering and mass spectrometry, appears to be applicable for measuring diffusion coefficients in this system down to about 3 × 10^-18 cm² s^-1.     

Microstructure and properties of ceramic coatings produced on 2024 aluminum alloy by microarc oxidation

The microstructures of the microarc oxidation coatings and 2024 aluminum alloy substrate were observed using the scanning electron microscope (SEM) and the phase composition of the coatings was analyzed by X-ray diffraction (XRD). Furthermore, the profiles of the nanohardness, H, and elastic modulus, E, along the coating depth were first determined using the mechanical properties microprobe. The microarc oxidation coatings consist of two layers—a loose layer and a compact layer. The H and E in the compact layer are about 18–32 GPa, 280–390 GPa, respectively. The H and E profiles are similar, and both of them exhibit a maximum value at a same depth of the coatings. The distribution of -Al₂O₃ phase content determines the H and E profiles in the coatings. The changes of -Al₂O₃ and -Al₂O₃ contents result from the different cooling rates of the molten alumina in the microarc discharge channel at the different depths of the coatings. After the microarc oxidation treatment, the microstructure of the alloy substrate, even near the Al/Al₂O₃ interface, has not been changed.     

Effects of thickness on electronic structure of titanium thin films

Effects of thickness on the electronic structure of e-beam evaporated thin titanium films were studied using near-edge X-ray absorption fine structure (NEXAFS) technique at titanium L _2,3 edge in total electron yield (TEY) mode and transmission yield mode. Thickness dependence of L _2,3 branching ratio (BR) of titanium was investigated and it was found that BR below 3·5 nm shows a strong dependence on film thickness. Mean electron escape depth (λ) in titanium, an important parameter for surface applications, was determined to be λ = 2·6 ± 0·1 nm using L _2,3 resonance intensity variation as a function of film thickness. The average L ₃ /L ₂ white line intensity ratio of titanium was obtained as 0·89 from the ratio of amplitudes of each L ₃ and L ₂ peaks and 0·66 from the integrated area under each L ₃ and L ₂ peaks. In addition, a theoretical calculation for pure titanium was presented for comparison with experimental data.     

Ladungsträger‐Tiefenprofilierung an ultra‐flachen pn‐Übergängen

Charge carrier depth profiling on ultrashallow pn‐junctions The Stepwise Oxidation Profiling (SWOP) technique has been applied to charge carrier depth profiling on boron ion implanted silicon. The procedure works by altering between electrical sheet resistance measurements on van‐der‐Pauw (VDP)‐ structures and Si layer removal by electrochemical anodic oxidation. It was shown that the SWOP profiles are matching well with SIMS reference measurements, and that a depth resolution of ≤ nm and a detection limit of 1·10¹⁶cm^?3 was achieved.     

The effect of fillers on chloropolyester blend CPB 4 and inhibition of double-base propellants

A direct bonding inhibition system based on chloropolyester blend CPB 4 has recently been developed for inhibition of double-base rocket propellants. The effect of alumina trihydrate (Al₂O₃ · 3H₂O) and antimony trioxide (Sb₂O₃) on various properties of CPB 4 has been studied, such as effect on gel time, exotherm peak temperature, tensile strength, per cent elongation, water absorption, nitroglycerine absorption, heat resistance, and flame retardant characteristics. The data on flame retardance and other characteristics indicate that CPB 4 with 30% Al₂O₃ · 3H₂O and CPB 4 with 20% Sb₂O₃ are suitable for inhibition of double-base propellants. The double-base propellant sustainers (containing 2-NDPA) have been inhibited with CPB 4 containing 30% Al₂O₃ · 3H₂O and CPB 4 containing 20% Sb₂O₃ separately (without the application of any barrier coating), and statically fired at ambient, sub-zero (after conditioning at ?40°C for 18 h) and high (after conditioning at +50°C for 18 h) temperatures. The pressure—time profiles were found to be smooth and flat in all cases, indicating that the pressure level was the same throughout the combustion duration, inferring the suitability of these systems for inhibition of double-base propellants without the application of any barrier coating.     

Subnanometer resolution in depth profiling using glancing Auger electrons

A new method for Auger depth profiling, employing a difference in the escape depth of the Auger electrons emitted at nearly normal and glancing angles, is proposed and verified. The depth profiles obtained under optimum ion sputtering conditions with registration of the glancing Auger electrons exhibit a subnanometer (0.8 nm) depth resolution. This technique was successfully applied to the study of high-quality In_xGa_1−x As/GaAs heterostructures with quantum wells grown by the method of metalorganic chemical vapor deposition.     

Machining residual stresses

As part of an extended investigation into the effects of pre-and post-processing on shot peening residual stresses, residual stresses due to a controlled turning process were investigated in the aircraft alloy 817M40. Cylindrical specimens were produced on a centre lathe with all machine parameters fixed except for feedrate. A variation in the feedrate was used to produce different surface roughnesses varying from 1·2 to 6·6 μm R_a. The residual stress field resulting from the varying feedrate was established by the well known centre hole drilling method, albeit with a modification which assisted in determining the variation of residual stresses with depth. The results indicated a definite variation in axial residual stress distribution with surface roughness, with a rough surface showing higher tensile residual stresses. This variation was however not duplicated for hoop or circumferential stresses. Maximum tensile residual stress varied from 90 MN m^?2 in the 6·6 μm R_a surface to 50 MN m^?2 in the 1·2 μm R_a surface. Although residual stresses are generally ignored in design, either because of a lack of experimental results or for ease of application, the results indicate that some consideration must be given to machining residual stresses as these can enhance or reduce the fatigue life of engineering components. The study also indicates that turning operations associated with large plastic deformations are encountered during the machining process.

MST/3230     

Fracture energy measurements of Ceramic Thermal Barrier Coatings

The fracture energy of plasma-sprayed thermal barrier coatings of ZrO₂ · MgO, ZrO₂ · Y₂O₃, ZrO₂ · CaO · Al₂O₃, and Al₂O₃ · TiO₂ on metal substrates is obtained for both adhesive and cohesive failure modes of the coatings using notched layer-bonded bend test specimens. The generalized energy release rate was employed as a measure of the fracture energy. It takes account of the nonlinearity found in the load-deflection curves of the specimens. The failure of the specimens within the coating or at the interface is accompanied by the formation and linking of secondary cracks in the coating. This causes the non-linearity in the deformation behaviour and a rate-dependent failure morphology.