Annealed Materials Research Articles

Effects of additive amount on microstructure and fracture toughness of SiCTiB 2 composites

Powder mixtures of β-SiC-30 wt% TiB 2 containing 5 wt% (ST1), 10 wt% (ST2), and 20 wt% (ST3) Al 2O 3Y 2O 3 as sintering additives were liquid-phase sintered at 1850 °C for 1 h by hot-pressing and subsequently annealed at 1950 °C for 2, 6, and 12 h. These materials had a microstructure of ‘in situ-toughened composites’ as a result of the β→α phase transformation of SiC during annealing. The introduction of larger amount of additives accelerated the grain growth of elongated α-SiC grains with higher aspect ratio, resulting in the improved fracture toughness. The fracture toughnesses of 12-h annealed materials with 5, 10, and 20 wt% additives were 5.7, 5.9, and 7.1 MPam sol1 2 , respectively.

Magnetic and electrical characterizations of thin NiFe and NiFeMo films

This work presents, as a function of deposition parameters, the comparative measurements performed on thin magnetic films (0.06–0.6 μm) of Ni 81Fe 19 and Ni 80Fe 15Mo 5 deposited by r.f. plasma sputtering. Magnetic measurements were performed using an alternating-gradient magnetometer. Electrical characterization consisted basically of resistivity measurement. For as-deposited thin films, we measured the influence of the deposition parameters, thickness and sample shape (which is a way to characterize the demagnetising field). We obtained typical values for saturation magnetization, in the range of 0.6–0.8 T, independent of deposition parameters. The coercive field lies in the range of 3–80 Am −1 for as-deposited films. The electrical resistivity of as-deposited films is around 65 μΩ cm for NiFeMo and 20 μΩ cm for NiFe. Measurements were also carried out on thin films annealed at different temperatures under an external magnetic field. We observe the magnetic anisotropy in the film plane. The coercive field of annealed films increases up to 1300 A m −1. We also present a comparative study of as-deposited and annealed materials.

Electrical, magnetic and structural characterization of fullerene soots

Although it is some five years since fullerenes were extracted in macroscopic quantities from the black, superficially amorphous sooty deposits produced by a carbon arc under helium, little is known in detail about the structure of the deposit or its electrical and magnetic properties. Here we provide evidence that this deposit, known as fullerene soot, is composed of defective networks of carbon atoms which do not have all valencies satisfied. We have studied these soots, before and after thermal annealing, using x-ray and electron diffraction, electron spin-resonance (ESR) spectroscopy, infra-red transmission and measurements of electrical conductivity. We find that localized states associated with such dangling bonds are removed from the soot on annealing and this process is accompanied by an ordering transition which modifies the electrical and magnetic properties. The fullerene soot particles appear to be encapsulated aggregates of highly defective carbon `onions'. Such metastable defective networks undergo a subtle ordering processes upon heat treatment which is accompanied by a rise in the electrical conductivity and a loss of paramagnetism due to the elimination of unsatisfied carbon atom valencies. Electrical conductivity and infra-red transmission measurements indicate that the centre of these `onions' is graphitic, with metallic properties. The temperature dependence of the electrical conductivity suggests that charge transport in both annealed and unannealed materials occurs by tunnelling between metallic islands in the sample. The ESR linewidth, arising from the spin centres in fullerene soots, is not significantly changed by exposure to oxygen. This suggests that the free radical centres in fullerene soots are extremely efficiently isolated from the atmosphere - presumably by encapsulation. This behaviour contrasts with that of amorphous carbons prepared by thermal decomposition of organic materials (chars). The ESR g-factors of the fullerene soots are lower than those of chars, which suggests that the radicals in fullerene soots have strong sigma character due to unsatisfied -type valencies. In this paper, a plausible structure and associated annealing mechanism for the fullerene soot is presented based on these experimental observations. .

Metastable iron nitrides by mechanical alloying

Mechanical alloying of iron nitrides, e-Fe 3 N and γ'-Fe 4 N together with α-Fe has been carried out in an attempt to produce the metastable α-Fe 16 N 2 phase. The distribution of nitrogen in as-milled and annealed materials is determined by Mossbauer spectroscopy. The distinctive feature in the Mossbauer spectrum of α-Fe 16 N 2 , the hyperfine component with B hf = 40 T attributed to Fe in 4d sites which are furthermost from nitrogen is not seen in any of the Mossbauer spectra. The as-milled product is nano-crystalline α-Fe with an amorphous intergranular phase of approximate composition Fe 80 N 20 . The magnetization of samples decreased on milling and returned to the starting values after annealing which recovers the equilibrium starting mixtures. In the case of the Fe 3 N + Fe experiments, annealing produced some Fe 4 N together with Fe 3 N and Fe.

Grain Growth and Fracture Toughness of Fine‐Grained Silicon Carbide Ceramics

Fine-grained silicon carbide ceramics with an average grain size of 0.11 {micro}m were liquid-phase sintered from fine {beta}-SiC powder by hot pressing. The hot-pressed materials were subsequently annealed to enhance grain growth. The diameters and aspect ratios of grains in the hot-pressed and annealed materials were measured on polished and etched surfaces. The bimodal grain size distribution in annealed materials was obtained at 1,850 C without appreciable phase transformation. The average diameter and average aspect ratio increased with annealing time. The fracture toughness of a fine-grained silicon carbide ceramic determined by the Vickers indentation method was 1.9 MPa {center_dot} m{sup 1/2}. The fracture toughness increased to 6.1 MPa {center_dot} m{sup 1/2} after grain growth by annealing at 1,850 C for 12 h. Higher fracture toughness of annealed materials is due to bridging by elongated grains as evidenced by R-curve-like behavior.

SIMOX: processing, layer parameters design, and defects control

In this paper, some of the important results based on SIMS, RBS, ion channelling, and TEM studies of the as-implanted and annealed SIMOX materials are presented. The mechanisms responsible for the buried oxide layer formation are discussed, together with a semi-empirical model for the design of layer parameters and the concept of the dose window necessary for producing high quality SIMOX.

Ball-milling of Fe-C (20–75% Fe)

Powder mixtures of Fe and activated C containing 20, 50 and 75 at % Fe have been milled in vacuum for periods of up to 210 h. X-ray diffraction and Mössbauer effect measurements of the as-milled and annealed materials (500°C, 15 min) show the presence of γ-phase austenite (typically ∼10%) and the Fe 3C phase at different stages of the milling process in all samples, with the Fe 7C 3 phase also present in the milled Fe 50C 50 material. The behaviour of Fe-C (activated) milled in vacuum is found to be similar to that of Fe-C (graphite) milled in a gaseous atmosphere.

Phase formation in cold-extruded and annealed titanium aluminide powder materials : T.J. Jewett et al (GKSS Research Centre, Geesthact, Germany)

Phase formation in cold-extruded and annealed titanium aluminide powder materials : T.J. Jewett et al (GKSS Research Centre, Geesthact, Germany)

The effect of gas nitriding on fatigue behaviour in pure titanium

The effect of gas nitriding on fatigue behaviour has been studied in commercial pure titanium under rotating bending. Smooth specimens were nitrided at 850 °C and 1000 °C for 9 h in pure nitrogen gas. The depths of the obtained nitrided layers were approximately 20 μm and 55 μm, respectively. It was found that the fatigue strengths of the nitrided materials were superior to those of the corresponding annealed or untreated materials; in particular, fatigue strength was markedly increased by nitriding at 850 °C, and was higher than that of the material annealed at 700 °C. Based on detailed observations of crack initiation, crack growth and fracture surfaces, it is concluded that the improved fatigue strength of the nitrided materials can be attributed to enhanced resistance to both crack initiation and growth.

Improved operational properties of superclean 3.5% NiCrMoV rotor steel: Mayer, K. H., Kachler, W. and Konig, H. Clean Steels Technology: Proc. R.I. Jaffee Memorial Symposium, Chicago, Illinois, USA, 2–5 Nov. 1992, pp 205–212

The effect of gas nitriding on fatigue behaviour has been studied in commercial pure titanium under rotating bending. Smooth specimens were nitrided at 850 °C and 1000 °C for 9 h in pure nitrogen gas. The depths of the obtained nitrided layers were approximately 20 μm and 55 μm, respectively. It was found that the fatigue strengths of the nitrided materials were superior to those of the corresponding annealed or untreated materials; in particular, fatigue strength was markedly increased by nitriding at 850 °C, and was higher than that of the material annealed at 700 °C. Based on detailed observations of crack initiation, crack growth and fracture surfaces, it is concluded that the improved fatigue strength of the nitrided materials can be attributed to enhanced resistance to both crack initiation and growth.

Mechanical Property Characterisation of Crystalline, Ion Implantation Amorphised and Annealed Relaxed Silicon with Spherical Indenters

ABSTRACTSilicon single crystals have been ion implanted with Si ions at various energies and doses sufficient to achieve amorphisation to a depth of more than 1μm. This surface was subsequently annealed at 450°C for 30 minutes in vacuum to relax the implanted amorphous silicon. Mechanical properties of the different materials (crystalline, amorphous and annealed) were measured using a nominally 10 μm radius diamond tipped indenter and two indenting procedures; continuous loading and load partial-unloading. The crystalline material exhibited similar force-displacement behaviour to that observed by Weppelmann et al. [1] including a critical pressure to induce deformation on loading and a "pop-out" event during unloading. The amorphous and annealed materials showed a greater degree of plastic deformation but did not exhibit "pop-out" behaviour at lower loads (200 mN). The results are analysed to determine the difference of mean pressure with depth of penetration for all the materials. The onset of ductility was 5.5 to 6 GPa for the amorphous material and 10.9 GPa for the crystalline material. The depth dependence of hardness for the amorphous and annealed material showed substantial evidence of work hardening whereas the crystalline material did not.

Preparation of superconducting BiPbSrCaCuO ceramics by melt casting

Abstract BiPbSrCaCuO bulk samples with nominal composition of Bi1.6Pb0.4Sr2Ca3Cu4Oy (2234) were prepared by a melt casting method. The melting process was carried out on two different powders; one consisting of the precursor materials, and one in which the precursor had been calcined. The effects of the melt-casting on the structure, the phase compositions and the superconducting properties have been investigated in as-cast and annealed materials. It was found that the high-Tc superconducting phase can be formed by annealing at 850°C. The annealed (850°C, 200h) sample of 2234 exhibited superconductivity with a Tc(zero) of 105K and a critical current density (77K, zero magnetic field) of 113 A.cm−2.

Nanoanalysis of semi-insulating polycrystalline silicon by high-spatial-resolution electron microscopy

Semi-insulating polycrystalline silicon (SIPOS) has been used extensively as a passivating layer in highvoltage power devices and as the wide bandgap material in solar cells. Little information, however, is available on the nano-scale nature of oxygen distribution and its redistribution upon thermal annealing, and the rnicrostructural characteristics of SIPOS thin films. In the present study, the atomic structure of SIPOS layers on Si wafers was characterized by HREM and the oxygen content was quantitatively determined by nanospectroscopy.SIPOS films were chemical vapor deposited on Si {001} wafers from a preset mixture of SiH4 and N2O. Annealing was done in dry N2 at 900°C for 30 min. Cross-sectional TEM specimens were prepared from both as-deposited and annealed materials. HREM was done in an ISI-002B at 200kV. Nanospectroscopy was performed at 100kV in a Philips EM400ST/FEG microscope coupled to a Gatan parallel-detection EELS, with better than 3 nm spatial resolution.

The Effect of Gas Nitriding on Fatigue Behaviour of Ti-6Al-4V Alloy.

The fatigue behaviour of a gas-nitrided Ti-6Al-4V alloy has been studied under rotating bending fatigue test. The results were compared to those of annealed materials on the basis of detailed observations on crack initiation, growth and fracture surfaces. Nitriding was performed using smooth specimens for 4 h and 15 h at 850°C in pure nitrogen gas, and the depths of the nitrided layer obtained were approximately 25 μm and 65 μm, respectively. The fatigue lives of material nitrided for 4 h were shorter than those of annealed material, but the fatigue limit increased. On the other hand, fatigue strength was reduced by nitriding for 15 h. It is concluded that the decrease in fatigue strength of nitrided materials is mainly attributed to inferior crack initiation resistance of the nitrided layer.

Low-frequency noise in depletion-mode SIMOX MOS transistors

Low-frequency noise measurements in depletion-mode SIMOX MOSFETs are reported. A simple model provides a reliable interpretation of the low-frequency noise in multi-interface depletion-mode transistors. An experimental procedure to separate noise contributions of front and back interfaces from noise due to bulk carrier fluctuations is described. The noises generated in the thin Si film and at the two Si-SiO/sub 2/ interfaces can be identified and characterized independently in terms of bulk properties and interface trap densities. Single-level traps at the back interface and defects in the volume are detected in high-temperature annealed materials.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microtomography observation of precipitates in semi-insulating GaAs materials

Defects introduced in GaAs materials during growth and post-growth thermal processes are known to largely influence the specifications of transistors. Various techniques have been improved to detect these defects and obtain images of their organization. Laser scanning tomography provides us with macroscale images of fault structures, the details of which up to now have not been resolved. In this paper we show that extending this technique to a microscopic scale reveals small individual scatterers which are at the origin of the tomography images: these scatterers are microprecipitates located on dislocations or condensed on point defects. Several examples of undoped, In doped, and annealed materials are reported and discussed: apart from the decoration precipitates which look rather large, smaller and abundant microprecipitates are observed, even in dislocation-free materials; their number is found to be consistent with microetched pit density responsible for the ‘‘microroughness’’ of etched surfaces. Ingot annealed materials developing a conventional cell structure are also shown to contain clouds of such microprecipitates concentrated in the central region of the cells. It is likely that the type and the arrangement of these particles are strongly related to the dislocation network and to the thermal history. There is no doubt that the chemical species involved play an important role at a microscale level in the local electronic properties of the material.

Rapid thermal annealing of si implanted gaas

Rapid thermal annealing (RTA) technology offers potential advantages for GaAs MESFET device technology such as reducing dopant diffusion and minimizing the redistribution of background impurities. LEC semi-insulating GaAs substrates were implanted with Si at energies from 100 to 400 keV to doses from 1 × 1012 to 1 × 1014/cm2. The wafers were encapsulated with Si3N4 and then annealed at temperatures from 850-1000° C in a commercial RTA system. Wafers were also annealed using a conventional furnace cycle at 850° C to provide a comparison with the RTA wafers. These implanted layers were evaluated using capacitance-voltage and Hall effect measurements. In addition, FET’s were fabricated using selective implants that were annealed with either RTA or furnace cycles. The effects of anneal temperature and anneal time were determined. For a dose of 4 × 1012/cm2 at 150 keV with anneal times of 5 seconds at 850, 900, 950 and 1000° C the activation steadily increased in the peak of the implant with overlapping profiles in the tail of the profiles, showing that no significant diffusion occurs. In addition, the same activation could be obtained by adjusting the anneal times. A plot of the equivalent anneal times versus 1/T gives an activation energy of 2.3 eV. At a higher dose of 3 × 1013 an activation energy of 1.7 eV was obtained. For a dose of 4 × 1012 at 150 keV both the RTA and furnace annealing give similar activations with mobilities between 4700 and 5000 cm2/V-s. Mobilities decrease to 4000 at a dose of 1 × 1013 and to 2500 cm2/V-s at 1 × 1014/cm2. At doses above 1 × 1013 the RTA cycles gave better activation than furnace annealed wafers. The MESFET parameters for both RTA and furnace annealed wafers were nearly identical. The average gain and noise figure at 8 GHz were 7.5 and 2.0, respectively, for packaged die from either RTA or furnace annealed materials.

回転電極法粉末を熱間静水圧プレスして製造したTi-6Al-6V-2Sn合金の組織と機械的特性

The effect of post-consolidation heat treatment on the microstructure and the resultant mechanical properties were evaluated both at room and cryogenic temperatures (77 K and 4 K) for hot isostatically pressed (HIP) Ti-6Al-6V-2Sn alloy powders made by the rotating electrode process (REP).The uniform, high integrity properties equivalent to wrought mill annealed material were obtained by this fabrication method.The post-consolidation heat treatment had a marked effect on the microstructural modification. The highest ductility was obtained for as-HIP fabricated and mill annealed materials. The solution treated and aged (STA) material showed the highest strength with moderate ductility, whereas the beta annealed materials exhibited the lowest strength and ductility. The fracture toughness showed the highest value in the as-HIP fabricated condition, and the lowest in the STA condition. The good properties combinations obtained in the as-HIP fabricated condition could be attributable to the formation of finer and lower aspect ratio alpha platelets during alpha-beta HIP treatment.The comparison with HIP consolidated REP Ti-6Al-4V alloy powders showed that strength was somewhat higher for Ti-6Al-6V-2Sn, whereas ductility was higher for Ti-6Al-4V, especially at cryogenic temperatures.

Void formation and solute segregation in ion-irradiated niobium-base alloys

The void-volume fraction in unalloyed Nb and Nb-base binary alloys containing either ~ 2.4 a/o Mo, Ti, Zr, Hf, Ni, Fe, V or Ta has been determined from observations of specimens by transmission electron microscopy following 3.0-MeV 58Ni + ion irradiation at 1225 K to ~ 50 dpa. Also, the thermal- and irradiation-induced segregation of these substitutional-atom solutes to the specimen surface and within the irradiation-damaged layer have been determined by use of the Auger Electron Spectroscopy technique. In addition, the segregation of the intrinsic, interstitial-O impurity (~ 0.06 a/o) in these irradiated or annealed materials has been determined. The void-volume fraction and the segregation of solutes have been shown to be correlated by the solute diffusivity and the relative chemical affinity of the substitutional solutes for O. The correlated diffusion of vacancy defects and O atoms is postulated to explain the experimental results.

Effect of environment on crack growth behavior in austenitic stainless steels under creep and fatigue conditions

Crack growth behavior at high temperatures under cyclic, static, and combined loads was studied in annealed and 20 pct cold-worked Type 316 and 20 pct cold-worked Type 304 austenitic stainless steels in air and vacuum. Under cyclic load, crack growth rates in annealed Type 316 steel are slightly lower in vacuum than in air, but this difference decreases with increase in crack growth rate. Most importantly, the effect of temperature on crack growth is present even in vacuum and arises mostly from the variation of elastic modulus with temperature. In the cold-worked Type 316 steel, the pronounced hold-time effects on fatigue crack growth in air reported in the literature persists even in vacuum. This implies that at high crack growth rates these hold-time effects arise mostly from creep-fatigue interaction rather than environment fatigue interaction. Environment has a negligible effect also on crack growth under static load. Thus, time dependent crack growth in these steels is due to creep processes. Crack growth behavior in annealed and cold-worked materials are compared and reasons for the enhanced time dependent crack growth in cold-worked material are discussed in detail.