On the compositional,optical and electrical characteristics of vacuum‐deposited GaAs1‐xPx films prepared by a successive evaporatron method

Abstract

GaAs_1‐xP_x thin films have been deposited onto glass substrates at a rate of 50Å/min. in a vacuum of 5 x 10^‐5 Torr using a successive evaporation method. Thin films of various compositions (X = 0.3–0.9) were obtained at gallium source temperature T_Ga = 870°C, arsenic source temperature T_As = 275°C, phosphorus source temperature T_P = 330°‐363°C and substrate temperature T_sub = 265°‐330°C. Compositional, optical (absorption) and electrical properties of the films in a thickness range of 1300–1900 Å were determined by using an X‐ray diffractometer, a grating spectrometer and an electrometer respectively. The experimental results were compared with those for simultaneous evaporation and discussed from the atomistic viewpoints.

The values of △X/△T_sub are ‐ 7 x 10^‐3 and ‐1 x 10^‐3 °C^‐1 for successive and simultaneous evaporation respectively, the difference of which can be explained by the absorption effect of a predeposited Ga layer in successive evaporation. The value of △X/△Tp is about +7 x 10^‐3°C^‐1 for the two evaporation methods, however, it levels off more distinctly at higher substrate temperatures. Absorption edge shift and relatively low resistivity suggest that successively vacuum‐deposited films have much more phosphorus vacancies and/or impurities than simultaneously vacuum‐deposited and chemically vapor‐deposited films.     

Effect of heat treatment on age hardening behaviour of electroless nickel–phosphorus coatings

Abstract

Electroless nickel–phosphorus (EN) coatings have been widely used in various industries such as oil, gas, electronic, chemical, automotive, aerospace, and mining. The EN coating process is based on a redox reaction in which a reducing agent is oxidised and Ni²⁺ ions are reduced on the substrate materials. Once the first layer of Ni is deposited, it acts as a catalyst for the process. Consequently, a linear relation between coating thickness and time usually occurs. If the reducing agent is sodium hypophosphite, the deposit obtained will be a nickel–phosphorus alloy. Also, the actual nickel and phosphorous levels in the EN deposit depend on the composition, temperature, and pH of the plating bath used. In this work, three types of EN coatings have been studied: low, medium, and high phosphorus Ni–P alloys. The techniques used were: differential scanning calorimetry (DSC), SEM, and hardness measurements. Heat treatment resulted in precipitation of nickel phosphides, e.g. Ni₃P, and nickel crystallites. Thus, the phosphorus content of the coating was reduced. The results of isochronal age hardening showed that the peak age hardening temperature for the three EN coatings occurred at ～673 K. However, the time to reach peak hardness during isothermal heat treatment at 593 K varied with phosphorus content. Also, it was found that the temperatures at which peak precipitation reactions occur during DSC scan are influenced by phosphorus content.     

Investigating effect of temperature and time of metalised layer sintering by SMPP method on tensile strength and thermal shock resistance

Abstract

Sintered metal powder process is one of the high technology methods in ceramic–metal joining processes. Improvement in joining zone properties is very important in this method. The present study reveals the effect of metalised layer sintering temperature and time, and applied layer thickness on tensile strength and thermal shock resistance of alumina–copper joint. The results reveal that primary sintering for holding time duration of 90 min at a temperature of 1530°C and applied layer thickness of 50 μm with proper different stages of plating and brazing leads to a tensile strength of 120 MPa in the joining zone. The specimens, which were joined in this condition, were thermal shock resistance.     

Evaluation of temperature effect on the corrosion process of 304 stainless steel in high temperature water with electrochemical noise

The effect of temperature on corrosion process of 304 stainless steel (SS) in high temperature water was investigated by electrochemical noise (EN), scanning electron microscope (SEM), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the corrosion process could be divided into two stages (passivity and active dissolution) with the increasing temperature. At 100 °C, the oxide film was a single layer mainly consisting of Cr₂O₃. However, at 250 °C, it became a double layer with an inner layer of Cr–Fe spinel compound and an out precipitated layer. The related growth mechanisms of the oxide film were also discussed.     

Relationship between tensile strength and preparation conditions for nickel foam

Abstract

The relationship between preparation conditions and tensile strength has been investigated for a nickel foam produced by electrodeposition on an organic foam. After sintering in a NH₃ decomposition atmosphere at 980°C for 40 min, the results show that the tensile strength is hardly influenced by burning in air at 600°C for 4 min beforehand, or by lowering the sintering temperature to 850°C. During conductive treatment of the organic matrix it was found that coating with graphite base conductive colloid or chemically plating with Ni–P alloy (～5 wt-%P) brought the same tensile strength for the eventual product.     

Preparation of Co-plated WC powders by a non-precious-Co-activation triggered electroless plating strategy

In this study, Co nanoparticles were mixed with WC powders by electroless plating with a new non-precious-Co-activation strategy. By soaking WC powders in a mixed solution of cobalt sulfate heptahydrate and sodium hypophosphite and then heat treated at 220 °C, Co active sites were seeded on WC powders to activate the following electroless plating of Co. The effects of reaction conditions on the weight gain and plating rate during electroless plating process were systematically investigated. As is evidenced by results, when the temperature, concentration of CoSO₄ and NaH₂PO₂·H₂O, and pH were 80 °C, 50 g/L, 45 g/L and 11 respectively, WC was evenly coated with Co. Notably, the XPS characterization indicated the content of zero-valence Co was elevated obviously after the plating process due to the effective reduction from two-valence Co.     

Formation of nickel aluminide/nickel hybrid coatings on alloy steels by two step process of nickel plating and low temperature pack aluminisation

Abstract

The present study investigates the conditions required for forming a hybrid coating consisting of an outer nickel aluminide layer and an inner nickel layer on alloy steels. A commercial alloy steel of 9Cr–1Mo was used as a substrate. Electroless and electronickel plating processes were used to form an initial nickel layer on the steel. The AlCl₃ activated packs containing pure Al as a depositing source were then used to aluminise the nickel deposit at temperatures ≤650°C. The effect of phosphorus or boron content in the initial nickel layer deposited with the electroless nickel plating solutions using hypophosphite or boron–hydrogen compound as reducing agent was investigated in relation to the spallation tendency of the coating either immediately after the aluminising process or during the thermal annealing post-aluminising process. Under the aluminising conditions used, the outer nickel aluminide layer formed was Ni₂Al₃. For the electroplated nickel deposit, the growth kinetics of the outer Ni₂Al₃ layer during the pack aluminising process was found to obey the parabolic rate law with a parabolic rate constant being 12·67 μm at 650°C for 2 wt-%AlCl₃ activated pack containing 4 wt-% pure Al as a deposition source.     

Effects of Aging on Interfacial Microstructure and Reliability Between SnAgCu Solder and FeNi/Cu UBM

Effects of thermal aging on the interfacial microstructure and reliability of the SnAgCu/FeNi‐Cu joint are investigated. It is found that aging effects depends strongly on the temperature. Aging at low temperature, e.g., at 125 °C, a submicron meter thick FeSn₂ IMC layer formed at the SnAgCu/FeNi‐Cu interface during reflowing grows at a rate twenty times slower than the growth rate of the IMC at the SnAgCu/Cu interface. At high temperature, e.g., at 180 °C, the Cu element is found to diffuse through FeNi layer to produce the (Cu, Ni)₆Sn₅ IMC and this IMC layer grows even faster than the IMC at the SnAgCu/Cu interface. Solder ball shear test results show that the SnAgCu/FeNi‐Cu joint has a comparable strength to the SnAgCu/Cu joint after reflowing, and the strength drop after aging at 125 °C is less than that of the SnAgCu/Cu joint. However, after aging at 180 °C, the strength of the SnAgCu/FeNi‐Cu joint is degraded to a low value, along with a shift in failure mode from the solder fracture to the brittle intermetallics fracture.     

Influence of molybdenum on austempering behaviour of ductile iron Part 1 – Austempering kinetics and mechanical properties of ductile iron containing 0·13%Mo

Abstract

Measurements of the austempering kinetics and mechanical properties are presented for a ductile iron of composition Fe–3·51C– 2·81Si–0·25Mn–0·39Cu–0·13Mo–0·04Mg (wt-%) for austempering temperatures of 285, 320, 375, and 400°C after austenitising at 870°C for 120 min. The kinetic studies show that the alloying level is insufficient to cause a significant delay in ausferrite formation in the intercellular boundaries. This implies that the heat treatment processing window is open for all austempering conditions studied. The mechanical property measurements show that with the correct selection of austempering temperature all the grades of the ASTM Standard 897M : 1990 and BS EN 1564 : 1997 can be satisfied. The hardenability of the present iron is limited and it is therefore unlikely that these standards will be achieved in thicker section components.     

Metadynamic recrystallization in C steels

Metadynamic recrystallization has been investigated in three plain carbon steels (ENIA, EN2 and EN24) through the use of hot interrupted compression tests on a wedge plastometer. Holding time was 0.5 s between passes. Strain rates of 0.05 and 0.12/s and small strain increments of 3, 5 and 7% were employed. Test temperatures were varied between 800 and 1100°C. Various incremental and continuous stress strain curves were highlighted at different temperatures and strain rates for 3 steels, ENIA, EN2 and EN24, resulting in varying flow stresses and strains. Highest peak stress was 180 MPa for EN24 at peak strain of 0.25 and 900°C, with a strain rate 0.12/s. Peak strain values for all steels at 1100°C was 0.133 at a strain rate of 0.05/s and 0.15 at a strain rate of 0.12/s. Strain accumulation resulted in dynamic and metadynamic recrystallization with refinement to about 15 μm for dynamic and 22 μm for metadynamic recrystallization. Fractional softening,X, decreased from 0.27 to 0.12 as recrystallization times in metadynamic recrystallization increased from 0.9 s to 1.5 s at 1100°C. Time for 50% metadynamic recrystallization was also reduced as temperature increased. For ENIA, a drop from 10000 s to 20 s, as temperature increased from 800 to 1100°C was observed. For EN24 and EN2 steels, a drop from 4000 s to 6 s for similar temperature rise was observed. Metadynamic recrystallization (at strains higher than critical strain) is observed to be a strong function of strain rate and a very weak function of temperature and strain. It significantly refined the austenite grain size prior to transformation.     

Isothermal transformation behavior of thermally-grown wüstite

Abstract

The transformation behavior of wüstite (FeO) below the FeO→ Fe+Fe₃O₄ eutectoid temperature of about 570°C was studied using laser Raman spectroscopy in conjunction with optical microscopy, backscattered electron microscopy, and electron probe microanalysis. A thermally-grown wüstite layer was initially formed by oxidizing a mild steel in air at 900°C for 100 s. The thermally-grown layer was then isothermally annealed at 100–500°C for up to 6 hours. The transformation behavior was found to be very dependent on degree of undercooling below the eutectoid temperature. At temperatures down to about 350°C, transformation was initiated by Fe₃O₄ precipitation and then followed by lamellar Fe+Fe₃O₄ growth. However, at a temperature of 270°C, the FeO transformed directly to a fine, granular mixture of Fe+Fe₃O₄. No transformation was observed at 200°C and lower. The kinetic results were used to construct isothermal transformation diagrams.     

Synthesis and some properties of Ti3SiC2 by hot pressing of Ti,Si and C powders Part 2 – Mechanical and other properties of Ti3SiC2

Abstract

Some properties of the remarkable Ti₃SiC₂ based ceramic synthesised by hot pressing of elemental Ti, Si, and C powders have been investigated. Its flexural strength by using three point bending tests and fracture toughness by using single edge notched beam tests were measured at room temperature to be in the range 310–427 MPa and about 7·MPa m^1/2, respectively. This material is a relative 'soft' ceramic with a low hardness of 4 GPa. Ti₃SiC₂ is similar to the soft metals and is a damage tolerant material that is able to contain the extent of microdamage. An oxidation test has been performed in the temperature range 1000–1400°C in air for 20 h. The oxidation resistance below 1100°C was good. Two oxidized layers were formed, the outer layer consisting of pure rutile-type TiO₂, and the inner layer a mixture of SiO₂ and TiO₂. The average coefficient of thermal expansion (CTE) of Ti₃SiC₂ was measured to be 9·29 × 10^?6 K^?1 in the temperature range 25–1400°C. The thermal shock resistance of Ti₃SiC₂ was evaluated by quenching the samples from 800°C, 1200°C, and 1400°C, respectively. The retained flexural strength drops dramatically at quenching temperature, but shows a slight increase after quenching from 1400°C compared with quenching from 800°C and 1200°C.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

Evolution of grain structure across joints in friction stir welded EN AW 5083 H111 plates during thermal exposure

Abstract

The mechanisms involved in the coarsening of the grain structure across FSW joints produced in EN AW 5083 H111 plates with different pin profiles were investigated. The grain coarsening across the FSW joints invariably starts inside the shoulder flow zones and involves both abnormal growth of the grains inside the dynamically recrystallised regions as well as recrystallisation of the deformed grains outside these regions. The elliptical nugget zones produced with the threaded circular pins appear to be more stable with respect to the basin shaped counterparts obtained with the triangular pin. It takes an annealing temperature of 550°C for the former to become fully coarse grained across the joint while the joint produced with the triangular pin is largely covered with coarse grains starting at 500°C. The higher resistance of the nugget zone obtained with a threaded circular pin to grain coarsening appears to be critical in the selection of the pin profiles when the manufacturing cycle of the welded EN AW 5083 plates involves post-welding heat treatments.     

Numerical modeling and experimental investigation of the superficial layer of SKD61 steel during laser surface hardening

Abstract

Laser heating of SKD61 steel usually causes the formation of a melting layer on the steel surface, which is of poor thermal conductivity and diffusivity. The modified Ashby‐Easterling heat‐transfer equation was used to simulate the temperature distribution for laser surface hardening of SKD61 steel. The phase transformation temperatures of SKD61 in the quenched and as‐received conditions were compared with each other for different laser energy densities. When the laser was focused on the steel, the temperature of the SKD61 was raised. Due to the effect of superheating, the critical phase transformation temperature in laser hardening became higher than the austenized temperature (1010°C) in traditional quenching. However, the critical phase transformation temperature of SKD61 decreased with increasing laser energy density.     

MicroRaman spectroscopy of protective coatings deposited onto C/C–SiC composites

Abstract

MicroRaman spectroscopy has been used in the present work to investigate the structure and composition of pyrolytic carbon (PyC) and SiC protective coatings formed under various chemical vapour deposition conditions. Analysis of spectra obtained during Raman line mapping experiments on samples with graded Si_xC_y layer in the region of about 700–1000 cm^?1 allows information to be extracted on different SiC polytypes. It was found that the graded SiC layered sample contained a mixture of 3C–SiC and 6H–SiC polytypes at the film/substrate interface, but for the major part of this layer the 3C–SiC (β-SiC) phase predominates. For pure PyC films, it was found that the formation of PyC layer begins at 1200°C and the layer formed at this temperature is more uniform with slightly larger crystallite size (～3 nm) compared to that in the layer formed at 1300°C.     

Study on the rate of decomposition of amoxicillin in solid state using high-performance liquid chromatography

Abstract

Amoxicillin sodium salt degradation in solid state relies on a sequential reaction consisting of two pseudo-first-order processes. Amoxicillin trihydrate, now used in pharmaceutical formulations, is significantly more stable than sodium amoxicillin. It degrades according to Prout-Tompkins model. We studied the stability of amoxicillin at temperatures of 37°, 50°, 80°, 90°, 100° y 110° C. HPLC was chosen as the analytical method. Amoxicillin and its decomposition products are separated by reversed-phase (C18) HPLC with gradient elution.     

Novel Applications of Fullerenes in Thermal Management Systems

Abstract

The new potential applications of fullerenes (buckyballs), such as advanced thermal protection coatings, fire retardant materials and cryogenic insulation materials were investigated. Based on experimental results, it was shown that due to low thermal conductivity and high emissivity, micron‐scale fullerene films were capable of withstanding elevated temperatures (up to 800°C) resulting in over 100°C temperature decrease on the “cold” surface of the underlying substrate. In addition, it was shown that due to the high heat of sublimation and low ablation rates, fullerenes can provide excellent ablative cooling in the temperature range of 600–1000°C. Consequently, unique flame‐retardant ability of fullerenes was demonstrated.     

A new ferritic stainless steel with improved thermo-mechanical fatigue resistance for exhaust parts

Abstract

Over the past few years, car manufacturers have been considering ever higher service temperatures for the engine in order to comply with the constraints of depollution standards. The requirements in terms of exhaust gas temperature could easily reach and overtake the limits of common stainless steel grades used for such applications in the coming years.

A new ferritic stainless steel – named K44X – with increased high temperature resistance has therefore been developed to withstand service temperature up to 1000 °C. K44X belongs to EN 1.4521 and AISI 444 classifications and is composed of approximately 19% Cr, 2%Mo and 0.6% Nb. This specific composition leads to better mechanical properties, higher creep and fatigue resistance than EN 1.4509, while keeping comparable weldability and formability. Its coefficient of thermal expansion is lower in comparison to austenitic stainless steel grades and its resistance to cyclic oxidation is improved significantly.

High-temperature properties (mechanical properties, creep, cyclic oxidation resistance, and high cycle fatigue) of K44X are presented in this paper and compared with common ferritic and austenitic stainless steels used in the hot end of exhaust lines. A thermal fatigue test – designed to reproduce exhaust manifold service conditions – has also been carried out with the highest temperatures of the cycle in the range of 850–1000 °C. The results of these thermal fatigue tests were compared with the above-mentioned stainless steels. A thermal fatigue damage criterion was then identified based on these experimental results and using a cyclic behaviour law obtained from isothermal low cycle fatigue tests.     

Facile electroless copper plating on diamond particles without conventional sensitization and activation

Conventional electroless plating of copper on diamond particles needs SnCl₂ sensitization and PdCl₂ activation pretreatments, which needs noble metal and consumes a large amount of reducing agent. In this paper, metallic tungsten coatings were first plated onto diamond particles by microwave-heating salt-bath plating (MHSBP) method, and then copper layer was directly plated onto the out surface of the tungsten layer by an electroless plating method with no need of SnCl₂ sensitization and PdCl₂ activation pretreatments. Composition and morphology of the coatings was analyzed by XRD, SEM, and EDS. The results show that the copper coating on the diamond surfaces can be adjusted by control the concentration of CuSO₄·5H₂O and plating temperature, and a full copper coating is achieved with content of CuSO₄·5H₂O of 19.6 g/L in the plating solution at 60 °C. The bending strength of the coated diamond/Cu composites is as high as 630 MPa, which increases 93.3% than the uncoated composites. This work presents an electroless plating of copper can directly on the surfaces of diamond particles with no need of conventional sensitization and activation, and a strong interface combination between coated diamond and copper.