Near-IR Emitting InyGa1 – ySb1 – xBix Solid Solutions

Inorganic Materials - This paper examines the formation of InyGa1 – ySb1 – xBix isovalently (Bi) doped solid solutions under temperature-gradient zone recrystallization conditions. We...     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 1 – Microstructural analysis

Abstract

Specimens of 16Cr - 5Ni - 1Mo stainless steel were solution treated at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, optical microscopy, scanning (SEM) and transmission (TEM) electron microscopy, and X-ray diffraction examinations were conducted. The microstructure of all aged specimens was found to consist of martensite with variable fractions of δ ferrite and reversed austenite. Very fine precipitates of Mo carbides were revealed in the specimens aged at 475 ° C. The specimens aged at 625 ° C showed a decrease in the dislocation density and a high volume fraction of austenite and precipitation of Fe₂Mo Laves phase was detected by X-ray analysis. Above 625 ° C, Cr₂₃C₆ and TiC became the predominate carbides heterogeneously precipitated in the martensitic matrix. Partial transformation of reversed austenite to unaged martensite was observed at temperatures above 625 ° C.     

Structural Perfection of Four-Layer Ga x In1 – x As y P1 – y Laser Heterostructures

The structural perfection and coherent growth conditions of epitaxial layers in four-layer Ga _x In_{1 – x} As _y P_{1 – y} heterostructures on InP(001) substrates were studied by x-ray diffraction and topography. The composition of the active layer corresponded to a peak photoluminescence wavelength of 1.34 m. The coherent growth region was delineated, and the critical thickness of epitaxial layers was determined as a function of the interfacial lattice mismatch. The critical thickness determined experimentally exceeds the calculated value. It is shown that heterostructures up to 9 m in layer thickness, free of interfacial dislocations can be grown in a broad range of elastic strains in adjacent layers.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 2 – Mechanical property characterisation

Abstract

Mechanical property characterisation has been carried out on specimens of 16Cr - 5Ni - 1Mo stainless steel, subjected to various aging cycles. The heat treatment cycles involved solution treatment at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, tensile, hardness, impact, and creep tests were conducted. Specimens aged at 475 ° C exhibited maximum values of tensile strength and hardness with minimum values of ductility and impact toughness, while specimens aged at 625 ° C had maximum values of impact toughness and ductility. The results were correlated with the microstructural data presented in Part 1 of this study. Softening of the martensitic matrix at 625 ° C occurs as a result of the elimination of internal stresses, the decrease in the dislocation density, and the high volume fraction of austenite which lead to the drop in values of tensile strength and hardness. The results of the study reveal that aging at 550 ° C for 4 h gives the optimum combination of strength, hardness, ductility and toughness for this steel.     

Determination of the Melt Undercooling Required for Producing Al x Ga y In1 – x – y Sb1 – z Bi z /InSb Heterostructures

Conditions for temperature-gradient epitaxial growth of Al _x Ga _y In_{1 – x – y} Sb_{1 – z} Bi _z /InSb heterostructures are examined. The factors are established which determine the initial melt undercooling required for preventing the thermal degradation of the substrate.     

Dielectric Properties of Melt-Grown Cd1 – xZnxTe Crystals

The real (") and imaginary (") parts of the complex dielectric permittivity of Cd_{1 – x} Zn _x Te (x= 0.1–0.2) crystals are measured as a function of temperature and frequency. The "-vs.-temperature data show a maximum, and " rises rapidly at about the same temperature. This behavior is interpreted in terms of compositional fluctuations, structural defects, and the associated internal electric fields.     

Growth and Properties of KTi1 – xSnxOPO4Crystals

Single crystals of KTi_{1 – x} Sn _x OPO₄solid solutions and KSnOPO₄were grown from off-stoichiometric flux, and their structure and physical properties were studied. The replacement of Ti by Sn was found to increase the unit-cell parameters, shift the ferroelectric transition to lower temperatures, and decrease the nonlinear optical susceptibility. Near t _C, some of the crystals exhibit a jump in electrical conductivity, typical of superionics.     

Growth and Properties of V-Doped CdxHg1 – xTe Crystals

Cd _x Hg_{1 – x} TeV (x= 0.9–0.95) crystals were prepared by two versions of Bridgman growth, and their optical homogeneity and transport properties were studied. The electrical resistivity of the crystals was 10⁴to 10⁸ m. From the temperature dependences of the Hall coefficient, the activation energy of the vanadium level in Cd _x Hg_{1 – x} TeV was determined to be 0.73–0.82 eV.     

Synthesis of boron nitride from ferroboron Part 1 – Nitriding

Abstract

Thermodynamic calculations and nitriding experiments have been carried out to convert ferroboron precursor to boron nitride in a mixture of NH₃ with N₂ gases under ambient pressure. The results show that complete nitridation can be achieved at 673 K with 20 vol.-%NH₃ in the gas mixture. The nitrided product consists of amorphous boron nitride, iron, and metastable iron nitrides. The measured weight gain follows a two stage, near parabolic kinetics accompanied by volume expansion, which causes spalling of the outer nitrided layer and facilitates further nitriding. An alternative reaction route using 100 vol.-%N₂ is also possible, but a higher reaction temperature (≥～1700 K) is needed. The product from the high temperature route contains partially crystallised (hexagonal) boron nitride, iron, and virtually no metastable iron nitride.     

Relaxor Behavior of Pb[(Mg0.5W0.5 )1 – x Ti x ]1 – y Sn y O3 Ceramics

The dielectric and ferroelectric properties of Pb[(Mg_0.5W_0.5)_{1 – x} Ti _x ]_{1 – y} Sn _y O₃ (x = 0.4–0.5, y = 0–0.15) solid solutions are studied. The results are used to elucidate the origin of the relaxor state developing in a temperature range between the para- and ferroelectric phases.     

Transient liquid phase bonding of magnesium alloy (Mg – 3Al – 1Zn) using copper interlayer

Abstract

The mechanism, microstructure and mechanical properties of transient liquid phase (TLP) bonded magnesium alloy (Mg – 3Al – 1Zn) joints using copper interlayers in an argon atmosphere have been investigated. The formation process of the TLP joint comprises a number of stages: plastic deformation and solid state diffusion, dissolution of the interlayer and base metal, isothermal solidification and homogenisation. The composition profiles and microstructures of the joint depend on the bonding time at a temperature of 530°C. With an increase in bonding time from 10 to 60 min, the concentration of copper and the amount of CuMg₂ compound in the joint decrease. For longer bonding times, the most pronounced features of the joint are composition homogenisation, grain coarsening and elimination of the bond line within the joint centre. The presence of brittle CuMg₂ and grain coarsening of the joint are the main reasons for impairing the joint shear strength. A joint shear strength of 70.2 MPa, which is 85.2% of the base metal strength (82.4 MPa), can be achieved by bonding at 530°C for 30 min.     

Vapor Growth of Pb1 – x In x Te Crystals

Vapor growth of In-doped PbTe crystals by the sublimation–condensation and vapor–liquid–solid (VLS) processes is examined. Well-faceted Pb_{1 – x} In _x Te crystals with x = 0.04–0.06 are prepared by the sublimation method. The effects of the charge composition on the facial development and growth rate in the range 0 x 0.02 are discussed. The growth process at x 0.02 is shown to follow the VLS mechanism. Bulk Pb_{1 – x} In _x Te crystals with x 0.05 are grown by a vertical VLS process. The crystal composition is shown to depend significantly on the rate of ampule translation through the temperature field of the furnace and the separation between the evaporation and condensation zones. The longitudinal indium profiles in the crystals are correlated with growth kinetics.     

Precipitation hardening of Cu – Ti – Zr alloys

Abstract

The influence of age hardening temperature and time on the hardness, tensile properties, electrical conductivity, and microstructure of Cu – 4Ti – 0.1Zr and Cu – 3Ti – 0.1Zr alloys has been investigated. The resulting microstructure of these alloys suggests that zirconium addition prohibited the formation of compositional modulations in the solution treated condition. These alloys exhibited maximum hardness and strength on peak aging at 450°C for 24 h by the formation of a coherent and metastable Cu₄Ti phase (β') in modulated structure while overaging occurred by the formation of equilibrium phase β-Cu₃Ti. The electrical conductivity of both the alloys increased moderately on aging. Unlike in an earlier study of binary Cu – Ti and some ternary Cu – Ti – X alloys, overaging did not cause any discontinuous precipitation in the Cu – Ti – Zr alloys investigated. Modulated structure formed on peak aging persisted on prolonged aging at 450°C for 80 h or at 500°C for 8 h.     

Temperature-Dependent Elastic Constants and Dielectric Properties of (Zn1 – x Cd x )3(P1 – y As y )2 Crystals

Crystals of constant-lattice-parameter (a const) and constant-thermal-expansion ( _a const) (Zn_{1 – x} Cd _x )₃(P_{1 – y} As _y )₂ solid solutions with 0.71 x 0.94 and 0.2 y 1 are prepared, and their elastic and dielectric properties are studied between 78 and 400 K. The elastic constants are found to decrease linearly with increasing temperature and to rise monotonically with increasing Cd and As content, up to x = 0.94 and y = 1. These findings are interpreted in terms of structural changes and bond rearrangement near the morphotropic structural transformation. Dielectric permittivity rises monotonically with temperature and solute concentration and shows a sharp upturn at x = 0.94 andy = 1. The extremely high dielectric permittivity is interpreted in terms of charge transfer between defect complexes responsible for deep levels in the band gap.     

Synthesis, Crystal Growth, and Acoustophotovoltaic Effect of TlIn1 – x Pr x Se2 and TlIn1 – x Pr x Te2

Procedures were developed for growing perfect TlIn_{1 – x} Pr _x Se₂ and TlIn_{1 – x} Pr _x Te₂ (0 x 0.08) single crystals. The growth charges were synthesized by a process involving partial cooling of a tilted, rotating tube. The crystals grown by the floating zone technique were found to readily cleave in two, mutually perpendicular mirror planes to give rectangular parallelepipeds. The crystals were shown to exhibit a sizeable acoustophotovoltaic effect: a combined action of radiation and sound waves produced an emf between the electrodes or a short-circuit current.     

Properties of Nd1 – x Gd x CoO3 Solid Solutions

NdCoO₃, GdCoO₃, and Nd_{1 – x} Gd _x CoO₃ solid solutions with x= 0.1–0.9 are prepared by solid-state reactions, their lattice parameters are determined, and their electrical conductivity and thermal expansion are measured between 300 and 1110 K in air. All of the solid solutions are found to have an orthorhombically distorted perovskite structure and to exhibit anomalies in conductivity and thermal expansion, due to a semiconductor–metal transition.     

Effect of thermal aging on pitting corrosion resistance of 16Cr – 5Ni – 1Mo precipitation hardening stainless steel

Abstract

Specimens of precipitation hardening 16-5-1 stainless steel were solution treated at 1050°C for 1 h followed by aging at temperatures in the range 400 – 750°C for various holding times (1 – 16 h). After heat treatment, two types of corrosion test (accelerated and immersion testing) were conducted in 6% ferric chloride solution. The results showed that the pitting corrosion resistance was affected by austenite content, δ ferrite and precipitation of molybdenum and chromium carbides. Three critical temperature ranges were identified, which were related to the phases formed: (a) high corrosion rate at 475°C (δ ferrite and Mo₂ C); (b) low corrosion rate at 550 – 625°C (reversed austenite and Laves phase); (c) intermediate corrosion rate at 750°C (Cr₂₃ C₆ and TiC). The morphology of the pitting was dependent on the form of the δ ferrite and carbides.     

Designing steel to resist hydrogen embrittlement: Part 1 – trapping capacity

A novel steel has been designed for use in the oil and gas industry, displaying properties comparable with the currently available F22 grade and possessing the additional quality of excellent hydrogen trapping capacity. Its high strength is derived from a martensitic microstructure containing a dispersion of fine vanadium-molybdenum carbides that evolve during thermal treatments. If the tempering cycle is controlled such that the precipitates maintain a degree of coherency with the matrix, then they act as hydrogen trapping sites, due to the associated strain fields, thus mitigating the problem of diffusible hydrogen. Using material modelling programmes and small-scale sample alloys this work describes the process of the new steel design and demonstrates its superior trapping capacity through thermal desorption analysis.     

Effect of solution heat treatments on superalloys Part 1 – alloy 718

Abstract

The hot ductility as measured by Gleeble testing of Alloy 718 at four different solution heat treatments (954°C/15 h, 954°C/1 h, 982°C/1 h and 1050°C/3 h+954°C/1 h) has been investigated. It is concluded that constitutional liquation of NbC assisted by δ phase takes place and deteriorates the ductility. Parameters established by analysing the ductility dependence on temperature indicate a reduced weldability of the material in the coarse grain size state (ASTM 3) while indicating an increased weldability when containing a large amount of δ phase due to a grain boundary pinning effect. The accumulation of trace elements during grain growth at the highest temperature is believed to be the cause for the observed reduced on-cooling ductility.     

Deposition of Pb1 – x Cu x S1 – δ Substitutional Solid Solutions from Aqueous Solutions

Thin films of Pb_{1 – x} Cu _x S_{1 –} metastable substitutional solid solutions containing up to 3.5 mol % Cu₂S were deposited from aqueous solutions and characterized by physicochemical methods.