Wear perfornance of 0·6%Cr alloyed cast and heat treated steels with carbon contents of 0·7, 1·0, and 1·3%

Abstract

The effect of carbon content and heat treatment on the abrasive wear performance of three 0·6%Cr alloyed cast steels with carbon contents near the eutectoid composition (0·7, 1·0 and, 1·3%) were investigated using a pin on drum abrasion tester. Specimens were austenitised at 870,970, or 1070°C for 1 h and quenched. Additionally, a 1·3%C specimen was spheroidised, then austenitised at 870°C and quenched. The microstructure, which was dependent on heat treatment and carbon content, significantly influenced the wear rate. The wear rate is related non-linearly to hardness. The lowest wear rate was obtained for the 1·3%C alloy austenitised at 1070°C producing a quenched microstructure of 40% retained austenite and 60% martensite. This specimen also exhibited the lowest quenched hardness. However, for a practical industrial heat treatment, the 1·0 %C alloy austenitised at 970°C provides the best wear performance.

MST/3130     

Spin canting phenomenon in cadmium doped cobalt ferrites, CoCd x Fe2−x O 4 ( x = 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), synthesized using sol–gel auto combustion method

Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd _x Fe_2???x O ₄ (x?= 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd^2?+? concentration is increased beyond x?= 0·4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ~595 cm^???1 and ~450 cm^???1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ~ 35 nm. The magnetic studies reveal that the saturation magnetization, M _s , increases up to x?= 0·4 and decreases when the value of x is >0·4. It is proposed that the incorporation of Cd^2?+? ion takes place into the tetrahedral sites and up to x?= 0·4, Neel’s model is followed. But for x?> 0·4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes p-type conduction behaviour for all the ferrite samples.     

Relaxor behaviour of (Ba0·5Sr0·5)(Ti0·6Zr0·4)O3 ceramics

Ba_0·5Sr_0·5Ti_0·6Zr_0·4O₃ ceramic has been prepared through solid state reaction route. X-ray diffraction shows that the sample has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependent dielectric study of the ceramic has been investigated in the frequency range 50 Hz-1 MHz. The density of the sample is determined using Archimedes’ principle and is found to be ∼99% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behaviour in the ceramics. The index of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie-Weiss law. The value of γ ∼ 1·72 indicates the strong relaxor nature of the ceramic. A remarkably good fit to the Vogel-Fulcher relation further supports such a relaxor nature.     

Preparation and electrochemical properties of SrCe 0·4 Zr 0·4 Yb 0·2 O 2·9 electrolyte

The perovskite Yb-doped strontium cerate–zirconate material, SrCe_0·4Zr_0·4Yb_0·2O_2·9, was prepared by solid-state reaction and the structure was characterized by X-ray diffraction. The calcination process of the powder was investigated by thermogravimetric/differential thermal analysis (TG–DTA). The high temperature conductivities were measured by d.c. four-probe technique in the temperature range from 500 to 950°C in wet hydrogen and effect of temperature on conductivity was investigated. The conductivity increased with the elevation of temperature from 500 to 950°C. The highest conductivity of 4·4 × 10^???2 S· cm^???1 was observed for SrCe_0·4Zr_0·4Yb_0·2O_2·9 at 950°C. The current–voltage (I–V) and current–power (I–P) characteristics of the single cell (H₂, Pt/SrCe_0·4Zr_0·4Yb_0·2O_2·9/Pt, O₂) at temperature range from 600 to 850°C were tested. With the temperature increasing from 600 to 850°C, the open circuit voltage (OCV) decreased from 1·164 to 1·073 V and the ionic transfer number decreased from 0·996 to 0·946. At 850°C, the maximum power density of 25·2 mW· cm^???2 was observed.     

Study of dependence of magnetic properties on seeding temperature in fine particles of Cu0·25Co0·25Zn0·5Fe2O4

Using a combination of X-ray diffraction, room temperature/low temperature Mössbauer studies and d.c. magnetization, the structural and magnetic properties of nano-sized Cu_0·25Co_0·25Zn_0·5Fe₂O₄, prepared using the coprecipitation method at different seeding temperatures, have been studied. Formation of α-Fe₂O₃ in these samples is observed to be very sensitive to the seeding temperature and is totally suppressed at a seeding temperature of 333 K. These results are explained in terms of the rate of coprecipitation of the different components as a function of temperature. Since α-Fe₂O₃ is antiferromagnetic, the presence and quantity of this impurity is also observed to deteriorate the overall magnetic properties of the spinel phase.     

Electrical conductivity and chemical stability of BaCe0·8 − x A x Gd0·2O3 − δ (A = In, Zr, Ta; x = 0, 0·1) ceramics

BaCe_0·8???x A _x Gd_0·2O_3???δ (A = In, Zr, Ta; x?=?0, 0·1) ceramics were synthesized by solid-state reaction method. Microstructure and electrical properties of BaCe_0·8???x A _x Gd_0·2O_3???δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 573–1073 K in different atmospheres. BaCe_0·8Gd_0·2O_3???δ , BaCe_0·7In_0·1Gd_0·2O_3???δ and BaCe_0·7Zr_0·1Gd_0·2O_3???δ ceramics exhibit a single cubic perovskite structure. BaCe_0·7In_0·1Gd_0·2O_3???δ ceramic has the highest conductivity of 4·6 × 10^???2 S·cm^???1 in air at 1073 K. BaCe_0·7In_0·1Gd_0·2O_3???δ and BaCe_0·7Zr_0·1Gd_0·2O_3???δ ceramics exhibit an excellent chemical stability against boiling water. Indium is a suitable doping element to promote the sintering densification and to enhance both electrical conductivity and chemical stability of Gd-doped BaCeO₃ at operating temperatures.     

Microstructural and compositional modification of In0·53Ga0·47As/In0·52Al0·48As multiquantum wells using rapid thermal annealing process

Abstract

Quantum well intermixing of In_0·53Ga_0·47As/In_0·52Al_0·48As multiquantum wells (MQWs) in an impurity free vacancy diffusion (IFVD) mechanism was investigated to observe the intermixing aspect and the effect of defects in MQWs with regard to the microstructural aspect using transmission electron microscopy. The MQWs were grown on a GaAs (100) substrate using compositionally graded buffer layers via molecular beam epitaxy, and the MQWs were annealed at 750 and 900°C for 30 s via rapid thermal annealing for quantum well intermixing using IFVD method. In the fabricated MQWs, defects, such as stacking faults, twins and dislocations, were not generated at 750°C. The diffusion of Ga in the well layer for the quantum well intermixing started from the top well layer, because the SiO₂ layer that supplied vacancies for the quantum well intermixing was at the top of the sample. Additionally, in the same well layer, the intermixing did not show equality, because these vacancies were not supplied homogeneously. Especially, in the 900°C annealed case, many dislocations were generated from the cladding layer. These dislocations contributed to new vacancy generation sites, thus the quantum well intermixing was accelerated.     

Relaxation effect of pulse current on Ti50·0Ni50·0 structure during rolling

Abstract

Using transmission electron microscopy and differential scanning calorimetry, the microstructure and martensitic transformation of the Ti_50·0Ni_50·0 alloy after cold rolling and after rolling with a pulse current were compared. A structural relaxation effect was observed in the alloy during rolling with current. The effect is manifested in the more slow kinetics of the structure formation and less intensive suppression of martensitic transformations at rolling with current compared to cold rolling with some deformation degrees.     

Effect of beryllium and calcium on aging behaviour of Al–0·75Mg–0·5Si alloy

Abstract

The effect of microadditions of Be and Ca on the aging behaviour of Al–0·75Mg–0·5Si alloy is investigated. It is shown that the addition of 0·1%Be significantly increases the hardening rate and the maximum hardness level attainable when the alloy is aged at various temperatures from room temperature to 300°C, while the addition of 0·2%Ca decreases both the hardening rate and the maximum hardness level attainable. Optical and scanning electron microscopical observations show a significantly higher precipitate density for the Be containing alloy and a slightly lower precipitate density for the Ca containing alloy when compared with the base Al–Mg–Si alloy. The results are consistent with an earlier kinetic study that indicated a Be enhanced nucleation rate for precipitation in the same alloy.

MST/936     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

Influence of temperature on structural and magnetic properties of Co0·5Mn0·5Fe2O4 ferrites

Co_0·5Mn_0·5Fe₂O₄ ferrites have been synthesized using a single-step sol-gel auto-combustion method in which the metal nitrate (MN)-to-citric acid (CA) ratio was adjusted to 0.5: 1 and pH to 7, respectively. The structural and magnetic properties of as-burnt and annealed samples were studied as a function of temperature. The inverse spinel structure was confirmed by X-ray diffraction (XRD) and crystallite size was estimated by the most intense peak (311) using Scherrer’s formula. Contrary to earlier studies reported in the literature, both as-burnt and annealed samples exhibit crystalline behaviour. Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM) with field strengths up to ±10 kOe. Lattice constant and crystallite size increased as the annealing temperature was increased. However, the coercivity (H _c) initially increased and then decreased with the increase of crystallite size. The variation in coercivity is ascribed to the transition from a multi-domain to a single-domain configuration.     

Precipitation and age hardening behaviour of AI–0·2Ti–0·2Be alloy

Abstract

The effect of 0·2%Be on the aging behaviour and microstructure of Al–0·2% Ti alloy is investigated. It is shown that the addition of Be induces some age hardening in non age hardenable AI–0·2Ti alloy and significantly increases the precipitate density, indicating a Be enhanced nucleation for the precipitate phase.

MST/1250     

Electrical conduction and thermal properties of Bi-doped Pr0·7Sr0·3MnO3 manganite

Electrical and thermal properties of Bi-doped Pr _0·7 Sr _0·3 MnO ₃ (PSMO) compounds are reported here. It is observed that Bi-doped PSMO compounds follow variable range conduction mechanism. Specific heat, thermal conductivity and thermo-power measurements show that larger Bi-ion, in place of smaller Pr ion, enhances their transition temperatures (T _MI, T _C, T _CP). Thermo-power measurements further strengthen our conclusion for the presence of magnetic polaron, generated due to hybridization of Bi ³⁺ –6s ² and O ^2? –2p orbital and polaronic conduction mechanism.     

Effects of ferrite grain size and martensite volume fraction on dynamic deformation behaviour of 0·15C–2·0Mn–0·2Si dual phase steels

Abstract

Effects of ferrite grain size and martensite volume fraction on quasistatic and dynamic deformation behaviour of 0·15C–2·0Mn–0·2Si dual phase steels were investigated in this study. Dynamic torsional tests were conducted on six steel specimens that had different ferrite grain sizes and martensite volume fractions, using a torsional Kolsky bar, and then the test data were compared in terms of microstructures, tensile properties, fracture mode, and adiabatic shear band formation. Under dynamic torsional loading, maximum shear stress and fracture shear strain increased with decreasing ferrite grain size and increasing martensite volume fraction. Observation of the deformed area beneath the fracture surface after the dynamic torsional test indicated that adiabatic shear bands of 5 to 15 μm in width were formed along the shear stress direction, and that voids or microcracks initiated at ferrites or martensite/ferrite interfaces below the shear band. The width of the shear band decreased as the ferrite grain size increased or the martensite volume fraction decreased. These phenomena were then analysed by introducing concepts of theoretical critical shear strain.     

Preparation, characterization and luminescent properties of europium oxide doped nano LaMn0·9Zn0·1O3+d by sol-gel processing

New compounds of rare earth complex oxides with perovskite structure in a combination of La with Eu ions and Mn with Zn ions, La_1−x Eu _x Mn_0·9Zn_0·1O_3+d (LEMZ) (0·0 ≤ x ≤ 0·32) in A and B sites, respectively were synthesized. X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and photoluminescence spectra (PL) were used to characterize the resulting nanoparticles. The powder X-ray diffraction peaks could be indexed as a rhombohedral cell. The results of FT-IR spectra were in agreement with those of XRD. High-quality nanopowders with controlled stoichiometry and microstructure were prepared at a temperature range of 700–800°C for 6 h, with mean particle sizes of ∼ 17·5 nm. Photoluminescence measurements showed Eu³⁺ ions characteristic red emission in crystalline LEMZ powders due to the ⁵ D ₀ → ⁷ F _J (J = 0–6) transitions of the 4f electrons of Eu³⁺ ions. The structure, homogeneity and particle size of the obtained compounds during different stages were investigated by scanning electron microscopy (SEM).     

Effect of modified austemper on tensile properties of 0·52%C steel

Abstract

The effect of a modified austemper on the tensile properties of 0·52%C steel has been studiedfor the purpose of developing the mechanical properties of upper bainitic steel. The modified austempering treatment involved intercritical annealing at 1018 K in the two phase region offerrite (α) and austenite (γ) followed by austempering at 673 K and subsequent water cooling. The results have been compared with those obtained from conventionally austempered steel, and quenched and tempered steel with a similar ultimate tensile stress. The modified austempered steel consisted of a mixed structure of upper bainite and 10 vol.-% ferrite in which ferrite appeared as layers along the rolling direction. The modified austempering treatment wasfound to significantly increase the product of ultimate tensile stress and total elongation, and also the notch tensile stress at 193 K. Conventional austenitising at 1173 K followed by subcritical annealing at 998 K in the two phase region of ex and y, and then austempering at 673 K and subsequent water cooling produced the same mixed structure of upper bainite and 10 vol.-% ferrite. However, this treatment yielded inferior mechanical properties to those obtained with the modified austempering treatment, independent of the test temperature. The results are described and discussed.

MST/3102     

Synthesis, non-isothermal crystallization and magnetic properties of Co0·75Zn0·25Fe2O4/poly(ethylene-co-vinyl alcohol) nanocomposite

The synthesis of Co_0·75Zn_0·25Fe₂O₄/poly(vinyl alcohol-co-ethylene) (ferrite/PEVA) nanocomposite was carried out through two steps: impregnation of the ferrite particules by PEVA and then mixing the ferrite/PEVA impregnated with PEVA solution. A non-isothermal study of the crystallization kinetic of ferrite/PEVA nanocomposite was carried out by differential scanning calorimetry (DSC), scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. It was observed that the Ozawa equation describes perfectly the primary process of non-isothermal crystallization of ferrite/PEVA system. There is a strong dependence of the ferrite/PEVA composition on the crystallization parameters. The crystallization activation energy (E _a ) calculated from the Xu and Uhlmann model increased by increasing the ferrite content in ferrite/PEVA nanocomposites between 3 and 7 wt% and decreased dramatically beyond these values. The results revealed that the ferrite nanoparticles were uniformly distributed throughout the PEVA matrix. The percentage of magnetization of the composite decreases as the concentration of the ferrite increases.     

Mn valence state and electrode performance of perovskite-type cathode La0·8Sr0·2Mn1 − x Cu x O3 − δ (x = 0, 0·2) for intermediate-temperature solid oxide fuel cells

Cu-free and Cu-doped LSM system, La_0·8Sr_0·2Mn_1???x Cu _x O_3???δ (x?=?0, 0·2), with perovskite structure were prepared using an EDTA combined citrate process and the effects of Cu ion at B-site were investigated. Electrical conductivity and polarization resistance of the Cu-doped LSM were 210 S·cm^???1 at 750 °C, and 2·54 Ω · cm² at 800 °C, respectively which were better than those of the Cu-free LSM. This indicated that the electrode performance of LSM was improved by the addition of Cu. The oxidation state of Mn ions increased with addition of Cu. The increase in the oxidation state of Mn ions was due to the formation of Mn^4?+? ions and oxygen vacancies. The addition of Cu ions to LSM systems could lead to enhanced electrode performance for oxygen reduction reactions originating from the change in valence of Mn ions.     

Evidence for high ionic conductivity in lithium–lanthanum titanate, Li0·29La0·57TiO3

Lithium–lanthanum titanate, Li_0·29La_0·57TiO₃, is prepared by solid-state reaction method and it is furnace-cooled to room temperature. X-ray diffraction results indicated that the compound has tetragonal perovskite-like structure and the lattice parameters are determined as a = 3· 8714 Å and c = 7· 7370 Å. The average grain size is found to be 5 μm from SEM micrograph. The analysis of FTIR and Raman spectra of the sample supported tetragonal structure inferred from XRD data. The impedance spectrum of the sample is separated into bulk and grain boundary parts by analysing the impedance data. The high bulk ionic conductivity is reported as 1· 12 × 10^???3 S cm^?1 at room temperature. D.C. conductivity measurements indicate that the compound is a good ionic conductor.     

Rietveld analysis, dielectric and impedance behaviour of Mn3+/Fe3+ ion-modified Pb(Zr0·65Ti0·35)O3 perovskite

The polycrystalline samples of Pb(Zr_0·65???x A _x Ti_0·35)O₃ (A = Mn/Fe), (x =0·00, 0·05) (PZM/FT) were synthesized by conventional solid-state reaction technique. X-ray diffraction (XRD) pattern was recorded at room temperature and the samples were found in single phase form. All the observed peaks could be indexed to R3c space group with rhombohedral symmetry. XRD pattern has been analysed by employing Rietveld method with the help of FullProf Program. The lattice parameters and unit cell volumes decrease from Mn^3?+? to Fe^3?+? ion concentrations. The bond lengths and angles have been calculated by using Powder Cell Programme. Microstructural analysis of the surface of the ceramic compound by scanning electron microscopy (SEM) exhibits that there is a significant change in grain size on introduction of Mn^3?+? and Fe^3?+? ions at the Zr-site of the compound. It is observed that both the substitutions (Mn^3?+? and Fe^3?+?) at Zr site induce an increase in dielectric constant and a shift in Curie temperature (T _c ). From a.c. conductivity analysis, we have estimated the activation energy for both ferroelectric and paraelectric regions. Both the modified samples are obeying Jonscher power law. From Nyquist plots, the activation energy of grain resistance, relaxation time and bulk conductivity are compared. The grain resistance of the material decreases with rise in temperature which indicates a semiconducting behaviour of the material.