Effect of composition on the transformation behaviour of duplex 316 weld metal

Several 316 manual metal arc weld metals produced with commercial and experimental consumables were aged between 600 and 850 °C. This resulted in the dissolution of the -ferrite with the appearance of new austenite, M₂₃C₆, intermetallics , and phase. During transformation, the -ferrite becomes progressively enriched in Cr, Mo and Si and, depending on the local composition of the -ferrite, eventually transforms to intermetallic or phases. A transformation model has been developed which indicates that solute diffusion via the / interface is the controlling mechanism. This enrichment process has been found to be important in controlling the formation of intermetallics. In the weld metals containing controlled residual additions of Ti and Ti + B, ageing resulted in the a fine dispersion of MX phase in the austenitic matrix.     

Preparation and transport properties of aqueous sol-gel synthesized NaCo2O4−δ

We have successfully prepared thermoelectric materials NaCo₂O_4– at lower temperature (700°C) using aqueous sol-gel methods. We find that the electrical resistivity and thermopower of NaCo₂O_4– depend strongly on the sintering temperature and partial pressure of oxygen. The oxygen content of NaCo₂O_4– is found to decrease with increasing sintering temperature. The sample prepared at the combination of 700°C and pure flowing oxygen exhibits the highest value of power factor.     

Dynamic mechanical properties of carbon-carbon composites

The dynamic mechanical analysis (DMA) method was utilized to investigate the dynamic mechanical properties of the carbon-phenolic composite, and of carbon-carbon (C/C) composites carbonized at 1000°C, and graphitized at 2200°C. The measurements were performed in the temperature range 50–450°C. Results show that the carbon-phenolic composite has the highest storage modulus, while the carbonized C/C composites possess higher storage modulus than the graphitized C/C composite. The storage moduli of carbonized and graphitized C/C composite do not change significantly in the test temperature range. The tan , loss factor, of carbonized C/C composites increases 59.5% during the tests from 50 to 450°C, and that of the graphitized C/C decreases 9.74% in the same temperature range; graphitized C/C shows the highest tan at 50 °C. The carbon-phenolic composite shows a damping peak at 250 °C, which is probably due to the transition from glassy state to rubbery state of the phenolic matrix. The higher tan of the graphitized C/C composite may be due to matrix graphitization, fibre-matrix debonding and crack formation, which were observed on the micrographs.     

Microstructure and phase transformations in duplex 316 manual metal arc weld metals: the role of carbon

The nature and kinetics of the phase transformation of metastable -ferrite in two duplex stainless steel manual metal arc weld metals has been studied at two carbon levels. 0.042 and 0.076 w t%. The lean deposit exhibited a rapid transformation to intermetallic phases on post-weld heat treatment, whilst the higher carbon deposit retained sable -ferrite after similar heat treatment. These results appear to be consistent with previously published transformation models for similar materials.     

Thermal and dielectric properties of zirconyl phosphate compact

Experimental results are presented on the measurements of thermal expansion (up to 1500°C), thermal conductivity (up to 1000°C), dielectric constant (up to 450 °C) and tan (up to 800 °C) of zirconyl phosphate compacts obtained by sintering at 1600°C. The thermal expansion coefficient of the samples at the temperature below 1100°C was less than 1.7 × 10^–6°C^–1. The samples showed a definite shrinkage at temperatures of 1110 and 1470°C due to the phase transformations. The expansion at 1500°C was less than that at 1100°C probably because of the phase transformation. The thermal conductivity at room temperature was a very small value (0.0046 to 0.0065 cal s^–1 cm°C^–1 cm^–2). The dielectric constant was close to 9. The value of tan° (–0.0001) measured is one of the lowest values for ceramic materials.     

Microstructure and phase transformations in duplex 316 submerged arc weld metal,an ageing study at 700° C

The transformation of metastable-ferrite has been studied in two duplex stainless steel weld metals. The kinetics and the nature of the equilibrium phases produced, depend upon the localized microsegregation of chromium and molybdenum to the-ferrite laths in the as-welded state. A transformation model is proposed which suggests that a longer term stability of the-ferrite may be achieved by alterations in the basic 316L composition used for the production of submerged arc weld metals.     

Phase transformation and impact properties of type 17-8-2 austenitic weld metals

The influence of stress relieving and ageing treatments in the range 600 to 900° C on the phase transformations and change in room temperature impact properties has been studied for two manual metal arc 17-8-2 weld metals. The transformation of the-ferrite in the range 600 to 800° C was found to conform to a classical Johnson-Mehl equation; the initial precipitates were M₂₃C₆ carbides followed by the intermetallic-phase. At higher temperatures a slower transformation rate was found suggesting a C curve type of behaviour and the dominant intermetallic phase changed to. Room temperature impact toughness values were found to change with ageing time. Below 800° C there was a consistent fall in these values which became very marked when the-phase developed at the/-boundaries, Above 800° C, spherodization of the carbides and intermetallic phases delayed the fall in the impact values, and led to significant increases in the early stages of ageing. Scanning electron microscopy confirmed that the change from ductile to brittle fracture mode was normally associated with the development of the and phases, but at 600° C the fall in impact properties could be atrributed to carbide development.     

Dynamic mechanical properties of hydrogenated nitrile rubber: effect of cross-link density,curing system,filler and resin

The effect of cross-link density, curing system, filler and resin on dynamic mechanical properties of hydrogenated nitrile rubber (HNBR) is reported. The storage modulus,G, increases and the loss angle, tan , decreases in the plateau zone with cross-link density. At equal cross-link density, the tan peak value at the transition zone of sulphur cured system, is less than that of peroxide cured system. Tan decreases from 90 to 180 °C and increases beyond 180 °C due to post vulcanization reaction and sulphidic linkage cleavage, respectively. The ZSC 2295 resin increasesG and decreases tan , and is found to be compatible with HNBR. The plateau modulus,G, increases with carbon black loading. The tan is lower for high structure carbon black in the transition zone and higher in the plateau zone when the surface area is high.     

Effect of copper coating on the mechanical properties of steels type 03Kh13N4G5M2 in a broad temperature range

It was established that martensitic-ferritic chrome-nickel steels type 03Kh13N4G5M2 are prone to embrittlement by solder based on copper at temperatures close to or somewhat exceeding the temperature of -y transformation. It was discovered that embrittlement may be of catastrophic nature. The temperature range of embrittlement depends on the content of -ferrite in the alloys. With increasing content of -ferrite the temperature of the onset of embrittlement becomes higher at first, and then it decreases. The discovered effect of high-temperature (above 950C) embrittlement of steels by a liquid-metal melt has some equal and some different traits from ordinary liquid-metal embrittlement (LME).Translated from Problemy Prochnosti, No. 2, pp. 48–54, February, 1994.     

Influence of a lead melt on plastic deformation of high-alloyed heat-resistant steels

The effect of liquid-metal embrittlement in lead melt is typical of Kh12MVSFBR ferrite-martensitic steel and is observed in the temperature range of 300 – 500°C at a deformation rate of 8 · 10^–4 sec^–1. The maximum decrease in the plasticity of tempered specimens occurs at a temperature of 450°C. A decrease in the amount of -ferrite in the composition (martensite hardening without high-temperature annealing) results in a substantial decrease in plasticity and in broadening of the temperature range of embrittlement. 08Kh16N11S3MB austenitic steel is not affected by liquid metal embrittlement in the investigated temperature range for the deformation rates under consideration.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 4, pp. 71–76, July – August, 1994.     

Splat cooling of iron-molybdenum-carbon alloys

Two molybdenum alloy steels, which normally undergo the austenite martensite phase transformation during solid state quenching, have been rapidly cooled from the melt in a controlled atmosphere gun splat cooling device. The matrix phases produced were-ferrite, martensite, and austenite; the carbide Mo₂C was also present in the as-quenched condition in the higher alloy composition studied. The amount of austenite retained to room temperature was found to be inversely related to the cooling rate. The morphology of the martensite in the splat-cooled alloys exhibited a marked change compared with its characteristic appearance in the conventionally solid-state quenched material. This was attributed to the dual effect of increased cooling rate on carbon segregation in the parent austenite and of decreased section thickness in which the martensite forms. The degree of solute segregation observed in the microstructures of the matrix phases was shown to depend on the extent of the equilibrium liquidus-solidus temperature range. The precipitation of Mo₂C during ageing in the range 600 to 700° C paralleled the behaviour of conventionally quenched and tempered alloys, although local inhomogeneities did produce precipitation phenomena not encountered in solid-state quenched material.     

Decomposition of CO2 and CO into carbon with active wüstite prepared from Zn(II)-bearing ferrite

CO₂ decomposition reaction into carbon was studied at 300 °C using the H₂-reduced Zn(II)-bearing ferrite which consisted of the Zn(II) oxide and the active wüstite. The H₂-reduced Zn(II)-bearing ferrite was prepared from Zn(II)-bearing ferrite by the reduction with H₂ gas at 300 °C. The wüstite (FeO) in the H₂-reduced Zn(II)-bearing ferrite had a higher value (=0.97, active wüstite) than those of the normal wüstites (0.90<<0.95) prepared at high temperatures (>570 °C). The decomposition reaction of CO₂ proceeds in two steps: (1) CO₂ reduction to CO, and (2) CO decomposition into carbon. In the initial stage, the reduction of CO₂ into CO takes place, accompanying both the oxidation of the active wüstite to the slightly oxidized wüstite, and the transformation of active wüstite and Zn(II) oxide into the Zn(II)-bearing ferrite. After the reaction of the initial stage attains equilibrium of an apparent state of rest, the adsorbed CO is decomposed into carbon, associated with the transformation of the slightly oxidized wüstite and the Zn(II) oxide into the Zn(II)-bearing ferrite.     

The mechanical properties and precipitation behavior of an Al-Cu-Li-(in,Be) alloy

The effect of In and Be on the mechanical properties and precipitation behavior of an Al-Cu-Li alloy, which has applications in aerospace and aircraft, has been studied using hardness and tensile tests, differential scanning calorimetry (DSC), and transmission electron microscopy(TEM). The formation of GP zones and ' phases was retarded, but the T₁ and ' phases formation were promoted by the addition of In to Al-Cu-Li alloy. However the formation of T₁ and ' phases, as well as the formation of GP zones and ' phases, were accelerated by the combined addition of In and Be to Al-Cu-Li alloy. The additional precipitation of T₁ phases which was formed at 160°C for a long aging time, was a main reason for the secondary peaks of hardness and tensile strength in Al-Cu-Li alloys added Be and In, or In. The Al-Cu-Li-In-Be alloy was suggested as a material of good combination of tensile strength, elongation and toughness.     

Effect of Low-Temperature Ion Exchange in Salt Melts on the Properties of High-TcSuperconductors

The reactions of Ba₂YCu₃O₇and Bi₂Sr₂CaCu₂O_{8 +} with salt melts were studied in the range 300–600°C with the aim of substituting alkali metals and Ag for Ba and Sr via low-temperature ion exchange. It is found that Na and K can be partially substituted on the Ba site in 123, and Ag substitutes for Sr in 2212. The incorporation of Ag has an adverse effect on the superconducting properties of 2212.     

The effect of hydrostatic pressure on transverse strength of glass and carbon fibre-epoxy composites

An attempt was made to measure indirectly the transverse tensile strengths of uniaxially aligned fibre pultrusions by the diametral compression of disc-shaped samples using concave loading anvils. Two types of composite were investigated, containing 60%V _f of either type AS carbon fibres (CFRP) or S glass fibres (GRP), both in an epoxy resin matrix. Testing was carried out at atmospheric and under superposed hydrostatic pressures, –H, extending to 300 M Pa. The resultant principal stresses at the disc centre were ₁ = _A +H; ₂ =H; ₃ = –3_A +H, where _A = 2P/dt for a disc of diameter,d, and thickness,t, subjected to a loadP. Deviations from linearity in the load-deflection response were detected throughout the pressure range at ã70% and ã90% of the failure load for CFRP and GRP, respectively, and these were associated with resin yielding. The pressure dependence of _A, approximately –0.1H, was consistent with a two-parameter yielding criterion predicting hypothetical yield stresses in simple tension and compression of ã81 and –109 MPa, respectively, for both matrix materials. Irrespective of pressureeventual fractures took place along the loading diameter, but in the CFRP specimens tested under pressure initial cracks at the disc centres were at ã45 ° to the loading axis, i.e. on the plane of maximum shear stress. Fractographic observations were consistent with transverse failure taking place by fibre-matrix decohesion in GRP and by resin fracture in CFRP. Other than the atmospheric datum point for CFRP, the pressure dependence of _A for failure, _F, was also approximately –0.1H. Of the various stress, strain and strain energy criteria for failure examined, only critical tensile strain was found consistent with this pressure dependence.     

Microstructural evolution in nanocrystalline alumina containing silicate glasses

Pure nanocrystalline -alumina powders were coated with different fractions (5, 10, and 15 vol%) of SiO₂-SrO glass using the sol-gel technique. The isostatically cold pressed powders were pressureless sintered in air for 5 h in the temperature range of 1250°C to 1550°C. The relative densities were ranged between 60 to 90% of the theoretical and were composition dependent. The density was increased with the sintering temperature. In pure alumina, the to phase transformation went to completion by sintering at 1250°C. However, in the glass-coated samples, transition -alumina was mostly retained after sintering at the same temperature. Pure nanocrystalline alumina sintered at 1350°C exhibited vermicular structure with isolated pores. The microstructure of the low glass-containing samples exhibited nanocrystalline to submicron size grains arranged in platelet-shaped clusters. Samples with higher glass contents exhibited also micron-size needle-shape grains of strontium aluminate.     

Low-temperature synthesis of binary cuprates from hydroxide precursor

Binary cuprates of Sr₂CuO₃₊ and SrCuO₂ have been synthesized at low temperatures below 500 °C under various values of partial oxygen-pressure by thermal decomposition of hydroxide precursors, Sr₂Cu(OH)₆ and SrCu(OH)₄, respectively. The tetragonal Sr₂CuO₃₊ ( 0.3) is obtained by the heat-treatment at 400 ° C and 0.2 atm. The value of appears to be independent of and unchangeable. On the other hand, the orthorhombic Sr₂CuO₃₊ ( 0) is obtained by the heat-treatment at 400 °C in flowing gas of N₂. For 0 < < 0.2 atm, a mixture of the tetragonal and orthorhombic phases is obtained. The orthorhombic SrCuO₂ is obtained by the heat-treatment at 500 ° C in flowing gas of N₂, although the tetragonal SrCuO₂, namely, the so-called infinite-layer compound is not obtained.     

A modification of the measuring cell for the investigation of the thermal conductivity of liquids and gases by the hot-wire method

The construction of an instrument for measurements by the absolute hot-wire method is described. The thermal conductivity of toluene, benzene, carbon tetrachloride, and air in the temperature range 20–160° C was measured to an accuracy of 1% Natural convection in the cylindrical gap (=0.675 mm) when the measuring cell is vertical occurs when GrPr > 3400.     

Dielectric properties of LaPO4 ceramics

Dielectric constant (K) and loss (tan), and hence conductivity (), have been measured for LaPO₄ ceramics prepared by a molten urea process in the frequency region 10² to 10⁷ Hz and in the temperature range –193 to 280° C. At room temperature ( 30°C),K decreases with frequency up to 10⁵ Hz, beyond which it attains a constant value; tan behaves in a similar way. The values ofK and tan at 30°C and 10⁶ Hz for this material are 14 and 2.7 × 10^–3, respectively. As a function of temperature,K exhibits two stages of increase: (i) a slow stage up to –30° C and (ii) a fast one beyond –30° C which is considerably frequency dependent,K having larger values at lower frequencies. Similar behaviour is exhibited by tan. Plots of against 1/T for LaPO₄ exhibit the usual extrinsic and intrinsic regions; the activation energy for conduction in the intrinsic region is calculated to be 0.61 eV. It seems possible to understand the results through space charge polarization effects due to lattice defects in LaPO₄.     

Viscoelastic properties of the matrix substance of chemically treated wood

The temperature variations of the storage modulus and the loss tangent along the grain for four kinds of chemically modified Sitka spruce (Picea sitchensis Carr.) woods were measured at 11 Hz over a temperature range of –150 to 200 °C. By using a cell-wall model in which the amorphous matrix substance is disposed parallel to the axis of cellulose fibrils inclined at an angle to the grain direction of the wood, the storage modulus, Em, and the loss tangent, tan m of the matrix substance were estimated, and the relaxation processes detected were discussed. In formalization, the restriction of the micro-Brownian motion of the main chains due to oxymethylene bridges between the hydroxyl groups resulted in a decrease in tan m above 0 °C. In acetylation and propylene oxide treatment, a marked reduction in Em was observed over the temperature range tested, by the introduction of bulky side chains, and the tan m remarkably increased in the high-temperature range. In polyethylene glycol (PEG) impregnation, the Em increased below 20 °C due to the freezing of the micro-Brownian motion of PEG molecules in the cell lumens as well as in the cell walls, while it was reduced above this temperature by the melting of PEG molecules.