Technical note Relationship between degeneration of M7 C3 and precipitation of M23 C6 in a cobalt base superalloy

Abstract

The relationship between degeneration of the primary M₇ C₃ carbide and precipitation of the secondary M₂₃ C₆ carbide has been investigated in a cobalt base superalloy after 100 h aging at 850°C. The results indicated that the primary M₇ C₃ carbide could not transform in situ into the secondary M₂₃ C₆ carbide. The M₂₃ C₆ formed by a direct reaction between chromium and carbon atoms. The dissolution of M₇ C₃ provided the precipitation of M₂₃ C₆ with essential carbon, which acted as a carbon reservoir. Near M₇ C₃ , the chromium content is a controlling factor of M₂₃ C₆ precipitation, while away from it, the carbon content dominated the reaction. The precipitate free zone around M₇ C₃ is attributed to chromium depletion which is inherited from the as cast condition.     

Sputtered YSZ based protective thin films for SOFCs

Abstract

Protective Zr(Y)O_2–δ based films, deposited using magnetron sputtering, onto apatite type ceramics, were appraised for potential applications in solid oxide fuel cells with silicate based solid electrolytes, where performance may suffer from surface decomposition processes in reducing atmospheres. While as prepared Zr(Y)O_2–δ films without copper additive were already crystallised and single phase, fresh Cu containing Zr(Y)O_2–δ are essentially amorphous, requiring high temperature treatment in air for crystallisation. Deposition rate of 0·50–0·75 μm h^–1 at sputtering power of 300 W was achieved. Surface morphology studies using atomic force microscope revealed typical film structures with small (<50 nm) grains. The hardness of films decreases from 15·8 to 8·4 GPa with increasing copper content. Polarisation studies of electrochemical cell with cermet anodes, applied over protective films, suggested that electrochemical reaction is essentially governed by oxygen anion transfer from zirconia phase and/or hydrogen oxidation in vicinity of zirconia film surface. Copper incorporation into Zr(Y)O_2–δ film leads to higher anode resistivity.     

轻放液压支架掩护梁强度有限元分析

本文以 YFJ/ GC一 2 40 0轻型放顶煤液压支架为例 ,利用 SOLID EDGE软件对液压支架掩护梁进行强度有限元分析 ,对液压支架设计生产具有重要的实际意义     

轻型放顶煤液压支架的三维建模方法的研究

以YFJ/GC— 2 4 0 0轻型放顶煤液压支架为例 ,利用SOLIDEDGE软件的零件、钣金、装配和工程图 4个模块 ,对轻型放顶煤液压支架进行三维建模 ,为轻型液压支架的研究工作提供了可靠保证 ,对液压支架设计生产具有重要的实际意义。     

Prediction of solid state structure based on eutectic and eutectoid transformation parameters in spheroidal graphite irons

Abstract

The aim of the present work is to predict experimentally the structural trend of liquid iron based on its solidification features and the subsequent solid state transition. Both transformation processes in SG iron samples are simultaneously studied by means of industrial thermal analysis techniques. Experimental parameters are established in both cases in order to quantify the main metallurgical facts and correlate them with the structural properties of different alloys used in real manufacturing processes. A computer aided program has been designed for the treatment of the cooling curves.

A large number of experimental tests using different chemical compositions were made. After curves treatment, several studies have been conducted to correlate the thermal parameters obtained and the structural properties detected via metallographic inspections. The influence of the solidification parameters on carbon diffusion process and the resulting structures is discussed. A new structural model was developed in order to predict the ferrite content on the basis of thermal evolution of SG iron. Nucleation potential (inoculation grade), carbide formation tendency and solid state evolution of metal are evaluated and final structure distribution is accurately estimated.     

Newly developed cordierite–zircon composites

Abstract

Cordierite-zircon ceramic composites were fabricated by die pressing a commercial cordierite powder with the addition of up to 10 wt-% zircon (ZrSiO₄). Sintering of cordierite was enhanced by the ZrSiO₄ addition through glass phase formation. With ZrSiO₄ additions above 2·5 wt-% no further effect on the mechanical properties of the composites was observed. The maximum flexural strength at 2·5 wt-%ZrSiO₄ addition was 84±7 MPa, about 30% higher than the 67±5 MPa found for pure cordierite. The strength of cordierite at 2·5 wt-%ZrSiO₄ increased with sintering temperature up to 1300°C, owing to the enhanced densification. Above 1300°C, however, the strength was reduced as a result of the formation of large pockets of glassy phase. The average fracture toughness of cordierite was increased from 1·0 to 1·5 MPa m^1/2 with the addition of ZrSiO . This toughening can be attri4 buted to crack deflection around ZrSiO₄ particles rather than to residual compressive stresses imposed on the cordierite owing to thermal expansion mismatch between cordierite and the ZrSiO₄ second phase.     

Mechanical response of amorphous and semicrystalline poly(ethylene terephthalate) and modelling in frame of quasi point defect theory

Abstract

The thermomechanical activation of deformation in amorphous and (38%crystalline) semicrystalline poly(ethylene terephthalate) (PET) has been investigated using dynamic mechanical tests and large strain experiments. Activation parameters for both materials are determined in the neighbourhood of the glass transition temperature using stress relaxation experiments. The complete mechanical behaviour of amorphous PET is then analysed in the frame of a molecular model or ‘quasi point defect’ theory. With this aim, a new method is proposed, based on only three isochronal measurements, and leading to the determination of the set parameters. This method makes it possible to reproduce the stress–strain curve over a range of temperatures, as well as the relevant activation parameters. Finally some qualitative explanations are given for the mechanical behaviour of semicrystalline PET.     

Residual stress and thermal cycling of planar solid oxide fuel cells

Abstract

The published literature relating to damage to planar solid oxide fuel cells caused by thermally induced stresses and thermal cycling is reviewed. This covers reported studies of thermal cycling performance and stresses induced by temperature gradients and differences in thermal expansion coefficients in typical planar SOFC configurations, namely electrolyte supported; anode supported and inert substrate supported cells. Generally good agreement is found between electrolyte residual stresses measured by X-ray diffraction or cell curvature and stresses calculated from simple thermo-elastic analysis. Finite element modelling of temperature distributions in cells and stacks in steady state operation are well advanced and capable of being extended to compute stress distributions. Failure criteria are then discussed for laminated cell structures based on critical energy release rate fracture mechanics models developed originally for coatings. However, in most cases the data required to apply the models quantitatively (such as elastic moduli of actual laminated material and fracture energies of materials and interfaces) are not available. Where data are available there are inconsistencies that require resolution. Seals are critical components in many planar solid oxide fuel cell configurations, but again there are discrepancies in experimental mechanical properties and the role of internal stresses in their fracture. In addition, there is as yet no firm evidence that thermal cycling damage involves any true materials fatigue process.     

Modelling Permanent-mould Casting Processes

Abstract

Numerical and experimental work is carried out to investigate liquid metal flow and heat transfer during the permanent moulding of cast iron. Heat conduction during the pouring and solidification of cast-iron plates, and liquid metal flow and heat transfer during the pouring and solidification of cylindrical cast-iron ingots is numerically and experimentally investigated. The castings are poured in permanent moulds, and temperature distributions in the castings and the moulds are recorded. The mathematical modelling indicates the significance of finite pouring time and liquid metal convection on the temperature distribution. Good agreement is obtained between the experimental data and the predictions of the heat and mass transfer computations. Temperature fields, solidus front shapes and velocity fields during pouring and solidification are simulated for both top and bottom gated cases.     

Influence of atomising gas on particle characteristics of Al,Al–1 wt-%Li,Mg, and Sn powders

Abstract

The influence of physical and flow properties of atomising gas on the particle characteristics of gas atomised Al, Al–1 wt-%Li, Mg, and Sn powders was investigated in a pilot plant gas atomiser with IN4/ON18/3·5–4·0 type ‘confined design’ nozzle. In the tests, Al powders were produced under high and low pressures of argon, under air, (N₂ + O₂ ) mixture, nitrogen, and helium; Al–1 wt-%Li binary alloy powders were produced under argon and helium; Mg powders were produced under high and low pressures of argon and helium; and finally Sn powders were produced under argon, nitrogen, and helium. The morphology, size, size distribution, and surface features of the powders used in the present study were examined under SEM together with dry and wet sieving, used for sizing the powders. It was observed that high gas velocities and/or low atomising gas densities not only affect powder particle size, but also shape and surface texture. The oxygen content of the atomising gases also has an influence on the powder particle shape. In this context, powders produced under helium are finer in size owing to efficient secondary breakup; more spherically shaped in their fine size fraction in non-oxidising or difficult to oxidise atomising liquids (such as Sn and Al), because the time to breakup is shorter than that for solidification; and more irregularly shaped in their coarse size fraction in oxidising atomising liquids (such as Mg and Al–Li) owing to oxygen (the time to breakup is longer than that for solidification) compared with other atomising gases such as argon, air, (N₂ +O₂ ) mixtures, and pure nitrogen.