S. Raju

The pressure derivative of bulk modulus of transition metals: An estimation using the method of model potentials and a study of the systematics

Abstract The pressure derivative of bulk modulus is calculated for the entire block of d-transition metals using a modified form of the recipe proposed by Wills and Harrison to represent the effective interatomic interaction. The calculated values are compared extensively with the available experimental and other semi theoretical values. The agreement between the calculated set and the experimental one is nominal, but the trend exhibited by the calculated values confirms broadly to the well established pattern. An interesting global correlation is revealed with respect to the bonding or the interstitial electron density, wherein, the present set of data pertaining to (d-transition metals fits nicely with the general trend exhibited by the highly incompressible ceramic solids and other solids of intermediate compressibility. It is established therefore that the pressure derivative of bulk modulus of diverse class of materials in fact scales with an average measure of bonding charge density. For the individual class of 3d, 4d and 5d transition metals the calculated B′00 values reveal with Miedema s electronegativity a correlation, which is shared by many other bulk properties.

The high temperature bulk modulus of aluminium: an assessment using experimental enthalpy and thermal expansion data

Abstract There exists a certain ambiguity with regard to the actual high-temperature bulk modulus of aluminium. In particular, there is a considerable disparity between various single crystal elastic constant measurements. This point has not been addressed on the theoretical front as well. In view of this situation, we seek to assess the existing bulk modulus data for their internal thermodynamic consistency and also obtain a reliable estimate using experimental data on thermal expansion, enthalpy and specific heat. The procedure adopted for this purpose makes use of a thermodynamic framework that relates thermal and elastic properties through Gruneisens hypothesis. The present analysis suggests that the oft-cited data of Gerlich and Fisher and the older one due to Sutton are not fully consistent with the existing thermal property data. The more recent data of Tallon and Wolfenden, although in better consonance with the requirements of thermodynamic consistency, are also found to be less reliable. A fresh calculation of the bulk modulus is made such that the estimated values exhibit a high degree of thermodynamic legitimacy with the selected thermal property data.

A study of ternary element site substitution in Ni3Al using pseudopotential orbital radii based structure maps

It is well known that ternary alloying additions are usually added in small quantities to structural intermetallics with a view to optimize their structural, physical, chemical and mechanical properties. Since structural intermetallics are highly ordered alloys, the added ternary solutes often reveal a preponderant tendency to substitute preferentially one of the sublattices. A knowledge of the basic factors governing the preferential site substitution behavior is useful in elucidating the role of ternary additions in controlling the materials properties. In this paper, the authors apply the concept of structure maps for explaining the site substitution behavior of ternary alloying additions in Ni{sub 3}Al.

Transition of Crack from Type IV to Type II Resulting from Improved Utilization of Boron in the Modified 9Cr-1Mo Steel Weldment

The roles of boron and heat-treatment temperature in improving the type IV cracking resistance of modified 9Cr-1Mo steel weldment were studied. Two different heats of P91 steel, one without boron, designated as P91 and the other with controlled addition of boron with very low nitrogen, designated as P91B, were melted for the current study. The addition of Boron to modified 9Cr-1Mo steel has increased the resistance against softening in fine-grained heat-affected zones (FGHAZ) and intercritical heat-affected zones (ICHAZ) of the weldment. Creep rupture life of boron containing modified 9Cr-1Mo steel weldment, prepared from 1423xa0K (1150xa0°C) normalized base metal, was found to be much higher than that prepared from 1323xa0K (1050xa0°C) normalized base metal because of the stabilization of lath martensite by fine M23C6 precipitates. This finding is in contrast to the reduction in creep rupture life of P91 weldment prepared from 1423xa0K (1150xa0°C) normalized base metal compared with that of the weldment prepared from 1323xa0K (1050xa0°C) normalized base metal. The trace of failure path from the weld metal to ICHAZ in P91B weldment was indicative of type II failure in contrast to type IV failure outside the HAZ and base metal junction in P91 weldment, which suggested that boron strengthened the microstructure of the HAZ, whereby the utilization of boron at a higher normalizing temperature seemed to be significantly greater than that at the lower normalizing temperature.

Thermal expansion characteristics of a titanium modified austenitic stainless steel: measurement by high-temperature X-ray diffraction and modelling using Grüneisen formalism

Abstract The thermal expansion of a titanium modified, swelling resistant austenitic stainless steel designated as D9 is studied by measuring the lattice parameter as a function of temperature in the range 300–1300 K by high-temperature X-ray diffraction technique. The thermal expansion data thus obtained is in reasonable agreement with the typical thermal expansion values reported for similar nuclear grade austenitic stainless steels. However, at temperatures exceeding 900 K, the measured thermal expansivity exhibits a pronounced non-linear increase due partly to the precipitation of complex carbide and intermetallic phases. The high-temperature thermal expansion data obtained in the present study are augmented by modelling the low-temperature thermal expansion behaviour by Gruneisen formalism.

Theoretical analysis of interstitial ordering and precipitation processes in the Ti-N system

Abstract The energetics of interstitial ordering was analysed using the quasi-chemical approach incorporating interactions up to second nearest-neighbours. It was found that the interstitial ordering is required because of strong repulsive interactions between interstitial atoms situated along the c -axis. A nitrogen occupation scheme with a view to minimizing this strong coulombic repulsion and to offer minimum lattice disturbance is proposed. Keeping in accord with the occupation scheme, the combined effect of first and second nearest-neighbour interactions was found to give rise to the formation of ordered superstructures. A martensitic transformation of the ordered domains as a result of the stress field associated with the interstitial atom is predicted to occur around the composition of 20 at. % nitrogen. The nature of the phase separation of the ordered superstructures and the crystallography of the lattice distortion are briefly discussed.

Effect of alloy content on microstructure and microchemistry of phases during short term thermal exposure of 9Cr-W-Ta-0⋅1C reduced activation ferritic/martensitic (RAFM) steels

This paper presents the results of an experimental study on the microstructural evolution in 9Cr reduced activation ferritic/martensitic steels during short term thermal exposures. Since the microstructure is strongly influenced by the alloying additions, mainly W, Ta and C contents, the effect of varying W and Ta contents on the martensite structure that forms during normalizing treatment and the subsequent changes during tempering of the martensite in the temperature regime of 923–1033 K have been studied. Microstructural changes like subgrain formation and nature of precipitates have been evaluated and correlated to hardness variations. The systematic change in size distribution and microchemistry of M23C6 carbide is studied with variation in W content at different temperatures.

An integrated thermodynamic approach towards correlating thermal and elastic properties: development of some simple scaling relations

Abstract This study presents a detailed thermodynamic analysis of the intricate interrelationship existing between thermal and elastic properties. By invoking only the principles of classical thermodynamics, the multifarious consequences of a possible linear relationship between logarithmic bulk modulus and relative enthalpy at constant pressure are probed. In particular, we identify two linear scaling relations between molar volume and relative enthalpy and between molar volume and logarithmic bulk modulus. These relations are valid at temperatures exceeding the Debye temperature. In addition, certain interesting deductions with respect to the temperature dependences of the Anderson–Gruneisen parameter and the volume thermal expansivity to isobaric specific heat ratio are obtained. In brief, a simple thermodynamic protocol that will be of use in an integrated treatment of the elastic and thermal quantities has been developed. As an illustrative case study, the high temperature bulk modulus of copper is estimated from its thermal properties data using the proposed framework.

Energetics of point defects in γ-TiAl

{gamma}TiAl has been receiving a great deal of attention in recent times owing to its industrial importance. This structural intermetallic is a candidate material for high temperature aerospace applications. Therefore, a study of point defect properties is useful in elucidating its physical metallurgy. In this brief communication, the authors discuss the vacancy and antisite defect properties of {gamma}-TiAl.

Decomposition modes of austenite in 9Cr–W–V–Ta reduced activation ferritic–martensitic steels

Abstract The present paper presents the results of an extensive electron microscopy investigation on the decomposition modes of high temperature austenite in 9Cr–W–V–Ta reduced activation ferritic–martensitic steels. Although the displacive martensitic transformation is predominant on austenitisation, low volume fraction of Fe rich M3C or M23C6 precipitates formed, when the tungsten content exceeded 1 wt-%. The compositional inhomogeneity introduced in the austenite by the nature, chemistry and kinetics of dissolution of the pre-existing carbides is dependent on the steel composition and austenitisation conditions. The extent of repartitioning of tungsten between M23C6 and ferrite largely influences the kinetics of austenite and martensite transformation, for the same austenitisation conditions. Supporting evidence from calorimetry analysis is also presented.