Kaustubh N. Kulkarni

Investigations of quaternary interdiffusion in a constituent system of high entropy alloys

Interdiffusion was investigated at 1000°C in a quaternary Fe-Ni-Co-Cr system, which is an essential constituent of many high-entropy alloys. The relative values of main and cross interdiffusion coefficients determined from concentrations and interdiffusion fluxes developed in a single diffusion couple indicate that significant diffusional interactions exist in this system. Thermodynamic interactions between the binary constituents were analyzed based on the activity coefficient relations and it is shown that the observed diffusional interactions of a component with others are consistent with relative thermodynamic interactions between them.

A transfer matrix analysis of quaternary diffusion

A transfer matrix method (TMM), developed recently by Ram-Mohan and Dayananda, has been employed for the first time to generate error function solutions for quaternary diffusion in solid–solid metallic diffusion couples. The method was validated with the aid of a hypothetical couple with known quaternary interdiffusion coefficients and applied to two experimental Cu–Ni–Zn–Mn quaternary couples annealed at 775°C. Quaternary interdiffusion coefficients were determined by the Dayananda analysis from the concentration profiles of the couples over selected composition ranges in the diffusion zone and employed for the subsequent TMM calculation of error function solutions. For the hypothetical test couple, identical sets of constant interdiffusion coefficients were determined on either side of the Matano plane and utilized for the calculation of concentration profiles by TMM. For the experimental Cu–Ni–Zn–Mn couples, interdiffusion coefficients determined over selected regions in the diffusion zone were employed for the TMM generation of the concentration profiles.

Preparation and characterization of maghemite nanoparticles from mild steel for magnetically guided drug therapy

Maghemite (γ-Fe2O3) nanoparticles for therapeutic applications are prepared from mild steel but the existing synthesis technique is very cumbersome. The entire process takes around 100 days with multiple steps which lack proper understanding. In the current work, maghemite nanoparticles of cuboidal and spheroidal morphologies were prepared from mild steel chips by a novel cost effective oil reduction technique for magnetically guided intravascular drug delivery. The technique developed in this work yields isometric sized γ-Fe2O3 nanoparticles in 6 h with higher saturation magnetization as compared to the existing similar solid state synthesis route. Mass and heat flow kinetics during the heating and quenching steps were studied with the help of Finite element simulations. Qualitative and quantitative analysis of the γ-Fe2O3 phase is performed with the help of x-ray diffraction, transmission electron microscope and x-ray photoelectron spectroscopy. Mechanism for the α-Fe2O3 (haematite) to γ-Fe2O3 (maghemite) phase evolution during the synthesis process is also investigated.Graphical AbstractMaghemite (γ-Fe2O3) nanoparticles were prepared bya novel cost effective oil reduction technique as mentioned below in the figure. The raw materials included mild steel chips which is one of the most abundant engineering materials. These particles can be used as ideal nanocarriers for targeted drug delivery through the vascular network.

Evolution of Concentration Profiles and Diffusion Paths in Single-Phase Multicomponent Multilayered Assemblies

An analysis of multilayered assemblies set up with multicomponent alloys selected in a single phase field has been recently developed on the basis of a matrix of constant interdiffusion coefficients. This analysis employs a transfer matrix method and is applicable to a study of evolution of concentration profiles and diffusion paths as a function of time for multilayered diffusion assemblies (MDAs) where any number of finite layers is sandwiched between two bulk terminal alloys. The analysis is utilized in this study to simulate concentration profiles and diffusion paths for MDAs assembled with (fcc) Cu-Ni-Zn alloys with two terminal alloys, A and B, sandwiching an alloy layer C in the middle. For short diffusion times the diffusion path of the ternary MDA, A/C/B, corresponds to two segments corresponding to the diffusion paths of the infinite diffusion couples, A/C and C/B. At longer times the diffusion zones of the two individual couples overlap and the diffusion path of the MDA varies continuously with time. The evolution of the concentration profiles and diffusion paths is presented and each intermediate path configuration is associated with a unique ratio of the middle layer thickness to the square root of diffusion time. The simulated concentration profiles clearly show the development of uphill diffusion and zero-flux planes (ZFP) for the individual components due to diffusional interactions among the components. At very long times, the diffusion path of the MDA approaches that of the infinite couple A/B between the two terminal alloys.

A novel approach for controlling precipitation kinetics based on diffusional and thermodynamic interactions in multicomponent systems

ABSTRACT A novel concept for selection of alloying elements based on diffusional and thermodynamic interactions is proposed. A general model to predict enhancement or reduction of diffusion flux of an element arising from the addition of another is described and specifically applied to determine the appropriate ternary alloying addition to reduce the fast precipitation kinetics observed in binary Ti–Fe based alloy. It is experimentally shown that addition of Cr and Mo decreases the kinetics of precipitation of TiFe, whereas addition of Ta and Nb enhances the kinetics, which is consistent with the predictions of the proposed model.

Diffusion in B2 NiAl and FeAl Intermetallics and Their Alloys

Both FeAl and NiAl with B2 crystal structure are envisaged for their usage in high temperature applications and hence, availability of diffusion data in these intermetallics is crucial in designing their alloys and processes as well as deciding their in-service performance. A comprehensive overview of diffusion data available in B2 FeAl and NiAl and their alloys is provided in this article. Nearest neighbor vacancy jumps in B2 intermetallic lead to a local disorder in the lattice and hence it is not necessarily the unit step of diffusion in these structures. Several mechanisms of diffusion proposed in the literature are discussed including nearest neighbor jumps, next nearest neighbor jumps, six-jump vacancy cycle, triple defect and antisite bridge. Relevance of these mechanisms in FeAl and NiAl is discussed. An overview is given on the self-and solute diffusion and interdiffusion data available in both binary FeAl and NiAl. Due to wide solubility range of both FeAl and NiAl as well as their alloying requirements for improved properties, it becomes pertinent to study the multicomponent diffusion in the alloys based on these B2 itnermetallics. Hence, in the latter part of the article, various methods used for determining multicomponent diffusion data are reviewed. A detail overview is also provided on the diffusion studies available in literature on ternary alloys based on FeAl and NiAl with an emphasis on highlighting the diffusional interactions observed in these systems.

Effect of strain path change on precipitation behaviour of Al-Cu-Mg-Si alloy

The effect of strain path change on precipitation behaviour of Al- Cu-Mg-Si alloy was investigated. Two different types of crystallographic textures were produced by changing the strain path during rolling. The deformed samples were subjected to a short recrystallization treatment and ageing to identify the effect of strain path change manifested in terms of crystallographic texture on precipitation behaviour. Preliminary characterization indicates that ageing kinetics as well as precipitate morphology vary depending upon the mode of rolling. The coherency strains associated with a coherent interface is relieved in a unlike manner for differently rolled samples.

Matrix Green’s function analysis of multicomponent diffusion in multilayered assemblies

In order to describe interdiffusion in layered structures in multicomponent systems, matrix Green’s functions may be employed in seeking solutions to multicomponent diffusion equations. A transfer matrix method employing a matrix notation is utilized for this analysis. For single-phase multilayered assemblies set up with thin alloy layers of different compositions between thick terminal alloy disks, expressions for the temporal and spatial evolution of the concentration profiles are developed on the basis of a set of constant interdiffusion coefficients. The theory is developed in general for multilayered diffusion assemblies containing any number of finite layers. It is applied to an experimental ternary diffusion assembly containing one layer sandwiched between two thick terminal alloys in the Cu–Ni–Zn system. The Cu–Ni–Zn layered diffusion assembly was assembled with three α (fcc) Cu–Ni–Zn alloys of different compositions and annealed at 775 °C for 4 days. The agreement between the experimentally obser...