K.R. Ravi

Role of Ultrasonic Treatment on Microstructural Evolution in A356/TiB2 In-Situ Composite

The present study explores the possibility of using ultrasonic treatment for the conversion of dendritic microstructure of in-situ A356/TiB2 composite into non-dendritic globular structure. A356/2TiB2 in-situ composite has been subjected to high intensity ultrasonic treatment in liquid metal state as well as during the process of solidification. Microstructural analysis shows that the ultrasonic treatment during the process of solidification is an effective technique for the transformation of dendritic morphology into fine globular structure along with the modification of Si needles.

Synthesis of Al–MgAl2O4 Master Alloy and its Grain Refinement Studies in Pure Aluminium

The effect of ultrasonic treatment (UT) on the synthesis of Al–MgAl2O4 master alloy has been studied by the reaction of SiO2 precursor with Al-2wt% Mg. The results show that SiO2 reaction is enhanced after UT and the corresponding mechanism is proposed. Grain refinement studies in pure Al showed that an increase in addition level of MgAl2O4 particles resulted in two to threefold reduction in grain size; whereas, UT intensified the grain size reduction by 11–12 fold. Significant grain refinement on UT is attributed to the cavitation enhanced wetting which activates MgAl2O4 particles as potent nucleating site for Al.

Effect of Ultrasonic Treatment on Microstructure and Mechanical Property of In Situ Al/2TiB Particulate Composites

Al/2TiB2in-situ composite was fabricated using salt-melt reaction method. Subsequently, it was re-melted and treated with high intensity ultrasonic waves for various time intervals. Substantial reduction in TiB2 particle size down to ~ 300 nm along with significant improvement in dispersion is achieved with the aid of ultrasonic treatment. Ultrasonic treatment has resulted significant increase in hardness of Al/2TiB2in-situ composite.

Microstructure and Mechanical Property of Fe-Al2O3 Nanocomposites Synthesized by Reactive Milling Followed by Spark Plasma Sintering

The in-situ Fe based nanocomposite containing Al2O3 particle is synthesized by reactive milling of Fe2O3-Al-Fe powder mixture in toluene medium followed by consolidation of powders using Spark Plasma Sintering process. Transmission electron microscopy investigation of consolidated Fe-Al2O3 nanocomposites has shown heterogenous grain structure of Fe consisting of nano, submicron and micron size grains together with nanometer Al2O3 particles. The hardness of Fe-Al2O3 nanocomposites consolidated at 800°C is 795 MPa.

Exploring Mg-Zn-Ca-Based Bulk Metallic Glasses for Biomedical Applications Based on Thermodynamic Approach

Magnesium (Mg)-based metallic glasses are considered as possible candidates in orthopedic implant applications. This paper aims to theoretically predict the glass-forming ability (GFA) in Mg-Zn-Ca alloy using a newly proposed thermodynamic model (PHHS), and the consistency of this model is verified through experimental analysis. PHHS is based on thermodynamic parameters such as enthalpy of chemical mixing, elastic enthalpy, and configurational entropy, thus incorporating the pivotal effects, i.e., electron transfer effects, effect of atomic size mismatch, and effect of randomness, which aid to high GFA. In essence, PHHS can be visualized as the energy barrier that exists between the transformations of random atomic structure of glass to ordered crystalline structure. When the PHHS value is more negative, the energy barrier will be high, supporting easy glass formation. Various Mg-Zn-Ca metallic glass compositions displayed almost an expected and supporting trend, where the critical diameter of the metallic glass rod increased with a more negative PHHS value. Among the predicted Mg-Zn-Ca systems, the Mg60Zn35Ca5 composition shows deviation from the expected trend. This discrepancy has been clearly elucidated using a eutectic phase diagram. In addition to the consistency of the PHHS parameter to verifying the GFA of various compositions, the unique ability of this model is to predict unexplored Mg-Zn-Ca glass-forming compositions using contour development. Thus, proving PHHS parameter to be used as an efficient tool in predicting new glass-forming compositions.

Spark Plasma Sintering of Fe-Cr-Mo-P-B-C-Si Amorphous Alloy

In the present work, synthesis of bulk Fe amorphous alloy by mechanical alloying of 70Fe-15Cr-4Mo-5P-4B-1C-1Si powders followed by consolidation of powders using Spark Plasma Sintering process is reported. The evolution of phase, microstructure, relative density and hardness of amorphous alloy as a function of spark plasma sintering temperature is discussed. Transmission electron microscopy investigation has shown partial divitrification of amorphous matrix into nanocrystalline phase during spark plasma sintering of amorphous Fe alloy. The hardness of amorphous alloy sintered at 525 – 575°C are in the range of 675 - 725 MPa.