• Satish C Gupta

      Articles written in Bulletin of Materials Science

    • α → ω transition in shock compressed zirconium: A study on crystallographic aspects

      G Jyoti K D Joshi Satish C Gupta S K Sikka G K Dey S Banerjee

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      In 1973, Usikov and Zilbershtein proposed that theα(hcp) →ω (a three atom hexagonal) transformation in Zr and Ti proceeds via theβ(bcc, a high temperature phase) intermediate. Based on this they derived two non-equivalent orientation relationships (OR) betweenα andω phases. Their transmission electron microscopy (TEM) study carried out on these elements, that wereαω-transformed under static high pressure, revealed only one of the two proposed ORs. Various TEM studies done thereafter on these elements and their alloys (ω transformed under static pressures) conform to either one of these ORs. In a recent TEM study by Song and Gray on Zr,ω-transformed under shock compression, a new OR has been observed which according to them is different than those given by UZ and they put forth the directαω transformation mechanism. In the present study, we have generated additional TEM data on shock compressed Zr samples and have reconciled the above conflicting results. We find all our ORs (which contain the OR of SG also) to be described by the OR reported by UZ. The latter OR (i.e. of SG) is shown to be a subset of the former. These observations show that the same type of mechanism of transformation is operative both, under static and shock compression. Mechanism of the transition is discussed in terms of the required strains.

    • Materials synthesis and phase transitions under shock waves

      Satish C Gupta

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      Shock wave compression of materials is accompanied by high pressure, high-strain-rate loading, elevated temperatures, large shear stresses and excessive plastic deformation. All these features create an unusual state in materials that is not possible in any processing method. Thus, in multi-component system of powders, these can lead to enhanced reactivity because of defect promoted diffusional flow of the reactants in a solid-solid chemical reaction for materials synthesis. On the other hand, in a one component system, these shock compression features may significantly influence the onset pressure, the kinetics, the mechanism and the reversibility of a phase transformation. We shall illustrate these using examples on the synthesis ofβ-C3N4 and our work on the crystal to amorphous phase transitions inq-GeO2 andα-FePO4.

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