Graduate Thesis Or Dissertation


Flash Sintering Techniques for Rapid and Sustainable Metal Processing at Room Temperature Public Deposited
  • Flash sintering has gained significant attention since it was first discovered in 2010, however, no study has conclusively studied the flash sintering of metal. The present study applied flash sintering technique to achieve rapid and sustainable sintering of metals including tungsten (W), nickel (Ni), and rhenium (Re).

    While ceramics require furnace heating to initiate flash sintering, metals do not. They can be sintered at room temperature by direct injection of current. Nevertheless, the experiment performed with tungsten presented results with and without a furnace, while nickel and rhenium were sintered without furnace. In all cases, sintering occurs when the specimen temperature is around 1000˚C.

    The pattern of flash sintering is similar in all the metals studied. The resistivity behavior when plotted as a function of temperature show similar behavior. The general features observed are as follow: (i) an incubation period where electric voltage breakdown is observed as inter-particle contact are established (ii) followed by the initiation of electroluminescence which has been seen between 5 and 7 A mm-2 in all metals. This optical emission signals the onset of flash characterized by a plateau in temperature and generation of defects. (iii) Finally, the temperature surges and abrupt sintering follows between 20 and 24 A mm-2.

    The role of large defect generation was emphasized in each of the metals studied – Ni, W, and Re. The difference between the input electrical energy and energy loss to black body radiation, convection and specific heat was calculated, and termed “energy deficit”. The energy deficit was divided by the formation enthalpy of the metal to obtain the mol fraction of Frenkel pairs generated during the flash sintering process. Point Defect estimated include 26mol% for W, 14 mol% for Re and 0.3-0.4 mol% for Ni. These values are several orders of magnitude higher than what is expected from thermal equilibrium.

    The result of variation of current rate in W and Ni studies showed that sintering depends on current density and not current rate. This result was rationalized by recognizing that the rate of mass transport by diffusion depends on the product of the defect concentration and the mobility of defects. If the defect concentration is large, then it may weaken the influence of mobility on the rate of mass transport. Since the defect concentration depends on the current density, it can be postulated that sintering will also predominantly depend on the current density.

    Comparison of the energy consumption during the flash sintering process and alternative sintering methods showed that flash sintering is has less energy footprint. This study associates this energy efficiency to the controllable direct injection of current into the specimen without any barrier or need for furnace heating, which is paramount in the alternative sintering methods.

    Finally, exploratory studies have shown the potential of metal flash sintering technique in several areas of applications such as additive manufacturing, surface coating/modification and alloy/composite fabrication. Importantly, Integrating flash sintering into metal additive manufacturing will enable rapid and more sustainable manufacturing of end-user components.

Date Issued
  • 2023-11-21
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Last Modified
  • 2024-01-17
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