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ScienceTomorrow uses spark discharge sintering (SDS), also known as spark plasma sintering (SPS) method [Figure below] for fabricating complex componentsfrom tungsten to plastic. In this method, a pulsed dc current simultaneously with an uniaxial pressure to consolidate.

 
Excellent properties of material fabricated by SDS method is due to discharge that is generated among particles. The spark discharge eliminates surface impurities on powder particles that enhances sintering even among highly dissimilar materials aided by voltage driven electro-migration and creation of virgin high energy surface with plenty of dangling bonds.

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The electric field will cause phase transformation and plastic deformation in the refractory metals.  It will also drive mass transfer as predicted by electro-migration theory as given in equation:



where, 

Ji is the flux of the diffusing ith species, Di is the diffusivity of the species, Ci is the concentration of the species, F is Faraday’s constant, z is the effective charge on the diffusing species, E is the electric field, R is the gas constant, and T is temperature in Kelvin

The initiation of the spark discharge in the gap between particles will be assisted by fine impurities and gases on and between the surfaces of the particles. The spark discharge will create a momentary local high-temperature state of up to 10,000°C, causing vaporization of both the impurities and the surfaces of the particles in the area of the spark. Immediately behind the area of vaporization, the surfaces of the particles will melt. Via electron draw during ON TIME and the vacuum of OFF TIME, these liquidized surfaces will be drawn together, creating "necks." The ongoing "radiant" Joule heat and pressure will cause these necks to gradually develop and increase. The radiant heat will also causes plastic deformation on the surface of the particles, which is necessary for higher-density applications. The gradual change in composition helps balance the strain energy due to temperature and elastic modulus difference.

During the SDS process, heat will be concentrated primarily on the surfaces of the particles. Particle growth will be limited due to the speed of the process and the fact that only the surface temperature of the particles will rise rapidly. The entire process—from powder to finished bulk sample—will be completed quickly, with high uniformity and without changing the particles' characteristics.

Primary advantages are:

  • Superior product quality.
  • Economic fabrication.
  • Seamless bonding with dissimilar materials.
  • Excellent load and heat transfer.