Self-Consolidation Mechanism of Ti5Si3 Compact Obtained by Electro-Discharge-Sintering Directly from Physically Blended Ti-37.5 at.% Si Powder Mixture

Abstract

Characteristics of electro-discharge-sintering of the Ti-37.5at.% Si powder mixture was investigated as a function of the input energy, capacitance, and discharge time without applying any external pressure. A solid bulk of Ti 5 Si 3 was obtained only after in less than 129 μsec by the EDS process. During a discharge, the heat is generated to liquefy and alloy the particles, and which enhances the pinch pressure can condensate them without allowing a formation of pores. Three step processes for the self-consolidation mechanism during EDS are proposed; (a) a physical breakdown of oxide film on elemental as-received powder particles, (b) alloying and densifying the consolidation of powder particles by the pinch pressure, and (c) diffusion of impurities into the consolidated surface.

Capacitor Electrical Discharge Consolidation of Metallic Powders—A Review

“…Ti [37] and Ti-6Al-4V powders [38] in 4 mm in diameter column and input energy of 2.86 kJ/g; or up to 522 MPa for 2.5 kJ/g and Ti-6Al-4V powders (stacked in a linear manner) in a 3.3 mm in diameter column [39]. Even much higher pinch pressures, of up to 2900 MPa are computed on Ti-Si37.5 powders stacked in a linear manner when processed with 15.29 kJ/g [40]. Pressure always decreases to 0 MPa in the periphery.…”

“…This later research group has also studied the Ti-6Al-4V alloy, initially in the US [39,72,107] and more extensively in Korea [38,45,61,[110][111][112][113][114]. In addition, MA Ti-Si 37.5 powders [115,116], mixed Ti-Si 37.5 powders [40], Ti-Al 25 [46,47], Ti-28Zr-20Ni [117], or mixtures Ti-TiC [73] have also been studied in Korea.…”

“…A calculated temperature of 5038 • C is likely to be enough to vaporize the powder mixture, but the short duration of the process, of about 129 µs, does only allow for the transformation into a liquid. On the other hand, the high pinch pressure, of up to 2900 MPa, pressurizes the liquid particles, eliminating porosity [40].…”

Low-Voltage Capacitor Electrical Discharge Consolidation of Iron Powder

“…Estimations based on the specific heat of the powder and the input power, calculated by integrating the current and voltage during the discharge, point out values as high as 1058 and 4925 • C for Ti and Ti-6Al-4V powder particles processed with 450 µF and up to 2.86 kJ/g [19,20], or about half of those values for Ti-6Al-4V powder under the processing conditions of 240 µF and 0.5 to 2.5 kJ/g [21]. Temperatures of up to 2593 to 6193 • C are reported in mixed Ti-Al25 powder processed with 450 µF and 1.67 to 5 kJ/g [22] or of up to 2004 to 5038 • C in mixed Ti-Si37.5 powder processed with 300 µF and 7.35 to 15.29 kJ/g [23]. Nevertheless, consolidation is also possible in the absence of external pressures for remarkable intensity of the current passing through the powder aggregate.…”

“…Under these circumstances, the action of internal electromagnetic pressures [16], due to the pinch effect (the magnetic field generated when an axial current circulates through a long cylindrical metal powder column, which tends to contract the column radially), should be considered. Estimated values in the powder column center were, for instance, up to 522 MPa for an energy input of 2.5 kJ/g and Ti-6Al-4V powder (stacked in a linear manner) in a 3.3 mm in diameter column [21] or even much higher pressures of up to 2900 MPa for Ti-Si37.5 powder stacked in a linear manner when processed with 15.29 kJ/g [23].…”