Liquid-phase sintering of very fine tungsten-copper powder mixtures

Effects of tungsten particle size and copper content on densification of liquid-phase-sintered W-Cu

“…At 1200 °C, the sintering temperature used in this study, W has a tensile strength of about 200 MPa, [25] and the value of ␥ lv for liquid Cu is 1.28 J/m 2 . [26] Critical X/D ratios are plotted as functions of particle size and coordination number in Figure 13. If the X/D ratio exceeds the value for a given particle size and coordination number, rearrangement is expected to be prevented by the (c)…”

Activated liquid phase sintering of W–Cu and Mo–Cu

“…For W-Cu, the solubility of W in Cu is less than 10 −3 at.% [10], and grain growth likely occurs by a combination of solutionreprecipitation [11][12][13] and coalescence [14][15][16]. For Mo-Cu the reported solubility of Mo in Cu of 0.5 to 1.3 wt.% at 1100 to 1500°C [17] would be expected to result in a dominant role for solution-reprecipitation, but reported grain growth rates are much lower, raising the probability of a significant contribution from coalescence [18].…”

Effect of liquid content on distortion and rearrangement densification of liquid-phase-sintered W-Cu

“…From 1080 °C to 1200 °C, ␥ lv for liquid Cu remains relatively constant at 1.28 J/m 2 . [23] The stress due to gravitational force is much lower in magnitude than the stress due to capillary force. [50] The maximum shear stress induced by gravity is given by [51] [ 10] where V is the volume fraction; is the density of the material; subscripts s and l designate the solid and liquid, respectively; g is the acceleration due to gravity; h is the height of the sample; and N c is the coordination number.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Composites with 10 to 20 wt pct (19.3 to 35.1 vol pct) Cu are most commonly used for thermal management, but the limited solubility of W in liquid Cu makes liquid phase sintering of these compositions to full density difficult. Submicron W powders and intimate mixing techniques, such as mechanical alloying, [13,[15][16][17][18][19][20][21] co-reduction of oxides, [22][23][24][25][26][27] or other thermochemical processes [28] are required to achieve pore-free components via liquid phase sintering. Such conditions promote solid-state sintering of the W skeleton in the presence of liquid Cu, which has been shown to sufficiently account for the experimentally observed densification behavior.…”