PLASTIC-FLOW OF A 2-PHASE SOLID-LIQUID METALLIC SYSTEM

Preliminary research on the gravity-induced distortion of W-Ni-Fe heav y metal parts (90-97%W) during liquid-phase sintering conditions (1450 -1550-degrees-C, less than 25.5% of liquid-phase volume fraction) show ed a departure from the linear-viscous creep usually observed in ceram ic-glass or other non-metallic systems deforming in the partially molt en state. The stress exponent (n congruent-to 2) and the activation en ergy of the deformation measured in the heavy metal suggested that gra in boundary sliding of the solid skeleton of interconnected tungsten p articles was the controlling deformation mechanism for its creep in pr esence of a moderate fraction of liquid phase. This paper presents a n ew series of tests aimed at obtaining more precise results on the rheo logy of the same system. The temperature range 1450 less-than-or-equal -to T less-than-or-equal-to 1600-degrees-C has been covered with two a lloys containing different amounts of liquid phase. Strains (and strai n rates) have been estimated from the gravity-induced creep of cylindr ical specimens (sigma less-than-or-equal-to 6 kPa, epsilon less than o r similar to 10(-5) s-1). The results confirm the previous conclusion about the dominance of the grain boundary sliding mechanism. Moreover, the volumetric strain associated with the compressive distortion, onl y qualitatively assessed in the previous research, has now been quanti fied. The unconstrained deformation of the two-phase mixture is accomp anied by a dilation of the sample regions undergoing the largest strai n. As a consequence, there is a redistribution of liquid phase that le ads to a contraction of the less deformed regions of the sample.