The effect of the size and volume fraction of Zr₂Cu on the sintering behavior of tungsten matrix composites during liquid-reactive sintering

In the present work, we investigate the effects of the size and volumetric fraction of Zr₂Cu on the density and mechanical strength of liquid-reactive sintered W/MWCNTs/ Zr₂Cu composites. Composite powders are formed by mechanical ball-milling and are sintered into a high density composite at 1400 C. During sintering, two major reactions occur: 1) C atoms in the MWCNTs reacted with the W matrix to form WC; 2) Zr in the Zr ₂Cu liquid phase, which flows through the capillaries between particles, reacts with WC in the W matrix to form ZrC. Based on our results, higher density composites with finer ZrC reinforcements are successfully produced using sub-micron size Zr₂Cu powders. In addition, the amount of Zr₂Cu is varied, and the optimal volumetric fraction of Zr ₂Cu that maximizes the hardness of the composite (1180 Hv) is equal to 30 vol.%. When the Zr₂Cu content is less than the critical value, and the density of the composite is too low due to an insufficient amount of liquid. The hardness of the composite decreases when the Zr₂Cu content is greater than 30 vol.%, because excess liquid yields a network structure of WC, ZrC, and Zr. The experimental results also reveal that the sintering time required to reach the maximum hardness (1180 Hv) significantly decreases as the size of Zr₂Cu is reduced from micron-scale to nano-scale.