MICROSTRUCTURES TiB2/TiC/Ni COMPOSITES FORMED BY REACTIVE, PULSE PLASMA SINTERING

Over the past decade, a new class of processing techniques classified as in situ has gained prominence for fabrication of refractory ceramics and ceramic matrix composites. In this paper, by subjecting elementary Ti, B, C and Ni powders to pulse-plasma sintering (PPS) we obtained a dense TiB2/TiC/Ni composite during a single technological operation. The synthesis was realized in two different ways: thermal explosion realized by high heating rate (10 degrees C/s) and a inhibiting synthesis reaction without thermal explosion realized by low heating rate (1 degrees C/s) as show in Figure 1. With both techniques, the synthesis to be completed required a shorter time (t < 20 min) and ran at a lower temperature (1160 degrees C) than is the case with the process of fabrication of the TiB2/TiC/Ni composites using the conventional techniques. Microstructure characterization of the materials obtained was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive analysis (EDS). Mechanical properties were only evaluated by measuring hardness. Depending on which synthesis technique was employed, the microstructure of the composite, its phase composition and properties (Table 1) were different. Representative microstructures of the composites synthesized via thermal explosion (a, b) and without (c, d) are shown in Figure 3. When sintered by the thermal explosion, the composite was composed of the hard TiB2/TiC ceramic (distinguished as a darker regions in SEM) with the islands of Ni3B/Ni (distinguished as a brighter regions in SEM, Fig. 3a), whereas when produced by the slow reaction without thermal explosion, the TiB2/TiC ceramic was distributed within an Ni matrix (Fig. 3c). The composite synthesized by the inhibiting reaction was denser (93% TD) and harder (2400 HV1) than that produced using the thermal explosion (80% TD, 2150 HV1). The use of the PPS method permitted producing a dense and hard TiB2/TiC/Ni composite at a relatively low temperature (1160 degrees C) and in a short time (about 10 min).