The typical microstructures of the fracture surfaces of the sintered bodies at different temperatures are shown in Fig. 1. For the samples sintered at 1100℃, the phase of Mo2NiB2 has been formed through solid state reaction according to the XRD patterns. However, densification could not be realized without liquid phase formation. So, there were many pores in the body as shown in Fig. 1a and b, and the mechanical properties were not good. Above 1200℃, the samples reached nearly full density. However, the grains did not combine closely for the sample sintered at 1200℃, so the main fracture mode was intergranular. The mean crystal grain size was about 2–4 lm for samples sintered at 1250℃. That was smaller than the reported grain size and was closely to the samples with Cr or V additives, and the specimen fractured through transgranular mode. The grain size increased evidently with only the 50℃ higher sintering temperature, which also induced the decreased mechanical properties.
Fig. 1. Fracture surface images of the samples sintered at different temperatures for 40 min (a, b: 1100℃; c, d: 1200℃; e, f: 1250℃; g, h: 1300℃).
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