Preparation and properties of hot-pressed NbMo-matrix composites reinforced with ZrB2 particles

The NbMo-matrix composites reinforced with (0-60 vol%) ZrB2 were fabricated by hot-pressing at 2400 °C for 10 min under a pressure of 50 MPa in dynamic vacuum in the induction heating furnace specially designed in our institute. The optimum ZrB2 content in NbMo solid solution was determined to be 30 vol% for excellent comprehensive mechanical property. NbMo-30 vol% ZrB2 has the highest density of 99.63%, the most uniform microstructure, high fracture toughness of 5.75 MPa m1/2. The highest ZrB2 concentration that reacts with NbMo solid solution is at the range of 30 to 45 vol%. The types of the formed niobium borides were decided by the original ratio of Nb to B. The distribution of Mo and Zr was mutually exclusive in low ZrB2 content composites, however, there was Mo2Zr in high ZrB2 content composite. Except for NbMo-45 vol% ZrB2, the compressive strength increased with ZrB2 content (from 927.09 MPa to 1635.91 MPa). The Young's modulus values were directly proportional to ZrB2 content. The fracture toughness (from 6.34 MPa m1/2 to 3.99 MPa m1/2) was inversely proportional to ZrB2 content. The big residual ZrB2 particles in high ZrB2 content samples such as NbMo-45 vol% ZrB2 and NbMo-60 vol% ZrB2 was the main reason for nonhomogeneous microstructure, low density (94.09% and 94.83%, respectively) and low fracture toughness (4.58 MPa m1/2 and 3.99 MPa m1/2, respectively).