Effect of B₄C on Thermal Stability of Nb-NbCr₂ Alloy

The Nb-NbCr₂ alloy with 0.5at.% B₄C was prepared by mechanical alloying and hot pressing. To investigate the effects of B₄C on thermal stability of Nb-NbCr₂ alloy, the samples were thermally exposed at 1 200℃ for 30~100 h in vacuum, respectively. The results show that composition phases of B₄C/Nb-NbCr₂ alloy have no obvious change after the thermal exposure process. The relative density of B₄C/Nb-NbCr₂ alloy increases from 98.6% to 98.7% and the change is significantly smaller than Nb-NbCr₂ alloy without B₄C addition. Laves phase NbCr₂ particles of B₄C/Nb-NbCr₂ alloy have a little aggregation and growth after the thermal exposure process, but the phenomenon of aggregation and growth of Laves phase NbCr₂ particles is much less than Nb-NbCr₂ alloy without B₄C addition. After thermal exposure for 50 h, the Vickers hardness of B₄C/Nb-NbCr₂ decreases by 10.1% after the first 50 h and decreases by only 1.7% after the later 50 h, and the change is significantly smaller than Nb-NbCr₂ alloy without B₄C addition. After thermal exposure for 100 h, the compressive strength and plastic strain of B₄C/Nb-NbCr₂ alloy change from 3 048 MPa and 12.7% to 2 788 MPa and 20.7%, respectively, and the change is significantly smaller than Nb-NbCr₂ alloy without B₄C addition. In general, it can be seen that the B₄C particles can improve the thermal stability of Nb-NbCr₂ alloy.