Effect of ball milling time on microstructure and oxidation resistance of self-passivating W alloys

Self-passivating W alloys exhibit excellent high temperature oxidation resistance and are expected to be used in key components in high temperature environments. In order to reveal the relationship between the microstructure and high temperature oxidation resistance of the alloy, a self-passivating W-Si alloy was prepared by mechanical alloying method combined with spark plasma sintering. The effect of different mechanical alloying time on the microstructure of the alloy was studied. And the high temperature oxidation resistance of the alloys was investigated. The results show that the alloys are composed of W, W₅Si₃ and SiO_x phases. When the ball milling time increases from 4 h to 20 h, the content of SiO_x in the alloys increases from 16.2% to 23.6%, while the content of W₅Si₃ decreases from 57.8% to 43.6%, and the grain sizes of W and W₅Si₃ are both reduced. The grain refinement contri-butes to the improvement of the microhardness of the alloys. After oxidized at 1000 ℃ for 10 h, the mass gain of the alloy prepared by ball milling for 4 h is 37.4 mg, while that of the alloy prepared by ball milling for 20 h reaches 141.6 mg, and their oxide layer thicknesses are about 167.0 μm and 415.7 μm, respectively. The alloy prepared with short ball milling time has better oxidation resistance, because the W₅Si₃ in this alloy is a continuous phase. The WO₃/SiO₂ composite oxide formed by in situ oxidation of W₅Si₃ is also a continuous phase, forming a protective oxide layer and effectively inhibiting the internal oxidation of the alloy.