Study on the Mechanism of Hole Formation in Molybdenum Plate Targets

Molybdenum (Mo) plate targets were prepared with three kinds of Mo powder under the same processing. The microstructure, hardness and density of Mo plate targets were measured. The results showed that the microstructure of Mo plate target prepared with Mo powder which had similar particle size and no aggregation exhibits uniform compact, the hardness and density were higher. The microstructure of Mo plate target prepared with Mo powder which had great difference in particle size and serious agglomeration was uneven and had some holes. The hardness and density were lower mainly because of the existence of holes. TEM and XPS were used to analyze the covering layer around the holes of Mo plate targets with microstructure defect, which showed that there were amorphous and nanocrystals here, and the impurity elements were enriched in these areas, mainly O element, and the oxides were mainly MoO3. The main reason for the formation of the holes is the differences in the morphology and oxygen content of Mo powder. The energy required for sintering varies with the particle size of Mo powder. At the same sintering energy, the grain growth trend is different among the Mo powders with different particle size. It will eventually lead to inhomogeneous sintering structure, and even, cracks or holes in the grain. In the subsequent rolling, extrusion or forging, the holes in grains are difficult to disappear.