Cause analysis of small black spots on molybdenum disc
After high temperature sintering, molybdenum powder is rolled into molybdenum discs. After polishing and corrosion, it is found that some batches of molybdenum discs have defects such as edge falling, delamination and small black spots on the surface. The molybdenum discs with these defects will affect its later service performance. On the one hand, the different defects on molybdenum discs are caused by the billet itself, on the other hand, they are caused by external factors during the processing, such as unreasonable process, lack of regular maintenance of equipment, and unclean roll surface in rolling process. This paper focuses on the problem that the defects of the blank may lead to the small black spot defects in the molybdenum disc. Generally, one or two small black spots appear occasionally on the surface of the molybdenum disc, which does not affect the service performance, so it has not been paid attention to. However, when there are many such black spots, the service life of the molybdenum disc will be doubled, and even become waste products, which will increase the use cost and cause great losses to processing enterprises and product users, In view of this phenomenon, the microstructure was observed by scanning electron microscope, and the possible causes were analyzed. The specific process was to analyze the formation process of raw materials and microstructure evolution.
The microstructure and chemical composition of small black spots on molybdenum disc were analyzed by scanning electron microscope (SEM). The main reasons for the formation of small black spots were as follows: (1) the formation of small black spots with dense microstructure was mainly caused by the scratch of grinding agent alo3; (2) the formation of small black spots with loose microstructure was caused by the local loose microstructure of molybdenum powder agglomerates during sintering.
