Molybdenum crucibles may indeed produce cracks during processing, but they can be effectively controlled by optimizing the process and parameters. The following is a specific analysis:
- Common causes of cracks in molybdenum crucible processing
Material properties
Molybdenum has a high melting point (2623°C), but is significantly brittle at low temperatures and is prone to cracking due to stress concentration during processing.
Impurities (such as C, O) will reduce the ductility of molybdenum and increase the risk of cracking.
Processing Technology
Spin forming: If the feed speed is too fast or the lubrication is insufficient, it may cause surface tearing.
Welding: If the heat input is not properly controlled during electron beam welding ( EBW ) or laser welding, thermal cracks are likely to occur.
Machining: Excessive cutting force during turning and drilling may cause cracks.
Heat Treatment
Too high sintering temperature or too fast cooling speed will cause internal residual stress and induce cracks.
- Key technologies for crack control
Material selection
Use high purity molybdenum (≥99.95%) to reduce the impact of impurities on ductility.
Adding rare earth elements (such as lanthanum and cerium) improves toughness and reduces crack sensitivity.
Process Optimization
Spinning:
Control feed speed (≤0.1 mm/rev) and use graphite emulsion lubrication.
Spinning in sections to avoid excessive deformation in a single operation.
welding:
Use low heat input welding processes (such as electron beam welding) and preheat to 300-500℃ to reduce stress.
After welding, vacuum annealing (1000-1200℃, 2 hours) is performed to eliminate residual stress.
Machining:
Use carbide tools to reduce cutting forces.
Use small feed (≤0.05 mm/rev) and low cutting speed (≤50 m/min).
Heat Treatment
After sintering, homogenization annealing (1500-1800℃, 4 hours) is carried out to eliminate grain boundary segregation.
Control the cooling rate (≤10℃/min) to avoid cracks caused by rapid cooling.
- Crack Detection and Repair
Detection Methods
Nondestructive testing: X-ray testing and ultrasonic testing can detect internal cracks.
Visual inspection: Observe surface microcracks with a high-power magnifying glass.
Restoration Technology
Laser cladding: Local cladding of cracked areas to repair cracks and enhance surface properties.
Molybdenum wire of the same material as the base material for repair welding, and perform heat treatment after welding.
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