Molybdenum sheet is a metallic sheet material mainly composed of high-purity molybdenum (Mo). It is processed through rolling, annealing, and other processes, and possesses characteristics such as high-temperature resistance, high strength, low thermal expansion coefficient, good electrical conductivity, and good thermal conductivity. Here is a detailed introduction to molybdenum sheet:
I. Basic Definition and Characteristics
Chemical Composition
- Main Component: Molybdenum (Mo), with a purity typically ≥ 99.95% (e.g., Mo1 grade). The content of impurities (such as Fe, Ni, C, O, etc.) is strictly controlled within the range of 0.001% – 0.05%.
- Alloying Elements: A small amount of titanium (Ti), zirconium (Zr), rhenium (Re), and other elements can be added to form TZM alloy (Mo-0.5Ti-0.1Zr) or molybdenum-rhenium alloy (Mo-41Re), further enhancing high-temperature strength, creep resistance, or neutron irradiation resistance.
Physical Properties
- Density: ≥ 10.2 g/cm³, close to the theoretical density, ensuring material strength.
- Melting Point: 2620°C, one of the highest among all metals, enabling it to maintain structural stability in high-temperature environments.
- Thermal Expansion Coefficient: Low expansion characteristic (5.8 × 10⁻⁶/°C), reducing deformation caused by thermal stress and making it suitable for scenarios with drastic temperature changes.
- Thermal Conductivity: 138 W/(m·K), providing efficient heat dissipation performance, suitable for thermal management scenarios.
- Electrical Resistivity: Low electrical resistivity, suitable for current transmission in electronic components.
Mechanical Properties
- Tensile Strength: It can maintain high strength at high temperatures. For example, TZM alloy can achieve a tensile strength of 200 – 300 MPa at 2000°C.
- Ductility: Ductility can be improved through annealing treatment to reduce work hardening, facilitating forming processes such as stamping and bending.
II. Core Parameter Analysis
Thickness Range
- Molybdenum sheet thickness usually ranges from 0.05 mm to 4.75 mm, including:
- Ultra-thin Molybdenum Foil: Thickness < 0.13 mm (e.g., 0.025 – 0.09 mm), used in high-precision scenarios such as vacuum coating and electronic packaging.
- Conventional Sheet: Thickness 0.187 – 4.75 mm, suitable for structural components such as high-temperature heating elements and heat shields.
Width and Length
- Width Range: 30 mm to 610 mm, with custom production able to exceed these limits.
- Length: Usually 300 – 3000 mm, adjustable according to processing requirements.
Purity and Impurity Control
- Purity Standard: ≥ 99.95% (e.g., Mo1 grade). The content of impurities (such as Fe, Ni, C, O, etc.) is strictly controlled within 0.001% – 0.05% to ensure high-temperature stability and electrical conductivity.
Surface Condition
- Cold-rolled Bright Surface: Low surface roughness, suitable for optical reflection and electronic devices.
- Alkali-washed Surface: The oxide layer is removed through chemical treatment to improve welding and coating adhesion.
- Polished Surface: Further reduces roughness to meet the requirements of precision processing.
Physical Properties
- Density: ≥ 10.2 g/cm³, close to the theoretical density, ensuring material strength.
- Melting Point: 2620°C, maintaining structural stability in high-temperature environments.
- Thermal Expansion Coefficient: Low expansion characteristic (5.8 × 10⁻⁶/°C), reducing deformation caused by thermal stress.
- Thermal Conductivity: 138 W/(m·K), providing efficient heat dissipation performance suitable for thermal management scenarios.
III. Processing Techniques and Process Optimization
Rolling Process Selection
- Hot Rolling: Suitable for initial slab breaking, with the temperature controlled at 1200 – 1300°C to reduce deformation resistance and avoid cracks.
- Warm Rolling: Conducted at 600 – 900°C for intermediate passes, balancing work hardening and recrystallization softening to control grain size.
- Cold Rolling: Cold rolling is used for the final pass (e.g., for foil materials below 0.1 mm). Tension rolling and multiple annealing (600 – 700°C/30 min) are employed to eliminate residual stress and improve surface quality.
Key Parameters of Annealing Treatment
- Recrystallization Annealing: The temperature is 1000 – 1200°C, and the holding time is adjusted according to the sheet thickness (e.g., 20 min is required for 0.1 mm foil) to obtain uniform equiaxed grains and improve plasticity.
- Stress Relief Annealing: Low-temperature annealing (600 – 700°C) is used for post-cold rolling treatment to reduce the impact of work hardening on subsequent processing.
Cutting and Forming Techniques
- Laser Cutting: Suitable for ultra-thin molybdenum foil (< 0.1 mm), with a small heat-affected zone and high edge quality.
- Water Jet Cutting: Avoids high-temperature oxidation and is suitable for medium-thickness sheets (0.5 – 3 mm).
- Stamping Forming: Pre-annealing is required to soften the material. The mold design should consider the low ductility of molybdenum, and a stepped stamping process should be adopted to reduce the risk of cracking.
Welding and Connection
- Electron Beam Welding: High energy density enables deep penetration welding, suitable for sealed connections in vacuum environments.
- Brazing: Active brazing filler metals (such as Ag-Cu-Ti) are selected, and the heating rate (5 – 10°C/min) is controlled to avoid thermal stress concentration.
Surface Treatment to Enhance Performance
- Electroless Nickel Plating: Improves corrosion resistance and weldability, with a plating thickness of 1 – 5 μm.
- Anodizing: Forms a dense oxide film (such as MoO₃) to enhance high-temperature oxidation resistance.
IV. Application Scenarios and Selection Suggestions
High-temperature Industrial Field
- Heat Shields and Heating Elements: Select 0.5 – 2 mm thick alkali-washed surface sheets, which can withstand temperatures up to 2000°C and show no deformation during long-term use.
- Sapphire Crystal Growth Furnaces: Use 1 – 3 mm thick polished surface sheets with a reflectivity > 90% to improve energy efficiency.
Electronics and Semiconductor Industry
- Sputtering Targets: Require 0.1 – 0.5 mm thick cold-rolled bright surface sheets with a grain size < 50 μm to ensure uniform sputtering.
- Integrated Circuit Lead Frames: Select 0.2 – 0.8 mm thick high-purity molybdenum sheets with a thermal expansion coefficient matching that of silicon chips to reduce thermal fatigue failure.
Aerospace and Defense
- Missile Nozzle Throats: Use 2 – 4 mm thick TZM alloy sheets (Mo-0.5Ti-0.1Zr) with a scouring resistance temperature > 3000°C.
- Nuclear Reactor Control Rods: Select 0.5 – 1 mm thick molybdenum-rhenium alloy sheets (Mo-41Re) with excellent neutron irradiation resistance.
V. Quality Inspection and Standard Compliance
- Thickness Tolerance: According to the ASTM B386 standard, the thickness tolerance for sheets is ±0.05 mm, and for foils, it is ±0.005 mm.
- Flatness Control: Detected using a laser flatness meter, with an allowable deviation ≤ 0.5% of the sheet length.
- Non-destructive Testing: Ultrasonic flaw detection is used to detect internal defects (such as cracks and inclusions) with a sensitivity of 0.1 mm level.