Alloy 48 is a nickel-iron controlled-expansion alloy with a nominal 48% nickel content, balance iron. It is specifically formulated to match the thermal expansion characteristics of soft lead and soda lime glasses, making it a standard material for glass-to-metal sealing in lighting and electronic applications.

1. Operating Limits & Selection Criteria

This alloy is selected based on its expansion curve rather than mechanical strength. Proper material matching is essential to prevent seal failure.

• Effective Temperature Range: Maintains controlled expansion characteristics suitable for service up to 450°C (840°F) .

• Material Matching: Specifically designed to match the coefficient of thermal expansion of soft lead glasses and soda lime glasses used in lighting and vacuum tube manufacturing.

• Sealing Compatibility: When properly annealed, the alloy forms hermetic seals that remain stress-free through thermal cycling.

• Comparison to Alloy 42/46: With higher nickel content than Alloy 42 or 46, Alloy 48 offers a different expansion curve tailored specifically to softer glass compositions. Select based on the specific glass type in your assembly.

2. Manufacturing Data & Specifications

• Chemical Composition (Typical)

  Element	Content (%)
  Nickel (Ni)	48.0
  Iron (Fe)	Balance
  Others	Remainder

• Physical Properties

  Property	Metric	Imperial
  Density	8.20 g/cm³	0.296 lb/in³

• Mechanical Properties (Typical, Annealed)

  Property	Metric	Imperial
  Tensile Strength	520 MPa	75.4 ksi
  Yield Strength	260 MPa	37.7 ksi
  Modulus of Elasticity	160 GPa	23,200 ksi

• Fabrication Considerations

  • Annealing: Essential for proper expansion characteristics. Perform at 850–1000°C (1560–1830°F) in a protective atmosphere to prevent oxidation and achieve correct grain structure.

  • Cold Working: Not recommended for finished components. Cold working introduces internal stresses that distort the coefficient of thermal expansion, leading to seal failure. If cold forming is necessary, a full anneal must follow.

  • Surface Preparation: For reliable glass sealing, surfaces must be clean and oxide-free to ensure proper glass wetting and bubble-free seals.

3. Applications

Alloy 48 is specified wherever soft glass must be sealed to metal with long-term hermetic integrity:

• Incandescent and fluorescent lamps: Glass-to-metal seals at lead-in wires

• Radio valves and vacuum tubes: Hermetic feedthroughs

• Industrial thermostats: Thermostat rods and bimetal components operating up to 450°C

• Electrical feedthroughs: For lighting and display applications

• Hermetic connectors: Where soft glass sealing is required

4. Available Product Forms & Supply

For engineers and procurement specialists requiring controlled-expansion alloys for glass sealing applications, ZYTC Alloy stocks certified Alloy 48 (Nilo 48) in a full range of mill forms:

• Round Bar

• Tube

• Sheet

• Coil

• Strip (precision slit)

• Wire

All material is supplied with full traceability and certification, suitable for lighting, electronics, and industrial thermostat applications. Contact ZYTC Alloy for stock availability and pricing.

Contact Us:

Email:daisy@zytcsteel.com

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