5. Material Families

1° Iron Base (Fe): Steels & Heat Treatments

Iron alloyed with carbon forms the framework of components subjected to friction and mechanical stress constraints:

• Steel (Fe + Carbon 1 to 2% C):

  Steel used in watchmaking strictly undergoes a complete two-step thermal cycle:

  • I. Hardening (Quenching): Steel is heated to 800°C until it turns bright red, then instantly cooled by immersion in water or oil.
    ➔ Result: Extreme hardening of the material, but the part becomes very fragile and brittle.
  • II. Tempering: The part is reheated to approximately 280°C to relieve internal stresses without losing surface hardness.
    ➔ Result: Elimination of brittleness while maintaining optimal strength.

• Parts made of hardened steel: Balance staff, pinions, ratchet wheel, crown wheel, screws, winding stem.
• Durnico® (600 Hv): High-strength alloy steel (Fe + C + Ni + Co). Very resistant and hard material, but difficult to machine. Used for resistant springs, intermediate wheels, and winding ratchets.

📷 ORIGINAL HANDWRITTEN NOTE (01-25) — Material Families & Iron Base (Steel, Quenching, Tempering, Durnico)

2° Copper Alloys (Copper Base)

Copper alloys are preferred for making frames (mainplates, bridges) and gear trains due to their machinability and non-magnetic qualities:

• Brass (180 Hv) — Copper + Zinc Alloy (Cu + Zn):
  • Advantages: Easy to machine, cuts easily during gear cutting, non-magnetic, good natural sliding coefficient.
  • Disadvantage: Oxidizes in open air! Must be strictly protected by galvanic surface plating: gilding, rhodium plating, nickel plating (classic deposition of 1 µm; greater than 5 µm = Plating).
  • Parts: Wheel blanks, bridges, mainplates, barrel drum and cover.
• German Silver / Maillechort (220 Hv) — Copper + Nickel + Zinc Alloy (Cu + Ni + Zn):
  • Properties: Harder and mechanically stronger than brass, practically stainless, does not alter over time.
  • History & Usage: Between 1840 and 1910, it was used raw without any galvanic treatment. Today, it is reserved for traditional high-end calibers with decorative surface treatment. Its cost is higher than brass.
  • Parts: Mainplates, high-end bridges, balance rim.
• Bronze — Copper + Tin Alloy (Cu + Sn):
  • Properties: Hard and brittle material, featuring an exceptional sliding coefficient with hardened steel.
  • Acoustics: Excellent acoustic resonance, traditionally used for gongs and bells of striking watches.
  • Parts: Anti-wear mechanical parts, bushings, main machinery.
• Glucydur® (380 Hv) — Copper + Beryllium Alloy (Cu + Be):
  • Properties: Beryllium bronze alloy with very high hardness and elasticity, non-magnetic, but very difficult to machine.
  • Parts: Chronometric precision balance wheels, special springs, engagement fingers (not used for the hairspring).

📷 ORIGINAL HANDWRITTEN NOTE (01-26) — Copper Alloys (Brass, German Silver, Bronze, Glucydur)

3° Corundum, Nickel Base (LIGA) & Pure Silicon

3. Synthetic Corundum (Al₂O₃ - Aluminium Oxide)

• Extreme Hardness: 2200 to 2400 Hv (located just below diamond on the Mohs scale).
• Properties: Near-zero friction coefficient in contact with polished hardened steel. Color is obtained by adding metallic oxides during thermal fusion:
  • Red: Ruby (pallet jewels, roller pin, pivot stones).
  • Blue / Transparent: Sapphire (protective watch crystals and transparent case backs).
• Historical Milestones:
  • 1704: Invention of the natural ruby drilling process for watch bearings.
  • 1904: Invention of the synthetic ruby fusion process (Verneuil process).

4. Nickel Base & Mimotec® Technology (580 Hv)

• Composition: Pure nickel or Nickel-Phosphorus alloy (Ni + P).
• Manufacturing Process: Precision galvanic growth by micro-machining (LIGA technology / electroforming).
• Properties: Extremely hard, lightweight, perfectly non-magnetic. Allows the design of complex, massive, or highly open-worked components.
• Parts: Chronograph cams, complex springs, retrograde display wheels.

5. Pure Silicon (Si)

• Density and Lightness: Density of 2.3 kg/dm³ (comparison: Aluminum 2.7, Titanium 4.5, Steel 7.9, Gold 19.3).
• Machining: Plasma beam etching (DRIE technology).
• Properties: Ultra-lightweight, extremely hard, very brittle, 100% non-magnetic. It remarkably withstands cyclic elastic fatigue but tolerates no plastic deformation.
• Parts: Balance spring hairsprings, escape wheels, pallet levers, innovative balance wheels.

📷 ORIGINAL HANDWRITTEN NOTE (01-27) — Corundum, Ruby, Mimotec® LIGA & Pure Silicon

Workshop Comparative Table: Hardnesses & Densities

Material	Formula / Alloy	Vickers Hardness	Density (kg/dm³)	Typical Watchmaking Components
Brass	Cu + Zn	180 Hv	8.4 – 8.7	Mainplates, bridges, wheels, barrels
German Silver	Cu + Ni + Zn	220 Hv	8.7	High-end frames, traditional bridges
Glucydur®	Cu + Be	380 Hv	8.25	High-precision balance wheels, fingers, springs
Mimotec® (LIGA)	Ni + P	580 Hv	2.3 – 8.9	Precision cams, retrograde gear trains
Durnico®	Fe + C + Ni + Co	600 Hv	8.0	Resistant springs, ratchets, intermediate wheels
Hardened Steel	Fe + C (1 to 2% C)	700 – 800 Hv	7.85	Balance staffs, pinions, screws, stems
Pure Silicon	Pure Si	1100 Hv	2.3	Non-magnetic hairsprings, modern escapements
Corundum (Ruby)	Al₂O₃	2200 – 2400 Hv	4.0	Bearing stones, pallet jewels, roller pin