90/10 copper-nickel (often abbreviated as C70600, its UNS number, or CN90/10) is a widely used binary copper-nickel alloy defined by its approximate 90% copper and 10% nickel composition. It is a staple in industries requiring exceptional corrosion resistance-particularly in marine, offshore, and aqueous environments-and balances mechanical performance, formability, and durability.
Unlike pure copper (which is prone to corrosion in saltwater) or higher-nickel alloys (e.g., 70/30 copper-nickel, which has 30% nickel), 90/10 copper-nickel is valued for its cost-effectiveness relative to its performance. Its key defining trait is its ability to form a protective, adherent oxide layer (rich in nickel and copper oxides) when exposed to oxygen or saltwater. This layer acts as a barrier against corrosion, including pitting, crevice corrosion, and erosion-corrosion-common issues for metals in seawater, brackish water, or industrial cooling systems.
Typical applications include:
Marine hardware: Ship hulls, propeller shafts, seawater intake screens, and heat exchanger tubes.
Offshore infrastructure: Subsea pipelines, platform components, and desalination plant tubing.
Industrial systems: Condenser tubes in power plants (using seawater as coolant) and chemical processing equipment.
It is also used in architectural applications (e.g., decorative trim) for its attractive silvery appearance and resistance to atmospheric corrosion.
The chemical composition of 90/10 copper-nickel is standardized by global bodies like ASTM (American Society for Testing and Materials) and ISO, with minor alloying elements added to enhance specific properties (e.g., strength, corrosion resistance). Below is the typical and standardized composition (by weight), based on UNS C70600 (the most common grade of 90/10 copper-nickel):
Notably, the exact ranges may vary slightly by standard (e.g., ASTM B111 for seamless tubes, ASTM B466 for welded tubes), but the core 90% Cu/10% Ni balance remains consistent to preserve the alloy's signature corrosion resistance.
The hardness of 90/10 copper-nickel depends primarily on its temper (heat treatment or cold-work state)-as cold working increases hardness by introducing internal stresses, while annealing softens the alloy. Hardness is typically measured using the Brinell Hardness Test (HB) or Rockwell Hardness Test (e.g., Rockwell B, HRB) for non-ferrous metals like copper-nickel. Below are the typical hardness values for common tempers:
Annealing (heating the alloy to ~650–750°C, holding, then cooling slowly) softens 90/10 copper-nickel to maximize formability (e.g., for bending, welding, or drawing into tubes).
Brinell Hardness (HB): ~60 – 80 HB (tested with a 500 kg load and 10 mm ball).
Rockwell Hardness (HRB): ~50 – 70 HRB (a common scale for soft to medium-hard non-ferrous metals).
This temper is ideal for applications requiring shaping, such as fabricating heat exchanger tubes or marine components.
Cold working (e.g., rolling, drawing, or extrusion without subsequent annealing) increases hardness and strength at the cost of reduced ductility. Common cold-worked tempers include "1/4 Hard," "1/2 Hard," and "Full Hard," with hardness increasing with the degree of cold work:
1/4 Hard: ~80 – 100 HB / ~70 – 80 HRB
1/2 Hard: ~100 – 120 HB / ~80 – 90 HRB
Full Hard: ~120 – 140 HB / ~90 – 100 HRB
Cold-worked 90/10 copper-nickel is used for applications requiring higher wear resistance or strength, such as fasteners, springs, or thin-gauge sheets for architectural trim.
