Havar (alloy)

Havar, or UNS R30005, is an alloy of cobalt, possessing very high mechanical strength. It can be heat-treated. It is highly resistant to corrosion and is non-magnetic. It is biocompatible. It has high fatigue resistance. It is a precipitation hardening superalloy.

Havar is composed of 42.0% (41-44%) of cobalt, 19.5% (19-21%) of chromium, 12.7% (12-14%) of nickel, 2.7% (2.3-3.3%) of tungsten, 2.2% (2-2.8%) of molybdenum, 1.6% (1.35-1.8%) of manganese, 0.2% (0.17-0.23%) of carbon, 0.02-0.08% of beryllium, and balance of iron. Its melting point is about 1480 °C. It will retain three quarters of its room temperature strengths up to 510 °C.^[1][2] Its density is 8.3 g/cm³. Its thermal conductivity is 13.0 W/m·K. Its tensile strength is 960-970 MPa and its modulus of elasticity is 200-210 GPa. It can be joined by welding (GMAW and resistance welding, soldering and brazing.

Havar foils of various thickness are used as diaphragms for pressure sensing in process control equipment, biocompatible medical implants, as particle beam windows in nuclear physics, and various other high temperature applications.^[3]

Havar foils are frequently used as window material for high-energy proton beams used in production of fluorine-18 from oxygen-18 enriched water.

Havar was originally developed in the late 1940s by Hamilton Watch Company as an alloy for the mainsprings used in watches, and named Dynavar. Later it was used as sensing diaphragms and other uses, under its current name Havar. Its corrosion resistance allows use in stress corrosion resistant springs and diaphragms in oilfield equipment handling sour crude oil. Havar outperforms 316L stainless steel in resistance to pitting corrosion and crevice corrosion in medical implant environment.^[4] In cold-rolled and aged form, its yield and tensile strength are higher than of other cobalt-based implant alloys.

In Green death, the Havar alloy does not corrode at all at room temperature, starts corroding rapidly (15 mm/year) at 70 °C, and reaches rate of 56 mm/year at boiling point.

Havar is difficult to machine, as it undergoes rapid work hardening under the cutting tool. The tool should be as sharp as possible and the machine should be rigid, with minimal backlash. Higher power is required than to machine ordinary steels of similar hardness.^[5]

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