Conichrome
General
Conichrome®, Phynox® and Elgiloy® are all trademark names for the cobalt-chromium-nickel-molybdenum-iron alloy specified by ASTM F1058 and ISO 5832-7. Batelle Laboratories originally developed the alloy for making watch springs, and it was patented in 1950.
As demonstrated in the table below, the current Conichrome alloy melt specification, specifically designed by Fort Wayne Metals, is equivalent to both Phynox and Elgiloy. The alloy is first melted using Vacuum Induction Melting (VIM) techniques. A secondary melt operation, Electro Slag Remelt (ESR), is then employed to further remove impurities and improve overall homogeneity. Conichrome derives its maximum properties from a combination of cold work and thermal processing, and is not a true precipitation-hardening alloy since the response to heat treatment is a function of the degree of cold work.
Physical Properties
| Density: | 0.300 lbs/in3 |
|---|---|
| Modulus of Elasticity: | 29.0 x 106 psi |
| Electrical Resistivity: | 996 µohms-mm |
| Thermal Conductivity: | 12.5 W/mK (0-100°C) |
Thermal Treatment
After cold working, the mechanical strength of this cobalt based super alloy can be increased by heat treating. In wire form, cold worked Conichrome will gain tensile strength at temperatures from 480-540°C when exposed for approximately 2-5 hours. Reducing or inert atmospheres are typically used for protection during thermal treatment. After annealing with a rapid quench, the alloy has a face-centered cubic structure.
Magnetic Resonance Imaging (MRI)
Surgical implants constructed of Conichrome wire can be safely imaged using magnetic resonance without risk of migration and with minimal image degradation because of the nonmagnetic characteristics of the material.
Biocompatibility
Although there is no universally accepted definition for biocompatibility of biomaterials, a medical device should be safe for its intended use. Conichrome alloy has been employed successfully in human implant applications in contact with soft tissue and bone for over a decade. Long-term clinical experience of the use of this material has shown that an acceptable level of biological response can be expected if the alloy is used in appropriate applications.
Surface Conditions
Cobalt based alloys develop a highly polished appearance as they are drawn to fine diameters. Surface roughness can be less than 5 RMS when processed using single crystal natural diamond (SCND) dies and measured with a profilometer. Diameters over 0.040" will not have as smooth a finish because they are drawn through polycrystalline dies. Wire measuring over 0.100" will have an even rougher surface because it is drawn through carbide dies. However, the surface of the wire can be enhanced with additional finish treatments.
Applications
Because of its excellent corrosion resistance, mechanical strength and fatigue resistance combined with high elastic modulus, Conichrome wire and rod is an attractive candidate for surgical implants. It is one of the preferred materials for the fabrication of various stents, pacemaker lead conductors, surgical clips, vena cava filters, orthopaedic cables, and orthodontic appliances. The alloy is also commonly used in the watchmaking industry as a precision spring material.
Typical Chemistry (%)
| FWM Average | Alternate Trade Names | ||||
|---|---|---|---|---|---|
| Conichrome | Elgiloy | Phynox | |||
| min | max | min | max | ||
| Carbon | 0.061 | - | 0.15 | - | 0.15 |
| Manganese | 1.97 | 1.5 | 2.5 | 1 | 2 |
| Silicon | 0.478 | - | 1.2 | - | 1.2 |
| Phosphorus | 0.005 | - | 0.015 | - | 0.015 |
| Sulfur | 0.0015 | - | 0.015 | - | 0.015 |
| Cobalt | 39.8 | 39 | 41 | 39 | 42 |
| Chromium | 19.9 | 19 | 21 | 18.5 | 21.5 |
| Nickel | 15.4 | 14 | 16 | 15 | 18 |
| Molybdenum | 7.1 | 6 | 8 | 6.5 | 7.5 |
| Beryllium | 0.0002 | - | 0.1 | - | 0.001 |
| Iron | bal. | bal. | bal. | bal. | bal. |
Mechanical Properties
| Cold Work % | UTS (psi) | Elongation %* |
|---|---|---|
| 0 | 150,000 | 55 |
| 20 | 205,000 | 9 |
| 37 | 245,000 | 5 |
| 50 | 275,000 | 3.9 |
| 60 | 295,000 | 3.8 |
| 68 | 312,000 | 3.8 |
| 75 | 325,000 | 3.9 |