Cobalt chrome is a hard, shiny metal blend built mainly from cobalt and chromium. It is one of the most common metals surgeons and dentists place inside the body, from artificial knees to partial dentures and heart stents. The same qualities that let it last decades in a joint also make it valuable in jet engines and industrial cutting tools. Its strength comes with trade-offs, though, especially when two cobalt chrome surfaces rub together.
What Cobalt Chrome Is Made Of
An alloy is a blend of metals melted together to get properties no single metal has. Cobalt chrome alloys typically contain 20 to 70 percent cobalt and 19 to 35 percent chromium by weight.1Patsnap Eureka. What Is Cobalt Chrome and What Is It Used For? Makers add small amounts of molybdenum, tungsten, nickel, or carbon to tune strength and durability.2Patsnap Eureka. What Is Cobalt Chrome and What Is It Used For? So “cobalt chrome” names a family of related recipes rather than one exact metal. The medical version is usually cobalt-chromium-molybdenum, often written CoCrMo on implant records.
Chromium by itself is hard but brittle, and cobalt by itself lacks the surface protection chromium supplies. Melted together, the blend gets cobalt’s toughness plus chromium’s corrosion defense. Changing the proportions changes the metal, which is why a dental lab alloy and an industrial valve alloy can both be called cobalt chrome yet behave differently.
On paperwork, you may see Co-Cr, CoCr, CoCrMo, or cobalt-chromium. These all point to the same alloy family. Stellite is a brand name for industrial versions. Cobalt chrome also isn’t chrome plating. Chrome-plated car parts have only a thin chromium coating over another metal, while cobalt chrome is solid alloy all the way through, so it doesn’t flake off the way plating can.
The family started in industry. In 1912 inventor Elwood Haynes introduced a cobalt-chromium-tungsten alloy called Stellite as a tool metal for his car plant.3Haynes International. Haynes International The Last 100 Years It cut some machining times by more than half.4Haynes International. Haynes International The Last 100 Years
Why Cobalt Chrome Is So Hard and Rust-Resistant
Tiny hard particles of chromium or tungsten carbide are spread through the metal, and they take the strain of rubbing and scraping.5Dynamic Metals Ltd. Cobalt Alloys 101: When Extreme Wear Resistance Really Counts As the softer metal around them wears away, new particles surface, keeping the alloy hard after long use.6Dynamic Metals Ltd. Cobalt Alloys 101: When Extreme Wear Resistance Really Counts Under heavy load, the metal’s internal crystal arrangement also shifts and the surface hardens further.7Dynamic Metals Ltd. Cobalt Alloys 101: When Extreme Wear Resistance Really Counts So worn surfaces actually resist further damage.8Patsnap Eureka. What Is Cobalt Chrome and What Is It Used For? Cobalt chrome pairs hardness with enough toughness to take repeated loads without cracking in normal use.
Rust resistance comes from a different mechanism. In body-like fluids the surface forms a thin oxide film that is about 90 percent chromium oxides.9Electrochimica Acta. Passive and transpassive behaviour of CoCrMo in simulated biological solutions This film shields the metal underneath from corrosion.10Electrochimica Acta. Passive and transpassive behaviour of CoCrMo in simulated biological solutions As with stainless steel, the film re-forms by itself if lightly scratched, which is why the metal can sit in salty body fluid for years. Heavy grinding or rubbing can strip it faster than it heals, a problem that comes up again under implant safety.
The toughness has a downside in the workshop. The alloy rapidly wears down cutting tools, and its poor heat conduction makes machining slow and costly. That is one reason many parts are cast or 3D printed instead.
Cobalt Chrome in Knee and Hip Replacements
Cobalt chrome’s hardness keeps a smooth gliding surface over years of movement.11SIGMA Orthopedics & Sports Medicine. Cobalt Chrome vs Titanium Knee Replacement: Which Is Better? So it is commonly used for the parts of a joint that slide against plastic. In a knee, that is usually the curved thigh-bone component. In a hip, it is often the ball on top of the stem. The opposite surface is typically hard plastic, and your implant card lists each component’s material.
The plastic is a tough, highly cross-linked version that wears much more slowly than older types. Because the plastic is the part designed to wear, the long-term concern is often plastic debris rather than metal. In hips, cobalt chrome heads on modern hard plastic wore at similar rates to ceramic heads, roughly 0.05 millimetres a year.12PubMed Central. Wear performance of cobalt chromium, ceramic, and oxidized zirconium on highly crosslinked polyethylene at mid-term follow-up
The long-term numbers are good. For one widely used cobalt chrome knee, 94.4 percent were still in place after 10 years for any reason.13PubMed. Ten-Year Results of the Press Fit Condylar Sigma Cobalt-Chrome Total Knee Replacement Only 1.6 percent needed redoing for mechanical problems rather than infection.14PubMed. Ten-Year Results of the Press Fit Condylar Sigma Cobalt-Chrome Total Knee Replacement A revision is a second operation to replace part of the implant. Most early revisions in the knee data were for infection, not metal failure. Patients’ pain and function scores improved substantially and stayed improved at 10 years.15PubMed. Ten-Year Results of the Press Fit Condylar Sigma Cobalt-Chrome Total Knee Replacement Newer wrought (forged) cobalt chrome also resists repeated stress better than older cast versions.16Cobalt-Base Alloys for Biomedical Applications. Metallurgy, Microstructure, Chemistry and Mechanical Properties of a New Grade of Cobalt-Chromium Alloy Before and After Porous-Coating
Persistent clicking, swelling, or pain well after recovery is worth mentioning to your surgeon, since normal recovery usually improves steadily.
Dental Work and Heart Stents
Cobalt chrome is the long-established standard metal for removable partial denture frameworks.17PubMed. Performance of polyetheretherketone (PEEK) versus cobalt chromium to fabricate removable partial denture frameworks: A systematic review Such a denture is a thin metal framework with clasps that hook around natural teeth, and plastic tooth-colored teeth are attached to it. It is much thinner than an all-plastic denture, so it feels less bulky. Laser 3D-printed frameworks hit the intended clasp grip of 5 to 10 newtons per tooth more consistently than cast ones.
Porcelain-covered cobalt chrome bridges and crowns performed acceptably over 3 to 7 years, even in mouths with gum disease.18PubMed. A clinical evaluation of cobalt-chromium metal-ceramic fixed partial dentures and crowns: A three- to seven-year retrospective study In a crown, the cobalt chrome forms a thin inner cap that supplies strength, and porcelain is baked on top to match your tooth. If gums recede, a dark line near the gum can appear where a sliver of metal edge shows, which is cosmetic rather than a sign of failure.19PubMed Central. Fit and Retention of Cobalt–Chromium Removable Partial Denture Frameworks Fabricated with Selective Laser Melting
To care for a partial denture, clean it daily with a soft brush and non-abrasive cleanser, since scratching the acrylic and metal makes plaque stick. Take it out at night if your dentist advises, and store it in water or a cleaning solution rather than leaving it dry. Avoid bleach-based soaks unless your dentist approves, because strong chlorine products can tarnish and damage metal frameworks.
In the heart, cobalt chrome is stronger than stainless steel at holding an artery open and shows up well on X-ray.20PubMed Central. Compliance of a cobalt chromium coronary stent alloy – the COVIS trial So stents can be made with thinner wire struts while staying visible to doctors.21PubMed Central. Compliance of a cobalt chromium coronary stent alloy – the COVIS trial
Is Cobalt Chrome Safe in the Body
Where implant parts are fitted together, tiny rubbing motions plus corrosion damage the surface in the body.22PubMed Central. Hip implant modular junction: The role of CoCrMo alloy microstructure on fretting-corrosion Rubbing can strip the protective oxide film,23Tribology – Materials, Surfaces & Interfaces. Fretting of CoCrMo and Ti6Al4V alloys in modular prostheses so metal particles and ions enter tissue, blood, and urine.24PubMed Central. Case report: Formation and recurrence of inflammatory pseudotumor after metal-on-metal hip arthroplasty More visible damage on knee implants matched higher cobalt and chromium in nearby tissue.25PubMed. Cobalt-Chromium-Molybdenum Femoral Knee Implant Damage Correlates With Elevated Periprosthetic Metal Concentrations
Metal-on-metal joints have a metal ball rubbing directly on a metal socket. Pairing cobalt chrome against itself sheds more metal than pairing it with titanium.26Tribology – Materials, Surfaces & Interfaces. Fretting of CoCrMo and Ti6Al4V alloys in modular prostheses In one group of metal-on-metal hip resurfacing patients, 4 percent had pseudotumors, non-cancerous inflamed tissue lumps, with higher metal levels and worse function.27PubMed. “Asymptomatic” pseudotumors after metal-on-metal hip resurfacing arthroplasty: prevalence and metal ion study Patients with those lumps were about twice as likely to have high blood cobalt.28PubMed Central. Correlation and diagnostic performance of metal ions in patients with pseudotumor after MoM hip arthroplasty: a systematic review and meta-analysis On the other hand, in one study, long-term metal-on-metal cobalt chrome knees did not harm hearing or worsen tinnitus.29PubMed Central. Long-Term Effects of Metal-on-Metal Cobalt-Chromium-Containing Prostheses Used in Total Knee Arthroplasty on Hearing and Tinnitus
Most people with cobalt chrome implants have no symptoms from metal release. Concern is greatest for metal-on-metal hips, particularly certain designs, and for implants that are poorly aligned or worn. Blood metal levels can be slightly raised in people with well-working implants, so a raised level alone does not always mean a problem.
After a metal-on-metal hip, report new groin pain, swelling, or clicking years after surgery, or a feeling of a lump near the joint. Doctors may order blood cobalt and chromium tests and an ultrasound or MRI. Some lumps cause no symptoms, so follow scheduled check-ups.
Allergy is a separate issue. Released ions can bind body proteins and trigger a delayed allergic reaction.30Coatings. Toxicity, Irritation, and Allergy of Metal Implants: Historical Perspective and Modern Solutions This can contribute to bone loss around the implant and loosening.31Coatings. Toxicity, Irritation, and Allergy of Metal Implants: Historical Perspective and Modern Solutions Some cobalt chrome also contains nickel, a common allergy trigger.32Patsnap Eureka. What Is Cobalt Chrome and What Is It Used For? Mention any reactions to jewelry, watch backs, or belt buckles to your surgeon, since they can point to nickel sensitivity. Alternatives such as titanium or ceramic may be offered. If you have metal allergies, ask your surgeon or dentist which exact alloy you received.
Cobalt Chrome vs Titanium
Cobalt chrome is about twice as stiff as titanium and resists repeated stress better.33GS Medical USA. Titanium vs. Cobalt-Chromium in Spinal Implants: Material Science, Biomechanics, and Clinical Tradeoffs So spine surgeons use cobalt chrome rods to hold corrected alignment firmly.34GS Medical USA. Titanium vs. Cobalt-Chromium in Spinal Implants: Material Science, Biomechanics, and Clinical Tradeoffs But a too-rigid implant can let surrounding bone carry less load and thin over time.35SIGMA Orthopedics & Sports Medicine. Cobalt Chrome vs Titanium Knee Replacement: Which Is Better? Titanium flexes more like bone and is preferred where bone needs to grow onto the implant.36GS Medical USA. Titanium vs. Cobalt-Chromium in Spinal Implants: Material Science, Biomechanics, and Clinical Tradeoffs
For sliding surfaces, cobalt chrome is generally more wear-resistant than titanium.37SIGMA Orthopedics & Sports Medicine. Cobalt Chrome vs Titanium Knee Replacement: Which Is Better? Many implants combine both, with titanium against bone and cobalt chrome where parts glide.
Useful questions for your surgeon: which parts of my implant are each metal, why this material for my bone quality and activity level, and does my metal allergy history change the choice?
Jet Engines, Tools, and 3D Printing
Gas turbine parts like vanes and combustion chambers have used cobalt alloys for decades.38Materials Science and Engineering. Protective coating formulation and application techniques Cobalt-based superalloys for applications in gas turbines Those parts sit in a stream of extremely hot gas, so they must stay strong and not oxidise or flake as temperatures rise. Cobalt alloys keep strength above 700°C and resist hot corrosive exhaust,39Patsnap Eureka. What Is Cobalt Chrome and What Is It Used For? holding their shape where many steels would soften. These versions need over 20 percent chromium to resist oxidation.40Materials Science and Engineering. Protective coating formulation and application techniques Cobalt-based superalloys for applications in gas turbines
Stellite alloys are also welded as thick coatings onto steel valves and machine parts to resist wear.41Welding in the World. Sliding wear behavior of cold metal transfer cladded Stellite 12 hardfacings on martensitic stainless steel This process melts a layer of cobalt alloy onto a worn surface, such as valve seats, pump parts, and cutting edges, which extends part life instead of replacing the whole piece.
Laser-printed cobalt chrome has much finer grain than cast metal.42Materials Today: Proceedings. Mechanical properties and corrosion resistance of cobalt-chrome alloy fabricated using additive manufacturing Printed parts reached a strength of about 1070 megapascals versus 655 for cast.43Materials Today: Proceedings. Mechanical properties and corrosion resistance of cobalt-chrome alloy fabricated using additive manufacturing It suits custom medical work because each partial denture or implant can be shaped from a scan, it avoids slow machining of a hard metal, and results are more consistent from piece to piece.