Specialty Metal
CNC Machining

Specialty metals (also called advanced or refractory metals) include cobalt alloys, tungsten, molybdenum, tantalum, and titanium-nickel shape memory alloys. They share extreme properties: very high melting points, exceptional hardness or strength, and strong chemical resistance — making them essential in aerospace, medical, nuclear, and defense applications. They are among the most challenging materials to machine because of extreme hardness, very low thermal conductivity concentrating heat at the cutting edge, rapid work-hardening, and chemical reactivity with standard tooling coatings. Each alloy demands a completely different tooling and parameter strategy.

Cobalt alloys (commonly known by the trade name Stellite) are cobalt-chromium-tungsten or cobalt-chromium-molybdenum alloys engineered for extreme wear resistance, high-temperature strength, and corrosion resistance simultaneously. Stellite 6 and Stellite 21 are the most widely machined grades. They are used for valve seat inserts, hardfacing overlays, cutting tools, surgical implants (CoCrMo alloys per ASTM F75), and turbine blade tip coatings. Cobalt alloys work-harden severely — cutting must be continuous and carbide tooling with positive rake is mandatory.

Pure tungsten has the highest melting point of any metal (3,422°C) and is brittle at room temperature, transitioning to ductile behavior only above its ductile-to-brittle transition temperature (approximately 200–400°C). Machining requires PCD tooling, very low cutting speeds (5–25 m/min for pure W), rigid vibration-free fixturing, and careful chip management. Tungsten heavy alloys (90–97% W with Ni-Fe binder) are significantly easier to machine due to the ductile binder phase — standard carbide tooling at moderate speeds is effective. WHA is the preferred form for most machined applications.

Molybdenum is a refractory metal with a melting point of 2,623°C, high thermal conductivity (138 W/m·K), low thermal expansion (5.1 ppm/K), and excellent strength at elevated temperatures. It is used in semiconductor heat spreaders (CTE matched to silicon and GaAs chips), vacuum furnace components, X-ray tube targets, and rocket nozzle liners. Pure molybdenum and TZM alloy (Mo-0.5Ti-0.08Zr) are the most commonly machined grades. Molybdenum is brittle at room temperature — sharp uncoated carbide tooling, low vibration, and controlled depths of cut are required to prevent edge chipping.

Tantalum resists virtually every acid at any concentration up to boiling point — including HCl, H₂SO₄, HNO₃, and aqua regia — making it the material of choice for the most aggressive chemical processing environments. It is also fully biocompatible and has a melting point of 3,017°C. Tantalum is relatively ductile compared to other refractory metals — the main machining challenge is its gummy cutting behavior and tendency to build up on tool faces. Sharp uncoated carbide with flood coolant is the preferred approach. It is used for chemical reactor liners, surgical implant hardware, capacitor anodes, and nuclear applications.

Nitinol is a near-equiatomic nickel-titanium shape memory alloy that exhibits either shape memory effect or superelastic behavior depending on composition and temperature. It is used for medical guidewires, stents, orthodontic archwires, actuators, and aerospace fasteners. Nitinol is one of the most difficult alloys to machine: it is superelastic (springs back significantly after cutting), work-hardens rapidly, generates extreme heat at the cutting zone, and is highly abrasive to tooling. Machining requires very sharp uncoated carbide or PCD tooling, high-pressure coolant, very slow speeds, continuous cuts without dwell, and iterative spring-back measurement and correction for precision dimensional features.

Achievable tolerances on specialty metals vary by material. Cobalt alloys (Stellite): ±0.02 mm standard, ±0.01 mm on precision features. Tungsten heavy alloys: ±0.02 mm standard, tighter with grinding. Pure tungsten: ±0.05 mm due to brittleness. Molybdenum and TZM: ±0.02–0.03 mm. Tantalum: ±0.02 mm. Nitinol: ±0.02–0.03 mm with spring-back compensation on precision bore and shaft features. CMM inspection and material certification are provided for all specialty metal components.

Yes. All specialty metal orders are supplied with material test reports (MTR) per the relevant standard: ASTM F75 for implant-grade cobalt alloys, AMS 7725 or ASTM B760 for tungsten heavy alloys, ASTM B386 for molybdenum, ASTM B708 for tantalum, and ASTM F2063 for Nitinol in medical applications. Heat number traceability is maintained throughout production. For medical device and aerospace applications, full first article inspection (FAI) reports, dimensional CMM reports, and chemical composition confirmation are available.