UNS R05252, universally recognized as Tantalum 2.5% Tungsten (Ta-2.5W), is an advanced refractory alloy engineered to solve the primary mechanical limitation of pure Tantalum: its relative softness. By precisely alloying the Tantalum matrix with a 2.5% solid-solution addition of Tungsten (W), the metal achieves a dramatic 30% to 50% increase in structural yield strength while retaining the legendary, glass-like immunity to boiling concentrated acids found in pure Tantalum.
Because Tungsten is completely miscible in Tantalum and possesses similar metallurgical characteristics, this alloy maintains exceptional ductility and weldability. Ta-2.5W fasteners are the ultimate, uncompromising choice for aggressive chemical processing environments—such as high-pressure sulfuric acid heat exchangers, pharmaceutical reactor vessels, and halogen synthesis towers—where pure Tantalum (R05200) would physically yield or deform under heavy mechanical clamping loads.
| Material Classification | Tungsten-Alloyed Refractory Metal (Ta-2.5W) |
|---|---|
| UNS Designation | R05252 |
| Microstructure | Body-Centered Cubic (BCC) Solid Solution |
| Magnetic State | Completely Non-Magnetic |
| Density | 16.65 g/cm³ (0.601 lb/in³) — Exceptionally Heavy |
| Size Range | Metric: M3 to M36 | Imperial: #4 to 1-1/2" |
| Primary Attribute | Extreme Acid Immunity Combined with Elevated Yield Strength |
Contains detailed pressure-vessel clamping load capacities, isocorrosion charts for boiling concentrated Hydrochloric Acid (HCl), and high-temperature yield retention curves.
⬇ DOWNLOAD DATASHEETIn extreme chemical engineering, the presence of trace interstitial gases (Oxygen, Nitrogen, Hydrogen) causes violent embrittlement of refractory metals. Ananka guarantees that every lot of Ta-2.5W is melted via strict Electron Beam (EB) or Vacuum Arc Reduction (VAR) processes, providing 100% audited mill traceability.
The R05252 specification mandates extreme baseline purity, identical to R05200, but introduces a deliberate 2.5% Tungsten alloy. Because Tungsten and Tantalum share very similar atomic radii and crystal structures, the Tungsten seamlessly substitutes into the Tantalum lattice, creating massive internal stress (strengthening the metal) without compromising its chemical inertness.
| Tantalum (Ta) | Tungsten (W) | Niobium (Nb) | Oxygen (O) | Carbon (C) | Nitrogen (N) |
|---|---|---|---|---|---|
| Balance (~97.4) | 2.00 – 3.50 | 0.10 Max | 0.015 Max | 0.010 Max | 0.010 Max |
| Mechanical Property | Typical Limits (Fully Annealed Temper) |
|---|---|
| Tensile Strength | 45,000 - 60,000 psi (310 - 415 MPa) |
| Yield Strength | 30,000 - 45,000 psi (205 - 310 MPa) |
| Elongation (in 2 inches) | 20% - 25% |
| Hardness (Vickers) | ~ 130 HV (approx. 72 HRB) |
| Standard / System | Designation |
|---|---|
| ASTM Specifications | ASTM B365 (Rod and Wire), ASTM B390 |
| Common Trade Names | Ta-2.5W, Alloy 63, Tantalum-Tungsten 2.5% |
| European Equivalent | TaW2.5 (Approximate) |
| Mating Bolts/Studs | Internal Threads (Nuts) | Washers / Sealing Components |
|---|---|---|
| R05252 CNC Machined Heavy Hex Bolts | R05252 Precision Hex Nuts | Virgin PTFE / TFM Gaskets & Washers |
While the 2.5% Tungsten addition makes R05252 noticeably harder and stronger than pure Tantalum, it remains a refractory metal prone to severe thread galling (cold-welding) when tightened dry. Clean, high-performance fluoropolymer (PTFE) thread pastes or the use of heavy PTFE isolating washers are absolutely mandatory during installation.
| Nominal Diameter | Threads Per Inch (UNC) | Max Target Torque (in-lbs) — PTFE Lubricated |
|---|---|---|
| 1/4" | 20 | 40 - 50 |
| 3/8" | 16 | 110 - 130 |
| 1/2" | 13 | 240 - 280 |
| 3/4" | 10 | 750 - 850 |
Tungsten (W) and Tantalum (Ta) are metallurgically "sister" elements. They are fully miscible, meaning they blend together flawlessly without forming brittle intermetallic phases. More importantly, Tungsten is one of the few elements that does not degrade Tantalum's incredible corrosion resistance. The 2.5% addition is the "sweet spot" that maximizes strength while ensuring the alloy can still be cold-formed and drawn into fastener wire.
Ta-10W (Alloy 60) contains 10% Tungsten and is phenomenally strong, boasting yield strengths approaching aerospace Titanium. However, Ta-10W is incredibly difficult to machine, terribly difficult to weld, and highly resistant to cold-heading. Ta-2.5W is explicitly favored for chemical processing fasteners because it provides the necessary structural boost while remaining highly workable and weldable.
Absolutely Not. Despite being alloyed with Tungsten, this material retains the Achilles' heel of all Tantalum alloys: Hydrofluoric Acid. Exposure to HF, even in very low concentrations, or hot fuming Oleum, will cause rapid, violent corrosion and total hydrogen embrittlement. For HF environments, specialized alloys like Monel 400 must be utilized instead.
