Inspecting Tungsten and Tungsten Carbide Parts

Because tungsten products are sintered from powder, density is the single most informative inspection result, since it reveals whether the part fully consolidated. Tungsten carbide (WC-Co) density depends on the cobalt binder content (a 6 percent cobalt grade runs around 14.9 g/cc, higher cobalt lowers it), pure tungsten approaches 19.3 g/cc, and W-Ni-Fe heavy alloys run roughly 17 to 18.5 g/cc depending on tungsten fraction. A density below the expected value signals residual porosity from incomplete sintering, which means lower strength and shorter life. Density is measured by the Archimedes (water-displacement) method, fast and non-destructive. For tungsten carbide, density is read alongside the cobalt content because they are linked, and a low density flags either porosity or a binder problem. The standard porosity inspection for carbide is metallographic, examining a polished section against ISO 4505 porosity rating charts that grade A-type (fine), B-type (coarse), and C-type (carbon/eta phase) porosity. A carbide part with excessive porosity wears and chips prematurely even at correct hardness. For heavy alloy counterweights and radiation shielding, density is often the primary specified property because the application wants mass in a small volume, so density verification is the core acceptance test. A W-Ni-Fe counterweight that is a few percent low in density is functionally short of its mass target, and the buyer cares about that directly. Density is where tungsten inspection starts and frequently where it ends for simpler parts.

Tungsten carbide hardness is verified on the Rockwell A scale or Vickers, with typical cutting and wear grades running 89 to 93 HRA. Hardness tracks both cobalt content (less cobalt is harder and more wear resistant but more brittle) and WC grain size (finer grain is harder). For carbide tooling, the combination of grain size and cobalt determines whether the part resists wear or resists impact, and inspection confirms the grade delivered the intended balance. A coarse-grain, high-cobalt grade and a fine-grain, low-cobalt grade can look identical and serve completely different duties. Grain size is verified metallographically, since WC grain size (submicron, fine, medium, coarse) is a primary grade variable. A fine-grain carbide that sintered with abnormal grain growth loses its hardness advantage, so for precision cutting tools and wear parts, grain-size verification confirms the microstructure. The eta phase (a brittle tungsten-cobalt-carbon phase from carbon imbalance) and free graphite are detrimental and checked metallographically; their presence indicates an off-stoichiometry sintering problem. Pure tungsten and heavy alloy hardness are verified too, but the inspection emphasis differs: pure tungsten is brittle and the concern is cracking and grain structure, while heavy alloy is tougher and machinable, and its hardness confirms the tungsten-binder ratio. Coercivity and magnetic saturation testing are also used on carbide as fast non-destructive proxies for cobalt content and grain size, giving production screening without sectioning every part.

Tungsten carbide and pure tungsten are brittle, so cracks, especially from grinding, are a primary defect. Carbide is shaped largely by diamond grinding and EDM rather than conventional machining, and aggressive grinding induces surface cracks and thermal damage. Fluorescent penetrant inspection adapted for carbide, and metallographic examination, detect grinding cracks. For precision carbide tooling, the ground surface integrity directly affects tool life, so finish and crack inspection on cutting edges matter. Pure tungsten is notoriously difficult and is often ground or EDM-machined because it is too brittle and hard for conventional cutting in many forms. Inspection of pure tungsten parts focuses on cracks, density, and dimensional accuracy achieved by grinding, with surface and edge cracks being the main reject cause. The honest note for buyers: if a print calls for conventionally machined pure tungsten with sharp internal corners and thin walls, the part may be impractical, and the realistic route is grinding, EDM, or a switch to machinable heavy alloy. A good supplier flags this rather than quoting an impossible part. Heavy alloy (W-Ni-Fe) is the exception, it machines like a tough steel and holds good tolerances, so its dimensional inspection is conventional CMM and gauge work. This is why heavy alloy is chosen for machined dense parts (counterweights, balance weights, vibration dampers) where carbide and pure tungsten would have to be ground. Matching the material to what can actually be inspected and held dimensionally is part of the quality conversation.

The three tungsten forms serve different industries and carry different acceptance priorities. Tungsten carbide cutting tools and wear parts (oil-gas drilling, machining, mining) are inspected for hardness, grain size, porosity, and edge integrity, since those govern wear life. Carbide for the most demanding applications gets the full ISO 4505 porosity rating plus coercivity and magnetic saturation screening. Heavy alloy parts split between aerospace and defense counterweights and balance weights (where density and dimensional accuracy dominate) and radiation shielding for medical and industrial use (where density, again, and freedom from voids that would let radiation leak through are critical). For medical radiation shielding, density uniformity verification ensures no thin or porous spots compromise shielding, sometimes checked by radiography of the shield itself. Pure tungsten serves high-temperature, electrical-contact, and radiation applications, and its inspection emphasizes density, purity (tungsten content, often 99.95 percent-plus), and crack freedom. Purity verification matters because trace contaminants degrade high-temperature and electrical performance. Across all three forms, the powder-metallurgy nature means the mill or sinter-house cert documenting density, composition, and grade is the anchor, with incoming verification on critical parts. ManufacturingBase lets buyers find suppliers experienced with the specific tungsten form rather than assuming a general machine shop can certify sintered tungsten quality.