Titanium Quality & Inspection

Karl Gillihan

🚀 TITANIUM

Titanium Quality Control and Inspection Services

Titanium inspection is dominated by contamination, not dimensions. Oxygen pickup forms a brittle alpha case skin during any hot processing, iron pickup from steel tooling creates corrosion sites, and the microstructure dictates fatigue life in a way no caliper can read. For Grade 5 (Ti-6Al-4V) flight hardware and Grade 23 implants, the inspection plan is really a contamination-and-metallurgy plan, and that is the expertise buyers come to ManufacturingBase to find.

AS9100NADCAPISO 13485

When titanium is heated in air above roughly 1100 to 1200 degF (forging, heat treat, some welding, even aggressive grinding), oxygen diffuses into the surface and forms alpha case, a hard, brittle, oxygen-enriched layer that cracks and seeds fatigue failures. It is invisible to the eye and dimensionally undetectable. Verification is metallographic: a mounted, polished, etched cross-section examined for the characteristic white alpha layer, often confirmed by a microhardness traverse showing the surface harder than the core. For aerospace and medical titanium, alpha-case checking after any hot process is mandatory. The practical control is to machine alpha case off (typically 0.005 to 0.015 in per surface depending on the process) or to process in vacuum or inert atmosphere so it never forms. Inspection confirms removal by sectioning a sample, and on critical parts an etch-and-inspect step verifies the finished surface is clean. A supplier that heat-treats titanium in an air furnace and ships without alpha-case verification is shipping latent fatigue failures. Grinding burn produces a localized alpha case too. Heavy-handed grinding of Ti-6Al-4V overheats the surface and forms a thin contaminated layer plus residual tensile stress that kills fatigue life. This is why titanium grinding is done with light passes, sharp wheels, and copious coolant, and why ground titanium fatigue parts may require an etch inspection or a controlled stress profile to confirm the surface is sound.

Microstructure and the role it plays in fatigue performance

Ti-6Al-4V properties depend heavily on microstructure, and microstructure depends on whether the material was processed above or below the beta transus (about 1830 degF for Grade 5). Equiaxed, bimodal, and lamellar structures give different fatigue, fracture toughness, and strength tradeoffs. For rotating aerospace parts and implants, the print or spec (often AMS 4928, AMS 4911 for sheet, or ASTM F136 for implants) calls a required microstructure, and verification is metallographic per established reference standards. A part that meets chemistry and hardness can still have the wrong microstructure and fail in fatigue. This is why titanium inspection includes metallography that steel rarely needs at the same intensity. A NADCAP metallurgical lab examines etched sections against acceptance micrographs, checking grain size, alpha-beta morphology, and the absence of defects like beta flecks or excessive grain growth. Buyers ordering flight-critical or implant titanium should expect microstructure verification in the quality plan, not just a hardness number. Hardness, conversely, is a weak inspection tool for titanium. Ti-6Al-4V runs around 30 to 36 HRC, but hardness barely moves with the metallurgical conditions that actually control fatigue, so a passing hardness number gives false confidence. Conductivity and hardness, useful for aluminum and steel, do not substitute for metallography on critical titanium. The inspection center of gravity shifts to microstructure and contamination.

Iron pickup and the dimensional discipline titanium still requires

Iron embedded from steel tooling, fixtures, or even steel wool creates corrosion and contamination sites on titanium, particularly an issue for medical and chemical-service Grade 2. Dedicated titanium tooling, non-ferrous deburring media, and passivation per ASTM A967 (yes, titanium gets passivated too, for free-iron removal) are the controls, and inspection may include a ferroxyl test or surface analysis to confirm the part is iron-free. Mixing titanium and steel work on the same equipment without controls is a contamination escape. Dimensionally, titanium machines to good tolerances but its low modulus (about half that of steel) means it deflects more under cutting and clamping force, so thin walls and long features need careful fixturing and the inspection has to account for part flex under the gauge. A thin Ti-6Al-4V wall can measure differently clamped versus free, so CMM probing force and fixturing strategy matter more than on stiffer metals. Galling and thread quality mirror the stainless problem: titanium galls badly, so threaded titanium features get functional gauging plus an assembly callout for anti-galling measures. The dimensional inspection itself is conventional CMM and gauge work, but the metallurgical and contamination checks are what make titanium inspection a specialty rather than routine.

Chemistry, NDT, and full traceability for regulated titanium

Titanium is interstitial-sensitive: oxygen, nitrogen, hydrogen, and iron content drive properties, and Grade 23 (ELI, extra-low interstitial) exists specifically because lower oxygen gives better fracture toughness for implants. Chemistry verification against AMS or ASTM F136/F1472 limits is part of the cert chain, and on critical work an incoming verification confirms the alloy and grade. Hydrogen content in particular causes embrittlement and is limited tightly; pickled and acid-processed titanium must be checked for hydrogen pickup. Nondestructive testing on titanium is heavily fluorescent penetrant (FPI per ASTM E1417) for surface cracks, because titanium is non-magnetic so magnetic particle does not apply. Ultrasonic and, increasingly, CT inspection find internal defects in forgings and additively manufactured titanium. Aerospace rotating titanium parts get rigorous FPI and ultrasonic, both NADCAP-controlled processes. For AM titanium, CT porosity inspection is becoming standard because lack-of-fusion porosity is the dominant defect. Traceability is absolute in this material. Aerospace and medical titanium ties every part to a mill heat with full chemistry, and the processing history (forge, heat-treat, machining lots) is recorded. ITAR controls apply to many defense titanium parts, so the supplier chain must be compliant. Counterfeit and mixed-grade titanium is a known supply-chain risk, which is why positive material identification and cert verification are standard practice on regulated programs rather than optional.

Frequently Asked Questions

Alpha case is a hard, brittle, oxygen-enriched surface layer that forms when titanium is heated in air above roughly 1100 to 1200 degF during forging, heat treatment, hot forming, or aggressive grinding. Oxygen diffuses into the surface and embrittles it, and because alpha case cracks easily, it seeds fatigue failures in service. It is invisible to the eye and undetectable with dimensional gauges. Inspection is metallographic: a sample is sectioned, mounted, polished, etched, and examined under a microscope for the characteristic white oxygen-rich layer, usually confirmed by a microhardness traverse showing the surface harder than the core. The control is to either prevent it by processing in vacuum or inert atmosphere, or to machine it off, typically removing 0.005 to 0.015 in per surface depending on the exposure. For aerospace Ti-6Al-4V and medical Grade 23, alpha-case verification after any hot process is mandatory and is done by a NADCAP-accredited metallurgical lab. A supplier that heat treats titanium in air and ships without alpha-case checks is shipping latent fatigue failures, so confirm this step is in the quality plan.

Because hardness barely tracks the properties that matter for titanium. Ti-6Al-4V runs about 30 to 36 HRC across a wide range of microstructural conditions, but its fatigue life, fracture toughness, and strength depend on whether it was processed above or below the beta transus (around 1830 degF for Grade 5) and what microstructure resulted: equiaxed, bimodal, or lamellar. Two parts with identical hardness can have very different fatigue performance. So the definitive inspection is metallographic examination of an etched cross-section, comparing grain size and alpha-beta morphology against acceptance micrographs in specs like AMS 4928 or ASTM F136. The lab also checks for defects like beta flecks, excessive grain growth, and alpha case. This is why titanium inspection requires a NADCAP metallurgical lab and is more involved than typical steel or aluminum inspection, where hardness and conductivity carry more of the load. For flight-critical rotating parts and implants, microstructure verification belongs in the quality plan, and a passing hardness number alone should never be accepted as proof of acceptable titanium.

Titanium is non-magnetic, so magnetic particle inspection does not work on it at all. The primary surface-crack method is fluorescent penetrant inspection (FPI) per ASTM E1417, a NADCAP-controlled process that floods surface-breaking defects with fluorescent dye visible under UV light. For internal defects in forgings and bar, ultrasonic testing is standard and is also NADCAP-controlled for aerospace. Additively manufactured titanium increasingly requires CT (computed tomography) inspection because lack-of-fusion and gas porosity are the dominant AM defects, and CT maps internal porosity that ultrasonic can miss in complex geometries. Aerospace rotating titanium parts typically get both FPI and ultrasonic, and AM aerospace titanium adds CT. Costs scale accordingly: FPI runs roughly 15 to 50 dollars per part at moderate volume, while CT can add 100 to 400-plus dollars per part plus a day or two of turnaround depending on size and resolution. Specify the NDT method and acceptance class on the print, and confirm the supplier or their subcontractor holds NADCAP accreditation for that process, because uncontrolled penetrant on flight hardware is a finding waiting to happen.

Iron embedded from steel tooling, fixtures, deburring media, or steel wool creates corrosion and contamination sites on titanium, a particular concern for medical Grade 23 implants and chemical-service Grade 2. Prevention is process discipline: dedicated titanium tooling and fixtures, non-ferrous deburring media, segregated work areas, and avoiding cross-contamination with steel work on shared equipment. Detection methods include the ferroxyl (potassium ferricyanide) test, which turns blue where free iron is present, and surface analytical methods on critical parts. Titanium also gets passivated per ASTM A967 to dissolve embedded free iron and clean the surface, and a passivation certificate plus a free-iron test verifies the result. For medical work under ISO 13485, iron contamination control is part of the validated process, and the supplier should document segregation and testing. Ask whether the shop runs dedicated titanium tooling or shares equipment with steel, because a shop that machines titanium and carbon steel with the same fixtures and tooling without controls is a contamination risk. Iron-free verification belongs in the quality plan for any corrosion-sensitive or implant titanium part.

Full traceability to the mill heat with complete chemistry, including the interstitials oxygen, nitrogen, hydrogen, and iron, since those drive titanium properties and Grade 23 ELI exists specifically for its low oxygen and superior fracture toughness. The cert chain should tie the part through every processing lot (forge, heat treat, machining) back to the heat number, with the controlling spec called out (AMS 4928 or 4911 for Grade 5, ASTM F136 or F1472 for medical). Hydrogen content verification matters after any acid pickling because hydrogen embrittles titanium. For defense work, ITAR compliance flows through the entire supply chain, and the supplier must be registered and handle technical data accordingly. Counterfeit and mixed-grade titanium is a documented supply-chain risk, so positive material identification on incoming stock plus cert verification is standard on regulated programs. Expect a NADCAP-accredited metallurgical lab to back the metallography and NDT, an AS9100 or ISO 13485 quality system, and retained samples for traceability. On ManufacturingBase you can filter titanium suppliers by AS9100, NADCAP, ISO 13485, and ITAR registration to find shops with this discipline already in place.

Last updated: July 2026

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