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Technical Notes
23 engineering notes on titanium, written for the people who have to specify the material, machine it and keep it in service. There is no marketing content here — only the mechanisms, the limits and the numbers that change a procurement decision.
The notes
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Each note is written from production experience and states the limits as plainly as the advantages: what the material does, where it is specified, and where it will let you down if the service conditions are never stated.
Reference
Titanium 101
A reference note on titanium: physical properties, the Kroll production route, the allotropic transformation, the alpha / alpha-beta / beta alloy families, what a grade callout means, and where the metal should and should not be specified.
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Materials Science
Titanium Alloys
How the alpha, alpha-beta and beta families differ, what the alloying and interstitial elements do, and how to read a titanium grade callout on a drawing.
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Materials Science
TC4 vs TC4 ELI
TC4 and TC4 ELI are the same alloy with different interstitial limits. What that buys, what it costs, and when a drawing should call for ELI.
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Alloy selection
TA18 tube alloy
TA18 sits between commercially pure titanium and TC4, and it exists because tube is made by a different route from bar. What the alloy buys in cold reduction and bending, and what it gives up in return.
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Functional materials
Functional titanium
Titanium is not only a structural metal. In NiTi it returns to a set shape, in NbTi it carries current with no resistance, and in TiFe it absorbs hydrogen. What each alloy asks of the melt, and why the same two properties keep reappearing.
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Corrosion
Corrosion by medium
Titanium is protected by an oxide film, not by the metal itself. How that film behaves in seawater, chlorides, oxidising and reducing acids, alkalis and organic media — and the conditions that take it away.
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Finishing
Surface treatment
Pickling, passivation, anodising, blasting and oxide removal all change a titanium surface — and they are routinely confused with each other. What each process does to the oxide film, the dimensions and the corrosion behaviour.
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Electrochemistry
Titanium anodes
In cathodic protection, chlor-alkali and electroplating duty the titanium is a substrate, not the working surface. What the mixed-metal-oxide coating does, how it is consumed, and which design decisions decide the anode's life.
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Manufacturing
Machining Titanium
The thermal and chemical reasons titanium is hard to cut, the tooling and process decisions that follow, and the contamination rules that must be respected.
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Machining
Thin sheet machining
Machining a thin titanium sheet is not a scaled-down version of machining a block. Stiffness falls with the cube of thickness while cutting forces do not, so the fixture decides the result before the cutter does.
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Process
Titanium forging
Titanium is forged above the beta transus for some purposes and below it for others. What temperature, reduction ratio, transfer time and cooling rate each decide — and how the choices show up in the finished part.
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Fabrication
Welding titanium
Titanium welds cleanly inside an inert shield and badly outside one. What oxygen, nitrogen, hydrogen and iron do to the joint, how the weld colour reads as a result, and how to write the requirement so it is enforceable.
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Components
Titanium flanges
A flange can be cut from plate, rolled from bar, ring rolled, forged or machined from solid. The route decides grain flow, inspection, lead time and price — and the drawing almost never says which one was intended.
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Advanced Manufacturing
Additive Manufacturing
Why titanium and aluminium dominate aerospace additive manufacturing, how they differ on strength, cost, thermal behaviour and corrosion, and why the powder characteristics of aluminium set a harder process problem than titanium does.
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Pipe Fittings
Seamless Tee Forming
Why seamless tee manufacture has no single process, how cold extrusion and end reduction differ, and how the room-temperature ductility of titanium, steel and nickel decides which route applies at which size.
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Titanium Tube
The six properties that justify specifying titanium tube over steel and stainless — specific strength, hot strength, corrosion resistance, cryogenic behaviour, chemical reactivity and the thermal and elastic consequences that shape how it must be worked.
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Product forms
Titanium wire
Titanium wire is bought as straight lengths or as spooled coil, and that choice is decided downstream. Diameter then moves the tolerance, the surface condition and the amount of cold work all at once.
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Buying and verification
Titanium bar selection
A grade is not a specification. Condition, tolerances, heat traceability and the inspection actually performed decide whether bar is fit for the drawing — and most rejections at goods-in come from an item nobody wrote down.
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Fasteners
Titanium fasteners
Titanium fasteners are not the strongest bolts available. They are the strongest per unit of weight, which is a different claim. What that buys in a joint, why threads seize, and what to specify instead of a tensile figure.
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Corrosion Engineering
Crevice Corrosion
Why titanium corrodes in tight gaps even though it is immune in open seawater, the incubation period and autocatalytic mechanism behind it, the geometry that governs it, and the alloy and surface treatments that suppress it.
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Surface Engineering
Titanium Coatings
Titanium and titanium-compound coatings applied to other substrates — PVD, CVD and electrochemical deposition compared, the properties they deliver, and the applications where each is specified.
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Biomedical Materials
Medical Titanium
The six properties that make titanium and its alloys the default implant material, the three generations of medical alloy development, and why vanadium-free beta alloys with low elastic modulus are the current direction of travel.
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Orders and compliance
Order documentation
A titanium order is only as firm as its paperwork: standard, certificate type, unit and packing decide whether the shipment clears — or who pays.
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