Titanium Solution
Overview
Titanium is an element with an atomic number of 22 in the periodic table. It is a subgroup element of the fourth period (IVB group). In addition to titanium, this group of elements also includes zirconium and hafnium. Its common feature is that it has a high melting point and forms a stable oxide film on its surface at room temperature.
Titanium is a silver-grey transition metal with low density and high strength, and its corrosion resistance in seawater, aqua regia and chlorine is exceptional. With about 60% of steel's density yet comparable strength, titanium is the material of choice where weight, temperature and a hostile chemical environment all matter at once — from aero structures to medical implants.
Properties
Comparison
Machining
Titanium conducts heat very poorly — about 1/13 of aluminium, 1/5 of steel, and 1/25 of copper. During cutting, titanium is very sticky to cutting tools, making it easy to break the tool and causing poor surface quality. Titanium alloy machining requires specially designed approaches.
The best coolant is water-soluble coolant. When there is very high heat generated and difficult cutting conditions, a soluble coolant solution is used and, in combination with appropriate machining conditions, gives good performance.
It is recommended to use YG6 / YG8 / YW1 / YW2 carbide inserts. Keep tools sharp, use a large clearance angle and ensure the insert is secure. Carbide end mills and drills are recommended for holes and surface finishing operations.
According to the specific situation, you need to choose the cutting fluid. Heat-base fluids, flood coolant machining, and carbon neutral cutting fluids are used. If you want to achieve the color of the film, you must do a pre-treatment before processing and cutting.
Welding
Titanium alloy generally uses a welding wire with less impurity composition than the base metal. Sometimes to improve joint toughness and reduce weld seam inclusions, a welding wire one grade lower than the base metal is used. Welding wires are typically TA1 or TA2 for commercially pure titanium, and special alloy wires for aerospace grade alloys.
The workpiece surface is very important. Oil and oxide residues must be removed before welding to ensure corrosion-resistance strength of the weld seam. Treatment methods include mechanical polishing and grinding, pickling, sandblasting and chemical cleaning — all must remove oxides from the alloy surface.
Gas Tungsten Arc Welding (GTAW/TIG) is the most common — it shields the arc and weld pool from atmospheric contamination. TIG welding can be performed with or without filler metal and gives cleaner results than MIG.
Electron Beam Welding (EBW) is performed in vacuum — no oxidation problem and an extremely narrow, deep weld. Laser beam welding (LBW) offers high energy density, fast welding speed, narrow weld and small distortion under inert gas cover.
Defects
Common defects in titanium alloy welding arise primarily from atmospheric contamination, residual stress and poor joint preparation.
Oxygen, nitrogen and hydrogen pickup harden and embrittle the weld. When atmospheric contamination is excessive, it is easy to produce stress cracking. Inert shielding throughout heating and cooling prevents it.
As titanium alloy welding metal solidifies, strength rapidly increases while hot plasticity drops. Welding stress induces hot and cold cracking. High-purity titanium rarely produces welding cracks, but the welded joint may be prone to stress corrosion cracking in certain media.
Welding pores are the most common defect in titanium alloy welding. The main cause is hydrogen from surface pollution, moisture and grease dissolved at high temperature then precipitated during solidification. Thorough pre-weld cleaning eliminates the source.
Select appropriate welding process and welding area according to the base metal material.
Use high-quality shielding gas with purity not less than 99.99%, dried before welding.
Clean the welding base material and weld area thoroughly to prevent oxide and interlayer contamination.
Take necessary argon protection measures for the molten pool and heat-affected area during welding.
Finishing
Due to the unique physical and chemical properties of titanium — such as low thermal conductivity, low surface hardness, high elastic recovery, easy oxidation, easy inhalation — conventional surface treatment methods are difficult to achieve the desired effect. Special processing methods and operating means must be used.
The sandblasting processing technology of titanium parts is generally better to use white corundum for rough blasting. The blasting pressure should be controlled below 0.45MPa. When the injection pressure is too high, the sand particles impact the titanium surface to generate internal sparks, causing secondary pollution.
Titanium has high chemical reactivity, low thermal conductivity, high viscosity, and low mechanical grinding rate. Use super-hard abrasives such as diamond or cubic boron nitride. The polishing line speed is generally 900–1800 m/min.
Due to the low conductivity of titanium and its strong oxidation performance, it is almost impossible to polish titanium with aqueous electrolyte at low voltage. Special electrolyte solutions are required to achieve a mirror-polished surface.
The anodizing technology of titanium is relatively easy. Under the action of applied voltage, the titanium anode can form a thick oxide film, improving corrosion resistance, wear resistance, and weather resistance. The electrolyte generally uses H₂SO₄, H₃PO₄, and organic acid aqueous solutions.
In order to increase the beauty of titanium, anodizing method can be used to use the interference effect of titanium oxide film on light to naturally develop color. By changing the cell voltage, colorful colors can be formed on the surface of titanium.
Joining
The oxide film on the surface is stable — titanium and its alloys have a high affinity with oxygen, forming a stable oxide film that prevents solder wetting and spreading. This must be removed during brazing.
It has a strong tendency to inhale — titanium and its alloys absorb hydrogen, oxygen, and nitrogen during heating. The higher the temperature, the more serious the absorption, sharply reducing toughness.
It is easy to form intermetallic compounds — titanium and its alloys can chemically react with most solder materials to form brittle compounds, resulting in brittle joints.
Organization and performance are easy to change — titanium and its alloys will undergo phase transformation and grain coarsening when heated. The higher the temperature, the more serious the coarsening.
Braze in a vacuum or inert atmosphere to prevent oxidation — vacuum brazing is preferred for aerospace grade components.
Use silver-, aluminium- or titanium-based filler matched to service temperature, and keep dwell time short to limit intermetallic growth.
Control the brazing temperature precisely — the lowest workable temperature that still wets the joint gives the strongest, finest-grained result.
