TB2 Titanium Alloy in the Beta Alloy Family
TB2 is a metastable beta-type titanium alloy listed in the Chinese titanium grade system of GB/T 3620.1, alongside the commercially pure grades TA0 to TA2 and the alpha+beta grades such as TC4 and TC16. Because the beta phase is retained at room temperature, the alloy can be shaped in the solution-treated condition and then strengthened by aging, so a production route for TB2 is normally divided into a forming stage and a separate strengthening stage. The grade is supplied as bar, rod, wire, sheet and strip, and the same heat may be drawn, rolled or forged depending on the delivery condition required by the end user.
Typical uses include spring and fastener stock, high-strength structural components, and parts that have to combine moderate density with good corrosion resistance in chloride-bearing environments. Titanium alloys have a density of roughly 4.5 g/cm3, about 60 percent that of steel, which is the main reason the grade is selected where weight reduction and corrosion resistance must be achieved at the same time. The practical difficulty is that TB2 has limited plasticity at room temperature, so cold working and hot working each need their own measures.
Cold Processing of TB2 Titanium Alloy
Cold processing is carried out at room temperature and includes cold drawing, cold rolling and cold heading. The poor room-temperature plasticity of TB2 means that greater forming force is required and that forming parameters must be controlled carefully to avoid cracks and unwanted deformation. In practice the following measures are combined:
Cold drawing for rod, wire and tube, with light reductions per pass and re-lubrication before every pass.
Cold rolling for strip and foil, where roll gap, tension and pass schedule determine thickness tolerance and flatness.
Cold heading for fasteners, where the billet is usually formed in the annealed or solution-treated condition to limit edge cracking.
Intermediate annealing between forming stages to restore ductility before the next reduction.
Reduction per pass, drawing speed, lubricant selection and die geometry are the variables that decide whether a cold forming sequence is stable. Tool surfaces must be kept free of built-up material, because galling at the tool and workpiece interface quickly turns into surface tearing.
Hot Processing Routes
Hot processing is carried out at elevated temperature, where plasticity is high and complex shapes can be formed under lower stress. Hot forging, hot rolling and hot extrusion are the usual routes, and the oxygen-enriched layer that forms on the surface during heating is normally removed by pickling or machining before the part is put into service, since a hard, brittle surface layer reduces fatigue performance.
| Route | Characteristic | Typical product |
|---|---|---|
| Hot forging | High plasticity, suitable for complex shapes, improves toughness | Discs, rings, near-net shape blanks |
| Hot rolling | Continuous reduction, good for long products | Bar, rod, plate, strip |
| Hot extrusion | Low forming stress, good for sections that are hard to roll | Tube, profile, bar |
Because the alloy is a beta grade, the finish temperature of the last hot forming step affects the structure that reaches the customer, and the forming record is normally kept together with the heat treatment record for traceability.
Heat Treatment: Solution Treatment, Aging and Annealing
Heat treatment is the stage that sets the final strength of a TB2 part. Solution treatment dissolves the alloying elements into the beta matrix and prepares the material for aging; aging then precipitates fine phases and raises strength and hardness to the target level; annealing is used earlier in the route to make the alloy workable.
| Treatment | Typical temperature | Purpose |
|---|---|---|
| Solution treatment | 800 to 1000 °C | Dissolves the dissolved phases into the matrix and prepares the alloy for aging |
| Aging treatment | 400 to 700 °C, from several hours to tens of hours | Raises strength and hardness to the required level |
| Annealing | Below the solution treatment regime | Makes the microstructure more uniform, lowers hardness and improves plasticity for later cold or hot working |
Solution temperature and aging time decide the balance between strength and ductility, and both must be verified against the property level requested on the drawing. Furnace uniformity and load thermocouples should be recorded for every batch. A solution treatment at the low end of the range leaves a coarser structure, while overheating coarsens the beta grain size, so the schedule is normally frozen for each product form and section thickness rather than adjusted per order.
Surface Treatment and Machining Practice
Shot peening and anodizing are the two surface processes most often applied to finished titanium parts. Shot peening introduces compressive stress in the surface layer, which raises fatigue performance, while anodizing builds a controlled oxide film that improves corrosion resistance, surface hardness and appearance quality. Both processes are carried out after the final heat treatment so that the benefit is not lost in a later furnace cycle.
TB2 has high hardness and a strong tendency for the cutting temperature to rise rapidly, so rapid tool wear, smearing and poor chip control are common. Specialised tooling and technique are needed: cutting tools made of high-speed tungsten carbide or multi-layer coated carbide, a rigid setup, sharp edges, and coolant delivered directly to the cutting zone. Cutting speed, feed rate and depth of cut must be held inside a narrow band so that the process stays stable and the workpiece does not overheat, because excessive heat disturbs the microstructure that the heat treatment stage has just established.
Quality Control for Processed TB2 Components
Verification of a finished TB2 part starts with the incoming material. Bar and rod are normally certified to ASTM B348, plate and strip to ASTM B265, and tube to ASTM B338, and a mill certificate according to EN 10204 3.1 covering chemical composition and mechanical properties should accompany each heat. In-process checks for machined and formed parts include hardness testing, bending testing and, for tubular products, hydrostatic testing.
Dimensional inspection of critical diameters, wall thickness and straightness before packing.
Surface inspection for laps, tears and embedded contamination after pickling.
Batch-level traceability from heat number to finished part, including the heat treatment record.
Export packing in standard wooden cases to protect machined surfaces during shipment.
Frequently Asked Questions
Q: Why is TB2 titanium alloy difficult to cold form?
Because the alloy has poor plasticity at room temperature, so higher force is needed and cracks or unwanted deformation appear if reductions per pass are too large.
Q: Which cutting tools are used for TB2 titanium alloy?
High-speed tungsten carbide or multi-layer coated carbide tools are used, with sharp edges and coolant delivered to the cutting zone to control the cutting temperature.
Q: At what temperature is solution treatment carried out?
Solution treatment is typically performed between 800 °C and 1000 °C, after which the alloy is ready for aging.
Q: What does aging treatment achieve?
Aging is carried out between 400 °C and 700 °C for several hours to tens of hours and raises the strength and hardness of the alloy to the required level.
Q: What is the purpose of annealing between forming passes?
Annealing makes the microstructure more uniform, lowers hardness and improves plasticity so that further cold or hot working can be carried out safely.
Q: Can anodizing improve the wear resistance of TB2 parts?
Yes. Anodizing forms an oxide film that improves corrosion resistance, surface hardness and appearance quality, while shot peening is used where fatigue performance is the priority.
