1. Chemical Composition
Titanium Grade 4: An unalloyed (commercially pure) titanium grade. Its composition is dominated by titanium (≥99.0% Ti) with only trace impurities, including controlled amounts of oxygen (≤0.40%), iron (≤0.50%), carbon (≤0.10%), nitrogen (≤0.05%), and hydrogen (≤0.015%). No intentional alloying elements are added.
Titanium Grade 5: A two-phase (α+β) titanium alloy, formally named Ti-6Al-4V (6% aluminum, 4% vanadium, balance titanium). Aluminum (Al) strengthens the α-phase and improves heat resistance, while vanadium (V) stabilizes the β-phase and enhances ductility. Impurities (e.g., O, Fe, C) are strictly limited to very low levels (e.g., O ≤0.20%, Fe ≤0.30%).
2. Mechanical Properties
3. Corrosion Resistance
Titanium Grade 4: Relies on a dense, stable titanium oxide (TiO₂) film for protection. It performs exceptionally well in mild to moderate corrosive environments, such as seawater, dilute acids (e.g., sulfuric acid below 10%), and most atmospheric conditions. However, it may corrode in highly concentrated acids (e.g., hot, concentrated hydrochloric acid) or strong oxidizers.
Titanium Grade 5: The oxide film is reinforced by aluminum (which forms a more stable Al₂O₃-TiO₂ composite layer), boosting resistance to harsher environments. It withstands higher-temperature corrosive media (e.g., hot seawater, acidic industrial effluents) and has better resistance to pitting and crevice corrosion than Grade 4.
4. Processing & Fabrication
Titanium Grade 4: High ductility and low strength make it easier to process via cold forming (e.g., rolling, stamping, deep drawing) without cracking. It also welds well (with proper shielding to avoid oxygen/nitrogen pickup) and requires less aggressive machining parameters.
Titanium Grade 5: Higher strength and lower ductility make cold forming more challenging-hot forming (at ~700–900°C) is often needed to avoid brittleness. Welding requires precise control (e.g., post-weld heat treatment) to prevent microstructural defects (e.g., α-case formation). Machining is also more difficult due to its high strength, requiring sharp tools and coolants to reduce heat buildup.
5. Cost
Titanium Grade 4: Lower cost. As an unalloyed grade, it avoids the expense of adding and refining alloying elements (aluminum, vanadium) and has simpler production processes.
Titanium Grade 5: Higher cost. The addition of high-purity aluminum and vanadium, plus more complex processing (e.g., hot forming, heat treatment), increases its production and fabrication costs-typically 2–3 times more expensive than Grade 4.
6. Typical Applications
Medical: Implantable components (e.g., dental posts, orthopedic plates) where biocompatibility and ductility matter.
Industrial: Chemical storage tanks, heat exchanger tubes (for low-temperature fluids), and marine hardware (e.g., boat hull fasteners).
Consumer goods: Watch cases, lightweight sports equipment.
Aerospace: Aircraft structural parts (e.g., wing spars, landing gear components), engine casings (for high-temperature operation).
Medical: Load-bearing implants (e.g., hip stems, knee prosthetics) where strength and biocompatibility are both required.
Industrial: High-pressure valves, offshore oil/gas drill components (resisting saltwater and acidic fluids), and turbine blades.
