Characteristics of Titanium

High Specific Strength: Titanium boasts a specific strength 1.3 times that of aluminum alloy, 1.6 times that of magnesium alloy, and 3.5 times that of stainless steel, making it the leader among metal materials.

High Thermal Strength: It can operate at temperatures several hundred degrees higher than aluminum alloy and can sustain long-term use at 450-500°C.

Good Corrosion Resistance: Titanium is resistant to acids, alkalis, and atmospheric corrosion, and is especially effective against pitting and stress corrosion.

Good Low-Temperature Performance: The titanium alloy TA7 retains its plasticity even at -253°C.

High Chemical Activity: At high temperatures, titanium reacts readily with gas impurities like hydrogen and oxygen in the air, forming a hardened layer.

Low Thermal Conductivity and Elastic Modulus: Its thermal conductivity is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum. The thermal conductivity of various titanium alloys is roughly 50% lower than that of pure titanium. The elastic modulus of titanium alloy is about half that of steel.

Classification and Uses of Titanium Alloys

Titanium alloys are categorized into heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (e.g., titanium-molybdenum, titanium-palladium), low-temperature alloys, and special functional alloys (e.g., titanium-iron hydrogen storage materials, titanium-nickel memory alloys). Although titanium and its alloys have a relatively short history of use, their outstanding performance has earned them the title of "space metal." Lightweight, strong, and heat-resistant, titanium is ideal for manufacturing aircraft and spacecraft. Approximately 75% of the world's titanium and titanium alloys are used in the aerospace industry, replacing many parts previously made of aluminum alloys.

Aerospace Applications of Titanium Alloys

Titanium alloys are used in aircraft and engine manufacturing, such as forged titanium fans, compressor discs and blades, engine covers, exhaust devices, and structural frame parts. In spacecraft, titanium's high specific strength, corrosion resistance, and low temperature resistance are leveraged to make various pressure vessels, fuel tanks, fasteners, instrument straps, frames, and rocket shells. Man-made satellites, lunar modules, manned spacecraft, and space shuttles also use titanium alloy welded parts.

In 1950, the United States first used titanium alloy on the F-84 fighter-bomber for non-load-bearing components. Since the 1960s, its use has expanded to include important load-bearing components in the mid-fuselage. By the 1970s, civil aircraft began using titanium alloys extensively. For example, the Boeing 747 uses over 3,640 kilograms of titanium, constituting 28% of the aircraft's weight. Advanced aircraft like the US F-14A and F-15A fighters have high titanium content, and the fourth-generation US fighters use 41% titanium, with the F119 engine incorporating 39% titanium, marking the highest titanium content in aircraft to date.

Reasons for Titanium Alloy's Widespread Use in Aviation

Modern aircraft can reach speeds over 2.7 times the speed of sound, causing significant heat from air friction. At 2.2 times the speed of sound, aluminum alloys cannot withstand the heat, necessitating the use of high-temperature resistant titanium alloys. When the thrust-to-weight ratio of aircraft engines increases and the compressor outlet temperature rises, low-pressure compressor discs and blades originally made of aluminum must be replaced with titanium alloys.

Recent advancements have increased the maximum operating temperature of titanium alloys from 550-600°C to 1040°C for new titanium aluminum (TiAl) alloys. Replacing stainless steel with titanium alloys in high-pressure compressor discs and blades reduces the structure's weight, saving fuel for aircraft and increasing range for rockets.

3C Applications of Titanium Alloy

In the competitive consumer electronics industry, leading manufacturers like Huawei, Apple, Xiaomi, and Honor are turning to titanium alloys to enhance their products' premium feel. Apple has used titanium alloy cases in its Ultra series of watches and the iPhone 15 Pro, which features an aviation-grade titanium body. Huawei uses titanium alloy in the structural parts of its Mate Xs2 folding screen phone and Watch 4 Pro. Honor's Magic Vs2 flagship phone and Xiaomi's 14 Pro also incorporate titanium. Samsung is expected to use titanium alloy in the Galaxy S24 Ultra.

Titanium alloy's high specific strength and lightweight properties make it ideal for consumer electronics, offering lighter, more comfortable devices.

Analysis of Titanium Alloy Processing Characteristics

Titanium alloys present several processing challenges:

Low Thermal Conductivity: This makes heat dissipation slow, resulting in high temperatures in the cutting area, which can cause significant tool wear and deformation of parts.

High Chemical Activity: At high temperatures, titanium alloys can react with tool materials, causing sticking, burning, and tool breakage.

Features of Machining Titanium Alloys

Using machining centers for titanium alloys offers several benefits:

Improved production efficiency and machining accuracy.

Enhanced product consistency.

Capability for multi-functional processing, such as milling, drilling, boring, and tapping.

Cost-effective, adaptable manufacturing without the need for special fixtures.

Reduced labor intensity and the potential for multi-axis processing.

Selection of Tool and Coolant Materials

Tool Materials: Tools must be much harder than titanium alloys, have sufficient strength and toughness, wear resistance, and low affinity with titanium to avoid chemical reactions.

Geometric Parameters: Tools with a smaller helix angle, larger chip removal grooves, and optimized rake and back angles help in cutting titanium alloys effectively.

Cutting Parameters: Lower cutting speeds, appropriate feed rates, reasonable cutting depths, and sufficient cooling are crucial for machining titanium alloys.

Coolant: Avoid chlorine-containing coolants to prevent toxic substances and hydrogen embrittlement. Use synthetic water-soluble emulsions, ensuring sufficient and fast coolant circulation.

Conclusion

Titanium alloys are a critical material in both aviation and consumer electronics due to their high strength, lightweight, and durability. Their use in various applications continues to grow, driven by advancements in processing technologies and the ongoing demand for high-performance materials.

References

Aerospace Applications of Titanium Alloys

Reasons for Titanium Alloy's Widespread Use in Aviation

3C Applications of Titanium Alloy

Analysis of Titanium Alloy Processing Characteristics