Why are aerospace materials and cell phones flocking to titanium alloys?

Properties of Titanium
High specific strength: 1.3 times that of aluminum alloys, 1.6 times that of magnesium alloys, 3.5 times that of stainless steel, the champion among metal materials.
High thermal strength: the use temperature is several hundred degrees higher than aluminum alloy, can work for a long time at a temperature of 450-500 ℃.
Good corrosion resistance: resistant to acid, alkali and atmospheric corrosion, especially strong resistance to pitting and stress corrosion.
Good low-temperature performance: titanium alloy TA7 with very low interstitial elements can maintain a certain degree of plasticity at -253℃.
High chemical activity: high chemical activity at high temperatures, easily reacts chemically with hydrogen, oxygen and other gaseous impurities in the air to generate a hardened layer.
Small thermal conductivity, small modulus of elasticity: the thermal conductivity is about 1/4 of nickel, 1/5 of iron, 1/14 of aluminum, and various titanium alloys have a thermal conductivity of about 50% lower than that of titanium. The modulus of elasticity of titanium alloy is about 1/2 of steel.
Classification and use of titanium alloy
Titanium alloys can be categorized according to their uses: heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium-molybdenum, titanium-palladium alloys, etc.), low-temperature alloys, and alloys with special functions (titanium-iron hydrogen storage materials, titanium-nickel memory alloys). Although titanium and its alloys have not been used for a long time, they have been awarded a number of honorable titles because of their outstanding performance. The first title is "space metal", which is light weight, high strength and high temperature resistant, especially suitable for the manufacture of airplanes and various spacecraft. At present, about 3/4 of the titanium and titanium alloys produced in the world are used in the aerospace industry. Many parts originally made of aluminum alloy have been replaced by titanium alloy.
Titanium alloy aerospace applications
Titanium alloy is mainly used for aircraft and engine manufacturing materials, such as forging titanium fans, pressurized air discs and blades, engine cowling, exhaust devices and other parts, as well as the aircraft's beams and compartments, such as structural frame parts. Spacecraft mainly use titanium alloys of high strength, corrosion resistance and low temperature resistance to manufacture a variety of pressure vessels, fuel storage tanks, fasteners, instrument straps, frames and rocket shells. Artificial Earth satellites, moon landing module, manned spacecraft and space shuttles also use titanium alloy plate welding parts.
In 1950, the United States for the first time in the F-84 fighter-bomber as the rear fuselage heat shield, wind shield and tail cowl and other non-bearing components. 1960s began the use of titanium alloy parts from the rear fuselage to the center fuselage, partially replacing the structural steel to make the spacer frame, beams, flaps slide and other important load-bearing components. 1970s onwards, the civil aircraft began to use a large number of titanium alloys, such as the Boeing 747 passenger aircraft with titanium The amount of titanium used in Boeing 747 airliner amounted to more than 3640 kilograms accounted for 28% of the weight of the machine. With the development of processing technology, in rockets, satellites and spacecraft, also used a lot of titanium alloy. The more advanced the airplane, the more titanium is used. U.S. F-14A fighter using titanium alloy, accounting for about 25% of the weight of the machine; F-15A fighter for 25.8%; U.S. fourth-generation fighters with titanium amount of 41% of the F119 engine with 39% of the amount of titanium, is the current amount of titanium with the highest amount of airplanes.
Titanium alloys are used in a large number of aviation reasons
Why does the material of air transportation aircraft have to use titanium alloy?
Modern aircraft navigation top speed has reached the speed of sound more than 2.7 times. Such a fast supersonic flight will make the airplane and the air friction and produce a lot of heat. When the flight speed reaches 2.2 times the speed of sound, the aluminum alloy can not withstand, must use high temperature resistant titanium alloy. When the aero-engine thrust-to-weight ratio from 4 to 6 to 8 to 10, the pressurized gas outlet temperature correspondingly from 200 to 300 ℃ to 500 to 600 ℃, the original low-pressure pressurized gas discs and blades made of aluminum must be changed to titanium alloy.
In recent years, scientists on the performance of titanium alloy research work, and constantly make new progress. The original titanium, aluminum, vanadium composed of titanium alloy, the maximum operating temperature of 550 ℃ ~ 600 ℃, and the newly developed titanium aluminum (TiAl) alloy, the maximum operating temperature has increased to 1040 ℃. Titanium alloy instead of stainless steel to manufacture high-pressure compressor disk and blade, can reduce the weight of the structure. Aircraft can save 4% of fuel for every 10% weight reduction. For rockets, for every 1kg of weight reduction, the range can be increased by 15km.
3C Applications of Titanium Alloys
At present, the consumer electronics industry represented by cell phones is very "involution", the head of the manufacturers are hoping to borrow titanium alloys to improve the product's premium capacity.

Huawei, Apple, Xiaomi, Honor and many other phones have imported the material. Apple began to standardize on titanium cases from the Ultra series of watches, and its newly released iPhone 15, of which the Pro version uses a new titanium body, becoming Apple's first cell phone to use aerospace-grade titanium; Huawei used titanium materials in the structural parts of the folding screen cell phone MateXs2, which was released in 2022, and used titanium bezels in the Watch4Pro; Glory Released on October 12, the light and thin large internal folding flagship phone Glory MagicVs2, using innovative materials such as Lupin titanium hinges; Xiaomi 14 new machine, the highest priced 14Pro titanium version.
It is reported that Samsung will use titanium alloy center frame on the GalaxyS24Ultra, the center frame part is similar to the original color titanium color scheme of the iPhone15Pro.

Overall, titanium alloy with both high specific strength and lightweight advantages become highly promoted as an important reason, which can make consumer electronics products more lightweight, consumer experience will be more comfortable.
Titanium Alloy Processing Characteristics Analysis
First of all, titanium alloy thermal conductivity is low, only 1/4 of steel, aluminum 1/13, copper 1/25, due to the slow heat dissipation in the cutting zone, not conducive to thermal balance, in the cutting process, the heat dissipation and cooling effect is very poor, easy to form a high temperature in the cutting zone, the deformation of the parts after processing rebound, resulting in increased torque on the cutting tool, the edge of the edge of the fast wear, durability is reduced.
Secondly, the low thermal conductivity of titanium alloy, so that the cutting heat accumulated in the cutting knife near the small area area is not easy to disseminate, the friction of the front face increases, not easy to chip, cutting heat is not easy to disseminate, accelerate tool wear. Finally, titanium alloy chemical activity is high, processing at high temperatures is easy to react with the cutting tool material, the formation of dissolution, diffusion, resulting in sticky knife, burning knife, broken knife and other phenomena.
The characteristics of machining center machining titanium alloy
Machining centers can process multiple parts at the same time to improve production efficiency. Improve the machining accuracy of parts, good product consistency. The machining center has tool compensation function, which can obtain the machining accuracy of the machine itself. There is a wide range of adaptability and greater flexibility, such as the arc processing, chamfering and transition filleting of this part, which can realize the multi-functionality of one machine. Machining center can be milling, drilling, boring, tapping and a series of processing. Accurate costing can be performed to control the production schedule. No need for special fixtures, save a lot of cost funds, shorten the production cycle. Greatly reduce the labor intensity of workers. Can be multi-axis processing with UG and other processing software.
Selection of tools and coolant materials
1. Tool material selection should meet the following requirements
Sufficient hardness, the hardness of the tool must be much greater than the titanium alloy hardness.
Sufficient strength and toughness, due to the tool cutting titanium alloy when subjected to a large torque and cutting force, so there must be sufficient strength and toughness.
Sufficient wear resistance, due to the titanium alloy toughness, machining cutting edge to be sharp, so the tool material must have sufficient wear resistance, so as to reduce work hardening. This is the most important parameter in selecting tools for machining titanium alloys.
Cutting tool materials and titanium alloy affinity to be poor, due to the high chemical activity of titanium alloy, so to avoid the formation of cutting tool materials and titanium alloy dissolution, diffusion into the alloy, resulting in sticking knife, burning knife phenomenon. After the domestic commonly used cutting tool materials and foreign cutting tool materials for the test shows that the use of high cobalt cutting tool effect is ideal, cobalt's main role can strengthen the secondary hardening effect, improve the hardness and hardness after heat treatment, and at the same time has a high toughness, wear resistance, good heat dissipation.
2. Geometric parameters of milling cutter
The machining characteristics of titanium alloy determines the geometric parameters of the cutter and the ordinary tool there is a big difference. Helix angle β choose a smaller helix rise angle, chip removal groove increases, easy chip removal, fast heat dissipation, but also reduce the cutting resistance in the cutting process. Front angle γ cutting edge sharp, cutting fast, avoid titanium alloy produce too much cutting heat, so as to avoid secondary hardening. The rear angle α reduces the wear rate of the cutting edge, facilitates heat dissipation and improves the durability to a great extent.

3.Cutting parameter selection
Titanium alloy machining should choose a lower cutting speed, appropriately large feed, reasonable depth of cut and finishing volume, cooling should be sufficient. Cutting speed vc = 30 ~ 50m/min, feed f roughing take larger feed, finishing and semi-finishing take moderate feed. Cutting depth ap = 1/3d is appropriate, titanium alloy affinity is good, chip removal is difficult, the depth of cut is too large, it will cause tool sticking, burning, fracture phenomenon. Finishing allowance moderate titanium alloy surface hardening layer of about 0.1 ~ 0.15mm, the allowance is too small, the knife edge cutting on the hardened layer, the tool is easy to wear, you should avoid the hardened layer of processing, but the cutting allowance should not be too large.
4. Coolant
Titanium alloy processing is best not to use chlorine-containing coolant, to avoid the generation of toxic substances and cause hydrogen embrittlement, but also to prevent high-temperature stress corrosion cracking of titanium alloy. Choose a synthetic water-soluble emulsion, can also be self-compatible with coolant. Cutting processing coolant to ensure sufficient, coolant circulation speed should be fast, cutting fluid flow and pressure should be large, machining centers are equipped with special cooling nozzles, as long as the attention of the adjustment will be able to achieve the desired results.