1. Cutting performance
Titanium alloys have high strength and hardness, so processing equipment is required to be powerful, and molds and cutting tools should have high strength and hardness. During cutting, the contact area between chips and rake face is small, and the stress on the tool tip is large. Compared with 45 steel, although the cutting force of titanium alloy is only 2/3-3/4, the contact area between the chip and the rake face is smaller (only 1/2-2/3 of 45 steel), so the tool The stress on the cutting edge is greater, and the tip or cutting edge is prone to wear; titanium alloy has a large friction factor and low thermal conductivity (only 1/4 and 1/16 of iron and aluminum respectively); the contact between the tool and the chip Due to its short length, cutting heat accumulates in a small area near the cutting edge and is not easily dissipated. These factors make the cutting temperature of titanium alloy very high, causing accelerated tool wear and affecting the processing quality. Due to the low elastic modulus of titanium alloys, the workpiece rebounds greatly during cutting, which can easily cause increased tool flank wear and deformation of the workpiece. Titanium alloys are highly chemically active at high temperatures and are prone to react with gas impurities such as hydrogen and oxygen in the air. The chemical reaction generates a hardened layer and further aggravates the wear of the tool; in titanium alloy cutting, the workpiece material is easily bonded to the tool surface, and coupled with the high cutting temperature, the tool is prone to diffusion wear and adhesive wear.
2. Grinding performance
Titanium alloys have active chemical properties and are easily compatible with and adhered to abrasives at high temperatures, clogging the grinding wheel, resulting in increased wear of the grinding wheel, reduced grinding performance, and difficulty in ensuring grinding accuracy. The wear of the grinding wheel also increases the contact area between the grinding wheel and the workpiece, causing the heat dissipation conditions to deteriorate, the temperature in the grinding area increases sharply, and a large thermal stress is formed on the grinding surface layer, causing local burns on the workpiece and causing grinding crack. Titanium alloy has high strength and toughness, which makes it difficult for the grinding chips to separate during grinding, increases the grinding force, and increases the grinding power consumption accordingly. Titanium alloy has low thermal conductivity, small specific heat, and slow heat conduction during grinding, causing heat to accumulate in the grinding arc zone, causing the temperature of the grinding zone to rise sharply.
3. Extrusion processing performance
When extruding titanium and titanium alloys, high extrusion temperature and fast extrusion speed are required to prevent the temperature from dropping too quickly. At the same time, the contact time between the high-temperature billet and the mold should be shortened as much as possible. Therefore, new heat-resistant mold materials should be used for the extrusion die, and the transportation speed of the billet from the heating furnace to the extrusion barrel should also be fast. Since metal is easily contaminated by gases during heating and extrusion, appropriate protective measures should also be taken. Appropriate lubricants should be selected during extrusion to prevent sticking to the mold, such as jacket extrusion and glass lubricated extrusion. Because titanium and titanium alloys have a large thermal effect of deformation and poor thermal conductivity, special attention must be paid to preventing overheating during extrusion and deformation. The extrusion process of titanium alloy is more complicated than that of aluminum alloy, copper alloy, and even steel, which is determined by the special physical and chemical properties of titanium alloy. During conventional hot reverse extrusion of titanium alloys, the die temperature is low, the surface temperature of the billet in contact with the die drops rapidly, and the temperature inside the billet rises due to deformation heat. Due to the low thermal conductivity of titanium alloy, after the surface temperature drops, the heat of the inner blank cannot be transferred to the surface in time to supplement, and a surface hardened layer will appear, making it difficult to continue deformation. At the same time, a large temperature gradient will occur between the surface layer and the inner layer. Even if it can be formed, it will easily cause deformation and uneven structure.
4. Forging processing performance
Titanium alloys are very sensitive to forging process parameters. Changes in forging temperature, deformation amount, deformation and cooling rate will cause changes in the structure and properties of titanium alloys. In order to better control the structural properties of forgings, in recent years, advanced forging technologies such as hot die forging and isothermal forging have been widely used in the forging production of titanium alloys.
The plasticity of titanium alloy increases with temperature. In the temperature range of 1000-1200℃, the plasticity reaches the maximum value, and the allowable deformation degree reaches 70%-80%. The forging temperature range of titanium alloys is narrow and should be strictly controlled according to the (α+β)/β transformation temperature (except for ingot opening), otherwise the β grains will grow violently and reduce the room temperature plasticity; α titanium alloys are usually in (α +β) two-phase zone forging, because the forging temperature above the (α+β)/β phase transformation line is too high, it will lead to the β brittle phase, and the initial forging and final forging of β titanium alloy must be higher than (α+β)/ β transition temperature. The deformation resistance of titanium alloys increases rapidly with the increase of deformation speed, and the forging temperature has a greater impact on the deformation resistance of titanium alloys. Therefore, conventional forging must be completed with minimal cooling in the forging die. The content of interstitial elements (such as O, N, C) also has a significant impact on the forgeability of titanium alloys.
