Superalloys have excellent high temperature strength, thermal stability and thermal fatigue resistance, so they are widely used in aerospace, marine, nuclear, power station and other industries, such as combustion chambers, turbine guide vanes and working blades of modern gas turbine engines. , high-speed rotating parts such as turbine disk and turbine rotor structural parts, aero-engine disk parts, ring parts, and the like.
Superalloy is one of the most difficult materials to process. If the workability of 45# steel is 100%, the relative processability of superalloy is only 5% to 20%. The cutting characteristics are as follows: 1The cutting force is large, 2 to 4 times that of ordinary steel. Superalloys contain many high-melting-point metal elements and form a dense austenite solid solution. The alloy has good plasticity and a very stable atomic structure. It requires a lot of energy to get the atom out of equilibrium, and the deformation resistance is large. 2 Cutting temperature is high, up to 1000 °C. The high-temperature alloy has a small thermal conductivity of only 1/4 to 1/3 of 45# steel. The friction between the tool and the workpiece is strong and the thermal conductivity is poor, so the cutting temperature is high. 3 The work hardening is serious, and the surface hardness is 50% to 100% higher than the hardness of the substrate. 4 plastic deformation is large, the elongation at room temperature can reach 30% to 50%. 5 tools are easy to wear, common diffuse wear, boundary wear, plastic deformation of the tip, crater wear and built-up edge. Due to these characteristics, the tool material for cutting high-temperature alloys should have high strength, high red hardness, good wear resistance and toughness, high thermal conductivity and adhesion resistance.
High-speed steel tool materials are tool materials used to process high-temperature alloys earlier, and are now being replaced by tool materials such as cemented carbides due to processing efficiency and the like. However, under the condition of some forming tools and poor rigidity of the process system, it is still a good choice to process high-temperature alloys with high-speed steel tool materials. On the other hand, machining efficiency is a comprehensive evaluation. High-speed steel cutting tools have low cutting speeds. Under certain conditions, the loss efficiency can be compensated by using a large cutting depth because high-speed steel tool materials have higher strength. And toughness, and the cutting edge can be sharper, resulting in lower cutting heat and lighter work hardening.
High-speed steel for processing high-temperature alloys, often high-performance high-speed steel such as cobalt high-speed steel, cobalt-containing super-hard high-speed steel and powder metallurgy high-speed steel.
After adding an appropriate amount of cobalt to the high-speed steel, since cobalt can promote the dissolution of carbides in the austenite, the thermal stability and secondary hardness of the high-speed steel can be improved, and the high-temperature hardness is improved; at the same time, the cobalt can also promote the high-speed steel back. The carbide of tungsten or molybdenum is precipitated from martensite during fire to increase the dispersion hardening effect, thereby improving the tempering hardness of the high speed steel and thereby improving the wear resistance of the high speed steel. Increasing the amount of cobalt in high-speed steel can improve its thermal conductivity, especially at high temperatures, which is beneficial to the improvement of cutting performance. Under the same conditions, the cutting edge temperature can be reduced by 30-75 °C. At the same time, the addition of cobalt to the steel reduces the coefficient of friction between the tool and the workpiece and improves its processability. For example, turning high temperature alloy GH132, using W2Mo9Cr4VCo8 (M42), workpiece D=33mm, n=180r/min, ap=2mm, f=0.15mm/r, oil cooling, cutting length 300mm, flank wear 0.2-0.3. Powder metallurgy high-speed steel is a tool that is directly pressed at high temperature (1100 ° C) and high pressure (100 Mpa) with a fine and uniform high-speed steel crystal powder. This process completely avoids the segregation of carbides. Under the same hardness conditions, the strength is increased by 20% to 80% compared with the molten steel, the hardness is increased with the increase of density, the structure is uniform, and the high temperature hardness is 0.5 to 1.0 HRC higher than that of the molten steel. Therefore, it has better cutting performance. If appropriate carbides (such as TiC, TiCN, NaC, etc.) are added thereto, the wear resistance and heat resistance can be increased, which is more advantageous for the cutting of high-temperature alloys, such as in the processing of aero-engine nickel-base alloy GH37 blades. At the time of hole, the powder metallurgy high-speed steel FT15 (FW12Cr4V5Co5) drill bit can drill 9 holes, while the M42 can only drill 1 to 3 holes. Milling threads on nickel-based alloy rocket engine parts, 5 pieces can be machined with 9/2" carbide thread milling cutters, and 33 pieces can be machined with powdered high-speed steel CPM76 (US) thread milling cutters.
Carbide tool materials have also been widely used in the processing of high temperature alloys. Due to the large cutting force of the processing superalloy, the cutting temperature is high and concentrated near the cutting edge, it is prone to chipping and plastic deformation. Therefore, it is common to use a class K alloy with good toughness and thermal conductivity and a class S alloy with high temperature performance. WC-Co type hard alloy (ultrafine particle cemented carbide) with an average grain size of 0.5 μm or less, the hardness of which can reach HRA90-93, and the flexural strength is 2000-3500 MPa, due to its hard phase and Cobalt is highly dispersed, increases the bonding area, improves the bond strength, and exhibits excellent cutting performance in the processing of high-temperature alloys. Nickel-based alloys can be obtained by using ultrafine grain alloys (HRA91.5, sbb=2800Mpa) containing WC89.5%, Co10%, Cr3C2 0.5%, grain size less than 0.2 μm, density 14.5, and compressive strength of 3700 MPa. GH141 square rod (152mm × 152mm × 7100mm) is a round rod. Under the condition of Vc=42m/min and f=0～3.5mm/r, the one-passing cutter is completely long.
PVD coated cemented carbides have proven to be effective in processing superalloys. After the PVD coating process, a very thin layer of TiAlN can be applied to the surface of the tool, so it is especially suitable for the coating of sharp cutting edges, which is especially important for the processing of superalloys. The PVD coated insert has a low coating temperature that maintains the high strength of the substrate and provides a compressive stress on the cutting edge of the tool that prevents the most prone to cracking during high temperature alloy cutting without reducing tool toughness, so it provides a The coated surface with high density and uniform metallographic structure extends tool life very well. For example, Iskar CNMG120408-TFIC908 is a fine-grained matrix TiAlN PVD coated insert for processing GH4169, Vc=50m/min, f=0.2mm/r, ap=2mm, and life expectancy of 40min. Recently, “new aluminum-rich coating†has also been applied to the processing of high-temperature alloys. The content of “Al†molecules in the AlTiN coating is increased to 65%-80%mol AlN, and the coating has higher density and high temperature hardness. . The "Al" molecule is the most active in the AlTiN coating. When it is cut, it combines with the oxygen in the air to form an aluminum oxide protective film on the surface of the tool. As a result, the coating is excellently improved without sacrificing toughness. The redness of the layer. For example, Iska's IC903 is an ultrafine particle alloy with 12% cobalt content and a PVD TiAlN coating for medium and high speed machining of nickel-based alloys. The life of the new aluminum-rich coating alloy Al-IC903 is 1~ of IC903. 2 times. At present, coated alloys for processing superalloys have been developed from several layers, and practice has proved that this combination is more effective than any other single coating in a wide range of applications, and therefore, for high temperatures The use of PVD composite coatings for alloys may be a highlight of new cemented carbide coatings for processing superalloys.
Ceramic tool materials have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metals. They have become one of the main tool materials for high-speed cutting high-temperature alloys. Alumina (Al2O3)-based ceramics (such as Al2O3) + TiC) can also maintain the hardness of HRA80 at 1200 °C for cutting, so it can process high-temperature alloys with a cutting speed 4 to 5 times higher than that of hard alloys, such as processing Nickel 718, Vc = 200 m/min, f = 0.2 mm/r. Silicon nitride (Si3N4) based ceramics have high strength and toughness (bending strength of 900 to 1500 Mpa), high heat resistance (up to 1300 to 1400 °C), and excellent thermal shock resistance (Al2O3) 2 to 3 times) and high thermal conductivity, when cutting nickel-based alloys, the cutting speed can reach more than 300m/min. For example, the processing of Inconel 901 cemented carbide Vc=310m/min, f=0.16mm/r, life 4min, and the life of cemented carbide tool is very short, the life of Al2O3) ceramic tool is also about 2min. For the outer circle of the workpiece of Inconel D400mm, use K-type hard alloy Vc=19m/min, ap=3.4mm, f=0.23mm/r, 0.33 pieces per blade, with silicon-based ceramic Vc=172m /min, ap=10.2mm f=0.18mm/r, one piece per blade can be processed, and the efficiency is 21 times that of cemented carbide.
Cubic boron nitride CBN has high hardness and wear resistance, its microhardness is 8000 ~ 9000 HV, has high thermal stability (up to 1400 ~ 1500 ° C), and has the ability to resist cyclic high temperature. CBN also has excellent chemical stability, good thermal conductivity (20 times that of cemented carbide) and low friction coefficient (coefficient value is 0.1-0.3, friction coefficient of cemented carbide is 0.4-0.6), low The friction coefficient and excellent anti-sticking ability make CBN tool not easy to form stagnant and built-up edge when cutting, so it is suitable for high-speed cutting of high-temperature alloy, such as processing Inconel 718, the best cutting speed is 100 ~ 120m / min.
PCBN is a polycrystalline material in which fine CBN materials are sintered together by alloying elements (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure, and contains 85% to 95% of CBN and a PCBN tool with a particle size of 2 to 3 μm. It can also be used for high-speed cutting of nickel-base superalloys. The cutting speed is generally 120-240m/min, the feed rate is 0.05-0.15mm/r, and the cutting depth is 0.1-3.0mm.
Diamond has extremely high hardness and wear resistance, a low coefficient of friction, high thermal conductivity, and a sharp cutting edge. Because diamond (carbon) has much less solubility in titanium than iron, it has little diffusion and wear and can be used to process titanium alloy superalloys, such as TC4 titanium alloy with natural diamond cutter under emulsion cooling conditions. The cutting speed can reach 200m/min (K-type hard alloy cutting speed 20~50m/min), and the diamond cutter has almost no wear after cutting for 30min. If the cutting fluid is not used, the allowable cutting speed is also 100m/min.
The excellent properties of superalloys present problems and costs on the tool. The cutting of these difficult-to-machine materials requires more energy than cutting ordinary steel parts and produces high cutting temperatures in the cutting zone. Tools that reduce cutting temperatures and high temperatures. To achieve high-efficiency cutting of high-temperature alloys, the correct choice of tool materials is the first important issue. Different tool materials have different applications. For example, milling of titanium alloys, K-type and S-type carbide tools can be correct. Choosing a better wear-resistant carbide tool can achieve higher cutting efficiency at a reasonable processing cost, but this reasonable processing cost is based on the premise that the tool must have "very high toughness" or resistance to impact. Generally, the brittleness of cemented carbide is much larger than that of high-speed steel. Therefore, in the processing of titanium alloy, it is possible that a new generation of high-speed steel will be a good substitute for cemented carbide. On the other hand, as mentioned above, the complex, multi-blade cutting of titanium alloys uses high-cobalt high-speed steel, powder metallurgy high-speed steel, etc., and can also cut titanium alloys efficiently, especially on small rigid machine tools. Resilient high-speed steel tools can achieve high-efficiency machining with large depth of cut rather than increased cutting speed.
High-speed cutting of high-temperature alloy is actually a high-temperature cutting process. The hardness of cemented carbide at high temperature (for example, 1000 ° C) is significantly lower than that of high-temperature alloy such as Inconel 718, and the tool fails in a short time. At the temperature, the CBN still maintains the hardness and strength at normal temperature, so that it is easier to process the workpiece that has become soft. Ceramic knives also have the same performance. However, the application of these tools has a premise: the machine-work-tool technology system must have sufficient power and rigidity, and the workpiece and the machine tool can withstand high cutting heat and large cutting forces such as deformation.
Of course, the tool material can only fully exert its proper performance by combining with reasonable geometric parameters, good tool structure and reasonable use methods.
Superalloy is one of the most difficult materials to process. If the workability of 45# steel is 100%, the relative processability of superalloy is only 5% to 20%. The cutting characteristics are as follows: 1The cutting force is large, 2 to 4 times that of ordinary steel. Superalloys contain many high-melting-point metal elements and form a dense austenite solid solution. The alloy has good plasticity and a very stable atomic structure. It requires a lot of energy to get the atom out of equilibrium, and the deformation resistance is large. 2 Cutting temperature is high, up to 1000 °C. The high-temperature alloy has a small thermal conductivity of only 1/4 to 1/3 of 45# steel. The friction between the tool and the workpiece is strong and the thermal conductivity is poor, so the cutting temperature is high. 3 The work hardening is serious, and the surface hardness is 50% to 100% higher than the hardness of the substrate. 4 plastic deformation is large, the elongation at room temperature can reach 30% to 50%. 5 tools are easy to wear, common diffuse wear, boundary wear, plastic deformation of the tip, crater wear and built-up edge. Due to these characteristics, the tool material for cutting high-temperature alloys should have high strength, high red hardness, good wear resistance and toughness, high thermal conductivity and adhesion resistance.
High-speed steel tool materials are tool materials used to process high-temperature alloys earlier, and are now being replaced by tool materials such as cemented carbides due to processing efficiency and the like. However, under the condition of some forming tools and poor rigidity of the process system, it is still a good choice to process high-temperature alloys with high-speed steel tool materials. On the other hand, machining efficiency is a comprehensive evaluation. High-speed steel cutting tools have low cutting speeds. Under certain conditions, the loss efficiency can be compensated by using a large cutting depth because high-speed steel tool materials have higher strength. And toughness, and the cutting edge can be sharper, resulting in lower cutting heat and lighter work hardening.
High-speed steel for processing high-temperature alloys, often high-performance high-speed steel such as cobalt high-speed steel, cobalt-containing super-hard high-speed steel and powder metallurgy high-speed steel.
After adding an appropriate amount of cobalt to the high-speed steel, since cobalt can promote the dissolution of carbides in the austenite, the thermal stability and secondary hardness of the high-speed steel can be improved, and the high-temperature hardness is improved; at the same time, the cobalt can also promote the high-speed steel back. The carbide of tungsten or molybdenum is precipitated from martensite during fire to increase the dispersion hardening effect, thereby improving the tempering hardness of the high speed steel and thereby improving the wear resistance of the high speed steel. Increasing the amount of cobalt in high-speed steel can improve its thermal conductivity, especially at high temperatures, which is beneficial to the improvement of cutting performance. Under the same conditions, the cutting edge temperature can be reduced by 30-75 °C. At the same time, the addition of cobalt to the steel reduces the coefficient of friction between the tool and the workpiece and improves its processability. For example, turning high temperature alloy GH132, using W2Mo9Cr4VCo8 (M42), workpiece D=33mm, n=180r/min, ap=2mm, f=0.15mm/r, oil cooling, cutting length 300mm, flank wear 0.2-0.3. Powder metallurgy high-speed steel is a tool that is directly pressed at high temperature (1100 ° C) and high pressure (100 Mpa) with a fine and uniform high-speed steel crystal powder. This process completely avoids the segregation of carbides. Under the same hardness conditions, the strength is increased by 20% to 80% compared with the molten steel, the hardness is increased with the increase of density, the structure is uniform, and the high temperature hardness is 0.5 to 1.0 HRC higher than that of the molten steel. Therefore, it has better cutting performance. If appropriate carbides (such as TiC, TiCN, NaC, etc.) are added thereto, the wear resistance and heat resistance can be increased, which is more advantageous for the cutting of high-temperature alloys, such as in the processing of aero-engine nickel-base alloy GH37 blades. At the time of hole, the powder metallurgy high-speed steel FT15 (FW12Cr4V5Co5) drill bit can drill 9 holes, while the M42 can only drill 1 to 3 holes. Milling threads on nickel-based alloy rocket engine parts, 5 pieces can be machined with 9/2" carbide thread milling cutters, and 33 pieces can be machined with powdered high-speed steel CPM76 (US) thread milling cutters.
Carbide tool materials have also been widely used in the processing of high temperature alloys. Due to the large cutting force of the processing superalloy, the cutting temperature is high and concentrated near the cutting edge, it is prone to chipping and plastic deformation. Therefore, it is common to use a class K alloy with good toughness and thermal conductivity and a class S alloy with high temperature performance. WC-Co type hard alloy (ultrafine particle cemented carbide) with an average grain size of 0.5 μm or less, the hardness of which can reach HRA90-93, and the flexural strength is 2000-3500 MPa, due to its hard phase and Cobalt is highly dispersed, increases the bonding area, improves the bond strength, and exhibits excellent cutting performance in the processing of high-temperature alloys. Nickel-based alloys can be obtained by using ultrafine grain alloys (HRA91.5, sbb=2800Mpa) containing WC89.5%, Co10%, Cr3C2 0.5%, grain size less than 0.2 μm, density 14.5, and compressive strength of 3700 MPa. GH141 square rod (152mm × 152mm × 7100mm) is a round rod. Under the condition of Vc=42m/min and f=0～3.5mm/r, the one-passing cutter is completely long.
PVD coated cemented carbides have proven to be effective in processing superalloys. After the PVD coating process, a very thin layer of TiAlN can be applied to the surface of the tool, so it is especially suitable for the coating of sharp cutting edges, which is especially important for the processing of superalloys. The PVD coated insert has a low coating temperature that maintains the high strength of the substrate and provides a compressive stress on the cutting edge of the tool that prevents the most prone to cracking during high temperature alloy cutting without reducing tool toughness, so it provides a The coated surface with high density and uniform metallographic structure extends tool life very well. For example, Iskar CNMG120408-TFIC908 is a fine-grained matrix TiAlN PVD coated insert for processing GH4169, Vc=50m/min, f=0.2mm/r, ap=2mm, and life expectancy of 40min. Recently, “new aluminum-rich coating†has also been applied to the processing of high-temperature alloys. The content of “Al†molecules in the AlTiN coating is increased to 65%-80%mol AlN, and the coating has higher density and high temperature hardness. . The "Al" molecule is the most active in the AlTiN coating. When it is cut, it combines with the oxygen in the air to form an aluminum oxide protective film on the surface of the tool. As a result, the coating is excellently improved without sacrificing toughness. The redness of the layer. For example, Iska's IC903 is an ultrafine particle alloy with 12% cobalt content and a PVD TiAlN coating for medium and high speed machining of nickel-based alloys. The life of the new aluminum-rich coating alloy Al-IC903 is 1~ of IC903. 2 times. At present, coated alloys for processing superalloys have been developed from several layers, and practice has proved that this combination is more effective than any other single coating in a wide range of applications, and therefore, for high temperatures The use of PVD composite coatings for alloys may be a highlight of new cemented carbide coatings for processing superalloys.
Ceramic tool materials have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metals. They have become one of the main tool materials for high-speed cutting high-temperature alloys. Alumina (Al2O3)-based ceramics (such as Al2O3) + TiC) can also maintain the hardness of HRA80 at 1200 °C for cutting, so it can process high-temperature alloys with a cutting speed 4 to 5 times higher than that of hard alloys, such as processing Nickel 718, Vc = 200 m/min, f = 0.2 mm/r. Silicon nitride (Si3N4) based ceramics have high strength and toughness (bending strength of 900 to 1500 Mpa), high heat resistance (up to 1300 to 1400 °C), and excellent thermal shock resistance (Al2O3) 2 to 3 times) and high thermal conductivity, when cutting nickel-based alloys, the cutting speed can reach more than 300m/min. For example, the processing of Inconel 901 cemented carbide Vc=310m/min, f=0.16mm/r, life 4min, and the life of cemented carbide tool is very short, the life of Al2O3) ceramic tool is also about 2min. For the outer circle of the workpiece of Inconel D400mm, use K-type hard alloy Vc=19m/min, ap=3.4mm, f=0.23mm/r, 0.33 pieces per blade, with silicon-based ceramic Vc=172m /min, ap=10.2mm f=0.18mm/r, one piece per blade can be processed, and the efficiency is 21 times that of cemented carbide.
Cubic boron nitride CBN has high hardness and wear resistance, its microhardness is 8000 ~ 9000 HV, has high thermal stability (up to 1400 ~ 1500 ° C), and has the ability to resist cyclic high temperature. CBN also has excellent chemical stability, good thermal conductivity (20 times that of cemented carbide) and low friction coefficient (coefficient value is 0.1-0.3, friction coefficient of cemented carbide is 0.4-0.6), low The friction coefficient and excellent anti-sticking ability make CBN tool not easy to form stagnant and built-up edge when cutting, so it is suitable for high-speed cutting of high-temperature alloy, such as processing Inconel 718, the best cutting speed is 100 ~ 120m / min.
PCBN is a polycrystalline material in which fine CBN materials are sintered together by alloying elements (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure, and contains 85% to 95% of CBN and a PCBN tool with a particle size of 2 to 3 μm. It can also be used for high-speed cutting of nickel-base superalloys. The cutting speed is generally 120-240m/min, the feed rate is 0.05-0.15mm/r, and the cutting depth is 0.1-3.0mm.
Diamond has extremely high hardness and wear resistance, a low coefficient of friction, high thermal conductivity, and a sharp cutting edge. Because diamond (carbon) has much less solubility in titanium than iron, it has little diffusion and wear and can be used to process titanium alloy superalloys, such as TC4 titanium alloy with natural diamond cutter under emulsion cooling conditions. The cutting speed can reach 200m/min (K-type hard alloy cutting speed 20~50m/min), and the diamond cutter has almost no wear after cutting for 30min. If the cutting fluid is not used, the allowable cutting speed is also 100m/min.
The excellent properties of superalloys present problems and costs on the tool. The cutting of these difficult-to-machine materials requires more energy than cutting ordinary steel parts and produces high cutting temperatures in the cutting zone. Tools that reduce cutting temperatures and high temperatures. To achieve high-efficiency cutting of high-temperature alloys, the correct choice of tool materials is the first important issue. Different tool materials have different applications. For example, milling of titanium alloys, K-type and S-type carbide tools can be correct. Choosing a better wear-resistant carbide tool can achieve higher cutting efficiency at a reasonable processing cost, but this reasonable processing cost is based on the premise that the tool must have "very high toughness" or resistance to impact. Generally, the brittleness of cemented carbide is much larger than that of high-speed steel. Therefore, in the processing of titanium alloy, it is possible that a new generation of high-speed steel will be a good substitute for cemented carbide. On the other hand, as mentioned above, the complex, multi-blade cutting of titanium alloys uses high-cobalt high-speed steel, powder metallurgy high-speed steel, etc., and can also cut titanium alloys efficiently, especially on small rigid machine tools. Resilient high-speed steel tools can achieve high-efficiency machining with large depth of cut rather than increased cutting speed.
High-speed cutting of high-temperature alloy is actually a high-temperature cutting process. The hardness of cemented carbide at high temperature (for example, 1000 ° C) is significantly lower than that of high-temperature alloy such as Inconel 718, and the tool fails in a short time. At the temperature, the CBN still maintains the hardness and strength at normal temperature, so that it is easier to process the workpiece that has become soft. Ceramic knives also have the same performance. However, the application of these tools has a premise: the machine-work-tool technology system must have sufficient power and rigidity, and the workpiece and the machine tool can withstand high cutting heat and large cutting forces such as deformation.
Of course, the tool material can only fully exert its proper performance by combining with reasonable geometric parameters, good tool structure and reasonable use methods.
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