A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloy

Abstract

The invention relates to a method for reducing the oxidation and burning loss of NbZrTi series refractory high entropy alloy during forging, and belongs to the technical field of alloys. The raw materials of each element in the NbZrTi series refractory high entropy alloy are weighed according to the atomic percentage, and vacuum consumable smelting is performed to obtain a rod forged in three fires; before each fire forging, a high-temperature anti-oxidation coating is brushed on the surface of the rod, and after each fire calcination, the rod is placed in a closed device with a circulating cooling water structure and argon gas is introduced for cooling. After the last cooling, the oxide scale is polished all over to obtain a NbZrTi series refractory high entropy alloy forging rod with a low oxidation loss rate. By optimizing the alloy composition and forging process, the oxidation and burning loss rate of the NbZrTi series refractory high entropy alloy during the forging process is effectively reduced and the grain size is refined.

Description

Technical Field

[0001] The invention relates to a method for reducing forging oxidation and burning loss of NbZrTi series refractory high entropy alloys, belonging to the technical field of alloys. Background Art

[0002] The forging process can not only close casting defects such as shrinkage cavities or shrinkage, but also realize mass production. However, for NbZrTi series refractory high entropy alloys, due to the presence of a large number of highly active elements such as Zr, Ti, Nb (especially Zr), the alloys undergo severe oxidation and burning during forging air cooling, with an oxidation burning rate of 36.8%. The oxidation product of this series of alloys is ZrO2. Severe oxidation and burning occur during the air cooling of forgings, releasing a large amount of heat, and the time for air cooling of forgings to room temperature is more than 40 minutes, which gives the grains enough energy and time to grow, resulting in coarse grains in the forgings, with an average size of more than 300~500μm. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a method for reducing the oxidation and burning loss of NbZrTi refractory high entropy alloy during forging. By optimizing the alloy composition and forging process, the oxidation and burning rate of NbZrTi refractory high entropy alloy during forging is effectively reduced and the grain size is refined.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows.

[0005] A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys, the method comprising the following steps:

[0006] (1) Weigh the raw materials of each element in the NbZrTi refractory high entropy alloy according to the atomic percentage, and perform vacuum consumable smelting. After the smelting is completed, the surface is peeled and the riser is cut off to obtain an ingot rod with a diameter of ≥180 mm; wherein the chemical formula of the NbZrTi refractory high entropy alloy is Nb a Zr b Ti c Al d M x , M is one or more of Hf, V, and Ta, 10≤a≤35, 20≤b≤60, 20≤c≤40, 0<d≤5, 0≤x≤15, and a+b+c+d+x=100;

[0007] (2) The rod is subjected to three-time forging; before each forging, a high-temperature anti-oxidation coating is applied to the surface of the rod; after each calcination, the rod is placed in a closed device with a circulating cooling water structure and argon gas for cooling; after the last cooling, the oxide scale is polished off to obtain a NbZrTi-based refractory high entropy alloy forging rod with a low oxidation loss rate;

[0008] Among them, during the first fire forging, the heating temperature is 0.55~0.75 times the melting point of the bar, and the deformation is 45%~50%; during the second fire forging, the heating temperature is 50~100℃ lower than the heating temperature of the first fire, and the deformation is 55%~65%; during the third fire forging, the heating temperature is (bar recrystallization temperature-0~20)℃, and the deformation is 55%~65%; the holding time after each fire heating is (1 / 2~7 / 10 of the ingot bar diameter) min, and the unit of the ingot bar diameter is mm.

[0009] Preferably, in step (1), 15≤a≤35, 25≤b≤50, and 25≤c≤40.

[0010] Preferably, in step (1), the diameter of the rod is 200-300 mm.

[0011] Preferably, in step (1), the thickness of the peeled skin is 4 to 10 mm.

[0012] Preferably, in step (2), the high temperature anti-oxidation coating is a yttria-based high temperature anti-oxidation coating composed of yttria and zirconium acetate, and the mass ratio of yttria to zirconium acetate is 5:1~3:2.

[0013] Preferably, in step (2), after applying the high temperature anti-oxidation coating, the coating is air-dried at room temperature for 10 to 30 minutes.

[0014] Preferably, in step (2), during the first forging, the number of draws is three draws and three draws or four draws and four draws; the number of draws in the second forging is one draw and one draw or two draws and two draws; the number of draws in the third forging is one draw and one draw, and the drawing is performed for shaping.

[0015] Preferably, in step (2), when the forging process fails, the ingot is returned to the furnace for insulation for (1 / 24 to 1 / 12 of the ingot bar diameter) min.

[0016] Preferably, in step (2), the flow rate of argon gas is 4-10 mL / min, the temperature of circulating cooling water is 20-30° C., and the flow rate of cooling water is 50-150 mL / min.

[0017] Preferably, in step (2), the time for introducing argon gas in the first firing is (0.03 to 0.06 times the diameter of the ingot bar) min, and the time for introducing argon gas in the second and third firings is 2 to 5 min less than that of the previous firing.

[0018] A NbZrTi-based refractory high entropy alloy forging bar with low oxidation loss rate is prepared by the above method.

[0019] Beneficial Effects

[0020] The invention provides a method for reducing oxidation and burning loss during forging of a NbZrTi-based refractory high entropy alloy. By adding a proper amount of Al element to the alloy composition and optimizing the forging process, the preparation of NbZrTi-based refractory high entropy alloy forgings with small oxidation and burning loss and fine grains is achieved.

[0021] In the present invention, by adding an appropriate amount of Al element, a dense oxide film is formed on the forging during heating in the furnace and forging out of the furnace, which hinders the further diffusion of oxygen into the matrix and plays a good anti-oxidation role. At the same time, adding the low-melting-point Al element is conducive to lowering the melting point of the NbZrTi series refractory high-entropy alloy and reducing the difficulty of smelting. At the same time, by controlling the heating temperature and deformation amount of each firing, the forged grains are effectively refined.

[0022] In the present invention, the forging is placed in an atmosphere filled with argon, which effectively prevents the forging from contacting with air and preventing it from oxidative burning. At the same time, the circulating cooling water can quickly take away the heat of the forging absorbed by the argon, quickly cool it to below the oxidative burning temperature, further preventing the forging from oxidative burning, and inhibiting the growth of grains, which has the effect of refining the forged grains. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific embodiments.

[0024] Example 1

[0025] (1) Alloy composition design: Based on NbZrTi alloy, 5at% Al element was added to obtain the modified NbZrTiAl5 alloy.

[0026] (2) Consumable smelting: NbZrTiAl5 alloy consumable ingots with a diameter of 240 mm were prepared by consumable smelting. The surface of the ingot was peeled off by 6 mm. After the peeling was completed, the riser was cut off.

[0027] (3) Forging: Based on the purpose of pressing shrinkage cavities or shrinkage cavities, reducing anti-oxidation loss, and refining grains to the greatest extent, the total number of forging fires is set to 3. One hour before the first fire forging, a yttrium oxide-based high-temperature anti-oxidation coating (thickness of 300μm, mass ratio of yttrium oxide to zirconium acetate of 3:2) is brushed on the surface of the ingot bar, and then air-dried at room temperature for 10 minutes. When the temperature of the box furnace rises to 1050℃, the ingot is placed in the furnace for heating. The heating time is set to 120min, the deformation is 45%, and the number of piercing and drawing is three piercing and three drawing. If the forging is not moving, it can be returned to the furnace for 20min of insulation. After the first fire forging is completed, the forging is placed in a closed device filled with argon gas, and the temperature is lowered by argon gas cooling. The circulating argon gas flow rate is set to 4mL / min, the temperature of the circulating cooling water outside the argon gas pipeline is constant at 25℃, the cooling water flow rate is set to 50mL / min, and the argon gas introduction time is set to 8min. After the forging reaches room temperature, it is taken out and the scale is polished all over, and then a yttrium oxide-based high-temperature anti-oxidation coating is applied, and the second forging is carried out. The heating temperature for the second forging is 1000°C, the deformation is 55%, the number of piercings is one piercing and one pulling, the argon gas flow time is 6 minutes, and the other conditions are the same as the first forging. After the forging is cooled to room temperature, it is taken out and the scale is polished all over, and then a yttrium oxide-based high-temperature anti-oxidation coating is applied, and the third forging is carried out. The heating temperature for the third forging is 700°C, the argon gas flow time is 4 minutes, the deformation is 35%, the number of piercings is one piercing and one pulling, and the forging is shaped into the required size after the piercing is completed. The other conditions are the same as the first forging, and finally a forging rough bar with a lower oxidation loss rate is obtained.

[0028] Through observation, it was found that during the argon cooling process after each forging, the degree of severe oxidation of the forgings decreased with time, and when the set argon flow time was reached, the severe oxidation phenomenon disappeared. After testing, the total loss was 19.9% ​​and the average grain size was 114μm.

[0029] Example 2

[0030] In this embodiment, NbZrTiTa 15 Alloy as the basis, adding 1at% Al element to obtain modified NbZrTiTa 15 Al alloy.

[0031] The heating temperature of the first fire was 1200° C., the heating temperature of the second fire was 1100° C., and the heating temperature of the third fire was 820° C. The circulating argon flow rate was 10 mL / min, the temperature of the circulating cooling water outside the argon pipeline was constant at 25° C., the cooling water flow rate was 150 mL / min, and the rest was the same as in Example 1.

[0032] Through observation, it was found that during the argon cooling process after each forging, the degree of severe oxidation of the forgings decreased with time, and when the set argon flow time was reached, the severe oxidation phenomenon disappeared. According to the test, the total loss was 24.6% and the average grain size was 186μm.

[0033] Example 3

[0034] In this embodiment, the deformation amount of the first fire is 50%, and the number of pier pulling is four piers and four pulls; the deformation amount of the second fire is 65%, and the number of pier pulling is two piers and two pulls; the deformation amount of the third fire is 40%, and the number of pier pulling is two piers and two pulls; the circulating argon flow rate is 10mL / min, the cooling water flow rate is 150mL / min, and the rest is the same as Example 1.

[0035] Through observation, it was found that during the argon cooling process after each forging, the degree of severe oxidation of the forgings decreased with time, and when the set argon flow time was reached, the severe oxidation phenomenon disappeared. According to the test, the total loss was 12.8% and the average grain size was 76μm.

[0036] Comparative Example 1

[0037] After forging, the forging was directly air-cooled, and the rest was the same as in Example 1.

[0038] It was found through observation that the forgings underwent severe oxidation during the air cooling process after each fire forging, with a total loss of 38.9% and an average grain size of 613 μm.

[0039] Comparative Example 2

[0040] In this comparative example, only one fire forging is performed, and the conditions of the first fire forging are consistent with the conditions of the first fire forging in Example 1.

[0041] Through observation, it was found that during the argon cooling process after each forging, the degree of severe oxidation of the forgings decreased with time, and when the set argon flow time was reached, the severe oxidation phenomenon disappeared. According to the test, the total loss was 16.3% and the average grain size was 206 μm.

[0042] Comparative Example 3

[0043] In this comparative example, the deformation amount of the first fire is 12%, and the number of pier pulling is one pier and one pull; the deformation amount of the second fire is 16%, and the number of pier pulling is one pier and one pull; the deformation amount of the third fire is 18%, the heating temperature is 1000℃, and the rest is the same as Example 1.

[0044] Through observation, it was found that during the argon cooling process after each forging, the degree of severe oxidation of the forgings decreased with time, and the severe oxidation phenomenon disappeared after air cooling. According to the test, the total loss was 21.5% and the average grain size was 903μm.

[0045] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys, characterized in that: The method steps include: (1) Weigh the raw materials of each element in the NbZrTi refractory high entropy alloy according to the atomic percentage, and perform vacuum consumable smelting. After the smelting is completed, the surface is peeled and the riser is cut off to obtain an ingot rod with a diameter of ≥180 mm; wherein the chemical formula of the NbZrTi refractory high entropy alloy is Nb a Zr b Ti c Al d M x , M is one or more of Hf, V, and Ta, 10≤a≤35, 20≤b≤60, 20≤c≤40, 0<d≤5, 0≤x≤15, and a+b+c+d+x=100; (2) The rod is subjected to three-time forging; before each forging, a high-temperature anti-oxidation coating is applied to the surface of the rod; after each calcination, the rod is placed in a closed device with a circulating cooling water structure and argon gas for cooling; after the last cooling, the oxide scale is polished off to obtain a NbZrTi-based refractory high entropy alloy forging rod with a low oxidation loss rate; Among them, during the first fire forging, the heating temperature is 0.55~0.75 times the melting point of the bar, and the deformation is 45%~50%; during the second fire forging, the heating temperature is 50~100℃ lower than the heating temperature of the first fire, and the deformation is 55%~65%; during the third fire forging, the heating temperature is the bar recrystallization temperature -0℃~20℃, and the deformation is 55%~65%; the holding time after each fire heating is 1 / 2~7 / 10 of the ingot bar diameter value, among which the unit of the holding time is min, and the unit of the ingot bar diameter is mm.

2. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1, characterized in that: In step (1), 15≤a≤35, 25≤b≤50, 25≤c≤40.

3. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1, characterized in that: In step (1), the diameter of the rod is 200-300 mm.

4. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1, characterized in that: In step (1), the thickness of the peeled skin is 4 to 10 mm.

5. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1, characterized in that: In step (2), the high temperature anti-oxidation coating is a yttrium oxide-based high temperature anti-oxidation coating, which is composed of yttrium oxide and zirconium acetate, and the mass ratio of yttrium oxide to zirconium acetate is 5: 1~3: 2; after brushing the high temperature anti-oxidation coating, it is air-dried at room temperature for 10~30 minutes.

6. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1, characterized in that: In step (2), during the first forging, the number of draws is three draws and three draws or four draws and four draws; the number of draws in the second forging is one draw and one draw or two draws and two draws; the number of draws in the third forging is one draw and one draw, and the drawing is performed for shaping.

7. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1 or 6, characterized in that: In step (2), when the forging process fails, the value of the remelting holding time is 1 / 24 to 1 / 12 of the ingot bar diameter, where the unit of the holding time is min.

8. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1, characterized in that: In step (2), the flow rate of argon gas is 4-10 mL / min, the temperature of circulating cooling water is 20-30°C, and the flow rate of cooling water is 50-150 mL / min.

9. A method for reducing forging oxidation and burning loss of NbZrTi refractory high entropy alloys according to claim 1 or 8, characterized in that: In step (2), the time for introducing argon gas in the first firing is 0.03 to 0.06 times the diameter of the ingot bar, wherein the unit of the time for introducing argon gas is min, and the time for introducing argon gas in the second and third firings is 2 to 5 minutes less than that of the previous firing.

10. A NbZrTi-based refractory high entropy alloy forging bar with low oxidation loss rate, characterized in that: It is prepared by the method according to any one of claims 1 to 9.