Surface strengthening process capable of improving high-cycle fatigue performance of TiAl alloy casting

Abstract

The invention discloses a surface strengthening process capable of improving the high-cycle fatigue performance of a TiAl alloy casting, which is characterized by comprising the following steps of: 1, carrying out sand blasting treatment on the casting with the mesh number of 40-120; secondly, dirt on the surface of the casting obtained in the first step is removed; and thirdly, shot blasting treatment is conducted on the casting obtained in the second step, and the shot blasting strength ranges from 0.1 mmN to 0.3 mmN. In the first step, the fatigue strength of the casting after sand blasting can reach the level of a standard smooth sample by reasonably selecting the mesh number of sand blasting sand, and then in the second step, the fatigue strength of the casting after sand blasting and shot blasting can be remarkably improved compared with that of the standard smooth sample by reasonably selecting the shot blasting strength. The surface strengthening process disclosed by the invention is simple, short in flow, low in requirements on production equipment and simple and convenient to operate, can be applied to high-temperature rotating parts such as aero-engine low-pressure turbine blades and automobile engine impellers, and has great application and popularization values.

Description

Technical Field

[0001] The invention relates to the technical field of surface strengthening, and in particular to a sandblasting+shot peening strengthening process capable of improving the high cycle fatigue performance of a TiAl alloy casting. Background Art

[0002] TiAl alloy has low density and high specific strength. It has partially replaced nickel-based high-temperature alloys in the range of 650-750℃ for forming the last 1-2 low-pressure turbine blades of aircraft engines, achieving lightweight engines and greatly improving thrust-to-weight ratio. It is the most promising lightweight high-temperature structural material. During the service life of aircraft engine TiAl alloy castings, they are constantly subjected to temperature and stress changes, which can easily lead to the risk of high-cycle fatigue failure. However, the high-cycle fatigue strength of TiAl alloy castings is low, which can no longer meet the high performance requirements of the new generation of advanced aircraft engines with high thrust-to-weight ratio for lightweight and high-temperature resistant materials.

[0003] Fatigue crack growth threshold ΔK of TiAl alloy th and the maximum stress intensity factor K at final failure max The interval between them is narrow, crack extension accounts for a very small proportion in the total fatigue life, and the total fatigue life is mainly determined by the crack initiation life.

[0004] Sandblasting and shot peening can produce residual compressive stress on the surface of the workpiece, offset or reduce the applied tensile stress, delay the initiation of fatigue cracks and reduce the early growth rate of fatigue cracks. For traditional materials such as stainless steel, maraging steel, aluminum alloy, titanium alloy and nickel-based alloy, sandblasting and shot peening can significantly improve damage tolerance and fatigue strength.

[0005] Therefore, sandblasting and shot peening of TiAl alloy castings to improve fatigue strength is a key technical point to meet the high performance requirements of lightweight and high-temperature resistant materials for the new generation of high thrust-to-weight ratio advanced aircraft engines. Summary of the invention

[0006] The technical problem to be solved by the present invention is to propose a surface strengthening process based on sandblasting + shot peening to improve the high cycle fatigue performance of TiAl alloy castings in response to the above technical status quo.

[0007] The technical solution adopted by the present invention to solve the above technical problems is: a surface strengthening process for improving the high cycle fatigue performance of TiAl alloy castings, characterized in that it comprises the following steps:

[0008] Step 1: Sandblast the casting with a mesh size of 40 to 120;

[0009] Step 2: Remove dirt from the casting surface after step 1;

[0010] Step 3: Shot peening is performed on the casting after step 2, and the shot peening intensity is 0.1-0.3 mmN.

[0011] Preferably, the sand used in the sandblasting in step 1 is made of silicon carbide, the pressure in the spray gun is 0.6 MPa, and the sandblasting is performed manually on a manual pressurized sandblasting machine.

[0012] Preferably, in step 2, the casting after step 1 is subjected to vibration alkali cleaning treatment to remove dirt on the surface of the casting, such as dust and oil stains.

[0013] Preferably, the shot material of the shot peening in step three is zirconium oxide with a particle size of 0.3 mm, the angle between the spray gun and the casting surface is 90°, the shot peening coverage is 100% (i.e., the casting surface is completely covered by shot pits after shot peening), and the shot peening is completed on a CNC shot peening machine.

[0014] Preferably, the average mesh size of the sand in step 1 is 100, which can reduce the surface roughness while ensuring the surface strengthening effect.

[0015] Preferably, the shot peening intensity in step three is 0.3 mmN, which can improve the uneven sand blasting caused by manual sand blasting, and can further reduce the surface roughness while improving the surface strengthening uniformity.

[0016] Furthermore, the method further comprises pretreatment, wherein the pretreatment comprises pickling the casting to remove a surface reaction layer before performing the step 1.

[0017] Furthermore, the pretreatment also includes hot isostatic pressing the casting before performing step one to close shrinkage cavities and loose defects.

[0018] Furthermore, the pretreatment further comprises heat treating the casting before performing the step 1 to obtain the α 2 The dual-state structure consists of γ / γ lamellae and equiaxed γ grains.

[0019] Furthermore, the pretreatment also includes protecting the non-reinforced surface of the casting before performing the step 1 to prevent the surface from being damaged by impact of sand and projectiles, thereby causing subsequent assembly problems.

[0020] Compared with the prior art, the present invention can make the fatigue strength of the casting after sandblasting reach the level of the standard smooth sample by reasonably selecting the mesh number of the sandblasting sand and setting the mesh number to 40-120. Then, in step 2, by reasonably selecting the shot peening intensity and setting the intensity to 0.1-0.3 mmN (i.e., the saturation point of the residual compressive stress layer depth measured by the N-type Almen test piece under the selected shot peening process parameters is 0.1-0.3 mm), the fatigue strength of the casting after sandblasting + shot peening can be significantly improved compared with the standard smooth sample. For example, the high-cycle fatigue strength of the Ti-47Al-2Cr-2Nb (at.%) precision casting fatigue specimen can be increased from 360MPa of the standard smooth sample to 400MPa after sandblasting + shot peening. The surface strengthening process disclosed by the present invention is simple, short in process, low in production equipment requirements, and easy to operate. It can be applied to high-temperature rotating parts such as low-pressure turbine blades of aircraft engines and impellers of automobile engines, and has great application and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the structure of the TiAl alloy Ti-47Al-2Cr-2Nb (at.%) casting after hot isostatic pressing and heat treatment according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings.

[0023] Example 1

[0024] The TiAl alloy casting in this embodiment is a precision casting fatigue specimen. Before the surface strengthening treatment, the casting should be pretreated. First, the specimen is pickled to remove the surface reaction layer; then, the specimen is hot isostatically pressed to close the shrinkage cavity and loose defects; third, the specimen is heat treated to obtain the α 2 The dual-state structure consisting of / γ lamellar clusters and equiaxed γ grains, such as Figure 1 shown.

[0025] After the pretreatment is completed, the casting is surface strengthened through the following three steps.

[0026] Step 1: The pretreated precision casting Ti-47Al-2Cr-2Nb (at.%) fatigue specimen is sandblasted. The sand material is silicon carbide, the average mesh size is 100 mesh, the pressure in the spray gun is 0.6MPa, and the sandblasting is done manually on a manual pressurized sandblasting machine.

[0027] Step 2: After step 1, the sample is subjected to vibration alkaline cleaning treatment to remove dirt such as dust and oil on the surface.

[0028] Step 3: Shot peening is performed on the sample after step 2. The material of the shot is zirconium oxide, the average particle size is 0.3 mm, the angle between the spray gun and the casting surface is 90°, the shot peening intensity is 0.1, 0.2 and 0.3 mmN, the shot peening coverage is 100%, and the shot peening treatment is completed on a CNC shot peening machine.

[0029] After completing the above surface strengthening treatment, the sample was subjected to an SN curve test to obtain fatigue strength. The loading method was a sine wave, the stress ratio was 0.1, the frequency was 100 Hz, and the temperature was 700°C.

[0030] Comparative Example 1

[0031] The TiAl alloy casting in this comparative example is a precision casting fatigue specimen. Before the surface strengthening treatment, the casting should be pretreated. First, the specimen is pickled to remove the surface reaction layer; then, the specimen is hot isostatic pressed to close the shrinkage cavity and loose defects; third, the specimen is heat treated to obtain the α 2 The dual-state structure consisting of / γ lamellar clusters and equiaxed γ grains, such as Figure 1 shown.

[0032] After the pretreatment is completed, the casting is surface-hardened only in the next step.

[0033] Step 1: The pretreated precision casting Ti-47Al-2Cr-2Nb (at.%) fatigue specimen is sandblasted. The sand material is silicon carbide, the average mesh size is 60 mesh and 100 mesh, the pressure in the spray gun is 0.6 MPa, and the sandblasting is completed manually on a manual pressurized sandblasting machine.

[0034] After completing the above surface strengthening treatment, the sample was subjected to an SN curve test to obtain fatigue strength. The loading method was a sine wave, the stress ratio was 0.1, the frequency was 100 Hz, and the temperature was 700°C.

[0035] The comparison of high cycle fatigue strength of the surface strengthening example of the precision cast Ti-47Al-2Cr-2Nb (at.%) fatigue specimen in Example 1 and Comparative Example 1 with the standard smooth specimen at 700°C is shown in Table 1.

[0036] Table 1 Comparison of high cycle fatigue strength of samples with different surface strengthening processes

[0037]

[0038] The 700°C high cycle fatigue strength of the Ti-47Al-2Cr-2Nb (at.%) precision casting fatigue specimen treated by the surface strengthening process of Example 1 is substantially stronger than that of the specimen treated by the surface strengthening process of Comparative Example 1 and the standard smooth specimen. Preferably, when Example 1 adopts 100 mesh sandblasting + 0.3 mmN shot peening, the high cycle fatigue strength of the specimen can be increased from 360 MPa of the standard smooth specimen to 400 MPa.

Claims

1. A surface strengthening process for improving the high cycle fatigue performance of TiAl alloy castings, characterized in that: The following steps are involved: Step 1: Sandblast the casting with a mesh size of 40 to 120; Step 2: Remove dirt from the casting surface after step 1; Step 3: Shot peening is performed on the casting after step 2, and the shot peening intensity is 0.1-0.3 mmN.

2. The surface strengthening process according to claim 1, characterized in that: The sand used in the sandblasting process in step 1 is made of silicon carbide, the pressure in the spray gun is 0.6 MPa, and the sandblasting process is performed manually on a manual pressurized sandblasting machine.

3. The surface strengthening process according to claim 2, characterized in that: In the step 2, the casting after the step 1 is subjected to vibration alkali washing treatment to remove dirt on the surface of the casting.

4. The surface strengthening process according to claim 3, characterized in that: The shot material of the shot peening treatment in step three is zirconium oxide, the particle size is 0.3 mm, the angle between the spray gun and the casting surface is 90°, the shot peening coverage is 100%, and the shot peening treatment is completed on a CNC shot peening machine.

5. The surface strengthening process according to claim 4, characterized in that: The average mesh size of the sand in step 1 is 100.

6. The surface strengthening process according to claim 4 or 5, characterized in that: The shot peening intensity of step three is 0.3 mmN.

7. The surface strengthening process according to claim 1, characterized in that: The method further comprises a pretreatment, wherein the pretreatment comprises pickling the casting to remove a surface reaction layer before performing the step 1.

8. The surface strengthening process according to claim 7, characterized in that: The pretreatment also includes hot isostatic pressing the casting to close shrinkage cavities and loose defects before performing step 1.

9. The surface strengthening process according to claim 8, characterized in that: The pretreatment further comprises heat treating the casting before performing the step 1 to obtain a dual-state structure consisting of α2 / γ lamellar clusters and equiaxed γ grains.

10. The surface strengthening process according to claim 9, characterized in that: The pretreatment also includes protecting the non-reinforced surface of the casting before performing the step 1 to prevent the surface from being damaged by the impact of sand and projectiles.

Images