Silicon-titanium alloy-containing in-situ silicide / dislocation composite structure strengthening layer and preparation method thereof

Abstract

The invention relates to the technical field of metal surface strengthening, in particular to a silicon-titanium alloy-containing in-situ silicide / dislocation composite structure strengthening layer and a preparation method thereof. The strengthening layer is composed of in-situ precipitated silicide particles, high-density dislocation, fine titanium alloy grains and residual compressive stress, the thickness of the strengthening layer is 100-1000 microns, the size of the in-situ silicide particles is not larger than 2 microns, and the content of the in-situ silicide particles is 0.5%-20%. The preparation method of the strengthened layer comprises the following steps: firstly, carrying out surface deformation strengthening treatment on the silicon-containing titanium alloy to prepare a plastic deformation layer with a large number of dislocations and fine grains; then vacuum heat treatment is carried out, and silicide particles are driven by high temperature to be separated out in situ at dislocation, grain boundary and other positions; and finally, re-introducing dislocation and residual compressive stress through secondary surface deformation strengthening treatment to form an in-situ silicide / dislocation composite structure strengthening layer. According to the strengthening layer, in-situ precipitated silicide particles are used for pinning dislocation, the stability of residual compressive stress is high, and the high-temperature fatigue performance of the titanium alloy can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal surface strengthening, and in particular to a silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer and a preparation method thereof. Background Art

[0002] Silicon-containing titanium alloys have excellent high temperature resistance, creep resistance and corrosion resistance, and are widely used in aerospace, oil and gas production and shipbuilding. Silicon-containing titanium alloys are subjected to alternating loads such as tension, compression, torsion and bending for a long time during service. Fatigue fracture caused by these alternating loads is the main form of failure of silicon-containing titanium alloys, accounting for more than 50% of all failure accidents.

[0003] The main causes of fatigue fracture are the initiation of fatigue cracks caused by cracking of the slip band on the metal surface or the concentration of stress at the surface damage and the extension of cracks from the surface to the inside. At present, the main method to improve the fatigue performance of silicon-containing titanium alloys is surface deformation strengthening, which can introduce dislocations to the alloy surface, transform the alloy surface state into a residual compressive stress state, inhibit the initiation and extension of fatigue cracks, and thus improve fatigue performance. However, during the high-temperature service process of silicon-containing titanium alloys after surface deformation strengthening, the movement of surface dislocations can easily lead to the relaxation of the residual compressive stress in the strengthening layer, weakening the gain effect of fatigue performance, making silicon-containing titanium alloys unable to meet the increasingly high performance requirements.

[0004] Therefore, there is an urgent need to develop a silicon-containing titanium alloy strengthening layer with strong dislocation pinning ability and strong residual compressive stress stability and a preparation method thereof to further improve the high-temperature fatigue performance of the silicon-containing titanium alloy. Summary of the invention

[0005] The purpose of the present invention is to provide a silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer and a preparation method thereof in view of the deficiencies in the prior art, utilizing the strong pinning effect of in-situ precipitated silicide particles on dislocations to inhibit dislocation movement, improve the stability of residual compressive stress in the strengthening layer, and thereby significantly improve the high temperature fatigue performance of the silicon-containing titanium alloy.

[0006] The technical solution of the present invention is as follows:

[0007] A silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer, which consists of in-situ precipitated silicide particles, high-density dislocations, fine titanium alloy grains and residual compressive stress, and the thickness of the strengthening layer is 100-1000μm; the in-situ precipitated silicide particles have a size of no more than 2μm, a content of 0.5%-20%, and a composition of TiZrSi ternary compound; the silicon-containing titanium alloy contains at least 0.2% Si element and 2% Zr element.

[0008] A method for preparing an in-situ silicide / dislocation composite structure strengthening layer of a silicon-containing titanium alloy comprises the following steps:

[0009] Step 1: performing a first surface deformation strengthening treatment on the silicon-containing titanium alloy to form a plastic deformation zone with a large number of dislocations and fine grains within a depth of at least 100 μm in the surface layer;

[0010] Step 2: vacuum heat treatment is performed on the silicon-containing titanium alloy after the surface deformation strengthening treatment, and the high temperature drives the Si element and the Zr element to segregate at positions such as dislocations and grain boundaries, and TiZrSi ternary silicide particles are precipitated in situ;

[0011] Step 3: The silicon-containing titanium alloy after vacuum heat treatment is subjected to a second surface deformation strengthening treatment to reintroduce dislocations and residual compressive stresses on the surface of the titanium alloy. A large number of dislocations gather around the in-situ precipitated silicide particles to form an in-situ silicide / dislocation composite structure strengthening layer.

[0012] The Si atomic fraction in the TiZrSi ternary compound is 20%-50%.

[0013] In step 1 and step 3, the surface deformation strengthening treatment can be carried out by various methods such as shot peening, rolling, extrusion, ultrasonic impact and laser impact.

[0014] In step 2, the vacuum heat treatment process is carried out at 400-800° C. for 1-5 hours.

[0001] Before performing step 1, the titanium alloy is also subjected to machining, cleaning and drying treatments, and after the treatments, the surface roughness of the titanium alloy reaches below Ra0.8.

[0015] The present invention has the following advantages and outstanding effects:

[0016] (1) The present invention utilizes in-situ precipitated silicide particles to strongly pin dislocations, greatly enhancing the stability of the residual compressive stress in the strengthening layer, and can achieve a significant improvement in the high-temperature fatigue performance of silicon-containing titanium alloys. (2) The silicide particles in the present invention are precipitated in-situ during the vacuum heat treatment process, and have a strong interface bonding with the titanium alloy matrix, which is beneficial to the pinning of dislocations. (3) The present invention utilizes two surface deformation strengthening treatments, and the strengthening layer has a larger residual compressive stress and a smaller grain size. (4) The two surface deformation strengthening treatments before and after the present invention can adopt various surface deformation strengthening processes, which are highly applicable and operational. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The invention provides a silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer, wherein: 1-strengthening layer, 2-in-situ precipitated silicide particles, 3-dislocation, 4-titanium alloy grains.

[0018] Figure 2It is the silicon-containing titanium alloy strengthening layer after the first surface deformation strengthening treatment.

[0019] Figure 3 It is a silicon-containing titanium alloy strengthening layer after vacuum heat treatment. DETAILED DESCRIPTION

[0020] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0021] Embodiment 1:

[0022] A Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si-0.06C titanium alloy in-situ silicide / dislocation composite structure strengthening layer, composed of in-situ precipitated silicide particles, high-density dislocations, fine titanium alloy grains and residual compressive stress. The strengthening layer thickness is 800μm, the in-situ precipitated silicide particles are spherical and ellipsoidal with a diameter of 0.2-0.5μm, the structure is (TiZr)5Si3 and (TiZr)6Si3, and the dislocations gather around the silicide to form a composite structure. The preparation method of this strengthening layer is:

[0023] Step 1: The titanium alloy is subjected to surface fine grinding, cleaning and drying treatments. After the treatments, the surface roughness of the titanium alloy reaches Ra0.8.

[0024] Step 2: Laser shock strengthening the treated titanium alloy surface with a laser energy density of 8GW / cm 2 , the overlap rate is 50%, the laser spot diameter is 1.8mm, and the plastic deformation zone composed of a large number of dislocations and fine grains is prepared within the surface depth of 800μm.

[0025] Step 3: The titanium alloy after surface deformation strengthening treatment is subjected to vacuum heat treatment, and the vacuum degree is controlled at 10 -2 Pa, the heat treatment temperature is 500℃, and the holding time is 1h. The high temperature drives the Si and Zr elements to segregate at dislocations and grain boundaries, and spherical and ellipsoidal (TiZr)5Si3 and (TiZr)6Si3 silicide particles of 0.2-0.5μm are precipitated in situ;

[0026] Step 4: The titanium alloy after vacuum heat treatment is subjected to a second laser shock strengthening, with a laser energy density of 10GW / cm 2, overlap rate is 50%, laser spot diameter is 1.8mm, dislocations and residual compressive stress are reintroduced on the titanium alloy surface, a large number of dislocations gather around the in-situ precipitated silicide particles, forming an in-situ silicide / dislocation composite structure strengthening layer. When serving at high temperatures, silicides will strongly pin dislocations, hinder dislocation movement, and thus prevent the relaxation of residual compressive stress introduced by surface deformation strengthening, significantly providing high temperature fatigue performance.

[0027] Embodiment 2:

[0028] A titanium alloy in-situ silicide / dislocation composite structure strengthening layer containing 0.5% Si element and 6% Zr element, which is composed of in-situ precipitated silicide particles, high-density dislocations, fine titanium alloy grains and residual compressive stress. The strengthening layer thickness is 500μm, the in-situ precipitated silicide is spherical, ellipsoidal and rod-shaped particles with a diameter of 0.5-1μm, and the structure is TiZrSi ternary silicide. The preparation method of this strengthening layer is:

[0029] Step 1: The titanium alloy is subjected to surface fine grinding, cleaning and drying treatments. After the treatments, the surface roughness of the titanium alloy reaches below Ra0.8.

[0030] Step 2: Laser shock strengthening the treated titanium alloy surface with a laser energy density of 6 GW / cm 2 , the overlap rate is 40%, the laser spot diameter is 2mm, and the plastic deformation zone composed of a large number of dislocations and fine grains is prepared within the surface depth of 500μm.

[0031] Step 3: The titanium alloy after surface deformation strengthening treatment is subjected to vacuum heat treatment, and the vacuum degree is controlled at 10 -2 Pa, the heat treatment temperature is 600℃, and the holding time is 2h. After heat treatment, silicide is precipitated in situ, the size of silicide is 0.5-1μm, the shape is spherical, ellipsoidal and rod-shaped, and the structure is (TiZr)5Si3 or (TiZr)6Si 3。

[0032] Step 4: Shot peening is performed on the titanium alloy after vacuum heat treatment, with a shot peening intensity of 0.2A, a shot diameter of 2.5 mm, a shot material of cast steel, and a coverage rate of 100%. Dislocations and residual compressive stresses are reintroduced on the surface of the titanium alloy to form an in-situ silicide / dislocation composite structure strengthening layer.

Claims

1. A silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer, characterized in that: The strengthening layer is composed of in-situ precipitated silicide particles, high-density dislocations, fine titanium alloy grains and residual compressive stress, and the thickness of the strengthening layer is 100-1000μm; the size of the in-situ precipitated silicide particles does not exceed 2μm, the content is 0.5%-20%, and the composition is a TiZrSi ternary compound; the silicon-containing titanium alloy contains at least 0.2% Si element and 2% Zr element.

2. A method for preparing an in-situ silicide / dislocation composite structure strengthening layer of a silicon-containing titanium alloy, characterized in that: The following steps are involved: Step 1: performing a first surface deformation strengthening treatment on the silicon-containing titanium alloy to form a plastic deformation zone with a large number of dislocations and fine grains within a depth of at least 100 μm in the surface layer; Step 2: vacuum heat treatment is performed on the silicon-containing titanium alloy after the surface deformation strengthening treatment, and the high temperature drives the Si element and the Zr element to segregate at positions such as dislocations and grain boundaries, and TiZrSi ternary silicide particles are precipitated in situ; Step 3: The silicon-containing titanium alloy after vacuum heat treatment is subjected to a second surface deformation strengthening treatment to reintroduce dislocations and residual compressive stresses on the surface of the titanium alloy. A large number of dislocations gather around the in-situ precipitated silicide particles to form an in-situ silicide / dislocation composite structure strengthening layer.

3. The silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer according to claim 1, characterized in that: The Si atomic fraction in the TiZrSi ternary compound is 20%-50%.

4. The method for preparing a silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer according to claim 2, characterized in that: In step 1 and step 3, the surface deformation strengthening treatment can be carried out by various methods such as shot peening, rolling, extrusion, ultrasonic impact and laser impact.

5. The method for preparing a silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer according to claim 2, characterized in that: In step 2, the vacuum heat treatment process is carried out at 400-800° C. for 1-5 hours.

6. The method for preparing a silicon-containing titanium alloy in-situ silicide / dislocation composite structure strengthening layer according to claim 2, characterized in that: Before performing step 1, the titanium alloy is also subjected to machining, cleaning and drying treatments, and after the treatments, the surface roughness of the titanium alloy reaches below Ra0.8.

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