Preparation method and application of coating for titanium alloy powder hot isostatic pressing efficient demolding

Abstract

The invention belongs to the technical field of powder metallurgy, and relates to a preparation method and application of a coating for titanium alloy powder hot isostatic pressing efficient demolding. The high-temperature stable coating composed of the yttrium oxide barrier layer and the hexagonal boron nitride surface layer is constructed on the surface of the steel core or the core sleeve, so that the titanium alloy matrix and the steel core or the core sleeve form a comprehensive protection system of chemical isolation, thermal stability protection and physical desorption in the hot isostatic pressing process; interface isolation of the titanium alloy matrix and the steel core or the core sleeve is achieved, metallurgical bonding in the hot isostatic pressing forming process is avoided, the demolding difficulty after forming is reduced on the basis that the surface integrity and size precision of an inner cavity of a titanium alloy workpiece are guaranteed, the machining efficiency and the repeated utilization rate of the steel core or the core sleeve are improved, and the production cost is reduced. Therefore, high-quality forming and high-efficiency demolding of the titanium alloy hot isostatic pressing part with the complex inner cavity structure are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of powder metallurgy, and relates to titanium alloy powder hot isostatic pressing forming and demolding technology, in particular to a coating preparation method for titanium alloy powder hot isostatic pressing efficient demolding and application. BACKGROUND

[0002] When a titanium alloy part with a complex internal cavity or a thin-walled structure is formed by adopting a canning-hot isostatic pressing process, in order to ensure that the part can maintain the required geometric shape under the high-temperature and high-pressure environment of hot isostatic pressing, a steel core or a core sleeve is usually arranged inside the part as a supporting structure to effectively resist the deformation of the external isostatic pressing when it is transmitted to the internal cavity, so that the wall thickness and cavity size of the part can be accurately controlled.

[0003] After the hot isostatic pressing forming is completed, the steel core or the core sleeve must be removed through post-processing to obtain the finally required hollow or complex structure titanium alloy part. The existing steel core or core sleeve removal methods mainly include: 1) mechanical processing / cutting method: the steel core is removed by drilling, wire cutting and the like, but the process is complex, the efficiency is low, and it is difficult to process deep cavities or tortuous channels; 2) chemical corrosion method: the steel core is dissolved by using pickling or electrochemical method, but it is easy to cause the problem of incomplete removal of the internal steel core and surface damage of the titanium alloy part, and the method has high requirements for environmental protection and safety.

[0004] In order to solve the problem, the existing technologies mainly include the following types: 1) using a demolding agent, Chinese patent document (publication number: CN201611042199.X, publication date: May 31, 2017) reduces diffusion and bonding by applying a demolding agent between the canning and the cold-pressed blank; 2) using an inert alloy core, American patent document (publication number: US4575327, publication date: March 11, 1986) reduces the reaction with the titanium matrix by selecting a nickel-based or iron-based high-temperature alloy as the core material.

[0005] However, the demolding agent is used at the interface between the canning and the matrix, and most of the existing demolding agents are single-layer organic and inorganic materials, which have insufficient temperature resistance and are easy to decompose and fail under the high-temperature conditions of hot isostatic pressing, and the single-layer coating has the risk of peeling off, resulting in unstable effect. In addition, although the inert alloy core can improve the demolding property, the alloy core material has a high cost, and element interdiffusion may still occur under the long-term hot isostatic pressing process.

[0006] Therefore, in view of the demolding difficulty of the steel core and the titanium alloy powder hot isostatic pressing forming for the complex internal cavity structure, it is urgent to develop a high-temperature composite coating preparation method for titanium alloy hot isostatic pressing efficient demolding to solve the problems existing in the prior art. SUMMARY

[0007] The present application aims to overcome the above-mentioned shortcomings of the prior art, and provide a coating preparation method for efficient demolding of titanium alloy powder hot isostatic pressing and application.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solutions: In one aspect, the present application provides a coating preparation method for efficient demolding of titanium alloy powder hot isostatic pressing, comprising the following steps: Step 1: pretreating the surface of the steel core or the core sleeve; the pretreatment is specifically: after sandblasting or shot blasting treatment of the surface of the steel core or the core sleeve, a roughened surface is obtained, and the surface impurities are removed by degreasing cleaning; the surface roughness after the sandblasting or shot blasting treatment is 2-5 μm.

[0009] Step 2: preparing a high-temperature stable slurry according to a specific ratio; the high-temperature stable slurry comprises yttrium oxide slurry and hexagonal boron nitride slurry; the yttrium oxide slurry is composed of 50-60 wt% yttrium oxide, 1-2 wt% nitrocellulose, 0.2-0.5 wt% dispersant, and ethanol; the hexagonal boron nitride slurry is composed of 15-25 wt% boron nitride, 1-2 wt% nitrocellulose or acrylic resin, and isopropyl alcohol or ethanol; the dispersant comprises fish oil or polyamide wax.

[0010] Step 3: sequentially applying the yttrium oxide slurry and the hexagonal boron nitride slurry on the surface of the steel core or the core sleeve; when the yttrium oxide slurry is first dip-coated or sprayed, the thickness of a single layer is 20-40 μm, each layer is dried at 60-80 °C for 10-30 min, and the process is repeated until the total thickness is 50-100 μm, then the temperature is kept at 120 °C for 1 h, followed by keeping the temperature at 200-250 °C for 1 h, and finally cooling to room temperature, to form a yttrium oxide barrier layer; then the hexagonal boron nitride slurry is dip-coated or sprayed to a thickness of 5-20 μm, dried at 60-80 °C for 10-30 min, and finally pre-baked at 150-180 °C for 30-60 min, to form a hexagonal boron nitride surface layer, and finally obtain a high-temperature stable coating composed of the yttrium oxide barrier layer and the hexagonal boron nitride surface layer.

[0011] Step 4: sintering the high-temperature stable coating to improve its heat resistance and density; the sintering treatment is specifically: sintering at a temperature of 1000-1200 °C in air or inert atmosphere for 1-2 h.

[0012] In another aspect, the present application provides the application of a steel core or a core sleeve prepared by the coating preparation method for efficient demolding of titanium alloy powder hot isostatic pressing as described above; the steel core or the core sleeve with the coating is assembled into a titanium alloy powder jacket, and after hot isostatic pressing, the steel core or the core sleeve is quickly removed by mechanical means.

[0013] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects: The present application realizes the comprehensive optimization of high-temperature stability, interface isolation and controllable demolding in the high-temperature and high-pressure environment of hot isostatic pressing by constructing the composite coating system of the yttrium oxide barrier layer + hexagonal boron nitride surface layer on the surface of the steel core or the core sleeve.

[0014] The yttrium oxide barrier layer has excellent thermal stability and chemical inertness, can remain structurally intact above 1100 DEG C, can effectively prevent the diffusion of elements such as Fe, Cr and Ni into the titanium alloy, and can inhibit the generation of intermetallic compounds between titanium and the steel core, thereby fundamentally avoiding the interface metallurgical reaction; in addition, the dense structure of the yttrium oxide layer can also maintain good mechanical support at high temperature and high pressure, so as to ensure that the coating as a whole does not peel off or crack. The outer layer of the hexagonal boron nitride surface layer has a layered crystal structure, and the molecules therein are combined by weak van der Waals force, which exhibits extremely low friction coefficient and excellent self-lubricity, can significantly reduce the adhesion between the titanium alloy powder and the surface of the steel core, and form a controllable interface slip layer after hot isostatic pressing and cooling, so that the steel core is easy to separate when mechanically removed. Under the synergistic action of the two kinds of composite coatings, the titanium alloy matrix forms a comprehensive protection system of 'chemical isolation + thermal stability protection + physical detachment' during hot isostatic pressing, which not only significantly improves the demolding efficiency and reduces the difficulty of post-processing, but also ensures the integrity and dimensional accuracy of the inner cavity surface of the titanium alloy part, thereby realizing the high-quality and high-efficiency forming and demolding of the complex inner cavity titanium alloy hot isostatic pressing part, and improving the reuse rate of the steel core or the core sleeve. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which are incorporated into and form part of the specification, are used to explain the principles of the present application together with the specification.

[0016] In order to more clearly illustrate the technical schemes in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows, and obviously, other accompanying drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1 The flowchart of the preparation method of the present application; Figure 2 The schematic diagram of the yttrium oxide barrier layer and the hexagonal boron nitride surface layer on the surface of the steel core or the core sleeve. DETAILED DESCRIPTION

[0018] The exemplary embodiments will be described in detail below with reference to the drawings. The embodiments described in the following exemplary embodiments do not represent all the embodiments consistent with the present application. Rather, they are merely examples consistent with some aspects of the present application as detailed in the appended claims.

[0019] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below in conjunction with the drawings and examples.

[0020] Referring to Figure 1 As shown, the present application provides a coating preparation method for titanium alloy powder hot isostatic pressing efficient demolding, comprising the following steps: Step 1, the surface of the steel core or the core sleeve is pretreated; the pretreatment is specifically: after the surface of the steel core or the core sleeve is treated by sand blasting or shot blasting, a roughened surface is obtained, and the surface impurities are removed by degreasing cleaning; the surface roughness after the sand blasting or shot blasting treatment is 2-5 μm.

[0021] Step 2, prepare a high-temperature stable slurry according to a specific ratio; the high-temperature stable slurry includes yttrium oxide slurry and hexagonal boron nitride slurry; the yttrium oxide slurry is composed of 50-60 wt% yttrium oxide, 1-2 wt% nitrocellulose, 0.2-0.5 wt% dispersant, and ethanol; the hexagonal boron nitride slurry is composed of 15-25 wt% boron nitride, 1-2 wt% nitrocellulose or acrylic resin, and isopropyl alcohol or ethanol; the dispersant includes fish oil or polyamide wax.

[0022] Step 3, apply the yttrium oxide slurry and the hexagonal boron nitride slurry on the surface of the steel core or the core sleeve in sequence; when the yttrium oxide slurry is first dip-coated or sprayed, the thickness of a single layer is 20-40 μm, each layer is dried at 60-80 °C for 10-30 min, and the process is repeated until the total thickness is 50-100 μm, then the temperature is kept at 100-150 °C for 1 h, followed by keeping the temperature at 200-250 °C for 1 h, and finally cooling to room temperature to form a yttrium oxide barrier layer; then the hexagonal boron nitride slurry is dip-coated or sprayed outside the yttrium oxide barrier layer to a thickness of 5-20 μm, dried at 60-80 °C for 10-30 min, and finally pre-baked at 150-180 °C for 30-60 min to form a hexagonal boron nitride surface layer, and finally a high-temperature stable coating composed of a yttrium oxide barrier layer and a hexagonal boron nitride surface layer is obtained.

[0023] Step 4, sintering treatment is performed on the high-temperature stable coating to improve its heat resistance and density; the sintering treatment is specifically: sintering temperature 1000-1200 °C, sintering time 1-2 h in air or inert atmosphere.

[0024] In order to prove the effect of the present application, the following examples are provided for verification: Example 1 The embodiment provides a coating preparation method for efficient demolding of titanium alloy powder hot isostatic pressing, and the specific steps are as follows: Step 1: substrate treatment: the surface of the Q235 steel core is subjected to sand blasting treatment to obtain a surface with a roughness of 2-5 μm, and the surface impurities are removed through degreasing and cleaning; Step 2: coating preparation: mixing 60wt% yttrium oxide, 2wt% nitrocellulose, 0.5wt% polyamide wax and ethanol solvent to prepare yttrium oxide slurry; mixing 25wt% boron nitride, 1wt% nitrocellulose and ethanol to prepare hexagonal boron nitride slurry; Step 3: drying and curing: first, spray the yttrium oxide slurry, the single-layer thickness is 30 μm, dry at 80°C for 20 min, repeat until the total thickness is 60 μm, and then heat at 120°C for 1 h, then heat at 250°C for 1 h for step-by-step pre-baking, and finally cool to room temperature to prepare the yttrium oxide barrier layer; then spray the hexagonal boron nitride slurry, the spraying thickness is 10 μm, dry at 80°C for 30 min, and finally pre-bake at 180°C for 40 min to prepare the hexagonal boron nitride surface layer, and finally obtain the high-temperature stable coating composed of the yttrium oxide barrier layer and the hexagonal boron nitride surface layer; Step 4: sintering treatment: the high-temperature stable coating is subjected to sintering treatment to improve its heat resistance and density; the sintering treatment is as follows: in air or inert atmosphere, sintering temperature is 1200°C, sintering time is 1 h; the prepared coating structure is as shown in Figure 2 ; Step 5: titanium alloy powder hot isostatic pressing forming application: the treated Q235 steel core is loaded into a TC4 titanium alloy powder jacket, and subjected to HIP treatment at a temperature of 920°C, a pressure of 120 MPa and a holding time of 2 h; after the hot isostatic pressing forming is completed, there is no metallurgical bonding between the Q235 steel core and the titanium alloy, and the rapid demolding can be realized through mechanical knocking.

[0025] Example 2 The embodiment provides a coating preparation method for efficient demolding of titanium alloy powder hot isostatic pressing, and the specific steps are as follows: Step 1: substrate treatment: the surface of the Q235 steel core is subjected to sand blasting treatment to obtain a surface with a roughness of 2-5 μm, and the surface impurities are removed through degreasing and cleaning; Step 2: coating preparation: mixing 60wt% yttrium oxide, 2wt% nitrocellulose, 0.5wt% polyamide wax and ethanol solvent to prepare yttrium oxide slurry; mixing 25wt% boron nitride, 1wt% nitrocellulose and ethanol to prepare hexagonal boron nitride slurry; Step 3 drying and curing: when first spraying yttrium oxide slurry, the single layer thickness is 25 μm, drying at 60 °C for 30 min, repeating until the total thickness is 100 μm, pre-baking at 150 °C for 1 h, then pre-baking at 200 °C for 1 h, and finally cooling to room temperature, to prepare a yttrium oxide barrier layer; when spraying hexagonal boron nitride slurry, the spraying thickness is 5 μm, drying at 60 °C for 10 min, and finally pre-baking at 150 °C for 50 min, to prepare a hexagonal boron nitride surface layer, to finally obtain a high-temperature stable coating composed of a yttrium oxide barrier layer and a hexagonal boron nitride surface layer; Step 4 sintering treatment: the high-temperature stable coating is subjected to sintering treatment to improve its heat resistance and density; the sintering treatment is specifically: sintering temperature 1000 °C, sintering time 2 h in air or inert atmosphere; the prepared coating structure is as shown in Figure 2 ; Step 5 titanium alloy hot powder isostatic pressing application: the treated 45# steel core is sleeved into a TA15 titanium alloy powder bag, and subjected to HIP treatment at a temperature of 920 °C, a pressure of 120 MPa, and a holding time of 2 h; after the hot isostatic pressing is completed, there is no metallurgical bonding between the 45# steel core and the titanium alloy, and the 45# steel core can be quickly demolded by mechanical knocking.

[0026] Example 3 The embodiment provides a coating preparation method for titanium alloy powder hot isostatic pressing efficient demolding, and the specific steps are as follows: Step 1 substrate treatment: the surface of a 20# steel made steel core is subjected to sand blasting treatment to obtain a surface with a roughness of 2-5 μm, and the surface impurities are removed through degreasing cleaning; Step 2 coating preparation: yttrium oxide slurry is prepared by mixing 55 wt% yttrium oxide, 1.5 wt% nitrocellulose, 0.3 wt% fish oil and ethanol solvent; hexagonal boron nitride slurry is prepared by mixing 15 wt% boron nitride, 1.5 wt% acrylic resin and ethanol; Step 3 drying and curing: when first spraying yttrium oxide slurry, the single layer thickness is 25 μm, drying at 60 °C for 30 min, repeating until the total thickness is 100 μm, pre-baking at 150 °C for 1 h, then pre-baking at 200 °C for 1 h, and finally cooling to room temperature, to prepare a yttrium oxide barrier layer; when spraying hexagonal boron nitride slurry, the spraying thickness is 5 μm, drying at 60 °C for 10 min, and finally pre-baking at 150 °C for 50 min, to prepare a hexagonal boron nitride surface layer, to finally obtain a high-temperature stable coating composed of a yttrium oxide barrier layer and a hexagonal boron nitride surface layer; Step 4 sintering treatment: the high-temperature stable coating is subjected to sintering treatment to improve its heat resistance and density; the sintering treatment is specifically: sintering temperature 1000 °C, sintering time 2 h in air or inert atmosphere; the prepared coating structure is as shown in Figure 2 ; Step 5 titanium alloy powder hot isostatic pressing forming application: the treated steel core is loaded into a Ti650 alloy powder jacket, and HIP treatment is carried out at a temperature of 950℃, a pressure of 120MPa, and a holding time of 2h; after the hot isostatic pressing forming is completed, there is no metallurgical bonding between the steel core and the titanium alloy, and rapid demolding can be achieved by mechanical knocking.

[0027] From Examples 1-3, it can be seen that the coating preparation method realizes effective isolation and demolding control of the steel core or core sleeve-titanium alloy interface in the titanium alloy powder hot isostatic pressing process through the synergistic effect of the yttrium oxide barrier layer and the hexagonal boron nitride surface layer. The yttrium oxide barrier layer has excellent thermochemical stability and density at high temperature and high pressure, forms a stable physical bond with the steel matrix, and at the same time, builds a high-melting-point inert barrier layer at the interface, which can significantly inhibit the diffusion of elements such as Fe, Cr, and Ni into the titanium alloy matrix, prevent the formation of intermetallic compounds such as Ti x Fe y , and maintain the chemical inertness of the interface; the hexagonal boron nitride surface layer is characterized by its layered crystal structure, weak interlayer bonding force, and low shear force, and exhibits excellent high-temperature lubrication and anti-adhesion properties. During hot isostatic pressing, the hexagonal boron nitride surface layer can form a stable low-friction interface film, reducing the adhesion tendency of titanium alloy powder to the steel core or core sleeve surface; at the same time, during the cooling stage, the micro-gaps caused by the difference in thermal expansion coefficient of the interface further weaken the interface bonding force, creating conditions for subsequent mechanical separation. The two coatings form a "inner chemical barrier + outer physical isolation" dual protection system, which can simultaneously prevent element diffusion, avoid metallurgical bonding, and resist high-temperature bonding during hot isostatic pressing forming, realizing the unity of high-temperature stability, low reactivity, and high demolding efficiency.

[0028] The above description is merely a specific implementation of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these examples will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application.

[0029] It should be understood that the present application is not limited to the above-described and that various modifications and changes can be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A coating preparation method for efficient demolding of titanium alloy powder hot isostatic pressing, characterized in that, The method comprises the following steps: Step 1, pretreating the surface of the steel core or the core sleeve; Step 2, preparing a high-temperature stable slurry according to a specific ratio; Step 3, uniformly applying the high-temperature stable slurry on the surface of the steel core or the core sleeve, and pre-drying and shaping after constant temperature drying to form a high-temperature stable coating; Step 4, sintering the high-temperature stable coating to improve its heat resistance and compactness.

2. The coating production method according to claim 1, characterized in that In step 1, the pretreatment specifically comprises: after sandblasting or shot blasting treatment on the surface of the steel core or the core sleeve, removing surface impurities through degreasing cleaning; the surface roughness after the sandblasting or shot blasting treatment is 2-5 μm.

3. The coating production method according to claim 1, characterized in that In step 2, the high-temperature stable slurry comprises yttrium oxide slurry and hexagonal boron nitride slurry.

4. The coating production method according to claim 3, characterized in that In step 2, the yttrium oxide slurry is composed of 50-60 wt% yttrium oxide, 1-2 wt% nitrocellulose, 0.2-0.5 wt% dispersant, and ethanol; the hexagonal boron nitride slurry is composed of 15-25 wt% boron nitride, 1-2 wt% nitrocellulose or acrylic resin, and isopropyl alcohol or ethanol.

5. The coating production method according to claim 4, characterized in that The dispersant comprises fish oil or polyamide wax.

6. The coating production method according to claim 3, characterized in that In step 3, the yttrium oxide slurry and the hexagonal boron nitride slurry are applied on the surface of the steel core or the core sleeve in sequence.

7. The coating production method according to claim 6, characterized in that When the yttrium oxide slurry is dip-coated or sprayed, the thickness of a single layer is 20-40 μm, each layer is dried at 60-80 °C for 10-30 min, and the process is repeated until the total thickness is 50-100 μm, then the coating is kept at 120 °C for 1 h, then at 200-250 °C for 1 h, and finally cooled to room temperature.

8. The coating production method according to claim 6, characterized in that When the hexagonal boron nitride slurry is dip-coated or sprayed to a thickness of 5-20 μm, it is dried at 60-80 °C for 10-30 min, and finally pre-baked at 150-180 °C for 30-60 min.

9. The coating production method according to claim 1, characterized in that In step 4, the sintering treatment specifically comprises: sintering at a temperature of 1000-1200 °C in air or inert atmosphere for 1-2 h.

10. Use of the steel core or the core sheath prepared according to the method for preparing a coating for efficient demolding of titanium alloy powder hot isostatic pressing according to any one of claims 1-9, characterized in that, The steel core or the core sleeve with the coating is assembled into a titanium alloy powder sleeve, and after hot isostatic pressing, the steel core or the core sleeve is quickly removed by mechanical means.

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