Plasma spraying method for thermal barrier coating of thin-wall special-shaped part and thin-wall special-shaped part

Abstract

The invention discloses a plasma spraying method for a thermal barrier coating of a thin-wall special-shaped part and the thin-wall special-shaped part. The plasma spraying method for the thermal barrier coating of the thin-wall special-shaped part comprises the following steps that S1, the surface of a base body is sequentially subjected to roughening treatment and preheating, and the preheated base body is obtained; s2, nickel-chromium-aluminum-yttrium powder is adopted for preparing a bonding layer on the surface of the preheated base body through plasma spraying; and preparing the ceramic layer on the bonding layer through plasma spraying by taking yttria-stabilized zirconia as a raw material. By optimizing the gun speed, the powder feeding rate, the matrix temperature and other process parameters, the porosity of the prepared thermal barrier coating can be stably controlled to be 8-15%, the bonding strength of the coating and the matrix is larger than or equal to 20 MPa, no separation or crack or other defects exist after a thermal shock test at 800 DEG C is repeated three times, the thermal conductivity is smaller than or equal to 1.2 W / (m.K), and the thermal barrier coating is excellent in heat insulation, binding force and thermal shock resistance.

Description

Technical Field

[0001] This invention belongs to the field of aerospace material surface treatment technology, and particularly relates to a plasma spraying method for thermal barrier coating of thin-walled irregular parts and the thin-walled irregular parts themselves. Background Technology

[0002] With the continuous development of aerospace and other technologies, thin-walled irregular-shaped parts are placing increasingly higher demands on the high-temperature performance of materials, and existing high-temperature alloys are no longer sufficient to meet these requirements. Thermal barrier coatings typically consist of a low-thermal-conductivity, high-insulation ceramic coating and a high-temperature oxidation-resistant metal buffer layer, possessing excellent properties such as resistance to high-temperature oxidation, resistance to thermal fatigue, and low thermal conductivity. Ceramic materials, due to their high melting point, high hardness, heat resistance, wear resistance, corrosion resistance, and chemical stability, have become ideal materials for thermal barrier coatings. Among them, zirconium oxide has become the preferred material for thermal barrier coatings after years of development.

[0003] However, when the coating object is a thin-walled irregular part, there are many problems in preparing zirconia ceramic thermal barrier coatings by plasma spraying: the high-speed impact of sand particles during sandblasting will cause surface roughness and disrupt the stress balance of the substrate; the large temperature difference between the front and back of the substrate during plasma spraying and the rapid heating and cooling of the coating will lead to inconsistent expansion and cooling of the substrate. In addition, subsequent mechanical straightening and other processes will increase the residual stress of the coating and the thin-walled irregular part, resulting in low coating accuracy and severe deformation of the parts, which has become the main bottleneck of this technology.

[0004] In existing technologies, traditional thermal barrier coating spraying techniques suffer from problems such as insufficient coating density, significant burn-off, and poor alloy composition stability when processing thin-walled irregular parts. While thermal blasting can provide some heating, activation, and roughening effects on the surface of thin-walled irregular parts, it is insufficient to reduce the risk of thermal stress caused by large temperature differences in the substrate, and key indicators such as surface quality and adhesion are difficult to meet requirements. Therefore, despite existing technological attempts, further process optimization is needed to address the issues of precision control and deformation management in thermal barrier coatings for thin-walled irregular parts. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a plasma spraying method for thermal barrier coatings on thin-walled irregularly shaped parts and the thin-walled irregularly shaped parts themselves.

[0006] The objective of this invention is achieved through the following technical solution: A plasma spraying method for thermal barrier coating on thin-walled irregularly shaped parts includes the following steps: S1. The surface of the substrate is roughened and preheated in sequence to obtain the preheated substrate; S2. On the preheated substrate surface, a bonding layer is prepared by plasma spraying using nickel-chromium-aluminum-yttrium powder; on the bonding layer, a ceramic layer is prepared by plasma spraying using yttrium-stabilized zirconium oxide as the raw material.

[0007] Preferably, the substrate in step S1 is a TC4 titanium alloy, an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy.

[0008] Preferably, after the roughening treatment in step S1, the surface roughness Ra of the substrate is 3.2~6.3μm.

[0009] Preferably, the preheating in step S1 refers to preheating the substrate temperature to 115~125°C. More preferably, the substrate temperature is preheated to 120°C.

[0010] In this invention, the preheating temperature of the substrate needs to be kept within a suitable range. If the temperature is too low, moisture will be present on the substrate, and the large difference in thermal expansion between the coating and the substrate will cause cracks. If the temperature is too high, the substrate will oxidize and deform thermally, thus affecting the processing accuracy.

[0011] Preferably, the parameters for preparing the adhesive layer by plasma spraying in step S2 include: spraying current of 550~600A, spraying voltage of 72~75V, argon flow rate of 2400~3000L / h, hydrogen flow rate of 62~68L / h, spraying distance of 128~132mm, powder feed rate of 35~50g / min, gun speed of 95~105mm / s, and coating thickness controlled at 0.09±0.05mm.

[0012] Preferably, the parameters for preparing the adhesive layer by plasma spraying in step S2 include: spraying current of 580A, spraying voltage of 73V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feeding rate of 40g / min, and spray gun moving speed of 100mm / s.

[0013] In this invention, the gun speed should be controlled when preparing the adhesive layer to avoid excessively thick local coatings due to excessively slow speeds or uneven coverage due to excessively fast speeds.

[0014] Preferably, the parameters for preparing the ceramic layer by plasma spraying in step S2 include: spraying current of 590~610A, spraying voltage of 67~69V, argon flow rate of 2050~2150L / h, hydrogen flow rate of 65~75L / h, spraying distance of 118~122mm, powder feed rate of 38~42g / min, gun speed of 100~110mm / s, and coating thickness controlled at 0.3±0.05mm.

[0015] In this invention, the current is controlled within a suitable range during the preparation of the ceramic layer. Too low a current will result in insufficient melting of the ceramic powder, while too high a current will cause excessive sintering of the coating. In addition, the substrate temperature needs to be maintained at 115~125℃, controlled by continuous air cooling, to avoid poor bonding between the coating and the adhesive layer due to excessively low temperature, or deformation of thin-walled parts due to excessively high temperature.

[0016] Preferably, the parameters for preparing the ceramic layer by plasma spraying in step S2 include: a spraying current of 600A and a spraying voltage of 68V, which work together to stabilize the power at 40.8kW, ensuring that the yttrium-stabilized zirconia powder is fully melted without excessive oxidation; an argon flow rate of 2100L / h, matching the flame enthalpy with the flow rate, resulting in optimal particle melting state and flight speed; a hydrogen flow rate of 70L / h, which helps to increase the flame temperature and further optimize the melting quality of the ceramic powder; a spraying distance of 120mm, with the particle temperature reaching the substrate at 1500~1600℃ and a velocity of 16... At a speed of 0~180m / s, the coating density and porosity (10~12%) are optimally balanced; with a powder feed rate of 40g / min, the powder melts fully and the deposition efficiency is moderate, and the thickness of a single pass of the ceramic layer is controllable (20~50μm), with no unmelted particles and obvious pores; with a spray gun moving speed of 100mm / s, the coating coverage is uniform, with no local accumulation and low residual stress; with a substrate temperature of 120℃, the thermal expansion coefficients of the coating and the adhesive layer and ceramic layer are optimally matched, resulting in a dense coating interface with no interface cracks and pores, while also preventing deformation of thin-walled irregular parts.

[0017] Preferably, the yttrium-stabilized zirconia in step S2 is 8% yttrium-stabilized zirconia powder. A thin-walled irregular part, the thermal barrier coating of which is prepared by the plasma spraying method described above.

[0018] Compared with the prior art, the beneficial effects of the present invention include: (1) Superior coating performance: By optimizing process parameters such as gun speed, powder feed rate, and substrate temperature, the porosity of the prepared thermal barrier coating can be stably controlled at 8~15%, which meets industry requirements; the bonding strength between the coating and the substrate is ≥20MPa (the actual measured strength can reach more than 35MPa), and there are no defects such as separation or cracks after repeated 3 thermal shock tests at 800℃. The thermal conductivity is ≤1.2W / (m·K), which shows better performance in terms of heat insulation, bonding force and thermal shock resistance.

[0019] (2) Effectively reduce part deformation: In response to the problem that thin-walled irregular parts are prone to deformation due to stress, the coating thickness is controlled by layered spraying, and the substrate preheating temperature and cooling method are optimized. This reduces the part deformation caused by temperature difference and residual stress during the spraying process, and solves the bottleneck of insufficient coating precision and part deformation in traditional processes.

[0020] (3) Higher process stability and controllability: PLC and mass flow meter are used to realize closed-loop control of the spraying process, and key parameters such as plasma current, voltage, gas flow rate and powder feeding rate are monitored in real time to ensure process consistency; at the same time, automatic sandblasting and spraying by robotic arms reduces human operation error, is suitable for mass production, and improves product qualification rate.

[0021] (4) Adapting to the special needs of thin-walled irregular parts: The process is designed specifically for the structural characteristics of thin-walled irregular parts. Through precise sandblasting pretreatment (to ensure uniform surface roughness), shielding protection (to avoid affecting non-coated areas) and parameter optimization, high-precision coatings can be efficiently prepared on the surface of thin-walled irregular parts, breaking through the application limitations of traditional processes on complex shaped parts.

[0022] (5) Better material and process matching: By selecting suitable 8% yttrium-stabilized zirconium oxide powder and nickel-chromium-aluminum yttrium binder material, combined with targeted spraying parameters, the thermal expansion coefficient of the coating and the substrate are better matched, reducing the risk of coating failure due to material property differences and extending the service life of parts. Attached Figure Description

[0023] Figure 1 The images shown are photographs of the coatings after the ceramic layer was sprayed on in Example 2 and Comparative Example 1, where (a) corresponds to Example 2 and (b) corresponds to Comparative Example 1.

[0024] Figure 2 The images show the surface SEM morphology of the ceramic layers prepared in Example 2 and Comparative Example 1, with the left image corresponding to Comparative Example 1 and the right image corresponding to Example 2.

[0025] Figure 3 The images shown are photographs of the coatings after the ceramic layer was sprayed on in Example 2 and Comparative Example 2, where (a) corresponds to Comparative Example 2 and (b) corresponds to Example 2.

[0026] Figure 4 The images show cross-sectional (vertical surface cut) SEM images of the ceramic layers prepared in Example 2 and Comparative Example 2, with the left image being Comparative Example 2 and the right image being Example 2. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Considering that the adhesive layer is a common material and its coating thickness is relatively thin, thus having little impact on thin-walled components, the following embodiments and comparative examples fix the preparation process of the adhesive layer and focus on the ceramic layer, conducting comparative studies by adjusting the preparation parameters of the ceramic layer.

[0029] The preparation process parameters of the adhesive layer described in the examples and comparative examples are statistically shown in Table 1.

[0030] Table 1. Adhesive layer preparation parameters for the examples and comparative examples

[0031] Example 1 A plasma spraying method for thermal barrier coating on thin-walled irregularly shaped parts, the specific steps of which are as follows: S1. The surface of TC4 titanium alloy (100mm×100mm×1mm) is roughened and preheated in sequence to obtain a preheated substrate with a surface roughness Ra=3.2μm. The TC4 titanium alloy is preheated to 120℃. S2. On the preheated substrate surface, a bonding layer is prepared by plasma spraying using nickel-chromium-aluminum-yttrium powder. The parameters for preparing the bonding layer by plasma spraying are: spraying current of 580A, spraying voltage of 73V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, and coating thickness of 0.09mm. On the adhesive layer, a ceramic layer is prepared by plasma spraying using yttrium-stabilized zirconia as raw material. The parameters for preparing the ceramic layer by plasma spraying are as follows: spraying current of 570A, spraying voltage of 73V, argon flow rate of 2650L / h, hydrogen flow rate of 62L / h, spraying distance of 129mm, powder feed rate of 39g / min, spray gun moving speed of 98mm / s, sample temperature of 118℃, and coating thickness of 0.3mm.

[0032] The thin-walled irregular part prepared in Example 1 has an intact overall appearance, and the coating is free from defects such as peeling, flaking, and visible cracks. Its thermal conductivity was measured to be 0.6 W / (m·K) at 200℃. No separation or cracks were found after three repeated thermal shock tests at 800℃. The porosity of the thermal barrier coating is 9.65%, and the bonding strength between the coating and the substrate is 29.2 MPa.

[0033] Example 2 A plasma spraying method for thermal barrier coating on thin-walled irregularly shaped parts, the specific steps of which are as follows: S1. The surface of TC4 titanium alloy (100mm×100mm×1mm) is roughened and preheated in sequence to obtain a preheated substrate with a surface roughness Ra=3.2μm. The TC4 titanium alloy is preheated to 120℃. S2. On the preheated substrate surface, a bonding layer is prepared by plasma spraying using nickel-chromium-aluminum-yttrium powder. The parameters for preparing the bonding layer by plasma spraying are: spraying current of 580A, spraying voltage of 73V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, and coating thickness of 0.09mm. On the adhesive layer, a ceramic layer is prepared by plasma spraying using yttrium-stabilized zirconia as the raw material. The parameters for preparing the ceramic layer by plasma spraying are as follows: spraying current of 585A, spraying voltage of 73.5V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, sample temperature of 120℃, and coating thickness of 0.3mm.

[0034] The thin-walled irregular part prepared in Example 2 has a complete overall appearance, and the coating is free from defects such as peeling, flaking, and visible cracks. Its thermal conductivity was measured to be 0.7 W / (m·K) at 200℃. No separation or cracks were found after three repeated thermal shock tests at 800℃. The porosity of the thermal barrier coating was 8.75%. The bonding strength between the coating and the substrate was 31.6 MPa.

[0035] Example 3 A plasma spraying method for thermal barrier coating on thin-walled irregularly shaped parts, the specific steps of which are as follows: S1. The surface of TC4 titanium alloy (100mm×100mm×1mm) is roughened and preheated in sequence to obtain a preheated substrate with a surface roughness Ra=3.2μm. The TC4 titanium alloy is preheated to 120℃. S2. On the preheated substrate surface, a bonding layer is prepared by plasma spraying using nickel-chromium-aluminum-yttrium powder. The parameters for preparing the bonding layer by plasma spraying are: spraying current of 580A, spraying voltage of 73V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, and coating thickness of 0.09mm. On the adhesive layer, a ceramic layer is prepared by plasma spraying using yttrium-stabilized zirconia as the raw material. The parameters for preparing the ceramic layer by plasma spraying are as follows: spraying current of 590A, spraying voltage of 74V, argon flow rate of 2800L / h, hydrogen flow rate of 68L / h, spraying distance of 131mm, powder feed rate of 41g / min, spray gun moving speed of 103mm / s, sample temperature of 123℃, and coating thickness of 0.3mm.

[0036] The thin-walled irregular part prepared in Example 3 has a complete overall appearance, and the coating is free from defects such as peeling, flaking, and visible cracks. Its thermal conductivity was measured to be 0.7 W / (m·K) at 200℃. No separation or cracks were found after three repeated thermal shock tests at 800℃. The porosity of the thermal barrier coating was 8.13%. The bonding strength between the coating and the substrate was 33.5 MPa.

[0037] Comparative Example 1 A plasma spraying method for thermal barrier coating on thin-walled irregularly shaped parts, the specific steps of which are as follows: S1. The surface of TC4 titanium alloy (100mm×100mm×1mm) is roughened and preheated in sequence to obtain a preheated substrate with a surface roughness Ra=3.2μm. The TC4 titanium alloy is preheated to 120℃. S2. On the preheated substrate surface, a bonding layer is prepared by plasma spraying using nickel-chromium-aluminum-yttrium powder. The parameters for preparing the bonding layer by plasma spraying are: spraying current of 580A, spraying voltage of 73V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, and coating thickness of 0.09mm. On the adhesive layer, a ceramic layer is prepared by plasma spraying using yttrium-stabilized zirconia as the raw material. The parameters for preparing the ceramic layer by plasma spraying are as follows: spraying current of 580A, spraying voltage of 73.5V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 50mm / s, sample temperature of 120℃, and coating thickness of 0.3mm.

[0038] Comparative Example 2 A plasma spraying method for thermal barrier coating on thin-walled irregularly shaped parts, the specific steps of which are as follows: S1. The surface of TC4 titanium alloy (100mm×100mm×1mm) is roughened and preheated in sequence to obtain a preheated substrate with a surface roughness Ra=3.2μm. The TC4 titanium alloy is preheated to 120℃. S2. On the preheated substrate surface, a bonding layer is prepared by plasma spraying using nickel-chromium-aluminum-yttrium powder. The parameters for preparing the bonding layer by plasma spraying are: spraying current of 580A, spraying voltage of 73V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, and coating thickness of 0.09mm. On the adhesive layer, a ceramic layer is prepared by plasma spraying using yttrium-stabilized zirconia as the raw material. The parameters for preparing the ceramic layer by plasma spraying are as follows: spraying current of 580A, spraying voltage of 73.5V, argon flow rate of 2700L / h, hydrogen flow rate of 65L / h, spraying distance of 130mm, powder feed rate of 40g / min, spray gun moving speed of 100mm / s, sample temperature of 90℃, and coating thickness of 0.3mm.

[0039] The preparation process parameters of the ceramic layers described in Examples 1-3 and Comparative Examples 1-2 are statistically shown in Table 2.

[0040] Table 2. Ceramic layer preparation parameters for examples and comparative examples

[0041] Figure 1 The images show photographs of the coatings after the ceramic layer was applied in Example 2 and Comparative Example 1, where (a) corresponds to Example 2 and (b) corresponds to Comparative Example 1. Figure 1 We can see that there are significant differences in the surface color of the ceramic layer prepared at different spray gun moving speeds. In Example 1, the spray gun moving speed was 100 mm / s, and the surface of the prepared ceramic layer was darker, while in Comparative Example 1, the spray gun moving speed was 50 mm / s, and the surface of the prepared ceramic layer was whiter.

[0042] Figure 2 The images show the surface SEM morphology of the ceramic layers prepared in Example 2 and Comparative Example 1, with the left image corresponding to Comparative Example 1 and the right image corresponding to Example 2. Figure 2 As we can observe, the coating surfaces prepared in Example 2 and Comparative Example 1 both exhibit an uneven, undulating morphology. The sprayed coating surface contains fine longitudinal cracks, which may propagate during service, leading to layered peeling. Furthermore, the sprayed coating contains pores, as it is composed of countless small droplets, inevitably resulting in a certain amount of porosity and air pockets. It is worth noting that a suitable amount of porosity helps reduce the thermal conductivity of the coating, thereby improving its thermal insulation performance. Further, it can be seen that when the spray gun speed is 50 mm / s (Comparative Example 1), obvious longitudinal cracks appear in the coating, penetrating the entire ceramic layer and mostly originating from incompletely melted particles. In contrast, when the gun speed is adjusted to 100 mm / s (Example 2), the coating morphology appears more uniform.

[0043] Figure 3 The images show actual photographs of the ceramic coatings after spraying in Example 2 and Comparative Example 2, where (a) corresponds to Comparative Example 2 and (b) corresponds to Example 2. From... Figure 3 We can see that when preparing the ceramic layer, the higher the substrate temperature, the lighter the color of the coating surface, exhibiting a more uniform light yellow hue, indicating that high temperature helps to obtain a denser and finer surface morphology.

[0044] Figure 4 The images show cross-sectional (perpendicularly cut) SEM images of the ceramic layers prepared in Example 2 and Comparative Example 2, where the left image is Comparative Example 2 and the right image is Example 2. Figure 4We can observe that pores, unmelted particles, and microcracks are still visible in the coating. As the substrate preheating temperature increases, the number of pores in the coating increases, and the coating structure becomes increasingly uneven. However, at the interface between the adhesive layer and the ceramic layer, we found that the higher the deposition temperature, the more uniform and fine the structure at the interface, with fewer pores. The structure at the interface is significantly more uniform than that of the upper layer, indicating that the substrate preheating temperature has a significant impact on the coating.

[0045] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method of plasma spraying of thermal barrier coatings on thin-walled profiled parts, characterized in that, The method comprises the following steps: S1, roughening and preheating the surface of the substrate in sequence to obtain a preheated substrate; S2, a bond coat layer is prepared on the surface of the preheated substrate by plasma spraying of a nickel-chromium-aluminum-yttrium powder; and a ceramic layer is prepared on the bond coat layer by plasma spraying using yttria-stabilized zirconia as a raw material.

2. The method of claim 1, wherein the thermal barrier coating is applied to a thin-walled, complex-shaped article. The substrate in step S1 is TC4 titanium alloy, iron-based alloy, nickel-based alloy or cobalt-based alloy.

3. The method of claim 1, wherein the thermal barrier coating is applied to a thin-walled, complex-shaped article. After the roughening in step S1, the roughness Ra of the surface of the substrate is 3.2-6.3 μm.

4. The method of claim 1, wherein the thermal barrier coating is applied to a thin-walled, complex-shaped article. The preheating in step S1 refers to preheating the substrate to a temperature of 115-125 ℃.

5. The method of claim 1, wherein the thermal barrier coating is applied to a thin-walled, complex-shaped article. The parameters for preparing the bond coat layer by plasma spraying in step S2 include: a spraying current of 550-600 A, a spraying voltage of 72-75 V, an argon flow rate of 2400-3000 L / h, a hydrogen flow rate of 62-68 L / h, a spraying distance of 128-132 mm, a powder feeding rate of 35-50 g / min, a gun speed of 95-105 mm / s, and a coating thickness controlled at 0.09±0.05 mm.

6. The method of claim 5, wherein the thermal barrier coating is applied to the thin-walled, complex-shaped article by plasma spraying. The parameters for preparing the bond coat layer by plasma spraying in step S2 include: a spraying current of 580 A, a spraying voltage of 73 V, an argon flow rate of 2700 L / h, a hydrogen flow rate of 65 L / h, a spraying distance of 130 mm, a powder feeding rate of 40 g / min, and a gun speed of 100 mm / s.

7. The method according to claim 1, wherein The parameters for preparing the ceramic layer by plasma spraying in step S2 include: a spraying current of 590-610 A, a spraying voltage of 67-69 V, an argon flow rate of 2050-2150 L / h, a hydrogen flow rate of 65-75 L / h, a spraying distance of 118-122 mm, a powder feeding rate of 38-42 g / min, a gun speed of 100-110 mm / s, and a coating thickness controlled at 0.3±0.05 mm.

8. The method of claim 7, wherein the method further comprises: The parameters for preparing the ceramic layer by plasma spraying in step S2 include: a spraying current of 600 A, a spraying voltage of 68 V, an argon flow rate of 2100 L / h, a hydrogen flow rate of 70 L / h, a spraying distance of 120 mm, a powder feeding rate of 40 g / min, and a gun speed of 100 mm / s.

9. The method according to claim 1, wherein The yttria-stabilized zirconia in step S2 is 8% yttria-stabilized zirconia powder.

10. A thin-walled profiled member, characterized by The thermal barrier coating is prepared by the plasma spraying method according to any one of claims 1-9.

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