Gradient Surface Modification Method for Hydrogen Embrittlement-Resistant Thick-Walled Pipes for Hydrogen-Energy Vehicles

Abstract

This invention relates to a gradient surface modification method for hydrogen-resistant thick-walled pipes used in hydrogen-powered vehicles, comprising the following steps: S1: pre-treating the thick-walled metal pipe wall; S2: depositing a bottom layer on the pre-treated pipe wall surface, wherein the bottom layer is a CrN and TiN composite layer; this invention uses a Si3N4 / SiCN composite intermediate layer as the main hydrogen barrier layer, utilizing the extremely low hydrogen diffusion coefficient of Si3N4 and its dense amorphous network structure to effectively block the penetration of hydrogen atoms into the metal matrix. Simultaneously, the DLC surface layer serves as the first line of defense, utilizing its high hardness and low friction coefficient to resist the erosion and wear of high-pressure hydrogen gas flow, extending the service life of the barrier layer.

Description

Technical Field

[0001] This invention relates to the field of hydrogen-resistant pipe technology, and more particularly to a gradient surface modification method for hydrogen-resistant thick-walled pipes used in hydrogen-powered vehicles. Background Technology

[0002] Hydrogen-powered vehicles use high-pressure hydrogen as their power source. Their hydrogen storage and transportation pipelines operate in a high-pressure hydrogen environment for extended periods. When metal pipelines operate in such environments, hydrogen atoms are easily adsorbed onto the material surface and diffuse into the metal lattice, leading to a decrease in material plasticity, a reduction in the crack initiation threshold, and hydrogen embrittlement fracture, which seriously threatens driving safety. Therefore, improving the hydrogen embrittlement resistance of the pipeline inner wall is a key technical challenge that urgently needs to be addressed for the industrialization of hydrogen-powered vehicles. This paper proposes a gradient surface modification method for hydrogen-embrittlement-resistant thick-walled pipelines for hydrogen-powered vehicles to solve this problem. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides the following technical solution: A method for gradient surface modification of thick-walled pipes resistant to hydrogen embrittlement for hydrogen fuel cell vehicles is provided, comprising the following steps: S1: Pre-treatment of the thick-walled metal pipe wall; S2: Deposit a base layer on the pretreated pipe wall surface, wherein the base layer is a CrN and TiN composite layer; S3: Deposit a middle layer on the bottom layer. The middle layer is a Si3N4 and SiCN composite layer. During the deposition process, TiC and NbC composite nanoparticles are introduced by co-sputtering or precursor pyrolysis. The nanoparticles agglomerate at grain boundaries and phase boundaries during growth to form a nanoscale hydrogen trap phase. S4: Deposit a surface layer on the intermediate layer, the surface layer being a diamond-like carbon (DLC) wear-resistant layer, and perform plasma activation on the surface of the intermediate layer before deposition.

[0004] As an improvement to the above technical solution, the deposition of the CrN and TiN composite layer in S2 is carried out by magnetron sputtering, with Cr and Ti targets co-sputtered, and N2 is introduced as the reaction gas, with the atomic ratio of Cr to Ti being 1:0.5~1:2.

[0005] As an improvement to the above technical solution, the total thickness of the CrN and TiN composite underlayer in S2 is 0.5~2μm.

[0006] As an improvement to the above technical solution, in the Si3N4 and SiCN composite layer in S3, the volume ratio of Si3N4 to SiCN is 1:0.3 to 1:1.5, and the total thickness is 1 to 3 μm.

[0007] In the TiC and NbC composite nanoparticles in S3, the mass ratio of TiC to NbC is 1:0.5 to 1:2, the particle size is 5 to 50 nm, and the volume fraction accounts for 1% to 8% of the volume of the middle layer.

[0008] As an improvement to the above technical solution, the co-sputtering method in S3 is as follows: co-sputtering with a Si target using a TiC target and an NbC target, with the sputtering power density of the TiC target being 2~8 W / cm². 2 The sputtering power density of the NbC target is 2~8 W / cm³. 2 .

[0009] As an improvement to the above technical solution, the precursor pyrolysis method in S3 is as follows: the precursor is selected as tetrakis(diethylamino)titanium and penta(dimethylamino)niobium, the carrier gas is Ar, and the pyrolysis temperature is 300~500℃.

[0010] As an improvement to the above technical solution, the conditions for plasma activation in S4 are: Ar ion bombardment, bias voltage -200~-400V, and processing time 3~10 minutes.

[0011] As an improvement to the above technical solution, the chemical reaction conditions for generating SiC in S4 are: introducing CH4 / H2 mixed gas, plasma-enhanced chemical vapor deposition (PECVD), power 200~400W, and deposition time 3~10 minutes.

[0012] As an improvement to the above technical solution, the thickness of the DLC surface layer in S4 is 0.5~1.5μm, and wherein sp 3 The hybrid carbon content is not less than 50%.

[0013] The beneficial effects of this invention are: Using a Si3N4 / SiCN composite middle layer as the main hydrogen barrier layer, the extremely low hydrogen diffusion coefficient and dense amorphous network structure of Si3N4 effectively block the penetration of hydrogen atoms into the metal matrix. Meanwhile, the DLC surface layer serves as the first line of defense, utilizing its high hardness and low coefficient of friction to resist the erosion and wear of high-pressure hydrogen gas flow, thus extending the service life of the barrier layer. To address the issue of a small number of hydrogen atoms penetrating the barrier layer, TiC / NbC composite nanoparticles are introduced into the Si3N4 / SiCN middle layer. These nanoparticles preferentially aggregate at grain boundaries and phase boundaries. The carbon vacancies in the TiC / NbC lattice have a strong chemical affinity for hydrogen atoms, which can chemically adsorb and fix diffused hydrogen atoms to form stable hydrides. The multiple heterogeneous interfaces formed by the TiC and NbC composites provide continuous trapping sites, resulting in a synergistic effect. This prevents hydrogen atoms from reaching and accumulating on the surface of the metal matrix, fundamentally inhibiting the initiation of hydrogen-induced cracks. By anchoring elements through diffusion between the CrN / TiN composite underlayer and the metal substrate, and generating metal silicides through solid-phase reactions of Cr-Si and Ti-Si between the underlayer and the middle layer, a strong chemical bond between the coating and the substrate is achieved, effectively solving the problem of easy peeling of the coating during high-pressure hydrogen cycling and ensuring long-term service stability. A three-layer gradient design is adopted, consisting of a CrN / TiN composite underlayer, a Si3N4 / SiCN composite middle layer, and a DLC surface layer, to gradually alleviate the thermal stress generated during deposition and use, and to avoid coating cracking caused by thermal expansion mismatch. Detailed Implementation

[0014] 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.

[0015] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products.

[0016] To block hydrogen permeation pathways, this invention uses a Si3N4 / SiCN composite middle layer as the primary hydrogen barrier layer. Utilizing the extremely low hydrogen diffusion coefficient and dense amorphous network structure of Si3N4, it effectively prevents hydrogen atoms from penetrating into the metal matrix. Simultaneously, the DLC surface layer serves as the first line of defense, leveraging its high hardness and low coefficient of friction to resist the erosion and wear caused by high-pressure hydrogen gas flow. To address the technical challenges of low interfacial bonding strength and easy cracking and peeling of the coating, a CrN / TiN composite bottom layer is constructed: CrN provides high hardness, and TiN provides good toughness. The two are combined to form a gradient transition layer with a gradient coefficient of thermal expansion, which alleviates the thermal stress between the metal substrate and the ceramic layer and avoids coating cracking caused by thermal expansion mismatch. A Si3N4 / SiCN composite middle layer is constructed: Si3N4 has an extremely low hydrogen diffusion coefficient and serves as the main hydrogen barrier layer. SiCN introduces free carbon to fill the micropores of the Si3N4 network, while improving surface chemical activity and providing bonding sites for the DLC surface layer. The DLC surface layer has high hardness and a low coefficient of friction, resisting the erosion and wear of high-pressure hydrogen gas flow, and serving as the first line of defense. Middle / surface SiC bonding: Plasma activation generates Si dangling bonds on the Si3N4 / SiCN surface, which react with the carbon active groups from CH4 cracking to generate SiC covalent bonds, forming a continuous chemical bond network from the ceramic layer to the DLC, resisting interfacial shear stress under dynamic fatigue loads.

[0017] Bottom / Middle Layer Cr-Si / Ti-Si Bonding: Under high deposition temperature, Cr / Ti reacts with Si in a solid-state reaction to form CrSi2 and TiSi2 metal silicides, achieving chemical bonding between the bottom and middle layers. During growth, TiC / NbC nanoparticles segregate at grain boundaries and phase boundaries. Carbon vacancies in the TiC / NbC lattice have a strong chemical affinity for hydrogen atoms, forming stable hydrides. The composite of TiC and NbC forms multiple heterogeneous interfaces, providing continuous hydrogen trapping sites, while the nanoparticles segregated at grain boundaries block the rapid diffusion channels of hydrogen along the grain boundaries. Hydrogen atoms are sequentially reflected by the DLC surface layer → blocked by the SiC anchoring interface → slowed diffusion in the Si3N4 / SiCN middle layer → and fixed by chemical adsorption in the TiC / NbC trap. Only a very small number of hydrogen atoms reach the metal matrix, which is far below the critical concentration for hydrogen embrittlement, thus achieving long-term protection against hydrogen embrittlement. Example 1

[0018] The thick-walled metal pipe wall is pretreated by sanding to remove surface oxide scale and impurities, ultrasonic cleaning with acetone for 15 minutes, rinsing with deionized water, and vacuum drying (temperature 80℃, time 30 minutes) to ensure that the pipe wall is free of oil, impurities and oxide layer. A base layer (CrN and TiN composite layer) was deposited on the pretreated pipe wall surface using magnetron sputtering. Cr and Ti targets were co-sputtered, and N2 was introduced as the reactant gas. The atomic ratio of Cr to Ti was 1:0.5, and the total thickness of the base layer after deposition was 0.5 μm. A middle layer (a composite layer of Si3N4 and SiCN) was deposited on the bottom layer, with a volume ratio of Si3N4 to SiCN of 1:0.3 and a total thickness of 1 μm. During the deposition process, TiC and NbC composite nanoparticles were introduced by co-sputtering, with a mass ratio of TiC to NbC of 1:0.5, a particle size of 5 nm, and a volume fraction of 1% of the middle layer volume. The co-sputtering parameters were: a sputtering power density of 2 W / cm² on the TiC target. 2 The sputtering power density of the NbC target is 2 W / cm². 2 The power density of the Si target sputtering is adapted and adjusted to ensure uniform growth of the composite layer. The nanoparticles are segregated at the grain boundaries and phase boundaries to form a nanoscale hydrogen trap phase. The intermediate layer surface was plasma activated under the following conditions: Ar ion bombardment, bias voltage -200V, and treatment time of 3 minutes. After activation, a surface layer (diamond-like carbon (DLC) wear-resistant layer) was deposited on the intermediate layer using plasma-enhanced chemical vapor deposition (PECVD). A CH4 / H2 mixed gas was introduced at 200W, and the deposition time was 3 minutes. The thickness of the DLC surface layer was 0.5 μm. 3 The hybrid carbon content is 50%; Example 2

[0019] The thick-walled metal pipe wall is pretreated by sanding to remove surface oxide scale and impurities, ultrasonic cleaning with acetone for 20 minutes, rinsing with deionized water, and vacuum drying (temperature 85℃, time 25 minutes) to ensure that the pipe wall is free of oil, impurities and oxide layer. A base layer (CrN and TiN composite layer) was deposited on the pretreated pipe wall surface using magnetron sputtering. Cr and Ti targets were co-sputtered, and N2 was introduced as the reactant gas. The atomic ratio of Cr to Ti was 1:1, and the total thickness of the base layer after deposition was 1.2 μm. A middle layer (a composite layer of Si3N4 and SiCN) was deposited on the bottom layer, with a volume ratio of Si3N4 to SiCN of 1:0.9 and a total thickness of 2 μm. During the deposition process, TiC and NbC composite nanoparticles were introduced by co-sputtering, with a mass ratio of TiC to NbC of 1:1, a particle size of 25 nm, and a volume fraction of 4.5% of the middle layer volume. The co-sputtering parameters were: a sputtering power density of 5 W / cm² on the TiC target. 2 The sputtering power density of the NbC target is 5 W / cm². 2 The power density of the Si target sputtering is adapted and adjusted to ensure uniform growth of the composite layer. The nanoparticles are segregated at the grain boundaries and phase boundaries to form a nanoscale hydrogen trap phase. The intermediate layer surface was plasma activated under the following conditions: Ar ion bombardment, bias voltage -300V, and treatment time of 6 minutes. After activation, a surface layer (diamond-like carbon (DLC) wear-resistant layer) was deposited on the intermediate layer using plasma-enhanced chemical vapor deposition (PECVD). A CH4 / H2 mixed gas was introduced at 300W, and the deposition time was 6 minutes. The thickness of the DLC surface layer was 1.0 μm. 3 The hybrid carbon content is 65%; Example 3

[0020] The thick-walled metal pipe wall is pretreated by sanding to remove surface oxide scale and impurities, ultrasonic cleaning with acetone for 25 minutes, rinsing with deionized water, and vacuum drying (temperature 90℃, time 20 minutes) to ensure that the pipe wall is free of oil, impurities and oxide layer. A base layer (CrN and TiN composite layer) was deposited on the pretreated pipe wall surface using magnetron sputtering. Cr and Ti targets were co-sputtered, and N2 was introduced as the reaction gas. The atomic ratio of Cr to Ti was 1:2, and the total thickness of the base layer after deposition was 2 μm. A middle layer (Si3N4 and SiCN composite layer) was deposited on the bottom layer, with a Si3N4 to SiCN volume ratio of 1:1.5 and a total thickness of 3 μm. During the deposition process, TiC and NbC composite nanoparticles were introduced by co-sputtering, with a TiC to NbC mass ratio of 1:2, a particle size of 50 nm, and a volume fraction of 8% of the middle layer volume. The co-sputtering parameters were: sputtering power density of 8 W / cm² for the TiC target. 2 The sputtering power density of the NbC target is 8 W / cm³. 2 The power density of the Si target sputtering is adapted and adjusted to ensure uniform growth of the composite layer. The nanoparticles are segregated at the grain boundaries and phase boundaries to form a nanoscale hydrogen trap phase. The intermediate layer surface was plasma activated under the following conditions: Ar ion bombardment, bias voltage -400V, and treatment time of 10 minutes. After activation, a surface layer (diamond-like carbon (DLC) wear-resistant layer) was deposited on the intermediate layer using plasma-enhanced chemical vapor deposition (PECVD). A CH4 / H2 mixed gas was introduced at 400W, and the deposition time was 10 minutes. The thickness of the DLC surface layer was 1.5 μm. 3 The hybrid carbon content is 80%. Example 4

[0021] The thick-walled metal pipe wall is pretreated by sanding to remove surface oxide scale and impurities, ultrasonic cleaning with acetone for 20 minutes, rinsing with deionized water, and vacuum drying (temperature 85℃, time 25 minutes) to ensure that the pipe wall is free of oil, impurities and oxide layer. A base layer (CrN and TiN composite layer) was deposited on the pretreated pipe wall surface using magnetron sputtering. Cr and Ti targets were co-sputtered, and N2 was introduced as the reactant gas. The atomic ratio of Cr to Ti was 1:1.2, and the total thickness of the base layer after deposition was 1.5 μm. A middle layer (Si3N4 and SiCN composite layer) was deposited on the bottom layer, with a volume ratio of Si3N4 to SiCN of 1:0.7 and a total thickness of 1.8 μm. During the deposition process, TiC and NbC composite nanoparticles were introduced by precursor pyrolysis. The precursors were tetrakis(diethylamino)titanium and pentapenta(dimethylamino)niobium, the carrier gas was Ar, and the pyrolysis temperature was 300 °C. The mass ratio of TiC to NbC was 1:0.8, the particle size was 15 nm, and the volume fraction accounted for 3% of the middle layer volume. The nanoparticles agglomerated at grain boundaries and phase boundaries, forming a nanoscale hydrogen trap phase. The intermediate layer surface was plasma activated under the following conditions: Ar ion bombardment, bias voltage -250V, and treatment time of 5 minutes. After activation, a surface layer (diamond-like carbon (DLC) wear-resistant layer) was deposited on the intermediate layer using plasma-enhanced chemical vapor deposition (PECVD). A CH4 / H2 mixed gas was introduced at 250W for a deposition time of 5 minutes. The thickness of the DLC surface layer was 0.8 μm.3 The hybrid carbon content is 55%; Example 5

[0022] The thick-walled metal pipe wall is pretreated by sanding to remove surface oxide scale and impurities, ultrasonic cleaning with acetone for 20 minutes, rinsing with deionized water, and vacuum drying (temperature 85℃, time 25 minutes) to ensure that the pipe wall is free of oil, impurities and oxide layer. A base layer (CrN and TiN composite layer) was deposited on the pretreated pipe wall surface using magnetron sputtering. Cr and Ti targets were co-sputtered, and N2 was introduced as the reaction gas. The atomic ratio of Cr to Ti was 1:1.8, and the total thickness of the base layer after deposition was 1.8 μm.

[0023] A middle layer (Si3N4 and SiCN composite layer) was deposited on the bottom layer, with a volume ratio of Si3N4 to SiCN of 1:1.2 and a total thickness of 2.5 μm. During the deposition process, TiC and NbC composite nanoparticles were introduced by precursor pyrolysis. The precursors were tetrakis(diethylamino)titanium and pentapenta(dimethylamino)niobium, the carrier gas was Ar, and the pyrolysis temperature was 500℃. The mass ratio of TiC to NbC was 1:1.8, the particle size was 40 nm, and the volume fraction accounted for 7% of the middle layer volume. The nanoparticles agglomerated at grain boundaries and phase boundaries, forming a nanoscale hydrogen trap phase. The intermediate layer surface was plasma activated under the following conditions: Ar ion bombardment, bias voltage -350V, and treatment time of 8 minutes. After activation, a surface layer (diamond-like carbon (DLC) wear-resistant layer) was deposited on the intermediate layer using plasma-enhanced chemical vapor deposition (PECVD). A CH4 / H2 mixed gas was introduced at 350W, and the deposition time was 8 minutes. The thickness of the DLC surface layer was 1.2 μm. 3 The hybrid carbon content is 70%; Comparative Example 1 The difference from Example 1 is that: instead of depositing the CrN / TiN composite underlayer, the intermediate layer (Si3N4 / SiCN composite layer) is directly deposited on the pretreated pipe wall surface. Comparative Example 2 The difference from Example 1 is that TiC / NbC composite nanoparticles were not introduced; Comparative Example 3 The difference from Example 1 is that only TiC nanoparticles are introduced (without NbC), that is, a single-component hydrogen trapping phase replaces the TiC / NbC composite hydrogen trapping phase; Comparative Example 4 The difference from Example 1 is that a CrN layer (without TiN composite) is deposited, that is, a single-component bottom layer replaces the CrN / TiN composite bottom layer; Comparative Example 5 The difference from Example 1 is that only a Si3N4 layer is deposited in S3 (without SiCN composite), that is, a single-component intermediate layer replaces the Si3N4 / SiCN composite intermediate layer.

[0024] Performance testing According to GB / T5210-2006 standard, the adhesion test of the sample was carried out using the digital display pull-off tester BGD500, the flexibility tester BGD560 was used for the film flexibility test, and the impact tester BGD304 was used for the film impact test. Full tensile and fatigue tests were conducted at room temperature using a Bairuo PLW-5050kN hydrogen environment electro-hydraulic servo fatigue testing machine. The stress amplitude was set to 500 MPa. The test was started after 24 hours of pre-filling with hydrogen, and the number of cycles at fracture was recorded. The performance of the samples prepared in Example 15 and Comparative Example 15 was tested, and the results are shown in Table 1. Table 1 As shown in Table 1, the adhesion of Examples 1-5 reached 9-12 MPa, the impact strength reached 45-51 kg·cm, the flexibility was 1-1.5 mm, and the hydrogen environment fatigue cycle reached 62450-68500 N. This indicates that through the multi-layer gradient design of CrN / TiN composite bottom layer, Si3N4 / SiCN composite middle layer and TiC / NbC composite nano hydrogen trap phase, combined with the SiC chemical bonding anchoring between the middle layer and the DLC surface layer, a strong chemical bonding interface between the coating and the substrate, and between coatings, was effectively constructed, providing higher interfacial bonding strength and resistance to hydrogen embrittlement fatigue.

[0025] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A gradient surface modification method for hydrogen-resistant thick-walled pipes used in hydrogen-powered vehicles, characterized in that, Includes the following steps: S1: Pre-treatment of the thick-walled metal pipe wall; S2: Deposit a base layer on the pretreated pipe wall surface, wherein the base layer is a CrN and TiN composite layer; S3: Deposit a middle layer on the bottom layer. The middle layer is a Si3N4 and SiCN composite layer. During the deposition process, TiC and NbC composite nanoparticles are introduced by co-sputtering or precursor pyrolysis. The nanoparticles agglomerate at grain boundaries and phase boundaries during growth to form a nanoscale hydrogen trap phase. S4: Deposit a surface layer on the intermediate layer, the surface layer being a diamond-like carbon (DLC) wear-resistant layer, and perform plasma activation on the surface of the intermediate layer before deposition.

2. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 1, characterized in that: The deposition of the CrN and TiN composite layer in S2 is performed by magnetron sputtering, with Cr and Ti targets co-sputtered and N2 introduced as the reaction gas. The atomic ratio of Cr to Ti is 1:0.5 to 1:

2.

3. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 1, characterized in that: The total thickness of the CrN and TiN composite underlayer in S2 is 0.5~2μm.

4. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 2, characterized in that: In the S3 composite layer of Si3N4 and SiCN, the volume ratio of Si3N4 to SiCN is 1:0.3 to 1:1.5, and the total thickness is 1 to 3 μm.

5. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 2, characterized in that: In the TiC and NbC composite nanoparticles in S3, the mass ratio of TiC to NbC is 1:0.5 to 1:2, the particle size is 5 to 50 nm, and the volume fraction accounts for 1% to 8% of the volume of the middle layer.

6. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 2, characterized in that: The S3 co-sputtering method is as follows: co-sputtering with a Si target using a TiC target and an NbC target, with the sputtering power density of the TiC target being 2~8 W / cm³. 2 The sputtering power density of the NbC target is 2~8 W / cm³. 2 .

7. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 2, characterized in that: The precursor pyrolysis method in S3 is as follows: the precursor is selected from tetrakis(diethylamino)titanium and penta(dimethylamino)niobium, the carrier gas is Ar, and the pyrolysis temperature is 300~500℃.

8. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 1, characterized in that: The conditions for plasma activation in S4 are: Ar ion bombardment, bias voltage -200~-400V, and processing time 3~10 minutes.

9. The gradient surface modification method for hydrogen-resistant thick-walled pipes for hydrogen-powered vehicles according to claim 7, characterized in that: The chemical reaction conditions for generating SiC in S4 are as follows: CH4 / H2 mixed gas is introduced, plasma-enhanced chemical vapor deposition (PECVD) is performed, the power is 200~400W, and the deposition time is 3~10 minutes.

10. The method according to claim 1, characterized in that, The thickness of the DLC surface layer in S4 is 0.5~1.5μm, and sp 3 The hybrid carbon content is not less than 50%.

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