阅读说明：本技术 一种NbC强化具有硬度梯度的纳米晶耐磨涂层及其制备方法 (NbC-reinforced nanocrystalline wear-resistant coating with hardness gradient and preparation method thereof ) 是由 魏祥 杨泽壬 陈志国 郝鹏磊 于 2020-08-10 设计创作，主要内容包括：本发明公开了一种NbC强化具有硬度梯度的纳米晶耐磨涂层及其制备方法,属于耐磨涂层领域。本发明中所述涂层包含NbC相和Nb在Fe中的固溶体相,并且这两种物相的晶粒尺寸都是纳米级的。其制备过程包括对合金模具钢基体进行表面处理,以纯Nb棒和以渗碳体为强化相的钢铁材料为电极材料,采用电火花沉积在基体材料表面进行交替沉积,并通过钢铁电极材料的成分和沉积工艺参数的控制实现具有硬度梯度的纳米晶耐磨涂层的制备。本发明中形成高硬度NbC相的碳元素来自于钢铁电极材料,并且通过电火花沉积极快的冷却速率获得了纳米晶涂层,不但能形成无缺陷,具有硬度梯度的大厚度涂层,而且涂层具有优异的耐磨耐性等优点。(The invention discloses an NbC reinforced nanocrystalline wear-resistant coating with a hardness gradient and a preparation method thereof, belonging to the field of wear-resistant coatings. The coating of the present invention comprises a NbC phase and a solid solution phase of Nb in Fe, and the grain size of both phases is on the order of nanometers. The preparation process comprises the steps of carrying out surface treatment on an alloy die steel substrate, taking a pure Nb rod and a steel material taking a cementite as a strengthening phase as electrode materials, carrying out alternate deposition on the surface of the substrate material by adopting electric spark deposition, and realizing the preparation of the nanocrystalline wear-resistant coating with the hardness gradient by controlling the components of the steel electrode material and the deposition process parameters. The carbon element forming the high-hardness NbC phase comes from a steel electrode material, and the nanocrystalline coating is obtained at a very high cooling rate through electric spark deposition, so that a large-thickness coating without defects and with hardness gradient can be formed, and the coating has the advantages of excellent wear resistance and the like.)

1. An NbC reinforced nanocrystalline wear-resistant coating with a hardness gradient is characterized in that: the NbC-reinforced nanocrystalline wear-resistant coating with the hardness gradient comprises an NbC phase and a solid solution phase of Nb in Fe, the grain sizes of the two phases are nano-scale, the NbC phase in the nanocrystalline coating is generated in situ in the process of electric spark deposition, the mass fraction of the NbC phase is more than 4.1%, and the hardness gradient of the nanocrystalline coating means that the hardness of the coating is gradually reduced from the surface of the nanocrystalline coating to a workpiece.

2. The preparation method of the NbC reinforced nanocrystalline wear-resistant coating with the hardness gradient according to claim 1, is characterized in that the coating is prepared by adopting an electric spark deposition process, and the specific process steps are as follows:

(1) carrying out surface treatment on the alloy die steel matrix material for electric spark deposition, wherein the surface treatment comprises derusting and deoiling, and if the surface has cracks, carrying out lathe cutting to eliminate a crack layer;

(2) the mass fraction of carbon is more than or equal to 0.3 percent and less than or equal to 0.6 percent, and cementite is usedIn order to carry out electric spark deposition on the surface of alloy die steel by taking a steel material of a strengthening phase as an electrode material, inert gas is adopted for protection in the deposition process, and the specific process parameters of the deposition are as follows: the output power is 1500-3000W, the output voltage is 200-300V, and the deposition rate is 5-10min/cm²；

(3) Adopting a pure Nb rod as an electrode material to carry out electric spark deposition on the surface of the coating prepared in the step (2), wherein inert gas is adopted for protection in the deposition process, and the specific process parameters of the deposition are as follows: the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm²；

(4) The method comprises the following steps of adopting a steel material with carbon mass percent more than or equal to 0.6% and less than or equal to 6.1%, taking cementite as a strengthening phase as an electrode material, carrying out electric spark deposition on the surface of a coating prepared in the previous step, and adopting inert gas for protection in the deposition process, wherein the specific process parameters of the deposition are as follows: the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm²；

(5) Adopting a pure Nb rod as an electrode material to carry out electric spark deposition on the surface of the coating prepared in the previous step, wherein inert gas is adopted for protection in the deposition process, and the specific process parameters of the deposition are as follows: the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm²；

(6) And (4) sequentially repeating the steps (4) and (5) to enable the thickness of the coating to be more than or equal to 15 microns and less than or equal to 100 microns.

3. The method of claim 2, wherein the NbC-reinforced nanocrystalline wear-resistant coating with a hardness gradient comprises: the carbon element of the NbC phase in the nanocrystalline wear-resistant coating comes from a steel electrode material taking cementite as a strengthening phase when the NbC phase is formed.

4. The method of claim 2, wherein the NbC-reinforced nanocrystalline wear-resistant coating with a hardness gradient comprises: the carbon content of the steel electrode material using cementite as a reinforcing phase used in the step (4) gradually increases with the increase of the thickness of the coating layer, each increase being in the range of 0.1% to C wt% to 3.3%.

5. The method of claim 2, wherein the NbC-reinforced nanocrystalline wear-resistant coating with a hardness gradient comprises: the output power and output voltage used in step (5) are constant or gradually decreased as the thickness of the coating increases.

6. The method of claim 2, wherein the NbC-reinforced nanocrystalline wear-resistant coating with a hardness gradient comprises: the deposition rate used in step (5) becomes progressively greater as the thickness of the coating increases.

Technical Field

The invention relates to a wear-resistant coating and a preparation method thereof, in particular to a NbC-reinforced nanocrystalline wear-resistant coating with a hardness gradient and a preparation method thereof.

Background

The surface engineering technology can prepare a coating or a cladding with special performances of wear resistance, corrosion resistance and the like on the surface of the material, which are different from those of a base material, and can change the form, chemical components and tissue structure of the surface and the near-surface area of the material by the most economical and effective method, thereby realizing the strengthening, modification, repair and remanufacture of the surface of the material. The technology is widely applied in practice and creates great economic benefits.

The spark deposition process is a surface treatment technique which utilizes spark discharge to melt and transfer electrode materials to the surface of a base material so as to form a coating with specific properties. The deposition principle is that when the electrode material as the anode is infinitely close to the base material (workpiece) as the cathode in a rotating or vibrating mode, short-period and high-current electric pulse discharge is utilized to generate high temperature of 5000-10000 ℃ to instantly melt or even gasify a tiny area infinitely close to the electrode material and the base material, and under the action of electric field force, the melted electrode material is transferred to the surface of the base material to be melted and rapidly solidified with the melted electrode material, so that a deposition layer in metallurgical combination is formed. Compared with other surface technologies, the electric spark deposition process has the following advantages: (1) the energy input is low, the matrix is kept at room temperature, and the heat affected zone is small, so that the influence of the matrix can be ignored; (2) the coating and the matrix are in metallurgical bonding, and the bonding strength is high and is obviously superior to that of thermal spraying; (4) the equipment is cheap and the operation is simple; (5) the method is suitable for in-situ or online repair, and is very important for repairing large workpieces or online equipment; (6) the molten electrode material can be rapidly solidified on the surface of the base material, and can form a nanocrystalline or even amorphous coating, so that the performance of the material is further improved. However, in the actual production of the wear-resistant coating prepared by the electric spark deposition, in order to obtain excellent wear-resistant performance, the electrode material used by the coating is generally high-hardness cemented carbide or cermet. Although such coatings have better wear resistance and are used in many applications, they also have some disadvantages. The high hardness of the high hardness cemented carbide or cermet results from its large amount of brittle hard phases, and spark deposition is a fast-setting surface treatment technique, and therefore, during spark depositionIn the prepared coating, longitudinal cracks are easy to generate, the wear resistance of the coating is not improved, and the coating is easy to peel off due to the existence of large thermal stress, so that the practical coating thickness is about 50 mu m generally, and the wear-resistant coating with large thickness cannot be obtained. In order to obtain a larger coating thickness and avoid the generation of cracks in the coating, recently, Koelreuteria paniculata et al reported the work of preparing Nb coating on the surface of alloy die steel H13 steel by taking Nb bar with better plasticity as electrode material based on electric spark deposition, and the result shows that the coating has continuous and compact cross-section structure, no obvious defects and contains Fe₂Nb and Fe_0.2Nb_0.8The hardness of the two phases reaches 642HV, which is 3.2 times of that of the matrix, and under the same friction and wear test conditions, the wear quality is only 1/3 of the matrix material, so that the service life of the H13 steel die is remarkably prolonged (Koelreuteria, et al. H13 steel surface spark deposition Nb coating organization and performance research, surface technology, 2019,48 (1): 285-289.). NbC has a ratio of Fe₂Nb and Fe_0.2Nb_0.8The two phases have much higher hardness and have been widely used in the fields of high temperature alloys (patent No.: CN 108467959B), cermets (patent No.: CN 105779951A), thin film materials (patent No.: CN 103894757A) and coatings (patent No.: CN103526198A, CN 103255414A). However, no published report is found on the research of preparing NbC reinforced nanocrystalline wear-resistant coating with hardness gradient on the surface of alloy die steel by adopting electric spark deposition.

Disclosure of Invention

The invention aims to provide an NbC reinforced nanocrystalline wear-resistant coating with a hardness gradient and a preparation method thereof.

In order to achieve the above purpose, the invention adopts the following technical scheme:

the NbC-reinforced nanocrystalline wear-resistant coating with the hardness gradient comprises a NbC phase and a solid solution phase of Nb in Fe, the grain sizes of the two phases are nano-scale, the NbC phase in the nanocrystalline coating is generated in situ in the process of electric spark deposition, the mass fraction of the NbC phase is more than 4.1%, the hardness gradient of the nanocrystalline coating means that the hardness of the coating is gradually reduced from the surface of the nanocrystalline coating to a workpiece, and the thickness of the coating is more than or equal to 15 mu m and less than or equal to 100 mu m.

The NbC reinforced nanocrystalline wear-resistant coating is prepared by adopting an electric spark deposition process, and the specific process steps are as follows:

(1) carrying out surface treatment on the alloy die steel matrix material for electric spark deposition, wherein the surface treatment comprises derusting and deoiling, and if the surface has cracks, carrying out lathe cutting to eliminate a crack layer;

(2) the method comprises the following steps of adopting a carbon mass fraction of more than or equal to 0.3% and less than or equal to 0.6%, adopting a steel material with cementite as a strengthening phase as an electrode material to carry out electric spark deposition on the surface of alloy die steel, adopting inert gas to protect in the deposition process, wherein the specific process parameters of the deposition are as follows: the output power is 1500-3000W, the output voltage is 200-300V, and the deposition rate is 5-10min/cm²。

(3) Adopting a pure Nb rod as an electrode material to carry out electric spark deposition on the surface of the coating prepared in the step (2), wherein inert gas is adopted for protection in the deposition process, and the specific process parameters of the deposition are as follows: the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm²。

(4) The method comprises the following steps of adopting a steel material with carbon mass percent more than or equal to 0.6% and less than or equal to 6.1%, taking cementite as a strengthening phase as an electrode material, carrying out electric spark deposition on the surface of a coating prepared in the previous step, and adopting inert gas for protection in the deposition process, wherein the specific process parameters of the deposition are as follows: the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm²。

(5) Adopting a pure Nb rod as an electrode material to carry out electric spark deposition on the surface of the coating prepared in the previous step, wherein inert gas is adopted for protection in the deposition process, and the specific process parameters of the deposition are as follows: the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm²。

(6) And (4) sequentially repeating the steps (4) and (5) to enable the thickness of the coating to be more than or equal to 15 microns and less than or equal to 100 microns.

Wherein, along with the increase of the thickness of the coating, the carbon content of the steel electrode material which takes cementite as a strengthening phase and is used in the step (4) is gradually increased, and the range of each increase to the previous increase is between 0.1 and 3.3 percent; the output power and the output voltage used in the step (5) are constant or gradually decreased, and the deposition rate is gradually increased.

By adopting the technical scheme, the nanocrystalline wear-resistant coating taking NbC as a strengthening phase and the preparation method thereof have the advantages that the prepared coating takes high-hardness NbC as the strengthening phase, so that the wear resistance of the coating is greatly improved, and the crystal grains of the prepared coating are in a nanometer level due to the extremely high cooling rate in the electric spark deposition process, so that the hardness and the wear resistance of the coating are further improved through a fine-grain strengthening mechanism; the plasticity and toughness of the coating are improved through fine grain strengthening, and the coating can release a large amount of thermal stress through plastic deformation in the rapid solidification process through the combined action of the coating and the solid solution phase of Nb with good plasticity in Fe in the coating, so that the generation of longitudinal cracks in the coating is effectively avoided, and the increase of the thickness of the coating is facilitated; the strengthening phase in the electrode material is cementite (Fe)₃C) The stability of the material is lower than that of NbC, so that a prerequisite is created for generating NbC in the process of electric spark deposition; in the preparation of the coating containing the NbC phase reported in the literature, the carbon element in the NbC is externally added, for example, in the form of graphite, and the carbon element is difficult to be uniformly distributed in the coating under the process condition, and the C element in the NbC comes from the electrode material, so that the problem is avoided; the high-hardness NbC phase in the NbC reinforced nanocrystalline wear-resistant coating is generated in situ, so that the interface bonding strength of the NbC phase and the solid solution phase of Nb in Fe is high, and the improvement of the comprehensive mechanical property and the wear resistance of the coating is facilitated. In the invention, the steel material taking cementite as a strengthening phase is deposited on the surface of the alloy die steel through electric spark deposition, so that conditions are created for forming the nanocrystalline wear-resistant coating taking NbC as the strengthening phase subsequently, the matrix material is not limited to the steel material taking cementite as the strengthening phase any more, and the invention expands the application range of the matrix materialThe application range of the technology. On the other hand, by the alternate deposition of the electrode material which is the pure niobium rod and the electrode material which is the steel material which takes the cementite as the strengthening phase, the beneficial effects are that the alternate deposition enables the coating to obtain large thickness, and the stress can be obviously released while the nanocrystalline structure is maintained; moreover, the method can be used for preparing the electrode material of the iron and steel by the components (the mass fraction of carbon is more than or equal to 0.3 percent and less than or equal to 6.1 percent) and the deposition process parameters (the output power is 500-3000W, the output voltage is 100-300V, and the deposition rate is 0.5-10min/cm². ) The control of the method realizes the preparation of the nanocrystalline wear-resistant coating with the hardness gradient, and further improves the wear resistance of the coating.

Detailed Description

The present invention will be further described with reference to the following examples.