阅读说明：本技术 一种NbC强化的大厚度纳米晶耐磨涂层及其制备方法 (NbC-reinforced large-thickness nanocrystalline wear-resistant coating and preparation method thereof ) 是由 魏祥 陈志国 杨泽壬 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强化的大厚度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。其制备过程包括选用以渗碳体为强化相的钢铁材料(0.02%≤C wt%≤1.1%)为基体材料,对基体材料进行表面处理,以纯Nb棒和渗碳体为强化相的钢铁材料(0.8%≤C wt%≤6.1%)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。本发明中形成高硬度NbC相的碳元素来自于基体材料和钢铁电极材料,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,大厚度的涂层,而且涂层具有高硬度,优异的耐磨耐性等优点。(The invention discloses an NbC reinforced large-thickness nanocrystalline wear-resistant coating 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 selecting steel material (0.02-1.1 wt% C) with cementite as strengthening phase as base material, performing surface treatment on the base material, and performing electric spark deposition on the surface of the base material by using pure Nb rod and steel material (0.8-6.1 wt% C) with cementite as strengthening phase as electrode material. The carbon element forming the high-hardness NbC phase is from a base material and a steel electrode material, and the nanocrystalline coating is obtained through the extremely fast cooling rate of the electric spark deposition, so that a defect-free coating with large thickness can be formed, and the coating has the advantages of high hardness, excellent wear resistance and the like.)

1. An NbC-reinforced large-thickness nanocrystalline wear-resistant coating is characterized in that: the NbC-reinforced large-thickness nanocrystalline wear-resistant coating 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 large-thickness nanocrystalline wear-resistant coating is generated in situ in the process of electric spark deposition, the mass fraction of the NbC phase is more than 5.2%, and the thickness of the coating is more than or equal to 50 mu m and less than or equal to 250 mu m.

2. The preparation method of the NbC reinforced large-thickness nanocrystalline wear-resistant coating according to claim 1, characterized by preparing the coating by adopting an electric spark deposition process, and comprising the following specific process steps:

(1) carrying out surface treatment on a base material for electric spark deposition, wherein the surface treatment comprises rust removal and oil removal, if cracks exist on the surface, the base material is a steel material which is 0.02 to 1.1 percent of carbon element by mass and takes cementite as a strengthening phase, and the C weight percent is more than or equal to 0.02 percent and less than or equal to 1.1 percent;

(2) adopting a pure Nb rod as an electrode material to carry out electric spark deposition, adopting inert gas to protect 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；

(3) Performing electric spark deposition on the surface of the coating prepared in the previous step by using a steel material with carbon mass percent more than or equal to 0.8% and less than or equal to 6.1% and cementite as a strengthening phase as an electrode material;

(4) adopting pure Nb rod as electrode material to carry out electric spark deposition on the surface of the coating prepared in the previous stepInert 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；

(5) And (4) repeating the steps (3) and (4) in sequence until the coating thickness requirement is met.

3. The method for preparing NbC-reinforced large-thickness nanocrystalline wear-resistant coating according to claim 2, characterized in that: when the NbC phase in the nanocrystalline wear-resistant coating is formed, the carbon element comes from steel matrix materials and electrode materials which take cementite as a strengthening phase.

4. The method for preparing NbC enhanced large-thickness nanocrystalline wear-resistant coating according to claim 3, characterized in that: the mass fraction of carbon element in the steel matrix material taking cementite as the strengthening phase is more than or equal to 0.1 percent and less than or equal to 1.0 percent by weight of C.

Technical Field

The invention relates to a wear-resistant coating and a preparation method thereof, in particular to a large-thickness nanocrystalline wear-resistant coating taking NbC as a strengthening phase 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 comes from a large amount of brittle hard phase, and the electric spark deposition is a fast-solidifying surface treatment technology, so that longitudinal cracks are easily generated in the prepared coating in the electric spark deposition process, the wear resistance of the coating is not favorably improved, and the coating is easy to peel due to the existence of large thermal stress, so that the practical coating thickness is about 50 mu m generally, and the large thickness cannot be obtainedThe wear-resistant coating of (1). 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 hot-work die steel H13 by using Nb bars with better plasticity as electrode materials based on electric spark deposition, and the results show 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 large-thickness nanocrystalline wear-resistant coatings by adopting electric spark deposition.

Disclosure of Invention

The invention aims to provide a large-thickness nanocrystalline wear-resistant coating taking NbC as a strengthening phase and a preparation method thereof.

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

the NbC-reinforced large-thickness nanocrystalline wear-resistant coating 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 large-thickness nanocrystalline wear-resistant coating is generated in situ in the process of electric spark deposition, the mass fraction of the NbC phase is more than 5.2%, and the thickness of the coating is more than or equal to 50 mu m and less than or equal to 250 mu m.

The NbC reinforced large-thickness 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 a steel material (the mass fraction of carbon is more than or equal to 0.02% and less than or equal to Cwt% and less than or equal to 1.1%) which is used for electric spark deposition and takes cementite as a strengthening phase, wherein the surface treatment comprises derusting and deoiling, and if cracks exist on the surface, firstly carrying out row cutting to eliminate a crack layer;

(2) adopting a pure Nb rod as an electrode material to carry out electric spark deposition, adopting inert gas to protect 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。

(3) The coating surface prepared in the previous step is subjected to electric spark deposition by adopting a steel material which contains carbon with the mass fraction of more than or equal to 0.8% and less than or equal to 6.1% and takes a cementite as a strengthening phase as an electrode material.

(4) 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。

(5) And (4) repeating the steps (3) and (4) in sequence until the coating thickness requirement is met.

By adopting the technical scheme, the large-thickness 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, the wear resistance of the coating is greatly improved, 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, and 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 matrix material and the strengthening phase in the steel electrode material are cementite (Fe)₃C) The stability of the material is lower than that of NbC, thereby creating a prerequisite for generating NbC in the process of electric spark depositionConditions; 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 matrix material per se, 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. Most importantly, the alternate deposition of the steel electrode material taking the pure niobium rod as the electrode material and the cementite as the strengthening phase has the beneficial effects that in order to obtain the high-wear-resistant coating with higher NbC content, the matrix material of the coating is not limited to medium and high carbon steel with higher carbon content any more when the coating is prepared, and the application range of the technology is expanded; the alternating deposition enables the coating to obtain large thickness, the nanocrystalline structure is kept, meanwhile, stress can be obviously released, and the large-range regulation and control of the mechanical property and the wear resistance of the coating are realized through the large-range regulation of the steel electrode material components (the mass fraction of carbon is more than or equal to 0.8 percent and less than or equal to 6.1 percent) which take cementite as a strengthening phase.

Detailed Description

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