A method for self-driven entry of hard nanoparticles into a steel substrate under all-solid-state

Abstract

The application provides a method for hard nano-particles to enter a steel base from below in a full solid state, and relates to the technical field of particle reinforced metal materials, wherein a dispersion suspension of hard nano-particles with a carbon base or a carbon-coated surface is used as a polishing agent to polish the surface of a steel base, and then the steel base is heated to a temperature below the melting point of the steel base under vacuum or inert gas protection, so that the hard nano-particles move and uniformly disperse into the steel base from the surface of the steel base without any mechanical external force. The method can make the hard nano-particles enter the steel base from the surface of the base metal at a temperature far below the melting point of the steel base without any mechanical external force, and the dispersion is good, and the method is a simple, easy-to-operate and low-cost method for preparing a nano-particle reinforced steel material. The method is especially suitable for thin sheet / thin wall workpieces which are difficult to be reinforced by hard particles through traditional methods.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of particle reinforced metal materials, in particular to a method for self-driving hard nano-particles into a steel substrate under a full solid state. BACKGROUND

[0002] Second phase particles are an important method for strengthening and toughening steel, which can take into account the strength, toughness and other service performance of steel. With the increasing requirement for the strength of steel in recent years, second phase particle strengthening and toughening plays an important role in new steel materials. Second phase particles in steel can hinder dislocation movement, twinning and other deformation processes, thereby realizing the strengthening of the material. Among them, nano-scale hard particles are particularly significant for improving the comprehensive mechanical properties of steel. Some second phase particles, such as carbonitride particles and graphite particles, are easy to precipitate during heat treatment. Some more stable and more significant strengthening particles, such as diamond particles and oxide particles, are difficult to generate in situ in the steel substrate and can only be artificially introduced from the outside. Taking nano-diamond particles as an example, nano-diamond has ultra-high strength, good deformation ability, extremely high thermal conductivity and chemical stability, and ultra-low friction system and thermal expansion coefficient, and is an ideal strengthening phase. However, because the nucleation potential barrier of diamond is extremely high, carbon atoms dissolved in the iron lattice tend to form carbides or graphite.

[0003] At present, the methods for introducing hard particles such as nano-diamond and nano-oxide into steel substrate mainly include powder metallurgy, laser cladding, 3D printing and casting. However, the above methods are mostly related to metal molten pool environment, and generally have problems such as easy agglomeration of nano-particles, uneven distribution of strengthening phase, poor combination of particles and substrate. In addition, the raw materials (such as alloy powder) and equipment cost are high, the process is complex, the structure and size of the workpiece are limited, and other problems also restrict the wide application of the above methods in steel products. Therefore, it is urgent to develop a method for introducing hard particles into steel materials with simple process and relatively low cost. SUMMARY

[0004] The present application relates to the technical field of particle reinforced metal materials, in particular to a method for self-driving hard nano-particles into a steel substrate under a full solid state.

[0005] To achieve the above object, the present application provides the following technical solutions:

[0006] The application provides a method for self-driving hard nano-particles into a steel base in a full solid state, which comprises the following steps: (1) preparing a dispersion suspension of hard nano-particles with a carbon base or a carbon-coated surface layer by adding the hard nano-particles into a dispersant and a solvent; (2) cleaning and initially polishing a surface of a steel base; (3) polishing the surface of the steel base by using the dispersion suspension as a polishing agent; and (4) placing the polished steel base into a furnace and heating the steel base to a temperature of 800-1000 DEG C under vacuum or in an inert gas atmosphere for 0.5-2 hours.

[0007] According to a preferred embodiment, the method comprises the following steps:

[0008] (1) preparing a dispersion suspension of hard nano-particles with a carbon base or a carbon-coated surface layer by adding the hard nano-particles into a dispersant and a solvent;

[0009] (2) cleaning and initially polishing a surface of a steel base;

[0010] (3) polishing the surface of the steel base by using the dispersion suspension as a polishing agent;

[0011] (4) placing the polished steel base into a furnace and heating the steel base to a temperature of 800-1000 DEG C under vacuum or in an inert gas atmosphere for 0.5-2 hours.

[0012] According to a preferred embodiment, the hard nano-particles comprise diamond, SiC, WC, Si3N4, TiN, Y2O3, Al2O3 or SiO2, and the particle size of the hard nano-particles is 50-500 nm.

[0013] According to a preferred embodiment, the hard nano-particles with a carbon-coated surface layer are non-carbon-based hard nano-particles, and the thickness of the carbon layer of the hard nano-particles with a carbon-coated surface layer is 1-10 nm.

[0014] The hard nano-particles with a carbon-coated surface layer are prepared by a method of catalytic heat treatment, coating organic pyrolysis or rotating vapor deposition.

[0015] According to a preferred embodiment, the steel base is industrial pure iron, low-carbon steel or low-alloy steel.

[0016] According to a preferred embodiment, in step (1), the concentration of the prepared dispersion suspension is 10-50 wt.%.

[0017] According to a preferred embodiment, in step (4), the polishing time is 10-30 minutes.

[0018] According to a preferred embodiment, in step (4), under the vacuum condition, the vacuum degree in the furnace is controlled to be 10-2 Pa and above.

[0019] According to a preferred embodiment, the method further comprises: after step (4), repeating steps (3) and (4) 2-5 times based on the sample thickness and the strengthening target.

[0020] Based on the above technical solution, the method for self-driving hard nano-particles into a steel substrate under a full solid state has at least the following technical effects:

[0021] The method for self-driving hard nano-particles into a steel substrate under a full solid state of the present application is to polish the surface of the steel substrate with a dispersion suspension of hard nano-particles with a carbon base or a carbon-coated surface as a polishing agent, and then heat it to a temperature below the melting point of the steel substrate under vacuum or inert gas protection, so that the hard nano-particles move and disperse uniformly into the steel substrate on their own without any mechanical external force. The method of the present application uses the chemical concentration gradient generated by the carbon on the surface of the hard nano-particles or in the carbon layer dissolving in the iron lattice as the thermodynamic driving force for self-motion, and realizes the self-motion of the hard nano-particles into the steel substrate under a full solid state without any liquid, effectively avoiding the agglomeration of the particles, and the particles are uniformly dispersed and well combined with the substrate interface.

[0022] On the other hand, the method of the present application uses a dispersion suspension of hard nano-particles with a carbon base or a carbon-coated surface as a polishing agent to polish the surface of the steel substrate, and the surface of the steel is still smooth after the hard nano-particles enter the steel substrate, i.e. the introduction of hard particles and surface polishing are realized at the same time. At the same time, the hard nano-particles enter quickly, and the average movement speed of the nano-particles in the steel substrate can reach 0.1-1mm / h (the entering speed is proportional to the size of the chemical concentration gradient and inversely proportional to the size of the particles). The method of the present application is simple and easy to operate, and the equipment used is mainly automatic polishing machine, heat treatment furnace and other commonly used equipment, and the cost is relatively low. The method of the present application is especially suitable for thin sheet / thin-walled workpieces that are difficult to be reinforced by traditional methods. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1is a schematic diagram of the embedding of nanodiamond particles into the iron substrate after polishing with a nanodiamond dispersion liquid in Example 1 (the upper left corner of the figure is a local enlarged view).

[0025] Figure 2 a is a real-time process of diamond particles gradually entering the iron substrate under heating conditions observed in a scanning electron microscope; Figure 2 b is a cross-section sample extracted by a focused ion beam after the nanodiamond particles enter the iron substrate; Figure 2 c is a Raman spectrum characterization of the nanodiamond particles after entering the iron substrate (characterized after the particles inside the substrate were exposed by etching);

[0026] Figure 3 is a diagram of the self-driven entry of non-carbon-based hard nanoparticles into a steel substrate in Example 2, wherein Figure 3 a is a hard nanoparticle coated with a carbon layer embedded in a steel substrate by polishing; Figure 3 b is the gradual decomposition of the carbon layer on the surface of the particles into carbon atoms and the diffusion of carbon atoms into the interior to form a carbon concentration gradient during the heating process; Figure 3 c is the self-driven entry of nanoparticles into the interior of the substrate under the action of a chemical potential gradient. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0028] The present application provides a method for the self-driven entry of hard nanoparticles into a steel substrate under all-solid-state conditions. The method uses a dispersion suspension of hard nanoparticles with a carbon base or a carbon-coated surface as a polishing agent to polish the surface of the steel substrate, and then heats it to a temperature below the melting point of the steel under vacuum or inert gas protection, so that the hard nanoparticles move and disperse uniformly into the interior of the steel substrate under the action of any mechanical external force.

[0029] Preferably, the hard nanoparticles include diamond, SiC, WC, Si3N4, TiN, Y2O3, Al2O3 or SiO2. The particle size of the hard nanoparticles is 50-500 nm. For the hard nanoparticles of non-carbon base, a carbon layer is coated on the surface, and the thickness of the carbon layer on the hard nanoparticles is 1-10 nm. The thickness of the carbon layer depends on the target depth of the particles into the substrate. The hard nanoparticles with the carbon layer on the surface can be prepared by the methods of catalytic heat treatment, coating organic pyrolysis or rotating vapor deposition in the prior art. Preferably, the steel substrate is industrial pure iron or low-carbon steel or low-alloy steel.

[0030] Further preferably, the method of the present application specifically comprises:

[0031] (1) The hard nanoparticles with a carbon base or a carbon layer on the surface are added into a dispersant and a solvent to configure a dispersion suspension with a certain concentration. Preferably, the dispersant is an inorganic electrolyte or a surfactant. The solvent is a polar solvent such as water or ethanol. The concentration of the configured dispersion suspension is 10-50 wt.%.

[0032] (2) The surface of the steel substrate is cleaned and preliminarily polished to ensure that the surface is substantially flat, free of oil stains, rust marks and large scratches. The steel material used is industrial pure iron, low-carbon steel or low-alloy steel.

[0033] (3) The dispersion suspension with a certain concentration is used as a polishing agent to polish the surface of the steel substrate which has been cleaned and preliminarily polished. Preferably, the polishing time is 10-30 min. The hard nanoparticles are used as the polishing agent to further polish the steel due to the fact that the hardness of the nanoparticles is much higher than that of the steel substrate. The steel surface becomes flat, and the nanoparticles are embedded into the steel surface in whole or in part.

[0034] (4) The polished steel substrate sample is placed in a furnace, and heated to 800-1000℃ (the melting point of iron is 1538℃) under vacuum condition (the vacuum degree is controlled at 10 -2 Pa or above) or under the protection of inert gas (under the pressure of low pressure or standard atmospheric pressure) for 0.5-2 h. The nanoparticles embedded in the steel surface enter the steel during the heating process.

[0035] (5) Steps (3) and (4) are repeated 2-5 times based on the thickness of the sample and the target of strengthening.

[0036] (6) The steel is subjected to subsequent heat treatment such as quenching and tempering according to specific requirements.

[0037] The method of the present application is described in detail by way of Examples 1 and 2.

[0038] Example 1:

[0039] This embodiment 1 provides a method for the self-driven insertion of hard nanoparticles into a steel substrate under all-solid conditions. The hard nanoparticles used in this embodiment 1 are nanodiamonds. The specific steps include:

[0040] (1) Mix nanodiamonds, alcohol and dispersant oleic acid, mix evenly by magnetic stirring, then add a certain proportion of base lubricating oil solvent, heat and magnetically stir to remove alcohol, obtain a 10% suspension, and ultrasonically treat for 0.5-4h to obtain a well dispersed nanodiamond suspension.

[0041] (2) The pure iron (99.99%) is wire cut, cleaned and the surface oxide layer is removed;

[0042] (3) Using a 10% nanodiamond suspension as a polishing agent, the pure iron surface was polished. After 10 minutes of treatment on an automatic polishing machine, the nanodiamond particles were uniformly embedded in the pure iron surface. Figure 1 As shown.

[0043] (4) Place the pretreated sample into a scanning electron microscope equipped with an in-situ heating stage and heat it to 1000°C. During the heating process, the vacuum level of the scanning electron microscope is maintained at 10. -3 Pa~10 -4 Within the Pa range.

[0044] like Figure 2 As shown, Figure 2 a presents the process by which nanodiamond particles gradually enter an iron substrate under heating conditions, as shown by scanning electron microscopy. Figure 2 b shows a cross-sectional sample extracted along the depth direction by a focused ion beam after the nanodiamond particles entered the iron substrate. The uniformly dispersed nanoparticles inside can be clearly seen. Figure 2 c represents the Raman spectral characterization of the nanodiamond particles after they entered the iron substrate. The results confirm that the nanodiamond particles did indeed self-drive into the interior of the iron substrate without any external force.

[0045] Example 2:

[0046] This embodiment 2 provides another method for the self-driven entry of hard nanoparticles into a steel substrate under all-solid conditions. The hard particles used in this embodiment 2 are non-carbon-based hard nanoparticles, Al2O3. Specifically, the method includes the following steps:

[0047] (1) Dissolve polyvinylidene fluoride (PVDF) powder in N-methyl-2-pyrrolidone (NMP) solvent, then add Al2O3 nano powder to obtain a suspension, and dry the suspension in vacuum at low temperature (<100℃) to evaporate the NMP solvent to obtain a powder. Transfer the powder into a furnace and pyrolyze at 650℃ under Ar atmosphere to obtain Al2O3 nano powder coated with carbon.

[0048] (2) Mix the powder prepared in step (1), alcohol and dispersant oleic acid, mix uniformly by magnetic stirring, then add a certain proportion of base lubricating oil solvent, heat and magnetically stir to remove alcohol, obtain a 10% suspension, and ultrasonic treat for 0.5-4h to obtain a well dispersed Al2O3 nano powder suspension.

[0049] (3) Linear cut, clean and remove the surface oxide layer of 20 steel.

[0050] (4) Use the prepared Al2O3 nano powder suspension as a polishing agent to polish the linear cut and cleaned 20 steel, and process on an automatic polishing machine for 10 minutes, so that the carbon-coated Al2O3 particles are embedded into the steel surface.

[0051] (5) Put the sample into a vacuum heat treatment furnace and heat to 950℃, and keep the vacuum degree at 10 -2 Pa~10 -3 Pa. During heating, the carbon layer on the surface of the particles gradually dissolves and diffuses into the substrate to form a certain chemical concentration gradient, and the Al2O3 nano particles are self-driven into the steel substrate along the gradient.

[0052] As Figure 3 shown, Figure 3 a hard nano particles coated with carbon layer are embedded into the steel substrate by polishing, Figure 3 b shows that during heating, the carbon layer on the surface of the particles gradually decomposes into carbon atoms and diffuses into the interior to form a carbon concentration gradient, Figure 3 c shows that the nano particles are self-driven into the interior of the substrate under the action of the chemical potential gradient.

[0053] The method of the present application can enable hard nano particles to enter the interior of the substrate metal from the surface of the substrate at a temperature much lower than the melting point of steel without any mechanical external force assistance, and the particles are well dispersed. Neither the particles nor the substrate are melted during the process. It is a simple, easy-to-operate and low-cost method for preparing nano particle reinforced steel material.

[0054] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for the self-driven entry of hard nanoparticles into a steel substrate in an all-solid state, characterized in that, The method involves using a dispersion suspension of hard nanoparticles with carbon base or surface coated with carbon as a polishing agent to polish the surface of a steel substrate. Then, the substrate is heated to a temperature below the melting point of the steel substrate under vacuum or inert gas protection, so that the hard nanoparticles can move autonomously from the surface of the steel substrate and be uniformly dispersed into its interior without any external mechanical force. The method includes the following steps: (1) Hard nanoparticles with carbon base or surface coated with carbon layer are added to dispersant and solvent to prepare a dispersion suspension with a certain concentration; (2) Clean and pre-polish the surface of the steel substrate; (3) Use a dispersion suspension with a certain concentration as a polishing agent to grind and polish the cleaned and pre-polished steel substrate surface; (4) Place the polished steel substrate sample into the furnace and heat it to 800℃~1000℃ under vacuum or inert gas protection for 0.5h~2h. The hard nanoparticles include diamond, SiC, WC, Si3N4, TiN, Y2O3, Al2O3 or SiO2, and the particle size of the hard nanoparticles is 50nm~500nm.

2. The method for self-driven entry of hard nanoparticles into a steel substrate under all-solid conditions according to claim 1, characterized in that, The hard nanoparticles with a carbon coating on their surface are non-carbon-based hard nanoparticles, and the thickness of the carbon layer in the hard nanoparticles with a carbon coating on their surface is 1~10 nm. The hard nanoparticles with a carbon coating are prepared by catalytic heat treatment, pyrolysis of coated organic matter, or rotary vapor deposition.

3. The method for self-driven entry of hard nanoparticles into a steel substrate under all-solid conditions according to claim 1, characterized in that, The steel substrate is industrial pure iron, low- or medium-carbon steel, or low-alloy steel.

4. The method for self-driven entry of hard nanoparticles into a steel substrate under all-solid conditions according to claim 1, characterized in that, In step (1), the concentration of the prepared dispersion suspension is 10 wt.% to 50 wt.%.

5. The method for self-driven entry of hard nanoparticles into a steel substrate in an all-solid state according to claim 1, characterized in that, In step (4), the polishing time is 10~30 min.

6. The method for self-driven entry of hard nanoparticles into a steel substrate under all-solid conditions according to claim 1, characterized in that, In step (4), under vacuum conditions, the vacuum level inside the furnace is controlled at 10⁻² Pa or higher.

7. The method for self-driven entry of hard nanoparticles into a steel substrate in an all-solid state according to claim 1, characterized in that, The method further includes: after step (4), repeating steps (3) and (4) 2 to 5 times based on the sample thickness and the strengthening target.

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