Preparation method of gradient composite material for in-situ synthesis of stainless steel layer on porous nickel surface

Abstract

The invention discloses a preparation method of a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface, which comprises the following steps of: 1, filling stainless steel powder and nickel powder into a pressing mold; 2, the tubular foil in the pressing die filled with the powder is pulled out; thirdly, the stainless steel powder and the nickel powder are pressed; 4, sintering the composite green body in a hydrogen furnace; 5, pre-densifying the outer surface of the composite sintered body; and 6, electrically depositing a hard chromium layer on the surface to obtain the porous nickel / stainless steel gradient composite material. The tubular foil middle layer is preset for powder filling pressing, a composite porous material compact with component and aperture double gradients is obtained, one-time compression molding of the gradient porous composite material is achieved, meanwhile, the outer layer of a workpiece is completely densified by combining outer surface pre-densification and subsequent electro-deposition densification of the hard chromium layer, and the product quality is improved. And a novel densification means suitable for the porous material is provided, so that the processing precision of the composite material is ensured, and the functionality and the light weight are also ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of porous material preparation and processing, and specifically relates to a method for preparing a gradient composite material by in-situ synthesizing a stainless steel layer on a porous nickel surface. Background Art

[0002] Porous nickel has a rich pore structure inside, and its porosity is often used as a functional component for heat transfer and mass transfer, such as heat pipe evaporator components. In the field of heat transfer, common porous nickel types are tubular and flat. Tubular components are more widely used due to their good isotropic uniformity. Due to functional needs, tubular porous nickel inevitably needs to be fixedly assembled in a dense cladding for the transfer of substances and fluids. However, due to the limitation of processing technology conditions, traditional tubular porous nickel needs to be matched with the outer dense stainless steel tube by interference fit, which leads to three main problems: 1. The porous nickel part needs to be prepared to high precision, and at the same time, the outer cylindricality and the high-precision inner hole of the outer stainless steel need to be assembled, which increases the difficulty of processing and manufacturing, especially the problem of pore blockage in the processing of porous components; 2. The strength of porous materials is relatively lower than that of dense materials of the same material. After assembly, there is always an interference fit, which makes the porous material in a metastable state under stress. The stress easily causes the porous part to break and cause the component to fail; 3. After assembly, there is always a gap between the porous part and the dense part, which inevitably increases the heat transfer resistance. Therefore, it is particularly important to improve the connection method between the porous part and the dense part to achieve seamless metallurgical bonding, which has become a key to improving the efficiency of heat transfer components such as heat pipes.

[0003] Therefore, a new connection technology for porous nickel and dense stainless steel composite is needed to solve the thermal resistance problem caused by the assembly gap of the traditional porous nickel dense outer layer. It is necessary to provide a method for preparing a gradient composite material with in-situ synthesis of a stainless steel layer on the porous nickel surface. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a gradient composite material with an in-situ synthesis of a stainless steel layer on a porous nickel surface in view of the deficiencies of the above-mentioned prior art. The method obtains a composite porous material compact with a dual gradient of composition and pore size by pre-setting a tubular foil intermediate layer for powder pressing, and realizes one-time pressing and forming of the gradient porous composite material. At the same time, the outer layer of the workpiece is completely densified by combining the pre-densification of the outer surface and the subsequent electrodeposition of a dense hard chromium layer, and a new densification method suitable for porous materials is proposed, which not only ensures the processing accuracy of the composite material but also ensures functionality and lightness.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a gradient composite material by in-situ synthesis of a stainless steel layer on a porous nickel surface, characterized in that the method comprises the following steps:

[0006] Step 1: Stainless steel powder and nickel powder are respectively loaded into the outer layer and inner layer of a pressing mold to obtain a powder-loaded pressing mold; the pressing mold comprises a convex-shaped base, a convex portion of the upper part of the convex-shaped base is covered with a tubular foil, a soft rubber sleeve is covered on the outside of the convex-shaped base, the area inside the tubular foil is the inner layer, and the area between the tubular foil and the soft rubber sleeve is the outer layer;

[0007] Step 2: axially pull out the tubular foil in the powder-filled pressing mold obtained in step 1, and simultaneously install a limiting ring and a limiting core rod on the upper part of the powder-filled pressing mold, remove the limiting ring and the limiting core rod after the tubular foil is completely pulled out, and then seal and fix them with a rubber plug to obtain a pressing mold filled with the material to be pressed;

[0008] Step 3, pressing the stainless steel powder and nickel powder in the pressing mold containing the material to be pressed obtained in step 2, and then removing the pressing mold to obtain a porous nickel / porous stainless steel composite green body;

[0009] Step 4: sintering the porous nickel / porous stainless steel composite green body obtained in step 3 in a hydrogen furnace to obtain a porous nickel / porous stainless steel composite sintered body;

[0010] Step 5: pre-densifying the outer surface of the porous nickel / porous stainless steel composite sintered body obtained in step 4;

[0011] Step 6: Electrodeposit a hard chromium layer on the surface of the porous nickel / porous stainless steel composite sintered body that has been pre-densified in step 5 to obtain a porous nickel / stainless steel gradient composite material.

[0012] The present invention designs a pressing mold, pre-places a tubular foil middle layer for stainless steel powder and nickel powder filling, ensures the shape and position accuracy of powder filling, and limits the powder during the lifting process of the tubular foil through the proprietary pull-out design, eliminates the influence of friction on powder filling, and obtains inner and outer layer gradient powder filling. Through the subsequent pressing and sintering process, a composite porous material with dual gradients of composition and pore size is obtained in one step, realizing the one-time pressing and forming of the gradient porous composite material, avoiding the problem of densification of the core porous material caused by multiple pressing, and at the same time ensuring the coaxiality of the internal porous core and the outer stainless steel layer. The subsequent process The outer surface is pre-densified and then fully densified by coating the hard chromium layer. During the outer surface pre-densification process, the strong extrusion movement during turning causes plastic deformation of the surface material of the workpiece, thereby achieving densification of the pores, laying the foundation for further densification and obtaining a high-precision gradient composite material. Finally, the surface of the porous stainless steel is fully densified by surface electrodeposition, and the remaining pores are fully densified, realizing the metallurgical bonding of the porous nickel and the stainless steel layer. There is no gap between the gradient layers, which effectively reduces the thermal resistance, electrical resistance, etc. compared with the assembled composite materials, ensuring the structural and functional integration of the porous nickel and the dense stainless steel.

[0013] In the present invention, the size of the rubber plug is matched with the soft rubber sleeve, and the diameter of the rubber plug is equal to or slightly larger than the inner diameter of the soft rubber sleeve, forming a transition or interference fit.

[0014] The above-mentioned method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface is characterized in that the particle size of the nickel powder in step 1 is 5μm to 150μm, and the grade of the stainless steel powder is 316L, and the particle size is 25μm to 150μm. The present invention controls the particle sizes of the stainless steel powder and the nickel powder so that both the nickel powder layer and the stainless steel layer have suitable pores, while ensuring that the nickel powder layer and the stainless steel layer have an excellent bonding effect.

[0015] The above-mentioned method for preparing a gradient composite material of in-situ synthesis of a stainless steel layer on a porous nickel surface is characterized in that the material of the tubular foil in step 1 is graphite, stainless steel or aluminum, the surface roughness is less than Ra0.8, and the thickness is 0.03mm to 0.05mm. The present invention controls the parameters of the tubular foil so that the tubular foil has the characteristics of high smoothness and low thickness. The friction force is small during the extraction process, and the powder filling will not be affected. At the same time, the low thickness can ensure that the two powders in the gap are meshed with each other during extraction, without affecting the size and geometric accuracy.

[0016] The above-mentioned method for preparing a gradient composite material with an in-situ synthesized stainless steel layer on a porous nickel surface is characterized in that when the stainless steel powder and nickel powder are respectively loaded into the pressing mold in step one, the stainless steel powder is loaded first and then the nickel powder is loaded, and the loading is coordinated with vibration, and the heights of the stainless steel powder and the nickel powder in the powder-loaded pressing mold are the same. The present invention first loads the stainless steel powder, and the compacting force of the stacking between the stainless steel powders can accurately further position and fix the tubular foil, which is convenient for the subsequent loading of the nickel powder inside. The compacting force of the powder stacking and the uniformity of the powder loading are further ensured by vibration. By controlling the height of the stainless steel powder and the nickel powder to be the same, the uniform structure of the two components in the prepared gradient composite material is ensured.

[0017] The above-mentioned method for preparing a gradient composite material of an in-situ synthesized stainless steel layer on a porous nickel surface is characterized in that, during the process of extracting the tubular foil in step 2, the lower end face of the limiting core rod and the upper end face of the nickel powder always remain coincident, and the lower end face of the limiting ring and the upper end face of the stainless steel powder always remain coincident. The present invention provides downward pressure through the limiting core rod and the limiting ring to ensure that the filling position of the stainless steel powder and the nickel powder does not change during the extraction of the tubular foil, thereby avoiding the influence of friction on the powder.

[0018] The above-mentioned method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface is characterized in that the pressing in step 3 is performed using a cold isostatic press, the pressing pressure is 140MPa to 160MPa, and the time is more than 30s. The present invention ensures the molding effect by controlling the pressure, which can ensure both the formability and a certain porosity, and prevents the problem of low strength of the pressed blank caused by a pressure less than 140MPa and low porosity caused by a pressure greater than 160MPa.

[0019] The above-mentioned method for preparing a gradient composite material with an in-situ synthesis of a stainless steel layer on a porous nickel surface is characterized in that the sintering process in step 4 is: heating to 700°C to 1050°C at a heating rate of 2°C / min to 10°C / min and then keeping the temperature for 1h to 2h. The present invention ensures metallurgical bonding by controlling the sintering parameters, and has a certain porosity while ensuring strength.

[0020] The above-mentioned method for preparing a gradient composite material with an in-situ synthesized stainless steel layer on a porous nickel surface is characterized in that the pre-densification treatment in step 5 is based on the outer cylindrical surface of the porous nickel / porous stainless steel composite sintered body, and the porous stainless steel layer is subjected to mechanical pre-densification treatment, and the processing accuracy is 0.02 mm, and the surface roughness is controlled to be less than Ra0.8;

[0021] The pre-densification treatment is carried out on a lathe, and the specific steps are:

[0022] Step 101, roughing machining allowance: select a tool made of YG6X fine-grained carbide, set the tool geometry angle, main deflection angle 75°, secondary deflection angle 8°~15°, cutting edge inclination angle -5°, rake angle 10°~15°, back angle 8°~12°, tool tip arc radius 0.3mm~0.5mm, then process at a cutting speed of 60m / min~70m / min, a feed rate of 0.2mm / r~0.3mm / r, and a cutting depth of 0.3mm~0.5mm;

[0023] Step 102, use a large arc turning tool to extrude and turn the outer circle: select a large arc turning tool made of YG6X fine-grained carbide, set the large arc turning tool geometric angle, the main deflection angle is 90°; the secondary deflection angle is 8°~15°, the blade inclination angle is -20°, the front angle is 10°~15°, the back angle is 8°~12°, the tool tip arc radius is 1mm, and then process at a cutting speed of 140m / min~150m / min, a feed rate of 0.1mm / r~0.2mm / r, and a cutting depth of 0.05mm~0.1mm. The present invention adopts a two-step pre-densification process, wherein the purpose of the first step is to roughly remove the machining allowance and rough-machine the outer surface of the porous nickel / porous stainless steel composite sintered body to achieve the required densification size. Here, a slow cutting speed and a large cutting depth are used to remove the allowance for rough machining in mechanical machining, and the control parameters are specially designed for the processing of porous nickel / porous stainless steel composite sintered bodies with porous structures, so as to avoid the influence of the processing on the pores themselves. The second step is to extrude the outer circle through a large arc turning tool, directly densify the surface layer at a high speed, increase the extrusion effect on the workpiece surface during turning, and cause plastic deformation of the workpiece surface material, thereby achieving the effect of closing the micropores. At the same time, the roughness of the outer circle surface is controlled below Ra0.8, laying the foundation for subsequent further densification, and obtaining a high-precision gradient composite material.

[0024] The above-mentioned method for preparing a gradient composite material with an in-situ synthesis of a stainless steel layer on a porous nickel surface is characterized in that the thickness of the hard chromium layer in step 5 is 0.05 mm to 0.2 mm. The present invention controls the thickness of the hard chromium layer, thereby ensuring the functionality of the dense part of the gradient composite material while also achieving the overall lightweight of the gradient composite material (except for the surface layer, the rest of the structure is still a porous structure).

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The present invention adopts separated composite powder filling technology to improve the powder filling accuracy. The subsequent form and position tolerance and position requirements can be guaranteed only through the powder filling process. Through the subsequent pressing and sintering process, the one-time forming of the porous gradient composite material is achieved. Compared with the traditional method of first pressing the porous core rod and then performing a second pressing, the overall process is shortened, and the influence of multiple pressing on the pore performance of the porous part is effectively avoided. At the same time, the porous nickel and the stainless steel layer are metallurgically bonded, and there is no gap between the gradient layers. Compared with the traditional manufacturing method of using a stainless steel shell and a porous core interference assembly, the method adopted by the present invention effectively reduces thermal resistance, electrical resistance, etc., and ensures the functional integration of the porous nickel and the dense stainless steel structure.

[0027] 2. The composite material connection technology proposed in the present invention first uses the pressing force to make different types of powders mesh with each other during powder filling, and then realizes the metallurgical bonding of porous nickel and stainless steel dissimilar materials by controlling the sintering process parameters, solving the problem of surface separation of dissimilar materials caused by different shrinkage rates of different materials.

[0028] 3. The present invention uses two densification treatments. First, the initial machining pre-densification ensures the processing accuracy of the original part, and at the same time densifies the pores by extruding the surface of the part. Finally, the remaining pores are completely densified by surface electrodeposition. The covering thickness can be controlled between 0.05mm and 0.2mm, which not only ensures the functionality of the dense part of the composite material but also achieves the lightweight of the overall material.

[0029] 4. The present invention solves the problem that traditional functional elements can only be composited through assembly, realizes the technical problem of simultaneous connection of heterogeneous materials (316L stainless steel-nickel) and dense-porous (dense 316L stainless steel-porous nickel), eliminates the gaps during assembly of traditional elements, effectively realizes the metallurgical bonding of porous nickel and stainless steel layers, and has no gaps between gradient layers. Compared with assembled composite materials, it effectively reduces thermal resistance, electrical resistance, etc., ensuring the functional integration of porous nickel and dense stainless steel structures.

[0030] 5. The present invention realizes continuous dual gradient of pores and components through unique powder filling means and surface densification technology, solves the metallurgical bonding problem of porous nickel and dense stainless steel dissimilar materials, effectively reduces the thermal resistance of functional components, and expands the gradient composite connection technology between porous materials of dissimilar materials and between porous and dense materials, and can also realize the bonding of porous materials and dense parts of other materials.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic structural diagram of the pressing die used in the present invention.

[0033] Figure 2 It is a schematic diagram of the tubular foil material in the powder-filled pressing die of the present invention being drawn out along the axial direction.

[0034] Figure 3 This is a SEM image of the outermost surface of the porous nickel / stainless steel gradient composite material prepared in Example 1 of the present invention.

[0035] Figure 4 This is a SEM image of the cross section of the porous nickel / stainless steel gradient composite material prepared in Example 1 of the present invention.

[0036] Description of reference numerals:

[0037] 1—convex base; 2—tubular foil; 3—soft rubber sleeve;

[0038] 4—limiting ring; 5—limiting mandrel; 6—nickel powder;

[0039] 7—Stainless steel powder. DETAILED DESCRIPTION

[0040] Figure 1 It is a schematic diagram of the structure of the pressing die used in the present invention, from Figure 1 It can be seen that the pressing mold includes a convex base 1, the convex part on the upper part of the convex base 1 is covered with a tubular foil 2, the outside of the convex base 1 is covered with a soft rubber sleeve 3, the area inside the tubular foil 2 is the inner layer, and the area between the tubular foil 2 and the soft rubber sleeve 3 is the outer layer.

[0041] Figure 2 Schematic diagram of the tubular foil material in the powder-filled pressing die of the present invention being drawn out along the axial direction, from Figure 2 It can be seen that the area inside the tubular foil 2 in the pressing mold is filled with nickel powder 6, the area between the tubular foil 2 and the soft rubber sleeve 3 is filled with stainless steel powder 7, the upper part of the nickel powder 6 is pressed with a limiting core rod 5, and the upper part of the stainless steel powder 7 is pressed with a limiting ring 4.

[0042] Example 1

[0043] This embodiment includes the following steps:

[0044] Step 1: 316L stainless steel powder with a particle size of 25 μm and nickel powder with a particle size of 5 μm are sequentially loaded into the outer layer and the inner layer of the pressing mold and compacted by vibration to obtain a pressing mold with the nickel powder and 316L stainless steel powder having the same powder loading height;

[0045] The pressing die comprises a convex-shaped base, the convex portion of the upper part of the convex-shaped base is covered with a tubular foil material with a thickness of 0.03 mm and a surface roughness of less than Ra0.8, and made of graphite, the outer part of the convex-shaped base is covered with a soft rubber sleeve, the area inside the tubular foil is the inner layer, and the area between the tubular foil and the soft rubber sleeve is the outer layer;

[0046] Step 2, the tubular foil in the powder-filled pressing mold obtained in step 1 is pulled out axially, and a limiting ring and a limiting core rod are installed on the upper part of the powder-filled pressing mold at the same time. During the process of pulling out the tubular foil, the lower end face of the limiting core rod and the upper end face of the nickel powder are always kept in overlap, and the lower end face of the limiting ring and the upper end face of the stainless steel powder are always kept in overlap. After the tubular foil is completely pulled out, the limiting ring and the limiting core rod are removed, and then they are sealed and fixed by a rubber plug to obtain a pressing mold filled with the material to be pressed;

[0047] Step 3: The nickel powder and 316L stainless steel powder in the pressing mold containing the material to be pressed obtained in step 2 are pressed by a cold isostatic press at a pressure of 140 MPa to 160 MPa for 30 seconds, and then the pressing mold is removed to obtain a porous nickel / porous stainless steel composite green body;

[0048] Step 4: heating the porous nickel / porous stainless steel composite green body obtained in step 3 to 700° C. at a heating rate of 2° C. / min in a hydrogen furnace in a reducing atmosphere, and then sintering the green body for 1 hour to obtain a porous nickel / porous stainless steel composite sintered body;

[0049] Step 5, pre-densification treatment is performed on the outer surface of the porous nickel / porous stainless steel composite sintered body obtained in step 4; the pre-densification treatment is based on the outer cylindrical surface of the porous nickel / porous stainless steel composite sintered body, and the porous stainless steel layer is mechanically pre-densified, and the processing accuracy is 0.02mm, and the surface roughness is controlled to be less than Ra0.8. After the pre-densification treatment, the thickness of the porous stainless steel is 0.51mm, and the surface sealing rate reaches 98.8%;

[0050] The pre-densification treatment is carried out on a lathe, and the specific steps are:

[0051] Step 101, roughing machining allowance: select a tool made of YG6X fine-grained carbide, set the tool geometry angle, main deflection angle 75°, secondary deflection angle 8°, cutting edge inclination angle -5°, rake angle 10°, back angle 8°, tool tip arc radius 0.3mm, and then perform machining at a cutting speed of 60m / min, a feed rate of 0.2mm / r, and a cutting depth of 0.3mm;

[0052] Step 102, using a large arc turning tool to extrude and turn the outer circle: select a large arc turning tool made of YG6X fine-grained carbide, set the large arc turning tool geometric angle, the main deflection angle is 90°; the secondary deflection angle is 8°, the blade inclination angle is -20°, the front angle is 10°, the back angle is 8°, the tool tip arc radius is 1mm, and then process at a cutting speed of 140m / min, a feed rate of 0.1mm / r, and a cutting depth of 0.05mm;

[0053] Step 6: Electrodeposit a hard chromium layer with a thickness of 0.05 mm on the surface of the porous nickel / porous stainless steel composite sintered body that has been pre-densified in step 5 to obtain a porous nickel / stainless steel gradient composite material with a completely densified surface.

[0054] Figure 3 This is a SEM image of the outermost surface of the porous nickel / stainless steel gradient composite material prepared in this example. Figure 4 This is a SEM image of the cross section of the porous nickel / stainless steel gradient composite material prepared in this example. Figure 3 and Figure 4 It can be seen that the surface layer of the porous nickel / stainless steel gradient composite material prepared in this embodiment is completely densified, and the stainless steel layer and the porous nickel part are well combined.

[0055] Example 2

[0056] This embodiment includes the following steps:

[0057] Step 1: 316L stainless steel powder with a particle size of 100 μm and nickel powder with a particle size of 74 μm are sequentially loaded into the outer layer and the inner layer of the pressing mold and compacted by vibration to obtain a pressing mold with the nickel powder and 316L stainless steel powder having the same powder loading height;

[0058] The pressing mold comprises a convex-shaped base, the convex portion of the upper part of the convex-shaped base is covered with a tubular foil material with a thickness of 0.04 mm, a surface roughness less than Ra0.8, and a material of stainless steel, the outer part of the convex-shaped base is covered with a soft rubber sleeve, the area inside the tubular foil is the inner layer, and the area between the tubular foil and the soft rubber sleeve is the outer layer;

[0059] Step 2, the tubular foil in the powder-filled pressing mold obtained in step 1 is pulled out axially, and a limiting ring and a limiting core rod are installed on the upper part of the powder-filled pressing mold at the same time. During the process of pulling out the tubular foil, the lower end face of the limiting core rod and the upper end face of the nickel powder are always kept in overlap, and the lower end face of the limiting ring and the upper end face of the stainless steel powder are always kept in overlap. After the tubular foil is completely pulled out, the limiting ring and the limiting core rod are removed, and then they are sealed and fixed by a rubber plug to obtain a pressing mold filled with the material to be pressed;

[0060] Step 3: The nickel powder and 316L stainless steel powder in the pressing mold containing the material to be pressed obtained in step 2 are pressed by a cold isostatic press at a pressure of 140 MPa to 160 MPa for 30 seconds, and then the pressing mold is removed to obtain a porous nickel / porous stainless steel composite green body;

[0061] Step 4: heating the porous nickel / porous stainless steel composite green body obtained in step 3 to 850° C. in a hydrogen furnace in a reducing atmosphere at a heating rate of 5° C. / min and then sintering the green body for 1.5 h to obtain a porous nickel / porous stainless steel composite sintered body;

[0062] Step 5, pre-densification treatment is performed on the outer surface of the porous nickel / porous stainless steel composite sintered body obtained in step 4; the pre-densification treatment is based on the outer cylindrical surface of the porous nickel / porous stainless steel composite sintered body, and the porous stainless steel layer is mechanically pre-densified, and the processing accuracy is 0.02mm, and the surface roughness is controlled to be less than Ra0.8. After the pre-densification treatment, the thickness of the porous stainless steel is 1.04mm, and the surface sealing rate reaches 99.5%;

[0063] The pre-densification treatment is carried out on a lathe, and the specific steps are:

[0064] Step 101, roughing machining allowance: select a tool made of YG6X fine-grained carbide, set the tool geometry angle, main deflection angle 75°, secondary deflection angle 12°, cutting edge inclination angle -5°, rake angle 12°, back angle 10°, tool tip arc radius 0.4mm, then perform machining at a cutting speed of 65m / min, a feed rate of 0.25mm / r, and a cutting depth of 0.4mm;

[0065] Step 102, using a large arc turning tool to extrude and turn the outer circle: select a large arc turning tool made of YG6X fine-grained carbide, set the large arc turning tool geometric angle, the main deflection angle is 90°; the secondary deflection angle is 12°, the blade inclination angle is -20°, the front angle is 12°, the back angle is 10°, the tool tip arc radius is 1mm, and then process at a cutting speed of 145m / min, a feed rate of 0.15mm / r, and a cutting depth of 0.08mm;

[0066] Step 6: Electrodeposit a hard chromium layer with a thickness of 0.1 mm on the surface of the porous nickel / porous stainless steel composite sintered body that has been pre-densified in step 5 to obtain a porous nickel / stainless steel gradient composite material with a completely densified surface.

[0067] After testing, it was found that the surface layer of the porous nickel / stainless steel gradient composite material prepared in this embodiment was completely densified, and the stainless steel layer was well bonded with the porous nickel part.

[0068] Example 3

[0069] This embodiment includes the following steps:

[0070] Step 1: 316L stainless steel powder with a particle size of 150 μm and nickel powder with a particle size of 150 μm are sequentially loaded into the outer layer and the inner layer of the pressing mold and compacted by vibration to obtain a pressing mold with the nickel powder and the 316L stainless steel powder having the same powder loading height;

[0071] The pressing mold comprises a convex-shaped base, the convex portion of the upper part of the convex-shaped base is covered with a tubular foil material with a thickness of 0.05 mm and a surface roughness of less than Ra0.8, and made of aluminum, the outer part of the convex-shaped base is covered with a soft rubber sleeve, the area inside the tubular foil material is the inner layer, and the area between the tubular foil material and the soft rubber sleeve is the outer layer;

[0072] Step 2, the tubular foil in the powder-filled pressing mold obtained in step 1 is pulled out axially, and a limiting ring and a limiting core rod are installed on the upper part of the powder-filled pressing mold at the same time. During the process of pulling out the tubular foil, the lower end face of the limiting core rod and the upper end face of the nickel powder are always kept in overlap, and the lower end face of the limiting ring and the upper end face of the stainless steel powder are always kept in overlap. After the tubular foil is completely pulled out, the limiting ring and the limiting core rod are removed, and then they are sealed and fixed by a rubber plug to obtain a pressing mold filled with the material to be pressed;

[0073] Step 3: The nickel powder and 316L stainless steel powder in the pressing mold containing the material to be pressed obtained in step 2 are pressed by a cold isostatic press at a pressure of 140 MPa to 160 MPa for 30 seconds, and then the pressing mold is removed to obtain a porous nickel / porous stainless steel composite green body;

[0074] Step 4: heating the porous nickel / porous stainless steel composite green body obtained in step 3 to 1050° C. in a hydrogen furnace in a reducing atmosphere at a heating rate of 10° C. / min and then sintering the green body for 2 hours to obtain a porous nickel / porous stainless steel composite sintered body;

[0075] Step 5, pre-densification treatment is performed on the outer surface of the porous nickel / porous stainless steel composite sintered body obtained in step 4; the pre-densification treatment is based on the outer cylindrical surface of the porous nickel / porous stainless steel composite sintered body, and the porous stainless steel layer is mechanically pre-densified, and the processing accuracy is 0.02mm, and the surface roughness is controlled to be less than Ra0.8. After the pre-densification treatment, the thickness of the porous stainless steel is 2.00mm, and the surface sealing rate reaches 99.2%;

[0076] The pre-densification treatment is carried out on a lathe, and the specific steps are:

[0077] Step 101, roughing machining allowance: select a tool made of YG6X fine-grained carbide, set the tool geometry angle, main deflection angle 75°, secondary deflection angle 15°, cutting edge inclination angle -5°, rake angle 15°, back angle 12°, tool tip arc radius 0.5mm, then process at a cutting speed of 70m / min, a feed rate of 0.3mm / r, and a cutting depth of 0.5mm;

[0078] Step 102, using a large arc turning tool to extrude and turn the outer circle: select a large arc turning tool made of YG6X fine-grained carbide, set the geometric angle of the large arc turning tool, the main deflection angle is 90°; the secondary deflection angle is 15°, the blade inclination angle is -20°, the front angle is 15°, the back angle is 12°, the tool tip arc radius is 1mm, and then process at a cutting speed of 150m / min, a feed rate of 0.2mm / r, and a cutting depth of 0.1mm;

[0079] Step 6: Electrodeposit a hard chromium layer with a thickness of 0.2 mm on the surface of the porous nickel / porous stainless steel composite sintered body that has been pre-densified in step 5 to obtain a porous nickel / stainless steel gradient composite material with a completely densified surface.

[0080] After testing, it was found that the surface layer of the porous nickel / stainless steel gradient composite material prepared in this embodiment was completely densified, and the stainless steel layer was well bonded with the porous nickel part.

[0081] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a gradient composite material by in-situ synthesis of a stainless steel layer on a porous nickel surface, characterized in that: The method comprises the following steps: Step 1: Stainless steel powder and nickel powder are respectively loaded into the outer layer and inner layer of a pressing mold to obtain a powder-loaded pressing mold; the pressing mold comprises a convex-shaped base, a convex portion of the upper part of the convex-shaped base is covered with a tubular foil, a soft rubber sleeve is covered on the outside of the convex-shaped base, the area inside the tubular foil is the inner layer, and the area between the tubular foil and the soft rubber sleeve is the outer layer; Step 2: axially pull out the tubular foil in the powder-filled pressing mold obtained in step 1, and simultaneously install a limiting ring and a limiting core rod on the upper part of the powder-filled pressing mold, remove the limiting ring and the limiting core rod after the tubular foil is completely pulled out, and then seal and fix them with a rubber plug to obtain a pressing mold filled with the material to be pressed; Step 3, pressing the stainless steel powder and nickel powder in the pressing mold containing the material to be pressed obtained in step 2, and then removing the pressing mold to obtain a porous nickel / porous stainless steel composite green body; Step 4: sintering the porous nickel / porous stainless steel composite green body obtained in step 3 in a hydrogen furnace to obtain a porous nickel / porous stainless steel composite sintered body; Step 5: pre-densifying the outer surface of the porous nickel / porous stainless steel composite sintered body obtained in step 4; Step 6: Electrodeposit a hard chromium layer on the surface of the porous nickel / porous stainless steel composite sintered body that has been pre-densified in step 5 to obtain a porous nickel / stainless steel gradient composite material.

2. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: The particle size of the nickel powder in step 1 is 5 μm to 150 μm, and the grade of the stainless steel powder is 316L, and the particle size is 25 μm to 150 μm.

3. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: The material of the tubular foil in step 1 is graphite, stainless steel or aluminum, with a surface roughness less than Ra0.8 and a thickness of 0.03 mm to 0.05 mm.

4. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: When the stainless steel powder and nickel powder are respectively loaded into the pressing mold in step 1, the stainless steel powder is loaded first and then the nickel powder is loaded. The loading is combined with vibration, and the heights of the stainless steel powder and the nickel powder in the pressing mold are the same.

5. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: During the process of extracting the tubular foil in step 2, the lower end surface of the limiting core rod always coincides with the upper end surface of the nickel powder, and the lower end surface of the limiting ring always coincides with the upper end surface of the stainless steel powder.

6. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: The pressing in step 3 is performed using a cold isostatic press, the pressing pressure is 140 MPa to 160 MPa, and the pressing time is more than 30 seconds.

7. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: The sintering process in step 4 is: heating to 700°C to 1050°C at a heating rate of 2°C / min to 10°C / min and then keeping the temperature for 1h to 2h.

8. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: The pre-densification treatment in step 5 is based on the outer cylindrical surface of the porous nickel / porous stainless steel composite sintered body, and the porous stainless steel layer is mechanically pre-densified, and the processing accuracy is 0.02mm, and the surface roughness is controlled to be less than Ra0.8; The pre-densification treatment is carried out on a lathe, and the specific steps are: Step 101, roughing machining allowance: select a tool made of YG6X fine-grained carbide, set the tool geometry angle, main deflection angle 75°, secondary deflection angle 8°~15°, cutting edge inclination angle -5°, rake angle 10°~15°, back angle 8°~12°, tool tip arc radius 0.3mm~0.5mm, then process at a cutting speed of 60m / min~70m / min, a feed rate of 0.2mm / r~0.3mm / r, and a cutting depth of 0.3mm~0.5mm; Step 102, use a large arc turning tool to extrude and turn the outer circle: select a large arc turning tool made of YG6X fine-grained carbide, set the large arc turning tool geometric angle, the main deflection angle is 90°; the secondary deflection angle is 8°~15°, the blade inclination angle is -20°, the front angle is 10°~15°, the back angle is 8°~12°, the tool tip arc radius is 1mm, and then process at a cutting speed of 140m / min~150m / min, a feed rate of 0.1mm / r~0.2mm / r, and a cutting depth of 0.05mm~0.1mm.

9. The method for preparing a gradient composite material for in-situ synthesis of a stainless steel layer on a porous nickel surface according to claim 1, characterized in that: The thickness of the hard chromium layer on the surface of the porous nickel / stainless steel gradient composite material in step 5 is 0.05 mm to 0.2 mm.

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