CN116657018A - High-entropy alloy layer piece and preparation method thereof - Google Patents
High-entropy alloy layer piece and preparation method thereof Download PDFInfo
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- CN116657018A CN116657018A CN202310688433.XA CN202310688433A CN116657018A CN 116657018 A CN116657018 A CN 116657018A CN 202310688433 A CN202310688433 A CN 202310688433A CN 116657018 A CN116657018 A CN 116657018A
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Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C30/00—Alloys containing less than 50% by weight of each constituent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
- B22F10/20—Direct sintering or melting
- B22F10/25—Direct deposition of metal particles, e.g. direct metal deposition [DMD] or laser engineered net shaping [LENS]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y10/00—Processes of additive manufacturing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
- B33Y40/10—Pre-treatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y70/00—Materials specially adapted for additive manufacturing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
- B22F2009/043—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by ball milling
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Abstract
The invention discloses a high-entropy alloy layer part and a preparation method thereof. And each high-entropy alloy layer is provided with at least two sublayers, so that the structure of the corresponding high-entropy alloy layer is more stable, and the transition effect is better on the whole. In addition, the prepared high-entropy alloy layer with five layers has relatively good wear resistance.
Description
Technical Field
The invention relates to a high-entropy alloy layer piece prepared on the surface of a workpiece and a preparation method of the high-entropy alloy layer piece, wherein the high-entropy alloy layer piece is a workpiece with a high-entropy alloy layer on the surface.
Background
A High-entropy alloy (HEA) is an alloy formed of five or more metals in equal or approximately equal amounts. High entropy alloys are of considerable interest in materials science and engineering, as they may possess many desirable properties. The major metal components in the prior alloy may be only one to two. For example, iron-based alloys are obtained by adding trace elements to improve their properties. In the conventional concept, the more the metal species added to the alloy, the more the material is embrittled, but the high-entropy alloy is different from the conventional alloy, and the more the metals are, the more the embrittlement is not, and the novel material is obtained.
High-entropy alloys were proposed in the nineties of the twentieth century, but many related studies were not carried out until 2010, and related products were gradually introduced, and in recent years high-entropy alloy products were in explosive growth.
The alloy presents a multi-principal element high entropy effect, can form a simple solid solution structure, and has excellent comprehensive performance. At present, the high-entropy alloy is mainly prepared by adopting methods such as vacuum arc melting, casting and the like, however, the method is easy to produce component segregation due to the low cooling speed, and is not easy to form parts with complex structures, thus being not beneficial to some practical application requirements of the high-entropy alloy.
In view of this, additive manufacturing techniques are the dominant high-entropy alloy rapid prototyping techniques that have emerged in recent years. Compared with the traditional material reduction manufacturing process, the material reduction manufacturing technology mainly applies the discrete stacking forming principle, and materials are directly melted and stacked into full-density and high-precision metal parts by utilizing high-energy beams according to 3D three-dimensional model data. The technology is mainly characterized by short preparation time of parts, insensitivity to complex structures, high material utilization rate and low manufacturing cost, and has great advantages for rapidly manufacturing high-entropy alloy with individualized structure topology and high forming precision requirement.
Functionally graded materials with continuous transformation of microstructure or composition within a single component are new generation innovative materials with the extraordinary ability to adapt to specific requirements or properties. Unlike conventional composite materials, there is a very good transition at the interface between the different regions of functionally graded material, which just helps to reduce mechanical and thermal stress concentrations.
Disclosure of Invention
As a further study for preparing a functionally graded high-entropy alloy layer by an additive technology, the invention aims to provide a high-entropy alloy layer piece with relatively good hardness and wear resistance, and also provides a preparation method of the high-entropy alloy layer piece.
In an embodiment of the present invention, a first aspect provides a high-entropy alloy layer member, including a substrate and a cladding layer deposited on a surface of the substrate by a laser cladding method, where the cladding layer is a high-entropy alloy layer;
the high-entropy alloy layer comprises five layers which are sequentially deposited, and the hardness of the five layers is gradually increased from inside to outside;
each layer has at least two sublayers, the sublayers contained in the same layer are made of the same material, and after one sublayer is formed and stabilized, the next sublayer is formed.
Optionally, each layer has a number of sublayers of three.
Optionally, the thickness of the outermost layer and the minor outer layer is no greater than 5mm.
Optionally, the five layers decrease in thickness from the inside to the outside.
Optionally, the five layers of high-entropy alloy materials from inside to outside are as follows: feCrCoNi, feCrCoNiMo0.5, feCrCoNiMo0.5W0.25, feCrCoNiMo0.5W0.5 and FeCrCoNiMo0.5W0.75.
In an embodiment of the present invention, there is provided a method for preparing a high-entropy alloy layer member for use in the preparation of the high-entropy alloy layer member of the aforementioned first aspect, the method comprising the steps of:
1) Cleaning, namely cleaning and drying the surface of the substrate, which is scheduled to be prepared with the high-entropy alloy layer;
2) Depositing, namely sequentially depositing selected high-entropy alloy powder in a laser material adding system to form five deposition layers;
each deposition layer has at least two sublayers, and the deposition of the next sublayer is carried out after the previous sublayer is deposited and stabilized in the deposition process.
Optionally, the stabilizing means that the current sublayer is cooled to a temperature which is lower than 0.45 times and not lower than 0.3 times the melting point temperature of the deposited high-entropy alloy powder after the deposition.
Optionally, according to the component molar ratio of the corresponding high-entropy alloy, putting into a ball mill for uniform mixing after weighing, and then drying to be used as raw material powder of a laser material-increasing system.
Optionally, in the cleaning step, firstly mechanically polishing the surface of the high-entropy alloy prepared by the sand paper, then placing the surface into an ultrasonic cleaning instrument, cleaning the surface by using alcohol as an organic solvent, further cleaning the surface by using deionized water, and then drying the surface.
Optionally, the process parameters of the laser additive manufacturing are:
the laser spot shape is circular, the powder feeding speed is 0.4L/min, the spot diameter is 2mm, the lap joint rate is 40%, and the scanning speed is 300mm/min.
In the embodiment of the invention, the prepared high-entropy alloy layer member is provided with a plurality of high-entropy alloy layers, the hardness of the high-entropy alloy layer member is sequentially increased from inside to outside, and the high-entropy alloy layer member can adapt to application environments such as heavy loads and the like based on the gradient change of the hardness. And each high-entropy alloy layer is provided with at least two sublayers, so that the structure of the corresponding high-entropy alloy layer is more stable, and the transition effect is better on the whole. In addition, the prepared high-entropy alloy layer with five layers has relatively good wear resistance.
Drawings
FIG. 1a is a schematic cross-sectional view of a high-entropy alloy layer according to an embodiment (as processed).
FIG. 1b shows the microscopic morphology of the high entropy alloy powder under an electron microscope.
FIG. 1c shows the formation sequence of the functional layers of the high-entropy alloy layer.
FIG. 2a is a metallographic micrograph of the top of a sample cut in one example.
FIGS. 2b and 2c are metallographic micrographs of the middle of a sample cut in one example.
FIG. 2d is a metallographic micrograph of the bottom of a sample cut in one example.
FIG. 3 is a graph of compressive engineering stress versus strain for a sample according to one embodiment.
FIG. 4 is a graph (in the as-built direction) of hardness distribution of a test specimen in an embodiment.
FIG. 5 is a graph comparing friction system versus friction time curves of a sample and a substrate according to an embodiment.
FIG. 6 is a graph comparing wear rates of a sample and a substrate in one embodiment.
In the figure: 1. matrix, high-entropy alloy layer, shielding gas and powder.
Description of the embodiments
According to the general definition of high-entropy alloy, in the examples of the present invention, if the content of each component of the relevant high-entropy alloy is not defined, it is expressed as an equimolar ratio, such as FeCrCoNi; if labeled with a subscript, the individual amounts (parts by mole) of the respective components are indicated, e.g. FeCrCoNiMo 0.5 The rest components are equimolar ratio. This is consistent with the general definition of high entropy alloys, as will be appreciated by those skilled in the art.
For continuous production, the related high-entropy alloy powder is proportioned high-entropy alloy powder and can be prepared and used at present, and the process arrangement of different companies is dependent. However, it should be noted that the direction of improvement of the present invention is not the improvement of the high-entropy alloy itself, but the high-entropy alloy layer and the preparation method of the high-entropy alloy layer, and therefore, the high-entropy alloy itself will not be described in detail.
It should be further appreciated that for continuous production on a production line, the high entropy alloy powder is typically canned, and is fed by, for example, a powder feeding mechanism, and will not be described in detail herein, as no improvement is contemplated by the present invention.
If the high-entropy alloy powder is wetted, the powder feeding uniformity and even pipeline blockage can be influenced, and of course, for small quantity of single-piece or small-batch production which are used for preparation at present, the corresponding high-entropy alloy powder can be dried after being uniformly mixed.
Thus, for example, for sample fabrication or small volume production, the mixed powders of different atomic percentages (molar ratios) may be prepared, for example, by weighing them using an electronic balance, and in one embodiment five high entropy alloy powders, specifically FeCrCoNi, feCrCoNiMo, are provided 0.5 、FeCrCoNiMo 0.5 W 0.25 、FeCrCoNiMo 0.5 W 0.5 And FeCrCoNiMo 0.5 W 0.75 . The five powders on the word sequence are sequentially increased from the view of alloy hardness, and are shown in fig. 1a, under the same process condition, the deposited FeCrCoN high-entropy alloy layer is positioned at the innermost layer from the view of hardness, metallurgical connection is formed between the deposited FeCrCoN high-entropy alloy layer and the substrate 1, other layers are sequentially deposited in sequence, the high-entropy alloy layer 2 with five layers shown in fig. 1a is formed, and the five layers of the high-entropy alloy layer 2 formed on the basis of the laser cladding process are graded from inside to outside due to the gradient change of the interlayer hardness, particularly the gradient gradually-increased state, and the gradient increase can ensure that the high-entropy alloy layer 2 has better toughness as a whole, dislocation is not easy to generate, and the wear resistance is also better.
In order to improve verifiability, the following processing manner is provided for a person skilled in the art to refer to how to mix the high-entropy alloy powder uniformly, in that the high-entropy alloy powder has a relatively large number of powder components, and if the powder components are mixed unevenly, for example, the attribute of a single metal phase in a part of the prepared high-entropy alloy layer 2 is relatively obvious, so that the overall performance of the high-entropy alloy layer 2 is affected. Therefore, after preparing a high-entropy alloy powder, the high-entropy alloy powder is put into a ball mill for mixing time of not less than 4 hours, preferably 5 hours, so as to ensure that the high-entropy alloy powder can be fully mixed and the components are uniformly dispersed.
When mixing in a ball mill, grinding balls with the material GCr15 are used, the ratio of the grinding balls to the high-entropy alloy powder is 3:1 (mass ratio), and the rotating speed of the ball mill is 200r/min.
The existing preparation is more required to solve the problem of moisture absorption, so that the high-entropy alloy powder needs to be dried after being uniformly mixed, and the uniformly mixed high-entropy alloy powder can be dried in a drying oven at 120 ℃ for 4 hours to remove moisture, so that the dryness of the high-entropy alloy powder is ensured.
As in the powder 4 and the high-entropy alloy powder in FIG. 1a, the powder 4 is generally conveyed through a pipeline, and the powder 4 is relatively dry and has good fluency and relatively good feeding uniformity.
The foregoing five high-entropy alloys are exemplified as a combination of high-entropy alloys, and it is to be understood that metallurgical connection is easy to form between the high-entropy alloys, irrespective of the kinds of the high-entropy alloys, and based on the concept of gradient increase of hardness, the combination of five high-entropy alloys determined by those skilled in the art should fall within the scope of the present invention.
For convenience of description, hereinafter, the five kinds of high-entropy alloy powders described above are taken as the raw material powders for the preparation of the high-entropy alloy layer 2, and steel with the designation Q235 is taken as an example for illustration.
It should be noted that, by means of a laser additive system (which is already mature process equipment and will not be described here again), depositing different high-entropy alloy functional layers (hereinafter simply referred to as layers) layer by layer is a common means in the art, and the formed layers are metallurgical connections based on laser cladding, so that the bonding strength is high.
Fig. 1b shows an electron microscope image of a high entropy alloy powder with a relatively uniform particle size, a relatively good dispersibility in a dry state, and easy transportation through a pipeline, suitable for use as a raw powder for a laser additive system.
In order to ensure the adhesion of the high-entropy alloy layer 2 to the substrate 1 (for example, a steel substrate with the brand number of Q235), the substrate 1 is pretreated, mainly to remove oxide layers and dirt on the surface of the substrate, the surface of the aggregate 1 is polished first by using sandpaper, for example, 200-mesh sandpaper, and then ultrasonically cleaned by using absolute alcohol (the process equipment is an ultrasonic cleaner).
Further, the deposition of the powder 4 on the substrate 1 is performed using, for example, a fiber laser additive manufacturing molding system having a maximum output power of 2000W, and the deposition is performed under a protective atmosphere using an inert gas, preferably argon. In view of the inherent configuration of laser additive systems, this is not described in detail herein.
Fig. 1a shows the positional relationship of five layers, in which the side closer to the substrate 1 is the inner side and the side farther from the substrate 1 is the outer side, and can be generally described as the upper and lower side, and the lowest side is the lowest side, and the uppermost layer is the opposite side.
Fig. 1c shows the formation sequence of five layers, the vertical arrow indicates the deposition in sequence from inside to outside, and the diagonal arrow indicates the way the laser spot scans back and forth.
Firstly, feCrCoNi powder is deposited, and the working parameters of a laser are selected as follows: the power is 1000W, the light spot shape is circular, the diameter is 2mm, the corresponding powder feeding speed is 0.4L/min, the light spot overlap ratio is 30%, and the scanning speed is 300mm/min.
After one sub-layer is deposited, the deposition is continued according to the working parameters, and three sub-layers are deposited in total. The total layer thickness of the three deposited sublayers is controlled between 6mm and 8 mm.
Then FeCrCoNiMo0.5 powder is deposited, the power of a laser is 1300W, the shape of a light spot is circular, the diameter of the light spot is 2mm, the lap joint rate of the light spot is 40%, the corresponding powder feeding rate is 0.3L/min, the scanning speed is 300mm/min, and after one sub-layer is deposited, the deposition is continued according to the working parameters, and three sub-layers are deposited in total. The total layer thickness of the three sublayers is controlled between 4mm and 6 mm.
Then, feCrCoNiMo0.5W0.25 powder is deposited, the power of a laser is 1300W, the shape of a light spot is circular, the diameter of the light spot is 2mm, the lap joint rate of the light spot is 40%, the corresponding powder feeding rate is 0.3L/min, the scanning speed is 300mm/min, and after one sub-layer is deposited, the deposition is continued according to the working parameters, and three sub-layers are deposited in total. The total layer thickness of the three sublayers is controlled between 4mm and 6 mm.
Then FeCrCoNiMo0.5W0.5 powder is deposited, the power of a laser is 1300W, the shape of a light spot is circular, the diameter of the light spot is 2mm, the lap joint rate of the light spot is 50%, the corresponding powder feeding rate is 0.2L/min, the scanning speed is 300mm/min, and after one sub-layer is deposited, the deposition is continued according to the working parameters, and three sub-layers are deposited in total. The total layer thickness of the three sublayers is controlled between 3mm and 5mm.
Finally, feCrCoNiMo0.5W0.75 powder is deposited, the power of a laser is 1300W, the shape of a light spot is circular, the diameter of the light spot is 2mm, the lap joint rate of the light spot is 50%, the corresponding powder feeding rate is 0.2L/min, the scanning speed is 300mm/min, and after one sub-layer is deposited, the deposition is continued according to the working parameters, and three sub-layers are deposited in total. The total layer thickness of the three sublayers is controlled between 3mm and 5mm.
As can be seen from the above description, each layer contains three sublayers, in other words, each high-entropy alloy powder is selectively deposited with three sublayers, because the microstructure of the same powder is more stable compared with that of the deposition of independent functional layers, a better transition effect can be achieved as a whole, and the material can obtain better mechanical properties. By experimental comparison, the compressive strength of the gradient functional material of each powder deposition three sublayers can reach 2041MPa, the hardness can reach 892HV, and the compressive strength of the gradient functional material of each powder deposition single layer is 1562MPa, and the hardness is 755HV. In addition, the thickness of the functional gradient material can be better built by depositing three sublayers, so that the actual working condition requirement is met. In other words, if the thickness of the individual layers is too large, the heat transmission efficiency is relatively low.
With one scan rate as described above, after one sub-layer is formed, the other sub-layer is cooled to a relatively low temperature very quickly. It will be appreciated that the greater the thermal step (the temperature difference between the object temperature and the ambient temperature), the faster the object loses temperature, and that the deposition of the next sub-layer can be performed without separate cooling, in general.
Further, it has been found through experimentation that if the temperature drops too rapidly after the deposition of one sub-layer, this will result in too great a thermal alternation during the deposition of the next sub-layer, which affects the overall mechanical properties, in particular the thermal brittleness, and therefore, in a preferred embodiment, it is desirable to avoid too rapid a loss of temperature of the object (the substrate 1 or the workpiece containing the other functional layers), it is very easy for the person skilled in the art to set the ambient temperature according to the temperature at the beginning of the current sub-layer after the deposition of one sub-layer, thereby controlling the amplitude of the thermal alternation, and preferably avoiding that the temperature at the beginning of the deposition of the object after the deposition of one sub-layer is less than 0.3 times its melting point, and preferably not more than 0.45 times its melting point.
Further, although materials of different total thickness can be obtained by varying the thickness of each high entropy alloy powder corresponding to a different layer. However, the layers of the fourth and fifth layers (numbered from the inside to the outside, or numbered in the direction of construction) of the high-entropy alloy layer 2 should not be too thick, and as mentioned above, cracks may occur on top of the functionally graded material when the thickness of the single layer of the fourth and fifth layers exceeds 5mm. This is due to the high melting point, high thermal conductivity and brittleness of Mo and W, the relative difficulty of additive manufacturing, cracking has been and still one of the most challenging problems in this field.
High entropy alloys incorporating Mo and W in large amounts produce large amounts of brittle second phase intermetallic compounds. Too thick deposition layer and too much brittle second phase intermetallic compound can lead to cracking of the material, and seriously affect the mechanical properties of the material. This is due to the fact that during the DED process, rapid heating and continuous heating and cooling cycles create a large amount of liquefied cracks and residual stresses, resulting in cracks in the material that propagate along the high angle grain boundaries of the material, and therefore the fourth and fifth layers are deposited as much as possible in opposite layer thicknesses, and in addition, the temperature at the beginning of the included sub-layer after deposition should be better controlled, alleviating the effects of thermal alternating temperature differentials.
The prepared work piece, in particular the work piece with the high entropy alloy layer 2 produced after the deposition is inspected. The portion of the workpiece containing the high-entropy alloy layer 2 was cut into 10mm by 10mm specimens with a wire-cut electric discharge machine for subsequent testing.
And placing the selected first group of samples into an ultrasonic cleaning instrument for cleaning, sequentially polishing the surfaces of the samples with the high-entropy alloy layer 2 by using sand paper with the meshes of 240 to 2000 and coarse to fine, and finally polishing by using a diamond polishing liquid through a polishing machine.
And then carrying out chemical corrosion on the polished sample, wherein the corrosive liquid is aqua regia solution. The etched samples were observed for the overall morphology of the cross section of the coating by a metallographic microscope (OM).
And then a microcomputer controlled electronic universal tester is used for respectively carrying out compression experiments on the substrate 1 and the high-entropy alloy layer 2 in the second group of samples.
And the cross-sectional hardness of the third set of samples was measured from the substrate to the top of the material using a vickers durometer (402 MVD) with a load of 500g for a duration of 15s.
Further, the fourth set of samples, as well as the substrate 1, were placed on a RTEC-MFT-50 tester in a reciprocating frictional wear tester to test wear resistance, with the frictional wear test parameters being the reciprocating frequency: 4HZ, applied load: 50N, temperature: room temperature, travel: 8mm, time: 30min.
Performance analysis: as shown in fig. 2a to 2d, the results are obvious, and it can be seen that the high-entropy alloy functionally graded material manufactured by laser additive has good quality, compact microstructure and no obvious air holes and cracks. Wherein some second phase intermetallic compounds are precipitated in the top region of the high entropy alloy functionally graded material as shown in figure 2 a. As shown in fig. 2b-c, epitaxially grown columnar crystals, elongated dendrites, and dense equiaxed crystals are the primary microstructures in the middle of the high entropy alloy functionally graded material. As shown in FIG. 2d, a planar crystal structure growing in a plane is generated between the matrix and the high-entropy alloy functionally graded material, and the appearance of planar crystals proves that good metallurgical bonding is formed between the matrix and the high-entropy alloy functionally graded material.
Fig. 3 is a compressive engineering stress-strain curve of the test specimen and the matrix 1. Since the matrix is plastic steel, compression fracture does not occur and the compression curve does not drop. Compared with the matrix 1, the compressive strength of the high-entropy alloy layer 2 formed by the high-entropy alloy functionally graded material is obviously more excellent. The compressive fracture stress and the fracture strain of the high-entropy alloy functionally graded material are 2041+/-45 MPa and 21.6+/-0.9%.
FIG. 4 is a graph of the hardness distribution of a sample prepared from the high-entropy alloy functionally graded material along the build direction, wherein the hardness of the high-entropy alloy functionally graded material exhibits a significant gradient change, indicating that the design of the high-entropy alloy functionally graded material is reasonable in terms of hardness enhancement. The hardness is a continuous rising process, and 892.5HV0.3 is reached on top of the high-entropy alloy functionally graded material, which is 4.95 times that of the matrix material Q235.
The results of the frictional wear test are shown in fig. 5 and 6. As shown in fig. 5, the friction coefficient of the high-entropy alloy layer 2 prepared from the high-entropy alloy functionally graded material at room temperature is far lower than that of the matrix Q235. In addition, as shown in fig. 6, the wear rate of the high-entropy alloy layer 2 prepared from the high-entropy alloy functionally graded material is significantly lower than that of the substrate 1, and the wear rate at room temperature is only 25.99% of that of the substrate 1. The magnitude of the wear rate can indirectly reflect the quality of the wear resistance, and the wear resistance of the high-entropy alloy functionally graded material is also excellent.
The excellent mechanical properties of the high-entropy alloy functionally graded material are derived from: (1) Mo and W have atomic radii much larger than those of Co, cr, fe and Ni, and when entering a crystal lattice to form a substitutional solid solution, the crystal lattice distortion effect is caused, the solid solution strengthening effect is enhanced, the internal energy and microscopic stress of the material are increased due to the crystal lattice distortion, dislocation slip deformation is hindered, and the strength of the high-entropy alloy functionally graded material is increased. (2) The large addition of W and Mo promotes the grain refinement of the high-entropy alloy functionally gradient material, and the fine grain strengthening greatly improves the strength of the high-entropy alloy functionally gradient material. (3) The high concentration of W and Mo promotes the formation of intermetallic compounds of mu phase and sigma phase, the mu phase and the sigma phase belong to hard phases, dislocation movement can be effectively restrained, the resistance of dislocation sliding is increased, and the dislocation is entangled near the hard phases in the deformation process. The more the content of the hard phase is, the stronger the obstruction to dislocation is, so that the second phase strengthening plays an important role in improving the compressive strength and the wear resistance of the high-entropy alloy functionally graded material. (4) In the laser additive manufacturing process, the high-entropy alloy functionally graded material is remelted and tempered continuously due to local melting and layer-by-layer addition, so that the interface hardness between layers is reduced. In addition, because of the large thermal gradient in the laser additive manufacturing process, a large amount of residual stress can be introduced, and under the condition of ensuring that the high-entropy alloy functional gradient material has no microcrack, the strength of the high-entropy alloy functional gradient material can be improved by the proper residual stress. (5) The high-entropy alloy functionally graded material has high dislocation density at the top, the higher the dislocation density is, the more the displacement in the crystal is, and the larger the inherent stress field of the crystal is, so that the strength of the high-entropy alloy functionally graded material is increased.
Claims (10)
1. The high-entropy alloy layer piece comprises a substrate and a cladding layer deposited on the surface of the substrate in a laser cladding mode, and is characterized in that the cladding layer is a high-entropy alloy layer;
the high-entropy alloy layer comprises five layers which are sequentially deposited, and the hardness of the five layers is gradually increased from inside to outside;
each layer has at least two sublayers, the sublayers contained in the same layer are made of the same material, and after one sublayer is formed and stabilized, the next sublayer is formed.
2. The high entropy alloy layer of claim 1, wherein each layer has a number of three sublayers.
3. The high-entropy alloy layer of claim 1, wherein the outermost layer and the minor outer layer have a thickness of no more than 5mm.
4. A high entropy alloy laminate according to claim 1 or 3, wherein the five layers taper in thickness from the inside to the outside.
5. The high-entropy alloy layer according to claim 1, wherein the five layers of high-entropy alloy material from inside to outside are in order: feCrCoNi, feCrCoNiMo 0.5 、FeCrCoNiMo 0.5 W 0.25 、FeCrCoNiMo 0.5 W 0.5 And FeCrCoNiMo 0.5 W 0.75 。
6. A method for preparing a high-entropy alloy layer member, which is used for preparing the high-entropy alloy layer member according to any one of claims 1 to 5, and is characterized in that the method comprises the following steps:
1) Cleaning, namely cleaning and drying the surface of the substrate, which is scheduled to be prepared with the high-entropy alloy layer;
2) Depositing, namely sequentially depositing selected high-entropy alloy powder in a laser material adding system to form five deposition layers;
each deposition layer has at least two sublayers, and the deposition of the next sublayer is carried out after the previous sublayer is deposited and stabilized in the deposition process.
7. The method according to claim 6, wherein the stabilizing means cooling the deposited high-entropy alloy powder to a temperature of 0.45 times or less and not less than 0.3 times the melting point of the deposited high-entropy alloy powder after the deposition of the current sub-layer is completed.
8. The preparation method according to claim 6, wherein the components of the high-entropy alloy are mixed uniformly by putting the high-entropy alloy into a ball mill after weighing, and then dried to be used as raw material powder of a laser material-increasing system.
9. The method according to claim 6, wherein in the cleaning step, the surface of the predetermined high-entropy alloy is mechanically polished by sand paper, and then the surface is cleaned by an ultrasonic cleaner using alcohol as an organic solvent, and further cleaned by deionized water and dried.
10. The method of claim 6, wherein the process parameters of the laser additive manufacturing are:
the laser spot shape is circular, the powder feeding speed is 0.4L/min, the spot diameter is 2mm, the lap joint rate is 40%, and the scanning speed is 300mm/min.
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