Gradient alloy thermal rectifier and preparation method thereof

Abstract

The invention relates to the technical field of thermal functional devices, in particular to a gradient alloy thermal rectifier and a preparation method thereof. The gradient alloy thermal rectifier is of an integrated structure and comprises a first metal material layer, a transition layer and a second metal material layer which are sequentially arranged in a contact mode. Wherein the heat conductivity of the first metal material and the heat conductivity of the second metal material are opposite along with the temperature change trend, and the transition layer is composed of the first metal material and the second metal material. According to the gradient alloy thermal rectifier, the structure of the gradient alloy thermal rectifier is optimized, a transition layer is introduced into two metal materials with the thermal conductivity (kappa) being opposite along with the change trend of the temperature (T), a high thermal rectification ratio can be guaranteed, and meanwhile stress concentration caused by sudden change of interface mechanical properties between different materials can be relieved.

Description

Technical Field

[0001] The invention relates to the technical field of thermal functional devices, and in particular to a gradient alloy thermal rectifier and a preparation method thereof. Background Art

[0002] Thermal rectification refers to the phenomenon that heat flow in a thermal system exhibits directional asymmetry. The most common configuration to achieve thermal rectification is the "thermal diode", which consists of two materials with different temperature dependence of thermal conductivity, providing it with the necessary nonlinearity. In the forward mode, the left material is hot and the right material is cold, and both materials have high temperatures, resulting in a large heat flux density; in the reverse mode, both materials have low heat flux, resulting in a smaller heat flux. This effect has a wide range of application prospects in various fields such as thermal management, energy harvesting and phonon computing.

[0003] Previously, researchers have made great progress in the study of nano thermal rectifiers by modifying nanomaterials such as carbon nanotubes and graphene films. Bulk "thermal diodes" are usually spliced ​​together by two materials with opposite thermal conductivity temperature dependence to achieve thermal rectification effect. The indicator for measuring thermal rectification performance is the rectification ratio, which is defined as the ratio of the heat flux under forward and reverse thermal bias minus 1 (TRR=j + / j - -1). For example, LaCoO3 and La 0.7 Sr 0.3 The thermal diode composed of CoO3 has a rectification ratio of 0.43 when the ambient temperature is 40 K and the temperature difference ΔT=60 K. In order to extend the working range to near room temperature, Takeuchi et al. used two aluminum-based alloys with a rectification ratio of only 0.1. Phase change materials such as Ag2Ch (Ch = S, Se, Te) have a drastic change in thermal conductivity due to phase change in the temperature range of 373~473 K.

[0004] However, the nano thermal rectifier devices mentioned above require fine processing of materials at the nanoscale, which is not conducive to industrial applications; most of the research on traditional bulk thermal diodes is limited to ultra-low temperatures, and their practicality is limited; although the phase change thermal rectifier has expanded the temperature range, its application still needs to be near the phase change point, which has limitations. In addition, the above thermal rectifier devices do not have good mechanical properties and cannot be used in harsh environments.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] In order to solve the problems in the prior art, the present invention provides a gradient alloy thermal rectifier and a preparation method thereof, which can significantly improve the mechanical properties while ensuring the thermal rectification ratio.

[0007] Based on this, the present invention has the following technical solutions: In a first aspect, the present invention provides a gradient alloy thermal rectifier, which is an integrated structure and includes a first metal material layer, a transition layer, and a second metal material layer which are sequentially contacted with each other; wherein the thermal conductivities of the first metal material and the second metal material change in opposite trends with temperature, and the transition layer is composed of the first metal material and the second metal material.

[0008] The present invention finds that by optimizing the structure of the gradient alloy thermal rectifier and introducing a transition layer between two metals whose thermal conductivity (κ) varies in opposite trends with temperature (T), a higher thermal rectification ratio can be ensured while also alleviating stress concentration caused by sudden changes in mechanical properties at the interface between different materials.

[0009] Preferably, the ratio of the total thickness of the first metal material layer, the transition layer and the second metal material layer to the thickness of the transition layer is 1:(0.1-0.2).

[0010] The present invention has found that by controlling the thickness of the transition layer to be within the above range, not only the mechanical properties can be further improved, but also the thermal rectification ratio can be kept almost unaffected.

[0011] In the present invention, pure metals generally have a negative κ-T relationship, and alloys have a positive κ-T relationship. Preferably, the first metal material is a pure metal, and the second metal material is an alloy.

[0012] Preferably, the first metal material includes one or more of titanium, copper, silver, iron, nickel, cobalt and lead; the second metal material includes one or more of titanium alloy, copper alloy, nickel alloy, cobalt alloy and iron alloy.

[0013] Preferably, the first metal material includes one or more of titanium, copper, gold and silver; the second metal material is one or more of titanium alloy, copper alloy, nickel alloy and iron alloy. Further preferably, the first metal material is industrial pure titanium TA1; the second metal material is dual-phase titanium alloy TC4.

[0014] In the present invention, the above alloy powder can be obtained from the market, or prepared by a gas atomization method.

[0015] The present invention finds that when the first metal material and the second metal material are the above-mentioned metals, both the mechanical properties and the thermal properties of the thermal rectifier can be improved.

[0016] Preferably, the number of transition layers is ≥1.

[0017] Preferably, the number of layers of the transition layer is greater than 1, and the component ratio of the transition layer changes gradually from the first metal material to the second metal material, and the gradient change is characterized in that along the direction from the first metal material to the second metal material, the amount of the first metal material gradually decreases, while the amount of the second metal material gradually increases.

[0018] As a preferred embodiment of the present invention, the number of layers of the transition layer is 2, including a first transition layer and a second transition layer; the gradient alloy thermal rectifier includes a first metal material layer, a first transition layer, a second transition layer and a second metal material layer which are sequentially contacted, the volume ratio of the first metal material and the second metal material in the first transition layer is 0.6~0.7:0.3~0.4, and the volume ratio of the first metal material and the second metal material in the second transition layer is 0.3~0.4:0.6~0.7.

[0019] As a preferred embodiment of the present invention, the number of transition layers is 3, including a first transition layer, a second transition layer and a third transition layer; the gradient alloy thermal rectifier includes a first metal material layer, a first transition layer, a second transition layer, a third transition layer and a second metal material layer which are sequentially contacted with each other, the volume ratio of the first metal material and the second metal material in the first transition layer is 0.7~0.8:0.2~0.3, the volume ratio of the first metal material and the second metal material in the second transition layer is 0.45~0.55:0.45~0.55, and the volume ratio of the first metal material and the second metal material in the third transition layer is 0.2~.0.3:0.7~0.8.

[0020] As a preferred embodiment of the present invention, the number of layers of the transition layer is 4 layers, including a first transition layer, a second transition layer and a third transition layer; the gradient alloy thermal rectifier includes a first metal material layer, a first transition layer, a second transition layer, a third transition layer, a fourth transition layer, and a second metal material layer which are arranged in contact with each other in sequence, the volume ratio of the first metal material and the second metal material in the first transition layer is 0.75~0.85:0.15~0.25, the volume ratio of the first metal material and the second metal material in the second transition layer is 0.55~0.65:0.35~0.45, the volume ratio of the first metal material and the second metal material in the third transition layer is 0.35~0.45:0.55~0.65, and the volume ratio of the first metal material and the second metal material in the fourth transition layer is 0.15~0.25:0.75~0.85.

[0021] In the present invention, as the number of transition layers increases, the mechanical properties can be further improved, but the improvement in thermal properties is not obvious; however, it should be noted that the preparation of transition layers with more layers is currently difficult and costly. Considering the cost and effect comprehensively, the number of transition layers is preferably 2 to 4 layers.

[0022] The present invention finds that by adopting the above-mentioned gradient alloy structure, the stress concentration at the interface between two metals can be effectively reduced, the mechanical properties of the device such as tensile strength, plasticity, impact toughness and fatigue strength can be improved, and material failure caused by thermal stress can be alleviated.

[0023] In the present invention, when the number of the transition layers is greater than 1, the thickness of each transition layer is equal.

[0024] In the present invention, the above-mentioned gradient structure is formed by using multi-component coaxial powder feeding 3D printing technology. This method can adjust the proportion of the two alloy powders in each deposition layer to achieve a continuously changing composition gradient layer. The thickness of the gradient layer is as small as possible within the accuracy allowable range of the 3D printing equipment used to ensure a high thermal rectification ratio.

[0025] In a second aspect, the present invention provides a method for preparing the gradient alloy thermal rectifier, comprising using directed energy deposition to print layer by layer to obtain the first metal material layer, the transition layer and the second metal material layer that are sequentially arranged in contact.

[0026] Preferably, during the directed energy deposition process, the laser power is controlled to be 800-1200 W, the scanning speed is 600-1000 mm / s, the powder feeding speed is 400-500 μm, and the scanning spacing is 1-2 mm.

[0027] The present invention provides a gradient alloy thermal rectifier and a preparation method thereof, which can effectively reduce the stress concentration caused by the sudden change of mechanical properties at the interface between different materials by optimizing the structure of the rectifier, while keeping the thermal rectification ratio almost unaffected. The present invention reveals the great potential of composition gradient alloys in achieving excellent thermal and mechanical properties at the same time, and the mass production of the scheme can be achieved through 3D printing technology, providing a promising solution for dynamic heat flow control in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1It is the thermal conductivity (κ)-temperature (T) dependence of the alloy for achieving thermal rectification provided by the present invention.

[0030] Figure 2 It is a schematic diagram of the gradient alloy thermal rectifier model provided by the present invention.

[0031] Figure 3 It is a theoretical rectification ratio curve diagram of Examples 1 to 3 and Comparative Example 1 provided by the present invention.

[0032] Figure 4 It is the axial stress distribution diagram of Examples 1~2 and Comparative Example 1 provided by the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Unless otherwise specified, the various raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0035] In the following examples, the κ-T relationship of two metals with opposite trends in thermal conductivity (κ) versus temperature (T) is shown in Figure 1 .

[0036] In the following embodiments, only one, two and four gradient transition layers are provided. Those skilled in the art can provide more transition layers according to actual conditions, which is not limited here. The schematic diagram of the gradient alloy thermal rectifier is shown in FIG. Figure 2 .

[0037] In the following examples and comparative examples, the length L of the thermal rectifier model is 10 mm, the diameter is 3 mm, the ambient temperature is 100 °C, the thermal bias temperature difference is 100 K, and the theoretical rectification ratio curve is shown in Figure 3 In order to verify the theoretical calculation, the thermal and mechanical properties were simulated by ANSYS. The mechanical properties were tested by uniaxial tension with a load of 1000 N applied at both ends. The axial stress distribution is shown in Figure 4 .

[0038] The 3D printing equipment used is the Metal+® 1007 powder-feed metal 3D printer produced by Nanjing Huirui Optoelectronics Technology Co., Ltd.

[0039] Example 1

[0040] This embodiment provides a gradient thermal rectifier, including a TA1 layer, a gradient transition layer and a TC4 alloy layer arranged in contact with each other in sequence, wherein the volume ratio of TA1 and TC4 alloy powders in the gradient transition layer is 1:1, and the thickness of the transition layer is 2 mm. Through calculation, the optimal combination is that the thickness of the TA1 layer is 5.6 mm, the thickness of the TC4 alloy layer is 2.4 mm, and the other forming conditions are the same, and the maximum rectification ratio is 0.203. The forward and reverse heat fluxes in the simulation results are 0.13996 W / mm 2 and 0.11647 W / mm 2 , the rectification ratio is 0.203, and the maximum axial stress gradient is 2.33 MPa / mm. Compared with the model without gradient structure, the rectification ratio decreases by less than 5%, while the peak stress gradient decreases by about 45%.

[0041] This embodiment further provides a method for preparing the gradient thermal rectifier, comprising the following steps: 1. Design a 3D model of the part and use slicing software to convert the 3D model into a printing path (G-code).

[0042] 2. Prepare the TA1 and TC4 alloy powders for use, which are usually spherical or nearly spherical powders to ensure good melting and fluidity; check the particle size distribution and chemical composition of the powders, and load them into the powder tank after drying and washing.

[0043] 3. Preheat the substrate to 200℃ to reduce thermal stress and improve printing quality. Then adjust the height and position of the printing nozzle with a high-energy laser beam source.

[0044] 4. Calibrate the powder delivery system to ensure uniform powder flow rate and distribution.

[0045] 5. The optimal process parameters were determined by process design and density comparison, and were set as the parameters of the powder feeder: laser power 1200 W, laser scanning rate 800 mm / s, powder feeding layer thickness 500~600 μm, and molten pool width 1~2 mm.

[0046] 6. Start the printing program, and the printing nozzle begins to move along the predetermined path, and the angle between two adjacent layer paths is set to 67°.

[0047] 7. The powder feeding system feeds the powder into the molten pool. At the same time, the high-energy laser beam is activated to melt the powder and deposit it layer by layer until the printing is completed and the part is removed.

[0048] Example 2

[0049] The present embodiment provides a gradient thermal rectifier, comprising a TA1 layer, a first gradient transition layer, a second gradient transition layer and a TC4 alloy layer which are sequentially arranged in contact, the volume ratio of the TA1 and TC4 alloy powders in the first gradient transition layer is 2:1; the volume ratio of the TA1 and TC4 alloy powders in the second gradient transition layer is 1:2, and the thickness of the two layers is equal to 1 mm. Through calculation, the optimal combination is that the thickness of the TA1 layer is 5.6 mm, the thickness of the TC4 alloy layer is 2.4 mm, and the maximum rectification ratio is 0.203, which is the same as the model of a single gradient layer. In the simulation results, the forward and reverse heat fluxes are 0.13999 W / mm respectively. 2 and 0.11622 W / mm 2 , the rectification ratio is 0.205. The maximum axial stress gradient is 1.52 MPa / mm, which is 64% lower than that without gradient.

[0050] This embodiment further provides a method for preparing the gradient thermal rectifier, which is the same as that of Embodiment 1.

[0051] Example 3

[0052] This embodiment provides a gradient thermal rectifier, comprising a TA1 layer, a gradient transition layer and a TC4 alloy layer arranged in contact with each other in sequence, wherein the volume ratio of TA1 and TC4 alloy powders in the gradient transition layer is 1:1, and the thickness of the transition layer is 1 mm. Through calculation, the optimal combination is that the thickness of the TA1 layer is 6.4 mm, the thickness of the TC4 alloy layer is 2.6 mm, and the maximum rectification ratio is 0.210. The maximum axial stress gradient is 2.35 MPa / mm.

[0053] This embodiment further provides a method for preparing the gradient thermal rectifier, which is the same as that of Embodiment 1.

[0054] Example 4

[0055] This embodiment provides a gradient thermal rectifier, which differs from the embodiment 1 only in that TA1 is replaced by pure copper and TC4 alloy is replaced by brass. Through calculation, the optimal combination is that the pure copper layer thickness is 5.6 mm, the brass layer thickness is 2.4 mm, and the maximum rectification ratio is 0.051.

[0056] This embodiment further provides a method for preparing the gradient thermal rectifier, which is the same as that of Embodiment 1.

[0057] Example 5

[0058] The present embodiment provides a gradient thermal rectifier, comprising a TA1 layer, a first gradient transition layer, a second gradient transition layer, a third gradient transition layer, a fourth gradient transition layer and a TC4 alloy layer which are arranged in contact with each other in sequence, wherein the volume ratio of the TA1 and TC4 alloy powders in the first gradient transition layer is 4:1, the volume ratio of the TA1 and TC4 alloy powders in the second gradient transition layer is 3:2, the volume ratio of the TA1 and TC4 alloy powders in the third gradient transition layer is 2:3, the volume ratio of the TA1 and TC4 alloy powders in the fourth gradient transition layer is 1:4, and the thickness of the four layers is equal to 0.5 mm. Through calculation, the optimal combination is that the thickness of the TA1 layer is 5.6 mm, the thickness of the TC4 alloy layer is 2.4 mm, and the maximum rectification ratio is 0.203. In the simulation results, the forward and reverse heat fluxes are 0.13971 W / mm respectively. 2 and 0.11575 W / mm 2 , the rectification ratio is 0.206. The maximum axial stress gradient is 0.82 MPa / mm.

[0059] This embodiment further provides a method for preparing the gradient thermal rectifier, which is the same as that of Embodiment 1.

[0060] Example 6

[0061] This embodiment provides a gradient thermal rectifier, which differs from the embodiment 1 only in that the thickness of the transition layer is 3 mm, the thickness of the TA1 layer is 4.6 mm, the thickness of the TC4 alloy layer is 2.4 mm, and the other forming conditions are the same, and the maximum rectification ratio is 0.192. The heat fluxes in the forward and reverse directions in the simulation results are 0.13418 W / mm 2 and 0.11264 W / mm 2 , the rectification ratio is 0.191, and the maximum axial stress gradient is 2.30 MPa / mm.

[0062] This embodiment further provides a method for preparing the gradient thermal rectifier, which is the same as that of Embodiment 1.

[0063] Comparative Example 1

[0064] This comparative example provides a gradient thermal rectifier without introducing a gradient transition layer. The thermal rectifier is made of TA1 and TC4 alloy powders by directed energy deposition printing. The length ratios of the two alloys in 3D modeling are 7.2 mm and 2.8 mm, respectively, according to theoretical calculation results, to obtain a maximum rectification ratio of 0.212. The forward and reverse heat fluxes in the simulation results are 0.14574 W / mm 2 and 0.12017 W / mm 2, the rectification ratio is 0.213, which verifies the theoretical analysis. The mechanical simulation results show that the maximum axial stress gradient is 4.24 MPa / mm.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gradient alloy thermal rectifier, characterized in that: The gradient alloy thermal rectifier is an integrated structure, comprising a first metal material layer, a transition layer, and a second metal material layer which are sequentially arranged in contact with each other; The thermal conductivities of the first metal material and the second metal material change in opposite trends with temperature, and the transition layer is composed of the first metal material and the second metal material.

2. The gradient alloy thermal rectifier according to claim 1, characterized in that: The ratio of the total thickness of the first metal material layer, the transition layer and the second metal material layer to the thickness of the transition layer is 1:(0.1-0.2).

3. The gradient alloy thermal rectifier according to claim 1, characterized in that: The first metal material is a pure metal, and the second metal material is an alloy.

4. The gradient alloy thermal rectifier according to claim 1, characterized in that: The first metal material includes one or more of titanium, copper, silver, iron, nickel, cobalt and lead; the second metal material includes one or more of titanium alloy, copper alloy, nickel alloy, cobalt alloy and iron alloy.

5. The gradient alloy thermal rectifier according to claim 1, characterized in that: The first metal material is titanium, and the second metal material is titanium alloy.

6. The gradient alloy thermal rectifier according to claim 1, characterized in that: The number of the transition layers is ≥1.

7. The gradient alloy thermal rectifier according to claim 6, characterized in that: The number of layers of the transition layer is greater than 1, and the component ratio of the transition layer changes gradually from the first metal material to the second metal material. The characteristic of the gradient change is that along the direction from the first metal material to the second metal material, the amount of the first metal material gradually decreases, while the amount of the second metal material gradually increases.

8. The gradient alloy thermal rectifier according to claim 7, characterized in that: The number of layers of the transition layer is 2, including a first transition layer and a second transition layer; the gradient alloy thermal rectifier includes a first metal material layer, a first transition layer, a second transition layer and a second metal material layer which are sequentially arranged in contact, the volume ratio of the first metal material to the second metal material in the first transition layer is 0.6-0.7:0.3-0.4, and the volume ratio of the first metal material to the second metal material in the second transition layer is 0.3-0.4:0.6-0.7; Or, the number of layers of the transition layer is 3, including a first transition layer, a second transition layer and a third transition layer; the gradient alloy thermal rectifier includes a first metal material layer, a first transition layer, a second transition layer, a third transition layer and a second metal material layer which are sequentially arranged in contact, the volume ratio of the first metal material to the second metal material in the first transition layer is 0.7-0.8:0.2-0.3, the volume ratio of the first metal material to the second metal material in the second transition layer is 0.45-0.55:0.45-0.55, and the volume ratio of the first metal material to the second metal material in the third transition layer is 0.2-0.3:0.7-0.8; Or, the number of layers of the transition layer is 4, including a first transition layer, a second transition layer and a third transition layer; the gradient alloy thermal rectifier includes a first metal material layer, a first transition layer, a second transition layer, a third transition layer, a fourth transition layer, and a second metal material layer which are arranged in contact with each other in sequence, the volume ratio of the first metal material to the second metal material in the first transition layer is 0.75~0.85:0.15~0.25, the volume ratio of the first metal material to the second metal material in the second transition layer is 0.55~0.65:0.35~0.45, the volume ratio of the first metal material to the second metal material in the third transition layer is 0.35~0.45:0.55~0.65, and the volume ratio of the first metal material to the second metal material in the fourth transition layer is 0.15~0.25:0.75~0.

85.

9. The method for preparing the gradient alloy thermal rectifier according to any one of claims 1 to 8, characterized in that: The method comprises adopting directional energy deposition to print layer by layer to obtain the first metal material layer, the transition layer and the second metal material layer which are arranged in contact with each other in sequence.

10. The method for preparing a gradient alloy thermal rectifier according to claim 9, characterized in that: During the directed energy deposition process, the laser power is controlled to be 800-1200 W, the scanning speed is 600-1000 mm / s, the powder feeding speed is 400-500 μm, and the scanning spacing is 1-2 mm.

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