Preparation method of NbCr2 / MoSi2 gradient material for scissors

Abstract

The present invention provides a method for preparing a Laves-phase NbCr2 / MoSi2 gradient material, belonging to the field of composite materials. The method comprises: thoroughly mixing the NbCr2 powder required for each layer and the element powder required for synthesizing MoSi2 according to the designed gradient components, number of gradient layers, and component content in each layer, and mechanically alloying the mixture to obtain the mixed powder required for each layer; cold-pressing the mixed powder required for each layer to obtain a semi-densified powder blank; then layering the semi-densified powder blank according to the designed gradient components, number of gradient layers, and component content in each layer to obtain a preform; placing the preform on a rolling mill and performing multiple cumulative roll-formings at a certain temperature to obtain a Laves-phase NbCr2 / MoSi2 gradient material for shears. The Laves-phase NbCr2 / MoSi2 gradient material prepared by the present invention exhibits sufficient reaction, high density, good bonding quality between gradient interfaces, simple process, and low cost.

Description

Technical Field

[0001] The invention relates to a method for preparing a NbCr2 / MoSi2 gradient material, belonging to the technical field of composite material preparation. Background Art

[0002] Most ceramic knives currently on the market are made from zirconium oxide. Zirconia powder is pressed into a blade blank at 2000°C and under 300 tons of pressure. This is then diamond-polished and fitted with a handle to create the finished ceramic knife. However, current ceramic knives often struggle to strike a balance between hardness and toughness. Ceramic knives with high hardness generally have poor toughness, are brittle, and easily break, while ceramic knives with high toughness lack high hardness. Furthermore, existing ceramic knives lack sharpness after sharpening, making them inconvenient to use and prone to blunting, making them unusable. Consequently, there is an urgent need to develop a material that combines high strength with high toughness, while maintaining sharpness after sharpening.

[0003] Laves-phase NbCr2 / MoSi2 gradient materials are novel materials in which NbCr2 and MoSi2 exhibit a continuous gradient across the thickness, resulting in a gradient in material properties. The most significant characteristic of this material is its gradual transition in composition or structure, lacking distinct internal interfaces and resulting in high bonding strength. Furthermore, gradient materials offer excellent designability, meeting the performance requirements of different locations. Summary of the Invention

[0004] In order to solve the shortcomings and deficiencies of the above-mentioned ceramic materials for knives and scissors, the object of the present invention is to provide a method for preparing a Laves phase NbCr2 / MoSi2 gradient material for knives and scissors that has both high strength and high toughness.

[0005] To achieve the above object, the present invention provides a method for preparing a Laves phase NbCr2 / MoSi2 gradient material, the preparation method comprising the following steps:

[0006] a. According to the designed gradient components, number of gradient layers and component content in each layer, the NbCr2 powder required for each layer and the Mo and Si element powders required for synthesizing MoSi2 are fully mixed and mechanically alloyed to obtain the mixed powder required for each layer;

[0007] b. Cold-pressing the mixed powder required for each layer separately to obtain a semi-densified powder blank; then layering the semi-densified powder blank according to the designed gradient components, number of gradient layers, and component content in each layer to obtain a preform;

[0008] c. performing a bidirectional vertical alternating hot rolling process on the preform, wherein the bidirectional vertical alternating hot rolling process comprises:

[0009] The preform is heated at a certain temperature for a certain time, and then hot rolled using a rolling mill with flat rolls for multiple rolling passes, wherein the roll temperature is room temperature, the hot rolling final rolling temperature is 950±50°C, and a certain single-pass deformation amount is used, and the rolling direction of each pass is perpendicular to the rolling direction of the previous pass; the reheating temperature between each pass is 950±50°C for a certain time; after the final rolling, the preform is air-cooled to room temperature to obtain a Laves phase NbCr2 / MoSi2 gradient material for knife shears;

[0010] According to the method of the present invention, the "gradient component" mentioned in step a refers to the specific raw materials used to prepare the Laves phase NbCr2 / MoSi2 gradient material, namely NbCr2 powder, Mo powder and Si powder;

[0011] The “number of gradient layers” refers to the specific designed number of layers of the Laves phase NbCr2 / MoSi2 gradient material, such as 6 layers in Example 2 of the present invention;

[0012] The “component content in each layer” refers to the ratio of different raw materials in each layer of the Laves phase NbCr2 / MoSi2 gradient material;

[0013] According to the method of the present invention, the cold pressing pressure in step b is 80-100 MPa, and the holding time is 5-10 min;

[0014] According to the method of the present invention, the "mixing" and "mechanical alloying treatment" in step a are conventional operations in the art. Those skilled in the art can select appropriate means to fully mix and mechanically alloy the NbCr2 powder and the Mo and Si element powders required for synthesizing MoSi2 according to the needs of on-site operations. In a preferred embodiment of the present invention, the above-mentioned "mixing" and "mechanical alloying treatment" processes are both completed in a planetary ball mill;

[0015] The present invention does not impose any requirements on parameters such as ball milling time, rotation speed and ball-to-material ratio involved in the ball milling process. Those skilled in the art can also select appropriate parameters for ball milling according to the needs of on-site operations, as long as the purpose of sufficient mixing and mechanical alloying treatment can be achieved; in a preferred embodiment of the present invention, the ball milling time is 2-3h, the rotation speed is 300-400r / min, and the ball-to-material weight ratio is 10:1-12:1.

[0016] In addition, those skilled in the art may also add ethanol solvent for wet grinding during the ball milling process according to the needs of on-site operations to avoid oxidation and reaction of NbCr2 powder and Mo and Si element powders required for synthesizing MoSi2. The present invention does not require the solid-liquid ratio of ethanol solvent to NbCr2 powder and Mo and Si element powders required for synthesizing MoSi2. Those skilled in the art may also select a suitable solid-liquid ratio for wet grinding according to the needs of on-site operations. In a preferred embodiment of the present invention, the solid-liquid ratio (volume ratio) is 5:1.

[0017] According to the method described in the present invention, preferably, the particle size of the NbCr2, Mo, and Si element powders in step a is -325 mesh to 500 mesh, and the powder morphology is a mixture of one or more of spherical, nearly spherical, or irregular morphologies.

[0018] According to the method of the present invention, preferably, in step c, the preform is heated to a temperature of 900°C-1000°C for a heating time of 3-5 minutes; the number of multi-pass rolling is 3-6 times; and the deformation of a single pass is 8%-12%.

[0019] Compared with the prior art, the present invention has the following advantages: (1) The gradient material for knives and scissors prepared by the present invention has a density greater than 99%, high density, and uniform microstructure. (2) The gradient material for knives and scissors prepared by the present invention contains high-hardness Laves phase NbCr2, which can achieve high sharpness and high toughness of the knife and scissors edge. (3) The present invention realizes the short process and low-cost preparation of high-performance Laves phase NbCr2 / MoSi2 gradient material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a metallographic image of the NbCr2 / MoSi2 gradient material with a layer structure of NbCr2: MoSi2=1:0.5 prepared in Example 2 of the present invention;

[0021] Figure 2 This is a metallographic image of the NbCr2 / MoSi2 gradient material with a layer structure of NbCr2: MoSi2=1:0.8 prepared in Example 2 of the present invention;

[0022] Figure 3 This is a metallographic diagram of the interface formed by the NbCr2:MoSi2=1:0.2 layer of the NbCr2 / MoSi2 gradient material prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0023] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0024] Example 1

[0025] The raw material powders of this embodiment are: Laves phase NbCr2 powder with a mesh size of -325, Mo powder and Si powder with a mesh size of 200, wherein the method comprises the following specific steps:

[0026] a. Ball milling: NbCr2 powder, Mo powder and Si powder were ball milled in a planetary ball mill for 2 h at a speed of 400 r / min. The ball-to-material volume ratio was 11:1. Ethanol solvent was added during the ball milling process to prevent oxidation of Mo and Si powders. The solid-liquid volume ratio was 4:1.

[0027] b. Cold pressing and layering. The number of gradient layers of the NbCr2 / MoSi2 gradient material in this embodiment is 6, and the thickness of each layer is 1mm. The powder ratio of each layer is (Mo+Si)100wt%, (Mo+Si)80wt% + NbCr220wt%, (Mo+Si)60wt% + NbCr240wt%, (Mo+Si)40wt% + NbCr260wt%, (Mo+Si)20wt% + NbCr280wt%, and NbCr2100wt%, wherein the molar ratio of Mo to Si is 1:2. After ball milling each layer of powder, it is placed in a mold and cold pressed at a pressure of 80MPa to obtain a semi-densified powder blank with a size of 40mm×40mm. The pressed blank is layered according to the designed number of gradient layers.

[0028] c. Hot rolling: The preform is heated at 900°C for 5 minutes, and then hot rolled using a rolling mill with flat rolls for 4 passes, wherein the roll temperature is room temperature, the hot rolling final rolling temperature is 950±50°C, the deformation of a single pass is 10%, and the rolling direction of each pass is perpendicular to the rolling direction of the previous pass; the reheating temperature between each pass is 950±50°C, and the heating time is 3 minutes; after final rolling, the preform is air-cooled to room temperature to obtain a Laves phase NbCr2 / MoSi2 gradient material for knife shears. The gradient composite material has a flexural strength of 2409 MPa, a Vickers hardness of 108 GPa, and a fracture toughness of 15.4 MPa•m 1 / 2 .

[0029] Example 2

[0030] The raw material powders of this embodiment are: Laves phase NbCr2 powder with a mesh size of 100, Mo powder and Si powder with a mesh size of 300, wherein the method comprises the following specific steps:

[0031] a. Ball milling: NbCr2 powder, Mo powder and Si powder were ball milled in a planetary ball mill for 2 h at a speed of 300 r / min. The ball-to-material volume ratio was 11:1. Ethanol solvent was added during the ball milling process to prevent oxidation of Mo and Si powders. The solid-liquid volume ratio was 5:1.

[0032] b. Cold pressing and layering. The number of gradient layers of the NbCr2 / MoSi2 gradient material in this embodiment is 6, and the thickness of each layer is 1 mm. The powder ratio of each layer is (Mo+Si) 50wt% + NbCr250wt%, (Mo+Si) 80wt% + NbCr220wt%, (Mo+Si) 40wt% + NbCr260wt%, (Mo+Si) 60wt% + NbCr240wt%, (Mo+Si) 80wt% + NbCr220wt%, (Mo+Si) 100wt%, wherein the molar ratio of Mo to Si is 1:2. After ball milling each layer of powder, it is placed in a mold and cold pressed at a pressure of 80 MPa to obtain a semi-densified powder blank with a size of 40 mm × 40 mm. The pressed blank is layered according to the designed number of gradient layers.

[0033] c. Hot rolling: The preform is heated at 950°C for 4 minutes, and then hot rolled using a rolling mill with flat rolls for 5 passes, wherein the roll temperature is room temperature, the hot rolling final rolling temperature is 950±50°C, the deformation of a single pass is 9%, and the rolling direction of each pass is perpendicular to the rolling direction of the previous pass; the reheating temperature between each pass is 950±50°C, and the heating time is 4 minutes; after final rolling, the preform is air-cooled to room temperature to obtain a Laves phase NbCr2 / MoSi2 gradient material for knife shears. The gradient composite material has a flexural strength of 2489 MPa, a Vickers hardness of 108.9 GPa, and a fracture toughness of 15.9 MPa•m 1 / 2 .

[0034] The metallographic image of the Laves phase NbCr2 / MoSi2 gradient material prepared in Example 2 is as follows: Figure 1 、 Figure 2 and Figure 3 As shown, it can be seen that the Laves phase NbCr2 / MoSi2 gradient material prepared in Example 2 of the present invention reacts fully and has good interface bonding quality.

[0035] Example 3

[0036] The raw material powders of this embodiment are: Laves phase NbCr2 powder with a mesh size of 100, Mo powder and Si powder with a mesh size of 400, wherein the method comprises the following specific steps:

[0037] a. Ball milling: NbCr2 powder, Mo powder and Si powder were ball milled in a planetary ball mill for 3 h at a speed of 300 r / min. The ball-to-material volume ratio was 10:1. Ethanol solvent was added during the ball milling process to prevent oxidation of Mo and Si powders. The solid-liquid volume ratio was 4:1.

[0038] b. Cold pressing and layering. The number of gradient layers of the NbCr2 / MoSi2 gradient material in this embodiment is 6, and the thickness of each layer is 1 mm. The powder ratio of each layer is (Mo+Si)100wt%, (Mo+Si)30wt% + NbCr270wt%, (Mo+Si)50wt% + NbCr250wt%, (Mo+Si)60wt% + NbCr240wt%, (Mo+Si)70wt% + NbCr230wt%, (Mo+Si)80wt% + NbCr220wt%, wherein the molar ratio of Mo to Si is 1:2. After each layer of powder is ball-milled, it is placed in a mold for cold pressing at a pressure of 90 MPa to obtain a semi-densified powder blank with a size of 40 mm × 40 mm. The pressed blank is layered according to the designed number of gradient layers.

[0039] c. Hot rolling: The preform is heated at 970°C for 5 minutes, and then hot rolled using a rolling mill with flat rolls for 6 passes, wherein the roll temperature is room temperature, the hot rolling final rolling temperature is 950±50°C, the deformation of a single pass is 9%, and the rolling direction of each pass is perpendicular to the rolling direction of the previous pass; the reheating temperature between each pass is 950±50°C, and the heating time is 5 minutes; after final rolling, the preform is air-cooled to room temperature to obtain a Laves phase NbCr2 / MoSi2 gradient material for knife shears. The gradient composite material has a flexural strength of 2480 MPa, a Vickers hardness of 109.1 GPa, and a fracture toughness of 16.1 MPa•m 1 / 2 .

Claims

1. A method for preparing a Laves phase NbCr2 / MoSi2 gradient material, characterized in that: The preparation method comprises the following steps: a. According to the designed gradient components, number of gradient layers and component content in each layer, the NbCr2 powder required for each layer and the Mo and Si element powders required for synthesizing MoSi2 are fully mixed and mechanically alloyed to obtain the mixed powder required for each layer; b. Cold-pressing the mixed powder required for each layer separately to obtain a semi-densified powder blank; then layering the semi-densified powder blank according to the designed gradient components, number of gradient layers, and component content in each layer to obtain a preform; c. performing a bidirectional vertical alternating hot rolling process on the preform, wherein the bidirectional vertical alternating hot rolling process comprises: The preform is heated at a certain temperature for a certain time, and then hot rolled using a rolling mill with flat rolls for multiple rolling passes, wherein the roll temperature is room temperature, the hot rolling final rolling temperature is 950±50°C, and a certain single-pass deformation amount is used, and the rolling direction of each pass is perpendicular to the rolling direction of the previous pass; the reheating temperature between each pass is 950±50°C for a certain time; after the final rolling, the preform is air-cooled to room temperature to obtain a Laves phase NbCr2 / MoSi2 gradient material for knife shears; The cold pressing pressure in step b is 80-100 MPa, and the holding time is 5-10 minutes.

2. The method according to claim 1, characterized in that In the step a, the particle size of the NbCr2, Mo, and Si element powders is -325 mesh to 500 mesh, and the powder morphology is a mixture of one or more of spherical, nearly spherical, and irregular morphologies.

3. The method according to claim 1, characterized in that In step c, the preform is heated to a temperature of 900° C.-1000° C. for a heating time of 3-5 minutes; the multi-pass rolling is performed 3-6 times; and the deformation of a single pass is 8%-12%.

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