阅读说明：本技术 一种硬质合金表层原位合成纤维状纳米碳化钨的方法 (Method for in-situ synthesis of fibrous nano tungsten carbide on surface layer of hard alloy ) 是由 郝胜智 彭文海 卢健 吴垚 杨勃行 姜梦琦 于 2019-10-29 设计创作，主要内容包括：一种硬质合金表层原位合成纤维状纳米碳化钨的方法,属于材料技术领域。通过利用强流脉冲电子束和低温回火,对硬质合金表层进行显微结构调控,强流脉冲电子束辐照的表层微区在满足纳米亚稳组织形成的热动力学和结晶学条件,而温度低于烧结温度的回火,使得固态相变仅仅发生于硬质合金表层的亚稳态组织中。制备时,(1)对硬质合金块体表面进行打磨后,清洗风干；(2)对硬质合金块体进行强流脉冲电子束表面辐照处理；(3)将辐照后的硬质合金块体置于真空管式炉中进行低温回火。本发明的工艺简单,可靠性高,操作方便；硬质合金表层晶粒快速熔凝及固态相变后得到的纳米碳化钨复合结构,这种稳定的纤维状纳米结构起到强化硬质合金表面的作用。(A method for in-situ synthesizing fibrous nano tungsten carbide on a hard alloy surface layer belongs to the technical field of materials. The microstructure of the surface layer of the hard alloy is regulated and controlled by using the high current pulse electron beam and low-temperature tempering, the micro area of the surface layer irradiated by the high current pulse electron beam meets the thermodynamic and crystallography conditions formed by a nano metastable structure, and the temperature is lower than the sintering temperature, so that the solid phase change only occurs in the metastable structure of the surface layer of the hard alloy. The preparation method comprises the following steps of (1) polishing the surface of a hard alloy block, and then cleaning and air-drying the hard alloy block; (2) performing high-current pulse electron beam surface irradiation treatment on the hard alloy block; (3) and (3) placing the irradiated hard alloy block in a vacuum tube furnace for low-temperature tempering. The invention has simple process, high reliability and convenient operation; the stable fibrous nano structure plays a role in strengthening the surface of the hard alloy.)

1. A method for in-situ synthesizing fibrous nanometer tungsten carbide on a hard alloy surface layer is characterized in that a strong current pulse electron beam and low-temperature tempering treatment are adopted in the preparation method to prepare a fibrous nanometer tungsten carbide composite structure on the hard alloy block surface layer in situ without changing the structure and the performance in the hard alloy block, and the method comprises the following steps:

(1) pretreatment of cemented carbide blocks

Polishing the surface of a hard alloy block sample to obtain a relatively flat surface, then sequentially carrying out ultrasonic oscillation cleaning for 5-15min by using alcohol and deionized water, and drying by cold air;

(2) inducing surface nano metastable tissue by irradiation of high current pulse electron beam

Fixing the hard alloy block obtained in the step (1) on a sample target in a vacuum chamber of a high-current pulse electron beam device according to the polished surface and the direction vertical to the electron beam axis, wherein the air pressure in the vacuum chamber is 5.5-7.5 multiplied by 10^-3Pa, electron beam energy density 2-8J/cm²Irradiating for 6-20 times under the conditions of the accelerating voltage of 27keV, the pulse width of 0.5-6 mus and the target pole distance of 10-15cm to obtain a hard alloy block with a nano metastable tissue on the surface layer;

(3) inducing nano metastable organization solid phase transition by utilizing low-temperature tempering

Placing the hard alloy block obtained in the step (2) in a vacuum tube furnace, vacuumizing, and introducing Ar gas as protection; the temperature of the tube furnace is increased to 550 ℃ and 750 ℃, the temperature is kept constant for 0.5 to 2.5 hours, and then the tube furnace is cooled to room temperature, so as to obtain the gradient hard alloy block body with the fibrous nano tungsten carbide on the surface layer.

2. The method for in-situ synthesis of the fibrous nano tungsten carbide on the surface layer of the hard alloy according to claim 1, wherein in the step (1), 180#, 360#, 800# and 1200# diamond millstones are sequentially selected for surface grinding of the hard alloy block sample.

3. The method for in-situ synthesis of fibrous nano tungsten carbide on the surface layer of cemented carbide as claimed in claim 1 or 2, wherein in the step (3), the temperature rise rate of the tube furnace is 5-15 ℃/min.

Technical Field

The invention belongs to the technical field of materials, and provides a method for in-situ synthesis of fibrous nano tungsten carbide on a hard alloy surface layer.

Background

The hard alloy is made into cutters and wear-resistant elements due to good mechanical properties, such as high hardness, high strength, good wear resistance and the like, and is widely applied to various fields of industrial production. It is a composite material prepared by powder metallurgy method, mainly composed of hard phase (refractory metal carbide) and binding phase (metal). Research shows that the grain size of the hard phase in the hard alloy has important influence on the mechanical property of the hard alloy, and the hardness, the strength and the wear resistance of the hard alloy material can be simultaneously improved by refining the hard phase grains. For preparing fine-grained cemented carbide, high-energy ball milling, thermochemical synthesis, plasma and mechanical alloying methods have been developed to prepare nanopowders, or metal inhibitors to limit the growth of hard phases have been added during sintering. The application of the hard alloy material is analyzed, and the surface strength and the wear resistance of the hard alloy material can be effectively improved by changing the surface structure of the hard alloy. Therefore, there are technologists working on developing cemented carbides with a gradient structure (i.e., fine surface grains and coarse matrix grains). However, the existing gradient hard alloy preparation process is still imperfect, the process flow is complex, the influence factors are many, and the maintenance cost of production equipment is high.

According to the tungsten-carbon phase diagram, there are three main types of tungsten-carbon compounds, WC and W₂C、WC_1-x. Wherein WC is the most stable as the hard phase of common cemented carbides; WC_1-xIs a metastable phase which is stable at a temperature above 2516 ℃ and below which decomposition to form WC and W occurs₂C. The non-equilibrium solidification thermodynamic analysis of the ultra-high-speed cooling shows that the cooling speed of the melt reaches 10⁸Nano-sized WC can be obtained at room temperature at DEG C/s_1-x. High current pulse electricityThe irradiation of the sub-beams can instantly melt and rapidly cool the surface layer of the block hard alloy at a cooling speed of 10^8-10The temperature/s can meet the non-equilibrium solidification condition, and metastable nanometer WC can be obtained_1-x. The stable nanometer WC surface layer can be obtained by properly heating and tempering the structure, and the preparation of the hard alloy with the gradient structure is realized.

Disclosure of Invention

The invention firstly uses strong current pulse electron beam to irradiate the surface of the hard alloy block body to lead the surface crystal grain to be melted and form the metastable nanometer WC in the ultra-high speed non-equilibrium solidification process_1-x(ii) a And then, tempering the irradiated hard alloy block at a proper low temperature to prepare the gradient structure hard alloy with the nano WC surface layer.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for in-situ synthesizing fibrous nanometer tungsten carbide on a hard alloy surface layer is characterized in that a strong current pulse electron beam and low-temperature tempering treatment are adopted to prepare a fibrous nanometer tungsten carbide composite structure in situ on the hard alloy block surface layer, the structure and the performance in the hard alloy block are not changed, the obtained fibrous nanometer tungsten carbide composite structure is fine in surface layer structure and high in hardness and strength, the special fibrous structure is also beneficial to improving the wear resistance of the hard alloy surface, and the method specifically comprises the following steps:

(1) pretreatment of cemented carbide blocks

And (3) polishing the surface of the hard alloy block sample by using a diamond grinding disc, then sequentially carrying out ultrasonic oscillation cleaning for 5-15min by using alcohol and deionized water, and drying by cold air to obtain the hard alloy block.

The polishing specifically comprises the following steps: and diamond millstones of 180#, 360#, 800#, and 1200# are selected in sequence for polishing to obtain a smoother surface, which is favorable for the electron beam energy to act on the micro-area of the surface layer of the hard alloy more uniformly.

(2) Inducing surface nano metastable tissue by irradiation of high current pulse electron beam

Fixing the hard alloy block obtained in the step (1) on a high-current pulse electrode in a manner that the polished surface is vertical to the axial direction of an electron beamThe sub-beam device is arranged on a sample target in a vacuum chamber, and the air pressure in the vacuum chamber is 5.5-7.5 × 10^-3Pa, electron beam energy density 2-8J/cm²Irradiating for 6-20 times under the conditions of the accelerating voltage of 27keV, the pulse width of 0.5-6 mus and the target pole distance of 10-15cm to obtain the hard alloy block with the nano metastable tissue on the surface layer.

(3) Inducing nano metastable organization solid phase transition by utilizing low-temperature tempering

And (3) placing the hard alloy block obtained in the step (2) into a vacuum tube furnace, vacuumizing, and introducing Ar gas for protection. The temperature of the tubular furnace is raised to 550-750 ℃ at the speed of 5-15 ℃/min, the temperature is kept for 0.5-2.5 hours, and then the temperature is cooled to room temperature along with the furnace, so that the gradient hard alloy block with the fibrous nano tungsten carbide on the surface layer is obtained, the internal structure of the hard alloy block is unchanged, and the fibrous nano tissue on the surface layer has better hardness, strength and wear resistance, thereby playing a good protection role.

The obtained surface fibrous gradient hard alloy block is subjected to surface microhardness test, the surface microhardness of the obtained surface fibrous gradient hard alloy block is greatly improved compared with that of a hard alloy block which is not subjected to any treatment, and the prepared gradient hard alloy block can be applied to wear-resistant parts such as cutting tools, drill bits, dies and the like, so that the service life of the parts, the processing precision and the quality of workpieces are improved.

The invention has the beneficial effects that:

(1) the energy density of the high-current pulse electron beam is high, and the temperature condition of the irradiation induction surface micro-area is more favorable for the hard alloy surface layer to form a fine nano metastable state structure; annealing the metastable structure at low temperature can form stable fibrous tungsten carbide with the same scale through solid-state phase transition.

(2) The whole preparation process is simple in flow, high in reliability and few in influencing factors; the prepared hard alloy with the fibrous nano-structure surface layer has higher surface hardness and better surface wear resistance.

Drawings

Fig. 1 is a scanning electron micrograph of untreated sintered cemented carbide.

FIG. 2 is the SEM image of the surface of the cemented carbide after the irradiation of the high current pulsed electron beam in example 2.

FIG. 3 is the SEM photograph of the surface of the cemented carbide after low temperature tempering in example 2.

FIG. 4 is a comparison of the micro-hardness of the surface of the cemented carbide of example 2.

Detailed Description

The present invention will be described in more detail with reference to the following examples, which are not intended to limit the scope of the present invention.