CN103121105B - Method for preparing micro spherical niobium (Nb)-wolfram (W)-molybdenum (Mo)-zirconium (Zr) alloy powder - Google Patents

Abstract

The invention belongs to the field of powder materials and particularly provides a method for preparing micro spherical niobium (Nb)-wolfram (W)-molybdenum (Mo)-zirconium (Zr) alloy powder. According to the method, the mechanical alloying technology is used for preparing Nb-W-Mo-Zr alloy powder, and then the radio frequency plasma spheroidization technology is used for treating the mechanical alloying alloy powder to obtain the micro spherical Nb-W-Mo-Zr alloy powder which is suitable for being used for manufacturing micro thin-wall parts in an injection forming mode, wherein the average particle diameter of the micro spherical Nb-W-Mo-Zr alloy powder is less than 20 micro meters. The method for preparing the micro spherical Nb-W-Mo-Zr alloy powder overcomes the defect that through a traditional niobium alloy powder preparation technology, only powder with particles which are in irregular shapes or have long diameters can be prepared, the average particle diameter of the prepared micro spherical Nb-W-Mo-Zr alloy powder is less than 20 micro meters, and the prepared micro spherical Nb-W-Mo-Zr alloy powder is high in degree of sphericity and good in flowability, is quite suitable for being used for manufacturing thin-wall Nb-W-Mo-Zr alloy parts in a powder metallurgy mode, is especially suitable for being used for manufacturing the thin-wall Nb-W-Mo-Zr alloy parts in the injection forming mode.

Description

A kind of method for preparing fine spherical Nb-W-Mo-Zr alloy powder

technical field

The invention belongs to the field of metal powder research, and particularly provides a method for preparing fine spherical Nb-W-Mo-Zr alloy powder.

Background technique

Due to their excellent high-temperature mechanical properties and special physical and chemical properties, niobium-based alloys are widely used in the fields of aerospace, atomic energy and superconductivity, and are considered to be the most promising structural materials that can be applied in high-temperature environments above 1500K. Nb-W-Mo-Zr alloy, as the mainstream niobium alloy structural material used in my country's aerospace industry, is widely used in the manufacture of rocket engine nozzles, rocket tail fins and other parts.

At present, the vast majority of niobium alloys are prepared by traditional processes, including smelting, casting, pressure processing, welding and many other processes, which have disadvantages such as low material utilization rate, large pollution, and difficulty in preparing parts with complex shapes. Especially for the manufacture of tiny niobium alloy parts with a size of only 10-30mm, a wall thickness of only a few mm, and complex structures such as blind holes, steps, grooves, and arcs, the preparation of traditional processing methods is very difficult. big. As an emerging powder metallurgy technology, Metal Powder Injection Molding (MIM) can near-net shape metal parts, especially suitable for mass production of fine parts with small size and complex structure. It has been widely used in titanium alloy, stainless steel, iron base, high Manufacture of parts for density, cemented carbide and other material systems. Due to the constraints of alloy powder production technology, the related research on MIM niobium alloys at home and abroad is rare.

Metal powder injection molding technology has special requirements on powder shape, particle size, fluidity and other indicators. Good sphericity, suitable powder particle size and high fluidity are the key to the preparation of high-quality injection molding feed, which can increase the feed loading, ensure the isotropy of the injection blank and the uniform shrinkage during the sintering process, thereby reducing the Small parts are deformed to ensure dimensional accuracy. Generally speaking, the most suitable metal powder for injection molding should be a spherical powder of about 20, and for thin-walled parts with particularly complex structures, the particle size of the powder needs to be smaller.

Due to niobium's high melting point (2460°C) and high activity (easy to react with alloying elements, interstitial carbon, oxygen, nitrogen, etc.), the preparation of niobium alloy powder has always been a major technical bottleneck restricting the production of niobium alloys in powder metallurgy. At present, the preparation methods of high-purity niobium alloy powder mainly include hydrogenation-dehydrogenation method, ion rotating electrode method, electron beam atomization, electron beam rapid solidification and mechanical alloying method. These production methods have their own shortcomings, and are not suitable for the production of niobium alloy injection molding powder, especially for the production of spherical niobium alloy powder with a particle size below 20 microns for the preparation of parts with small size and thin-walled structure. .

The hydrogenation-dehydrogenation method uses the difference in mechanical properties of niobium after hydrogen absorption and dehydrogenation to prepare powder, mainly including three steps of hydrogenation, powder making and dehydrogenation. The first is the hydrogenation of the niobium alloy. After the element powder is smelted into a niobium alloy ingot, it is divided into small pieces and heated at a high temperature in a hydrogen atmosphere to infiltrate hydrogen, and then cooled to room temperature. The second is pulverization, using crushing and pulverizing equipment to crush and classify block niobium hydride with a diameter of no more than 2.5cm under the protection of inert gas to prepare hydrogenated niobium alloy powder. The last is dehydrogenation. Under low temperature conditions, the hydrogenated niobium alloy powder is repeatedly heated and dehydrogenated in a vacuum furnace to obtain an irregularly shaped niobium alloy powder with the same microstructure as the original niobium alloy ingot. The niobium powder prepared by this method has irregular shape and poor fluidity, which is not suitable for preparing powder metallurgy parts, but its excellent superconducting property can be used to prepare superconducting materials.

The electron beam atomization process is currently the only industrialized means to obtain high-purity refractory metals. The principle is that under vacuum conditions, the niobium ingot smelted by VAR in the EB chamber moves under the electron gun, and the high-energy electron beam makes it melt continuously, and drops melt on the rapidly rotating water-cooled copper plate, and the molten drop is thrown away by the rotating plate. The droplet is spherical due to the effect of surface tension, and rapidly cools into alloy powder when it collides with the container wall. In addition to vacuum conditions, niobium alloy powders can also be prepared under helium or argon atmosphere. The niobium alloy powder prepared by this method has fewer interstitial inclusions and higher purity, but the production cost is high and the powder particle size is coarse (average particle size is 350 μm), which is not suitable for the preparation of tiny, thin-walled injection-molded niobium alloy parts.

The working principle of the plasma rotating electrode atomization method is to process the niobium alloy ingot into a rod-shaped consumable electrode. The end face of the high-speed rotating electrode rod is melted by the plasma arc, and the molten droplets on the end face of the rod fly under the action of centrifugal force. out, and rapidly solidify into spherical powder particles in a cooling medium (vacuum, helium or argon). The average particle size of the powder prepared by this method is also about 150 μm, which is also not suitable for the preparation of tiny, thin-walled injection-molded niobium alloy parts.

The electron beam rapid solidification method is a method of slightly improving the electron beam centrifugal atomization device, so that the atomized flow of the alloy droplets directly hits a water-cooled copper plate to obtain a rapidly solidified flake alloy powder. The flake niobium alloy powder prepared by this method has a higher cooling rate in the interdendritic region than the EBA and PREP powders, and these dendrite structures have nucleated as early as the alloy droplet state before rapid solidification. The niobium alloy powder prepared by the method is flake-like, has poor fluidity, is not suitable for injection molding, and can be used in fields such as plasma spraying.

The mechanical alloying method is to place the well-proportioned element powder and balls in a ball mill tank filled with inert gas for high-energy ball milling. The violent impact of the grinding ball on the powder is used to force the input of energy, so that the powders are repeatedly deformed, cold welded, broken, etc., and the diffusion between elements is promoted to form alloy powder. Although the particle size of the powder produced by this method is small, the shape is not spherical, the fluidity is poor, and it is not suitable for preparing injection molding fine and thin-walled parts.

Radio Frequency Plasma (RF) spheroidization technology is to inject irregularly shaped powder particles into the plasma torch from the carrier gas through the feeding gun, and melt rapidly in the high temperature environment of the plasma torch, and the melted particles are under the action of surface tension. Highly spherical droplets are formed and rapidly solidified under extremely high temperature gradients to obtain fine spherical powders.

Contents of the invention

The purpose of the present invention is to provide a method for preparing fine spherical Nb-W-Mo-Zr alloy powder. The Nb-W-Mo-Zr alloy powder prepared by this method has high sphericity and small powder particle size, which can be used in powder injection molding production, especially suitable for preparing Nb-W-Mo-Zr alloy parts with small size and thin-walled structure .

The present invention adopts the method of mechanical alloying to prepare Nb-W-Mo-Zr alloy powder, and then adopts radio frequency plasma spheroidization technology to process the mechanical alloying powder, so as to obtain an average particle size suitable for injection molding of tiny and thin-walled parts. Nb-W-Mo-Zr alloy powder with a diameter below 20 microns. The technological process of this method is as shown in Figure 1:

First, weigh the required element powder according to the element ratio;

Secondly, the element powder is ball milled in high-purity argon or vacuum atmosphere, the speed of the ball mill is controlled within the range of 200-500r/min, and the ball milling time is 20-70h;

Figure 2 and Figure 3 are SEM photos before and after powder mechanical alloying. It can be seen from the figure that elemental powders with different particle sizes and shapes are ball milled into uniform and fine equiaxed powders.

Further, the powder obtained by ball milling is subjected to radio frequency plasma spheroidization treatment, by adjusting the power of the equipment between 65-75KW, the feeding rate at 4-8g/min, the system pressure between 97-100 KPa, and the flow rate of the carrier gas at 1.5 -2.5 L/min, the central air flow is between 2-3 L/min, and the side air flow is between 85-95 L/min to control the spheroidizing effect;

Figure 4 and Figure 5 are the SEM photos and XRD diffraction patterns of the spheroidized powder, respectively. It can be seen from the figure that the spheroidized powder has been alloyed, the powder has good sphericity, high spheroidization rate, fine powder, and large The particle size of most powders is below 20 μm;

Finally, the spheroidized powder is inspected, packaged and sealed.

The advantages of the present invention are that the prepared Nb-W-Mo-Zr niobium alloy powder is fine, the average powder particle size is less than 20 μm, the sphericity is high, and the fluidity is good, which can meet the needs of the injection molding process to produce tiny, thin-walled niobium alloy parts. powder requirements.

Description of drawings

Fig. 1 is a process flow diagram of the present invention

Figure 2 is the elemental powder without mechanical alloying treatment

Figure 3 shows the powder after mechanical alloying treatment

Figure 4 shows the powder after radio frequency plasma spheroidization

Figure 5 is the XRD diffraction pattern of the powder after radio frequency plasma spheroidization

detailed description

Embodiment 1: adopt the present invention to prepare fine spherical Nb-5wt% W-2wt% Mo-1wt% Zr alloy powder

Nb powder with a purity of >99.8% and a particle size of -325 mesh; W powder with a purity of >99.9% and a particle size of 3-5 μm; Mo powder with a purity of >99.9% and a particle size of 1-2 μm; purity >99.5% with a particle size of 4-8μm Zr powder as raw material;

According to the alloy composition is Nb-5wt%W-2wt%Mo-1wt%Zr to weigh and mix powder;

The prepared powder is mechanically alloyed on a planetary ball mill, the ball milling speed is 400r/min, and the ball milling time is 50h;

The powder after mechanical alloying was subjected to radio frequency plasma spheroidization treatment, the power of the equipment was 70 KW, the feeding rate was 6 g/min, the system pressure was 99 KPa, the flow rates of carrier gas, center gas and side gas were 2 L/min, 2.5 L/min and 90 L/min;

The powder after plasma spheroidization is inspected, packaged, and sealed. The sphericity of the powder is above 97%, the spheroidization rate is above 98%, the maximum particle diameter is not more than 25μm, and the average particle size is 15μm.

Claims (2)

1. A method for preparing a fine spherical Nb-W-Mo-Zr alloy powder with an average particle diameter below 20 μm, characterized in that the method comprises the following steps: First, weigh the required element powder according to the element ratio; Secondly, the element powder is ball milled in high-purity argon or vacuum atmosphere, the speed of the ball mill is controlled within the range of 200-500r/min, and the ball milling time is 20-70h; Further, the powder obtained by ball milling is subjected to radio frequency plasma spheroidization treatment, by adjusting the power of the equipment between 65-75KW, the feeding rate at 4-8g/min, the system pressure between 97-100KPa, and the flow rate of the carrier gas at 1.5- 2.5L/min, the central air flow is between 2-3L/min, and the side air flow is between 85-95L/min to control its spheroidizing effect; Finally, the spheroidized powder is inspected, packaged and sealed. 2. preparation method as claimed in claim 1 is characterized in that the method is specially: Nb powder with purity>99.8% and particle size of -325mesh; W powder with purity>99.9% and particle size of 3-5μm; Mo powder with purity>99.9% and particle size of 1-2μm; purity>99.5% and particle size of 4 -8μm Zr powder as raw material; According to the alloy composition of Nb-5wt%W-2wt%Mo-1wt%Zr, the powder is weighed; The prepared powder is mechanically alloyed on a planetary ball mill, the ball milling speed is 400r/min, and the ball milling time is 50h; The mechanically alloyed powder is subjected to radio frequency plasma spheroidization treatment, the equipment power is 70KW, the feeding rate is 6g/min, the system pressure is 99KPa, and the flow rates of carrier gas, center gas and edge gas are 2L/min and 2.5L/min respectively and 90L/min; The powder after plasma spheroidization is inspected, packaged and sealed.