JPS6237682B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an alloy powder containing molybdenum and tungsten, which is suitable for producing a stable composite carbide composed of molybdenum and tungsten. Conventionally, the manufacturing method of MoC-WC solid solution is as follows:
WC, Mo and C powder or W, Mo and C
The usual method is to add cobalt to the powder to make a mixed powder, then fill it in a carbon container and react at a temperature of 1,600 to 2,000 degrees Celsius (W. Dawihl, Z. anorg.
chem. 262 (1950), 212). At this time, cobalt is said to help the formation of carbides and promote the solid solution of Mo and C in WC, and it is also known that a solid solution of (Mo, W)C cannot be obtained if Co is not present. It is being However, when the (Mo,W)C powder obtained by this method was used as a substitute for WC in the production of cemented carbide, it was found that (Mo,W)C was found in the alloy.
decomposes and precipitates acicular crystals as (Mo, W) ₂ C, and a small amount of Mo ₂ C in the alloy aggregates and precipitates, significantly deteriorating the alloy strength. For these reasons, until now no attempt has been made to actively use MoC as a substitute for WC. The inventors believe that if (Mo, W)C is stable in the alloy, this powder can be used as a substitute for expensive WC, and have been studying methods for producing stable (Mo,W)C. However, this time (Mo, W)C
We obtained the following new findings regarding the production process. In producing a solid solution of (Mo,W)C, first
It is necessary to heat at a temperature of 1,600° C. or higher, in order to cause the Mo, W metal or carbide powders to diffuse into each other to form a uniform solid solution. However, in order to diffuse and form a solid solution of Mo and W metal powders of several μm with each other as in the conventional method, high temperatures and long-time heating as shown in Table 1 are required.

[Table] On the other hand, if the powder particles are very fine, diffusion will be easily carried out, and since iron group metals as diffusion aids will be unnecessary, it will be possible to obtain high-quality carbides. Therefore, it becomes a challenge to produce fine (Mo, W) metal powder. Traditionally, in the production of (Mo, W) metal, mechanical mixing of hydroxide in a slurry state and chemical co-precipitation of hydroxide have been mainly used; This has the disadvantage that mixing at the molecular level cannot be achieved, and the latter has the disadvantage that the acid concentration (PH) at which molybdenum and tungsten oxides are precipitated by acid decomposition is different, so the precipitated composition is not constant. Mo, W) metal could not be obtained. The inventors have now discovered that finely dispersed (Mo, W) metal can be produced for the first time by freeze-drying, and have arrived at the present invention. Freeze-drying is originally a method of drying substances that are easily decomposed by heat or that easily foam by freezing them under a high vacuum and then removing them as water vapor by sublimating the ice. When producing carbide, by using (Mo, W) metal produced by freeze-drying, it is possible to simply combine (Mo, W) metal and carbon without using a diffusion aid such as cobalt as in the past. By mixing and carbonizing the mixture, it has become possible to produce a carbide having a theoretical combined carbon content. In the present invention, the ammonium salts of molybdenum and tungsten are freeze-dried and then roasted in the air to uniformly refine the oxides of tungsten and molybdenum, which are then subjected to a reduction process to form an alloy to produce an alloy powder. The alloy powder is reacted with carbon powder to produce a composite carbide consisting of molybdenum and tungsten having a solid solution crystal structure of hexagonal monocarbide. The suitable composition of the tungsten-molybdenum solid solution particles is Mo/W=0.005 to 10 in terms of weight ratio,
If it is less than 0.005, the oxidation resistance and heat resistance will be equivalent to pure W, and the characteristics of Mo will not be utilized, and if it is more than 10, it will not have a simple hexagonal crystal form equivalent to WC in the carbide stage, so it is not suitable. Therefore, it is preferable that Mo/W=0.005 to 10 (weight) even at the stage of alloy production. After the oxides of tungsten and molybdenum are uniformly refined, a known reducing agent such as hydrogen or carbon (which performs reduction and carbonization at the same time) is used to reduce the oxides of tungsten and molybdenum. The reaction temperature is the activation temperature of carbon, that is, 800°C or higher. In producing the above-mentioned alloy powder, an ammonium salt of one or more metals in the A, A, and A groups other than molybdenum and tungsten can be added, which can be expected to refine and stabilize the alloy. The amount added is preferably 0.5 to 40% by weight. That is, if it is less than 0.5% by weight, no significant addition effect is observed, and if it is more than 40% by weight, the alloy tends to decompose into two or more phases, which is not appropriate. Example 1 200 ml of ammonium solution (liquid temperature 25°C) of 0.7 mol molybdenum and 0.3 mol tungsten was
sprayed into liquid nitrogen at a rate of ml/sec,
Frozen quickly. After reducing the pressure to 0.01 torr, the sample was transferred from liquid nitrogen to dry ice, salt +
The temperature was gradually increased through ice, ice, and an aqueous solution to sublimate the ice, and about 50 g of white powder was obtained after 8 hours. This powder was heated to 400° C. in the atmosphere for 1 hour and roasted for 40 minutes while flowing air at 10/min to obtain 34 g of oxide powder. As a result of structural analysis by X-ray diffraction and average particle size distribution measurement by laser scattering method, it was found that a homogeneous oxide with an average particle size of 0.16μ was formed. The obtained oxide was heated for 1 hour in a hydrogen atmosphere (hydrogen flow 10/min).
The temperature was raised to 900°C over an hour, and the temperature was maintained at 900°C for 1 hour to perform reduction, and 20g of alloy powder was obtained. When the lattice constant of the obtained alloy was measured using X-rays, it was found to be 3,152 Å, indicating that it was a complete solid solution. The average particle size was 0.18μ. Reference Example 1 91.0% by weight of the alloy powder produced as in Example 1 and 9.0% by weight of carbon powder were mixed, and this mixed powder was reacted in a hydrogen stream at 1700° C. for 30 minutes.
When the properties of the obtained carbide were investigated, as shown in Table 2, the amount of bonded carbon was sufficiently close to the theoretical value, and all of the carbides were WC type monocarbide.

[Table] Example 2 Using the method of Example 1, 200 ml of an ammonium solution containing 0.7 mol of molybdenum, 0.25 mol of tungsten, and 0.05 mol of chromium was mixed into 1 ml/ml at a liquid temperature of 50°C.
Spray into liquid nitrogen at a rate of seconds and freeze quickly. The ice was sublimated in the same manner as in Example 1 over 10 hours to obtain about 45 g of white powder.
This powder was heated to 400℃ in the atmosphere for 1 hour, and
Roasting was performed at ℃ for 40 minutes to obtain 31 g of oxidized powder. As a result of structural analysis using X-ray diffraction and particle size distribution measurement using laser scattering method, it was found that it was a homogeneous oxide with an average particle size of 0.18μ. This powder was heated to 900° C. in 1 hour in a hydrogen flow of 10/min, and was maintained at 900° C. for 1 hour to perform reduction, and 22 g of alloy powder was obtained. This powder had an average particle size of 0.19μ, a lattice constant of 3.162Å, and was a complete solid solution.

Claims (1)

[Claims] 1. The invention is characterized in that the ammonium salts of molybdenum and tungsten are freeze-dried and then roasted in the air to uniformly refine the oxides of tungsten and molybdenum, which are then subjected to a reduction process to form an alloy. A method for producing an alloy powder consisting of molybdenum and tungsten. 2 In the ammonium salt of molybdenum and tungsten, a, other than molybdenum and tungsten,
2. The method for producing an alloy powder according to claim 1, wherein an ammonium salt of one or more metals of Group A and Group A is added.