JPS62192501A - Co-w coated wc powder - Google Patents

Abstract

PURPOSE:To produce excellent Co-W coated WC powder for powder metallurgy by subjecting the WC powder to an activation treatment and immersing the same into an electroless cobalt plating bath contg. tungstate and hydrazine compd. CONSTITUTION:The WC powder (about 0.1-50mu average grain size) is treated with, for example, an SnCl2-PdCl2 activating soln. by which the surface thereof is activated. The activated WC powder is immersed into the electroless cobalt plating bath contg. the tungstate (sodium tungstate, etc.) and hydrazine compd. (hydrazine hydrochloride, etc.). Cobalt chloride, etc., are used for the cobalt plating bath and the concn. of the cobalt is made about 0.02-0.4mol/l. The concn. of the tungsten is made usually about 0.001-0.6mol/l. The Co-W alloy is thereby precipitated in the form of a uniform layer on the surface of the WC powder and the excellent coating is formed without forming dendrite.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a tungsten carbide (abbreviated as WC) powder suitable for use in powder metallurgy and a method for producing the same.

<Prior art and its problems> Cemented carbide powder, especially that of WC, is widely used as a material for sintered alloys.Normally, N1 or Co powder is mixed as a binder for sintering, but the sintering is not uniform. Because of the lack of properties, attempts have been made to coat the WC powder itself with Ni or Co by electroless plating. However, in such conventional methods, Ni or Co precipitates as dendrites on the surface of the WC powder and does not form a uniform layered coating.

Conventionally, electroless plating baths using primary hypophosphites or boron hydride compounds as reducing agents have been used, but with such reducing agents, P or B is contained in the film at a rate of 3 to 15%, respectively. Alternatively, since it is alloyed by 0.1 to 5%, it gives unfavorable results to the product. Also, WC liberates C during sintering.

Adding a small amount of V has also been done to capture this. The present invention provides a new WC powder that overcomes these drawbacks.

The present inventors added tungstate to a cobalt electroless plating solution and reduced it with hydrazine to obtain a previously unknown and excellent WC powder for powder metallurgy.

<Configuration of the Invention> According to the present invention, WC coated in a layered manner with a Co-W alloy
A powder is provided.

According to the present invention, there is also a method for producing WC powder layered with a Co-u alloy, comprising: activating the WC particles;
A method is provided comprising immersing in an electroless cobalt plating bath containing a tungstate and a hydrazine compound.

The average particle size of the WC powder used in the method of the present invention is not particularly limited, but is usually in the range of 0.1 to 50 μ■,
Preferably it is in the range of 0.5 to 30μ.

To apply Co-u coating to WC powder according to the present invention,
The surface of the wc powder is activated by first treating it with an activation solution of 1, for example, 5nC1, -PdC11. This activation process itself is known and the amount of residual Sn, Pd, etc. is less than 0.1 wt% with respect to WC and has no positive meaning.

Next, a Co-It film is applied by electroless plating. In the present invention, hydrazine and its derivatives are used as reducing agents in the electroless plating bath. The hydrazine compounds used here include hydrazine and hydrated hydrazine,
These include derivatives of hydrazine nitrate, hydrazine sulfate, hydrazine hydrochloride, hydrazine maleate, hydrazine phosphate, and hydrazine carbonate. Since these are used as reducing agents, about 0.3 vt% of N enters into the coated alloy, but it does not have a positive meaning.

Further, in the present invention, in order to alloy Co with V, tungstate is added to the cobalt electroless solution. As a result, V is induced into Cod and W becomes a Co-M alloy.
Precipitates on the surface of C particles. Cobalt salts that can be used include cobalt chloride, cobalt sulfate, cobalt carbonate, and cobalt acetate. Tungstates include ammonium tungstate, potassium tungstate, calcium tungstate, magnesium tungstate, sodium tungstate, and the like. The cobalt concentration in the plating bath is 0.
02mo1/1~0.4mo1#l preferably 0.04
*ol#1~0.15 servings o1/Q. The tungsten concentration is determined by the amount of W to be alloyed, but is usually 0. OO1+sol/Ω to 0.6-ol#l, preferably 0.005mol/l to 0.2s+ol/W.

However, the amounts of Co and W actually precipitated on the powder are not proportional to the concentrations of Co and It in the plating solution.

According to the method of the present invention, the Co-W alloy precipitates uniformly in a layer on the surface of the WC powder, forming an excellent coating without forming a layer.

<Specific description of the invention> The present invention will be specifically illustrated by Examples and Comparative Examples.

Example 1 WC 1001 (5nC1, 10g with an average particle size of 5μ)
/j! , IC120m1l#! It was immersed in a solution containing water for 2 minutes, stirred, separated by decantation, and washed with water.
Next, it was immersed and stirred for 2 minutes in a solution containing PdCl, 1 g/L HCI 2ta (1/Q), decanted, and washed with water.

Separately, adjust the pH of an electroless cobalt plating bath containing cobalt chloride 0.1 *ol #1 Sodium tungstate 0.05 mol/12 Sodium citrate 0.4 ■ ol/1 Hydrazine hydrochloride 0.5 mol/1 with sodium hydroxide. P.H.
Adjusted to 11.0. Sodium citrate is added for the purpose of complexing cobalt. This bath IQ was heated to 80°C and the above! The 11C powder was immersed and stirred, and after confirming that the reaction had completed completely and the color of the bath became clear and colorless, it was separated by decantation, washed with water, and dried. FIG. 1 is an electron micrograph of this particle at 2000 times magnification. As seen there, each particle is not covered with dendrites but in layers.

When the particles were immersed in nitric acid to completely dissolve the plating film and analyzed, 10 particles were coated with a 2% Co-based alloy containing about 0.3% N.

The coverage was about 6% based on WC, and the cobalt in the bath was completely consumed. The contents of Pd and Sn were 43 mg and 6 mg, respectively.

Comparative Example When the same process as in Example 1 was repeated for a cobalt plating bath that did not contain sodium tungstate, the second
A coated powder as shown in the figure was obtained. As can be seen, the cobalt coating becomes dendrite and the WC particles are not completely coated.

Examples 2 to 8 Examples were carried out under the same conditions as in Example 1, but with different tungstate concentrations.

Sodium tungstate concentration Woi/ffi
Coating Example 2 0.001
Layered 3 0.002 4 0.005 5 0.001 6 0.05 7 0.1 8 0.6
#The present invention provides a uniform layered coating by plating the I1IC powder using a Co plating solution containing V.

Additionally, V for free carbon capture can be supplied.

Claims (1)

[Claims] 1. WC powder coated with a layer of Co-W alloy. 2. A method for producing WC powder coated in layers with a Co--W alloy, which comprises activating the WC powder and immersing it in an electroless cobalt plating bath containing a tungstate and a hydrazine compound.