PROCESS FOR THE PREPARATION OF PRE-ALLOYED POWDERS FOR DIAMOND TOOLS, AND THE POWDERS SO OBTAINED

Abstract

A metal powder has a formula FeaCubNicCodSnePfMogWhAxOy, wherein, in weight %, a>50, 5<b<25, c<20, d<5, e<5, 0.5<f<5, 0.5<g+h<5, x+y<5, and a+b+c+d+e+f+g+h+x+y=100. A represents one or more elements having a Gibbs free energy of oxidation at 700 C. which is lower than the Gibbs free energy of oxidation of Mo at 700 C. The pre-alloyed powder is useful for the manufacture of metal-bonded diamond tools. The powder can have a low cobalt content, or even be cobalt-free, yet remain suitable for the production of diamond-loaded segments having harness and bending characteristics approaching or exceeding that of cobalt.

Claims

1. A metal powder according to the formula FeaCubNicCodSnePfMogWhAxOy, with, in weight %, a>50, 5<b<25, c<20, d<5, e<5, 0.5<f<5, 0.5<g+h<5, x+y<5, and a+b+c+d+e+f+g+h+x+y=100; whereby A represents one or more elements having a Gibbs free energy of oxidation at 700 C. which is lower than the Gibbs free energy of oxidation of Mo at 700 C.

2. The metal powder according to claim 1, wherein the metal powder comprises a plurality of metal particles, wherein a major part of the individual metal particles comprises Fe and Cu and P and one or both of Mo and W.

3. The metal powder according to claim 1, wherein x<0.50.

4. The metal powder according to claim 1, wherein the ratio (g+h)/f<2.00.

5. A precursor for preparing a metal powder, the precursor comprising: one or more P-bearing compounds, wherein P is present in an oxidised state, and metal-bearing compounds bearing Fe, Cu and one or both of Mo and W, wherein the Fe, Cu and one or both of Mo and W are present in the metal bearing compounds in an oxidised state.

6. The precursor according to claim 5, wherein the one or more P-bearing compounds comprise diammonium hydrogen phosphate.

7. The precursor according to claim 5, wherein the metal bearing compounds comprise ammonium dimolybdate and/or ammonium metatungstate.

8. The precursor according to claim 5, wherein the metal bearing compounds comprise Fe-oxide, -hydroxide, -oxyhydroxide, -carbonate, and/or -oxalate and wherein the metal bearing compounds comprise Cu-oxide, -hydroxide, -oxyhydroxide, -carbonate, and/or -oxalate.

9. A pre-alloyed powder according to the formula FeaCubNicCodSnePfMogWh, with, in weight %, a>50, 5<b<25, c<20, d<5, e<5, 0.5<f<5, 0.5<g+h<5, and a+b+c+d+e+f+g+h>95%; wherein the powder is obtainable from a precursor according to claim 5.

Description

Example 1: Preparation of a Powder Fe20% Cu2% Mo2% P

[0088] A mixture containing respectively 128 g/L and 33 g/L of iron and copper chloride is prepared. This mixture is then added at a rate of 3 L/min to 6.02 L of sodium hydroxide at 300 g/L. The pH is maintained between 9 and 12 and the temperature of the reagents is kept below 80 C. A hydroxide precipitate is obtained, which is filtered and washed with distilled water heated to 60 C. The wet hydroxide is repulped in a solution containing 35 g of ammonium di-molybdate and 82 g of diammonium hydrogen phosphate. This suspension is then dried under air and reduced for 2 hours at 630 C. under a hydrogen flow rate of 300 L/h. The aggregated powder is crushed and sieved. The Fisher particle size is 2.2 m, and the oxygen content is 0.68% by weight.

Example 2: Preparation of a Powder Fe10% Cu2% Mo2% W1% P

[0089] A mixture containing respectively 108 g/L and 13 g/L of iron and copper chlorides is prepared. This chloride mixture is then added at a flow rate of 3 L/min to 8.3 L of sodium hydroxide at 300 g/L. The pH is maintained between 9 and 12 and the temperature of the reagents is kept below 80 C. A hydroxide precipitate is obtained, which is filtered and washed with distilled water heated to 60 C. The wet hydroxide is repulped in a solution containing 41 g of ammonium di-molybdate and 39 g of diammonium metatungstate. This suspension is then dried under air and reduced for 5 hours at 680 C. under a hydrogen flow rate of 300 L/h. The aggregated powder is crushed and sieved. The Fisher particle size is 6.8 m, and the oxygen content is 0.38% by weight.

Example 3: Densification of a Powder Fe10% Cu2% Mo2% P

[0090] The powder according Example 1 is compressed to 200 MPa so as to obtain green articles, having dimensions 251010 mm. These are free sintered under pure hydrogen for 1 hour at 850, 900, 950 and 1000 C., applying a heating rate of 200 C./h, and followed by natural cooling. Density measurements according to ISO3369 and Vickers hardness determinations according to ISO6507: 2018 are carried out. The results are summarized in Table 1.

TABLE-US-00001 TABLE 1 Sintering temperature Pressure ( C.) (MPa) Density HV10 850 200 7.53 231 900 200 7.80 269 950 200 7.85 266 1000 200 7.84 287

[0091] A temperature of at least 900 C. is needed to obtain dense articles having an optimal harness.

Example 4: Effect of Copper on the Composition FeCu2% Mo2% P

[0092] Three different powders are prepared according to Example 1, to determine the effect of copper on the hardness, as a function of the sintering temperature. The powders are compressed at 200 MPa and then free sintered under hydrogen for 1 h at 900 and 1000 C. The results are summarized in Table 2.

TABLE-US-00002 TABLE 2 Cu Sintering temperature (%) ( C.) HV10 5 900 243 1000 282 10 900 269 1000 266 20 900 219 1000 255

[0093] With about 5% of copper, a sintering temperature of 950 C. is required to reach an optimal hardness. This same rather high temperature of 950 C. is required with 20% of copper. Remarkably, with about 10% of copper, more particularly with 8 to 12% of copper, the optimal harness is already obtained at only 900 C., which is advantageous.

Example 5: Effect of Mo and P on the Composition Fe10% CuMoP

[0094] In this example, the hardness and flexural properties of several compositions are compared by varying the concentrations of molybdenum and phosphorus. The copper content is 10%, with iron balancing the composition. Each powder is prepared according to Example 1, compressed at 200 MPa and then free sintered at 900 C. The results are summarized in Table 3.

TABLE-US-00003 TABLE 3 Composition Density after Mo P sintering at Hardness Bending test Alloy (%) (%) 900 C. (HV10) (N) 1 Cobalt 8.50 237 1337 2 0.75 1 7.80 260 1353 6 0.75 4 7.59 298 1137 7 4 1 7.92 253 1516 8 4 4 7.75 303 1075 9 2 2 7.79 266 1247 10 2 1.5 7.78 252 1295 11 2 0.5 7.85 222 No breaking 12 2 1 7.67 220 1299 13 0.75 0.5 7.64 196 No breaking

[0095] The skilled person will have the possibility to optimize the amounts of Mo and P in function of the desired harness and ductility of the end products. The above table can serve as a guide. The versatility offered by matching the characteristics of the product to the intended use is unique and is not available when using pure cobalt powder.

Example 6: Comparison with Conventional Powder Blending Process

[0096] Three different powders are prepared according to Example 1 and shaped either by free sintering or by hot pressing. These same three compositions are also prepared according to the conventional route, i.e. using a mixture of powders. The powders used are carbonyl iron and standard copper, iron phosphide at 10% by weight of phosphorus, and molybdenum powder, all powders having a Fisher size of 8 m or less. The results are summarized in Table 4.

TABLE-US-00004 TABLE 4 Hard- Den- ness Case Composition Process Sintering sity (HV10) 1 FeCu10P2Mo2 Powder Free sinter- 7.22 193 mixture ing at 200 (Compar- MPa & 900 ative) Ex- C. 7.79 266 ample 1 2 FeCu20P2Mo1 Powder Hot press 7.68 248 mixture sintering (Compar- at 800 C. ative) Ex- 7.79 317 ample 1 3 FeCu10P2Mo2 Powder Hot press 7.65 256 mixture sintering (Compar- sing at 800 ative) Ex- C. 7.70 349 ample 1

[0097] In the 1.sup.st case, using free sintering at 900 C., the powder mixing process (Comparative example) delivers a product having a low density, and consequently also a low hardness.

[0098] In the 2.sup.nd and 3.sup.rd cases, using hot press sintering at 800 C., the powder mixing process (Comparative example) delivers a product having an adequate density, but showing a relatively low hardness comparing to products prepared according to the invention.

[0099] In all powders of the examples, the Fe.sub.3P-phase was observed by means of XRD.

[0100] The process of Example 1, according to the invention, consistently delivers a suitable product.