HK1075475B - Pre-alloyed bond powders - Google Patents

Description

Prealloyed bond powder

There are various methods for manufacturing diamond tools. In each case, the diamond is first mixed with a bonding powder consisting of one or more metal powders and possibly some ceramic powder or organic binder. This mixture is then pressed and heated to form a solid mass in which the bonded powder forms bonds the diamonds together. Hot pressing and free sintering are the most common methods of forming bonds. Other methods are not commonly used, such as hot coining and hot isostatic pressing of pre-sintered parts. Cold pressed powders that require a subsequent heating step to form a bond are often referred to as green bodies and are characterized by their green strength.

The most commonly used metal powders in diamond cutter applications are fine cobalt powders having a diameter of less than about 7 μm as measured by the fischer tropsch particle size tester (FSSS), mixtures of fine metal powders, such as mixtures of fine cobalt, nickel, iron and tungsten powders, and fine prealloyed powders composed of cobalt, copper, iron and nickel.

The use of fine cobalt powder gives good results from a technical point of view; its main drawbacks result from high prices and strong price fluctuations. Furthermore, cobalt is suspected of damaging the environment, so new regulations encourage avoidance of cobalt. With a mixture of metal powders, the strength, hardness and wear resistance of the resulting bond are relatively low. The use of pre-alloyed powders offers significant advantages over elemental powder mixtures, as the homogeneity of the mixture has ｃA substantial effect on the mechanical properties of the final tool, as demonstrated in EP- ｃA-0865511 and EP- ｃA-0990056. These bonded powders are conventionally prepared by the methods described in the above-mentioned patents. The reason is that this is the only economical way to obtain sufficiently fine particles so that they have sufficient sintering reactivity, while at the same time being able to make suitable compositions to make the properties of the sintered mass sufficient, in particular its hardness, ductility, wear resistance and diamond retention.

However, in the diamond tool industry, bonding needs to exhibit better performance than that obtained with state-of-the-art pre-alloyed powders or fine metal powder mixtures. Better joining properties mean a combination of higher hardness and sufficient ductility. Ductility is indicated by impact resistance. It should preferably be up to 20J/cm on non-notched test specimens, measured according to the Charpy method (Charpy) according to ISO 5754 on a Charpy (Charpy) apparatus as described in ISO 184²Is measured. Low Charpy (Charpy) values are indicative of brittle bonding. Another indication of ductility is the fracture plane of the fracture bond. It should preferentially reveal (micro) ductility.

Hardness is expressed in terms of Vickers hardness (HV10), and when hardness values are given, they can be assumed to be determined according to ASTM E92-82. It is believed that empirical rules alone generally dictate higher hardness with corresponding higher mechanical strength, higher wear resistance and better diamond retention. HV10 values of 200-350 are common in this field.

Increased wear resistance is required for cutting abrasive materials such as fresh concrete or asphalt. The state of the art is to use tungsten carbide and/or the addition of tungsten. These raw materials are mixed together with the rest of the binding powder. The homogeneity of the resulting mixture is important to the performance of the cutter. The tungsten and/or tungsten carbide rich region is typically very brittle. Moreover, since tungsten and tungsten carbide are difficult to sinter, their use increases the local porosity, resulting in a local weakening of the mechanical properties of the bond.

In addition to the binding properties described in the preceding paragraph, the properties of the binding powder are also important. Depending on the application, the bonding powder may need to have good sintering properties and wet strength.

The wet strength is determined by means of the drum test (Rattler test). Placing a green compact having a height of 10mm and a diameter of 10mm, pressed at 350MPa, on a container made of a material having a thickness of 1mm²In a rotating cylinder (length 92mm, diameter 95mm) made of fine wire mesh. After 1200 revolutions in 12 minutes, the relative weight loss was determined. This result is hereinafter referred to as the "tumbler value". Lower tumbler values indicate higher wet strength. In applications where wet strength is important, tumbler values of less than 20% are considered satisfactory, while values of less than 10% are considered excellent.

In powder metallurgy, it is important that metal powders exhibit good sintering reactivity. This means that they can be sintered at relatively low temperatures to near true density, or the sintered mass needs only a short time to reach true density. The minimum temperature required for good sintering should be low, preferably not higher than 850 ℃. Higher sintering temperatures can lead to disadvantages such as reduced sintering die life, diamond degradation, and high energy costs. Good sinterability is an indication of the relative density obtained. The relative density of the sintered bond powder should be at least 96%, preferably 97% or greater. Typically, a relative density of 96% or greater is considered to be close to the true density.

The sintering reactivity depends mainly on the composition of the powder. However, there is often not much choice as to the components, either for cost reasons or because certain properties of the sintered product, such as hardness, cannot be obtained if the components are changed. Another factor affecting sintering reactivity is surface oxidation. Most metal powders, when exposed to air, oxidize to some extent. The surface oxide layer thus formed prevents sintering. A third factor that is very important for the sintering reactivity is the particle size. All else being equal, fine powders have a higher sintering reactivity than coarse powders.

In order to improve the sintering properties of the bonded powder, bronze (Cu — Sn alloy) or brass (Cu — Zn alloy) is sometimes added: they lower the melting point and thus the sintering temperature. Typically used bronze powders have a Sn component of 15-40%. However, the use of these powders often results in brittle bonding or the formation of a liquid phase during sintering. Both of which are detrimental to the quality of the final bond. Moreover, the addition of bronze or brass softens the bond, thus partially eliminating the effect of the W or WC addition.

The state of the art in diamond tool technology has not provided a real solution to the problems of increased hardness while maintaining low sintering temperatures, ease of machining, sufficiently high impact resistance, and sufficient wet strength. In the prior art, no powder or mixture having all these properties is present.

Prealloyed Powder is defined as "a metal Powder consisting of two or more elements alloyed by Powder manufacturing process, wherein the particles are all the same nominal component", see Metals Handbook, Desk Edition, ASM (american metal association), Metals Park, Ohio (Ohio), 1985 or Metals Handbook, vol.7 (volume seventh), Powder Metallurgy, ASM (american metal association), Ohio (Ohio), 1984.

It is an object of the present invention to provide a pre-alloyed powder which has sufficient strength for conventional processing when cold pressed and which sinters at a minimum temperature of not more than 850 ℃, and in which the final bond exhibits sufficient ductility and increased hardness when sintered. They contain no or much less Co/or Ni than existing pre-alloyed metal powders of comparable hardness. This makes them potentially inexpensive and also superior from an environmental point of view. Alternatively, the present invention may be said to provide a pre-alloyed metal powder which results in a bond of higher hardness than pre-alloyed metal powders which already have the same amount of Co and/or Ni. The metal powders of the present invention, in addition to their use in the diamond tool industry, have great potential in other applications because they are rare powders that combine hardness and ductility.

Another object of the invention is related to the price of the bonding powders, which is still much higher than the more coarse (typically 20-100 microns) pure or alloyed metal powders produced with non-hydrometallurgical methods such as atomization, even though many hydrometallurgical methods can produce suitable bonds at acceptable costs. However, these coarse powders do not generally have the sintering properties required to make them suitable for diamond tools.

A widely known method for producing pre-alloyed powders is mechanical alloying. In this method, elemental powders are coarsely mixed and then mechanically alloyed in a suitable machine (usually an approximately high-strength ball mill). It relies on repeated breakage and eventual cold pressing of the unmixed metal material that becomes mixed on the atomic scale by this method. This method has long been known, see for example: U.S. Pat. No. 3,591,362.

Metal powders produced by mechanical alloying processes have a higher sintering reactivity than alloyed powders produced by different methods, such as atomization, or hydrometallurgical processes as described in the prior art. This is also found to be true for elemental metal powders, or by methods such as atomization, when they are treated similarly as is required for mechanical alloying elemental powder mixtures. Even though the powders according to the prior art are finer and thus are expected to have a higher sintering reactivity, the direct comparison is the opposite; mechanically treated powders have higher sintering reactivity.

The pre-alloyed powder according to the invention contains Cu and Fe as two basic alloying elements, Fe and Cu being immiscible. Thus, the powder particles contain two phases, one rich in Fe and the other rich in Cu. To ensure a sufficiently low sintering temperature, Sn is added to the Cu rich phase, which lowers the melting point and thus also the sintering temperature. To increase the strength of the alloy and to ensure a developable alloy close to the peritectic component of the binary alloy Cu — Sn at Sn levels, the Fe-rich phase is strengthened by at least one of Mo, Ni, Co and W. In addition, the dispersion reinforcement (DS) may be added as an Oxide (ODS), Carbide (CDS), or as a combination of both. Useful oxides are those of metals that cannot be reduced by hydrogen below 1000 deg.C, such as Mg, Mn, Ca, Cr, Al, Th, Y, Na, Ti and V. Useful carbides are carbides of Ti, Zr, Fe, Mo and W.

The powder according to the invention has the formula:

Fe_aCobNi_cModW_eCu_fSn_g(DS)_h

and obey the following compositional constraints:

the total of the weight percentages a, b, c, d, e, f, g, h of the alloy components equals 100%, and the word "component" refers to those elements of the alloy that are deliberately introduced and therefore do not include impurities and oxygen unless oxygen is part of the ODS, so that a + b + c + d + e + f + g + h is 100.

To prevent excessive brittleness, Mo should not exceed 8% and W should not exceed 10%. Thus d.ltoreq.8 and e.ltoreq.10. Preferably c.ltoreq.30.

To ensure sufficient homogeneity of the sintered powder, the dispersion strength should not exceed 2%. Therefore h is less than or equal to 2. Preferably h.ltoreq.1 and more preferably h.ltoreq.0.5.

The total of Sn and Cu should be at least 5% but not more than 45%. The lower limit ensures proper sintering properties and the upper limit ensures that the bond is not too soft. Therefore, f + g is 5-45. Preferably 7. ltoreq. f + g. ltoreq.40, more preferably 11. ltoreq. f + g. ltoreq.32.

The Cu/Sn ratio should be between 6.4 and 25. The lower limit ensures that the formation of brittle phases in the Cu region is avoided and the upper limit ensures sufficient activity of Sn as a reducing element at the sintering temperature. Thus, 6.4. ltoreq. f/g. ltoreq.25. Preferably 8.7. ltoreq. f/g. ltoreq.20 and more preferably 10. ltoreq. f/g. ltoreq.13.3.

The composition of the powder obeys the following compositional constraints:

1.5≤[a/(b+c+2d+2e)]-4h≤33(1)。

optionally, the following equation is followed:

1.5≤a/(b+c+2d+2e+50h)≤33(2)，

and b + c +2d +2e is not less than 2.

The lower limits in equations (1) and (2) above ensure that the homogeneity of the sintered powder and the price of the powder are acceptable; the upper limit ensures that the sintered powder is sufficiently hard. The preferred lower limit is 1.6, more preferably 2 and most preferably 2.5. Preferably the upper limit is 17 and more preferably 10.

In order for prealloyed powders to effectively address the disadvantages of the state of the art and to produce superior bonding, they should have an oxygen content, as determined by ISO 4491-2: 1989 loss of hydrogen, not more than 2%, preferably not more than 1% and more preferably not more than 0.5%. This method cannot determine oxygen chemically linked to intentionally added ODS. The oxygen content needs to be small because the presence of oxygen is detrimental to the sintering reactivity of the powder and the ductility of the sintered bond.

In one embodiment of the invention, suitable bonding powders can be more economically produced for diamond tools, which are activated by using inexpensive atomized powders and by mechanical alloying.

In another embodiment of the invention the particle size of the powders, expressed by their FSSS value, is not more than 20 μm, preferably not more than 15 μm, more preferably not more than 10 μm. This is to ensure a compromise between low sintering temperatures and short reduction times (for precursors used in the powder manufacturing process).

The concentrations of Co and Ni are preferably kept low because these elements are highly suspected of damaging the environment. A powder containing neither Co nor Ni is advantageous from an ecological point of view. The concentration of Mo and W is also preferably not too high, so alloys with high Mo and W tend to produce deposits of W or Mo at the grain boundaries of the Fe-rich phase, making the bond less soft.

The pre-alloyed powders of the invention are characterized by the fact that they are very porous. This is achievedAdvantageously, the specific surface area, measured by the BET method mentioned above, is much greater than in the case of solid particles, such as atomized particles. In general, it is believed that a larger specific surface area is an indication of high sinterability for metal powders of the same composition. Typically, the prealloyed powders of the present invention have a specific surface area that is at least twice as large as the solid case specific surface area (calculated on the basis of the FSSS diameter). The specific surface area of the powder, expressed by its BET value, is preferably greater than 0.1m²/g。

The invention provides a composition of Fe_aCo_bNi_cMo_dW_eCu_fSn_g(DS)_hA, b, c, d, e, f, g, h represent the weight percentages of the components, DS is one or more oxides of metals selected from the group consisting of Mg, Mn, Ca, Cr, Al, Th, Y, Na, Ti and V, or one or more carbides of metals selected from the group consisting of Fe, W, Mo, Zr and Ti, and mixtures of said oxides and carbides, and the other components are unavoidable impurities, wherein

a+b+c+d+e+f+g+h＝100，

d≤8，e≤10，h≤2，

5≤f+g≤45，

F/g is not less than 6.4 and not more than 25 and

1.5≤[a/(b+c+2d+2e)]-4h≤33，

in addition, the powder is reduced in hydrogen with a mass loss of not more than 2%, which is determined according to standard ISO 4491-2: 1989.

The prealloyed powder described above, produced by mechanical alloying, has an average particle size d50 of less than 500 μm.

The invention also relates to the use of a pre-alloyed powder as described above in the manufacture of metal objects.

FIG. 1 is a graphical representation of the Vickers hardness versus Co/Fe ratio for powders prepared according to the present invention.

The applicant's understanding of the interaction of Cu, Sn and Fe will now be explained. The presence of Cu in the pre-alloyed powder tends to soften the bond. This effect can be compensated by the addition of suitable Sn. This also has the effect of helping to reduce the sintering temperature required for sintering the pre-alloyed powder. It can be seen from the binary Cu-Sn phase diagram that for Sn contents exceeding 13.5% but less than 25.5%, the peritectic reaction occurs at 798 ℃. At this temperature, a two-phase structure consisting of alpha and beta phases will exist. If cooling is continued, the beta phase will transform into a brittle delta phase, thereby greatly reducing the ductility of the alloy. Lowering the Sn content reduces the risk of introducing brittle delta phases, but also raises the solidus of the alloy. The solidus is relatively steep. Therefore, in order to obtain the effect of lowering the full sintering temperature caused by Sn, while avoiding the negative effects of brittle δ -phase formation, it should be ensured that the peritectic component of the binary alloy is as close as possible, but not exceeded.

When the pre-alloyed metal powder also contains Fe, as is the case in the present invention, reference is made to the binary phase diagrams Cu-Fe and Fe-Sn. Cu-Fe, Fe-Sn and Cu-Fe alloy phase diagrams are available from many sources. One source is the ASM handbook published by ASM international, material park1992, ohio, volume three, alloy phase diagram, Cu-Fe at page 2.168, Cu-Sn at page 2.178, Fe-Sn at page 2.203, which suggests that the equilibrium solubility of Sn in Fe is about 10% at 700 ℃. From the Cu-Fe diagram, it can be obtained that the equilibrium solubility of Cu in the Fe phase at 700 ℃ is much lower, less than 0.3%, and in the ternary system these solubility limits are slightly different, but not very large.

Given that Cu and Fe are immiscible, it is speculated that Sn will always be more soluble than copper in the Fe lattice at 700 ℃ or higher. In ternary Cu-Fe-Sn alloys, the Cu-rich phase will therefore deplete Sn during the sintering step. From the binary Cu — Sn phase diagram, it is therefore inferred that the melting point increases. In order to more fully profit from the Sn melting point lowering effect (purpose of Sn addition), alloys should therefore have Sn/Cu ratios higher than the peritectic ratio of 13.5/86.55 or 1/0.4. However, as explained above, this can lead to the formation of an undesirable brittle delta phase.

When cool bonded, most of the Sn diffuses back into the Cu rich phase because Sn has negligible solubility in Fe at room temperature. This causes local enrichment of Sn at the grain boundaries near Cu, making the formation of brittle δ -phase more likely. The same back diffusion of Sn in Cu can cause the important Sn/Cu ratio of 1/6.4 to be exceeded locally, even in materials with an overall Sn/Cu ratio below 1/6.4. Therefore, it is difficult to design an alloy in the Cu-Fe-Sn system that can make full use of the effect of lowering the melting point of Sn and strengthening Cu while avoiding the formation of a brittle delta phase.

However, the addition of one of the reinforcing elements Mo, W, Ni or Co affects the mechanical properties explained above in a very interesting way: the Fe-rich phase is strengthened by solid solution strengthening, and these strengthening elements effectively prevent Sn atoms from diffusing into the Fe lattice. Thus, Sn remains in the Cu phase during heating of the bond powder: thus, the advantageous effect of Sn on the sintering behavior can be fully exploited. In a predetermined Cu/Sn

The combined effect of the ratio and the strengthening element that prevents Sn diffusion into the Fe phase is the core of the present invention. It allows the combination of adequate strength and high ductility characteristics when prealloyed is sintered at relatively low temperatures.

It is desirable that the components be as finely dispersed as possible. For oxides/carbides, this follows from the fact that the shorter the mean free channels between the oxides/carbides, the smaller the oxides/carbides, the more pronounced their strengthening action is. This follows from the fact that for metallic elements a homogeneous microstructure can improve the mechanical properties. This is described in EP- ｃA-0865511 ｃA and EP- ｃA-0990056, where it is also disclosed that the pre-alloyed powder provides higher strength than the elemental powder mixture. Of course, the alloy needs to be as homogeneous as possible for the solution strengthening to be more active. When Mo and W are added to strengthen Fe crystal chromium, their homogeneous distribution is especially important because Mo and W exhibit very low diffusion coefficients at temperatures typically applied to diamond tools. Suitable synthetic methods are now described.

The powder of the present invention may be prepared by heating the precursor or a homogeneous mixture of two or more precursors in a reducing atmosphere. These precursors are organic or inorganic compounds of the alloy components. The precursor or homogeneous mixture of precursors must contain the elements of the components, except C and O, in relative amounts corresponding to the desired components of the powder. In the production method, there are differences between so-called elements in class 1 (Co, Ni, Fe, Cu, Sn and ODS elements, excluding V) and elements in class 2 (W, Mo, V and Cr).

The precursor can be prepared by any combination of the following methods (a) to (f).

(a) For elements in category 1: an aqueous solution of a salt of one or more components and an aqueous solution of a matrix (carbonate, carboxylic acid, carboxylate salt, or mixtures thereof) are mixed to form an insoluble or poorly soluble composition. Only those carboxylic acids or the corresponding carboxylic acid salts are suitable for forming insoluble or poorly soluble compositions with the aqueous solution of the salt of the component. Examples of suitable carboxylic acids and carboxylates are oxalic acid or potassium oxalate. On the other hand, acetic acid and metal acetate are not suitable. The resulting precipitate is then separated from the aqueous phase and dried.

(b) For elements in categories 1 and 2: mixing an aqueous solution of a salt of an element of class 2 with an aqueous solution of one or both salts of class 1 to form a mixture of salts of general formula (class 1 element)_x(Category 2 element)_yO_zWherein x, y and z are determined by the valency of the elements in the solution. An example of a compound herein is CoWO₄. The resulting precipitate is then separated from the aqueous phase and dried.

(c) For elements in category 2: mixing an aqueous solution of a salt of one or more elements of class 2 with an acid to form a salt of general formula, such as MoO₃·xH₂O or WO₃·xH₂Insoluble or poorly soluble compounds of O. The variable x represents the amount of change in crystal water, and is generally less than 3. The precipitate is then separated from the aqueous phase and dried.

(d) For all elements in categories 1 and 2: the mixture is dried by mixing, e.g., a, b and c, a precipitate containing a portion of the appropriate soluble salts with one or more alloying components.

(e) For all elements of categories 1 and 2: by drying a mixed aqueous solution of salts of the alloy components.

(f) For all elements in categories 1 and 2: by thermal decomposition of any of (a), (b), (c), (d) and (e).

Whenever a drying process is mentioned in the previous section, it must be understood that the drying must be fast enough so that the different components remain mixed during the drying process. Spray drying is a suitable drying method. Not all of the salts mentioned under (a), (b), (c), (d) and (e) are suitable. It is not suitable to leave salts containing impurities of the elements not present in the composition after the reduction treatment mentioned in the first paragraph of this section below. Other salts are suitable.

A homogeneous mixture of the two or more precursors mentioned above can be prepared by preparing a sludge of these precursors in a suitable liquid, typically water. The sludge is vigorously stirred for a sufficient period of time and dried under conditions such that the components, except ODS or CDS, are completely or nearly completely reduced, as indicated by the oxygen content mentioned in the description of the invention, however, the FSSS diameter does not exceed 20 mu. Typical reducing conditions for the powder according to the invention are temperatures of 600 to 730 ℃ and times of 4 to 8 hours. However, suitable reduction conditions for each powder must be established experimentally, since there is an equilibrium between the reduction time and the reduction temperature, and not all furnaces operate in the same manner. Finding suitable reduction conditions can be readily accomplished by the skilled artisan by simple experimentation using the following guidelines:

if the FSSS diameter is too large, the reduction temperature should be lowered;

if the oxygen content is too high, the reduction time should be increased;

in addition, if the oxygen content is too high, the reduction temperature can be increased, but only without increasing the FSSS diameter beyond the limits of the invention.

The reducing atmosphere is typically hydrogen, but may also contain other reducing gases such as methane or carbon monoxide. Inert gases such as nitrogen and argon may also be added.

If CDS is formed during the reduction, the reaction must be carried out in an atmosphere with sufficient carbon activity.

In summary, the prealloyed powder subject of the invention allows to overcome all the aforementioned drawbacks and, moreover, has the following advantages:

powders are produced chemically, resulting in porous particles and rough surface morphology and high specific surface values, thus positively affecting cold pressing and sintering properties;

co, Mo, Ni or W, Mo and W being particularly effective, the addition of Mo and W greatly increases the hardness. ODS and CDS have the same role;

the system is in the composition window range that provides sufficient impact resistance, and the addition of Co, Mo, Ni or W allows for a sufficiently high content of Sn to have an overall effect on the sintering temperature while maintaining a sufficient ductile structure.

The powder can be sintered at relatively low temperatures using standard sintering methods without the need for complex process steps.

The production process of the binding powders according to the invention and their characteristics are illustrated in the following examples.

EXAMPLE 1 preparation of Fe-Co-Mo-Cu-Sn alloy

This example relates to the preparation of a powder according to the invention by precipitation reaction of a mixed hydroxide and subsequent reduction of this hydroxide.

Water soluble mixed metal chloride solutionsContains 21.1g/l Co, 21.1g/l Cu, 56.3g/l Fe (may be Fe)²⁺And/or Fe³⁺) And 1.6g/l Sn, added while stirring, to 45g/l aqueous NaOH solution until a pH of about 10 is obtained. An additional 1 hour was carried out to complete the reaction, during which time the pH was monitored and maintained at 10, if necessary adjusted with a metal chloride solution or NaOH. Under these conditions, more than 98% of each metal precipitated.

The absolute value of the concentration of the metal in question is an indication that it can vary between the total metal content and the solubility limit by only a few g/l. The ratio of the metal concentrations is expressed in terms of the finished product obtained. Similarly, the concentration of the NaOH solution may vary within the same limits, but it must be sufficient to bring the pH of the mixture between 7 and 10.5. The final pH is not critical and may be between pH 7 and 10.5, but generally falls within the range of 9 to 10.5.

The precipitate was separated by filtration, washed with purified water until essentially free of Na and Cl, and ammonium heptamolybdate ((NH)₄)₆Mo₇O₂₄·4H₂O) mixing. The concentration of precipitate and ammonium heptamolybdate in the mixture is not critical as long as the viscosity of the formed sludge is sufficiently pumped and the viscosity of the precipitate and ammonium heptamolybdate corresponds to the ratio of metals in the desired alloying metal powder. In addition to ammonium heptamolybdate, ammonium dimolybdate ((NH)₄)₆Mo₂O₇) May also be used. The mixture was dried in a spray dryer and the dried precipitate was reduced in a furnace at 730 ℃ for 7.5 hours in a stream of 200 l/hour hydrogen.

A porous metal block, ground to give a powdered metal product (hereinafter referred to as powder 1), consisting of 20% Co, 20% Cu, 53.5% Fe, 5% Mo, 1.5% Sn (these percentages are only in terms of metal parts) and 0.48% oxygen (as measured by hydrogen loss).

Powder of 1, Fe_53.5Co₂₀Mo₅Cu₂₀Sn_1.5Are components according to the invention. The powder particles had an average diameter of 9.5 μm as determined by FSSS.

EXAMPLE 2 preparation of Fe-Mo-Cu-Sn alloy

The procedure of example 1 was used, but the concentrations of the different metal salts were adjusted so as to obtain different final compositions, under which conditions the reduction temperature was 700 ℃.

A metal powder (hereinafter referred to as powder 2) composed of 20% Cu, 73.5% Fe, 5% Mo, 1.5% Sn (these percentages are only in the metal portion) and 0.44% oxygen was prepared. The powder particles had an average diameter of 8.98 μm as determined by FSSS.

Powder 2Fe_73.5Mo₅Cu₂₀Sn_1.5Unlike powder 1, all Co was replaced by Fe, so powder 2 contained no Co and Ni. This powder falls within the scope of the present invention.

EXAMPLE 3Fe-Co-W-Cu-Sn alloy

This example relates to the preparation of powders according to the invention by a single metal hydroxide precipitation reaction, the subsequent mixing of these substances into a sludge, followed by drying and reduction of this mixture of hydroxides.

Individual hydroxides or hydroxide compounds of Co, Cu, Sn and Fe are prepared from individual metal chlorides by precipitation reactions, filtration and washing as described in example 1, and sludge is prepared from a mixture of these individual hydroxides. The concentration of the individual metal hydroxides corresponds to the desired pre-alloyed powder composition. To the sludge, ammonium meta-tungstate ((NH) in water was added₄)₆H₂W₁₂O₄₀·3H₂O) solution, in concentrations and amounts corresponding to the final composition of the pre-alloyed powder. In addition to ammonium meta-tungstate, ammonium para-tungstate ((NH)₄)₁₀H₂W₁₂O₄₂·4H₂O) may be used as well.

The elements of the sludge were thoroughly mixed, spray dried, reduced and ground according to example 1. A metal powder consisting of 20% Co, 20% Cu, 53.5% Fe, 1.5% Sn, 5% W tin (these percentages are only for the metal portion) and 0.29% oxygen (hereinafter referred to as powder 3) was obtained. The powder particles had an average diameter of 4.75 μm as determined by FSSS.

Powder 3Fe_53.5Co₂₀W₅Cu₂₀Sn_1.5Fall within the scope of the components of the invention; it differs from powder 1 in that Mo is replaced by W.

Example 4 preparation of Fe-W-Cu-Sn alloy with ODS

The method of example 1 was employed and the concentrations of the various metal chlorides in the starting solution were adjusted to obtain different final compositions; y, in soluble YCl₃In the form of a salt, is added to the solution. Ammonium metatungstate was used instead of ammonium heptamolybdate.

A composition of 20.45% Cu, 75% Fe, 1.8% Sn, 2.5% W, 0.25% Y was obtained₂O₃(these percentages are only for the metal part) and 0.44% oxygen (referred to as powder 4 hereinafter). The powder had an average diameter of 2.1 μm as determined by FSSS.

Powder 4 Fe75W_2.5Cu_20.45Sn_1.8(Y₂O₃)_0.25Fall within the composition range of the present invention and are completely free of Co and Ni.

Example 5 green strength and sintering test

This example relates to a series of tests comparing powders 1, 2 and 3 with standard cohesive powders, the following comparative powders also being tested.

(a) Ultra-fine cobalt powder (Umicore EF), produced by Umicore, is considered a standard powder for making diamond tools, sintered under the same conditions as the pre-alloyed powder. The Umicore EF has an average diameter, measured by FSSS, of 1.2-1.5 μm and has an oxygen content of between 0.3 and 0.5%. Its Co content is at least 99.85%, excluding oxygen, and the balance unavoidable impurities. The measurement of Umicore EF is mentioned as reference.

(b) Tong (Chinese character of 'tong')Cobalite from Umicore^®601 refers to a commercially available pre-alloyed powder consisting of 10% Co, 20% Cu and 70% Fe.

(c)Cobalite^®801 refers to another commercially available pre-alloyed powder manufactured by Umicore, consisting of 25% Co, 55% Cu, 13% Fe and 7% Ni. Two kinds of cobalt^®The powders are all produced according to the invention as described in EP-A-0990056.

To evaluate the wet strength, a roll mill test was performed on powders 1-4. The results are shown in Table 1

TABLE 1Wet strength of bonded powder

Powder of	Roller milling value (%)
		Umicore EF	＜5
Cobalite®601	＜5
		Cobalite®801	＜5
Powder 1	＜5
		Powder 2	＜5
Powder 3	＜5
		Powder 4	＜5

The results show that the green strength of the new powder is as good as the reference powder.

A series of tests comparing the sinterability of powders 1-4 and the reference powders were carried out as follows: disk-shaped compacts having a diameter of 20mm were sintered in a graphite mold at 35MPa for 3 minutes at different temperatures, and the relative densities of the sintered compacts were measured. The results are shown in Table 2.

TABLE 2Relative density of the sintered powder

Powder of	Density at sintering temperature (%)
						750℃	800℃	850℃	900℃
Umicore EF	95.4	97.1	97.6	97.5
					Cobalite®601	97.9	97.3	97.8	98.3
Cobalite®801	96.7	97.7	97.2	97.2
					Powder 1	97.5	97.2	98.8	97.9
Powder 2	99.4	99.5	99.7	99.7
					Powder 3	97.7	97.6	98.4	97.2
Powder 4	98.2	98.3	98.7	98.5

The results show that densities close to the theoretical density of the alloy can be obtained for the new powder by sintering under pressure. But also high density values are obtained at relatively low temperatures. Sintering above 850 ℃ does not improve the relative density of the powders 1-4.

EXAMPLE 6 mechanical Properties of Fe-Co-Ni-Mo-W-Cu-Sn alloy

This example relates to a series of tests comparing the mechanical properties of powders 1 to 4 with those of the reference powder.

The size is 55X 10mm³The rod-shaped compact of (2) is sintered in a graphite mold at a temperature of 35MPa and 800 ℃ for 3 minutes. The Vickers hardness and compressive capacity of the sintered compacts were determined by the Charpy (Charpy) method. The results are shown in Table 3. In the presence of Umicore EF, Cobalite^®601，Cobalite^®801 values determined on similar inserts were used as reference.

TABLE 3Hardness and ductility of the sintered powder

Powder of	Vickers hardness (HV10)	Compressive property (J/cm)2)
			Umicore EF	280	87-123
Cobalite®601	250	74
			Cobalite®801	221	77
Powder 1	327	54
			Powder 2	240	48
Powder 3	322	33
			Powder 4	221	55

The results show that the Co-containing powders 1 and 3 are harder than the reference powder. This increased hardness is obtained without exceeding the ductility boundary value. Co-free powders 2 and 4 proved to be suitable replacements for the reference powders, with the advantage of not containing metals suspected to be damaging to the environment.

Fig. 1 shows the full potential of the invention. It represents the hardness of the blade sintered from the pre-alloyed powder as a function of the Co to Fe ratio, without Ni. All the powders used for drawing this figure were produced according to the process of the invention, containing 18-20% Cu. In the case of the prealloyed powder according to the invention, the Mo or W content is 5% and the Sn content is 1.8-2%. The powder was sintered at 750, 800, 850 ℃. From the three results for each powder, the optimum temperature was selected as the temperature with the highest hardness. If the ductility is at least 20J/cm². This optimum hardness is made in figure 1. The conclusion is that the sintered inserts from the powder prepared according to the invention exhibit a higher hardness than inserts prepared according to the same method but sintered without the addition of Sn, Ni, W or Mo powder. It can also be said that powder sintered inserts can be produced according to the inventionThe same hardness as the inserts sintered from the powder prepared according to the prior art, but containing less Co.

EXAMPLE 7 Properties of sintering ODS-containing powder

In this example, the ODS-containing powder according to the invention, such as powder 4, was compared with the ODS-free powder according to the invention.

The size is 55X 10mm³The rod-shaped compact of (2) was sintered in a graphite mold at a temperature of 35MPa and 800 ℃ for 3 minutes. The Vickers hardness, compression resistance and density of the sintered cake were measured. The results are shown in Table 4

TABLE 4Influence of ODS

Powder of	Density (%)	Hardness (HV10)	Compressive property (J/cm)2)
				Fe75.2W2.5Cu20.5Sn1.8	98.8	211	60
Fe75W2.5Cu20.45Sn1.8(Y2O3)0.25(*)	98.3	221	55
				Fe74.8W2.5Cu20.4Sn1.8(Y2O3)0.5	99.3	227	42

(^*) Powder 4

The results show that the addition of an oxide enhancer can achieve better hardness without sacrificing sinterability and with only a limited effect on ductility.

Example 8 Effect of Sn and W

This example demonstrates the effect of Sn addition on powder sinterability and ductility of the resulting insert. Diamond cutter manufacturing often adds W and Mo to increase the strength and hardness of their inserts. To prove this, a Cobalite-based material was manufactured^®601 but with Mo and W partially replacing the pre-alloyed powder of Fe. The blade is in a graphite mold. 35MPa, and sintering at 850 ℃ and 900 ℃ for 3 minutes respectively. The results are summarized in table 5.

TABLE 5Density and hardness of Sn-containing sintered powder

Powder of	Density at sintering temperature (%)		Hardness (HV10)
				850℃	900℃
	Fe67.4Co10Cu20Mo2.6	89.7	93.0				266
Fe68.75Co10Cu20W1.25				94.1	96.1	229

The density of the powder containing Mo or W, not containing Sn, is too low to produce good blades.

On the other hand, if the weight fraction of Sn is high, this may result in a very brittle blade, due to the formation of the δ -phase. This is shown in table 6. This table summarizes the values of the compression resistance of 3 test specimens which may contain 5% Sn and have a composition similar to that of powders 1-3. The Sn/Cu ratio for all samples was about 0.25, which is clearly outside the scope of the present invention. The blade was sintered in a graphite mold at a temperature of 800 ℃ for 3 minutes at 35 MPa.

TABLE 6Compressive properties of sintered powders with excess Sn

Powder of	Compressive property (J/cm)2)
		Fe63Co9Mo5Cu18Sn5	0.6
Fe70Mo5Cu20Sn5	1.7
		Fe63Co9W5Cu18Sn5	0.7

The reduction of the Sn content maintains ductility if the diffusion of Sn into fe-crystal chromium can be prevented, as shown in the following table. The powder and the blade prepared according to the invention were sintered in a graphite mould at a temperature of 800 ℃ for 3 minutes at a pressure of 35 MPa.

TABLE 7Mechanical properties of Sn and W sintered powder

Powder of	Density (%)	Hardness (HV10)	Compressive property (J/cm)2)
				Fe77Cu21.1Sn1.9(*)	99.7	195	5.8
Fe75.1W2.5Cu20.5Sn1.9	100	230	70
				Fe73.2W5Cu20Sn1.8	99.7	235	93
Fe71.2W7.5Cu19.5Sn1.8	100	248	33
				Fe69.3W10Cu18.9Sn1.8	97.0	239	20

(^*) Powders not in accordance with the invention

The results demonstrate that the addition of a reinforcing element to the Fe phase is necessary to maintain ductility. These data also clearly show that the limit for the addition of W is about 10%. For higher values, the ductility is too low.

EXAMPLE 10 preparation of Fe-Co-W-Cu-Sn- (WC) alloy

The precursor was prepared according to the method of example 3, but with different compositions. 20g of this precursor were heated in the presence of the gas mixture, using a flow rate of 100 l/h. The mixture consisted of 17% Co and 87% H2. The heating procedure was as follows:

-50 ℃/min to 300 ℃;

-2.5 ℃/min to 770 ℃.

Then, the temperature was kept constant for 2 hours, and then the atmosphere was changed to 100% H₂While maintaining the 770 ℃ temperature for an additional 1 hour. Then, the atmosphere was changed to 100% N₂And then the furnace is turned off.

A metal powder consisting of 20% Cu, 58.5% Fe, 1.5% Sn, 10% W, 10% Co (these percentages are only for the metal part) and 0.88% oxygen was obtained. X-ray diffraction indicates the presence of a peak corresponding to WC, indicating the partial conversion of W to WC. The powder particles have an average diameter of 2.0 μm as determined by FSSS and fall within the composition range of the present invention.

Example 11 other compositions according to the invention

A chemically multi-alloyed powder of Fe-Cu-Co-W-Mo-Sn-ODS system was obtained in a similar manner to that used in examples 1 to 4. Table 8 gives an overview of these powders, having greater than about 20J/cm after sintering at temperatures of 850 ℃ or less²Charpy (Charpy) compression resistance. All of these compositions have a hardness of 200 HV10 or greater. All of these compositions fall within the scope of the present invention.

Example 12 composition not according to the invention

A chemically multi-alloyed powder of Fe-Cu-Co-W-Mo-Sn-ODS system was obtained in a similar manner to that used in examples 1 to 4. Table 9 gives an overview of these powders, having less than about 20J/cm after sintering at temperatures of 850 ℃ or less²Charpy (Charpy) compression resistance. These powders are not covered by the present invention.

TABLE 8Other compositions according to the invention (without Ni)

Powder no	a％Fe	b％Co	d％Mo	e％W	f％Cu	g％Sn	h％ODS	f/gCu/Sn	[a/(b+c+2d+2e)]-4h
										5	70.2	5	5		18	1.8		10.0	4.7
6	72	10		5	12	1		12.0	3.6
										7	58	10		10	20	2		10.0	1.9
8	58.5	10		10	20	1.5		13.3	2
										9	59	10		10	20	1		20.0	2
10	57.5	10		6	24	2.5		9.6	2.6
										11	58.5	10		2	26	3	0.5	8.7	2.2
12	60	10			26.5	3	0.5	8.8	4.0
										13	61.9	10.5		5	21	1.6		13.1	3
14	65.3	11			22	1.7		12.9	5.9
										15	60.2	15	5		18	1.8		10.0	2.4
16	59.2	15		4	20	1.8		11.1	2.6
										17	58.2	15		5	20	1.8		11.1	2.3
18	57.2	15		6	20	1.8		11.1	2.1
										19	55.7	15		7.5	20	1.8		11.1	1.9
20	54.2	15		9	20	1.8		11.1	1.6
										21	56	18		6	18	2		9.0	1.9
22	59	18	3		18	2		9.0	2.5
										23	57.7	20	2.5		18	1.8		10.0	2.3
24	55.2	20	5		18	1.8		10.0	1.8
										25	52.7	20	7.5		18	1.8		10.0	1.5

26	53.5	20	5	0	20	1.5		13.3	1.8
										27	53.2	20		5	20	1.8		11.1	1.8
28	53.5	20		5	20	1.5		13.3	1.8
										29	54.8	20.1		1.5	21.5	2.1		10.2	2.4
30	56	21			21	2		10.5	2.7
										31	56	21			21.1	1.9		11.1	2.7
32	52.7	25	2.5		18	1.8		10.0	1.8
										33	84.75		4.5		10	0.75		13.3	9.4
34	79.3			5.3	14	1.4		10.0	7.5
										35	77.5			7.1	14	1.4		10.0	5.5
36	76.2			5.1	17	1.7		10.0	7.5
										37	74.5			6.8	17	1.7		10.0	5.5
38	75.2		5		18	1.8		10.0	7.5
										39	69.4			10	18.9	1.7		11.1	3.5
40	75.1			2.5	19.9	2	0.5	10.0	13
										41	74.5		5		20	0.5		40.0	7.5
42	74		5		20	1		20.0	7.4
										43	74.6			3.9	20	1.5		13.3	9.6
44	73.5			5	20	1.5		13.3	7.4
										45	76		2.5		20	1.5		13.3	15.2
46	74.6		3.9		20	1.5		13.3	9.6
										47	73.5		5		20	1.5		13.3	7.4
48	73.2			5	20	1.8		11.1	73
										49	73.1			4.9	20	2		10.0	7.5
50	71.5			6.5	20	2		10.0	5.5
										51	76.64			1.17	20.3	1.64	0.25	12.4	31.8
52	74.8			2.5	20.4	1.8	0.5	11.3	13
										53	75			2.5	20.45	1.8	0.25	11.4	14
54	75.2			2.5	20.5	1.8		11.4	15
										55	70			4.7	23	2.3		10.0	7.4
56	68.5			6.2	23	2.3		10.0	5.5
										57	66.9			4.5	26	2.6		10.0	7.4
58	65.4			6	26	2.6		10.0	5.5
										59	68.5			2	26	3	0.5	8.7	15.1
60	68			2	26.5	3	0.5	8.8	15
										61	64.35		3.4		30	2.25		13.3	9.5

TABLE 9Not formed in accordance with the invention

Powder no	a％Fe	b％Co	d％Mo	e％W	f％Cu	g％Sn	h％ODS	f/g	[a/(b+c+2d+2e)]-4h
										62	59	9		10	17	5		3.4(*)	2
63	59	9	10		17	5		3.4	2
										64	63	9		5	18	5		3.6	3.3
65	63	9	5		18	5		3.6	3.3
										66	56	9.5		6	25	3	0.5	8.3	0.6
67	63.2	10		4.5	20	1.5	0.8	13.3	0.1
										68	63.5	10		4.5	20	1.5	0.5	13.3	1.3
69	58.5	10	10		20	1.5		13.3	2
										70	53.5	20		4.5	20	1.5	0.5	13.3	-0.2
71	50.2	25	5		18	1.8		10.0	1.4
										72	70		5		20	5		4.0	7
73	68.5		10		20	1.5		13.3	4.4

(^*) The scribed data is out of specification

Example 13 Effect of mechanical alloying on sintering reactivity

In tables 10a to 10eThe sintering reactivity of the fine prealloyed powder produced by reduction of the precursor was compared to the coarse powder produced by mechanical alloying. Powders prepared from the reduction of the precursor were made according to the methods detailed in examples 1-3. Mechanically alloying powders by reaction in a Simoloyer^TMCM8 high-power ball mills (manufactured by ZOZ Gmbh, germany) were produced by treating a simple mixture of individual metal powders for 3 hours. Both types of powders were sintered in a hot press at a specific temperature for 3 minutes under a pressure of 350Bar, and the density of the resulting compacts was measured.

TABLE 10aAccording to the invention Fe_53.5Co₂₀Mo₅Cu₂₀Sn_1.5Reactivity of powder sintering

Process for the preparation of a coating	Reduction of precursor	Mechanical alloying
			Sympatec d50(μm)	7.3	51
Oxygen (%)	0.16	0.45
			Sintering (. degree.C.)	Relative density (%)	Relative density (%)
725	91	94
			750	95	97
775	98	98
			800	99	98

TABLE 10bAccording to the invention Fe_73.5Mo₅Cu₂₀Sn_1.5Reactivity of powder sintering

Process for the preparation of a coating	Reduction of precursor	Mechanical alloying
			Sympatec d50(μm)	16.2	52
Oxygen (%)	0.44	0.41
			Sintering (. degree.C.)	Relative density (%)	Relative density (%)
750	＜80	99
			800	85	99
850	99	99
			900	99	99

TABLE 10cAccording to the invention Fe_74.5Mo₄Cu₂₀Sn_1.5Reactivity of powder sintering

Process for the preparation of a coating	Reduction of precursor	Mechanical alloying
			Sympatec d50(μm)	18.3	28
Oxygen (%)	0.41	0.45
			Sintering (. degree.C.)	Relative density (%)	Relative density (%)
750	78	96
			800	84	98
850	96	99
			900	97	99

TABLE 10dAccording to the invention Fe_53.2Co₂₀W₅Cu₂₀Sn_1.8Reactivity of powder sintering

Process for the preparation of a coating	Reduction of precursor	Mechanical alloying
			Sympatec d50(μm)	9.8	55.8
Oxygen (%)	0.28	0.50
			Sintering (. degree.C.)	Relative density (%)	Relative density (%)
650	81	95
			675	89	97
700	90	97
			725	98	98

TABLE 10eAccording to the invention Fe_58.5Co₁₀W₁₀Cu₂₀Sn_1.5Reactivity of powder sintering

Process for the preparation of a coating	Reduction of precursor	Mechanical alloying
			Sympatec d50(μm)	9.4	54
Oxygen (%)	0.30	0.32
			Sintering (. degree.C.)	Relative density (%)	Relative density (%)
650	87	91
			675	91	94
700	95	95
			725	98	98

From tables 10a-10e, it can be seen that the mechanically alloyed powder can be efficiently sintered at a temperature of about 100 ℃ (lower than the temperature required for the powder obtained by reduction of the precursor). This is true even if the powder produced by mechanical alloying is coarser than the powder produced by reduction of the precursor.

Claims (11)

1. A composition of Fe_aCo_bNi_cMo_dW_eCu_fSn_g(DS)_hA, b, c, d, e, f, g, h represent the weight percentages of the components, DS is one or more oxides of metals selected from the group consisting of Mg, Mn, Ca, Cr, Al, Th, Y, Na, Ti and V, or one or more carbides of metals selected from the group consisting of Fe, W, Mo, Zr and Ti, and mixtures of said oxides and carbides, and the other components are unavoidable impurities, wherein

a+b+c+d+e+f+g+h＝100，

d≤8，e≤10，h≤2，

5≤f+g≤45，

F/g is not less than 6.4 and not more than 25 and

1.5≤[a/(b+c+2d+2e)]-4h≤33，

in addition, the powder is reduced in hydrogen with a mass loss of not more than 2%, which is determined according to standard ISO 4491-2: 1989.

2. A pre-alloyed powder according to claim 1, manufactured by mechanical alloying and having an average particle size d50 of less than 500 μm.

3. Prealloyed powder according to claim 1 characterized in that the particle size, as determined by means of a fisher-tropsch granulometer, does not exceed 20 μm.

4. A prealloyed powder according to any one of claims 1-3 wherein b-0 or c-0 or b + c-0.

5. A pre-alloyed powder according to claim 3, characterized in that the particle size does not exceed 15 μm, measured with a fisher-tropsch granulometer.

6. A prealloyed powder according to claim 5 characterized in that the particle size, as measured by a Fisher-Tropsch particle measuring instrument, does not exceed 10 μm.

7. Prealloyed powder according to claim 1, characterized in that the powder has at least 0.1m²Specific surface area in g, determined according to the BET method.

8. Prealloyed powder according to claim 1, characterized in that the powder is reduced in hydrogen with a mass loss of not more than 1%, according to standard ISO 4491-2: 1989.

9. Prealloyed powder according to claim 8, characterized in that the powder has a mass loss, determined according to the method of standard ISO 4491-2.1989, reduced in hydrogen of not more than 0.5%.

10. Use of the pre-alloyed powder according to any one of claims 1 to 8 in the manufacture of metal objects.

11. Use of the pre-alloyed powder according to any one of claims 1 to 9 in the manufacture of diamond tools by hot sintering or hot pressing.