Pre-alloyed powder

Details Pre-alloyed powder Pre-alloyed powder

2000-11-15

2003-04-29

Wyszomierski, George (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or purifying free metal powder or producing or...

C075S369000, C075S371000, C075S373000, C075S374000

Reexamination Certificate

active

06554885

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to metal powders consisting of one or more of the elements Fe, Ni, Co, Cu, Sn and optional, in small amounts of Al, Cr, Mn, Mo, W, a process for their production as well as their use.
BACKGROUND OF THE INVENTION
Alloy powders have a variety of applications in the production of sintered materials by powder metallurgy. The main feature of powder metallurgy is that appropriate metal powders and alloy powders are compacted and then sintered at elevated temperature. This method has been introduced on the industrial scale for the production of complicated articles which otherwise cannot or can be produced only with a large degree of expensive finishing. The sintering can be a solid state sintering or by forming a liquid phase, as, for example, of hard metals or heavy metals. A very important application of alloy and pure metal powders is as tools for cutting and working metal, stone and wood. In these cases they are two-phase materials, wherein the hard constituent (for example, carbides or diamonds) is embedded in a metallic matrix, which is responsible for the required strength and toughness properties of these composites. The hard metals (in the case of carbides or carbonitrides) or diamond tools (in the case of diamonds) thus produced are of considerable economic importance.
The element cobalt is especially important, because it has some distinctive and unique properties as a metallic matrix in diamond and hard metal tools. Because it wets tungsten carbide and diamonds particularly well, traditionally it is preferably used for both types of tools. Through the use of cobalt for the metallic binder phase in composites based on tungsten carbide or diamond, a particularly good adhesion of the hardening constituent in the metallic binder phase is achieved. Also important is the fact that, in the case of cobalt, the tendency towards the formation of carbides of the type Co3W3C (“eta phases”), which lead to embrittlement in hard metals, is less distinct than, for example, in the case of iron. Moreover, diamonds are attacked by Co less, for example, than by iron, which easily forms Fe
3
C. For these technical reasons, cobalt is traditionally used in the hard metal and diamond tool industry.
For the production of hard metals, one normally starts from cobalt metal powders of 0.8 to 2 &mgr;m FSSS (ASTM B 330), which, together with the hard materials, compressing aids and a grinding liquid, are subjected to a mixed grinding in attritors or ball mills, which contain balls of hard metal as grinding media. The suspension obtained is then separated from the grinding media, spray-dried, and the granular material obtained is pressed into moulds. The subsequent liquid-phase sintering at temperatures above the melting point of the W—Co—C eutectic mixture produces dense sintered bodies (hard metals). An important property of the hard metals thus produced is their strength, which is weakened by porosity. Industrial hard metals have a porosity of better than or equal to A02B00C00 in accordance with ASTM B 276 (or DIN ISO 4505). The microporosity is referred to as A porosity, whereas B porosity denotes the macroporosity. Unlike hard materials, cobalt metal powders are ductile, and during the mixed grinding the particles will be plastically deformed and agglomerated particles will be deagglomerated. If the cobalt metal powders used contain large, compactly sintered agglomerates, these are transferred in deformed form into the spray-dried granular material and produce A and B porosity in the sintered hard metal, frequently associated with local concentration of the binder phase, the so called binder lakes.
Diamond tools, as the second important group used, contain as cutting or grinding components sintered parts (segments), which consist mainly of diamonds embedded in a metallic binder phase, mainly cobalt. Besides that, optionally further hard materials or other metal powders are added in order to match the wear properties of the binder to the diamonds and to the materials to be worked. To prepare the segments, metal powder, diamonds and optionally hard material powder are mixed together, optionally granulated and densely sintered in hot presses at increased pressure and elevated temperature. The requirements placed on the binder metal powders, apart from the necessary chemical purity, are: good compressibility, a high sintering activity, a hardness which is matched to the diamonds and to the medium to be worked, adjusted via the particle size or grain size after sintering, as well as low attack on the diamonds, which are metastable at the sintering temperature (graphitisation).
The porosity generally decreases with increasing sintering temperature, that is, the density of the sintered part approaches its theoretical value for high enough temperatures. For reasons of strength, the sintering temperature chosen is therefore as high as possible. On the other hand, however, the hardness of the metallic matrix decreases again above an optimal temperature, as coarsening of the grains takes place. In addition, it should be taken into account that at elevated temperature there is an increased attack on the diamonds. For these reasons, preferred binder powders for segments are those which attain their theoretical density at the lowest possible sintering temperatures and can be easily compacted.
The only limited availability of cobalt, the great price variations, the environmental aspects and the desire for technical improvement have led to numerous efforts to replace cobalt in the hard metal and diamond tool industry.
Thus there have already been a number of proposals to replace cobalt at least partially by iron and/or nickel or their alloys as binder metal (Metall, 40, (1986), 133 to 140); Int. J. of Refractory Metals & Hard Materials 15 (1997), 139 to 149).
A disadvantage in manufacturing of diamond tools by using metal powders of single elements and of bronze powders is that the metallic composition, distribution and bonding is very inhomogeneous after sintering, as the sintering temperature and sintering time are insufficient to achieve homogenisation. Moreover, where commercially available iron metal powders are used, there arise high forces and pressures due to the worse compactibility of these powders which wear out the pressing tools and lead to green compacts having low strengths (for example, breaking off of the edges). This can mainly be attributed to the body-centred cubic lattice type of the iron, which has fewer gliding planes than do the face-centred cubic types of the cobalt and nickel or copper metal powders. In addition, the finer carbonyl iron powders available contain high quantities of carbon, which can lead to loss in strength in the segments. Atomised metal powders or alloys have insufficient sintering activity, so that compaction is still insufficient at temperatures justifiable for the diamonds. In the manufacture of hard metals by carbonyl iron powder there are problems regarding distribution of the binder (A- and/or B-porosity). This can be compensated by a more intensive milling, resulting, however, in widening of grain size distribution.
Thus there have also been a number of proposals to produce metallic alloy powders by precipitation, partially in the presence of organic phases, and subsequent reduction (WO 92/18 656, WO 96/04 088, WO 97/21 844).
The object of the invention is to provide metal powders and alloy powders containing at least one of the metals iron, copper, tin, cobalt or nickel, which meet the above-mentioned requirements placed on binder metals for hard metals and diamond tools.
The metal and alloy powders according to the object of the invention can be doped by small amounts of the elements Al, Cr, Mn, Mo and W and in such a way be modified and be suited to special requirements.
DESCRIPTION OF THE INVENTION
This invention provides, first of all, a process for the production of metal powders and alloy powders by mixing aqueous metal salt solutions with a carboxylic acid solution, separating the precipitation produc

Affiliated with

Also associated with

Rating

Pre-alloyed powder does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Pre-alloyed powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pre-alloyed powder will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3087812