NO131513B - - Google Patents

Description

Metallic material on a magnesium basis.

The present invention relates to a magnesium-based metallic material with two main lattice constituents, and it is characterized in that it has a composition as stated in claim 1.

As heat-resistant magnesium alloys, those with cerium-

and thorium content known, and which is usually given a finer grain structure with zirconium. However, their area of application ends at approx. 320°C. Their tensile strength values at 20°C lie between 14 and 28 kp/mm 2 , their densities between 1.77 and 1.83 g/cm 3. In the production of such materials from powder mixtures of a magnesium-zirconium alloy on the one hand and aluminum or an aluminum-magnesium alloy, on the other hand, tensile-2 2 strength values of pa. 36.5 kp/mm and a tensile strength of 31 kp/mm at an extension of 8%, in recent times further improvements with yttrium and finally scandium addition, which however seems to greatly increase costs. For applications such as highly stressed building elements in the aircraft and vehicle toy industry and engine parts, the aforementioned materials are preferably used because of their low weight and the relatively favorable ratio between strength and weight, and because of the good machinability. However, there is still a desire for an increase in the strength values and the application area at elevated temperature. Numerous attempts to develop alloys have only made negligible progress here, as larger alloy additions always entailed a negative influence on the toughness properties through the formation of brittle intermetallic phases. In contrast to this, with the object of the present invention, a new path is taken for magnesium-based materials, the addition of a cubic space-centered, in turn well-formable inter-metallic phase of the NiTi type, generally speaking, the so-called AB type with CsCl structure and lattice constants between 2.60 and 3.20 Angstroms, in weight fractions of 5% to 97%, preferably to 65%, which in the solid state are only slightly soluble in hexagonal magnesium lattice.

The properties of this CsCl structural phase have been thoroughly investigated over the last decade on a number of characteristic compositions, especially binary MTi alloys with proportions between 54 and 60 weight percent nickel and other soluble or illegible alloy additions, but also e.g. . mixed crystal series NiTi-FeTi. Especially the former, under the name "Nitinul", have found considerable interest and use as wear- and corrosion-resistant, highly softening and "memory" alloys. Thus, 55-Nitinol in the annealed state exhibits tensile strength values of 88 kp/mm <2> at 17 kp/mm <2> tensile strength, a total elongation of 60% and a constriction of 20%, after cold forming a breaking strength of up to 175 kp/mm 2 at up to 133 kp/mm 2 tensile strength and a minimum elongation of 12%. The 60-Nitinol alloy can be obtained with hardness values between 30 and 62 Rc. The density values of this phase lie between 6.45 and 7.1.

From the compilation of these strength properties, it is already clear to what extent the addition of this phase according to the mixing rule is suitable for increasing the strength and hardness of the technically common magnesium-based starting materials, by simultaneously improving the forming properties. Through this, the density also rises depending on the composition, e.g. at 10 volume percent corresponding to 29 weight percent alloy addition to 2.2 g/ cxs?, at 20 volume percent corresponding to 48 weight percent alloy addition to 2.68 g/cm^, i.e. in the latter case to the density of technical aluminum alloys. However, the specific firmness, the ratio of firmness to weight, which is used as a basis for construction planning, rises much more strongly. On the other hand, however, the density can be significantly lowered again by adding lithium to the magnesium phase, e.g. at an alloy with 20% by volume corresponding to 5.4% by weight lithium and 10% by volume NiTi corresponding to 17.9% by weight nickel and 14.7% by weight titanium, to 1.97 g/cm^.

An alloy of 50 volume percent magnesium, 40 volume percent lithium and 10 volume percent NiTi phase, i.e. of 50.4 weight percent magnesium, 12.3 weight percent lithium, 20.5 weight percent nickel and 16.8 weight percent titanium even has a density of only 1 .73 g/cm^, i.e. roughly equivalent to the density of pure magnesium, and beyond that consists of a phase mixture a:T only two cubic-space-centered phases, then by adding more than approx. 10 weight percent lithium, its cubic space-centered lattice takes the place of the hexagonal magnesium, thereby effecting a further improvement in formability. Thereby, the tensile value of glass fiber-reinforced plastics of 2.11 g/crn^ is significantly below that of a purely metallic fiber material. Even the density of carbon fiber resin of 1.55 g/cm^ can be undercut by a pure metallic magnesium-lithium-nickel-titanium fiber material, which is solid above 220 o C, with e.g. 1.37 g/cnr 3 for 20 volume percent corresponding to 25.5 weight percent magnesium, 70 volume percent corresponding to 27.2 weight percent lithium and 10 volume percent corresponding to 47.3 weight percent NiTi or 26 weight percent nickel and 21.3 weight percent titanium.

In general, the upper service temperature is given by the magnesium to titanium alloy ratio according to the state diagram; the stability of the materials according to the present invention is provided by the above 1200°C solid phase with CsCl structure.

The composition range of the magnesium-based materials according to the present invention is otherwise defined such that the cubic space-centered phase of the AB type can generally for A contain the metals nickel, cobalt and iron individually or combined, and for B can contain the metals titanium, aluminum , or, when A does not contain iron, beryllium singly or combined within the stability limits of that from the two-component system nickel-titanium between 50 and 64 wt. Under these restrictions, it is uniquely given by the formula Nil-x-yCoxFeyTil-u-vA1uBev where x :1' y X' u < and v-< 1> itself

if the composition range cannot be specified numerically accurately without extensive experimental investigations. Furthermore, it can be varied by a wide variety of alloying additions, especially with up to 30 weight percent chromium, up to 10 weight percent vanadium, up to 20 weight percent zirconium, up to 4 weight percent molybdenum and tungsten, up to 2 weight percent copper, up to 3 weight percent manganese, up to 1 weight percent silicon , respectively a combination of these elements.

The magnesium-rich phase can contain up to 55 wt% lithium, up to 8 wt% aluminum, up to 8 wt% cadmium, up to 8 wt% solv, up to 12 wt% zinc, up to 3 wt% manganese, up to 20 wt% indium, up to 2 wt% copper, up to 0.5 wt% silicon, up to 4 wt% barium, up to 4.0 wt% strontium, up to 4 wt% Ce or Ce mixed metal, up to 2.5 wt% didymium (neodymium + praseodymium), up to 4 wt% thorium, up to 1 wt% zirconium, up to 0.1 wt% beryllium, respectively a combination of these elements in solid solution. In addition to this, other solid phases may appear with up to 20% volume share in the structure, which form e.g. by separation in the solid state from the two main phases, e.g. Ni^Ti, or is separated immediately from a melt in conjunction or even in equilibrium with the CsCl structural phase or with "the magnesium-rich phase. In addition to this, it is part of the present invention that the elements in the magnesium-rich phase within the initially exclusively or mainly metallic two- or multi-phase material can be completely or partially converted by oxidation into high-temperature-resistant oxides, and the magnesium-rich phase itself into oxide fibers or skeletons, for which now the cubic-space-centered phase of AB- the type alone forms the tough base mass.

Materials according to the present invention can

depending on the alloy composition, powder or melt

pp

metallurgically using a wide variety of prealloys, also as impregnation material.

Due to the large difference in the melting points of the two main phases, the possibility arises of bringing in compacts from the granulated, especially pre-sprayed high-melting phase into a magnesium-rich melt under vacuum, protective gas or under a salt blanket, as well as sintering powder mixtures in the presence of a melting liquid phase, also under elevated pressure, to obtain particularly fine-grained alloys, preferably when the micro-grain plasticity that usually occurs with grain sizes of approx. 1 <y>um must be used for later forming work. In order to achieve a fine grain structure in both phases, and the highest strength values, it is also appropriate to cool the melt-flowing materials at the fastest possible speed, e.g. more than 100°C per second, by spraying into powder or rapid cooling, rolling and drawing into foils, ribbons or thin threads, which are immediately used or further processed in powder metallurgy.

In the powder metallurgical production of the materials

according to the present invention, it is appropriate if the pre-treated alloy powder?1" and metal powder already have approximately the previously mentioned composition of the desired equilibrium phase of the material. First, the coincidence of the high ductility of the cubic-space-centered phase of The NiTi type, which undergoes a martensite transformation at temperatures below 200°C, with the malleable magnesium-rich phase, leads to the well ductile, hitherto unknown materials.

An essential feature of the object of the present invention is that these magnesium-based materials can also, by strong hot or cold forming, be brought to "highest strength values, as they are known, for example, from high-strength steels. This results -in practice two-phase- materials, which allow cross-sectional reduction down to a few µm fiber cross-section and below, respectively such a sheet thickness to the individual adjacent and overlying crystallites to the two phases thanks to their large expansion. magnesium-rich phase, in particular recrystallization annealing for this phase, is also sufficient for softening the high-melting cubic space-centered phase.

For the production of roll or strand profiles of materials according to the present invention, one advantageously starts from powder mixtures of the two phases, with the finest possible grain size, e.g. ^ 60 yum.

It is therefore expedient for the cubic space-centred phase to exist in a granulated, powder-sprayed, quenched or between 800 and 1000°C annealed state. In order to achieve a good fibre, respectively leaf structure, repeated strand pressing, rolling, respectively package rolling and, if necessary, drawing also with intermediate annealing, are necessary.

Particularly favorable for the strength and expansion properties of the described fiber materials is, when the composition of the

two metallic structural components are so matched to each other that both are stretched approximately equally in the forming direction by rolling, strand pressing and/or drawing at the selected forming temperature. For the production of materials with a lamellar or layer structure, it is similarly advantageous when, by forging, stunning, hammering, pressing, diagonal and/or cross rolling or explosion forming, the two metallic structural components become flat, parallel lying parts with approximately equal, even stretch and spread.

By adding up to 80 volume percent glass powder of corresponding grain size, calculated on the total material volume, of a type of glass with a low softening point below the solidus temperature of the magnesium-rich phase, preferably of lead glass, you arrive at three-phase materials, where particularly high strength properties are achievable. Depending on the viscosity of the glass phase and the flow properties of the two solid metal phases at higher temperatures, the three-dimensional arrangement of the individual fibers or blades in such glass fiber-metal composite materials can be varied arbitrarily, and the surface of the individual phases can be substantially increased , so that especially e.g. the glass fibers are completely isolated from each other and enclosed by metal fibers. The glass parts shrink on cooling after the last annealing treatment due to their smaller thermal expansion less than the metallic parts, especially the magnesium phase, thereby contributing, apart from their intrinsic strength, to a further increase in the firmness of the metallic fibers. In relation to the usual separate production of glass fibers and threads, and their impregnation with metal or insertion in a metallic melt, the described production method is particularly economical and also gives very uniform pieces of material.

Likewise, from the beginning it is possible, in a powder mixture of the two ductile metallic phases, to introduce up to 70 volume percent high-strength fibers or threads, e.g. uncoated or possibly with silicon carbide coated carbon fibres, ceramic fibres, boron wires, glass wires, whiskers or drawn thin wires, e.g. of beryllium, stainless steel, chrome alloys or tungsten or also ceramic powders and fibers or similar strands, mats or fabrics, and to strand press these. Thereby, the fiber orientation is reinforced in the strand pressing direction, the metal powder parts are likewise stretched into fibres, these float around the introduced high-strength fibres, which in turn change only slightly, and, if it is a question of endless threads, can also be torn to pieces to the orien- terred fiber pieces with a high length-to-cross-section ratio, which are separated from each other by the magnesium-rich phase and the intermetallic phase of the NiTi type.

Finally, the heat treatment below the magnesium melting point has a particular effect on the structure and properties of the magnesium base mass, which can be hardened in a known manner, or which itself can be hardened by oxidation. However, it is also possible to harden the high-melting main phase after the chip-free forming below the melting temperature of the magnesium-rich phase by rapid cooling and annealing, or in addition to harden by cooling at a regulated speed over other solid phases that initially remained in solution.

In all the prescribed sintering, gliding and heat treatments, it turns out to be advantageous that the particles in the two metallic phases are connected particularly strongly to each other by partial diffusion to their interfaces. The same applies to stop pieces and pressure stop pieces made of materials according to the present invention. These are distinguished by a very favorable ratio of firmness to density, and allow particularly thin wall thicknesses.

The "mixed materials" described above are particularly suitable as lightweight construction materials with high strength for space and aerospace engineering as well as for the vehicle industry and engine parts, however

also for weapons technology, for sports equipment, containers and the like.

They can be used instead of glass-fibre or metal-fibre-reinforced materials on a plastic basis at much higher temperatures, and due to their higher strength and also transverse strength allow less wall thickness from the start, and thereby further weight savings. From a connection point of view, they do not pose any difficulties and are also very easy to work with in terms of chip separation.

When used in air at elevated temperatures, the magnesium-rich phase is preferably protected by formed thin oxide films, but remains temporarily metallic in the interior.

However, it is also possible to oxidize these phases completely by annealing these alloys at constant or rising temperatures to above the melting point; and in this way to arrive at metal ceramics with MgO, respectively complex oxides and e.g. glass fiber inserts as high-melting ceramic phase components, which are held together by the intermetallic phase of the NiTi type. To the extent that the latter is also oxidized, its toughness is restored by a reduction treatment. A pressure effect during the oxidation serves in particular to densify the resulting mixed material to compensate for the possible shrinkage of the magnesium phase.

In this way, a goal is achieved especially for high oxide proportions, the good binding by a metallic phase, something which until now, on

due to the poor wetting of oxides as starting material with metals or alloys in the production of metal ceramics by impregnation or sintering methods, has created considerable technical difficulties and additionally made adhesives necessary.

Solid and thermal shock-resistant high-temperature materials with high porosity, low density and with good heat and electrical conductivity are obtained, which at the same time exhibit a high hardness and edge resistance and a high chemical and abrasive resistance, but which can also be formed chip-free or chip-separating . They are applicable especially up to the melting point of the NiTi-type phase. They can be used for electrical contacts, cutting materials, gas turbine blades, wear-resistant machine parts for cold and hot work such as damping materials, nozzle materials for solid fuel rockets and for heat shields with coupling by melting the metallic part, where compared to the hitherto common, relatively heavier tungsten-silver- heat shields, by which the silver evaporates, the higher specific heat and heat of fusion of the_metallic phase compared to silver can be advantageously utilized.

The metal ceramics described can be obtained in any

preferably shapes such as forgings and castings, pressure castings, elongated shaped parts such as rods, tubes, bands, foils or covers, the latter e.g. over plating, application welding or application spraying of the metallic starting materials. In any case, a subsequent oxidation is necessary for ceramics. It is therefore always advantageous that an alloy formation occurs which also holds up to the subsequent oxidation and which causes the desired bond between the two metallic phases of the starting material and the substrate to be armored or coated.

This applies in particular if the magnesium materials according to the present invention are used as ceramic solder.

At the same time, one has the advantage of a low working temperature which, depending on the composition of the solder paste, can be selected down to close to the melting point of the magnesium-rich phase, and of an active solder paste depending on the composition, and can still select the operating temperature of the soldered parts after oxidation of the low-melting metallic phase to close below the melting point of the high-melting metallic starting phase. As ceramic solder paste, the materials according to the present invention are applicable for metal ceramics as well as for full ceramics, graphite, carbon fiber materials and for high-melting metals, such as e.g. zirconium tungsten, molybdenum,, titanium, cast iron and their compounds among themselves.

Claims (4)

1. Magnesium-based metallic material with two main lattice constituents, characterized in that it consists of 5-97% by weight, preferably 5-65% by weight, of particles of a cubic space-centered phase of the AB type with a CsCl structure and lattice constants between 2.60 and 3.20 Å, where A stands for the metals nickel, cobalt and iron, singly or combined, and B stands for the metals titanium, aluminum and, when A does not contain iron, also beryllium, singly or combined, and 3-95% by weight of a hexagonal or a likewise cubic space-centered phase with a lower melting point than the phase with CsCl lattice and consisting of a magnesium-lithium alloy with up to 55 weight-% lithium and up to a total of 3 weight-% of the elements in the phase with CsCl lattice in solid solution, and that the material possibly contains up to 10 volume-% of a further solid-state separated metallic phase that is built up from the same elements as the main phases and which stand in heterogeneous equilibrium with these, optionally up to 80% by weight of a glass phase with a softening point below the solidus temperature of the magnesium-rich phase and optionally up to 70% by weight of pre-produced carbon fibers, ceramic fibers, glass wires, boron wires and/ or whiskers, and pre-manufactured high-melting and high-strength metallic threads or fibers. 2. Material according to claim 1, characterized in that the magnesium-rich phase contains up to 8 wt% aluminum, up to 8 wt% cadmium, up to 8 wt% silver, up to 12 wt% zinc, up to 3 wt% manganese , up to 20 wt.% indium,.up to 2 wt.% copper, up to 0.5 wt.% silicon, up to 4 wt.% barium, up to 4 wt.% strontium, up to 4 wt.% cerium or cerium alloy metal, up to 2.5% by weight didynium (neodymium + prasedym), up to 4% by weight thorium, up to 1% by weight zirconium, up to 0.1% by weight beryllium respectively a combination of these elements in solid solution. 3. Material according to claims 1 and 2, characterized in that the phase with CsCl structure contains up to 30 wt.% chromium, up to 10 wt.% vanadium, up to 20 wt.% zirconium, up to 4 wt.% molybdenum and tungsten , up to 2% by weight of copper, up to 3% by weight of manganese, up to 1% by weight of silicon, respectively a combination of these elements in solid solution. 4. Material according to one or more of claims 1-3, characterized in that the magnesium-rich phase is oxidized to magnesium oxide, respectively complex oxides.