DE1801594C3 - High-temperature anisotropically solidified cast body with aligned filamentary or lamellar carbide precipitations - Google Patents

Description

depends largely on the volume fraction and properties of the unidirectional fibrous Reinforcement, with the continuous metal matrix serving as a stress transmission medium and imparts toughness to the composite. Considerable Strengths at high temperatures are achieved when the reinforcement phase is strong and the The microstructure of the composite is stable at elevated temperatures.

The embedding of a reinforcement with a high modulus of elasticity in a metal matrix with a lower The modulus of elasticity results in a cast body of higher strength, especially with regard to fatigue fractures, as has also been observed, for example, with aluminum alloys reinforced with boron fibers.

It is known that systems are made of particular material, including certain unidirectional solidified eutectics that form ordered microstructures in which a phase is formed from the melt parallel rods that solidify in a matrix phase like that are embedded. When the fibrous phase of the regulated eutectic solidified in this way is so selected will have the desired high strength, high modulus reinforcement in the matrix lower modulus is obtained, the resulting composites can be used immediately. It is known that the aforementioned regulated eutectics are preferred crystallographic ones Have boundary layers with low free energy and thus stable microstructures. Therefore, if this Exposing microstructures to high temperatures for long periods of time does not result substantial coarsening. Furthermore, since all phases are in equilibrium, the eutectics are not exposed to chemical incompatibility with compounds produced by other processes occur, which can lead to a severe impairment of their mechanical properties.

In order to obtain the desirable aligned microstructure through a regulated solidification of the eutectic, solidification must be achieved along a flat front. Surprisingly, it was found that this is the case with the alloys from which the invention Cast body exist, occurs. In these alloys, carbides serve as a reinforcement medium, although they are thermodynamically less stable than the oxides. The melting points of the carbides are im generally the highest of all possible compounds, and carbides can be obtained by melting processes can easily be embedded in the above-mentioned metal matrix, so that the troubles are avoided resulting from the powder processing customary for oxides.

The relative thermodynamic stabilities of the Carbides are very important, and the normal free energies of formation of some carbides are shown in FIG. 3 plotted as a function of temperature in a diagram. It was observed that the carbides with the smallest negative free education >> energies in Graphitize nickel and cobalt. Silicon carbide graphitizes, for example, with nickel, cobalt or Chromium and boronocarbide are graphitized with either nickel or cobalt. The others in Fig. 3 specified However, monocarbides are thermodynamically stable in both nickel and cobalt, and so is it gives eutectics between these metals and these monocarbides.

Various researchers have classified the eutectics based on certain factors, including the Entropy of fusion. If one proceeds from the latent heats of fusion of the carbides and their melting points, In particular of niobium carbide, titanium carbide, tantalum carbide and zirconium carbide, flat solidification can occur at the front of the eutectics consisting of metal and monocarbide are not expected and which the desired fine-fiber structure therefore appears unattainable. Despite the theoretical considerations, it was however, even growth is carried out at the front of the systems described and a number of anisotropic objects made from these systems.

The systems investigated according to the invention are given in Table I below.

Table I.

Volume Enamel tensile strenght C) system percent temperature C) amplifier kp / cm = (T) C) Ni-TiC 5.5 1254 _ Ni - NbC 11th Ί33Ο (9000 (24 ° (1800 (1093 ° Co-NbC 12th 1366 70: 0 (24 ^C. Co-VC 20th - -

In the Ni - NbC system selected for analysis became, as Fig. Figure 4 shows a eutectic at about 10 weight percent (13 volume percent) NbC found at 1330 ° C. With a melt of Ni-0.5-12 percent by weight NbC underwent unidirectional solidification at speeds of 1 to 9.8 cm / h - as specified in more detail in Table II - found.

Table Il

Solidification Microstructure system speed (GevN not percent) age (cm h) partially regulated Ni - 10 NbC 3.0 eutectic colonies Ni-10 NbC 5.2 regulated eutecti Ni-10 NbC 2.8 cum regulated Ni-10 NbC 2.8 Eutectic proeutectic NbC Ni-11 NbC 2.8 proeutectic NbC Ni-11 NbC 2.9 proeutectic NbC Ni - 12 NbC 2.8 proeutectic NbC Ni-12NbC 2.8 single phase Ni Ni-0.5NbC 3.0 regulated Ni-10 NbC 2.9 Eutectic regulated Ni-10 NbC 2.8 Eutectic regulated Ni-10 NbC 2.8 Eutectic regulated Ni-10 NbC 2.8 Eutectic regulated eutectic Ni-10 NbC 1.9 Colonies primary NbC Ni-11 NbC 7.2 primary NbC Ni-11 NbC 6.8

Of the Ni - NbC ingots that grew in closed-ended alumina crucibles, only those showed

^{5 6}

an aligned microstructure, which was tested with speed and elongation at break with Eutek

at a rate of less than 3 cm / h solidified. Vertica with a carbide fiber spacing of approximately

however, several ingots were executed in one direct 7.5 micron; the results are shown in FIG. 7th

th block subjected to water cooling generated, shown.

a flat growth starting from the front 5 In the Ni - TiC system, a eutectic became at at speeds above those in approximately 11.3 weight percent titanium and 0.9 Ge crucibles with the end closed. weight percent carbon with ternary eutectics

The fiber spacing of the carbide in an ingot, which is located on either side of the pseudobinary eutectic, the

solidified at 3 cm / h was approximately 7.3 microns, whiphite at 1271 ° C and Ni _? Ti at 1296 ° C with TiC and Ni

at the distance contains with increasing solidification io. At the eutectic temperature

speed decreased. It has been found that the pseuso-binary eutectic consists of an an

mechanical properties of the fiber-reinforced Le-Titanium range from solid solution matrix of nickel

Alloys not only from the volume fraction of in the and about 5.5 volume percent titanium carbide. One

Alloy existing fiber reinforcement, but unidirectional solidification at 2.3 cm / h was successful.

also depend on the fiber spacing. So 15 got rich, although there was a pronounced ramification of the

found that when the fiber spacing was reduced, it showed a fibrous structure. In general, each

by a factor of 2 by increasing the solidification but the directionally solidified eutectic despite the

speed, the creep rupture strength at 250 ⁰ C and winding geometry referred to as fine-fiber

1050 kg / cm * from less than four hours to more than will be. However, this eutectic seems to be for the

54 hours increased, while the minimum creep 20 application in turbines because of the low vol-

speed is less valuable by more than two places, the lumen portion of the dispersed phase

was reduced. A decrease in fiber spacing as the Ni - NbC eutectic (13 percent by volume) increases

arises from an increase in solidification.

speed. The rate of solidification of the Co - NbC eutectic is said to be about 11 degrees. The solidification rate is 25 percent by weight. Carbide was determined at 1366 ° C, but was limited by the tendency of the system to change from a microstructure consisting of rods and platelets to a planar to a cellular boundary layer directed between liquid and solid metal, rigidification with 2, 9 cm / h generated. Tests showed when the speed is too high. This is due to the reinforcement behavior of the fibers with a state of subcooling of the liquid immediately 30 of 7030 kg / cm ² and an elongation of 0.65%.
on the front side of the solidifying boundary layer The Co-VC eutectic with about 10 attributed, by a combined effect, weight percent carbide has an accumulation of impurities exceeding 20% and the never-volume fraction of vanadium carbide. A one-sided thermal gradient caused directional solidification in the liquid resulted in primary cobalt. Im will. 35 Co-VC system exist, as has been established,

The mechanical properties of a Ni - NbC- two eutectics; the higher melting eutectic

The eutectic that solidified at a directional rate of 3 cm / h is the pseudo-binary part of the ternary eutectic

the following: tensile strength 9000 kp / cm ² , modulus of elasticity between Co and VC with 10 percent by weight Va-

3.02 · 10 "kp / cm ² and an elongation at break of more nadium and 1.7 percent by weight carbon

than 9 ° / ₀ . 40 the binary eutectic range of the bar

Assuming that the strength of the matrix taken fibers by X-rays is about 2460 kgf / cm ² , see FIG. 5, investigation identified as vanadium carbide,
shows the mixing rule that the average load on the carbide phase when the samples were solidified is at least 0.6 castings of the eutectic systems by induction 10 ^s kp / cm ¹ if the components for the carbide phase begin to melt An argon measured elastic modulus of 3.52 x 10 "kgf / cm ² atmosphere was produced. All eutectics were assumed to be clay. Ground crucibles were used; each ingot was broken into smaller ones

The rule of mixing can be expressed by: pieces cut up and into long cylindrical pieces

Crucibles arranged in which the eutectics again

"e ⁼ Kw + (1 - Vf) Om, 50 were melted and under an argon atmosphere

. Sphere directed unilaterally solidified by the crucible

wherein means: th to _un was used from a heat zone,

δα the tensile strength of the fiber-reinforcing alloy - ^if η ° ^ι «& either by induction heating

_tion or in a resistance heated graphite furnace

Vf is the volume of the fibrous phase that was generated.

i _f the average strength of the fibrous The tensile test of the unidirectional solidified

Phase and alloys were carried out using test pieces,

d _m the strength of the matrix at the time of loading, which were machined in such a way that the loading direction

limit of the alloy. ^{zar growth direction was} parallel. The specimens

60 were made using a Tinios-Olsen method

Directionally solidified Ni - NbC eutectics and TD search engine to break with a stress nickel were also under tension at increased speed of 0.25 mm / min, at room temperature examined in air; the test result and a speed of 1.78 mm / min, nits are in Fig. 6, which shows that the stressed at elevated temperature The creep limit Eutectic material at all test temperatures 65 was tested in a Satec Model D creep rupture tester is stronger than TD-Nickel and also the tensile elongation at various loads under the protection of of the Ni - NbC eutectic was measured to be much larger than that of argon and the elongation was measured by K reuz-TD nickel at elevated temperatures. head rash measured.

Continuous determinations of weight gain were made on plate samples in oxygen atmospheric pressure in the range of 700 to 950 ° C using a thermal balance of A i η s w ο r t h carried out.

The strength of the carbide fibers in the alloys approaches the theoretical elongation at break. the

Eutectics show a stretching stress that is greater than the elastic extensibility of the carbide fibers. The microstructures are stable at the elevated temperatures, which are of practical importance both with regard to metallurgical processing and the chemical behavior of the eutectics.

For this purpose 2 sheets of drawings

309 «9/2 ©

Claims (2)

I 2 heat exchanger tubes are suitable, but not patent claims: can take the place of superalloys. From the German patent specification 1061 520 are 1. High-temperature anisotropically solidified cast Co - Ni - V alloys with a Vickers hardness and body with aligned filament or lamellar 5 a Ε module, which at temperatures above 500 ⁰ C shaped carbide precipitates, consisting of remain constant over time, known; a cast body of the alloy of nickel with the monocarbide of the structure according to the invention can, however, not be inferred from this publication of titanium or niobium in quasi-binary eutek-. table composition. The quasi-binary eutectics of the alloys, from 2. High-temperature anisotropically solidified castings which the cast body according to the invention consists of with aligned filamentary or lamellar rigid in a face-centered cubic structure, and their shaped carbide precipitates consisting of solidification runs, as from the USA patent specification the alloy of cobalt with the monocarbide 3 124 452 known, in one direction, so that a of vanadium or niobium in a quasi-binary ordered microstructure, which generally consists of eutectic composition. 15 parallel rods or lamellae of the predominant Carbide phase consists, which are embedded in a solid solution matrix of the metal. An orderly one Microstructure of this type is hereinafter referred to as fine-fiber and the reinforcing phase as fiber-like toe-20 draws. The cast bodies according to the invention not only have In order to compare the thrust and performance characteristics of strengths with those of the TD nickel To increase gas turbines, the turbine inlet alloys at 1093 ^: C are rather comparable Temperatures above the temperature resistance also show a clear superiority over ability of the usual superalloys on the basis of 25 these in the temperature below 982 ° C been increased by nickel and cobalt. From these areas. Machine parts made from alloys require the invention will be described below with reference to the therefore cooling at these high temperatures. Drawing further explained. It shows Although from the use of refractory metal I i g. 1 is a photograph of the microstructure of a alloys for uncooled machine parts per se 3 ° Ni NbC eutectic, which is directed on one side with Advances are possible, this alloy is subject to solidification at a rate of 2.8 cm / h; the In general, rapid oxidation and absorption occurs across the direction of solidification, Erosion. Coatings for these alloys which have a fig. 2 a photograph of the microstructure - im corresponding resistance to the attack longitudinal section - a Ni V- NbC eutectic, the of gas on the metal in a jet turbine required- 35 directed unidirectionally at a speed of if necessary, can form for thousands of hours, has solidified 2.5 cm h; the fibrous phase consists are currently not available. predominantly made of carbide. Alloys reinforced by dispersion on FIG. ? a graph of normal free energies Base of nickel and cobalt, like the TD-nickel in the formation of some carbides as a function of the tem (98 ° "nickel, 2 °" thorium dioxide), are the usual 40 temperature, Superalloys at 1093 C and more clearly F i g. 4 a given condition think. This superiority is represented by a curve diagram of the Ni - NbC alloy, Impairment of strength at 982 ¹ C and below. F i g. 5 a graph of the stress-strain the flexibility and the corrosion resistance while maintaining the Ni-NoC alloys, elevated temperatures, as well as a limited Her- 45 F i g. 6 is a graph showing the tensile strength of the counteractability. Ni - NbC eutectic and a TD nickel alloy The present invention is based on the object, depending on the temperature: the to remedy this disadvantage. The solution of this on-Ni NbC eutectic did not fail during one would allow a highly heat-resistant anisotropic period of 258 hours. Rigid cast body with aligned filamentary or 5 ° Fig. A comparison of the tensile strength of a TD-Nik lamellar carbide precipitate, which according to the tapered alloy and the Ni - NbC eutectic in the present invention from alloys of nickel depends on the temperature,
With a monocarbide of titanium or niobium in a quasi-binary eutectic composition or from say the usual alloys based on alloys of cobalt with a monocarbide of nickel and cobalt often with the operating conditions of vanadium or niobium in a quasi-binary eutectic gas turbine , because there is already 93 C and less under-composition. operating temperature half of its melting point From the German patent specification 1,225,394, the microstructures of the alloys are damaging Niobium carbide precipitates affect reinforced nickel borrowed. The effectiveness of a particle alloy known. This reference discloses 60 reinforcement and solid solution reinforcement however, neither an alloy of nickel and niobium is also significantly affected because a carbide in eutectic composition still a thermal activation to an undesirable pla-nickel alloy, which leads to elastic deformation through fibers made of niobium carbide. is reinforced. A fiber reinforcement is important for the production of elevated temperatures the well-known alloy does not appear at all; these 65 set components have the metal fiber reinforced Alloy is said to be promising due to its good conductivity and ten metal matrix composites characterized by high strength, so that alloys are shown this type for the production of capacitor and The mechanical strength of these substances depends in