RU1813818C - Method of production of monocrystals of nickel-containing alloy with dendrite structure - Google Patents

Abstract

Usage: metallurgists single crystals of heat-resistant nickel alloys. SUMMARY OF THE INVENTION: crystals are grown by directional crystallization of a melt in a crucible in a temperature gradient in an angle of 20-30 °; with a direction of 100, the crystal-melt phase boundary is created with an angle of inclination of its normal to the crystallization direction of at least 30 °. 4 tab. 1 ill.

Description

The invention relates to the metallurgy of single crystals and can be used to optimize the technology for producing single crystal products from heat-resistant nickel-based alloys.

The purpose of the invention is to increase the uniformity and perfection of the structure of single crystals.

The goal is achieved in that in the known method, including directional crystallization with speeds and temperature gradients that ensure the formation of the dendritic structure of single crystals of nickel alloy, the interfacial surface is formed asymmetric with an angle of inclination of its normal to the direction of growth of 30 ° and provide, for example, using seeds

such a single crystal orientation that the crystallographic direction 100 is normal to the interface at a goal of 0-10 °.

The proposed method is based on the following physical laws of structure formation of dendritic single crystals of nickel alloys during directional crystallization. The structure of the resulting samples is formed by a children’s ensemble developing from one center or seed, along with the main trunks (first order), branches of the 2nd and 3rd order develop well. (1). The development of primary trunks and higher order branches occurs in crystallographic directions of type 100.

00

(A) 00

00

The essence of the method lies in the targeted transformation of the axisymmetric interphase surface into an asymmetric one, inclined at an angle to the direction of growth in combination with the optimal orientation of the single crystal in the direction of growth.

The angle of inclination / between the growing direction and the normal to the interface should be greater than or equal to 30 ° C. In this case, provided that the angle between the normal to the interphase surface and the crystallographic direction of type 100 (o) is sufficiently small (n 10 °), it is possible to achieve a homogeneous structure of the dendritic ensembles, characterized by the constant dendritic parameter (distance between the primary trunks) by the diameter of single crystals. Note that for single crystals obtained under such conditions, the number of spurious grains formed as a result of fluctuating separate independent crystallization centers is significantly reduced. At (3 30, the manifestation of the effect is significantly weakened.

In the proposed method, the angle of inclination of the interface and the crystallographic orientation of its normal have a significant effect on the development of the substructure in single crystals of a nickel alloy with a dendritic structure. Under the condition of / 30 ° in combination with and 10 °, large substructure blocks separated by low-angle intergrowths (one of the main structural defects in dendritic single crystals of nickel alloys grown at an axisymmetric interface) does not form. The number of fragments (small sections of the crystal separated from the matrix by small-angle boundaries of 1-3 °) and the angle of maximum misorientation of the single crystal also decrease.

From the foregoing, sen is the mechanism for the formation of structurally perfect single crystals with a dendritic structure with an inclined interface in the proposed technical solution. It is known that the perfection of such single crystals is determined by the stability of the dendritic ensemble to the formation of separate independent (in orientation) grains, to the fluctuation of the crystallization front profile, to nonequilibrium capture of vacancies, etc.

An example of the method. Single crystals with a dendritic structure of a highly alloyed alloy were grown

5

0

5

0

5

0

5

0

5

nickel-based alloy MAR-M200, containing tungsten, chromium, aluminum molybdenum, titanium, cobalt, carbon, vanadium, niobium (the total amount of alloying elements did not exceed May 40%) and the binary alloy NI - 27% W. For each alloy, 2 series of experiments were carried out - with an axisymmetric interface and with an inclined surface. When growing, a universal high-temperature apparatus was used for directional crystallization of the design of the Institute of Crystallography of the USSR Academy of Sciences. Growth conditions were selected to ensure the stable development of dendritic ensembles for single crystals of both alloys. For a highly alloyed alloy, the melt crucible was removed from the heating zone at a speed of 1.4 mm / min, for a binary 10 mm / min. The diameter of the samples is 9.5 mm, and the length is 80 mm. An asymmetric interface was formed by asymmetrically positioning the crucible in a concentric heater. The slope of the interface was determined by metallographic analysis of samples obtained in special experiments with stopping the movement of the crucible and rapid cooling after solidification of half of the sample. The crystallographic orientation of the normal to the interfacial surface was determined using the X-ray method of the reverse survey (according to Laue) in combination with metallographic studies. The single crystal substructure was investigated by the method of X-ray topography (angular scanning method) developed at the Institute of Physics of the Ural Branch of the USSR Academy of Sciences.

The drawing shows X-ray diffraction topograms of the cross sections of single crystals of a binary alloy NI - 27% W. obtained at symmetric (a) and asymmetric (b) interfaces. The topograms show a pattern of extinction contrast typical of single crystals with a dendritic structure. On the topogram (a), large macroblocks are visible, separated by small-angle boundaries (white areas), the disorientation of individual sections inside the macroblocks is visible. Topogram (b) indicates the high perfection of the dendritic single crystal - small-angle boundaries are very poorly developed, individual dendritic trunks are visible.

The experimental results are presented in Tables 1--4, which show the main parameters characterizing the structurally perfect

samples and notes on the features of their structure. The following notations are used in the tables: in the angle of maximum misorientation of the single crystal, QI is the average misorientation angle of neighboring blocks, di / d2 is the ratio of the average values of the dendritic parameter corresponding to the peripheral and central regions of the single crystal (in cross section) and (see above). When comparing Table 1 with Table 2 and Table 3 with Table 4, it can be seen that for both alloys, single crystals grown with an asymmetric interphase surface are significantly superior in structural perfection to samples obtained with an axisymmetric interphase surface, provided that the angle ft is 30 ° and at the same time, the angle cr 10 °. It is also seen that, along with an increase in the degree of structural perfection in parameters 0), & i, di / d2, single crystals obtained with an asymmetric interphase surface are more resistant to the formation of individual grains and fragmentation (see the note to the tables). Thus, the experimental results indicate the effectiveness of the claimed technical solution and substantiate the feasibility of the stated limits of the angle / slope of the normal of the interface to the direction of growth of the single crystal and the angle (a) between the crystallographic direction of 100 and the normal to the interface.

Thus, the proposed method due to the use of an inclined interface and the optimal orientation of the grown single crystal provides the following advantages compared to the prototype: it increases the radial uniformity of dendritic single crystals of nickel alloys, increases the degree of structural perfection of dendritic single crystals by suppressing the development of substructural components, increases the stability of a growing single crystal to parasitic grain formation and fragmentation, increases yield of mo nocrystals (approximately from 60 to 90%).

Claims (1)

The claims A method for producing single crystals of a nickel-containing alloy with a dendritic structure by directional crystallization of a melt in a crucible in the presence of a temperature gradient at the phase boundary crystal is a melt, characterized in that, in order to increase the homogeneity and perfection of the structure of single crystals, crystallization is carried out on an oriented seed in a direction comprising an angle of 20-30 ° with a direction of 100, and a phase boundary is created with an angle of inclination of its normal to the crystallization direction of at least 30 °. Table 1 The main characteristics of the structural perfection of single crystals grown with an axisymmetric interface. High alloy nickel based alloy Table 2 The main characteristics of the structural perfection of single crystals grown with an asymmetric interface. High alloy nickel based alloy  Ta bla tsa 3 The main characteristics of the structural perfection of single crystals grown with an axisymmetric interface. Nickel-based binary alloy Table a The main characteristics of the structural perfection of single crystals grown with an asymmetric interface. Nickel based binary spd  -. . fci. . l ..-.:. L -, H B, -y%%  : f.J, / :, V ..; . . -, t: X-r1b  -, - / H V; l1.