JPS61567A - Treatment of grain oriented growth of crystal grain - Google Patents

Abstract

PURPOSE:To accelerate the grain oriented growth of crystal grains and to improve the high temp. mechanical property by hot working a mechanical part made of alloy to the directional crystal grain growth direction to obtain the fine crystal grain structure, mounting an activating metal sheet of a specified compsn. on a desired end surface of a working material and heating, holding the body in a heating furnace. CONSTITUTION:The mechanical part made of Ni base heat resisting sintered alloy contg. Cr, W, Mo, Ta, Al, Ti, Y2O3 is hot worked by extrusion, etc. to make the structure to fine crystal grain structure. Next, a sheet material 3 made of activating metal consisting of Ni base alloy contg. m.p. lowering element such as Cr, B is mounted on the end surface 2 perpendicular to the direction to which main stress is applied during usage of the working part 1, i.e. the direction which is desirable for crystal grain growth, and the body is heated and held at temp. lower than m.p. of the part 1 and higher than m.p. of the metal 3 in a heating furnace 4. By the reaction with the working part by the melt of the metal 3, crystals grow to the main stress applying direction over whole length of the part 1, and the mechanical characteristics at high temp. is improved.

Description

[Detailed Description of the Invention] (Field of Application of the Invention) This invention relates to an improvement in a method for growing the crystal grains of an alloy, particularly a heat-resistant alloy, by aligning them in one direction. The present invention relates to a method for enabling directional growth of grains in alloys containing hard to disperse grains.

(Prior Art and Problems to be Solved) As a means of improving the high-temperature mechanical properties of heat-resistant alloys, elongation of grains in the direction of principal stress makes the length-to-diameter ratio very large, and the size of grains is increased. or to improve the mechanical strength of grain boundaries.

Among these methods, a method for elongating crystal grains in the principal stress direction is to align relatively elongated crystal grains in one direction by performing directional solidification when casting machine parts made of such alloys. It is known to do. To achieve this, there is a method to advance solidification by removing heat while maintaining the directionality so that the crystal grains grow almost along the direction in which the principal stress acts during the solidification process in the mold. Various proposals regarding the structure etc. have been made.

However, in alloys such as particle dispersion strengthened alloys, particles agglomerate in the molten state during casting, and in other alloys, it is unavoidable that considerable segregation occurs from one end of the directionally solidified part to the other. .

In order to improve this problem, a method has been proposed in which the internal structure of the alloy in its solid state is changed to a columnar grain structure (Special Publication No. 5).
3-35887, Special Publication No. 56-41686).

In these methods, a mechanical part workpiece having a fine grain structure generated by hot working is zone-heated to a temperature below the metal melting start temperature in a zone heating furnace 12 as shown in FIG. Place the heating zone 13 on the part 11.
By moving from one end 11a to the other end 11b, crystal grains 14 are grown in one direction.

The larger the temperature gradient in the heating zone, the better the structure after zone heating, but since there is a limit to the gradient value, it may be difficult to implement depending on the type of alloy, and it may not be possible to achieve a structure other than simple shapes such as rods. However, in practice, it is difficult to perform zone heating under a uniform and sufficient temperature gradient.

(Objective of the present invention and means for solving the R point) In view of the above circumstances, the present invention aims to provide a treatment method for directional growth of crystal grains that does not require zone heating. In the processing method, hot working is performed on an alloy machine part workpiece in the direction in which directional grain growth is desired, resulting in a fine grain structure, which can be easily applied to the desired end face of the workpiece. After providing a low melting point metal layer containing a melting point lowering element that dissolves and diffuses, the mechanical part workpiece is heated and maintained in a heating furnace at a temperature below the melting point of the workpiece alloy and above the melting point of the metal layer. The present invention relates to a method for processing directional growth of crystal grains.

(effect) The operation of the method of the present invention will be explained as follows.

In order to maintain the alloy machine part workpiece 1 (hereinafter simply referred to as the workpiece) to be subjected to crystal grain directional growth treatment to have a fine grain structure that changes into coarse crystal grains relatively quickly, extrusion molding etc. are performed as a preparatory process. It is necessary to perform hot working to obtain a fine grain structure.

Next, on the end face 2 which is preferably perpendicular to the direction in which principal stress acts during use, that is, the direction in which crystal grains are desired to grow, a metal layer (hereinafter referred to as When the activated alloy 3 is melted by heating it in a heating furnace 4 to a temperature below the melting point of the workpiece alloy and above the melting point of the activated alloy, the workpiece alloy 1 and its contact area are heated. 2 to lower the melting point of the core, and even though the workpiece 1 is in a solid state, the contact part 2 becomes a melt.

Examples where the effect of applying the method of the present invention is noticeable include N containing Cr-W-MO, Ta-A1, Ti, and Y2O3.
It is not effective for particle dispersion strengthened alloys such as i-alloys, which tend to undergo uniform grain growth when heated, and alloys which tend to undergo directional grain growth even when using a general heating furnace.

Suitable activation alloys include Ni, Co, and Fe-based alloys containing at least one of the melting point depressing elements B, Si, P, and C, and are applied as a thin strip or as a paste powder. Alternatively, it may be attached to the end surface of a workpiece by chemical vapor deposition or plasma irradiation.

If the workpiece and the activated alloy are heated in a heating furnace to a temperature between the melting point of the workpiece and the activated alloy in this way, an alloy formed between the activated alloy and the workpiece will be formed. The material melts and becomes a molten material, but this is only temporary; as time passes, alloying gradually progresses toward the workpiece, and eventually the concentration of activated alloy becomes thinner and it is no longer a molten material.

As mentioned above, by holding the workpiece at a temperature below the melting point of the workpiece alloy and above the melting point of the activated alloy for a period of time necessary to cause grain growth along the entire length of the workpiece, the workpiece alloy is regenerated at the contact area. Grain growth nuclei generated due to a change in crystal properties, for example, a decrease in recrystallization temperature, erode fine grains and grow due to surface tension. In many cases, the grain growth rate in the processed product is anisotropic, and the processing direction is significantly larger than the direction perpendicular to it (for example, Japanese Patent Publication No. 56-4168
No. 6 Publication Fig. 5 (This is why the grains extend in the extrusion direction in the crystal grain structure when normal annealing is performed as shown in bl).

The method of the present invention does not require a zone heating furnace, since the workpiece can be uniformly heated by placing it in a sufficiently large heating furnace.

However, the same effect can be obtained by inserting the workpiece into a relatively small heating furnace with both ends open from the end surface provided with the activated alloy and gradually moving the workpiece to heat it locally to the opposite end. will be easily understood.

(Example) 15% Cr, 5% W, 2% Mo- of the above particle dispersed alloy
1%Ta・4%AI・1.5%Ti1.3%Y2O3・
Using a hot extruded sintered Ni alloy extruded rod (13 mm diameter) with balance Nt as a sample, one end face was coated with 15% Cr and 2.5%.
B. A thin alloy plate (thickness: 80 μm) with the balance being Ni was placed and
2kgf/an! The thin plate was pressed against the end face by heating at 1250° C. in a vacuum (10 to 10” Torr) for 1 hour, and then cooled to room temperature in a vacuum container.

J As seen in the photograph of the microscopic structure of the longitudinal section of the sample shown in Figure 2, an elongated coarse grain structure 5 is formed that extends in a direction perpendicular to the surface on which the activated alloy 3 of the workpiece 1 is placed. Ta. Note that 6 in the figure is a holding plate.

(Effects) As explained above, according to the method of the present invention, a low melting point alloy containing a melting point depressing element that can be easily solid-dissolved and diffused into the material alloy of the workpiece to be processed is crystallized for recrystallization activation. placed on an end surface preferably perpendicular to the direction in which the grains are desired to grow, and heated to a temperature below the melting point of the workpiece alloy and above the melting point of the activated alloy to improve the recrystallization properties of the reaction zone of both alloys;
When one or several crystal nuclei that become the seeds of coarse crystal grains are generated, they grow while eroding the fine grains due to surface tension and grow into elongated crystal grains. Not only does it not require a heating furnace, it also enables directional growth even in alloys in which grain growth nuclei are difficult to generate due to recrystallization.

Also, unlike the method of growing crystal grains by moving a heating zone with a temperature gradient from one end of the workpiece to the other, a small number of nuclei are grown on a plane preferably perpendicular to the direction in which the grains are desired to grow. Since coarse crystal grains are generated and then grown in a predetermined direction, there is no need for a device that adds a temperature gradient, and the effects are extremely large, such as the ability to grow coarse crystal grains in any desired shape. .

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the outline of the method of the present invention, Figure 2 is a micrograph (25x, curling solution corrosion) showing an example of oriented grain structure formed by the method of the present invention, Figure 3 1 is a sectional view showing the main points of a conventional method. 1... Machine part workpiece, 2... End face perpendicular to the direction in which crystal grains are to grow or the direction in which principal stress acts, 3
...Activated alloy thin plate, 4...Heating furnace, 5...Coarse crystal structure grown in one direction Applicant's representative Patent attorney Kamoshi 1) Second son 3 Figure 10

Claims (1)

[Claims] A method for processing an alloy for directional grain growth, which comprises hot working an alloy mechanical component workpiece in a direction in which directional grain growth is desired to produce a fine grain structure; After providing a low melting point metal layer containing a melting point lowering element that easily dissolves and diffuses into the alloy on the desired end face of the object, the machine part workpiece is heated to a temperature below the melting point of the workpiece alloy in a heating furnace. A method for directional growth treatment of crystal grains, characterized by heating and maintaining the temperature at a temperature higher than the melting point of the metal layer.