RU2729240C1 - Method of connecting a diamond monocrystal to a metal tool holder based on iron alloys - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to production of diamond tools by powder metallurgy and can be used in production of single-crystal diamond tools. Metal holder – tool base – is made of steel with carbon content of not more than 0.1 wt%. Base of diamond crystal, opposite to its working top, is flat and placed on horizontally located cavity of metal holder. During heating-sintering in vacuum, a mechanical force is applied to the working vertex of the diamond so that the pressure exerted by its flat base on the surface of the holder cavity is equal to 100–300 kPa. Method then includes heating to 1,165 °C and held at this temperature for 10–15 minutes.

EFFECT: as a result, efficient use of diamond raw material and reliable and strong connection of diamond monocrystal with metal tool base with reduction of production reject.

1 cl, 1 dwg

Description

The field to which the invention relates

The invention relates to a technology for the manufacture of diamond tools using powder metallurgy methods, in particular, to a method of fixing diamond grains with iron alloys and can be used in the manufacture of a wide class of single-crystal diamond tools, such as diamond in a mount, diamond needles, cutters, diamond tips for hardness testers and etc.

State of the art

In the manufacture of a wide class of single-crystal diamond tools, two main methods of fixing a diamond crystal with a metal base of the tool are widely used and widespread: the method of mechanical engagement (pressing or pinching) and the soldering-sintering method using solders of various compositions, including components adhesion-active to diamond and (Fundamentals of design and manufacturing technology of abrasive and diamond tools. Edited by VN Bakul. - M .: Mechanical engineering, 1975, pp. 254-279, RF Patent No. 2042478) [1, 2].

The closest in technical essence and essential features to the claimed invention is the method of connecting a single crystal of diamond with a metal base of the tool, described in the USSR author's certificate No. 275784 [3]. The claims and the description of the present invention indicate and describe the use of the formation of a relatively low-melting alloy of the eutectic metal-carbon composition as a result of contact heating of the diamond with metals. In this case, neither the metal upon contact heating with which carbon forms or can form an alloy of eutectic composition, nor the parameters, nor the heating conditions under which a strong connection of the diamond with the metal base of the tool is obtained or can be carried out, is specified.

Disclosure of invention

The objective of the claimed invention is to create a technologically simple and reliable method of joining a single crystal of diamond with a steel holder through the use of two complementary mechanisms of their adhesion: as a result of thermally activated chemical adhesive interaction of diamond with a metal melt at the diamond-metal interface and mechanical adhesion - compression (pinching) of the crystal diamond with a solidified melt of eutectic composition.

The technical result achieved when solving this problem is to obtain a reliable and durable connection of a diamond single crystal with a steel base - a tool holder, which ensures the effective use of expensive diamond crystals as a result of a decrease in the amount of scrap in the process of joining the diamond with the metal base of the tool.

Essential features characterizing the invention

- Restrictive: location of a diamond single crystal on the horizontal surface of a flat recess made in the original metal tool holder, ensuring direct contact of the said surfaces, heating them in vacuum to form an alloy of eutectic metal-carbon composition, holding at this temperature and subsequent cooling;

- Distinctive: a metal holder is made of steel with a carbon content of not more than 0.1% by weight, a single crystal of diamond from the side opposite to one of its vertices, selected as a working one, is preliminarily given a flat shape, during heating, a single crystal is applied to the working vertex mechanical force so that the value of the pressure exerted by the flat base of the diamond on the surface of the holder recess is in the range of 100-200 kPa, while heating is carried out to a temperature of 1165 ° C and is kept at this temperature for 10-15 minutes.

The technical result is achieved as follows:

The metal holder is made of low-carbon steel with a carbon content of not more than 0.1% wt. A diamond crystal from the side opposite to one of its vertices, selected as a working one, is preliminarily given a flat shape - a base to increase the area of the contact surface and tightly mate it with a flat depression of the metal holder. Depending on the shape and relief of the surface of the original diamond crystal, the flattening of its base can be carried out by sawing, followed by grinding or simply grinding. When placing a contact pair diamond - metal holder in a vacuum furnace, a mechanical force is applied to the working tip of the diamond crystal so that the pressure exerted by the flat base of the diamond on the surface of the holder recess is 100-200 kPa. Heating is carried out according to a given rate up to a temperature of 1165 ° C and is kept at this temperature for 10-15 minutes.

When diamond is heated in contact with iron, a liquid eutectic iron-carbon alloy is formed, and the temperature of the appearance of such a melt is more than 360 ° C lower than the melting point of iron (1534 ° C), which is of no small importance, since excessive heating of diamond to high temperatures leads to its intense graphitization and weakening of diamond due to the formation of microcracks. Under the influence of mechanical force applied to the top of the diamond crystal, most of the liquid eutectic alloy is squeezed out from under its base, filling the flat depression of the metal holder. In this case, the diamond crystal, squeezing out the melt, in accordance with the Archimedes law, slightly shifts vertically downward. In the process of cooling, the part of the eutectic alloy remaining under the flat base of the diamond crystal, solidifies, forms a thin intermediate layer, firmly entangled due to chemical interaction, both with the diamond crystal and with the steel holder. In this case, the part of the eutectic melt squeezed out from under the base of the diamond crystal, when solidified, grabs it around the entire perimeter, thereby providing mechanical diamond retention with a metal holder.

The use of a metal tool holder made of steel with a carbon content of more than 0.1% wt., As well as the heating temperature of the diamond - metal holder contact pair, exceeding ~ 1165 ° C in vacuum, is undesirable, since in these cases the rate of catalytic graphitization of the diamond surface significantly exceeds the rate of dissolution of carbon from diamond to metal melt. As a result, when the melt solidifies on the side of the diamond surface, a continuous layer of graphite with low strength can form, which will lead to a decrease in strength at the diamond-intermediate layer interface.

At the given values of the maximum temperature and the heating time interval, the value of the pressure exerted by the base of the diamond crystal on the eutectic melt, in the range of 100-300 kPa, is optimal from the point of view of reliability and strength of the diamond-metal holder connection. At pressures less than 100 kPa, the eutectic melt will not be squeezed out in the amount required for spreading and gripping the diamond along its entire perimeter, which will not ensure high mechanical adhesion of the diamond to the metal holder. At pressures exceeding 300 kPa, the thickness of the intermediate layer becomes excessively small, since practically the entire eutectic melt is squeezed out from under the diamond, which can reduce the strength of the diamond - intermediate layer - metal holder bond due to the temperature stresses arising during cooling due to the difference their coefficients of thermal expansion. Brief Description of Drawings

FIG. 1 shows a diagram of the arrangement in two projections (side and top view) of a diamond crystal and a metal (steel) base of the tool before (a) and after (b) the process of their heating (sintering) in a vacuum furnace.

Implementation of the invention

The implementation of the invention, characterized by the above set of essential features, is confirmed by an example of the implementation of the method, which is a description of the process of fixing a diamond on a metal holder in the manufacture of a tool - "diamond in a frame" used to dress grinding wheels with complex - shaped profiles (Fig. 1).

As a rule, for the manufacture of a tool, a diamond crystal is pre-selected (sorted) according to its shape and quality. Usually, they take, for example, as in our case, a diamond crystal in the form of an octahedron, which has natural sharp defect-free vertices and edges. To effectively use a high-quality diamond crystal, instead of not reinstalling the diamond crystal when one of its vertices is worn out during operation, an octahedron-shaped diamond crystal is cut to obtain two diamonds from it, each of which has the shape of a pyramid, the tops of which will be serve as working parts of two tools. If necessary, the surface of the diamond opposite to its working tip is subjected to additional processing - regrinding on a polishing machine with a disc charmed with diamond micropowder in order to obtain a flat surface - a base that would be in close contact with a flat depression of the metal tool holder.

The metal base-tool holder 1 is made of low-carbon steel with a carbon content of not more than 0.1% wt. (Fig. 1). A diamond crystal 3 is placed on its depression 2 with a flat bottom. On the top of the diamond crystal 3, in our case having a base with dimensions of ~ 3.75 × 3.10 mm, a mechanical force is applied using a weight 4 with a mass of 200 grams. With a mass of 4 with a mass of 200 grams, the pressure exerted by the flat base of the diamond on the surface of the recess 2 of the holder 1 will be ~ 168.60 kPa. The load 4 is held by a special device (it is not shown in Fig. 1). The heating of contact samples of a diamond crystal - a metal holder is carried out in a vacuum furnace with a residual pressure at a maximum temperature of not more than 4.0-7.0⋅10 ^-4 mm Hg. During heating in the temperature range 1147-1165 ° C at the diamond-metal contact boundary, a melt is formed - a liquid phase of the Fe-C eutectic alloy.

Under the influence of the mechanical load exerted by the load 4, a part of the eutectic melt 5 is squeezed out from under the base of the diamond crystal 3 and flows down into the depression 2. In this case, some of the melt remains under the base of the diamond crystal 3, and the diamond crystal 3 itself shifts somewhat vertically downward by an amount h from its original position (Fig. 1 b), raising the level of the melt in the depression 2 of the metal holder 1. During the cooling process, a part of the eutectic melt remaining under the diamond crystal, solidifying, forms an intermediate layer, firmly connecting the diamond crystal 3 with steel holder 1. In this case, the extruded part of the eutectic melt, solidifying, grabs the diamond crystal along the entire perimeter, providing its mechanical engagement with the metal holder.

Thus, the claimed method provides high reliability and durability of the diamond - metal holder connection in the manufacture of single-chip tools by providing two complementary adhesive mechanisms for their connection, which makes it possible to efficiently use high-quality diamond raw materials and eliminate or minimize the amount of scrap in the manufacture of diamond tools.

Used sources:

[1] - Basics of design and manufacturing technology of abrasive and diamond tools. " Edited by V.N. Bakul. - M .: Mechanical Engineering, 1975, p. 254-279.

[2] - RF Patent No. 2042478, IPC: В23В 51/00, priority 12/17/1992, publ. 27.08.1995

[3] - USSR author's certificate No. 275784, IPC: B24D 3/08, priority 12.04.1968, publ. 07/03/1970

Claims (1)

A method of joining a diamond single crystal with a metal tool holder, including the arrangement of a diamond single crystal on the horizontal surface of a flat recess on the original metal tool holder, ensuring direct contact of the said surfaces, heating them in vacuum to form a liquid alloy of the eutectic metal-carbon composition, holding at this temperature and subsequent cooling, characterized in that the metal tool holder is made of steel with a carbon content of not more than 0.1% wt., a single crystal of diamond from the side opposite to one of its vertices, selected as a working one, is preliminarily given a flat shape, and during heating a mechanical force is applied to the working vertex of the single crystal to ensure the value of the pressure exerted by the flat base of the diamond on the surface of the recess of the metal holder, which is 100-300 kPa, while heating is carried out to a temperature of 1165 ° C and t at this temperature for 10-15 minutes.

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