BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of metal alloys used for various types of housings. More specifically, the invention relates to compositions of binder material used to bind metallic powders into solid housings or bodies for such purposes as petroleum wellbore drilling bits.
2. Description of the Related Art
Petroleum wellbore drilling bits include various types that contain natural or synthetic diamonds, polycrystalline diamond compact (PDC) inserts, or combinations of these elements to drill through earth formations. The diamonds and/or PDC inserts are bonded to a bit housing or “body”. The bit body is typically formed from powdered tungsten carbide (“matrix”) which is bonded into a solid form by fusing a binder alloy with the tungsten carbide. The binder alloy is typically in the form of cubes, but it can also be in powdered form. To form the body, the powdered tungsten carbide is placed in a mold of suitable shape. The binder alloy, if provided in cube form is typically placed on top of the tungsten carbide. The binder alloy and tungsten carbide are then heated in a furnace to a flow or infiltration temperature of the binder alloy so that the binder alloy can bond to the grains of tungsten carbide. Infiltration occurs when the molten binder alloy flows through the spaces between the tungsten carbide grains by means of capillary action. When cooled, the tungsten carbide matrix and the binder alloy form a hard, durable, strong framework to which diamonds and/or PDC inserts are bonded or otherwise attached. Lack of complete infiltration will result in a defective bit body. Typically, natural or synthetic diamonds are inserted into the mold prior to heating the matrix/binder mixture, while PDC inserts can be brazed to the finished bit body.
The chemical compositions of the matrix and binder alloy are selected to optimize a number of different properties of the finished bit body. These properties include transverse rupture strength (TRS), toughness (resistance to impact-type fracture), wear resistance (including resistance to erosion from rapidly flowing drilling fluid and abrasion from rock formations), steel bond strength between the matrix and steel reinforcing elements, and strength of the bond (braze strength) between the finished body material and the diamonds and/or inserts.
One particular property of the binder alloy which is of substantial importance is its flow or infiltration temperature, that is, the temperature at which molten binder alloy will flow around all the matrix grains and attach to the matrix grains. The flow temperature is particularly important to the manufacture of diamond bits, in which case the diamonds are inserted into the mold prior to heating. The chemical stability of the diamonds is inversely related to the product of the duration of heating of the diamonds and the temperature to which the diamonds are heated as the bit body is formed. Generally speaking, all other properties of the bit body being equal, it is desirable to heat the mixture to the lowest possible temperature for the shortest possible time to minimize thermal degradation of the diamonds. While binder alloys which have low flow temperature are known in the art, these binder alloys typically do not provide the finished bit body with acceptable properties.
Many different binder alloys are known in the art. The mixtures most commonly used for commercial purposes, including diamond drill bit making, are described in a publication entitled, Matrix Powders for Diamond Tools, Kennametal Inc., Latrobe, Pa. (1989). A more commonly used binder alloy has a composition by weight of about 52 percent copper, 15 percent nickel, 23 percent manganese, and 9 percent zinc. This alloy has a melting temperature of about 1800 degrees F (968 degrees C) and a flow (infiltration) temperature of about 2150 degrees F (1162 degrees C). Other prior art alloys use combinations of copper, nickel and zinc, or copper, nickel and up to about 1 percent tin by weight.
Tin is known in the art to reduce the melting and flowing temperature of the binder alloy. However, it was believed by those skilled in the art that tin concentrations exceeding about 1 percent by weight in the binder alloy would adversely affect the other properties of the finished bit body material, particularly the toughness, although transverse rupture strength and braze strength can also be adversely affected.
It is desirable to have a binder alloy having as low as possible a flowing temperature consistent with maintaining the toughness, transverse rupture strength and braze strength of the finished body material.
SUMMARY OF THE INVENTION
One aspect of the invention is a matrix material used, for example, in drill bit bodies. The matrix material includes powdered tungsten carbide, and binder alloy consisting of a composition by weight of manganese in a range of about zero to 25 percent, nickel in a range of about zero to 15 percent, zinc in a range of about 3 to 20 percent, tin in a range of more than 1 percent to about 10 percent, and copper making up the remainder by weight of the alloy composition. In one embodiment, the alloy includes about 6 to 7 percent tin by weight.
Another aspect of the invention is a method for forming drill bit bodies. The method includes inserting into a mold a mixture including powdered tungsten carbide and a binder alloy consisting of a composition, by weight, of manganese in a range of about zero to 25 percent, nickel in a range of about zero to 15 percent, zinc in a range of about 3 to 20 percent, tin in a range of more than 1 percent to about 10 percent, and copper making up the remainder by weight of the alloy. The matrix material is heated to the flow temperature of the binder alloy to infiltrate through the powdered tungsten carbide. In one embodiment, the binder alloy includes about 6 to 7 percent tin by weight.
Other compositions of binder alloy according to the invention can have, by weight, nickel in the range of about zero to 15 percent; manganese in the range of about zero to 25 percent; zinc in the range of about 3 to 20 percent, and tin more than 1 percent up to about 10 percent. The remainder of any such composition is copper. The preferred amount of tin in the binder alloy is about 6 to 7 percent. Although nickel and manganese can be excluded from the binder alloy entirely, is should be noted that nickel helps the mixture “wet” the tungsten carbide grains, and increases the strength of the finished bit body. Manganese, when included in the recommended weight fraction range of the binder alloy composition, also helps lower the melting temperature of the binder alloy. While it is known that tin will lower the melting and flowing temperature of the binder alloy, too much tin in the binder alloy will result in the finished body 11 having too low a toughness, that is, it will be brittle. Including tin in the recommended weight fraction in the binder alloy composition results in a substantial decrease in the infiltration temperature of the binder alloy, as well as improved wettability of the binder alloy, particularly of the diamonds. The other properties of the finished bit body material will be maintained with commercially acceptable limits, however.