Method of bonding by use of a phosphorus containing coating

A method of bonding a cemented carbide surface to a metal surface is provided. The method involves applying an alloy layer to one or both of the surfaces, the alloy comprising a major amount of nickel or copper and a minor amount of phosphorus, heat treating the alloy layer below its liquidus temperature to cause it to diffusion bond to the surface top to which it is applied and bonding the surfaces together by means of a solder or braze alloy which preferably has a liquidus of no more than 750.degree. C. The method has particular application to bonding cutting inserts to drill bits and cutting tools for mining machines.

BACKGROUND OF THE INVENTION 
This invention relates to a bonding method and more particularly a method 
of bonding a cemented carbide surface to a metal surface. 
Abrasive compacts are well known in the art and are used extensively in 
industry for the abrading of various workpieces. They consist essentially 
of a mass of abrasive particles present in an amount of at least 70 
percent, preferably 80 to 90 percent, by volume of the compact bonded into 
a hard conglomerate. Compacts are polycrystalline masses having some 
direct particle-to-particle bonding. The abrasive particles of compacts 
are invariably superhard abrasives such as diamond and cubic boron 
nitride. Abrasive compacts are made under conditions of temperature and 
pressure at which the abrasive particle is crystallographically stable. 
Abrasive compacts may be provided in a variety of forms such as circular 
discs, or segments thereof or fragments of other shapes. 
Abrasive compacts may be bonded directly to a tool or shank for use. 
Alternatively, they may be bonded to a backing such as a cemented carbide 
backing which itself is bonded to the tool or shank. Abrasive compacts 
bonded to a cemented carbide backing are known in the art as "composite 
abrasive compacts". 
Examples of abrasive compacts and composite abrasive compacts can be found 
in many patent specifications, for example British Patent Specification 
Nos. 1,489,130; 1,456,765 and 2,048,927 and U.S. Pat. Nos. 3,745,623; 
3,743,489 and 4,224,380. 
Composite abrasive compacts are used as cutting inserts for a variety of 
tools such as drill bits and mining picks. In many of these applications, 
it is necessary to bond the carbide backing firmly to the tool. 
In other applications, the composite abrasive compact is bonded to a 
cemented carbide pin which is then located in a recess in the working 
surface of a drill bit and bonded thereto. One method which has been 
proposed for bonding the composite abrasive compact to the cemented 
carbide pin is described in European Patent Publication No. 0 090 657. 
This patent publication describes the bonding of the composite abrasive 
compact to a metal-containing substrate through a bonding layer comprising 
nickel, copper, cobalt, iron or an alloy containing one or more of these 
metals, bonding being achieved by means of solid state diffusion bonding. 
The metal-containing substrate is generally a cemented carbide substrate. 
It is to be noted that no working examples are provided of bonding a 
carbide surface to a metal surface. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a method of bonding a 
cemented carbide surface to a metal surface including the steps of 
applying an alloy layer to one or both of the surfaces, the alloy 
comprising a major amount of nickel or copper and a minor amount of 
phosphorus, heat treating the alloy layer below its liquidus temperature 
to cause it to diffusion bond to the surface to which it is applied and 
bonding the surfaces together by means of a braze alloy. It has been found 
that the heat treatment causes the alloy layer to diffuse substantially 
into the surface to which it is applied. 
DETAILED DESCRIPTION OF THE INVENTION 
It has been found that the method of the invention produces a strong and 
effective bond between the cemented carbide surface and the metal surface. 
This is particularly so when the metal surface is a steel surface. It is 
preferred, particularly when the metal surface is a steel surface, that 
the alloy layer is applied only to the metal surface. The alloy on the 
heat treatment diffuses substantially into the surface to which it is 
applied. The thus treated surface, it has been found, bonds readily to the 
braze alloy. 
The method of the invention has particular application to the bonding of 
composite abrasive compacts to metal surfaces, particularly steel 
surfaces. In such cases, it will be a carbide surface of the carbide 
support which will be bonded to the metal surface. 
The metal surface may be provided by the working surface of a tool such as 
a drill bit or a cutting tool for a mining machine. Such cutting tools are 
described, for example, in U.S. Pat. No. 3,342,532. The composite abrasive 
compact may be located in a recess in the working surface and then bonded 
to that surface using the method of the invention. 
One preferred alloy contains a major amount of nickel and 5 to 15 percent 
by weight of phosphorus. Generally this alloy will contain only the 
phosphorus and the nickel, with only trace amounts of other elements being 
present. 
Another preferred alloy of the invention contains a major amount of copper 
and 3 to 10 percent by weight of phosphorus. The alloy will generally 
contain only the phosphorus and the copper, with only trace amounts of 
other elements being present. The alloy layer will be a thin layer and 
will generally not exceed 50 microns in thickness. 
The heat treatment of the alloy layer is such as to cause it to diffusion 
bond to the surface to which it is applied. The heat treatment is 
preferably carried out at a temperature of 500.degree. to 1200.degree. C. 
for a period of 5 to 300 minutes. Preferably the heat treatment is carried 
out at a temperature within this range and for a period of 5 to 60 
minutes. The heat treatment will generally take place in a vacuum, or a 
reducing or inert atmosphere. 
The alloy is preferably formed on the surface by electrolessly or 
electrolytically plating nickel or copper thereon. In such a process the 
phosphorus reports in the nickel or copper coating thereby producing the 
alloy in situ. 
Once the surface or surfaces have had the alloy layer diffusion bonded 
thereto, the surfaces are bonded together by means of a braze alloy. 
Examples of such braze alloys are those having a liquidus of no more than 
750.degree. C. and include soft solders having a liquidus in the range 
140.degree. to 400.degree. C. such as those sold under the trade name 
Degussa Soldamol 280 and copper/tin/silver alloys. It is to be understood 
that in the specification, the term "braze alloy" includes soft solders. 
These low melting braze alloys generally do not to have the strengths of 
higher melting alloys. Surprisingly and notwithstanding this, it has been 
found that excellent bond strengths are achieved between the two surfaces. 
The braze alloys may also have liquidus temperatures above 750.degree. C. 
The surfaces may be bonded together by heating the braze alloy to its 
liquidus temperature by known means such as a braze torch or induction 
heating.

The invention will now be illustrated by means of the following examples. 
EXAMPLE I 
A steel drill bit had a plurality of shallow recesses formed in the working 
surface thereof. This bit had a nickel coating of the order of 20 microns 
in thickness electrolessly applied to it. The nickel coating formed a 
uniform coating over the surface of the drill bit. Incorporated in the 
nickel was about 8 weight percent of phosphorus. The coating was thus a 
nickel/phosphorus alloy. 
The alloy coated drill bit was heat treated at a temperature of 930.degree. 
C. for a period of one hour in an atmosphere of argon. 
A plurality of composite diamond abrasive compacts each consisting of a 
diamond compact bonded to a cemented carbide support were manufactured 
using known techniques. Each composite compact was located in the working 
surface such that its carbide backing was accommodated in a recess. 
Provided between the carbide backing of each compact and the steel surface 
of the drill bit was the braze alloy Degussa 5009 having a liquidus 
temperature of 660.degree. C. The drill crown was subjected to induction 
heating at a temperature slightly in excess of 660.degree. C. causing the 
braze alloy to melt and bond to each surface. An excellent bond was 
achieved between the carbide supports and the steel surface of the drill 
bit and one which was stronger than could be achieved using the braze 
alloy alone. 
EXAMPLE II 
The procedure set out in Example I was followed except in this case a 
carbide insert was bonded to the steel working surface of a cutting tool 
(or pick) for a mining machine. A nickel/phosphorus alloy was applied 
electrolessly to the working end of the pick and heat treated in the 
manner set out in Example I. The carbide insert was then bonded to the 
pick using the Degussa 4003 braze alloy. Again, an excellent bond between 
the carbide tip and the steel surface of the cutting tool was obtained. 
EXAMPLE III 
A tungsten carbide cutting insert had a nickel/phosphorus alloy 
electrolessly applied to it in the manner set out in Example I. The coated 
insert was then heat treated in the manner set out in Example I. This 
insert was bonded to the steel surface of a cutting tool, also treated 
with a nickel/phosphorus alloy as set out in Example I, using a 
lead/tin/zinc soft solder having a liquidus of about 280.degree. C. This 
soft solder generally produces a fairly weak bond. However, it was 
surprisingly found that a strong bond was achieved between the tungsten 
carbide insert and the steel surface of the cutting tool.