US3439188A - Method for treating titanium - Google Patents

Description

United States Patent O U.S. Cl. 20437 3 Claims ABSTRACT OF THE DISCLOSURE A process for treating titanium to make it more Workable which comprises solvent cleaning the titanium workpiece, mechanically cleaning the workpiece to remove surface oxides and nitrides, copper plating with ultrasonic agitation, and heating to temperatures of 16501725 C., in a reducing atmosphere, followed by quenching the workpiece when it has cooled to ambient temperature.

This invention relates to a process for the treating of titanium and to a process for plating of copper on titanium.

Titanium has been found to possess high strength to weight ratio which particularly adapts titanium for use in various applications such as aircraft. One of the problems involved in the commercial use of titanium and its alloys is their tendency to gall and seize when in contact with metal parts. One manner of avoiding this problem might involve the plating of the titanium with copper. In the past, however, it has been difficult or impossible to place a a thick adherent coat of copper on titanium.

One object of the present invention is to provide an improved process for plating copper on titanium and its alloys.

A further object of the invention is to provide a process for plating copper on titanium and its alloys in such a manner that there is no blistering of the copper.

Another object of this invention is to provide a process for plating a relatively thick coating of copper on titanium and its alloys in such a manner that there is no blistering of the copper.

Still another object of the invention is to provide a process for plating a relatively thick coating of copper on titanium and its alloys in a relatively short period of time and in such a manner that there is no blistering of the copper.

An important object of the invention is to provide a process for surface hardening of titanium and its alloys.

Another object of the invention is to provide a process for improving the properties of titanium and its alloys.

Still another object of the invention is to provide a process for treating titanium and its alloys to produce a surface thereon which can be ground and yet retain good file hardness having a reduced coefficient of friction.

Related objects and advantages will appear as the description proceeds.

In accordance with the invention, these and other objects are attained by solvent cleaning a titanium workpiece to remove surface oils and contaminants, blasting the workpiece with a grit between 90 and 300, copper plating the workpiece in a bath by electrolysis with one ampere of current provided for each 10 to 100 square inches of surface being plated, agitating the electroplating bath during at least the initial portion of said plating by inducing ultrasonic vibration in the bath, and heating the workpiece to a temperature of between 1650 F. and 1725' F. for a period of at least minutes.

The invention is presented in more detail in the following examples:

3,439,188 Patented Apr. 15, 1969 EXAMPLE I A finished workpiece which is an alloy of titanium of the following approximate composition: 6 percent by weight aluminum, 4 percent by weight of vanadium and percent by weight of titanium, is chemically cleaned in a trichlorethylene degreaser apparatus. The workpiece is then sand blasted with aluminum oxide 150' grit to remove surface oxides, nitrides and other impurities and to thereby provide an active metal surface. The blasting operation is accomplished with a Vacu-blast cabinet although any suitable apparatus of this type may be used. The workpiece is then promptly submerged in an electroplating copper cyanide bath with the bath at a temperature of 120 F.:5. The copper cyanide bath consists of the following approximate ingredients: 4 oz. copper, 1 /2 02. sodium cyanide and 1 02. sodium hydroxide per gallon of water.

Plating of copper onto the titanium alloy is accomplished by providing approximately one ampere of current for each 40 square inches of surface to be plated. In conventional manner the current is controlled by the amount of voltage applied to the electrodes. Simultaneously with the electrolysis, the electrolyte is vigorously agitated by ultrasonic vibrations of sufficient amplitude to prevent the gas bubbles formed during the electrolysis from remaining on the titanium part. A suitable mechanism for this purpose is, for example, Model #T32001 manufactured by Ultrasonics Industries, Incorporated, Al-bertson, N.Y. It is particularly important that the bath or the titanium electrode be agitated. to remove these bubbles which otherwise cause blisters to form and that this agitation be accomplished during the initial portion of the plating. After the part is completely covered with copper plating is continued with or without ultrasonic agitation as described until over .001 inch of copper is plated onto the titanium alloy which requires. about two hours plating time.

EXAMPLE II This embodiment of the invention is identical to the above described embodiment with the exception that 90 grlt aluminum oxide was used in the blasting operation.

EXAMPLE III This embodiment of the invention is identical to the above described Example I with the exception that 300 grit aluminum oxide is used in the blasting operation.

EXAMPLE IV This example is identical to the above described Example I with the exception that the current provided for plating is one ampere for each square inches of plated surface. In this example plating required a longer period than two hours to produce the .001 thickness of plating.

EXAMPLE V This example is identical to Example I with the exception that one ampere of current is provided for each 10 square inches of plated surface. This procedure does not give as good adhesion of the copper to the titanium alloy workpiece as does Example I, and tends to blister when used to produce copper thicknesses in excess of .0005 inch.

EXAMPLE VI This form of the invention is identical to Example I except that a titanium alloy workpiece including 92 percent titanium, 4 percent aluminum, 3 percent molybdenum, 1 percent vanadium is used (all percentages being approximate by weight).

3 EXAMPLE vn This form of the invention is identical to Example I except that a workpiece consisting of commercially pure titanium is used.

Various other alternatives n Example I are also within the scope of the invention. Thus the procedure of Example I is usable to copper plate a semi-finished workpiece as well as a finished workpiece.

EXAMPLE VIII This example is identical to Example I but includes the following additional steps. The workpiece is heated to a temperature of approximately 1700 F. in a reducing (carburizing) atmosphere for a period of four hours and is then cooled in water, oil or air to room temperature. The surface of the workpiece is then in condition for grinding or polishing with a good file hardness of Rockwell C50 to 55 or its equivalent. The effect of the present treatment is to cause the copper to diffuse into the portion of the titanium adjacent the surface thereof and to form a hard alloy with some or all of the other metals present. In the present example a hard case having a depth of approximately .010 is produced.

FURTHER EXAMPLES As regards the thickness of the copper plating in Example VIII above, at least .001 inch is preferred so that the resulting case is sufficiently thick to permit grinding. If the plated thickness of the copper is less, the workpiece should be heated for a shorter period of time. This heating causes diffusion. Too long a period of heating produces too much diffusion with also the probability of surface cracking. Shorter periods of heating result in reduced case depth. If the plated copper has a thickness of only .0001 inch, then heating should be carried on for only minutes. Greater thickness of copper plate requires proportionately greater periods of heating. A maximum period of heating beyond which the process is not operable (i.e. produces cracking of the surface), is 10 hours.

The temperature of the heating is preferably between 1675 and 1700 F. with the outside practical limits being 1650 F. and 1725" F. No acceptable products have been produced outside of this latter temperature range. It should be mentioned that the speed of quenching has little effect on the case hardness. Quenching is accomplished primarily for handling and to provide certain properties in the titanium or titanium alloy core. The process of Example VIII can be carried out with any of Examples II, III, IV, V, VI or VII replacing the initial Example I beginning portion of Example VIII. Also some success has been obtained using prior art methods of plating copper on titanium and then using the subsequent heat treating step of Example VIII. One such prior art method might be in accord with the method described in Patent No. 2,801,213. In order to obtain consistently good results, however, it has been found necessary to use the plating procedures described in Examples I through VII inclusive.

From the above description it will be evident that the present invention provides an improved process for plating a relatively thick coating of copper on titanium and its alloys in a relatively short period of time and in such a manner that there is no blistering of the copper. It will also be evident that the present invention provides a process for treating titanium so as to produce a surface thereon which can be ground, if desired, and will retain good file hardness having a reduced coefficient of friction. It will be further evident that the present invention provides a process for treating titanium parts so as to produce a hard surface thereon thick enough to withstand considerable wear, and which will be file hard after several thousandths of surface have been removed by grinding, lapping or polishing, if so desired.

The invention claimed is:

1. A method of treating titanium workpieces and titanium alloy workpieces which comprises solvent cleaning the workpiece to remove surface oils and contaminants, mechanically cleaning the workpiece to remove surface oxides and other impurities by blasting with an aluminum oxide grit between grit and 300 grit, copper plating the workpiece in a copper cyanide bath by electrolysis with one ampere of current being provided for each 10 to square inches of surface being plated, and simultaneously vigorously agitating the bath by inducing ultrasonic vibration therein during at least the initial portion of said plating, heating the copper plated workpiece to a tempearture between 1650 and 1725 degrees Fahrenheit in a reducing atmosphere and maintaining said workpiece at such elevated temperature for between ten minutes and ten hours.

2. A method of treating titanium workpieces and titanium alloy workpieces which comprises chemically cleaning the workpiece to remove surface oils and contaminants, mechanically cleaning the workpiece to remove surface oxides and nitrides by blasting with an aluminum oxide grit between 90 grit and 300 grit, copper plating the workpiece in a copper cyanide bath by electrolysis with one ampere of current being provided for each 10 to 100 square inches of surface being plated, and simultaneously violently agitating the bath by inducing ultrasonic vibration therein during the initial portion of said plating, heating the copper plated workpiece to a temperature between 1650 and 1725 degrees Fahrenheit in a reducing atmosphere and maintaining said workpiece at such elevated temperature for between ten minutes and ten hours, and quenching the copper plated workpiece in water which is at ambient temperature.

3. A method of treating titanium workpieces and titanium alloy workpieces which comprises chemically cleaning the workpiece to remove surface oils and contaminants, mechanically cleaning the workpiece to remove surface oxides and other impurities "by blasting with an aluminum oxide grit, copper plating the workpiece in a copper cyanide bath by electrolysis with one ampere of current being provided for each 40* square inches of surface being plated, and simultaneously vigorously agitating the bath by inducing ultrasonic vibration therein during the initial portions of said plating, terminating said plating after approximately one hour with a plated thickness of over .001 inch, heating the workpiece to a temperature of approximately 1700 degrees Fahrenheit in a reducing atmosphere and maintaining said Workpiece at such elevated temperature for approximately four hours, and quenching the workpiece in water which is at room temperature.

References Cited UNITED STATES PATENTS 2,522,082 9/1950 Arnold 1848 2,835,630 5/1958 Huddle et al. 204--1.5 3,147,547 9/1964 Kuebrick et al. 29-528 OTHER REFERENCES Young et al.: article, Metal Industry, December 1938, pp. 560562, 204/521.

JOHN H. MACK, Primary Examiner.

W. B. VANSISE, Assistant Examiner.

US. Cl. X.R. 2o4 29, 52