Field of Invention
Electroless Nickel plating of titanium has diversified applications in aircraft industry.
Protection of hydraulic control systems in aerospace industry where resistance to wear
is of paramount importance.
Background of the invention
Present invention is about nickel coating onto the titanium substrate by simple dipping
of the cleaned titanium test sample in the already prepared nickel plating solution.
Titanium alloys are used in aircraft industry due to its light weight high strength and
excellent corrosion resistance. But wear resistance of titanium is very poor compare to
other alloys like steel, aluminium etc. Electroless nickel plating and post heatreatment _
of titanium is one the method to increase the wear resistance of the metal al|oy.But,
difficulties faced during nickel plating due to high hardness of the alloy, which leads to
improper adherence of nickel with thetitanium substrate which results in peel up off the
metal coating from the underneath substrate. The present invention provides a method
which enables a very high quality deposit and superb adherent deposit of nickel coating
onto the substrate of titanium alloy.
Summary of the invention
The present invention provides a method for depositing nickel metal layer onto the
_ titanium substrate without current. The method provides an adherent deposit that does
not peel off or during mechanical testing i.e lapping operation. The method requires the
use of simple conventional plating baths or glass beakers for small size components. .
Object of the invention _
To improve the wear resistance of titanium alloys by electroless nickel coating onto
titanium alloy substrate. The present invention fulfills this need, and further provides
related advantages.
;.....;.
Detailed description of the invention
Example-1
Present invention provides a process for depositing an electroless nickel coating onto
titanium alloys (composition: Ti—base, Al:2-5%, Mn:O.8—2%,C:O.1%). However, the
invention is not limited to such coatings and substrates. As used herein, the term
"titanium" means pure titanium and also its alloys. _
A sample substrate of a titanium alloy was taken for plating. in accordance with the
invention. Electroless nickel plating of titanium comprises different steps: First, organic
cleaning of the test sample with naptha or acetone followed bychemical degreasing in a
bath composition of sodium silicate:10—20g/l, sodium carbonate:20—25g/I, trisodium
phosphate: 30-70 g/l, caustic soda:5—15g/l. The sample was then dry sand blasted using
fine corundum sand (of size 125um, appx) at a pressure of 3-4kg/cm2.Pickling of the
test sample was carried out next in a solution of hydrofluoric acid (25—30ml/ltr, 40%
purity) and hydrochloric acid (40—50ml/ltr) for one minute. Activating the surface of test
sample then, in a mixture of mixture of sulphuric acid (250ml) and hydrochloric acid
(750ml) for about 60—90minutes. After completion of activation of the titanium piece, the
same is removed from the activation solution and rinsed in cold water thoroughly.
Electroless nickel plating is then carried over the test sample by placing the piece into
an aqueous mixture of nickel sulphate,NiSO4(20g/l),sodium acetate HCOONa(10g/I),
and sodium hypophophite,NaH2PO2(10g/I) at a temperature of 85°—90° C. Nickel is
deposited atthe rate of about 10-15pm per hour by this method. The mixture of the
three chemicals prepared in beaker (pot) for one time use only. For achieving higher
thickness the more no of pots may be required accordingly. After electroless plating is
completed, the piece is rinsed in cold water thoroughly. To improve the adhesion of the
plating to the titanium piece, the composite is heat treated in a conventional air cooling
furnace at a temperature 300—350°C for about 30—60minutes.Three test samples after
plating and heat treatment are tested. The test samples were repeatedly bent through
180 degrees in an attempt to debond the electroless nickel plate, but the plate remained
well bonded and could not be removed even after repeated bending. The bond line was
inspected at 20X magnification, and no debonding was found.
-fl'gi"V’li
We claim:
1. Process of electroless nickel plating onto a titanium substrate, consists of following
steps :
Cleaning of piece of titanium;
Dry sand blasting of titanium piece with corundum sand,
Pickling of the test sample in a mixture of hydrochloric acid (HCI) 25—30ml/lit and .
Hydrofluoric acid (HF) 40—50m|/lit for one minute,
Activation of the titanium piece in mixture of hydrochloric acid (HCI) 750ml and
Sulphuric acid (H2804) 250ml for 60-90 minutes,
Electroless nickel plating of the piece of titanium piece in a mixture of nickel
sulphate, sodium acetate, and sodium hypophosphite at a temperature of
85 -90°C and heat treatment of nickel plated titanium;
. The method according to claim 1, heat treatment of the titanium alloy piece is carried
out at 300—350°C for 30-60minutes after nickel plating/.
3. The method according to claim 1,hardness of titanium sample after heat treatment
achieved hardness value about 1000VPN,
10—15pm per hour,
. The method according to claim 1, rate of ‘deposit of nickel on to titanium alloy piece is
5. The method according to claim 1, concentration chemicals for electroless nickel
plating of titanium sample piece is:
Nickel sulphate,NiSO4 ; 20g/I
Sodium acetate HCOONa:10g/l, and’
Sodium hypophosphite, NaH2PO2; 10g/l,
pH value: 4.5,( temperature: 85 -90°C)