Laser Electroplating of Nickel Phosphorus Tungsten Carbide

Tungsten carbide particles have a series of advantages, such as chemical stability, high hardness, almost comparable to the hardness of diamond, and extremely high wear resistance. The bonding strength between deposited tungsten carbide particles and Ni-P coatings will affect the performance of the composite coatings. Therefore, improving the bonding strength between coating and matrix and the bonding between deposited tungsten carbide particles and nickel phosphorus cells and avoiding the falling off of deposited particles become the key to ensure the effectiveness of composite coating.

Laser surface modification technology has the advantages of high power density, concentrated energy, fast heating speed, small heat-affected zone, small deformation and small thermal stress. Laser treatment can effectively change the bonding properties between coating and matrix or different phases, improve the bonding force, improve the compactness and uniformity of coating structure, and become an important means of surface modification. The laser plating process of Ni-P-W-C composite coating needs the following treatment:

1.Mechanical polishing of the alloy steel sample to make the surface smooth and bright, then ultrasonic cleaning with deionized water, then immersing the sample in the ultrasonic cleaner of acetone solution for 5 minutes, removing grease, rinsing and drying with deionized water, then acid washing with 15%-20% sulfuric acid solution and activation treatment for 3 minutes, and rinsing with deionized water;

2. Preparation of Electroless Plating Bath and Powder Composite Electroless Plating Bath
The composition ratio of electroless plating bath is expressed in g/L as follows: nickel sulfate 25, sodium hypophosphite 30, sodium acetate 30, ammonium sulfate 30, lead acetate 1.

The plating solution is used as the base plating solution for pre-plating and re-plating as well as for the preparation of powder composite electroless plating solution.

3.Composition ratio of powder composite electroless plating bath expressed by g/L is: nickel sulfate 25, sodium hypophosphite 30, sodium acetate 30, ammonium sulfate 30, lead acetate 1, sodium dodecylbenzene sulfonate 1, tungsten carbide powder 3, particle size less than 10 um.

4.Pre-plated nickel-phosphorus base
Take a certain amount of electroless plating solution in step (3), adjust the pH=7, and control the temperature at 70 C. Plating the sample after step (2) activation into the neutral plating solution immediately for 20-30 minutes, magnetic stirring, rotating speed 200 r/min, and obtain a certain thickness of nickel-phosphorus bottom layer.

5.Tungsten Carbide Powder Composite Electroless Plating
Amount of steps (3) powder composite electroless plating bath (h), temperature control at 70 ~85 C, pH control at 6 ~ 7, magnetic stirring, speed 200 r/min. Step (4) The pre-plated samples were immediately placed and plated for 60 minutes to obtain the composite coating of Ni-P-W-C powder.

6.double plating
The electroless plating solution obtained by a certain amount of steps (3) is used as the plating solution for the re-plating, adjusting the pH 6-7, temperature 70-85, magnetic stirring and rotating speed 200 r/min; the sample after the step (5) composite plating is taken out, cleaned with deionized water at 80 ~C, and immediately put into the re-plating solution for plating for 20-30 minutes.

7.Uniform nickel-phosphorus-tungsten carbide composite coating with metallic luster was obtained by removing the sample, cleaning and drying with deionized water. The thickness of the coating was 30-40 microns, and the surface hardness of the coating was 727 HV.

8.Pulse laser processing
The coating was treated by pulsed nanosecond laser with a wavelength of 1064 nm, a working frequency of 1-10 Hz, a beam spot diameter of 9 mm, a voltage of 500 V and an average hardness of 808 HV.

The amorphous coating can be maintained by rapid heating treatment with pulsed laser, and the hardness of the coating can be improved significantly. That is to say, the amorphous coating can be maintained while the hardness and wear resistance of the coating are improved, which is also beneficial to the corrosion resistance of the coating.

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