Coated article and method for making the same

A coated article includes a substrate, a bonding layer formed on the substrate, an anti-corrosion layer formed on the bonding layer. The substrate is made of aluminum or aluminum alloy. The bonding layer is a silicon layer. The anti-corrosion layer is a silicon nitride layer. The coated article has improved corrosion resistance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is one of the eleven related co-pending U.S. patent applications listed below. All listed applications have the same assignee. The disclosure of each of the listed applications is incorporated by reference into all the other listed applications.

BACKGROUND

1. Technical Field

The present disclosure relates to coated articles and a method for making the coated articles.

2. Description of Related Art

Physical vapor deposition (PVD) is an environmentally friendly coating technology. Coating metal substrates using PVD is widely applied in various industrial fields.

The standard electrode potential of aluminum or aluminum alloy is very low. Thus the aluminum or aluminum alloy substrates may often suffer galvanic corrosions. When the aluminum or aluminum alloy substrate is coated using PVD with a decorative layer such as a titanium nitride (TiN) or chromium nitride (CrN) layer, the potential difference between the decorative layer and the substrate is high and the decorative layer made by PVD will often have small openings such as pinholes and cracks, which can accelerate the galvanic corrosion of the substrate.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION

FIG. 1shows a coated article10according to an exemplary embodiment. The coated article10includes a substrate11, a bonding layer13formed on the substrate11, an anti-corrosion layer15formed on the bonding layer13and a decorative layer17formed on the anti-corrosion layer15. The coated article10may be used as a housing of a computer, communication device, or a consumer electronic device.

The substrate11is made of aluminum or aluminum alloy.

The bonding layer13is a silicon (Si) layer and has a thickness of about 0.1 μm to about 0.2 μm.

The anti-corrosion layer15is a silicon nitride (SiN) layer and has a thickness of about 0.5 μm to about 1.0 μm.

The decorative layer15may be colored according to choice. The decorative layer17may be a titanium nitride (TiN) or chromium nitride (CrN) layer. The decorative layer17has a thickness of about 1.0 μm to about 3.0 μm. A vacuum sputtering process may be used to form the bonding layer13, the anti-corrosion layer15and the decorative layer17.

FIG. 2shows a vacuum sputtering device20, which includes a vacuum chamber21and a vacuum pump30connected to the vacuum chamber21. The vacuum pump30is used for evacuating the vacuum chamber21. The vacuum chamber21has silicon targets23, titanium or chromium targets24and a rotary rack (not shown) positioned therein. The rotary rack holding the substrate11revolves along a circular path25, and the substrate11is also rotated about its own axis while being carried by the rotary rack.

A method for making the coated article10may include the following steps:

The substrate11is pretreated. The pre-treating process may include the following steps: electrolytic polishing the substrate11; wiping the surface of the substrate11with deionized water and alcohol; ultrasonically cleaning the substrate11with acetone solution in an ultrasonic cleaner (not shown), to remove impurities such as grease or dirt from the substrate11. Then, the substrate11is dried.

The substrate11is positioned in the rotary rack of the vacuum chamber21to be plasma cleaned. The vacuum chamber21is then evacuated to about 1.0×10−3Pa. Argon gas (abbreviated as Ar, having a purity of about 99.999%) is used as the sputtering gas and is fed into the vacuum chamber21at a flow rate of about 250 standard-state cubic centimeters per minute (sccm) to about 500 sccm. A negative bias voltage in a range from about −300 volts (V) to about −800 V is applied to the substrate11. The plasma then strikes the surface of the substrate11to clean the surface of the substrate11. The plasma cleaning of the substrate11takes from about 3 minutes (min) to about 10 min. The plasma cleaning process enhances the bond between the substrate11and the bonding layer13.

The bonding layer13is vacuum sputtered on the plasma cleaned substrate11. Vacuum sputtering of the bonding layer13is carried out in the vacuum chamber21. The vacuum chamber21is heated to a temperature of about 100° C. to about 150° C. Ar is used as the sputtering gas and is fed into the vacuum chamber21at a flow rate of about 100 sccm to about 200 sccm. The silicon targets23are supplied with electrical power of about 2 kw to about 8 kw. A negative bias voltage of about −50 V to about −200 V is applied to the substrate11and the duty cycle is from about 30% to about 80%. Deposition of the aluminum layer131takes about 20 min to about 40 min

The anti-corrosion layer15is vacuum sputtered on the bonding layer13. Vacuum sputtering of the anti-corrosion layer15is carried out in the vacuum chamber21. Nitrogen (N2) is used as the reaction gas and is fed into the vacuum chamber21at a flow rate of about 50 sccm to about 100 sccm. The flow rate of Ar, temperature of the vacuum chamber21and the negative bias voltage are the same as vacuum sputtering of the bonding layer13. Deposition of the anti-corrosion layer15takes about 90 min to about 180 min.

The decorative layer17is vacuum sputtered on the anti-corrosion layer15. Vacuum sputtering of the decorative layer17is carried out in the vacuum chamber21. Nitrogen is used as the reaction gas and is fed into the vacuum chamber21at a flow rate of about 20 sccm to about 170 sccm. Silicon targets23are powered off and titanium or chromium targets24are supplied with electrical power of about 8 kw to about 10 kw. The flow rate of Ar, temperature of the vacuum chamber21and the negative bias voltage are the same as vacuum sputtering of the anti-corrosion layer15. Deposition of the decorative layer17takes about 20 min to about 30 min.

The bonding layer13can play an important role in combining the substrate11to the anti-corrosion layer15, thus the bond between the anti-corrosion layer15and the substrate11is more stable. The anti-corrosion layer15is composed of ceramic materials; the insulating properties of ceramic materials can slow down galvanic corrosion of the substrate11. Thus, the corrosion resistance of the coated article10is improved. The decorative layer17has stable properties and gives the coated article10a long lasting pleasing appearance.

It is believed that the exemplary embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its advantages, the examples hereinbefore described merely being preferred or exemplary embodiment of the disclosure.