Abstract:
A process for coating articles is provided. The coated article includes a substrate, abase layer formed on the substrate; a chromium oxynitride layer formed on the base layer; and a silicon nitrogen layer formed on the chromium oxynitride layer. The chromium oxynitride layer and silicon nitride layer protect the substrate from oxidizing at high temperatures, extending the life of the coated article. A method for making the coated article is also described.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a process for coating an article and a method for making the coated article. 
     2. Description of Related Art 
     Die steel is widely used in forging, stamping, cutting, die-casting and other tool-making processes. The die steel is usually required to be oxidation-resistant at high temperatures. Typically, physical vapor deposition technology has been used to manufacture coatings which are oxidation-resistant. A coating of transition metal nitride and carbide is one of the most popular choices for the surface hardening material of the die steel due to its high hardness and good chemical stability. However, there are some defects, such as high brittleness, high residual stress and poor adhesion with the substrate. When the temperature of die steel is high, a coating of transition metal nitride and carbide may nevertheless be subject to oxidization. 
     Therefore, there is room for improvement within the art. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURE 
       Many aspects of the process for coating an article and the method for making the coated article can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the coated article and the method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment. 
         FIG. 1  is a cross-sectional view of an exemplary embodiment of a coated article; 
         FIG. 2  is a schematic view of a vacuum sputtering device used in the coating process to create the coated article in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a coated article  10  according to an exemplary embodiment. The coated article  10  includes a substrate  11 , a base layer  13  formed on the substrate  11 , a chromium oxynitride (CrON) layer  15  formed on the base layer  13  and a silicon nitride (SiN) layer  17  formed on the CrON layer  15 . 
     The substrate  11  may be made of stainless steel or die steel. 
     The base layer  13  is a layer of chromium. An vacuum sputtering process may form the base layer  13 . The base layer  13  has a thickness of approximately 0.1 micrometers (0.1 μm) to 0.2 μm. 
     An vacuum sputtering process may be used to form the CrON layer  15 . The CrON layer  15  has a thickness of about 0.5 μm to 1.5 μm. The CrON layer  15  is composed of small nanocrystals with a very small gap between the crystals, thus the Cr—O—N layer  15  is dense enough to delay the penetration of outside oxygen through to the substrate  11 . 
     An vacuum sputtering process may be used to form the Si—N  17 . The silicon nitride layer  17  has high hardness and good wear resistance, thus effectively protecting the Cr—O—N layer  15 . The silicon nitride layer  17  has a thickness of about 0.5 μm to 1.0 μm. 
     The CrON layer  15  and silicon nitride layer  17  can protect the substrate  11  from oxidizing at high temperature, which effectively prolongs the service life of the coated article  10 . 
       FIG. 2  shows a vacuum sputtering device  20 , which includes a vacuum chamber  21  and a vacuum pump  30  connected to the vacuum chamber  21 . The vacuum pump  30  is used for evacuating the vacuum chamber  21 . The vacuum chamber  21  has a number of chromium targets  23 , a number of silicon targets  24  and a rotary rack (not shown) positioned therein. The rotary rack is rotated as it holds the substrate  11  (circular path  25 ), and the substrate  11  revolves on its own axis while it is moved along the circular path  25 . 
     A method for making the coated article  10  may include the following steps: 
     The substrate  11  is pretreated, the pre-treating process may include the following steps: 
     The substrate  11  is positioned in an ultrasonic cleaning device (not shown) which is filled with ethanol. 
     The substrate  11  is plasma cleaned. The substrate  11  is positioned in the rotary rack of the vacuum chamber  21 . The air in the vacuum chamber  21  is evacuated to about 3.0×10 −5  Pa. Argon (Ar) gas, having a purity of about 99.999%) is used as sputtering gas and is fed into the vacuum chamber  21  at a flow rate of about 500 standard-state cubic centimeters per minute (sccm). A negative bias voltage in a range of about −200 volts (V) to −500 V may be applied to the substrate  11 , and high-frequency voltage is introduced in the vacuum chamber  21  and the Ar gas is ionized into plasma. The plasma strikes the surface of the substrate  11  to clean the surface of the substrate  11 . The plasma cleaning of the substrate  11  may take between 3 and 10 minutes. The plasma cleaning process will enhance the bonding between the substrate  11  and the base layer  13 . 
     The base layer  13  is vacuum sputtered onto the pretreated substrate  11 . The vacuum sputtering of the base layer  13  is implemented in the vacuum chamber  21 . The vacuum chamber  21  is evacuated to about 8.0×10 −3  Pa and heated to between about 100° C. and 150° C. Ar gas is used as the sputtering gas and is fed into the vacuum chamber  21  at flow rates of about 150 sccm to 200 sccm. The chromium targets  23  are subjected to between about 8 kw and 10 kw of electrical power. A negative bias voltage between about −150V and −250V is applied to the substrate  11  and the duty cycle is about 50%. The depositing of the base layer  13  may take about 5 to 10 minutes. The base layer  13  has a thickness of about 0.1 μm to 0.2 μm. 
     The CrON layer  15  is vacuum sputtered onto the base layer  13 . The vacuum sputtering of the CrON layer  15  is implemented in the vacuum chamber  21 . Oxygen (O 2 ) and nitrogen (N 2 ) are used as reaction gases and these are fed into the vacuum chamber  21  at flow rates of about between 40 sccm and 80 sccm and about 30 sccm and 60 sccm, respectively, otherwise the conditions are the same as for the vacuum sputtering of the base layer  13 . The depositing of the CrON layer  15  takes between about 30 min and 60 min. The CrON layer  15  is formed by a magnetron sputtering process and has a thickness of about 0.5 μm to 1.5 μm. 
     The silicon nitride layer  17  is vacuum sputtered onto the CrON layer  15 . The vacuum sputtering of the silicon nitride layer  17  is implemented in the vacuum chamber  21 . Nitrogen is the reaction gas and is fed into the vacuum chamber  21  at flow rates of about 60 sccm to 120 sccm, and Ar gas is used as the sputtering gas, being fed into the vacuum chamber  21  at flow rates of about 150 sccm to 200 sccm. The silicon targets are subject to from about 4 kw to 6 kw of electrical power. And the duty cycle is about 50%. A negative bias voltage of about −30 V to −50 V is applied to the substrate  11 . The depositing of the silicon nitride layer  17  may takes about 1 hour to 2 hours. The silicon nitride layer  17  has a thickness of about 0.5 μm to 1.0 μm. 
     EXAMPLES 
     Some experimental examples of the present disclosure are described as follows. 
     Example 1 
     The vacuum sputtering device  20  in example 1 is a medium frequency magnetron sputtering device (model No. SM-1100H) manufactured by South Innovative Vacuum Technology Co., Ltd. 
     The substrate  11  is made of 316 stainless steel. 
     Plasma cleaning: Ar gas is fed into the vacuum chamber  21  at a flow rate of about 500 sccm. A negative bias voltage of about −500 V is applied to the substrate  11 . The plasma cleaning of the substrate  11  took 10 min. 
     Sputtering to form the base layer  13 : The vacuum chamber  21  is heated to about 120° C. Ar gas is fed into the vacuum chamber  21  at a flow rate of about 150 sccm. The chromium targets  23  are subjected to about 9 kw of electrical power and a negative bias voltage of about −200 V is applied to the substrate  11 . The depositing of the base layer  13  took about 5 min. The base layer  13  had a thickness of about 0.1 μm. 
     Sputtering to form the CrON layer  15 : Oxygen and nitrogen are fed into the vacuum chamber  21  at flow rates of about 80 sccm and 60 sccm, respectively; otherwise conditions are the same as for the vacuum sputtering of the base layer  13 . The depositing of the CrON layer  15  took about 30 min. The CrON layer  15  had a thickness of about 0.5 μm. 
     Sputtering of the silicon nitride layer  17 : Ar gas and nitrogen are fed into the vacuum chamber  21  at flow rates of about 150 sccm and 120 sccm, respectively. The silicon targets  24  are subjected to 4 kw of electrical power and a negative bias voltage of about −50 V is applied to the substrate  11 . The depositing of the silicon nitride layer  17  took about 60 min. The silicon nitride layer  17  had a thickness of about 0.5 μm. 
     Example 2 
     The vacuum sputtering device  20  used in example 2 is the same in example 1. 
     The substrate  11  is made of  316  stainless steel. 
     Plasma cleaning: Ar gas is fed into the vacuum chamber  21  at a flow rate of about 500 sccm. A negative bias voltage of about −500 V was applied to the substrate  11 . The plasma cleaning of the substrate  11  took about 10 min. 
     Sputtering to form the base layer  13 : The vacuum chamber  21  is heated to about 120° C. Ar gas is fed into the vacuum chamber  21  at a flow rate of about 150 sccm. The chromium targets  23  are subjected to about 8 kw of electrical power. A negative bias voltage of about −200 V was applied to the substrate  11 . The depositing of the base layer  13  took about 10 min. The base layer  13  had a thickness of about 0.2 μm. 
     Sputtering of the CrON layer  15 : Oxygen and nitrogen are fed into the vacuum chamber  21  at flow rates of about 40 sccm and 30 sccm, respectively; other experiment conditions is the same with vacuum sputtering of the base layer  13 . The depositing of the CrON layer  15  took about 60 min. The CrON layer  15  had a thickness of about 1.0 μm. 
     Sputtering to form the silicon nitride layer  17 : Ar gas and nitrogen are fed into the vacuum chamber  21  at flow rates of about 150 sccm and 80 sccm, respectively. The silicon targets are subjected to about 5 kw of electrical power and a negative bias voltage of about −50 V was applied to the substrate  11 . The depositing of the silicon nitride layer  17  took about 90 min. The silicon nitride layer  17  had a thickness of about 0.8 μm. 
     Results of the Above Examples 
     The coated articles  10  made in examples 1 and 2 were subjected to a high-temperature oxidation test and an abrasion test. 
     High-temperature oxidation test: a tube furnace applied a heating rate was 10° C./min, heating temperature was about 800° C., the holding time was about 10 h. The coated articles  10  made in example 1 and 2 both displayed no oxidation and no peeling. 
     Abrasion test: a linear wear tester applied a load of about 1 kg, the stroke length was 2.0 inch, the wear rate was 25 times/min. The coated articles  10  made in example 1 and 2 both showed no peeling after 1 min. 
     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.