Patent Publication Number: US-2007116956-A1

Title: Mold having multilayer diamond-like carbon film

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is related to commonly-assigned co-pending applications (application Ser. No. 11/309,308) entitled, “ARTICLE WITH MULTILAYER DIAMOND-LIKE CARBON FILM”, filed on the 25th of July, 2006, and “ARTICLE WITH MULTILAYER DIAMOND-LIKE CARBON FILM”, filed ______ (Attorney. Docket No. US9307). Disclosures of the above identified applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD  
      The present invention generally relates to a diamond-like carbon film, and more particularly relates to a mold having a diamond-like carbon film with graduated composition and multilayered structure.  
     BACKGROUND  
      Diamond-like carbon film was first deposited by Aisenberg et al. and from then on a variety of different techniques for diamond-like carbon film deposition have been developed.  
      Diamond-like carbon is a mostly metastable amorphous material but can include a microcrystalline phase. Diamond-like carbon contains both sp 2  and sp 3  hybridised carbon atoms. Diamond-like carbon includes amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) with significant sp 3  bonding. The amorphous carbon where more than 85% of the carbon atoms form sp 3  bonds is called highly tetrahedral amorphous carbon (ta—C). The sp 3  bonding provides the diamond-like carbon film with valuable diamond-like properties such as mechanical hardness, low friction, optical transparency and chemical inertness. The diamond-like carbon film has some other advantages, such as being capable of deposition at room temperature, deposition onto a steel substrate, a plastic substrate, and superior surface smoothness.  
      Diamond-like carbon film can be used as a protective film of a mold because of excellent properties such as a corrosion resistance and a wear resistance. However, it is difficult for conventional diamond-like carbon film to adhere to the mold substrate because of residual stresses therein. Thus, the configuration leads to an unsatisfactory combination between the diamond-like carbon film and the mold substrate.  
      What is needed, therefore, is a mold having a diamond-like carbon film with good corrosion resistance, good wear resistance and high adhesion to the mold substrate.  
     SUMMARY  
      One preferred embodiment provides a mold including a main body, a doped diamond-like carbon composite film formed on the main body and an undoped diamond-like carbon film formed on the doped diamond-like carbon composite film. The doped diamond-like carbon composite film includes a number of doped diamond-like carbon layers stacked one on another. Each of the doped diamond-like carbon layers is composed of carbon, hydrogen and a filler component selected from a group consisting of metal, metal alloy and metal nitride. A content of the filler component in each doped diamond-like carbon layer gradually decreases with increasing distance away from the main body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      Many aspects of the embodiments can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of embodiments. Moreover, in the drawing, like reference numerals designate corresponding parts.  
       FIG. 1  is a schematic view of a mold having a doped diamond-like carbon composite film and an undoped diamond-like carbon film according to a preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Embodiments will now be described in detail below and with reference to the drawings.  
      Referring to  FIG. 1 , a mold  100  including a main body  10 , a doped diamond-like carbon composite film  20 , and an undoped diamond-like carbon film  30  according to a preferred embodiment is shown. The doped diamond-like carbon composite film  20  has a graduated composition and is formed on the main body  10 . The undoped diamond-like carbon film  30  is formed on the doped diamond-like carbon composite film  20 .  
      The main body  10  can be made of mirror-polished stainless steel. The surface roughness (Ra) of the main body  10  should be less than 10 nanometers. The main body  10  can be a material selected from a group consisting of ferrum-carbon-chromium (FeCCr) alloy, ferrum-carbon-chromium-molybdenum (FeCCrMo) alloy, ferrum-carbon-chromium-vanadium-molybdenum (FeCCrVMo) alloy, and ferrum-carbon-chromium-vanadium-silicon-molybdenum (FeCCrVSiMo) alloy.  
      The doped diamond-like carbon composite film  20  includes n number of layers, i.e., a first layer  11 , a second layer  12 , . . . , a (n−1)th layer  16 , and an nth layer  17  stacked one on top of the other in that order, wherein n is an integer preferably in a range from 5 to  30 . The first layer  11  is an innermost layer of the doped diamond-like carbon composite film  20  that is adapted to adhere to the main body  10 . The second layer  12  is formed on the first layer  11 . Similarly, the (n−1)th layer  16  is the second layer counting from the outer layer of the doped diamond-like carbon composite film  20 , and a nth layer  17  is formed on the (n−1)th layer  16 . Particularly advantageously, the doped diamond-like carbon composite film  20  is formed directly on a molding surface of the main body  10 , and each succeeding layer is directly formed on (i.e., in contact with) the layer preceding it in the series.  
      Each doped diamond-like carbon layer has a different composition. Each doped diamond-like carbon layer is composed of carbon, hydrogen and a filler component  50 . The filler component  50  can be metal, metal alloy or metal nitride. The filler component  50  can be selected from a group consisting of chromium, titanium, zinc, chromium-titanium alloy, chromium nitride, titanium nitride, zinc nitride and any combination thereof. The filler component  50  in each doped diamond-like carbon layer gradually decreases in content from the first layer  11  to the nth layer  17 . For example, if an mth layer is any one of the doped diamond-like carbon layers of the doped diamond-like carbon composite film  20 , a composition of the mth layer can be represented by a formula of a-C:H:(n−m+1)X, wherein m is an integer in a range from 1 to n, C represents a carbon component, H represents a hydrogen component, and X represents a filler component. Therefore the composition of each doped diamond-like carbon layer can be represented by a formula, for example, the first layer  11  can be represented by a-C:H:nX, the second layer  12  can be represented by a-C:H:(n−1)X, . . . , the (n−1)th layer  16  can be represented by a-C:H:2X, and the nth layer  17  can be represented by a-C:H:X.  
      An atomic percentage of the filler component  50  in each doped diamond-like carbon layer gradually decreases from the first layer  11  to the nth layer  17 . For example, the nth layer  17  in the doped diamond-like carbon composite film  20  has least atomic percentage of the filler component  50 . The atomic percentage of the filler component  50  in the nth layer  17  is represented by x n , wherein x n  is in a range from 0.2% to 1.0%. The atomic percentage of the filler component  50  in the mth layer is represented by x m , according to the formula of a-C:H:(n−m+1)X, the content of the filler component  50  in the mth layer is (n−m+1) times x n .  
      The filler component  50  can strengthen the diamond-like carbon layer, whilst the corrosion resistance and wear resistance of the diamond-like carbon layer are weakened. Therefore, the properties of each doped diamond-like carbon layer depend on the atomic percentage of the filler component  50  thereof. The first layer  11  in the doped diamond-like carbon composite film  20  has greatest atomic percentage of the filler component  50 , therefore having lowest corrosion resistance and wear resistance. The nth layer  17  in the doped diamond-like carbon composite film  20  has least atomic percentage of the filler component  50 , thereby having greatest corrosion resistance and wear resistance.  
      The first layer  11  is the innermost layer of the doped diamond-like carbon composite film  20  that is adapted to contact with the main body  10 . The main body  10  is composed of a metal, thus an increased content of the metal-containing filler component  50  in the first layer  11  of the doped diamond-like carbon composite film  20  facilitates an adhesion to the main body  10 . In other words, the doped diamond-like carbon composite film  20  adheres relatively easily to the main body  10 .  
      The content of the filler component  50  in each doped diamond-like carbon layer gradually decreases from the first layer  11  to the nth layer  17 , so that each doped diamond-like carbon layer can adhere to each other more tightly. The composition of the nth layer  17  of the doped diamond-like carbon composite film  20  is similar to the undoped diamond-like carbon film  30 , thus, the undoped diamond-like carbon film  30  can adhere to the doped diamond-like carbon composite film  20  tightly.  
      The doped diamond-like carbon composite film  20  may have good corrosion resistance, adhesion, and wear resistance by optimizing the graduated composition of each doped diamond-like carbon layer thereof.  
      A thickness of each doped diamond-like carbon layer is in a range from 1 nanometer to 30 nanometers. In this embodiment, a thickness of the doped diamond-like carbon composite film  20  can be in a range from 5 nanometers to 900 nanometers. Preferably, the thickness of the doped diamond-like carbon composite film  20  should be in a range from 30 nanometers to 450 nanometers.  
      The undoped diamond-like carbon film  30  without any filler component is formed on the nth layer  17  of the doped diamond-like carbon composite film  20 . The undoped diamond-like carbon film  30  has some excellent properties such as hardness, smoothness, corrosion resistance and wear resistance, etc. A thickness of the undoped diamond-like carbon film  30  can be in a range from 1 nanometer to 10 nanometers. Preferably, the thickness of the undoped diamond-like carbon film  30  should be in a range from 2 nanometers to 5 nanometers.  
      Therefore, the total thickness of the whole film including the doped diamond-like carbon composite film  20  and the undoped diamond-like carbon film  30  can be in a range from 6 nanometers to 910 nanometers. Preferably, the total thickness of the whole film including the doped diamond-like carbon composite film  20  and the undoped diamond-like carbon film should be from 30 to 500 nanometers.  
      The doped diamond-like carbon composite film  20  and the undoped diamond-like carbon film  30  can be deposited by radio frequency (RF) diode sputtering or radio frequency magnetron sputtering. The doped diamond-like carbon composite film  20  is deposited on the main body  10  of the mold  100  in vacuum environment in a radio frequency sputtering process. Firstly, the main body  10 , a carbon target and a filler component target in a radio frequency sputtering system are placed in position, and then sputter gas is fed into the radio frequency sputtering system. Secondly, the doped diamond-like carbon composite film  20  is formed using a sputtering process. The atomic percentage of the filler component  50  in each doped diamond-like carbon layer should gradually decrease from the first layer  11  to the nth layer  17 . Finally, the filler component target is removed from the radio frequency sputtering system and the undoped diamond-like carbon film  30  is formed.  
      The sputter gas into the radio frequency sputtering system can be selected from a group consisting of a mixture of argon and methane (where a percentage by volume of methane is in a range from 5% to 20%), a mixture of argon and hydrogen (where a percentage by volume of hydrogen is in a range from 5% to 20%), a mixture of argon and ethane (where a percentage by volume of ethane is in a range from 5% to 20%), a mixture of krypton and methane (where a percentage by volume of methane is in a range from 5% to 20%), a mixture of krypton and hydrogen (where a percentage by volume of hydrogen is in a range from 5% to 20%), and a mixture of krypton and ethane (where a percentage by volume of ethane is in a range from 5% to 20%).  
      While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.