THE PERFORMANCE OF HARDNESS COATING BY ION PLATING（2）

4 The color of films

4.1 The color of metal and alloy films

The common metal films and colors:

Silver: silver, chromium, zirconium, or adding a small amount of nitrogen in zirconium and chromium.

Grey: titanium, stainless steel.

Golden: Pure gold and various K gold. Pure gold is 24K gold, gold added silver and copper is called K gold, different amounts and proportions show different colors, which can be the gold of 22K, 18K, 14K, 9K. Table 1 provides the standard formulas and the colors of gold. These alloy can be used for sputtering different K gold films. Rose gold is gold copper alloy.

Table 1 shows alloy compositions and colors with N number of Swiss gold.

Table 1   Standard of Swiss Gold

   No.            Composition（atoms，per 1000） Color

                  Au       Ag        Cu

   0N                   585     300—340 remaing    yellow green

   1N                   585     240—265 remaing    pale yellow

   2N           750     150—160 remaing    bright yellow

   3N           750     120—130 remaing    yellow

   4N           750     85--95    remaing    rose

   5N           750     45—55   remaing     red

4.2 Decorative films of binary compound

Commonly used materials are TiN, ZrN, CrN, TiC, ZrC, CrC, TiO, ZrO, CrO etc.

TiN: similar like the golden yellow color, but the tone is not dazzling as gold. The film color of TiN changes with the variation nitrogen content. The higher nitrogen content reduces reflectivity completelyl, appearing yellower and darker. Excessive nitrogen would make films darker yellow (old gold), adding more nitrogen makes it shows bronze (brown). High nitrogen content makes TiN yellowish and reddish, low nitrogen makes TiN pale yellow with cyan. Regulating ratios between nitrogen and titanium can bring up the pale yellow, yellow, deep yellow, purplish and reddish yellow.

ZrN: closer to cyan compared with TiN,

TiN partial green color, ZrN has many advantages. Hardness higher than 2500Kg/mm2, harder and brighter than TiN. The film color of ZrN changes with the variation nitrogen content, similar to the trend of TiN, using various nitrogen content for the ZrN deposition in order to adjust different colors to make them match the color of brass, which is used for decorative films for sanitary wares.

CrN: color is silver, very similar to hardness chromium films by wet electroplating, and can be used for sanitary wares and parts of electronic products, also used for hardness.

TiC, ZrC, CrC appear grayish black, deep black with excess carbon。

TiO, ZrO, CrO are transparent films, which can be used for interference to appear various colors.

4.3 Ternary and multiple compound decorative film

Colors TiCN and ZrCN: introduce carbon into the TiN and ZrN films, it found that colors are changed obviously. TiCN and ZrCN films shift towards red with the increase of carbon. TiCN and ZrCN have a wide range of colors, with the regulation of nitrogen and carbon, colors can appear pale bronze, bronze, gold, bronze, grey, black. Rose gold also can be tuned.

TiAlN and TiAlCN color:

TiAlN and TiAlCN can be tuned with very rich color, it tends to be light colors with low aluminum, deep colors with high aluminum, light brown with low nitrogen and dark blue, deep brown with high nitrogen; purplish and reddish by adding least acetylene, purplish and blackish adding most acetylene, which can tune yellow brown, bronze, coffee color, purple brown, dark brown, black.

4.4 Films classified with colors

Imitation gold series: TiN, ZrN, TiN+Au, ZrN+Au

Rose Gold Series: TiCN, TiAlN, TiCN+Au--Cu, TiAlN+Au, Cu

Silver white series: CrN, CrSiN, Zr (micro N)

Grey series: Ti, stainless steel (S.S), (S.S) N

Coffee color series: TiCN, TiAlCN, ZrC

Blue series: TiO, CrO, TiALN

Black Series: TiC, TiC+iC, TiCN, TiAlN, TiAlCN, Ti (C, O) and DLC

4.5 The commonly used black decorative films.

Black films are being used include TiC, TiC+iC, TiCN, TiAlN, TiAlCN, Ti (C, O) and DLC etc.. The tones of black films by ion plating vary according to targets and chemical and physical properties of films, which could be applied on various products required. The most practical applications are TiCx CrCx (X>1) and DLC, DLC is the abbreviation of of Diamond-Like Carbon films, which refers to the amorphous carbon films containing diamond structure. TiC,CrC become amorphous structure when carbon is excessive, becoming the metal doped amorphous carbon films. The black degree of films might relate to the amount of graphite like electronic structures(SP2) contained in films.

4.6 TiO2 interference color films

(1) Metal oxide films extend the film colors by PVD, but the generation of colors is different from the nitride, carbide of selective absorption of visible light, while it comes from the interference effect of metal oxide films of transparent or near transparent to visible light.

(2) Metal oxide films including Zr, Ti, Cr have a similar effect, feeding Ar and O2 metal sputtering target reaction deposition, process parameters are oxygen flow rates and deposition time. The film can be obtained with high a*, b* absolute value of strong yellow, red, green, blue, colors of course are related to film thicknesses.

(3) Someone didn’t control the film thickness deliberately, the TiO films with non-uniformity have varied interference colors, different zones show different colors, appearing fantasy effect.

5 The brightness of films

Surface brightness and texture of metal has attracted the attention of customers, brightness performance index is proposed.

5.1 Brightness and L* value

The surface brightness is not as same as L* value in color coordinates of films.

The brightness is characterized as the reflection degree of light on the surface of films, the brightness is the reflection of illuminant, the color it reflected is the color of illuminant, which does not involve the color of objects, even black materials have different brightness. While the color is the selective absorption of incident light by electrons from several atomic layers near the surface. L* is just a representation of an axis in color coordinates system, the definition of L* is the brightness of materials color, it relates to the material color, it indicates the number of photons of corresponding wavelength to the corresponding colors reflected, high number means high brightness, high L* value. Even the color of the material(L*) is same, brightness could be different.

The brightness of films should be a performance index to evaluate the decorative films. Brightness meter can be used to measure the brightness of objects.

5.2 High brightness films

To make the metal coating has a high brightness: firstly, the surface of substrates is clean enough, secondly, coating surface must be dense and smooth; thirdly, films have metal-like electric structure.

5.3 The phenomenon of appearing misty on films

It appears quite frequently the so-called misty in coating, which appears a fog-like layer of pale white, decreasing the brightness of the layer, even covering the original color tone, which makes it as NG good. As is known to all, the arc spot of cathode arc deposition emits metal droplets from the target form various sizes of dense convexities, appearing misty in practical production, see Figure 4, the misty is caused by the diffuse reflection of light from the dense little convexities. There are various factors to appear misty, which will be described in details in the chapter of causes and countermeasures of films defects.