HIPping CYCLE
Quality 2 Radid cracking
Quality 3 Edge chipping Quality 4 Localised spallation Quality 5 Quality 6
Gross adhesive failure
Cracking substrateVisible
3.5.10. Colourimetrv.
Colourimetry may be defined as the quantitative measurement of perceived colour, encompassing the illumination of the sample, its reflectance and the visual response of the observer. Determination of a sample's colour involves illuminating the sample surface with a standard source (normally from a xenon halogen discharge tube) and detecting the reflected light using a range of photocells, individually filtered to accept one of the primary colours. The colourimeter detects tristimulus values ( X,Y,Z - red, green, blue) over wavelengths ranging from 400-700nm, converts them into
chromaticity components of colour (hue & intensity) and compares them against a reference calibration (white-black) where the deviation is calculated. The colour difference detected defines a position in CIELAB colour space based on human colour perception, established by the Commission Internationale de l'Eclairage in 1976 (27), which has 3 orthogonal axes (figure 3.22).
L*- The difference in lightness or reflectance (black to white).
Figure 3.22. The CIELAB colour space. White +L* <
f
Yellow -a* /G rev ^+f
Green V /J
Red Blue/
-b* Black -L*The colourimeter is a useful instrument in PVD technology enabling:- • Colour matching of decorative coatings.
• Indications of changes in stoichiometry and composition (28,29).
• Detection of changes in surface roughness produced by ion bombardment. • A standard, non-visual method of accurately describing film colour.
During this research project two types of colourimeter were utilised, a Dr.Lange micro- colourimeter and an Applied Colour Systems Chroma Sensor-3.
3.5.11. Surface roughness profiling.
The measurement of surface roughness, a parameter which can critically affect the
decorative, frictional and tribological properties of the coating-substrate composite, involves the movement of a fine stylus across the surface of a sample at a constant velocity. The small vertical displacements transmitted to the stylus contact as it traverses the sample are monitored to produce a surface profile output of vertical displacement as a function of trace distance. Modem instruments are interfaced to
E /X p C I U U C U U U
computer control systems which allow various statistical analyses of the profile raw
data.
Ra - The average roughness - Defined as the arithmetical mean of the absolute values of the profile's departures within a measuring length L.
Rz - Defined as the average value of the absolute values of the heights of the five
highest profile peaks (p) and the depths of the five deepest profile valleys (v) within a measuring length L.
Rt - Defined as the distance between the highest peak and the lowest valley within a measuring length L.
The surface profiler is a useful tool for the surface engineer to assess not only the coating roughness and hence its coefficient of friction, but also the extent of defects or voids within the film, the uniformity of coating coverage and macro-particle
incorporation from arc etching or deposition techniques.
The surface roughness equipment used were Rank Taylor Hobson 120-L and Mitutoyo
2 1 1 form taly surfs.
3.6. Summary of equipment and techniques. Evaporation and sputtering equipment.
• Experimental electromagnetic steered arc evaporation facility at S.H.U, U.K. • Industrial scale unbalanced magnetron sputtering facility at F.E.M, F.R.G.
• Industrial scale Arc-Bond Sputter combined arc / magnetron facility at S.H.U, U.K.
Target manufacturing apparatus.
• Segmented targets- Autoclave Isohipper and National Forge HIP vessels. • TiAl ABS targets- Powder metallurgical HIP route manufactured by Heraeus
GmbH.
• Ti and Zr ABS targets- Melting and casting route manufactured by Titanium Inti Ltd.
Characterisation techniques.
• X-ray diffraction - Philips PW1710 CuKa powder diffractometer. • Scanning electron microscopy - Philips XL40 and Jeol 840A. • Transmission electron microscopy - Philips CM20 STEM. • Optical microscopy - Olympus Vanox-T.
• Glow discharge optical emission spectroscopy - LECO GDS-750.
• Vickers hardness test - Vickers Armstrong engineering tester.
• Knoop micro-hardness test - Tukon MO and Mitutoyo MVK-G1.
• Calotest - Eifeler Nord Caloprap.
• Scratch adhesion test - ST200 Teer Coating Services Ltd. • Rockwell-C indentation test - Avery 1412.
• Colourimetry - Dr.Lange micro-colourimeter and Applied Colour Systems Chroma
Sensor-3.
• Surface roughness profile - Rank Taylor Hobson Form 120-L and Mitutoyo 211
taly surfs.
E ,A JJC I l l I l C I l l c l l
References.
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3. W-D.Miinz, D.Schulze, F.J.M.Hauzer - Surf.Coat.Tech, 1992, 50, 169. 4. R.M.Walker, D.J.Roberts, B.A.Rickinson - "Component assembly using HIP
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20. A.Schulz, H.R.Stock, P.Mayr - Mat.Sci.Eng, 1991, AMO, 639. 21. J.Valli, U.Makela, A.Matthews - Surf.Eng, 1986,2(1), 49. 22. D.S.Rickerby - SurfCoat.Tech, 1988, 36, 541.
23. M.Olsson - PhD thesis, 1989,200, Uppsala University, Sweden.
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26. Verein Deutscher Ingenieure - Richtlinie 3198, 1992, Dusseldorf, F.R.G.
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28. B.Zega - SurfCoat.Tech, 1989, 39-40, 507.
29. G.Reiners, H.Hantsche, H.A.Jehn, U.Kopacz, A.Rack - SurfCoat.Tech, 1992, 54- 55, 273.