α-alumina coatings on WC/Co substrates by physical vapor deposition
Summary (1 min read)
- Hard physical vapor deposited (PVD) coatings may be coated by a variety of methods, e.g. direct current (DC) magnetron sputtering in Ar inert gas.
- Albeit stable, BPDMS has only been repeatedly successful in depositing γ-alumina, which is a drawback if phase stability of the coating is of concern.
- So far, commercial α-alumina coatings have only been grown by chemical vapor deposition (CVD) at relatively high substrate temperatures.
- Therefore one drawback with HiPIMS has been the inherently low growth rate.
- Recently, it was shown that high rate sputtering is possible, and that long time stable operation of Ar/O2 discharges is possible without feedback control of the reactive gas .
- Coatings were made in a laboratory scale ultra-high vacuum system, with a base pressure of less than 3×10-5 Pa.
- Cemented carbide, WC10%Co (H10F), substrates were mounted flat on a resistive heater directly above the magnetron, at a distance of 11 cm.
- The temperature reported herein is always the set nominal temperature, however, not the estimated temperature.
- To the extent of the analyses performed in the present work the process was reproducible, in that consecutive runs under the Page 4 of 18 same conditions yielded coatings with similar properties.
- TEM cross-section samples were produced by means of classical sample preparation by first mechanical dimpling with diamond particles and finally thinned to electron transparency by Ar ion etching.
On the HiPIMS Process
- HiPIMS resembles ordinary magnetron sputtering in many aspects.
- In many cases the sputtering yield is lower for the compound now covering the target, and the deposition rate drops.
- These coatings were deposited at 650ºC nominal temperature, but it is estimated that the real extending almost throughout the total film thickness.
- XRD of this particular sample did, however, not indicate anything else but a pure α-alumina coating, a fact probably due to a very small γ-grain size.
- Since it is anticipated that alumina will improve the chemical stability of the tool surface on which the chips flow a test was selected that emphasizes the wear on the rake face.
- In this study the HiPIMS technique was used to deposit alumina coatings on WC/Co substrates and tools.
- Α-alumina was succesfully deposited on WC/Co substrates at 650 °C. .
- The deposition rate was found to be independent of substrate bias and substrate temperature in the range of 500 to 650 °C. .
- The crystalline structure depended on deposition temperature.
- Hence, these first tests are promising in terms of the potential for using HiPIMS deposited alumina as a wear-resistant coating in metal cutting applications.
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Q1. What have the authors contributed in "Α-alumina coatings on wc/co substrates by physical vapor deposition" ?
In this paper, high power impulse magnetron sputtering ( HiPIMS ) was used to deposit alumina coatings on WC/Co substrates and tools.