The Choice of Optimal Microhardness Testing Conditions for Amorphous and Polycrystalline Films
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THE CHOICE OF OPTIMAL MICROHARDNESS TESTING CONDITIONS FOR AMORPHOUS AND POLYCRYSTALLINE FILMS I.MANIKA AND J.MANIKS Latvian Academy of Sciences,
229021,
Institute
of Physics,
Salaspils,
Latvia
ABSTRACT The microhardness of polycrystalline and amorphous coatings on substrates of various hardness has been studied in a wide range of loads. The limits for indentation depth providing optimal conditions for microhardness testing have been found. Basing on the results of integral hardness testing of coated samples at comparatively high loads, a method has been proposed for the microhardness and thickness evaluation. INTRODUCTION One of main problems associated with microhardness measurements of thin films and coatings is reasonable choice of indentation depth conditions. To obtain true hardness values, a certain ratio of the coating thickness t and the indentation depth h must be maintained. As a rule, the ratio t/h)IO is used taking into account that the maximum size of the deformation zone under the indentor is by about an order of magnitude known greater than the indentation depth I]. However, it is that the critical value of t/h can be changed within a wide range (t/h , I -13) depending on the coating and substrate hardness ratio and other specific conditions as well[2,3 . The present paper deals with the effect of coating structure on the indentation zone. In this respect, the critical t/h values for amorphous and polycrystalline coatings were obtained in a wide range of the layer/substrate hardness ratio Hf/Hs. EXPERIMENTAL PROCEDURE The systems to be investigated were galvanic coatings of nickel on copper and iron, chromium on brass and steel, gold on Fe-Ni-Co alloy, vacuum deposits of copper, lead and tin on glass, TiN on steel, amorphous As 2 S 3 on quartz and bulk As 2 S 3 , thickness amorphous silicon on quartz. Coatings of uniform providing good adhesion to substrate were used. It allowed us to diminish errors connected with coating debonding arround Mat. Res. Soc. Symp. Proc. Vol. 239. 01992 Materials Research Society
350
the impression. The coating thickness was determined directly from metallographically prepared cross-sections or measured in situ by the laser interferometry technique. Vicker's microhardness tests were performed by the device [41 which is insensitive to vibrations and suitable for accurate hardness measurements over a load range from 3 . io-3 to 2 N. The impression diagonal length d was measured by optical microscope Neophot-2 with use of immersion technique at a magnification of 1600x. To obtain reasonably good accuracy 5 impressions were made at each load with loading time 15 s. The scatter of 1.5 - 3% for impressions d > I5J•m was observed, but for the smallest ones (I. 5)m) it rose up to 22%. The indentation depth was calculated as 1/7 of the impression diagonal. Microhardness measurements for each system of coating/ substrate were carried out in a wide range of loads, including small loads, when deformation is localized in coating, as well as large ones, when the critical t/h
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