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Trans. JWRI, Vol. 29 (2000), No. 2, pp. 31-36.


Mechanical Properties of Nanostructured Cr-B Films Produced by RF Sputtering

Masakazu MORI, Toshiya SHIBAYANAGl, Masakatsu MAEDA and Masaaki NAKA

ABSTRACT

     Much attention has been focused on nanostructured materials and some novel properties such as inverse Hall-Petch effect have been reported so far, although little information concerning thermal stability at high temperature has been obtained for nanostructured super-saturated solid solutions. The objectives of this paper are to come to a basic understanding of these characteristics in nanostructured Cr-B alloys thin foils.
     The magnetron RF sputtering method was utilized to produce Cr-B alloy thin foils ranging 10 to 20 µm in thickness using a pure Cr (99.9 mass%) target and pure B (99. 9 mass%) pieces added to it to change composition. The base pressure was below 2.0 x 10-5 Pa and the Ar gas pressure for sputtering was 0.8 Pa. Microstructural evaluation was performed utilizing XRD, EPMA and TEM techniques. Grain size was measured by XRD peak analysis using the Scherrer equation as well as TEM observation. Mechanical properties were evaluated with micro-hardness tests at room temperature.
     XRD analysis revealed that the alloys showed crystalline states up to 9.0 at%B and an amorphous phase appeared beyond this content. The crystalline specimens decreased grain sizes from 40 to 9 nm as B content increased, and a strong (110) texture appeared regardless of the content.
     Microhardness of the specimen increased with the solute content up to 5 at% and showed maximum values of 20.5 GPa which decreased for further contents. As grain size also changes with B content, so nano-size effect may have an dominant role in the range of B content from 5.0 to 9.0 at% in this alloy where the grain size is less than 50 nm.


KEY WORDS: nanostructure, Cr-B alloy, hardness, RF sputtering

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