Annealing effect on structure and mechanical properties of AlxCoCrCuFeNi multi-element oxide films

• Main Authors: Cheng-Shuan Lin, 林承璿
• Other Authors: Ming-Show Wong
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/26464487593947574231

碩士 === 國立東華大學 === 材料科學與工程學系 === 99 === In this thesis, AlxCoCrCuFeNi (x=0, 1, 2, 3, 4, ∞) oxide films were prepared by reactive co-sputtering under different O2/Ar ratio (R=0.5 and 1) using a tri-cathode sputtering system. When R=0.5 with low x value, the as-deposited films are in cubic-spinel structure with very fine grains. As R increases to 1, the grains in the films become finer and finally form amorphous structure under high x value. Hardness of the AlxCoCrCuFeNi oxide films increases with the increasing R and x values (from 0, 1, to 4). The maximum hardness values for the as-deposited Al4CoCrCuFeNi oxide film and pure alumina achieved are over 20 GPa, the which is among the hardest oxides ever reported. The enhancement of film hardness may be attributed to two main reasons: the increases of Al content forming stronger bonding with oxygen and the very fine grains embedded in a strong amorphous matrix inhibiting dislocation formation and movement. TEM analysis of the oxide films indeed reveals a nono-composite structure consisting of ~5 nm nano-size grains of spinel embedded in an amorphous matrix of AlxCoCrCuFeNi and of α-Al2O3 in an amorphous alumina, respectively. Annealing the oxide films at 500℃ and 700℃in air for 5 hours resulted in phase transformation from cubic-spinel to tetragonal-spinel. The hardness of films decreases slightly after annealing at 500℃ due to grain growth. On the other hand, precipitates were found on the surface of the films with low x value when annealing at 500℃ and 700℃. At 700℃, not only precipitates but also pores and cracks were found on the surface. These defects might be the main reason that the hardness of the oxides drops a lot after annealing at 700℃.