Influence of Al on Structure and Mechanical Properties of YN and HfN

Lan Wang

Research output: ThesisDiploma Thesis

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Abstract

Transition metal nitrides (TMN) are industrially well acknowledged standard coating materials, as they often exhibit outstanding properties compared to their metallic counterparts. Severe working environments in industrial scale cutting and milling operations, require high hardness and wear resistance, but also good oxidation and excellent corrosion resistance. Being in the focus of research for already several decades, binary TMN are often on the limit with respect to the physical and chemical requirements present in state-of-the-art cutting operations. Hence, the systematic investigation of ternary, aluminium containing TMN compounds, TM-Al-N is in the focus of current research activities, since Al is known to form a dense and stable oxide. However, the solubility of Al in TMN is rather limited, leading to a multitude of possible phases. In the present work, binary and ternary TM-Al-N coatings, e.g. YNz, Y-Al-N and Hf-Al-N, are investigated in terms of their microstructure, mechanical properties and oxidation resistance, as a function of Al content. An unbalanced magnetron sputtering process was used, applying N2 as reactive gas and Ar as working gas, a bias voltage of -50 V, a target power density of ~9 W/cm2 and a deposition temperature of 500 °C. Rapid oxidation of YNz takes place after exposure to ambient air. By placing Al discs on the target race track, the growth of the oxide scale on the resulting Y1-xAlxN thin films (0.29 <x 0.56. The oxidation of the Y1-xAlxN films effectively decreases with increasing Al contents up to x = 0.52, while higher Al contents, especially within the single phase wurtzite regime do not form a detectable oxide scale. In contrast, the formation of Hf1-xAlxN films (0.23 <x <0.77) results in stable coatings in terms of oxidation in ambient air at room temperature. Hf1-xAlxN exhibits a dual phase region (cubic and wurtzite) for x <0.33, which causes a hardness decrease from ~25.2 GPa (x = 0.23) to ~23.9 GPa (x = 0.33), consistent with increasing amount of wurtzite phase in the films. Competing phases during growth result in a fine grained structure, as obtained from XRD and SEM investigations. In the single w-Hf1-xAlxN regime, observed for x > 0.38 the film hardness slightly increases from ~ 19.7 GPa (x = 0.38) to ~21.2 GPa (x = 0.77) due to the higher crystallinity of the films. In conclusion, the incorporation of Al into c-YN and c-HfN results in an effective oxidation protection at ambient conditions. Al alloying further strongly affects the coating structure and mechanical properties of Y1-xAlxN and Hf1-xAlxN, involving a higher hardness for the cubic compared to the dual phase or single phase wurtzite phase field in Hf1-xAlxN. These preliminary investigations are promising for the understanding and development of alloying concepts for high performance coatings.
Translated title of the contributionEinfluss von Al auf die Struktur und mechanischen Eigenschaften von YN und HfN
Original languageEnglish
QualificationDipl.-Ing.
Supervisors/Advisors
  • Rachbauer, Richard, Co-Supervisor (internal)
  • Mayrhofer, Paul Heinz, Supervisor (internal)
Award date1 Jul 2011
Publication statusPublished - 2011

Bibliographical note

embargoed until null

Keywords

  • Y-Al-N
  • Hf-Al-N
  • structure
  • hardness
  • phase-stability

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