AlCr(Si,B)N – Design and Performance of Quaternary Nitride Coatings
Research output: Thesis › Doctoral Thesis
Al-Cr-N is a well-established coating applied on cutting tools and in the hot forging as well as the metal forming industry. CrN based coatings reveal good mechanical properties as well as good thermal stability and oxidation resistance. However, the ever increasing demand on films for high-temperature applications stimulates the development of metal nitride films with outstanding performance. In order to accomplish an improvement of Al-Cr-N coatings, different approaches were conducted within this thesis. The chemical composition was modified by forming quaternary Al-Cr-Si-N and Al-Cr-B-N systems with different contents of Si and B, respectively. These quaternary nitrides were analyzed with respect to their behaviour by varying the substrate bias voltage during deposition. Finally, multilayer coatings consisting of Al-Ti-N and Al-Cr-B-N individual layers and varying architecture were synthesized with the aim of combining their beneficial properties to further enhance the performance and durability of tools in service. All these coatings were synthesized by means of cathodic arc evaporation in an industrial scale deposition plant, which makes the results immediately available for application. Al-Cr-Si-N and Al-Cr-B-N films are both based on the Al-Cr-N coating system. Addition of elements like Si and B results either in formation of a single-phase or a nanocomposite structure consisting of Al-Cr-(Si,B)-N grains embedded in an amorphous SiNx or BNx tissue phase, respectively, depending on the content of the alloying element. The main hardening mechanisms in these quaternary coatings are solid solution, Hall-Petch and nanocomposite hardening. Small amounts of Si or B are incorporated into the face-centered cubic AlCrN phase and cause local stress fields and thus increased hardness. Higher contents of alloying elements foster the formation of a nanocomposite structure, where the amorphous phase hinders growth of the Al-Cr-(Si,B)-N grains and causes an additional hardness increase according to the Hall-Petch effect. Al-Cr-Si-N coatings exhibit enhanced oxidation resistance in comparison to Al-Cr-N films, as they form a slowly growing dense oxide scale composed of (AlxCr1-x)2O3 and SiOx. Tribological benefits can be observed by using B as alloying element in Al-Cr-N films. Al-Cr-B-N films reveal improved wear resistance, resulting in an order of magnitude lower wear coefficients compared to Al-Cr-N coatings without B addition. Also Al-Ti-N/Al-Cr-B-N multilayer films show a significantly improved wear behaviour in comparison to Al-Cr-B-N and commercially applied Al-Cr-N and Al-Ti-N single layer films. Cuttings tests confirmed the outstanding performance of these multilayers.
|Translated title of the contribution||AlCr(Si,B)N – Design und Performance von quaternären nitridischen Schichten|
|Publication status||Published - 2013|