title: Screening for intrinsically hard and tough ceramic-like materials
Creators: name: Müllauer, Lukas
Publisher: name: TU Wien
Year: 2019
Subjects: subject: Werkstoffwissenschaft
subject: Werkstoffauswahl
subject: Dichtefunktionaltheorie
subject: Härte
subject: Zähigkeit
subject: Materials Science
subject: Density Functional Theory
subject: Hardness
subject: Toughness
subject: Physical Vapor Deposition

description: Finding new hard and tough materials is a complicated process, described in this thesis. The steps taken in this work will be briey summarised in this chapter, after that the conclusions will be discussed and lastly the question why this work is important will be answered and some questions for further research will be posted. In the rst chapter, the question why hard and tough materials are needed and what the main factors in composing hard and tough materials are, were answered. Furthermore methods to calculate these properties from literature were introduced and compiled in an comprehensive overview. With this knowledge, the formulas were taken to the test in chapter two, where the hardness and fracture toughness of transition metal nitrides, carbides, borides and oxides with properties taken from literature were calculated, compared and the dierent methods were evaluated. While all formulas show good results for specic materials, the two (H v and K IC ) best suited for the application in ceramic-like materials were then applied in chapter 3, to calculate hardness and fracture toughness of 4.700 compounds available in the database "Materials Project". Some of the calculated values were compared with data used to evaluate the formulas, general trends were discussed. In chapter four ternary transition metal compounds were investigated, by applying a method, that uses data from the underlying binary compounds (which is readily available), to calculate the hardness of the ternary compound (solid solution strengthening). Finally one of the ternary compounds was synthesised using PVD, and the agreement of experimental to calculated hardness was shown. The question that needs to be answered next is, what can we learn from these ndings. Firstly some general remarks about the methods. As stated before, all formulas have their applications, where they provide excellent results. However for ceramic-like hard materials the formula proposed by Chen et al. and Niu et al. predict hardness and fracture toughness, respectively, with the highest accuracy. showed to be the most useful. Secondly knowledge about bond type can help provide more accurate predictions, by using the most suitable model, however in transition metal compounds this is a complicated undertaking. With these conclusions at hand, what are some questions that could not be answered in this work. The most important one is probably the characterisation of bond types. In this work only intrinsic properties of ideal crystals were discussed, however in reality crystal lattices have defects and extrinsic strengthening mechanisms like the Hell-Petch eect are applied, which are needed to be account for in order to improve the prediction accuracy for real materials.. On a nal note, the importance of high quality experimental data should be mentioned. For future works a database of experimental H and K IC values could make a dierence in the time needed to evaluate methods, but also the quality of the evaluation.