Montag, 8. November 2021

Upcoming Seminar Dr. Michael Tkadletz

Dr. Michael Tkadletz from the Department of Materials Science, Montanuniversität Leoben will held a presentation (via zoom) in the frame of IGK within the SFB-TR 87 on Wednesday, December 1st, 2021, 10:00 h – 12:00 h, at Materials Chemistry in Aachen.

Part I:
Nanolamellar chemical vapor deposited fcc-Ti1-xAlxN – History, peculiarities and future perspectives

With an Al metal ratio x of ~0.8 while still maintaining a single phase face-centered cubic (fcc) structure, chemically vapor deposited (CVD) Ti1-xAlxN represents an intriguing counterpart to physically vapor deposited (PVD) Ti1-xAlxN, which usually exhibits an fcc/wurtzitic dual phase structure already at Al metal ratios of ~0.6-0.7. Considering the metastable nature of fcc-Ti1-xAlxN and the high deposition temperatures of ~800-900 °C necessary in thermally activated CVD processes, which are commonly considered to result in conditions close to thermal equilibrium, this is even more exceptional. The formation of a predominantly fcc structure at such high Al metal ratios is related to the typically observed unique microstructure of CVD fcc-Ti1-xAlxN, consisting of comparatively large grains with alternating Ti-rich and Al-rich fcc-Ti1-xAlxN nanolamellae exhibiting a periodicity of ~10 nm. Within this talk, the historical evolution and the current state of research on CVD Ti1-xAlxN coatings will be outlined, with a special emphasis on the nanolamellar structure. Important aspects such as thermal stability, age hardening be-havior and oxidation resistance will be discussed on the basis of in situ and ex situ character-ization techniques and the results will be compared with PVD Ti1-xAlxN counterparts. Finally, the role of the deposition parameters, contradictions of recent studies and future perspectives will be illuminated.

Part II: 
Synchrotron radiation based X-ray diffraction techniques for the advanced microstruc-
tural characterization of transition metal nitride coatings  

Within this talk, different synchrotron radiation based X-ray diffraction (XRD) techniques which significantly contribute to the establishment of microstructure-property relationships of complex coating systems will be presented. Special emphasis will be laid on requirements, advantages and disadvantages of the different approaches including sample preparation, experimental ex-ecution, calibration as well as data treatment and evaluation. The presentation will cover high resolution 1D powder XRD for the investigation of phase composition and lattice parameters at room and elevated temperature. In situ 2D powder XRD studies performed in inert and am-bient atmosphere will be discussed to highlight the strength of modern evaluation techniques such as sequential and parametric Rietveld refinement. The potential of the unique instrumen-tal combination of in situ powder XRD with simultaneous differential scanning calorimetry to study the thermal and oxidation stability will be demonstrated, allowing to directly correlate phase changes with the recorded heat flow, while in situ experiments performed on compact coating samples reveal the macroscopic strain throughout such events. In addition, the utiliza-tion of laterally resolved diffraction techniques will be discussed on the example of cross-sec-tional X-ray nanodiffraction applied to graded coating samples. Concluding, synchrotron and lab-based XRD techniques and their pros and cons will be compared.