Mats Ahlgren

Bio: Mats Ahlgren is an academic researcher from Sandvik Coromant. The author has contributed to research in topics: Coating & Annealing (metallurgy). The author has an hindex of 9, co-authored 17 publications receiving 196 citations.

Thermal stability of wurtzite Zr1−xAlxN coatings studied by in situ high-energy x-ray diffraction during annealing

Abstract: We study the thermal stability of wurtzite (w) structure ZrAlN coatings by a combination of in situ high-energy x-ray scattering techniques during annealing and electron microscopy. Wurtzite structure Zr1−xAlxN coatings with Al-contents from x = 0.46 to x = 0.71 were grown by cathodic arc evaporation. The stability of the w-ZrAlN phase depends on chemical composition where the higher Al-content coatings are more stable. The wurtzite ZrAlN phase was found to phase separate through spinodal decomposition, resulting in nanoscale compositional modulations, i.e., alternating Al-rich ZrAlN layers and Zr-rich ZrAlN layers, forming within the hexagonal lattice. The period of the compositional modulations varies between 1.7 and 2.5 nm and depends on the chemical composition of the coating where smaller periods form in the more unstable, high Zr-content coatings. In addition, Zr leaves the w-ZrAlN lattice to form cubic ZrN precipitates in the column boundaries.

Wear behavior of ZrAlN coated cutting tools during turning

Abstract: In this study we explore the cutting performance of ZrAlN coatings. WC:Co cutting inserts coated by cathodic arc evaporated Zr 1 − x Al x N coatings with x between 0 and 0.83 were tested in a longitudinal turning operation. The progress of wear was studied by optical microscopy and the used inserts were studied by electron microscopy. The cutting performance was correlated to the coating composition and the best performance was found for the coating with highest Al-content consisting of a wurtzite ZrAlN phase which is assigned to its high thermal stability. Material from the work piece was observed to adhere to the inserts during turning and the amount of adhered material and its chemical composition is independent on the Al-content of the coating.

Phase transformations in nanocomposite ZrAlN thin films during annealing

Abstract: Nanocomposite Zr0.52Al0.48N1.11 thin films consisting of crystalline grains surrounded by an amorphous matrix were deposited using cathodic arc evaporation. The structure evolution after annealing of the films was studied using high-energy x-ray scattering and transmission electron microscopy. The mechanical properties were characterized by nanoindentation on as-deposited and annealed films. After annealing in temperatures of 1050–1400 °C, nucleation and grain growth of cubic ZrN takes place in the film. This increases the hardness, which reaches a maximum, while parts of the film remain amorphous. Grain growth of the hexagonal AlN phase occurs above 1300 °C.

Phase stability and alloy-related trends in Ti–Al–N, Zr–Al–N and Hf–Al–N systems from first principles

Abstract: Transition metal aluminium nitride (TM–Al–N) thin films are valued for their excellent mechanical (e.g. hardness) as well as protective (e.g. oxidation resistance) properties. This paper addresses the structure and phase stability of group IVB TM–Al–N systems Ti1−xAlxN, Zr1−xAlxN, and Hf1−xAlxN. The predicted stability regions of the rock salt cubic structures are x ≤ 0.7, x ≤ 0.45, and x ≤ 0.45, respectively, while the wurtzite-type single phase field is obtained for x ≥ 0.7, x ≥ 0.68, and x ≥ 0.62 respectively. The predicted phase stability regions and the broad dual-phase transition regions in the case of Zr1−xAlxN and Hf1−xAlxN are validated by experiments. Furthermore, the phase transition from cubic to wurtzite with increasing Al content in the alloys is correlated with changes of electronic structure and bonding in the systems.

Microstructure and dielectric properties of piezoelectric magnetron sputtered w-ScxAl1-xN thin films

Abstract: Piezoelectric wurtzite ScxAl1−xN (x = 0, 0.1, 0.2, 0.3) thin films were epitaxially grown by reactive magnetron co-sputtering from elemental Sc and Al targets. Al2O3(0001) wafers with TiN(111) seed and electrode layers were used as substrates. X-ray diffraction shows that an increase in the Sc content results in the degradation of the crystalline quality. Samples grown at 400 °C possess true dielectric behavior with quite low dielectric losses and the leakage current is negligible. For ScAlN samples grown at 800 °C, the crystal structure is poor and leakage current is high. Transmission electron microscopy with energy dispersive x-ray spectroscopy mapping shows a mass separation into ScN-rich and AlN-rich domains for x ≥ 0.2 when substrate temperature is increased from 400 to 800 °C. The piezoelectric response of epitaxial ScxAl1−xN films measured by piezoresponse force microscopy and double beam interferometry shows up to 180% increase by the addition of Sc up to x = 0.2 independent of substrate temperature, in good agreement with previous theoretical predictions based on density-functional theory.