Microstructural influence of the thermal behavior of arc deposited TiAlN coatings with high aluminum content

The influence of the microstructure on the thermal behavior of cathodic arc deposited TiAlN coatings was studied as a function of isothermal annealing. Two compositionally similar but structurally different coatings were compared, a Ti0\ub734Al0\ub766N0.96 coating with a fine-grain structure consisting of a mixture of cubic (c) and hexagonal (h) phases, and a Ti0\ub740Al0\ub760N0.94 coating with a coarse-grain structure of cubic phase. By in situ wide-angle synchrotron x-ray scattering, spinodal decomposition was confirmed in both coatings. The increased amount of internal interfaces lowered the decomposition temperature by 50 \ub0C for the dual-phase coating. During the subsequent isothermal anneal at 1000 \ub0C, a transformation from c-AlN to h-AlN took place in both coatings. After 50 min of isothermal annealing, atom probe tomography detected small amounts of Al (∼2 at.%) in the c-TiN rich domains and small amounts of Ti (∼1 at.%) in the h-AlN rich domains of the coarse-grained single-phase Ti0\ub740Al0\ub760N0.94 coating. Similarly, at the same conditions, the fine-grained dual-phase Ti0\ub734Al0\ub766N0.96 coating exhibits a higher Al content (∼5 at.%) in the c-TiN rich domains and higher Ti content (∼15 at.%) in the h-AlN rich domains. The study shows that the thermal stability of TiAlN is affected by the microstructure and that it can be used to tune the reaction pathway of decomposition favorably

Understanding the microstructure-properties relationship of low-temperature carburized austenitic stainless steels through EBSD analysis

The present article is dedicated to the microstructural characterization of the surface layer of two different austenitic stainless steels, 304L and 904L, subjected to a low-temperature carburizing process (Kolsterising\uae,Bodycote) and a subsequent annealing at high-temperature. The carburizing treatment forms a hard expanded austenite in both materials. However, thermal decomposition occurs at high temperatures through precipitation of chromium-carbides, hence compromising the surface hardness of the treated materials.The purpose of this paper is to explore the potential applicability of electron backscatter diffraction (EBSD) technique to reveal the correlation between phase transformation and hardness. First of all, EBSD was used to create kernel average misorientation (KAM) maps of the modified surface layers to identify the internal strains. Moreover,the preferential sites for precipitation of chromium-compound during annealing were identified. We provehere that EBSD can provide useful information to distinguish the main hardening mechanisms within modifiedsurface layers at different annealing conditions. When combined with nano-indentation, X-ray diffraction(XRD) and glow discharge optical emission spectrometry (GDOES), an effective bridge between macro and microanalysis can be obtained. Solid solution hardening was found to be the dominant mechanismin as-carburized materials, with pre-existing strain promoting a higher supersaturation. In the annealed materials, the alloy composition and surface finish can also dictate the preferential sites of precipitation and can therefore affect the residual hardening