The crystal growth direction within a single grain is typically assumed to be uniform. However, this study presents the first observation of spontaneous intra-grain crystal rotations in (Ti,Al)N grains with an internal nanolamella structure. The rotation occurs spontaneously during grain growth in a chemical vapor deposition process. The crystal rotations exhibit a highly symmetrical pattern linked to the (Ti,Al)N grain morphology: a pyramid comprising three {001}-faceted domains. The crystal lattices systematically rotate within each domain toward the pyramid tip, with the largest rotations concentrated at the pyramid edges. Within a single (Ti,Al)N grain, the crystal orientation can shift up to 15° from base to tip, with a typical gradient of 1°/µm. The rotation gradient reaches a peak of 3 – 4°/µm in the horizontal direction near the pyramid edges. This phenomenon is attributed to the high density of grown-in dislocations, arising from interface mismatches between the (Ti,Al)N grain domains and hexagonal AlN nano-precipitates that form at the domain boundaries. Analysis of three (Ti,Al)N samples with varying nanolamella structures reveals that the presence of more nanolamellae corresponds to larger crystal rotations. These findings provide useful insights into controlling crystal rotation and its potential influence on material properties, opening new avenues for materials design and optimization.

Zr-based nuclear fuel claddings operate under the coupled stressors of irradiation damage and hydrogen uptake. Integrating first-principles calculations with multi-scale characterization, we demonstrate that solute redistribution is governed by a fundamental synergy where irradiation acts as both a structural template for hydride nucleation and a kinetic gatekeeper for transport. We reveal a hierarchical de-alloying mechanism: while fast-diffusing interstitial species are thermally expelled upon the formation of the structural template, the redistribution of slow-diffusing substitutional solutes is strictly contingent upon irradiation-induced vacancy flux. This synergy reconciles the complete de-alloying observed at dislocation loops with the kinetic trapping of solutes in bulk hydrides, where the kinetic gatekeeper remains closed. Our findings establish a predictive framework for solute-defect interactions in structural alloys under extreme, multi-field stressors.

A novel chemical vapor deposition (CVD) multilayer coating intended for cutting applications was designed to achieve high wear and heat resistance during metal machining. The coating consists of three layers: a TiCN layer deposited on top of a TiAlN layer, which was grown on a layer of TiN that was deposited onto a cemented carbide substrate. The detailed microstructure of the coating was examined using a combination of electron microscope techniques. Two pyramidal surface morphologies and textures were observed, which could be related to the substrate roughness. Two growth modes were found: epitaxial growth of (211) oriented TiCN on <211> oriented TiAlN on <211> oriented TiN, leading to tilted TiCN pyramids at the coating surface; and epitaxial growth of (111) TiCN on <111> TiAlN on <111> TiN, leading to symmetrical TiCN pyramids at the coating surface.

In this work, the deposition of x-Al2O3 on textured (Al,Ti)N coatings using chemical vapour deposition (CVD) is explored. Two TiN/(Al,Ti)N/x-Al2O3 coatings with different texture for the (Al,Ti)N layer, (111) and (100), have been investigated. The coatings were characterized using X-ray diffraction, scanning electron microscopy, transmission and scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. The x-Al2O3 layer deposited on the (111) textured (Al,Ti)N layer has a (001) texture, while the x-Al2O3 deposited on the (100) textured (Al,Ti)N layer shows no clear texture. The difference in x-Al2O3 texture is driven by the (Al,Ti)N facets available for alumina nucleation. x-Al2O3 forms on {111} (Al,Ti)N facets, while y-Al2O3 forms on {100} (Al,Ti)N facets. y-Al2O3 growth is not stable and is subsequently overgrown by x-Al2O3. The surface of the (100) textured (Al,Ti)N layer is dominated by {100} facets, while the surface of the (111) textured (Al,Ti)N layer is built up of a mixture of {100} and {111} facets. This explains the observed microstructure for the x-Al2O3 layers in the two coatings. Thus, to optimize the deposition of x-Al2O3 on (Al,Ti)N, the latter should exhibit {111} facets.

The life-time-limiting factors of zirconium-based fuel cladding in water-cooled and-moderated nuclear power reactors are corrosion and associated hydrogen pickup. Corrosion performance in reactor is significantly worse in comparison to autoclave exposure. The accelerated degradation becomes particularly severe with the accumulation of radiation damage that is caused by fast neutrons. This work aims to expand the understanding of the underlying mechanisms governing the in-reactor corrosion process by nano-scale characterization of highburnup fuel cladding tubes from operation in the boiling water reactor Oskarshamn 3 mainly by atom probe tomography. We present data from the oxide and the oxide-metal interface and point out the differences with the comparatively well-known behaviour in autoclave corrosion tests. The main aspect is the interaction between alloying elements, irradiation-induced defects and zirconium oxidation: Irradiation-induced FeCrNi clusters seem to slightly accelerate the diffusion of oxygen within the basal plane of the hexagonal metal matrix and dissolve in the oxygen-saturated zirconium metal that develops before zirconia formation takes place, and c-component dislocation loops, characteristic of high damage levels, might offer enhanced oxide nucleation sites that potentially explain the rapid degradation observed after some years of reactor operation. In addition, pores can be construed as a potential pathway for accelerated hydrogen pickup, similar to processes postulated in the literature. The results in this study give some novel insights into the mechanisms of in-reactor degradation of zirconium-based alloys and highlight the necessity to characterize materials from actual reactor operation.

Cemented carbide inserts coated with CVD alpha-alumina, particularly those exhibiting a (0001) texture, have proven highly effective in steel turning. Despite the established superior performance of (0001) textured alumina coatings, the underlying reasons remain unclear. This study explores the influence of the crystallographic texture of alumina on wear mechanisms in various chip-tool contact zones on the insert rake face. The objective is to establish a fundamental understanding of the active degradation mechanisms and machining performance by relating coating texture to the orientation and deformation of individual Al2O3 grains. Two multilayered coatings, Al2O3 on Ti(C,N), featuring (0001)- and (1120)-textured CVD alpha-alumina, were assessed in dry turning of a bearing steel. The wear rate of the (1120) coating was double that of the (0001) coating. Worn coatings exhibit nano-terrace formation at the insert edge, likely due to chemical etching. In the sticking zone, plastic deformation leads to larger facets for grains oriented with the chip flow direction, while rounded surfaces result if this condition is not met. In the transition zone, both (0001) and (1120) textured coatings undergo increased plastic deformation accompanied by sub-surface dislocations. (0001) texture deforms more by basal slip creating a wavy coating pattern with steps present at larger misalignments of the lattice planes in neighboring grains while (1120) texture deforms by several slip systems creating elongated ridges and ruptured-like areas resulting in rougher surface. This difference in surface morphology is then inherited by the abrasion of submicron coating fragments embedded in the chip (more in (1120) texture) in the sliding zone resulting in an even rougher surface. Chemical reaction with the hot chip may also contribute to wear acting as an additional mechanism. This fundamental understanding contributes to the potential enhancement of steel machining using texture-controlled CVD alumina coatings, ultimately improving coated cutting tool performance.

Competitive growth usually occurs during deposition of polycrystalline coatings and is associated by the formation of crystal facets. Knowing the facet planes in the crystal coordinates is thus essential for understanding the coating growth process and optimizing corresponding experimental parameters. However, the crystal facets of polycrystalline coatings have not been explored enough due to a lack of easy-to-use experimental methods. In this work, we apply an electron backscattered diffraction (EBSD)-aided scanning electron microscopy (SEM) trace analysis for determining the crystal facets of the chemical vapour deposition (CVD) polycrystalline (Ti,Al)N and Ti(C,N) coatings. Using this method, the crystal orientation of an interesting grain relative to the specimen coordinates is first determined by the EBSD point analysis, and the crystal orientations of edges shared by neighbouring facets are then determined using trace analysis. Finally, the facet normals are calculated by the cross-product of the crystal orientations of edges on the corresponding facet. The (Ti,Al)N coating is found to have {100} crystal facets, which is consistent with the results obtained using transmission electron microscopy in previous work. The Ti(C,N) coating is found to have {211} crystal facets. In principle, the method proposed in this work can be applied to any crystals with planar facets and sharp edges. A possible improvement of the method is also discussed.

High-burnup Zr-based nuclear fuel claddings exhibit accelerated irradiation growth, corrosion and hydrogen pick-up, all correlated with the emergence of c-component dislocation loops. We made use of sub-nm-resolution atom probe tomography to characterize the nanoscale chemistry of c-loops in fuel cladding from boiling water reactor operation. We found segregation of Fe, Ni and Sn to dislocation lines and depletion of Sn and O inside the loops, resulting in nearly pure Zr islands. We also observed nucleation of suboxide inside one c-loop, pointing to a possible mechanism of accelerated in-reactor corrosion. Such Zr-islands might also promote hydride precipitation and associated degradation.

Un-doped and Cr-doped WC-10 vol% Co cemented carbides with a WC grain size of 1.4 mu m have been investigated before and after hot compressive creep tests under an applied load of 900 MPa at 1000 degrees C and 300 MPa at 1100 degrees C. The Cr-doped material showed a much higher creep resistance at 1000 degrees C and a somewhat higher creep resistance at 1100 degrees C than the un-doped material. Quantitative microscopy showed that WC grain growth occurred in the plane perpendicular to the load axis during creep deformation and that the growth process was slower in the Cr-doped material. In addition, binder phase redistributed and a number of WC grain boundaries were infiltrated with binder phase. This suggests that accommodated WC grain boundary sliding occurred during creep deformation. The formation of intergranular cavities implies that also unaccommodated grain boundary sliding occurred, especially at 1000 degrees C. It is suggested that WC grain growth perpendicular to the load axis is rate limiting in the creep deformation process, and that Cr segregation to WC/binder phase boundaries hinders grain growth. The weak effect of Cr on creep resistance at 1100 degrees C at 300 MPa is explained by Cr giving a larger volume fraction of binder phase and therefore a larger number of infiltrated grain boundaries, facilitating grain growth.

This work indicates that the matrix content of the alloying elements iron, chromium, and nickel in as-produced commercial Zircaloy-2-type materials is lower than what has been indicated by many previous studies. Atom probe tomography in voltage pulse mode was used to study the matrix content of solutes in Zircaloy-2 of type LK3/L and a similar model alloy, called Alloy 2, of the same heat treatment. Both alloys were analyzed in the as-produced state and after reactor exposure. In the as-produced materials, the concentrations of iron, chromium, and nickel were all below the detection limits of around 10 wt. ppm. After reactor exposure, these alloying elements were observed to reside in clusters at loops, and the matrix content (including clusters) of iron had increased to about 1,200 wt. ppm in the fueled region of the rod and to about half that value in the plenum region. The chromium content in the fueled region was approximately 100 wt. ppm, and the nickel content was approximately 200 wt. ppm. In the plenum region, the content of these elements was lower. However, due to an uneven distribution of clusters, there was a wide scatter in the measured concentrations in the irradiated materials. Additionally, the matrix concentrations of solute elements in (nonirradiated) Zircaloy-2 were investigated for a series of samples subjected to α annealing at 770°C followed by cooling at different rates. From these measurements, the solubilities at 770°C were estimated to be around 65 wt. ppm for chromium, at least 37 wt. ppm for iron, and below 9 wt. ppm for nickel. Slow cooling resulted in virtually no iron, chromium, or nickel in the matrix. The concentration of aluminum in the matrix was observed to be between 10 and 20 wt. ppm for all α-annealed samples and for the as-produced materials of commercial heat treatment.

The performance of Cr-coated Optimized ZIRLO™ as accident tolerant fuel cladding material for pressurized water reactors (PWRs) is assessed. The coating oxidation mechanisms, oxide stability, and the transformation of the Cr-coating/Optimized ZIRLO™ interface are among the studied phenomena. For this purpose, samples were exposed at 1200°C in steam for 3 min, 20 min and 40 min. As-fabricated coated claddings, plus specimens tested in autoclave at 415°C for 90 days in simulated PWR water chemistry were employed for comparison. Characterization techniques such as scanning electron microscopy, energy dispersive x-ray spectroscopy, electron backscattered diffraction, and transmission electron microscopy were used to determine the chemistry and crystalline structure of the various phases formed during the different exposures. When exposed to loss-of-coolant accident (LOCA) conditions for 40 min, a layer of Cr2O3 up to 8 µm thick was measured on the outer surface of the Cr-coating. No significant oxidation of the underlaying Optimized ZIRLO™ alloy occurred, and the applied coating appears to be very effective at delaying the cladding degradation under accident conditions. At the coating-substrate interface, a 1–2 µm thick layer of (Cr,Fe)2Zr Laves phase was found. The presence of this phase appears to have no detrimental effects on the coating performance, and it might play a role in slowing down the dissolution of the coating into the substrate. ZrO2 particles were frequently found at grain boundaries in the coating after exposure to LOCA conditions. For longer exposure time, these particles are expected to grow into a ZrO2-network, creating a fast diffusion path for O, and compromising the oxidation protection offered by the coating.

At high fluence and prolonged reactor operation Zr-based nuclear fuel claddings exhibit accelerated (often termed ‘breakaway’) irradiation growth, corrosion, and hydrogen pick-up. These degradation processes are correlated with the emergence of c-component dislocation loops on basal planes caused by damage from fast neutrons. We made use of the unique capabilities of atom probe tomography – namely chemical characterization with sub-nm resolution in 3D – to analyze the nano-chemistry of c-loops formed in Zircaloy-2 type cladding tubes during boiling water reactor operation. We found segregation of Fe, Ni and Sn to dislocation lines and – more surprisingly – depletion of Sn and O in the strain field of the stacking fault inside the loops, resulting in nearly pure Zr islands. We furthermore found nucleation of ZrO (‘suboxide’) inside one c-loop, pointing to a possible mechanism of accelerated in-reactor corrosion. Such pure Zr-islands might to also promote hydride precipitation and associated degradation.

In high-speed metal machining, cutting tools in the form of cemented carbide inserts coated with thin wear -resistant coatings are commonly used. These coatings are often made of metal carbonitrides with cubic rock salt crystal structure and different growth textures. However, the influence of the crystallographic texture of the coatings on their wear by plastic deformation due to the chip flow during machining needs to be revealed further. In this work, in order to analyse the ability of polycrystalline fibre-textured coatings with a rock salt structure to undergo plastic deformation, a method was developed for calculating Schmid factors of such textured coatings as a function of the loading angle of an external force. The Schmid factors were calculated for coatings with 100 and 211 growth textures, and {100} <110>, {110}<110> and {111}<110> as possible slip systems. For the {111}< 110> slip systems, the Schmid factors are not much influenced by the force angle and coating texture, which is contrary to the {100}<110> and {110}<110> slip systems. The simulations were compared to wear on the rake face of two textured Ti(C,N) coatings after short longitudinal turning tests. The variation of the degree of plastic deformation of Ti(C,N) coatings with growth texture and external force angle indicates that the dominant activated slip systems are {110}<110> using the machining conditions applied in this work.

Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray deposition process is studied. Microstructure and chemistry of this material are investigated before and after exposure to autoclave corrosion testing with scanning electron microscopy, energy dispersive spectroscopy analysis, electron backscattered diffraction, transmission electron microscopy and atom probe tomography. The results are used to assess what changes have occurred upon autoclave exposure. The formation of a compact, 80 – 100 nm thick Cr2O3 layer is observed on the surface of the exposed samples. Nucleation of ZrCr2 intermetallic phase is discovered at the Cr/Zr interface. This Laves phase nucleates inside the intermixed bonding layer that can be found in both pristine and exposed samples, and decorates the interface in the form of small particles (less than 50 nm in size). Using transmission electron microscopy and atom probe tomography the growth of a Zr-Cr-Fe phase was detected. This phase is found in the region of the Zr-substrate immediately adjacent to the coating, up to a few hundred nanometres distance from the Cr/Zr interface. A small degree of recrystallization occurs upon autoclave exposure in the 1-2 µm thick nanocrystalline layer produced on the Zr-substrate by the cold spray deposition method utilized for the fabrication of the Cr-coating.

Atom probe tomography was used in this work to study the metal close to the metal/oxide interface in the zirconium alloy Zircaloy-2 exposed to three and nine annual cycles of operation in a commercial boiling water reactor. The two exposure times correspond to before and after the onset of acceleration in corrosion, hydrogen pickup, and growth. The alloying elements Sn, Fe, Cr, and Ni were observed to be redistributed after exposure. After both three and nine cycles, clusters containing Fe and Cr and typically of a spheroidal shape with an approximate diameter of 5 nm were observed to be located in layers presumed to be layers of -loops. On average, the cluster number density was slightly higher after nine cycles, with larger and more Cr-rich clusters. However, there were large grain-to-grain variations, which were larger than the differences between the two exposure times. Ni was only occasionally observed in the clusters. Sn was observed to be slightly enriched in the Fe–Cr clusters, but the Sn concentration was higher between than inside the layers of clusters. After nine cycles, clusters of Sn were detected in regions that were depleted of Fe and Cr. Enrichment of Sn, Fe, and Ni at features that appeared to be -component loops was observed after nine cycles, whereas no such features were observed after three cycles. Enrichment of Sn and Fe, and small amounts of Cr and Ni, was observed at grain boundaries after both exposure times. After three cycles, a partially dissolved second phase particle of Zr(Fe,Cr)2 type that contained about ten times more Cr than Fe was observed.

The development of coatings for accident-tolerant fuels (ATFs) for light water reactor (LWR) applications promises improved corrosion resistance under accident conditions and better performances during operation. CrN and TiN coatings are characterized by high wear resistance coupled with good corrosion resistance properties. They are generally used to protect materials in applications where extreme conditions are involved and represent promising candidates for ATF. Zr cladding tubes coated with 5 µm-thick CrN or TiN, exposed in an autoclave to simulated PWR chemistry and BWR chemistry, were characterized with SEM, EDS, and STEM. The investigation focused on the performance and oxidation mechanisms of the coated claddings under simulated reactor chemistry. Both coatings provided improved oxidation resistance in a simulated PWR environment, where passivating films of Cr2O3 and TiO2, less than 1 µm-thick, formed on the CrN and TiN outer surfaces, respectively. Under the more challenging BWR conditions, any formed Cr2O3 dissolved into the oxidizing water, resulting in the complete dissolution of the CrN coating. For the TiN coating, the formation of a stable TiO2 film was observed under BWR conditions, but the developed oxide film was unable to stop the flux of oxygen to the substrate, causing the oxidation of the substrate.

Understanding the mechanisms at the tool/chip interface during metal cutting is crucial in the production of almost every metallic component used in engineering applications. It is critical to have rapid, durable, and reliable machining processes. This work contributes to the understanding of mechanisms occurring on the tool in the secondary shear zone, and it is focusing on the tool side of the contact. Crystallographic textured Chemical Vapor Deposited (CVD) α-Al2O3 coated cutting tools are dominating the steel turning area, as they show an increased performance compared to coatings with randomly oriented grains. In this study, we investigate the effect of three different CVD α-Al2O3 textures on the initial rake crater behavior. This was done using a turning test designed to generate crater wear only in the alumina layer, which was deposited onto an inner Ti(C,N) layer, which in turn was deposited on a cemented carbide insert. With this approach, the influence of the underlying coating layer and substrate was reduced. Pre- and post-machining characterization of the different contact areas on the surfaces of the three textured CVD α-Al2O3 coatings, (0001)(0001), (011‾2) and (112‾0), was performed using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and energy dispersive X-ray spectroscopy (XEDS). Plastic deformation, micro-rupture, abrasion and chemical reactions with the workpiece material are all identified as mechanisms involved in crater formation during turning. For the (0001)-textured coating, the observed low wear-rate is attributed to homogeneous basal-slip dominating plastic deformation, while for the (011‾2) and (112‾0) textures the main deformation mechanisms are attributed to heterogeneous plastic deformation, causing micro-rupture and abrasion, leading to higher wear-rates. The effect of a larger coating grain size is mainly seen as the formation of wider ridges and valleys, while the effect on wear rate was limited.

In this work, Ti1-xAlxN (TiAlN) coatings were synthesized by low pressure chemical vapour deposition (LPCVD), and the influence of a rotational precursor gas supply on the coating microstructure was studied. The microstructure of the TiAlN coatings were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and electron backscattered diffraction (EBSD). It is shown that a rotational precursor gas supply induces an oscillatory surface reaction, which causes a nanolamella architecture. When the gas beam directly hits the sample, the local gas flow velocity is high, which increases the deposition rate of Ti and a Ti(Al)N lamella is formed. When the gas beam rotates away, the local gas velocity is low, so the deposition rate of Ti decreases, and an Al(Ti)N lamella is formed. As this is repeated a periodic nanolamella architecture is formed. The nanolamellae grow epitaxially on three {001} facets of the 111 textured grains, which leads to a pyramidal surface morphology. Without gas supply rotation, a high Al content cubic phase was still obtained, but no nanolamella was formed. This indicates that Ti-rich lamellae are not necessary to stabilize an Al-rich cubic TiAlN phase. In addition, spinodal decomposition is not likely to be the driving force behind the nanolamella formation in LPCVD TiAlN, as this would also have happened in the sample without a rotational gas supply. Finally, the nanolamella periodicity is found to be tunable via controlling the rotation speed of the precursor supply relative to the coating growth rate.

This study is complementary to previous atom probe tomography (APT) studies of irradiation effects in the zirconium alloy Zircaloy-2. Using APT in voltage pulse mode, a difference in morphology was observed between clusters of Fe and Ni and clusters of Fe and Cr in Zircaloy-2 exposed to a high fast neutron fluence in a commercial boiling water reactor. The Fe–Ni clusters were disc-shaped with a diameter of 5–15 nm, whereas the Fe–Cr clusters were spheroidal with a diameter of approximately 5 nm. Both types of clusters appeared to be located at irradiation-induced -type dislocation loops aligned in layers normal to the -direction. The concentration of Fe was higher in the Fe–Cr clusters than in the Fe–Ni clusters. The dilute Fe–Ni clusters, which seem to be segregation of Fe and Ni inside the loops, had formed on all three families of first-order prismatic planes with some deviation from perfect -axis alignment. The Fe–Cr clusters might be very small precipitates with a nucleation associated with the loops.