Zirconium carbide (ZrC) is a candidate material for extreme environments due to its exceptional thermal and mechanical properties. However, its oxidation behavior, particularly the formation of the Zr–C–O layer, requires further clarification. In this study, we investigated the oxidation of spark plasma sintered ZrC under varying temperatures and oxygen partial pressures, revealing a double-layer oxide scale. At the interface between ZrC and the Zr–C–O layer, we identified previously unreported oxidation front stripes composed of cubic zirconia, along which elliptical submicropores formed, suggesting preferential CO₂ release pathways. The Zr–C–O layer itself was significantly enriched with amorphous free carbon. Based on these findings, we developed a phenomenological model that incorporated the formation of the compact Zr–C–O layer to predict oxide scale growth. This multiscale approach provides new insights into ZrC oxidation mechanisms and supports the design of oxidation-resistant ceramics for aerospace and nuclear applications.

The sensitivity of the single-phase, low thermal expansion (LTE) alloy 36 (Fe-36Ni) to intergranular cracking hinders its processability during additive manufacturing. This study investigates the effect of accelerated cooling via a CO₂ jet and the addition of TiC particles on the cracking susceptibility of the LTE36 alloy during wire-arc additive manufacturing (WAAM). Results show that accelerated cooling reduces inter-pass deposition times and the susceptibility to cracking due to increased heat dissipation. A crack-free microstructure was achieved only with the addition of TiC particles, which pinned the high-angle grain boundaries and induced tortuosity, thereby limiting grain growth and mitigating intergranular cracking. Mechanical performance was restored compared to the cracked condition, and the critical LTE property of the as-deposited LTE36 alloy was improved due to the enhanced ferromagnetic character of the alloy. Therefore, the combined approach effectively mitigated intergranular cracking while retaining the LTE behaviour during WAAM of the LTE36 alloy.

Successful implementation of third generation advanced high strength steels (3rd gen AHSS) can be accelerated by developing steels that can be heat treated in existing industrial lines. Here, we develop new carbide free bainitic (CFB) steels in which bainite formation is accelerated by a 0.2 volume fraction of prior martensite and thus can be realized in 5 min, making them suitable for manufacturing in modern continuous annealing lines for bare steel strips. The resulting microstructure consists of bainitic ferrite, tempered martensite, and retained austenite. Carbon and silicon had the most pronounced effect on the mechanical properties among the studied alloying elements (manganese, niobium, chromium, and molybdenum) because of their influence on the fraction and stability of retained austenite. Our proposed treatment, which we call bainite accelerated by martensite (BAM), showed higher strength and lower global formability than traditional CFB without prior martensite (also called TRIP-assisted bainitic ferrite, TBF) and quenched and partitioned (Q&P) steels. Five of the designed steels showed tensile strength higher than 1370 MPa, a total elongation higher than 8%, and hole expansion capacity higher than 30%, and thus meet the requirements for the strongest commercial grades of complex phase steels with improved formability. This work broadens the possibilities of using existing industrial lines for manufacturing novel 3rd gen AHSS.

An oxide dispersion strengthened (ODS) steel with nominal composition Fe–14Cr–2W–0.4Ti–0.3Y₂O₃ (wt%) has been manufactured by mechanical alloying of pre-alloyed powders with nanosized Y₂O₃, compacted by hot isostatic pressing and hot cross rolled. In order to evaluate the long-term thermal resistance of the alloy, it has been subjected to 2000 h of thermal aging at 873 K, which is a relevant temperature for nuclear reactor applications. A thermodynamic equilibrium simulation indicates the precipitation of Laves phase under the aging parameters used. This prediction is confirmed from the detailed multi-technique characterization performed. Before aging, Ti-rich oxides, Cr-W-rich precipitates (M₂₃C₆ type) and a homogeneous Y-rich nanoprecipitate dispersion are observed. After aging, some W-rich precipitates are identified as Laves phase, while M₂₃C₆ carbides, Ti-rich oxides and Y-rich nanoprecipitates remain stable. Mechanical characterization performed in a previous research showed higher hardness, a loss of total elongation and a slight shift of the ductile-to-brittle transition temperature (DBTT) towards a higher value after aging, with similar strength values before and after the long-term thermal treatment. These changes can be due to the redistribution of precipitates together with the Laves phase formation. The mechanical properties not being dramatically affected seem to be due to the observed stability of Y-rich nanoprecipitates distribution.

Superelastic metallic materials possessing large recoverable strains are widely used in automotive, aerospace and energy conversion industries. Superelastic materials working at high temperatures and with a wide temperature range are increasingly required for demanding applications. Until recently, high-temperature superelasticity has only been achievable with multicomponent alloys fabricated by complex processes. In this study, a novel framework of multi-scale models enabling texture and microstructure design is proposed for high-performance NiTi fabrication via laser powder bed fusion. Based on the developed framework, a Ni-lean Ni(49.4 at.%)-Ti alloy is, for the first time, endowed with a 4% high-temperature compressive superelasticity. A 001 texture, unfavorable for plastic slip, is created to realize enhanced functionality. The unprecedented superelasticity can be maintained up to 453 K, which is comparable with but has a wider superelastic temperature range (∼110 K) than rare earth alloyed NiTi alloys, previously only realizable with grain refinement, and other complicated post-processing operations. At the same time, its shape memory stability is also improved due to existing textured 100 martensite and intergranular precipitation of Ti₂NiOx. This discovery reframes the way that we design superior performance NiTi based alloys through directly tailoring crystallographic orientations during additive manufacturing.

For Pd thin films, microstructural changes involved during hydrogen cycling provide the information needed to predict and optimize the film's mechanical strength. In this paper, a systematic study of the morphology, microstructure, texture, and stress has been performed on Pd thin films during hydrogen loading and deloading cycles at room temperature. Pd thin films of similar morphology were prepared by magnetron sputtering on substrates of different compliances, i.e., Si-oxide, Titanium (Ti) and Polyimide (PI). The evolution of the morphology, grain-orientation distribution (texture), state of stress, and dislocation densities are analyzed for each of the film substrate types for 20 hydrogen loading/deloading cycles. The lattice expansion and contraction caused by the transition from Pd to Pd-hydride and back result in a strong stress increase. This stress increase stabilizes after a few cycles by grain boundary motion that leads to a gradual enhancement of the (111) texture and changes in the dislocation density for Pd films that are strongly clamped on to an oxidized Si(100) wafer substrate with an intermediate layer (Ti or PI). For Pd on PI, the stress is also partly released by a crack-based (crack widening/growth/propagation) pathway. Pd films on Ti and PI do not buckle or blister after 20 hydrogen cycles. By providing a sufficiently compliant substrate the traditional problems of buckle-delamination of a film on a stiff substrate are mitigated.

Laser powder bed fusion (L-PBF), categorized as additive manufacturing technique, has a capability to fabricate NiTi (Nitinol) shape memory alloys with tailorable functional properties and complex geometries. An important processing parameter, hatch distance (h), is often related to macroscale structural defects; however, its role on controlling the microstructure and functional properties is usually underestimated in L-PBF of NiTi. In this work, equiatomic NiTi (50.0 at% Ni) parts were fabricated with various hatch distances to tailor the microstructure and their shape memory characteristics. Contrary to what is observed in Ni-rich NiTi alloys, in this work, we demonstrate that phase transformation temperatures of L-PBF equiatomic NiTi do not decrease proportionally with hatch distance but rather relate to a critical hatch distance value. This critical value (120 μm) is derived from the synergistic effect of thermal stress and in situ reheating. Below this value, epitaxial grain growth and in situ recrystallization are enhanced, while above, irregular grains are formed and dislocations induced by thermal stresses decrease. However, the critical value found herein is characterized by high dislocation density and fine grain size, resulting in a superior thermal cyclic stability. The proposed finite element model is proven to be an effective tool to understand and predict the effect of hatch distance on grain morphology and dislocation density evolutions in L-PBF NiTi SMAs. In the present study, we provide a comprehensive understanding for in situ controlling L-PBF NiTi microstructure and functional characteristics, which contributes to designing 4-dimensional shape memory alloys.

Sr is known to transform the morphology of the eutectic silicon phase as well as the Fe-rich β phase in Al-Si alloys, improving their mechanical properties. However, little is known about the effect Sr has on the (local) corrosion properties of aluminium alloys. This study investigates the effect of Sr addition to a modified AA3003 heat exchanger material on the morphology of the different phases present, especially the Fe-rich phases, as well as on the (local) corrosion properties of this material. This work reports the formation of a Sr-rich phase, which slightly increases the macrohardness of the material. The Fe-rich phases are not shown to be refined/influenced by the addition of Sr Potentiodynamic polarization experiments showed an increase in pitting potential by increasing the amount of Sr in the material up to 0.4 wt.%. Nevertheless, the analysis of the corrosion morphology revealed that the Sr-containing particles did not contribute to the corrosion process despite their cathodic behaviour compared to the Al matrix as measured by Scanning Kelvin Probe Force Microscopy. This behaviour was attributed to the thicker oxide layer found on the Sr-rich particles.

Recently, lattice titanium manufactured by additive manufacturing (AM) techniques has been utilized in various applications, including biomedical. The effects of topological design and processing parameters on the fatigue behaviour of such meta-biomaterials have been studied before. Most studies show that the fatigue life of additively manufactured lattice structures is limited. Post-processing techniques could play a major role in improving the fatigue of these promising biomaterials. This study aims to provide an in-depth investigation into the effects of heat treatments, hot isostatic pressing (HIP), sand blasting, and chemical etching on the microstructure, surface morphology, strength and fatigue resistance of selective laser melted titanium meta-biomaterials. It was found that the combination of microstructural design and surface engineering, induced by HIP and sand blasting respectively, allows to increase the endurance limit of these lattice meta-biomaterials by a factor of two. HIP treatment substantially decreased the internal porosity and transformed the microstructure to a more ductile mixture of α + β phases. Sand blasting allowed to eliminate surface imperfections and induced favourable compressive stress in the surface layer of the struts. Statement of Significance: Additively manufactured metallic meta-biomaterials are progressively being used as bone replacement orthopedic implants. While there is a great amount of research related to topological designs and their effect on mechanical (e.g. stiffness), physical (e.g. mass transport), and biological (e.g. osseointegration) properties, fatigue lifetime of such structures remains limited. This study provides fundamental investigation into the combined effect of microstructural design and surface engineering of titanium meta-biomaterial, enabled through various post treatment methods ranging from heat treatments to physical and chemical surface modifications. The findings show that fatigue life is significantly improved by applying developed herein novel method, which effortlessly can be used on other bone-mimicking metallic meta-biomaterials.

By means of high-energy synchrotron X-ray diffraction, the interplay between martensite and retained austenite phases in steel during the application of stress has been analyzed. Martensite properties were varied through controlled reheating heat treatments in a low carbon Quenched and Partitioned (Q&P) steel consisting of retained austenite and martensite. The reheating treatments significantly altered martensite strength while keeping the same fractions of retained austenite as the non-reheated Q&P microstructures, resulting in different degrees of stress partitioning and work hardening of the individual microconstituents. Results of this study show that the strength ratio between the different phases in the microstructure plays a crucial role in the onset and rate of mechanically induced decomposition of retained austenite. Consequently, the strength ratio between phases controls the yielding and work-hardening of the material.

The role of retained austenite on tensile behavior in quenched and partitioned (Q&P) steels has been studied extensively, but the deformation behavior of martensite, which comprises the majority of Q&P microstructures, has received less attention. In this investigation, martensite properties were varied through heat treatment in a low carbon Q&P steel consisting of retained austenite and martensite. Additional conditions were produced by reheating the Q&P steel to 450 °C for 30 min or to 700 °C followed immediately by quenching. The reheated microstructures contained similar fractions of retained austenite as the non-reheated Q&P microstructures, but reheating tempered the martensite, thereby decreasing martensite dislocation density. The reheated conditions had a lower yield stress and initial work hardening rate than the non-reheated Q&P condition. However, the reheated conditions had a greater work hardening rate at larger strains and greater uniform strain due to less stable retained austenite. Furthermore, the tensile strength of the condition reheated to 450 °C was nearly equal to the non-reheated condition. In addition to retained austenite to martensite transformation, the early stage work hardening rate of martensite is critical to ductility and is dependent on martensite dislocation density, which can be decreased through tempering.