The degradation of CuCr1Zr electrodes during resistance spot welding (RSW) is a critical issue in the automotive industry, primarily driven by microstructural softening at the electrode tip. While electrode thermal cycles during RSW are well-documented, the role of electromigration - induced by high intensity electric currents - on the evolution of precipitation, grain structure, and mechanical properties remains poorly understood. This study investigates the microstructural and nanomechanical responses of a precipitation-hardened CuCr1Zr alloy subjected to sub-critical annealing treatments at 500 degrees C, 600 degrees C, and 700 degrees C, using for the first time three distinct heating modes: conventional radiative heating, direct current (DC), and pulsed current (PC) Joule heating. Using CuCr1Zr/steel/CuCr1Zr sandwich-type samples to simulate electrode aging in RSW conditions, we employ nanoindentation, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) to characterize the evolution of nanohardness, precipitate distributions, and grain boundary structures. Our results reveal a first-order temperature dependence of alloy softening, consistent with previous studies on thermal aging. However, electromigration induced by DC and PC significantly enhances the precipitation of fine (100-200 nm) particles at 500 degrees C, a phenomenon not observed under conventional heating. At 700 degrees C, twinning-assisted recrystallization occurs across all annealing modes, but electromigration - particularly under pulsed current - promotes a higher fraction of Sigma 3 twin boundaries, suggesting an acceleration of grain boundary mobility. The hardness reduction at 700 degrees C is most pronounced under pulsed current (31% decrease relative to the as-received state), compared to 25% and 23% for DC and radiative heating, respectively. These findings highlight the role of current-induced atomic diffusion in microstructural evolution, with implications for electrode lifespan and RSW process optimization.

Precipitation kinetics of Al3Mg2 in Al-Mg binaries and Al-Mg-Sc-Zr alloys were studied during artificial ageing in the range [170 degrees C-250 degrees C], with the aim to determine the influence of Al3(Sc, Zr) dispersoids on Mg precipitation and resistance to corrosion. A calibration with model alloys enabled a quantitative determination of the evolution of Mg content in solid solution which was coupled with APT measurements performed on samples aged for a long time. Precipitate morphology and distribution were analyzed via SEM and TEM techniques, identifying two phases, /3' and /3. The /3 phase is known to form a continuous network of precipitates on grain boundaries, making it sensitive to corrosion. Corrosion tests using nitric acid mass loss on aged samples demonstrated the role of Al3(Sc, Zr) dispersoids in enhancing intergranular corrosion resistance. Results showed mass losses 4.5 times higher for the Al-Mg alloy compared to the alloy containing dispersoids. To illustrate the contribution of different nucleation sites and thus their role in corrosion resistance, the competition between homogeneous and heterogeneous nucleation of Al3Mg2 was modeled based on Classical Nucleation and Growth Theories (CNGTs). Overall, this study, shows that Al3(Sc, Zr) dispersoids accelerate the precipitation kinetics of Al3Mg2 by a decade by lowering the nucleation energy barrier, thereby improving the sensitization resistance of Al-Mg alloys.

In this study, through electron-beam powder bed fusion additive manufacturing, we prepared Co–27Cr–6Mo (wt.%) alloys with different C concentrations up to the eutectic composition (~2.5 wt.%). The Rockwell hardness of the as-built alloy specimens increased linearly with an increase in the carbon concentration, reaching approximately 60 HRC at 2.5 wt.% C. The as-built 2.5C alloy contained a fine carbide network consisting of M7C3- and M23C6-type carbide phases. Increasing the carbon concentration not only increased the carbide fraction and changed the carbide phases but also altered the solidification behavior from cellular at low carbon concentrations to dendritic and finally to eutectic. Quantitative X-ray tomography revealed that carbon addition also affected the gas pore behavior in the melt pool, significantly reducing the porosity when a flat solid/liquid front existed upon solidification (i.e., planar and eutectic). The developed high-carbon alloys cannot be obtained through conventional metal processing; hence, this study opens new avenues for industrial applications of additive manufacturing.

The state of bone tissue around dental implants is a crucial factor influencing their early clinical outcomes. Currently, this state is mainly defined by its primary stability, both in terms of biomechanical analysis and clinically. The clinical methods used for quantifying this stability-such as the Implant Stability Quotient (ISQ) and Insertion Torque (IT)-are indirect measures. While these methods provide insights into the overall mechanical behavior of the bone-implant system, they do not account for the impact of implant morphology on the surrounding bone. The method presented here aims to analyze the peri-implant bone using image analysis and volume correlation techniques combined with computed tomography to assess the bone strain field and densification resulting from dental implant placement. The study utilized two types of implants with distinct designs-one cylindrical and the other self-tapping-on five iliac crest bone samples harvested from butcher pigs. The results indicated that the self-tapping implant caused significantly greater bone densification near the implant compared to the cylindrical one (46% of densification in the first 30 μm, against 21% for cylindrical implant). Additionally, the volume of strained peri-implant bone appeared to be larger for the self-tapping implant (38% of the volume was mechanically affected above 0,5% VM strains for self-tapping implant, against 31% for the cylindrical implant), though this difference was not statistically significant. Furthermore, established descriptors from the literature struggled to effectively differentiate between the two implant types. Despite the study's limitations, the proposed method shows promise for distinguishing implants based on the densification and deformation of peri-implant bone, and can serve as a complementary approach to standard ISQ and IT measurements.

Austenitic steel was the reference cladding material in sodium cooled fast neutron nuclear reactors. These alloys exhibit good high temperature mechanical properties and they can withstand very high irradiation doses. To further increase the performance of these alloys, two distinct ways of improvement are possible: oxides dispersion strengthening or ultra fine grain microstructure. In order to achieve the desired enhanced material, powder metallurgy and in particular mechanical alloying route is promising. However, the high ductility of austenitic steel significantly reduces the powder production yield and worsens the supersaturation of oxides during mechanical alloying. To overcome this issue, multiple batches were produced using high-energy horizontal attritor at times ranging from 5 to 40 hours and consolidated by Spark Plasma Sintering (SPS). This paper tackles the characterization of powders after mechanical alloying and SPS compacts.

Biocompatible titanium-based bulk metallic glasses (Ti-based BMGs) are attractive for application in minimally invasive medical devices. They present a desirable set of properties, including low Young's modulus (E approximate to 100 GPa) and high yield strength (sigma approximate to 2000 MPa). However, their implementation into practical applications is in part hindered by their limited glass forming ability (GFA) compared to BMG systems already commercialised. Due to their limited GFA, Ti-BMGs are more susceptible to crystallisation. This study investigates the crystalline heterogeneities found in Ti40Zr10Cu36Pd14 (at.%) glasses cast in automated equipment operating under close-toindustrial conditions. Distinct categories of crystallites are identified through microstructural observations and statistical analyses. Insight is provided on the complex crystallisation pathways that may be followed during cooling. Beyond the scientific contribution, the results indicate directions for the development and improvement of the manufacturing of Ti40Zr10Cu36Pd14.

Thin films of molybdenum (Mo) were grown on aluminium nitride (AlN) substrates by pulsed laser deposition for heat sink applications. The effect of experimental growth parameters on the films ' structural properties were investigated by Scanning Electron Microscopy, X -Ray Diffraction and Atomic Force Microscopy. Thermal characterization was achieved by measuring the in -plane thermal diffusivity of the grown layers by means of a photothermal beam deflection technique using an IR heating laser. Within the experimental parameters studied in this work, a substrate temperature of 600 & ring;C and an ambient argon gas pressure of 10 mTorr were identified as the optimal growth conditions for the synthesis of smooth and well -crystallized Mo layers. Concurrently, the thermal diffusivity of the films is significantly affected by film growth parameters. Under the optimal growth conditions, a thermal diffusivity value as high as 5.42x10 -5 m 2 /s was measured, a value that is very close to that of bulk Mo, and which would be a result of the synthesis of polycrystalline Mo films whose grains ' size is greater than the heat carriers mean free path, namely the free electrons. The temperature dependence of the thermal diffusivity was also investigated, and the films were found to be stable up to an operating temperature of 200 degrees C. Beyond this temperature, photothermal beam deflection imaging shows the onset of film delamination from the underlying substrate.

Due to their outstanding elastic limit, biocompatible Ti -based bulk metallic glasses (BMGs) are candidate materials to decrease the size of medical implants and therefore reduce their invasiveness. However, the practical use of classical Ti-BMGs in medical applications is in part hindered by their high copper content: more effort is thus required to design low -copper Ti-BMGs. In this work, in line with current rise in AI -driven tools, machine learning (ML) approaches, a neural -network ML model is used to explore the glass -forming ability (GFA) of unreported low -copper compositions within the biocompatible Ti-Zr-CuPd system. Two types of models are trained and compared: one based on the alloy composition only, and a second based on various features derived from the alloying elements. Contrary to expectation, the predictive power of both models in evaluating GFA is similar. The compositional space identified by ML as promising is experimentally assessed, finding unfortunately low GFA. These results indicate that the ML approach may be premature for specific composition tuning of amorphous metallic materials. We emphasise that the development of ML tools in GFA prediction requires an improvement of the dataset, in terms of homogeneity, size and GFA descriptors, which must be supported by increased reporting of high -quality experimental GFA measurements, both positive and negative.

Modelling the microstructural evolutions and mechanical properties during the tempering of Dual Phase steels is a key objective for industrials as this phenomenon has a strong impact on the final properties. After having determined the tempering kinetics of fully martensitic steels between 100°C and 550°C using thermoelectric Power and hardness measurements, time–temperature equivalences were applied to determine the activation energies of the mechanisms controlling martensite tempering. Two tempering stages were clearly identified and thanks to the use of TEM, SEM and tomography techniques, they could be attributed to cementite precipitation, its spheroidization and recovery phenomena. The second stage was found to be retarded with increasing the manganese content of the steel contrary to the first stage. From these studies, a JMAK model was developed to predict the microstructurals evolutions during tempering. Then, an extension of the Hybrid-mean Field Composite model developed in a previous paper to predict the tensile curves of fresh martensite was proposed to take into account the microstructural evolutions of martensite during tempering. The model was tested for a wide range of physical parameters of the microstructure (phase fraction and chemical composition) and for different tempering heat treatments and gave good agreement with experimental tensile curves.

The influence of the electric current on the diffusion of carbon in an ARMCO iron sample is studied. The sample, placed between two graphite punches, is heated in the intercritical domain (between 736 °C and 912 °C) thanks to Joule heating. The diffusion of C in ferrite induces its transformation into austenite. After cooling, the microstructure of the sample gives information on the transformation fronts positions and C concentration profiles. The transformation front velocity is higher in the direction of the electric current and lower in the opposite direction. To understand and predict this phenomenon, a new model accounting both for the allotropic phase change and the electromigration of C in iron is proposed. Some model parameters are fitted comparing the predicted and the measured interface positions. With these parameters, the simulated C concentration profile is in good agreement with the experimental one.

Versatility of powder metallurgy was used to design new duplex and compositionally graded steels. Rapid consolidation by Spark Plasma Sintering (SPS) and longer consolidation by Hot Isostatic Pressing (HIP) were applied on two austenitic 316L and martensitic Fe-9Cr powders, either homogeneously blended or uniaxially graded before sintering.The microstructural investigations by micro-hardness, SEM, EDX and EBSD showed a continuous crystal-lographic structure at the austenite-martensite interface and a similar grain size in SPS and HIP samples, whereas a larger interdiffusion length of Cr and Ni was observed in the HIP sample, as confirmed by diffusion calculations. The tensile behaviour of materials could not be described by a simple law of mixtures. To better understand this phenomenon, the obtained materials were described as a composite and iso-strain and iso-stress models were used and discussed. The microstructural characterizations show that during the consolidation, diffusion of the chemical species modifies the nature and the respective fractions of phases, which explains the discrepancy between the models and the experimental mechanical behaviour of the duplex alloys.

One of the limitations to the use of certain bulk metallic glasses is related to the formation of crystalline zones or defects, often called “spherulites”, during the casting process. In the case of Ti 40 Zr 10 Cu 36 Pd 14 (at.%) metallic glass, which is a candidate for biomedical applications, spherulites of diameter up to few hundreds of microns were previously reported, but their crystallographic features and their role in the mechanical behavior and the corrosion resistance remain to be determined.In this work, a detailed description of the microstructure of spherulites is provided. Tensile, compression and fatigue tests were carried out. In addition, corrosion behavior was studied by global and local electrochemical measurements. The spherulites have a deleterious effect on the tensile and fatigue strength of the alloy, even if it retains properties that are far superior to conventional crystalline materials. The electrochemical studies do not show any difference in potential between the spherulite and the amorphous matrix, which indicates that the presence of spherulites is probably not the direct cause of the pitting phenomenon observed, which is unfortunately a clear drawback of this alloy when considering implants.

An X-ray tomography setup is developed in this work in order to characterize liquid metal embrittlement (LME) cracks and internal defects in 3D in homogeneous advanced high strength steel resistance spot welds, non destructively. For the first time, the propagation of the LME inner crack could be monitored in the course of ex situ tensile shear loading. While propagating in a stable way through the sheet thickness in the vicinity of the weld nugget, the LME inner crack does not modify the final fracture path, all investigated welds failing at the faying surface (full interfacial failure type).

A thermodynamic prediction model of the austenite-to-martensite phase transformation kinetics and of the martensitic transformation start temperature ( $$ M_{{\text{s}}} $$ ) has been developed. A strong drop in $$ M_{{\text{s}}} $$ temperature was experimentally observed on a state containing 60 pct martensite. The classical hypothesis of austenite carbon enrichment and grain size refinement on the $$ M_{{\text{s}}} $$ temperature is not sufficient to explain this drop. The partitioning of substitutional elements at the interface is responsible for the phase transformation delay. Two heat treatments have been proposed to obtain a different partitioning at the interface for an identical phase fraction. A coupling of the $$ M_{{\text{s}}} $$ temperature prediction model with a phase transformation prediction model allowed reproducing the experimental results. Finally, the prediction of the martensitic transformation kinetics was validated compared to the experimental kinetics.

An advanced tracking algorithm based upon 4D X-ray tomographic data was developed to enable a more robust and full field approach to ductile damage characterisation. By following each individual void, the three ductile damage mechanisms (void nucleation, void growth and void coalescence) could be separated and be studied in more detail, with enriched 4D information available for each of the three damage mechanisms. Here, a successful application of the developed tracking algorithm on a pure iron sample is presented. Two different notch geometries were chosen for the demonstration of analysis technique to further study the influence of triaxiality on ductile damage.

The use of different steel powders allows to obtain either multi-material junctions, when they are stacked, or new duplex alloys when they are blended.This study focuses on new materials obtained by Spark Plasma Sintering (SPS) or Hot Isostatic Pressing (HIP) with an austenitic 316L steel and a martensitic Fe-9Cr steel powders. These materials are characterized at different scales: from metallography to electron microscopy with EDX and EBSD, hardness and tensile tests.The mechanical behaviour of materials cannot be described by a simple law of mixtures. To better understand this phenomenon by describing the obtained materials as a composite, Reuss and Voigt models are used and discussed.The microstructural characterizations show that during the consolidation, the diffusion of the chemical species modifies the nature and the amount of phases, which makes it possible to understand why the models do not completely account for the experimental behaviour.