Investigating the Influence of Cold Rolling on Precipitation in Industrial AA2024 using Advanced Microscopy Techniques

Precipitation hardened aluminium alloys are widely used for various applications due to their properties, such as low density to strength ratio and high corrosion resistance. AA2024 is a commonly used aluminium alloy in the aerospace industry with a quite simple precipitation sequence including co-cluster and Guinier-Preston-Baragyatski (GPB) zone formation during natural ageing and precipitation of the equilibrium S-phase (Al2CuMg) during artificial ageing [1]. This study aims to investigate the influence of pre-deformation by cold rolling (CR) on subsequent precipitation during artificial ageing in industrial AA2024. Electron backscatter diffraction (EBSD) was used to analyse the deformation microstructure focusing on the arrangement of dislocation substructures. Atom probe tomography (APT) and differential scanning calorimetry (DSC) were used to characterize co-clusters in naturally aged AA2024-T3, showing that they are destroyed during cold rolling and not reconstituted during subsequent natural ageing. Precipitates evolution during artificial ageing of cold-rolled (CR) samples was investigated by transmission electron microscopy (TEM). Hence, although heteregenous nucleation on dislocation was observed, the precipitates appear with a spacially homogeneous distribution at peak hardness (Fig. 1). Dark-field imaging and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography were performed to study the size distribution and three-dimensional arrangement of the S-phase precipitates. A refinement of precipitates in the preveously cold-rolled samples was observed, connected to changes in the aspect ratio of precipiates. The study demonstrates how advanced microscopy techniques contribute to understanding of microstructural changes and precipitation behaviour in aluminium alloys and therefore contribute to the development of novel production processes

Advanced microscopy techniques for investigation of the precipitation in pre-strained Al-Cu-Mg alloy (AA2024)

Age-hardenable Al–Cu–Mg alloys are widely used for various applications due to their properties, such as low density to strength ratio and increased corrosion resistance. The commercial 2024 aluminium alloy (AA2024) is one of the most used alloys in aircraft manufacturing with a quite simple precipitation sequence including co-clusters and Guinier-Preston-Baragyatski (GPB) zones formed during natural ageing and precipitation of the equilibrium S-phase (Al2CuMg) during artificial ageing. This study aims to investigate the impact of pre-straining, performed by cold rolling, on precipitation of the S-phase in AA2024. First, the deformation microstructure, mainly the arrangement of dislocation substructures, was analysed using electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Atom probe tomography (APT) and differential scanning calorimetry (DSC) were further used to characterize co-clusters in naturally aged AA2024-T3 after subsequent cold rolling, showing that they are destroyed during pre-straining and not reconstituted during following natural ageing. Evolution of S-phase precipitates during artificial ageing of cold-rolled (CR) samples was investigated by transmission electron microscopy (TEM) modes. Hence, despite initial dominant heterogeneous nucleation due to dislocations induced by the cold rolling, the precipitates of S-phase were distributed homogeneously at peak hardness. To explain this result, in situ heating was performed in TEM and mechanisms of nucleation and growth of S-phase precipitates in cold-rolled samples were investigated. The size distribution of S-phase precipitates was investigated using dark-field imaging. A refinement of precipitates was observed due to cold rolling with changes in the aspect ratio. Refinement and homogeneous distribution of S-phase precipitates in cold rolled samples after further artificial ageing were confirmed as well by electron tomography. The study demonstrates the valuable contribution of combined advanced microscopy techniques to understand microstructural changes and precipitation behaviour in aluminium alloys and therefore contribute to the development of novel production processes

Intrinsic heterogeneity of grain boundary states in ultrafine-grained Ni: a multi-level study by SIMS and radiotracer analyses

International audienceUltra-fast diffusion rates were largely reported in ultrafine-grained (UFG) materials procuded by severe plastic deformation (SPD) and were explained by the formation of specific non-relaxed high-angle "deformation-modified" grain boundaries exhibiting an increased free energy density, higher diffusion rates and a significant residual microstrain [1]. The increase of the grain boundary (GB) diffusion coefficients accounts for one to several orders of magnitude with respect to relaxed interfaces with similar misorientation characteristics [1]. In this work, using both radiotracer and SIMS techniques [2] Cr diffusion in UFG Ni was investigated at low temperatures ranging from 403 to 603 K and a whole spectrum of possible grain boundary states was addressed. The combination of the two methods provided unprecedented insights into structure properties relationships in severely deformed Ni. Abnormally high diffusion rates of Cr are measured and the presence of the deformation-modified state of a fraction of the high-angle GBs is verified. For the first time, a co-existence of relaxed and deformation-modified high-angle GBs in UFG Ni is unambiguously established, addressing the different interfaces by different techniques on the same samples. The temperature/time evolution of the deformation-modified state of high-angle GBs is followed by dedicated measurements of the atomic transport and the microstructure characteristics. The combination of the two complementary techniques allows a unique cross-scale multi-level characterization of the grain boundary diffusion properties spread over a large number of orders of magnitude in the same material.References[1] X. Sauvage, G. Wilde, S.V. Divinski, Z. Horita, R.Z. Valiev, Materials Science and Engineering: A. 540 (2012) pp. 1-12. [2] D. Gärtner, L. Belkacemi, V.A. Esin, F. Jomard, A.A. Fedotov, J. Schell, J.V. Osinskaya, A.V. Pokoev, C. Duhamel, A. Paul, S.V. Divinski, Diffusion Foundations. 29 (2021) pp. 31-73

Meta-analysis of chemotherapy in head and neck cancer (MACH-NC): An update on 107 randomized trials and 19,805 patients, on behalf of MACH-NC Group

Background and purposeThe Meta-Analysis of Chemotherapy in squamous cell Head and Neck Cancer (MACH-NC) demonstrated that concomitant chemotherapy (CT) improved overall survival (OS) in patients without distant metastasis. We report the updated results.Materials and methodsPublished or unpublished randomized trials including patients with non-metastatic carcinoma randomized between 1965 and 2016 and comparing curative loco-regional treatment (LRT) to LRT + CT or adding another timing of CT to LRT + CT (main question), or comparing induction CT + radiotherapy to radiotherapy + concomitant (or alternating) CT (secondary question) were eligible. Individual patient data were collected and combined using a fixed-effect model. OS was the main endpoint.ResultsFor the main question, 101 trials (18951 patients, median follow-up of 6.5 years) were analyzed. For both questions, there were 16 new (2767 patients) and 11 updated trials. Around 90% of the patients had stage III or IV disease. Interaction between treatment effect on OS and the timing of CT was significant (p < 0.0001), the benefit being limited to concomitant CT (HR: 0.83, 95%CI [0.79; 0.86]; 5(10)-year absolute benefit of 6.5% (3.6%)). Efficacy decreased as patients age increased (p_trend = 0.03). OS was not increased by the addition of induction (HR = 0.96 [0.90; 1.01]) or adjuvant CT (1.02 [0.92; 1.13]). Efficacy of induction CT decreased with poorer performance status (p_trend = 0.03). For the secondary question, eight trials (1214 patients) confirmed the superiority of concomitant CT on OS (HR = 0.84 [0.74; 0.95], p = 0.005).ConclusionThe update of MACH-NC confirms the benefit and superiority of the addition of concomitant CT for non-metastatic head and neck cancer