Extreme conditions research using the large-volume press at the P61B endstation, PETRA III

High-Entropy Alloys and Their Affinity with Hydrogen: From Cantor to Platinum Group Elements Alloys

Properties of high-entropy alloys are currently in the spotlight due to their promising applications. One of the least investigated aspects is the affinity of these alloys to hydrogen, its diffusion, and reactions. In this study, high pressure is applied at ambient temperature and stress-induced diffusion of hydrogen is investigated into the structure of high-entropy alloys (HEA) including the famous Cantor alloy as well as less known, but nevertheless important platinum group (PGM) alloys. By applying X-ray diffraction to samples loaded into diamond anvil cells, a comparative investigation of transition element incorporating HEA alloys in Ne and H2 pressure-transmitting media is performed at ambient temperature. Even under stresses far exceeding conventional industrial processes, both Cantor and PGM alloys show exceptional resistance to hydride formation, on par with widely used industrial grade Cu-Be alloys. The observations inspire optimism for practical HEA applications in hydrogen-relevant industry and technology (e.g., coatings, etc), particularly those related to transport and storage.

Crystal structures of two new high-pressure oxynitrides with composition SnGe4N4O4, from single-crystal electron diffraction

SnGe4N4O4 was synthesized at high pressure (16 and 20 GPa) and high temperature (1200 and 1500°C) in a large-volume press. Powder X-ray diffraction experiments using synchrotron radiation indicate that the derived samples are mixtures of known and unknown phases. However, the powder X-ray diffraction patterns are not sufficient for structural characterization. Transmission electron microscopy studies reveal crystals of several hundreds of nanometres in size with different chemical composition. Among them, crystals of a previously unknown phase with stoichiometry SnGe4N4O4 were detected and investigated using automated diffraction tomography (ADT), a three-dimensional electron diffraction method. Via ADT, the crystal structure could be determined from single nanocrystals in space group P63mc, exhibiting a nolanite-type structure. This was confirmed by density functional theory calculations and atomic resolution scanning transmission electron microscopy images. In one of the syntheses runs a rhombohedral 6R polytype of SnGe4N4O4 could be found together with the nolanite-type SnGe4N4O4. The structure of this polymorph was solved as well using ADT.

Thermal Equation of State of Cubic Silicon Carbide at High Pressures

We have performed in situ X-ray diffraction measurements of cubic silicon carbide (SiC) with a zinc-blende crystal structure (B3) at high pressures and temperatures using multi-anvil apparatus. The ambient volume inferred from the compression curves is smaller than that of the starting material. Using the 3rd-order Birch-Murnaghan equation of state and the Mie-Grüneisen-Debye model, we have determined the thermoelastic parameters of the B3-SiC to be K0=228±3 GPa, K0',=4.4±0.4, q=0.27±0.37, where K0, K0' and q are the isothermal bulk modulus, its pressure derivative and logarithmic volume dependence of the Grüneisen parameter, respectively. Using the 3rd-order Birch-Murnaghan EOS with the thermal expansion coefficient, the thermoelastic parameters have been found as K0=221±3 GPa, K0',=5.2±0.4, α0=0.90±0.02 ⋅ 10-5 ⋅ K-1, where α0 is the thermal expansion coefficient at room pressure and temperature. We have determined that paired B3-SiC - MgO calibrants can be used to estimate pressure and temperature simultaneously in ultrahigh-pressure experiments up to 60 GPa.

Nitride Synthesis under High-Pressure, High-Temperature Conditions: Unprecedented In Situ Insight into the Reaction

High-pressure, high-temperature (HP/HT) syntheses are essential for modern high-performance materials. Phosphorus nitride, nitridophosphate, and more generally nitride syntheses benefit greatly from HP/HT conditions. In this contribution, we present the first systematic in situ investigation of a nitridophosphate HP/HT synthesis using the reaction of zinc nitride Zn3N2 and phosphorus(V) nitride P3N5 to the nitride semiconductor Zn2PN3 as a case study. At a pressure of 8 GPa and temperatures up to 1300 °C, the reaction was monitored by energy-dispersive powder X-ray diffraction (ED-PXRD) in a large-volume press at beamline P61B at DESY. The experiments investigate the general behavior of the starting materials under extreme conditions and give insight into the reaction. During cold compression and subsequent heating, the starting materials remain crystalline above their ambient-pressure decomposition points, until a sufficient minimum temperature is reached and the reaction starts. The reaction proceeds via ion diffusion at grain boundaries with an exponential decay in the reaction rate. Raising the temperature above the minimum required value quickly completes the reaction and initiates single-crystal growth. After cooling and decompression, which did not influence the resulting product, the recovered sample was analyzed by energy-dispersive X-ray (EDX) spectroscopy.

Self-Catalyzed Hydrogenated Carbon Nano-Onions Facilitates Mild Synthesis of Transparent Nano-Polycrystalline Diamond

Transparent nano-polycrystalline diamond (t-NPD) possesses superior mechanical properties compared to single and traditional polycrystalline diamonds. However, the harsh synthetic conditions significantly limit its synthesis and applications. In this study, a synthesis routine is presented for t-NPD under low pressure and low temperature conditions, 10 GPa, 1600 °C and 15 GPa, 1350 °C similar with the synthesis condition of organic precursor. Self-catalyzed hydrogenated carbon nano-onions (HCNOs) from the combustion of naphthalene enable synthesis under nearly industrial conditions, which are like organic precursor and much lower than that of graphite and other carbon allotropes. This is made possible thanks to the significant impact of hydrogen on the thermodynamics, as it chemically facilitates phase transition. Ubiquitous nanotwinned structures are observed throughout t-NPD due to the high concentration of puckered layers and stacking faults of HCNOs, which impart a Vickers hardness about 140 GPa. This high hardness and optical transparency can be attributed to the nanocrystalline grain size, thin intergranular films, absence of secondary phase and pore-free features. The facile and industrial-scale synthesis of the HCNOs precursor, and mild synthesis conditions make t-NPD suitable for a wide range of potential applications.

The development of internal pressure standards for in-house elastic wave velocity measurements in multi-anvil presses

Ultrasonic systems are powerful tools to determine elastic wave velocities of minerals and materials at high pressure and temperature and have been extensively developed in recent decades. However, accurate measurement of sample length is required to convert travel times into wave velocities, limiting their use to synchrotron facilities or room temperature experiments in laboratories. We have made use of a close collaboration between the Bayerisches Geoinstiut and the P61B end-station beamline (PETRA III - DESY) to install ultrasonic systems and develop a novel dual travel time method for in situ pressure determination without the need for synchrotron radiation. Our method relies on the travel times of elastic waves through a reference material; it requires a thermocouple and is non-intrusive, with the reference material replacing the backing plate of the high-pressure assembly. Pressures obtained from this dual travel time method show excellent agreement with those obtained from x-ray diffraction using synchrotron radiation on standard materials. Our novel method enables in situ pressure determination at varying temperatures during in-house ultrasonic interferometry experiments. This allows us not only to determine the elastic behavior of minerals and materials but also to investigate phase diagrams, solidus, or liquidus conditions at varying pressures and temperatures during in-house experiments. During the installation of the pulse-echo ultrasonic system, we identified critical parameters for obtaining reliable data. While these requirements are well-known to experts, this study presents a comprehensive review of the different characteristics of ultrasonic systems, providing user-friendly guidelines for new users installing and operating such systems in high-pressure and high-temperature conditions.

Texture-based residual stress analysis of laser powder bed fused Inconel 718 parts

Although layer-based additive manufacturing methods such as laser powder bed fusion (PBF-LB) offer an immense geometrical freedom in design, they are typically subject to a build-up of internal stress (i.e. thermal stress) during manufacturing. As a consequence, significant residual stress (RS) is retained in the final part as a footprint of these internal stresses. Furthermore, localized melting and solidification inherently induce columnar-type grain growth accompanied by crystallographic texture. Although diffraction-based methods are commonly used to determine the RS distribution in PBF-LB parts, such features pose metrological challenges in their application. In theory, preferred grain orientation invalidates the hypothesis of isotropic material behavior underlying the common methods to determine RS. In this work, more refined methods are employed to determine RS in PBF-LB/M/IN718 prisms, based on crystallographic texture data. In fact, the employment of direction-dependent elastic constants (i.e. stress factors) for the calculation of RS results in insignificant differences from conventional approaches based on the hypothesis of isotropic mechanical properties. It can be concluded that this result is directly linked to the fact that the {311} lattice planes typically used for RS analysis in nickel-based alloys have high multiplicity and less strong texture intensities compared with other lattice planes. It is also found that the length of the laser scan vectors determines the surface RS distribution in prisms prior to their removal from the baseplate. On removal from the baseplate the surface RS considerably relaxes and/or redistributes; a combination of the geometry and the scanning strategy dictates the sub-surface RS distribution.

High-pressure synthesis and magnetic properties of tetragonal R2BaCuO5 (R = Sm and Eu)

We report the experimental discovery of a new structural phase of well-known orthorhombic R ₂BaCuO₅ (R = Sm and Eu), exhibiting a tetragonal crystal structure with space group P4∕mbm. The high-pressure tetragonal phase is isostructural with the brown phase R ₂BaCuO₅ (R = La, Pr, and Nd). In this structure, the Cu ions form an isolated square planar environment, contrary to the orthorhombic phase, where the Cu ions are located in a distorted square pyramid. Magnetization and specific heat measurements reveal the long-range antiferromagnetic order of the Cu²⁺ and/or Sm³⁺ moments for the Sm-sample, with the magnetic specific heat accounting for only 35% of the magnetic entropy. Interestingly, the Eu-sample remains paramagnetic down to the lowest temperature. The high Curie-Weiss temperature of -140 K and magnetic entropy of 3% of the expected value indicates that the system is highly frustrated. We estimated the isothermal entropy change and investigated the magnetocaloric effect for Eu₂BaCuO₅, and the maximum entropy change detected at a field of 70 kOe at 3 K reaches 5.6 J kg^-1K^-1.

Formation and Polymorphism of Semiconducting K2SiH6 and Strategy for Metallization

K2SiH6, crystallizing in the cubic K2PtCl6 structure type (Fm3̅m), features unusual hypervalent SiH62- complexes. Here, the formation of K2SiH6 at high pressures is revisited by in situ synchrotron diffraction experiments, considering KSiH3 as a precursor. At the investigated pressures, 8 and 13 GPa, K2SiH6 adopts the trigonal (NH4)2SiF6 structure type (P3̅m1) upon formation. The trigonal polymorph is stable up to 725 °C at 13 GPa. At room temperature, the transition into an ambient pressure recoverable cubic form occurs below 6.7 GPa. Theory suggests the existence of an additional, hexagonal, variant in the pressure interval 3-5 GPa. According to density functional theory band structure calculations, K2SiH6 is a semiconductor with a band gap around 2 eV. Nonbonding H-dominated states are situated below and Si-H anti-bonding states are located above the Fermi level. Enthalpically feasible and dynamically stable metallic variants of K2SiH6 may be obtained when substituting Si partially by Al or P, thus inducing p- and n-type metallicity, respectively. Yet, electron-phonon coupling appears weak, and calculated superconducting transition temperatures are <1 K.

Acoustic emission detection of micro-cracks under high pressure and high temperature in a deformation large-volume apparatus at the endstation P61B, PETRA III

We successfully developed an in situ acoustic emission (AE) detection setup that allows recording of AE waveforms (triggered and streaming) and simultaneous x-ray diffraction and imaging on samples deformed at high pressure and high temperature (HPHT) conditions in the Aster-15 Large Volume Press at the synchrotron beamline station P61B. This high pressure AE detection system is a powerful tool to investigate AE phenomena from the HPHT chamber. Six commercial acoustic sensors, protected by a tungsten carbide support ring on each anvil of the same material, have excellent survivability throughout each successive experiment. By pulsing each sensor in succession, the average wave velocity through the anvils and cell assembly can be determined at any press load. The distance between the sensors is obtained by x-ray radiography and by logging the positions of each hydraulic ram. This provides a basis for accurately locating AE events in the sample. The feasibility of this AE detection setup was confirmed by compression and deformation test runs using several different self-designed AE sources in specialized assemblies. The present setup proves to be extremely efficient and accurate in measuring brittle processes in samples under HPHT. It is now available for applications for beam time and experiments without x rays at P61B. Combined with synchrotron x rays, in situ pressure, temperature, strain rate and stress, and phase changes can be monitored while recording AE activity. We provide a powerful tool to investigate the origin of earthquakes, for example, causing AE emissions due to brittle dehydration reactions or phase transformations in the Earth.

Metastable CrMnNi steels processed by laser powder bed fusion: experimental assessment of elementary mechanisms contributing to microstructure, properties and residual stress

The complex thermal history imposed by the laser-based powder bed fusion of metals (PBF-LB/M) process is known to promote the evolution of unique microstructures. In the present study, metastable CrMnNi steels with different nickel contents and, thus, different phase stabilities are manufactured by PBF-LB/M. Results clearly reveal that an adequate choice of materials will allow to tailor mechanical properties as well as residual stress states in the as-built material to eventually redundantize any thermal post-treatment. The chemical differences lead to different phase constitutions in as-built conditions and, thus, affect microstructure evolution and elementary deformation mechanisms upon deformation, i.e., twinning and martensitic transformation. Such alloys designed for additive manufacturing (AM) highlight the possibility to tackle well-known challenges in AM such as limited damage tolerance, porosity and detrimental residual stress states without conducting any post treatments, e.g., stress relieve and hot isostatic pressing. From the perspective of robust design of AM components, indeed it seems to be a very effective approach to adapt the material to the process characteristics of AM.

The Microbeam Insert at the White Beam Beamline P61A at the Synchrotron PETRA III/DESY: A New Tool for High Dose Rate Irradiation Research

Simple Summary

The excellent preservation of normal tissue function after high dose rate radiotherapy has been shown in pre-clinical studies. Normal tissue in the tumor environment is well preserved even after target doses of several hundred Gy while reliably destroying the tumor cells. These results have triggered the establishment of appropriate research structures at the synchrotron PETRA III on the DESY campus in Hamburg, Germany. Dose rates of hundreds of Gy/s can be achieved, compared to 6–20 Gy/min in clinical radiotherapy. We describe the design, development, key parameters, and first use of a mobile insert for high dose rate radiotherapy research, a new research instrument at P61A, the first polychromatic beamline of PETRA III. The data obtained at the end station P61A will support the international interdisciplinary effort to improve radiotherapy concepts for patients with malignant tumors that are considered radioresistant with the currently established clinical radiotherapy techniques.

Abstract

High dose rate radiotherapies such as FLASH and microbeam radiotherapy (MRT) both have developed to the stage of first veterinary studies within the last decade. With the development of a new research tool for high dose rate radiotherapy at the end station P61A of the synchrotron beamline P61 on the DESY campus in Hamburg, we increased the research capacity in this field to speed up the translation of the radiotherapy techniques which are still experimental, from bench to bedside. At P61, dose rates of several hundred Gy/s can be delivered. Compared to dedicated biomedical beamlines, the beam width available for MRT experiments is a very restrictive factor. We developed two model systems specifically to suit these specific technical parameters and tested them in a first set of experiments.