Subsequent Hot Isostatic Pressing Research Articles

Development of high superconductor fraction (Ba, K)Fe2As2 wires with improved uniformity by two-axial rolling

Iron-based superconductors are regarded as prospective candidates for high magnetic field applications since they have very high upper critical field and low anisotropy. For practical applications, it is important to develop superconducting wires with strong current carrying capability. In this work, Cu/Ag composite sheathed (Ba, K)Fe2As2 (Ba-122) iron-based superconducting wires were fabricated by a two-axial rolling deformation process and a subsequent hot isostatic pressing (HIP) heat treatment. Compared with the previously reported Cu/Ag/Ba-122 wires prepared by groove rolling, the two-axial rolling allowed to use much thinner Cu/Ag composite sheath for wire fabrication, thus greatly increasing the filling factor of superconducting materials by about 5 times to 24 %, and lowering the volume fraction of silver down to 16 % in wires. By a comparative study on the microstructure and superconducting properties between the wires made by two-axial rolling and groove rolling processes, it is found that besides the significantly increased engineering critical current density, the former also exhibits improved homogeneity of mass distribution and uniformity of Ba-122/Ag interfaces, resulting in significantly enhanced n-values over 40 in magnetic fields up to 14 T. Our work suggests that two-axial rolling, combined with HIP processes, presents a promising approach to prepare iron-based superconducting wires with high filling factor, high uniformity and low cost for practical applications.

Pre-softening HIP treatment enabled crack-healing and superior mechanical properties for René 142 superalloy fabricated via laser powder bed fusion

The generation of defects, such as cracks and pores, presents significant challenges for high-strength metals and alloys fabricated by the quick-emerging additive manufacturing technology, and subsequent post-processing treatments are often necessary before their practical applications. In this work, a novel heat treatment approach, involving a pre-softening treatment before hot isostatic pressing (HIP), is developed to facilitate the crack-healing in René 142 superalloy produced through laser powder bed fusion. Results demonstrate that René 142 alloy exhibits a propensity for severe cracking across a wide range of printing parameters, primarily in the form of solidification cracks and liquation cracks. These cracks are formed mainly due to a wide solidification range, the presence of a liquid film, and the concentration of residual stress. The pre-softening solution heat treatment significantly reduces dislocation density and residual stress levels, and the subsequent HIP together leads to a defect-free, dense structure for René 142 superalloy. Consequently, the René 142 alloy processed by the pre-softening HIP treatment achieves an excellent combination of yield strength (850 MPa), ultimate tensile strength (1227 MPa), and elongation (13.7 %), with pseudo-equiaxed grains (120–150 μm) and square γ′ precipitates (approximately 540 nm). These findings provide valuable insights for exploring crack elimination methods in other nickel-based superalloys fabricated through additive manufacturing.

Additive manufacturing of high nitrogen austenitic steel using shell-core strategy

Laser Powder Bed Fusion/Metal (PBF-LB/M) is a promising technology for industrial applications, but challenges such as long process times remain. Innovations such as the shell-core approach aim to address this by creating a dense shell around a minimally exposed powder core, significantly reducing processing times, with full densification and property adjustments achieved by subsequent hot isostatic pressing (HIP). This study focuses on the fabrication of shell-core samples using a powder mixture of austenitic steel and Si3N4 to produce high nitrogen steel PBF-LB/M components, which are otherwise difficult to produce due to the limited nitrogen solubility in the melt. PBF-LB/M induces Si3N4 decomposition, resulting in Si and N loss through laser-powder interaction. Si3N4 particles in the still powdered regions serve as a source of N enrichment during HIP, circumventing the limitations of nitrogen solubility in the melt and exploiting the higher solubility in the solid. After HIP, energy dispersive spectrometry and electron backscatter diffraction reveal a fully austenitic matrix with Si diffusion seams mainly in non-laser-exposed areas. The Si3N4 dissolution during HIP contributes to an interstitial dissolved N content of about 0.189 mass%, which, together with the higher Si content, increases hardness. Wavelength dispersive spectrometry (WDS) and nanoindentation line scans show decreasing Si and N concentrations from core to shell, resulting in reduced (nano)hardness in the shell. This innovative approach demonstrates the potential to produce AM components with enhanced properties by overcoming the limitations of nitrogen solubility in the steel melt during PBF-LB/M.

Two-Photon Polymerization of Nanocomposites for Additive Manufacturing of Transparent Magnesium Aluminate Spinel Ceramics.

Transparent polycrystalline magnesium aluminate (MAS) spinel ceramics are of great interest for industry and academia due to their excellent optical and mechanical properties. However, shaping of MAS is notoriously challenging especially on the microscale requiring hazardous etching methods. Therefore, a photochemically curable nanocomposite is demonstrated that can be structured using high-resolution two-photon lithography. The printed nanocomposites are converted intro transparent MAS by subsequent debinding, sintering, and hot isostatic pressing. The resulting transparent spinel ceramics exhibit a surface roughness Sq of only 10nm and can be shaped with minimum feature sizes of down to 13µm. This technology will be important for the production of microstructured ceramics used for optics, photonics, or photocatalysis.

Effect of CaF2 on the preparation and optical property of MgAl2O4 transparent ceramics

To achieve optimal light transparency in MgAl2O4 transparent ceramics, a higher sintering temperature is required to eliminate pores. However, inevitable rapid grain growth occurs, leading to lower mechanical properties. To address this problem, calcium fluoride (CaF2) is utilized as a sintering additive to enhance the transparency of MgAl2O4 ceramics. The influence of CaF2 on the densification process and microstructure evolution is investigated. CaF2 demonstrates notable abilities in facilitating densification and lowering the sintering temperature. Moreover, it inhibits grain growth during the final sintering stage. However, the sintering temperature must be controlled because the secondary phases (calcium aluminate) precipitate at a higher temperature, thereby affecting the homogeneity of the ceramic microstructure. After optimizing the sintering process, ceramics (with a thickness of 5 mm) containing 0.05 wt% CaF2 exhibited the highest in-line transmittance of 81 % and 87 % in the visible and near-infrared wavelengths, respectively, after pre-sintering at 1505 °C for 3 h and subsequent hot isostatic pressing (HIPing) at 1550 °C for 3 h.

Consolidation of water-atomized chromium–nickel-alloyed powder metallurgy steel through novel processing routes

When processing powder metallurgy (PM) steels, the conventional press and sinter route can reach a relative density up to 95%, which is insufficient for applications when dynamic mechanical performance is critical. In this study, a novel route is demonstrated consisting of cold isostatic pressing (CIP) followed by sintering and capsule-free hot isostatic pressing (HIP), allowing to achieve full density PM steels. Water-atomized steel powder admixed with 2 wt.% Ni was subjected to CIP and followed by sintering in 90N2/10H2 atmosphere at 1120 and 1250°C, and in vacuum (10−2 mbar) at 1250 and 1350°C, respectively. At the highest explored CIP pressure of 600 MPa, the three high-temperature sintering runs at 1250°C in 90N2/10H2 atmosphere and vacuum, and 1350°C in vacuum resulted in relative density of ∼94% and closed surface pores. This condition with necessary closed porosity then allowed subsequent capsule-free HIP after sintering, resulting in full densification of the components.

Synthesis of MgO powders by precipitant for transparent ceramics

In this experiment, MgO powder was prepared through co-precipitation using NH3·H2O and NH4HCO3 as precipitant. The study aimed to investigate the effects of precipitant content and type on the yield of MgO powders. It was found that the highest MgO yield was obtained using a mixture of NH4HCO3 and NH3·H2O as the precipitant. Furthermore, NH3·H2O as the sole precipitant resulted in the smallest particle size. However, an increase in the precipitant content led to a decrease in the specific surface area of the powders and caused powder agglomeration. Subsequently, MgO transparent ceramics were fabricated using a hybrid sintering method involving hot pressing followed by a subsequent hot isostatic pressing treatment. The best microstructure and the highest infrared transmittance of 81% at 5.81 μm were achieved for the MgO transparent ceramic samples hot-pressed at 1500 °C and then subjected to hot isostatic pressing at 1500 °C. The relative density reached 99.97%.

Analysis of orientation-dependent deformation mechanisms in additively manufactured Zr using in-situ micromechanical testing: Twinning and orientation gradient

Orientation-dependent plasticity in zirconium (Zr)-alloy, which is produced through ultrasonic additive manufacturing (UAM) with subsequent hot-isostatic pressing (HIP), was analyzed by recording electron backscattered diffraction (EBSD) data during in-situ micromechanical testing. Three (0001) plane orientations of a hexagonal close-packed (HCP) structure were analyzed parallel to (1) the rolling direction [X||tensile direction (TD)], (2) the build direction [Z], and (3) the transverse direction [Y]. The analysis revealed that the grains with ∼<0001>||TD show twin-dominant plasticity with three variants from {10 1‾ 2}<1‾ 011>; minor slipping with (101‾ 1)[2‾ 113], and (112‾ 2)[1‾1‾ 23] pyramidal slip has also been observed. However, grains with orientation ∼<0001>⊥TD are mainly sensitive to dislocations assisted plasticity-leading to orientation gradients formation. Furthermore, the neck formation was identified as originating from higher populated micro-crack locations and their association with localized plasticity at defect points in the UAM material. These results demonstrate that minimization of impurities to enable grain growth across prior foil interfaces makes HIP an effective methodology for producing Zr plate, with deformation characteristics expected for conventionally manufactured Zr.

MICROSTRUCTURE AND PHASE CONTENT OF INCONEL 718 SUPERALLOY PRODUCED VIA SELECTIVE LASER MELTING PRO-CESS, HOT ISOSTATC PRESSING AND HEAT TREATMENT

Purpose. Study of microstructure and phase content of Inconel 718 nickel-chromium-iron superalloy obtained via selective laser melting with subsequent hot isostatic pressing (HIP) and standard heat treatment with high-temperature homogenization and two-steps long term ageing.&#x0D; Research methods. Microstructure analysis and phase content investigation was carried out with optical and scanning electronic metallography on optical and electronic microscope respectively.&#x0D; Results. Material structure of in-built specimens are investigated that is characterized by layer-by-layer fusing in the form of arcuate lines with a presence of epitaxial growth of columnar dendrites. Strengthening of alloy is achieved after heat treatment, basically, due to intermetallic γ″- phase (with Ni3Nb type) precipitation. With metallographic investigation showed that active segregation of niobium in interdendritic spaces, provided due high crystallization rate during selective laser melting and subsequent heat treatment, lead to forming orthorhombic d- phase in alloy structure with lamellar morphology. HIP application before standard for Inconel 718 heat treatment, promotes more homogeneous structure.&#x0D; Scientific novelty. New data’s was obtained for phase state of Inconel 718 alloy after HIP and heat treatment. Fine structure of Ni-Cr-Fe-superalloy obtained via selective laser melting was studied.&#x0D; Practical value. Obtained results expands possibilities for Inconel 718 alloy application and allow to determine perspectives of practical usage of selective laser melting process for aviation parts production.

Effect of CaO additive on the densification of MgO and MgO-YGAG:Ce ceramics

Highly transparent MgO ceramic was prepared by hot isostatic pressing (HIP) technique of vacuum-sintered MgO compact using CaO as the sintering additive. Densification process of MgO ceramic is significantly enhanced by doping 0.5 at% CaO at the vacuum-sintering temperature of 1100–1350 °C. By subsequent HIP sintering at 1650 °C, the relative density of 0.5% CaO-doped MgO ceramic vacuum-sintered at 1350 °C increases from 94.67% to 99.97%. It attains high in-line transmittance of 70.78% at 600 nm and 87.59% at 6000 nm, respectively. Meanwhile, the thermal conductivity reaches 53.2 W/(m∙K), demonstrating that CaO-doped MgO is a promising candidate material as the secondary phase of phosphor composite ceramics. Herein, 0.5% CaO-doped MgO-YGAG:Ce (Y2.82Gd0.18Al5O12:Ce) composite ceramic with stable binary-phase structure, high relative density of 99.1% and thermal conductivity of 32.6 W/(m∙K) was synthesized by vacuum-sintering at 1350 °C and the luminescence performance under blue laser excitation was evaluated.

Pure Tungsten Fabricated by Laser Powder Bed Fusion with Subsequent Hot Isostatic Pressing: Microstructural Evolution, Mechanical Properties, and Thermal Conductivity

Pure Tungsten Fabricated by Laser Powder Bed Fusion with Subsequent Hot Isostatic Pressing: Microstructural Evolution, Mechanical Properties, and Thermal Conductivity

Influence of SHS Precursor Composition on the Properties of Yttria Powders and Optical Ceramics

This study looked at optimizing the composition of precursors for yttria nanopowder glycine-nitrate self-propagating high-temperature synthesis (SHS). Based on thermodynamic studies, six different precursor compositions were selected, including with excesses of either oxidant or fuel. The powders from the precursors of all selected compositions were highly dispersed and had specific surface areas ranging from 22 to 57 m2/g. They were consolidated by hot pressing (HP) with lithium-fluoride sintering additive and subsequent hot isostatic pressing (HIP). The 1 mm thick HPed ceramics had transmittance in the range of 74.5% to 80.1% @ 1μm, which was limited by optical inhomogeneity due to incomplete evaporation of the sintering additive. Two-stage HIP significantly improves optical homogeneity of the ceramics. It was shown that an excess of oxidizer in the precursor decreases the powders' agglomeration degree, which forms large pore clusters in the ceramics.

Ductile and ultrahigh-strength eutectic high-entropy alloys by large-volume 3D printing

3D printing of high-strength alloys enables efficient manufacturing of complex metallic components. Yet, the as-built parts are often characterized by unsatisfied ductility due to micro-defects, requiring additional heat treatment to optimize the structure before in-site applications. The post heat-processing, however, often changes the shape of the printed parts, deteriorating the quality of the printed components. In addition, many printed large-scale alloy parts with complex shapes are difficult to be processed by hot isostatic pressing. This requires that the alloys can be printed with good strength and ductility without the necessity of additional thermal processing. Here, we show that excellent ductility and ultrahigh strength can be achieved in a eutectic high-entropy alloy (EHEA) by large-volume 3D printing. The as-printed EHEA has a tensile yield strength of 1040 MPa, and a total elongation of 24%, as well as superior corrosion resistance in seawater environment. The excellent combination of properties outperforms that of all other existing metallic materials. Note that these astonishing properties are from specimens directly after 3D printing without any subsequent heat treatment and hot isostatic pressing. The exceptional mechanical properties are mainly ascribed to the fine lamella spacing in the composite structure consisting of face-centered cubic matrix and B2 precipitates, which renders high resistance for dislocation movement and extends work hardening capability. The EHEA printed in large volume without post processing thus shows high applicability for mass-production at an industrial scale.

Fabrication of 4 at.% La3+ ion doped (TbxLu0.96−x)2O3 transparent ceramics by using NC-PLSH technology and characterisation of their magneto-optical properties

Nanocrystalline powders and pressureless sintering (NC-PLSH) were used in a H2 atmosphere to fabricate 4 at.% La3+ doped (TbxLu0.96−x)2O3 magneto-optical transparent ceramics. La3+ was utilised as a sintering aid, and Lu3+ was used as a phase stabiliser. A component of the (TbxLu0.96−xLa0.04)2O3 magneto-optical material was designed and investigated based on powder sinterability and green compact sintering. Transparent (TbxLu0.96−xLa0.04)2O3 ceramics were obtained by using a one-step sintering process in H2 atmosphere, without the need for subsequent hot isostatic pressing. The in-line transmittance of the as-polished 4 at.% La3+:(Tb0.8Lu0.16)2O3 ceramic was 79% at 1400 nm. The measured Verdet constant at wavelengths of 633 nm and 1064 nm was 354 rad/(T·m) and 100.2 rad/(T·m), respectively. The required length of the (Tb0.8Lu0.16La0.04)2O3 ceramics was 63% less than that of Tb3Ga5O12 ceramics.

Microstructural Origins of the Corrosion Resistance of a Mg-Y-Nd-Zr Alloy Processed by Powder Bed Fusion - Laser Beam.

Magnesium alloys are biocompatible, biodegradable and have the ability to promote bone ingrowth, making them ideal candidate materials for replacing auto- and allografts in future treatments of large bone defects. Powder bed fusion–laser beam (PBF-LB) additive manufacturing of these alloys would further allow for the production of complex structures, optimized for bone grafting. However, the corrosion rates of structures processed by PBF-LB remain too high. An improved understanding of the influence of the microstructure generated during PBF-LB on the corrosion properties is considered key to their future implementation in implants. In this study, the effect of PBF-LB processing and subsequent hot isostatic pressing (HIP) on the microstructure and texture in different sample directions was studied and related to the corrosion behavior of a Mg-Y-Nd-Zr alloy. The results were compared with an extruded Mg-Y-Nd-Zr alloy. A higher amount of secondary phases resulted in a higher rate of localized corrosion for the PBF-LB processed material compared to that for the extruded one. Due to growth of the secondary phases, the corrosion rate was further increased after HIP. Moreover, a strong texture was observed in the PBF-LB material, and it was also enhanced in the HIP material. While this affected the electrochemical activity as measured by potentiodynamic polarization tests, any texture effect appeared to be masked by the contribution of the secondary phases in the longer-term mass change and hydrogen evolution tests. Future work should look further into the influence of individual process parameters on the microstructure and the resulting corrosion behavior of the material, to further clarify its interdependence.

Effects of Zr Content on the Microstructure of FeCrAl ODS Steels

FeCrAl oxide dispersion strengthened (ODS) steels are an important kind of cladding material for accident-tolerant fuels. Their radiation resistance and mechanical properties are closely related to the grain size and dispersed second phases. In order to tailor the microstructure and provide an experimental basis for the composition design of FeCrAl ODS steels, in this paper FeCrAl ODS steels with different Zr contents were prepared by mechanical alloying and the subsequent hot isostatic pressing (MA-HIP) process. The effects of Zr content on the grain size distribution and the precipitation of dispersed second phases in FeCrAl ODS steels were investigated by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that the grain size decreased first and then increased as the Zr content increased, and that the average grain size achieved the minimum value of 2.092 μm when the Zr content was 0.6 wt.%. The Zr content had a negligible effect on the grain orientation of FeCrAl ODS steels, but the dispersed second phase changed from the Al2Y4O9 phase with monoclinic structure to the Y4Zr3O12 phase with hexagonal structure as the Zr content increased.

Fatigue performance of shelled additively manufactured parts subjected to hot isostatic pressing

Additive manufacturing (AM) of metal components is increasingly used in high performance applications, especially in the aerospace industry. Laser powder bed fusion (L-PBF) of metals is the most widely used and mature process for this purpose, but it comes with some challenges. One of these challenges involves manufacturing quality and associated mechanical properties that can be negatively influenced by the presence of process-induced porosity, directional microstructure, residual stress and more. Hot isostatic pressing (HIP) has emerged as a key technology for post-processing such components, acting to improve the mechanical properties and especially the fatigue properties. This process is often required as a routine and mandatory step to ensure metal AM components can be used for critical applications and to mitigate potential manufacturing problems. It has recently been demonstrated that metal AM components can be manufactured through printing of a shell only – therefore with process powder remaining enclosed in the part – whereby the subsequent HIP cycle fully densifies the material. This approach has some advantages, including primarily a reduction in laser processing time during the L-PBF process, acting to reduce total costs. In this present work, the fatigue performance of this hybrid L-PBF and HIP process is investigated, in comparison to the equivalent solid processing route.

Effect of HIP at 1000–1200 °C on microstructure and properties of extruded Be-Ti composites

Solid titanium beryllide blocks will be used for neutron multiplication in the helium-cooled pebble bed (HCPB) blanket concept of EU DEMO. A combination of hot extrusion of Be-Ti powders and subsequent hot isostatic pressing (HIP) of the obtained Be-Ti composites has been proposed for manufacturing such blocks. This work is devoted to the study of the effect of HIP at 1000–1200 °C on the structure and properties of Be-Ti composites in order to optimize the HIP parameters. The HIP at 1000–1200 °C resulted in an almost single-phase titanium beryllide (TiBe12) with small amounts of Be and other phases, which gradually dissolve with an increase in the HIP temperature. Such a treatment at 1000 and 1100 °C provides a very fine-grained microstructure of TiBe12 with an average grain size of 0.3 and 0.6 μm, respectively. The resulting titanium beryllide is characterized by high microhardness of 1350–1480HV0.1 depending on the HIP temperature. According to the nanoindentation tests of the Be-Ti composite after HIP at 1100 °C, the indentation modulus of TiBe12 can be estimated as 295GPa. The fracture toughness of the TiBe12 was determined as 1.5–1.7 MPa·m1/2. The temperature of 1100 °C was chosen as optimal for the HIP of Be-Ti composites after hot extrusion. The titanium beryllide obtained in this way was used to manufacture a reduced size mockup of Ø20mm × 18 mm. The mockup has no visible surface defects and can be used for further experiments.

Investigation of the structural characteristics, dielectric properties, and infrared reflectivity spectra of AlON transparent ceramics

Al(8+x)/3O4−xNx (x = 0.299–0.575) transparent ceramics were fabricated by presintering and subsequent hot isostatic pressing (HIP) technology. The XRD and SEAD analyses verified that a complete solid solution with a cubic spinel structure was achieved in the entire composition range. The SEM characterization confirmed that the x = 0.299−0.510 samples are highly dense with rare residual pores, which was further demonstrated by HRTEM observations. In combination with phonon modes extracted by far-infrared reflectivity spectra, the intrinsic dielectric properties of AlON ceramics were estimated, which were consistent with the experimental results, revealing that the contribution to dielectric properties is dominated by the absorption of structural phonons. Moreover, as the nitrogen content increased, the measured permittivity (εr) of the samples was found to gradually increase from 9.41 to 9.68 at 7 GHz, while the quality factor (Q × f) values fluctuated from 43,750 to 76,923 GHz. Accordingly, the reported AlON transparent ceramics with exceptional dielectric performances are promising candidates for high-frequency 5 G applications.

Influence of starting Y2O3 and Nd2O3 powders characteristics on optical properties of highly transparent Nd:Y2O3 ceramics

The present paper systematically investigated the correlation of the starting powder characteristics and optical properties of neodymium doped transparent Y2O3(Nd:Y2O3) ceramics by hot pressing without a subsequent hot isostatic pressing (HIP) treatment. It was found that the in-line transmittance of Nd:Y2O3 was improved by using coarser primary particle size of Y2O3 and Nd2O3. Additionally, an increase in the hot pressing temperature from 1500 to 1600 °C was effective for improvement on optical qualities of Nd:Y2O3 ceramics without an exaggerated grain growth. These results demonstrate the possibility of fabricating highly transparent ceramics by a simple and cost-effective powder process and sintering technique.