Hot Isostatic Pressing Samples Research Articles

Effect of Ti‐metal addition on hot‐isostatically pressed (HIPed) Synroc‐C

AbstractSynroc, a candidate nuclear wasteform and Synroc technology, a waste treatment solution utilizing hot‐isostatic pressing (HIPing) have significant potential for the immobilisation of challenging nuclear wastes from both current and innovative reactors and fuel cycles. Hot isostatic press (HIP) consolidation is undertaken within sealed metal HIP canisters, where metal buffers (e.g., Ti, Fe and Ni) can be incorporated to control the redox environment within the canister. This study, for the first time, reports the effect of varying Ti‐metal addition (0, 2, 4, and 8 wt.%) on phase formation, microstructural characteristics, and wasteform performance for HIP consolidated Synroc‐C containing 20 wt.% simulated PUREX type (PW‐4b) high level waste. Quantitative X‐ray diffraction analysis, scanning electron microscopy‐energy dispersive X‐ray spectroscopy (EDS) and transmission electron microscopy‐EDS analyses were undertaken for analytical investigations. The chemical durability of the samples was assessed using ASTM C1220‐21 standard test. Hot‐isostatically pressed (HIPed) samples with 0 and 8 wt.% Ti added for redox control produced unfavourable phase formation. However, the HIPed samples with Ti additions of 2 and 4 wt.% as a redox buffer showed the desired phase formation of Synroc‐C without any significant change to the partitioning of waste elements among the phases along with compatible durability results, when compared to previous literature for hot uniaxial pressing (HUPed) or sintered materials.

Mechanical Properties of LPBF-Built Titanium Lattice Structures—A Comparative Study of As-Built and Hot Isostatic Pressed Structures for Medical Implants

We compare different lattice structures with various elementary cell sizes built by laser powder bed fusion with and without hot isostatic pressing as post treatment. Cylindrical lattice structures are mechanically tested upon static and dynamic load in order to achieve high elasticity, high fracture strength and a high number of cycles to failure with respect to applications as medical implants. Evaluating the Young’s modulus, a high stiffness for the body diagonal structure and a low fracture stress for the G-structure are measured. Hot isostatic pressing results in a higher Young’s modulus and is ambiguous in terms of fractural stress. While samples without hot isostatic pressing reveal a shear fracture, the hot isostatic pressed samples have a high ductile area where the lattice layers are wrapped and pressed into the underlying layers without a fracture. Under dynamic load, the samples without hot isostatic pressing mostly are unable withstand 106 cycles at typical loads of the human body. Hot isostatic pressing has no significant influence on the strength at high loads and low cycle numbers, but at low loads all samples survived 106 cycles. As a consequence, dode-thick and rhombic dodecahedrons with 2 mm and 1.5 mm lattice size after hot isostatic pressing are recommended for medical implants because of the high elasticity, high fracture stress and high resistance against dynamic loads, which fulfill implant requirements.

Effect of Hot Rolling on the Microstructure and Properties of Nanostructured 15Cr ODS Alloys with Al and Zr Addition.

Oxide dispersion strengthened (ODS) alloys with Al and Zr addition have excellent radiation tolerance, high-temperature strength, and corrosion resistance. The 15Cr-Al-Zr-ODS alloys are processed by mechanical alloying (MA), hot isostatic pressing (HIP), subsequent hot rolling to large strains of 70%, and further annealing. The effect of hot rolling on the microstructure, and the properties of nanostructured 15Cr ODS alloys with Al and Zr addition, were investigated. The microstructure after hot rolling and annealing showed obvious anisotropy. The cubic texture (φ1 = 0°, Φ = 0°, φ2 = 0°) {0 0 1} <1 0 0> and brass-R texture (φ1 = 0°, Φ = 55°, φ2 = 45°) {1 1 1} <1 1 0> were observed. The similar size distribution of precipitates was obtained for the comparison of the hot rolling samples with the hot isostatic pressed samples, which can be attributed to excellent thermal stability. After hot rolling, the alloy showed higher yield strength but did not lose too much plasticity.

Effect of LiF on the optical transmittance of magnesium aluminate spinel

The effect of LiF as a sintering aid to the optical transparency of magnesium aluminate (MgAl2O4) spinel ceramics is studied. The spinel ceramics is prepared in a process proved to be suitable for commercial production. LiF, in different concentrations ranging from 0–2.5 wt%, is doped into MgAl2O4 powders prepared by sol-gel method. Sample MgAl2O4 ceramic discs are fabricated by ball milling, cold pressing, and hot-pressing, or hot-isostatic-pressing of the powder mixtures. Optical transparency measurements show that, hot-pressed samples exhibit higher transparency when more LiF is added. While for hot-isostatic pressed samples, excessive LiF content leads to a decrease in optical transparency. The optimal LiF doping quantity is suggested for the present technique.

Compressive creep of fine and coarse-grained T 3SiC 2 in air in the 1100–1300 °C temperature range

Herein, we report on the compressive creep behavior of hot isostatically pressed (HIPed) fine-grained (FG) and coarse-grained (CG) Ti 3SiC 2 in the 1100–1300 °C temperature range. The creep behavior is characterized by three regimes, a primary, quasi-steady state and a tertiary. At lower stresses, the creep rates of the two microstructures are comparable suggesting that dislocation creep is operative. At ≈2, the stress exponents in the quasi-steady state regime are comparable to those measured in tension; the creep rates in compression, however, are roughly an order of magnitude lower. At relatively high stresses and/or temperatures, the stress exponents of the FG samples increase dramatically and the creep rates of the CG samples are higher than their FG counterparts. Both observations suggest a change of mechanism from dislocation creep to possibly sub-critical crack growth, in which delaminations play an important role. This conclusion is bolstered by post-deformation microstructural analysis that shows evidence for sub-critical crack growth. The minimum creep rates of pressureless sintered Ti 3SiC 2 samples were roughly an order of magnitude higher than HIPed samples, with comparable grain size strongly suggesting that some form of grain boundary related deformation, such as decohesion and/or sliding, is playing an important role in the sintered samples.

Characterization of sol-gel derived zirconia with additions of yttria and ceria. Origin of high fracture toughness in ceria-stabilized samples

Fine powders of $ZrO_2$ containing cubic or tetragonal phases in the systems $Y_2O_3-ZrO_2$ and $CeO_2-ZrO_2$ have been prepared using the sol-gel technique without the addition of any catalysts. The powders have been compacted and either sintered at 1823 K or hot isostatic pressed (HIPed) at 1723 K (1 h) under a pressure of 140 MPa (argon atmosphere). The sintered and HIPed samples have been examined for the fracture toughness $(K_{IC})$ and biocompatibility. The $K_{IC}$ values ranged from 7-12 MPa $m^{1/2}$ and all the samples have been found to exhibit a good biocompatibility. Formation of $Ce_2Zr_2O_7$ (pyrochlore) in the case of 15Ce-TZP/HIPed sample has been interpreted using a chemical reaction which is very likely to be a spinoidal decomposition. The high value of $K_{IC}$ observed in 15Ce-TZP/HIPed has been rationalized by a probable decomposition of pyrochlore during crack propagation.

Gas Diffusion During Containerless Hot Isostatic Pressing of Liquid‐Phase Sintered Ceramics

Diffusion and dissolution of gases are considerably higher in glasses than in most crystalline materials. Thus, materials with a glassy grain‐boundary phase are susceptible to gas permeation when they are containerless hot isostatic pressed. Annealing of sinter‐hot isostatic pressed alumina—magnesium aluminosilicate glass (3 to 10 vol%) composites and pure glass samples at 1200° to 1600°C results in dedensification by matrix bloating and swelling. The degree of dedensification increases with the hot isostatic pressing pressure, temperature, and time and increasing annealing temperature. A theoretical prediction of high‐pressure gas permeation is developed based on a diffusion model. The analysis allows a satisfactory explanation for the gas diffusion effect on hot isostatic press densification. The analysis is also useful for developing design criteria for the hot isostatic press schedule and encapsulation materials. Annealing of hot isostatic pressed samples at 1100°C prior to high‐temperature annealing results in no dedensification as a result of out‐diffusion of the internal gases.

Metallographical Study of Hot Isostatically Pressed Copper Encapsulation of Nuclear Fuel Elements

AbstractLight optical and electron microscopy have been used to study both laboratory-scale and full scale hot isostatically pressed (HIPed) copper as employed for encapsulation of spent nuclear fuel elements. Particular attention has been paid to the degree of densification achieved, as well as to the status of the joins between the sleeve, lid and the HIPed powder. The work includes the development of computing models for predicting the optimal conditions for HIPing copper and other possible encapsulation materials such as lead and alumina. Mechanical testing of HIPed samples has also been carried out.The current method of using hydrogen to reduce oxides at powder surfaces prior to HIPing is questioned on the basis that metallography reveals definite signs of hydrogen embrittlement. An alternative method of reduction is to use CO/CO2 mixtures instead of hydrogen, and it is suggested that this approach could be strongly advantageous in future.