Hot Isostatic Pressing Research Articles

Microstructural Evolution and Mechanical Properties of Ti-6Al-4V Alloy through Selective Laser Melting: Comprehensive Study on the Effect of Hot Isostatic Pressing (HIP)

This study explores the profound impact of varying oxygen content on microstructural and mechanical properties in specimens HO and LO. The higher oxygen concentration in specimen HO is found to significantly influence alpha lath sizes, resulting in a size of 0.5-1 μm, contrasting with the 1-1.5 μm size observed in specimen LO. Pore fraction, governed by oxygen concentration, is high in specimen HO, registering a value of 0.11%, whereas specimen LO exhibits a lower pore fraction (0.02%). Varied pore types in each specimen further underscore the role of oxygen concentration in shaping microstructural morphology. Despite these microstructural variations, the average hardness remains consistent at ~370 HV. This study emphasizes the pivotal role of oxygen content in influencing microstructural features, contributing to a comprehensive understanding of the intricate interplay between elemental composition and material properties.

Hot Deformation Behavior of a Hot-Isostatically Pressed Ti-6Al-4V Alloy from Recycled Powder.

In this work, a new use of mixed Ti-6Al-4V powder, consisting of the retained powder after screening for additive manufacturing and the recycled powder after multiple printing, has been exploited. The powder mixture has been hot-isostatically-pressed (HIPed) at 930 °C/120 MPa for 3 h to reach full density. The hot deformation behavior of the as-HIPed powder compacts were investigated through isothermal compression tests, kinetic analyses, and hot processing maps. Finally, the optimized hot working parameters were validated using upsetting tests. The results show that the as-HIPed Ti-6Al-4V alloy has a fine and homogeneous microstructure. The activation energies were calculated to be 359 kJ/mol in the α + β phase regime and 463 kJ/mol in the β phase regime, respectively. The optimal hot working parameters are a deformation temperature above 950 °C and strain rate higher than 0.1 s-1. The hot workability of as-HIPed powder compacts is better than the as-cast billets. The deformed microstructure can be finer than that of as-HIPed state, and the mechanical performance can be further improved by the optimal thermo-mechanical processing treatment.

A low-cost granular-medium hot quasi-isostatic pressing method for enhancing compressive properties of 3D printed structures

3D printed structures suffered weak bead-to-bead interfacial bonding due to the layer-by-layer manufacturing process. The hot isostatic pressing (HIP) method was effective in improving the micro-structures and enhancing the mechanical properties of 3D printed structures, but it was limited due to the high-cost device and process. Inspired by the HIP method, and aimed at improving the compressive properties of 3D printed thin-walled structures, this work proposed a low-cost granular-medium hot quasi-isostatic pressing (GMHQIP) method realized by the homemade equipment. The hot quasi-isostatic ambient pressure could be produced by pressing the granular medium in the high-temperature environment. The thin-walled structures treated by the GMHQIP method showed a more regular progressive deformation mode than non-treated structures. Compared to the non-treated structure, the specific energy absorption of thin-walled structures treated at 200 °C with 2 MPa for 8 h significantly increased by 170.4 % to the value of 4.95 J/g. The results indicated that the strength and toughness of 3D printed materials improved significantly after the GMHQIP treatment. The interfacial bonding of 3D printed structures was enhanced by using the GMHQIP method. This work offered a low-cost and efficient post-processing method for 3D printed structures to improve compressive properties.

Influence of copper on the microstructure and mechanical properties of titanium ortho-alloy produced by selective laser melting

This study explores an intermetallic orthorhombic titanium alloy produced by incorporating varying copper concentrations ranging from 0 to 6 wt. % through in-situ doping during selective laser melting (SLM) fabrication, coupled with simultaneous substrate preheating. The investigation delves into the influence of copper introduction on grain refinement within the primary B2/β-phase and subsequent alterations in mechanical properties. Through X-ray diffraction analysis and scanning electron microscopy, the microstructure characterized by the presence of the B2/β-phase and orthorhombic phase precipitates was identified. Additionally, the detection of a minor quantity of the α2-Ti3Al-phase was noted, with its proportion increasing proportionally with the augmentation of copper content. Differential scanning calorimetry revealed a shift in the phase transformation temperatures towards higher temperatures and a constricted α2-Ti3Al + B2/β + Ti2AlNb region, attributed to the inclusion of copper. The addition of copper, up to 6 wt. %, resulted in the softening and embrittlement of the orthorhombic alloy, forming a fine-grained microstructure with an average grain size of 8.3 μm. Energy dispersive X-ray spectroscopy confirmed the presence of an intermetallic O-phase along the grain boundaries, contributing to a 12 % increase in hardness compared to the orthorhombic alloy without copper after SLM with substrate heating at 850 °C. An alloy containing 4 wt. % copper exhibited superior plastic properties and a tensile strength of 1080 MPa, comparable to the strength of the orthorhombic alloy obtained via SLM followed by hot isostatic pressing.

An investigation over microstructure and HIP processing effects on wear performance of pure chromium parts fabricated by laser powder bed fusion

Chromium (Cr) and its alloys have long been valued for their exceptional properties, including corrosion resistance and high-temperature stability, rendering them indispensable in industrial applications such as chemical processing, energy production, and aerospace. However, due to the difficulties in Cr-based alloy manufacturing, there is a need for novel manufacturing methodologies. Additive Manufacturing (AM) emerges as a promising approach, particularly Laser Powder Bed Fusion (LPBF), which allows for intricate designs, reduced material waste, and simplified assembly. However, certain issues still need to be addressed, including defects like cracks and porosities in the manufactured parts. Post-processing techniques such as Hot Isostatic Pressing (HIP) have gained prominence for enhancing the material properties and quality of AM parts, including those produced using LPBF. HIP treatments are effective in eliminating internal pores, although some challenges remain, notably the presence of trapped argon and grain coarsening side effects of HIP process parameters. This study focuses on LPBF-processed pure chromium parts with crystallographic texture and investigates their properties after HIP treatment, including microstructure, hardness, and tribological performance. According to the obtained results: the HIP process reduced cracks, especially in the center region, but increased gaps in the side region. HIP also hindered grain realignment, limiting grain growth, and resulting in high HAGB density and low MUD values. Elevated HIP processing pressure negatively affected tribological performance due to increased grain size, and reduced hardness. This study, for the first time, realized the effect of HIP conditions on the microstructure and tribological performance of LPBF-processed pure Cr.

High critical current density in low-cost iron-based superconducting round wires annealed at ambient pressure

Superconducting round wires with isotropic architecture are preferred in fabrications of cables and magnets. To diminish the obstacles to supercurrent, e.g., voids, cracks and bubbles, over-pressure heat treatment or hot isostatic pressing is indispensable in the final annealing process. Here, we fabricated a stainless steel/Cu/Ag sheathed Ba0.6K0.4Fe2As2 superconducting round wire without the aid of high-pressure sintering. It was found that high-strength outer sheaths and groove rolling synergistically enhance the core density to ∼100%. Combined with the fiber and concentric texture of the superconducting core, the J c reaches 4.45 × 104 A cm−2 at 4.2 K and 10 T. Furthermore, the specially designed conductor architecture not only reduces material costs by lowering the proportion of Ag to ∼3.1%, but also provides high mechanical and thermal stability. This straightforward and cost-effective process can be scaled up for the massive production of long wires for high-field applications.

Effect of heat treatments on strengthening mechanisms in electron beam melted superalloy Inconel 718

Additive manufacturing of Inconel 718 (IN718) has gained significant interest due to its application in various industries such as aerospace and nuclear industry. In the present study, IN718 was fabricated by additive manufacturing using Electron beam melting (EBM). The superalloy was subjected to hot isostatic pressing (HIP) at 1120 °C for 4 h at a pressure of 100 MPa. It was then subjected to two different aging treatments. The standard heat treatment involved a solution treatment (954 °C/1 h), followed by a two step aging (740 °C/8 h + 635 °C/8 h) cycle (HIP + STA). In the second heat treatment, solutionizing (954 °C/1 h), as well as aging (740 °C/4 h + 635 °C/1 h) was carried out inside the hot isostatic press (combined HIP cycle). This leads to shortening of the heat treatment time as well as allows the heat treatment to be done in a single cycle. The investigation of microstructure and mechanical properties of EBM IN718 was carried out for as-built, combined HIP cycle and HIP + STA conditions. All the samples show strong <100> texture along the build direction. The as-built sample shows 0.47 ± 0.3 % defects. No defects were observed in heat treated samples. The volume fraction (%) of the γ″ (Ni3Nb) precipitates in as-built, combined HIP cycle and HIP + STA sample was ∼12%, ∼15% and ∼13% respectively. The contribution by various strengthening mechanisms to the overall yield strength was calculated by considering solid solution, grain boundary, dislocation and precipitation strengthening. The primary contribution to the overall yield strength was by precipitation strengthening. For as-built, combined HIP cycle and HIP + STA samples, the estimated precipitation strengthening contribution was ∼723 MPa, ∼701 MPa and ∼551 MPa, respectively. The difference may be attributed to the volume fraction, aspect ratio and size of the precipitates present. The as-built sample shows a lower experimental yield strength than its theoretical yield strength. This may be attributed to the defects present in the as-built sample. The combined HIP cycle is recommended as it leads to best mechanical properties. Reasons for this are discussed.

Effect of heat treatment on microstructure and mechanical properties of AlSi10Mg fabricated using laser powder bed fusion

Thermal heat treatment is an important step in many metal additive manufacturing processes, particularly laser powder bed fusion (PBF-LB), as it can homogenize the microstructure and enhance the properties of the resulting parts. The effects of post-processing via direct ageing (DA), stress-relieving (SR), and DA or SA followed by annealing or hot isostatic pressing (HIP), on the microstructure, porosity, and resultant mechanical properties of AlSi10Mg samples manufactured using PBF-LB were investigated in this study. Samples were fabricated over a range of processing conditions to probe different starting microstructures and pore features. Porosity and sub-grain solidification cells were characterized because these features are known to influence strength, ductility, and microhardness. DA increased strength at the expense of ductility due to the precipitation of Si-rich particles while SR improved ductility at the expense of strength due to the broken Al/Si eutectic microstructure. Subsequent annealing of DA samples resulted in further breakdown of the Al/Si eutectic microstructure as well as coarsening of Si-rich precipitates, resulting in lower strength and higher ductility than DA alone. HIP resulted in near fully dense and homogenized samples with coarse Si particles, significantly increasing elongation over all other heat treatments. This study shows that processing parameters and heat treatments can be used to tailor porosity, cell size, and resultant mechanical properties of PBF-LB AlSi10Mg.

Mechanical properties and joining mechanism of hot isostatic pressing (HIP) diffusion bonded Ni60A-0Cr18Ni10Ti heterogeneous joint

Ni-Cr-B-Si alloys, as alternative alloys for Co-based alloys, are expected to be used in pump in nuclear power plants owing to their excellent wear resistance and lower dose rate. In this work, Ni60A (Ni-Cr-B-Si) hardfacing layer with high hardness (average 898 HV0.2) and excellent bonding strength (ultimate tensile strength 549 MPa) was fabricated onto 0Cr18Ni10Ti (GB/T 1220–2007) austenite steel by hot isostatic pressing (HIP) diffusion bonding technique. The Ni60A-0Cr18Ni10Ti heterogeneous joint was divided into four regions based on the microstructural difference, namely Ni60A hardfacing layer, transition zone, deformation zone and 0Cr18Ni10Ti substrate. The Ni60A hardfacing layer was mainly composed of CrB, Cr7C3, Ni3B, Ni3Si and rarely γ-Ni phases, and the synergistic effects of hard phase contents and fine grain sizes resulted in the high hardness. The transition zone was predominantly composed of equiaxed (Ni, Fe) solid solution ((Fe, Ni)ss), which was attributed to diffusion-induced recrystallization (DIR). The deformation zone exhibited discernible deformation texture, which was induced by the plastic deformation of the substrate during the HIP process. Meanwhile, nano-twins (NTs) and Cr2B borides were observed in the deformation zone near the interface, while Cr-rich carbides were observed in the deformation zone away from the interface. Uniaxial tension results of the joint revealed that the failure initiated on the Ni60A side, approximately 70 μm away from the interface, was attributed to a greater prevalence of Cr7C3 precipitates with notable stacking faults.

High-Temperature Thermal Stability of Hot Isostatic Pressed Co25.1Cr18.8Fe23.3Ni22.6Ta8.5Al1.7 (at%) Eutectic High-Entropy Alloy

An eutectic high-entropy alloy (EHEA) consisting mainly of a face-centered cubic (FCC) phase and a C14 Laves phase with the compositions of Co25.1Cr18.8Fe23.3Ni22.6Ta8.5Al1.7 (at%) was successfully prepared by hot isostatic pressing. The present EHEA exhibits a skeleton-type Laves phase structure, deviating from typical EHEA structures. After a series of annealing treatments at 1000 °C for different durations (ranging from 0 to 150 h), the Co3Ta phase precipitated after annealing. The mechanical properties measured at 850 °C showed a tensile strength of 441 MPa and an elongation of 3.3%. The results of the high-temperature tests showed that the mechanical properties of this alloy did not change significantly before and after annealing, and its microstructure showed a high degree of stability, which suggests that the material has some potential for use in high-temperature environments.

Effects of Thermal Exposure on the Microstructure and Mechanical Properties of a Ti-48Al-3Nb-1.5Ta Alloy via Powder Hot Isostatic Pressing.

Research on how thermal exposure affects the microstructure and mechanical properties of the Ti-48Al-3Nb-1.5Ta (at. %) alloy, which is prepared via powder hot isostatic pressing (P-HIP), is essential since this low-density alloy shows promise for use in high-temperature applications, particularly for aero-engines, which require long-term stable service. In this study, a P-HIP Ti-48Al-3Nb-1.5Ta (at. %) alloy was exposed to high temperatures for long durations. The phase, microstructure and mechanical properties of the P-HIP Ti-48Al-3Nb-1.5Ta alloy after thermal exposure under different conditions were analyzed using XRD, SEM, EBSD, EPMA, TEM, nanomechanical testing and tensile testing. The surface scale is composed of oxides and nitrides, primarily Al2O3, TiO2, and TiN, among which Al2O3 is preferentially generated and then covered by rapidly growing TiO2 as the thermal exposure duration increases. The nitrides appear later than the oxides and exist between the oxides and the substrate. With increasing exposure temperature and duration, the surface scale becomes more continuous, TiO2 particles grow larger, and the oxide layer thickens or even falls off. The addition of Ta and Nb can improve the oxidation resistance because Ta5+ and Nb5+ replace Ti4+ in the rutile lattice and weaken O diffusion. Compared with the P-HIP Ti-48Al-3Nb-1.5Ta alloy, after thermal exposure, the grain size does not increase significantly, and the γ phase increases slightly (by less than 3%) with the decomposition of the α2 phase. With increasing thermal exposure duration, the γ phase exhibits discontinuous coarsening (DC). Compared with the P-HIP Ti-48Al-3Nb-1.5Ta alloy, the hardness increases by about 2 GPa, the tensile strength increases by more than 50 MPa, and the fracture strain decreases by about 0.1% after thermal exposure. When the depth extends from the edge of the thermally exposed specimens, the hardness decreases overall.

Atomic-scale insights into liquid phase sintering of intermittent hot isostatic pressing (HIP) experiments

In this work, liquid phase sintering (LPS) process in hot isostatic pressing (HIP) is systematically investigated at atomic scale with the help of advanced spherical aberration correction transmission electron microscope and nanoindentation. Five intermittent HIP experiments of a self-designed 90W-4.2Ni-1.8Fe-4Cu (wt. %) alloy are interrupted and characterized. Together with DSC curve, the pressure-assisted LPS could be divided into two stages, the incipient and fully LPS stages. The results show that the relative density is saturated immediately at the incipient LPS stages and particle rearrangement takes place, leading to the formation of large matrix pools. However, the matrix elements are separated into nano-precipitates during the cooling of liquid phase in the matrix pool. On the other hand, the elements are mixed into a solid solution phase during fully LPS stage, even though the dispersed particles (in our case W) grow bigger and bigger. The mechanical tests show that the solid solution strengthening of matrix phase and redistributed microstructure driven by external hydrostatic pressure and capillary force after fully LPS result in the improved mechanical properties at higher pressure.

In situ synthesis of titanium alloy powders reinforced with nanoparticles for powder bed fusion: A step towards safer and more sustainable manufacturing

Additive manufacturing technologies for metallic materials based on powder bed fusion, either with electron (PBF-EB/M) or laser beam (PBF-LB/M) have enormous industrial potential. It is known that the reinforcement of nanoparticles in the metallic matrix improves the mechanical properties. This study presents a novel method for manufacturing reinforced powder particles for PBF technology. The method involves dispersing and dissolving reinforcing nanoparticles in the metallic matrix, resulting in a composite material. The method was applied to a Ti‐6Al‐4V matrix with SiC nanoparticles as reinforcement to develop a new Titanium Matrix Composite (TMC). A route for atomizing the composite material has been developed to scale up the process on an industrial level. The atomized material has been designed to be used as feedstock with PBF-EB/M and PBF-LB/M. The feedstock is a composite powder obtained by the Electrode Inert Gas Atomization (EIGA) process after mixing and dispersing SiC nanoparticles in the Ti‐6Al‐4V matrix and consolidating the mixture into an ingot bar using Hot Isostatic Pressing (HIP). The powder bed fusion process parameters have been studied to obtain specimens with a density greater than 99.9%, and close to 100% after HIP process. The conditions for some heat treatments, such as HIP and stress relief, have been determined. The conditions of machining processes, such as milling and turning, have been studied. The material’s properties, such as chemical composition, microstructure, mechanical strength, and fatigue behavior have been evaluated. Compared to Ti‐6Al‐4V according to the ASTM F2924 standard, both the ultimate tensile strength and yield strength have been improved by 28%, and the elongation at break by between 30% and 60%. Regarding fatigue behavior, an increase of around 30–50% (high-low cycles) has been observed.

Microstructure and Mechanical Properties of a Novel Al-Mg-Sc-Ti Alloy Fabricated by Laser Powder Bed Fusion.

(TiH2 + ScH3)/Al-Mg composite powders with different Ti contents were produced by ball milling. These composite powders were fabricated to cube and cuboid shape samples via a laser powder bed fusion process with optimal processing parameters. The TiH2 and ScH3 particles underwent dehydrogenation during the laser powder bed fusion process, and these composite powders ultimately formed Al-Mg-Sc-Ti alloys. The relative density, printability, microstructure, hardness and tensile properties of these alloy samples were investigated. The results show that these Al-Mg-Sc-Ti alloys have lower hot-crack sensitivity, having fine equiaxed grains. An Al18Mg3(Ti,Sc)2 intermetallic phase and in situ L12-Al3(Sc,Ti) precipitations formed during the laser powder bed fusion process, which is beneficial for nucleation and dispersion strengthening. The ultimate tensile strength of the Al-Mg-0.7Sc-1.0Ti alloy was 313.6 MPa with an elongation of 6.6%. During the hot isostatic pressing treatment, most of the Mg element precipitated from the matrix and changed the Al3(Sc,Ti) into a Al18Mg3(Ti,Sc)2 precipitate completely. The Al-Mg-Sc-Ti alloys were nearly fully dense after the hot isostatic pressing treatment and exhibited better mechanical properties. The ultimate tensile strength of the Al-Mg-0.7Sc-1.0Ti was 475 MPa with an elongation of 8.5%.

Highly transparent Tb3Al5O12 ceramics for kilowatt‐level Faraday isolator

AbstractTb3Al5O12 (TAG) ceramics with high optical quality were fabricated successfully by a solid‐state reaction method combined with hot isostatic pressing (HIP) post‐treatment. The microstructure, optical transmittance, Verdet constant, and thermo‐optical properties were investigated. The obtained TAG ceramics showed a dense microstructure, and the in‐line transmittance reached 82.8% at 1070 nm after laser‐grade polishing. The Verdet constant of TAG ceramics was measured to be 50.9 rad·T1·m−1 at 1070 nm, which is higher than that of commercial Tb3Ga5O12 crystals. The Faraday isolator based on TAG ceramics can provide an isolation ratio of 30 dB with a laser power of more than 1 kW. With excellent optical quality, high Verdet constant, and maximum working power, TAG transparent ceramics are promising for applications of kilowatt‐level Faraday isolators.

Processing, Microstructure, and Properties of Bimetallic Steel-Ni Alloy Powder HIP

This work explores technical feasibility in hot isostatic pressing (HIP) manufacturing of an integral bimetallic component using steel and Ni alloy powder for supercritical carbon dioxide (sCO2) turbomachinery. Lab-scale bimetallic HIP specimens using HAYNES® 282® and SS316L or SS415 powder are investigated in powder configuration, heat treatment, microstructure, and tensile properties up to 400 °C. Interdiffusion profiles at dissimilar alloy interfaces caused by HIP cycle is predicted by DICTRA simulations and validated by electron probe microanalysis (EPMA). The interdiffusion distance of most elements is around 100 μm, while C and N have a higher interdiffusion distance. Dense distribution of Ti-rich carbonitrides and alumina particles are found to decorate prior particle boundaries near joining interface on the 282 side, affecting tensile strength across interface as well as tensile failure location. A higher amount of excessive carbonitride formation near interface is observed in SS316L/282 than in SS415/282, which is consistent with the predicted greater degree of interdiffusion effect in SS316L/282. Typical HAYNES® 282® heat treatment condition is applicable to 282/SS316L and 282/SS415 combinations, resulting in a higher strength than cast CF8M and CA6NM. A pilot-scale bimetallic SS415/282 pipe is then demonstrated to show the promise of scaleup.

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.

High luminous efficiency and high saturation threshold in highly transparent LuAG:Ce phosphor ceramics for laser diodes lighting.

Lu3Al5O12:Ce (LuAG:Ce) phosphor ceramics (PCs) with the excellent thermal stability and high saturation threshold are considered as the best green-fluorescent converters for high-power laser diodes (LDs) lighting. In this study, the effects of sintering additives and sintering processes on the transmittance and microstructure of LuAG:Ce PCs were systematically studied, and the luminescence performance of ceramics with different transmittance was compared. LuAG:Ce PCs with the transmittance of 80% (@800 nm, 1.5 mm) were obtained by using 0.1 wt.% MgO and 0.5 wt.% TEOS as sintering additives, combined with optimized vacuum pre-sintering and hot isostatic pressing. Compared to the non-HIP samples, the transmittance had increased by 11%. The microstructure of ceramics indicated that high transparency was closely related to the decrease in intergranular pores. Notably, the luminous efficiency of 253 lm/W and its saturation thresholds of > 46 W/mm2 were obtained simultaneously in green-emitting LDs devices. Moreover, under 3W laser irradiation, highly transparent ceramics had the low surface temperature of 66.4 °C, indicating the good heat dissipation performance. The observed high luminous efficiency and high saturation threshold of LuAG:Ce PCs were attributed to fewer pores and oxygen vacancies. Therefore, this work proves that highly transparent LuAG:Ce PCs are promising green-fluorescent converters for high-power LDs lighting.

The Impact of HIP Process and Heat Treatment on the Mechanical Behaviour of an Al–Si–Mg Alloy Component

AbstractThis study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.