Hot Isostatic Pressing Process Research Articles

Experimental studies of prototype models of bimetallic blisks of a high-temperature turbine with cooled blades for advanced gas turbine engines

The traditional approach to designing turbine blisks based on the application of disk-blade pawl-coupling does not allow improving the design from the point of view of increasing the service life, reducing the wheel mass and improving the engine efficiency on the whole. This problem can be solved by using dissimilar materials in the integrated bimetallic wheel (blisk). Bimetallic blisk prototype models of a high-temperature turbine have been produced for strength durability research. The bimetallic blisk prototype model consists of one monocrystal cooled blade and a granulated Ni-based disk part. These elements are connected by the hot isostatic pressing (HIP) method. Capsular equipment is designed for producing the prototypes. It ensures the air tightness of the zone of joining of the blisk elements and preservation of the cooling lines in the blades during the HIP process.  Investigations of micro- and macrostructures of prototype joining zones have been carried out. High-cycle fatigue tests of bimetallic blisk prototype models have been carried out. It has been found that fatigue cracks originate in the blade material, whereas the zone of diffusion bonding of the two alloys in test conditions proved to be stronger than the blade material.

Iodine immobilization: Development of solidification process for spent silver-sorbent using hot isostatic press technique

The iodine filters which are used after nuclear fuel reprocessing contain radioactive iodine (129I), almost all of which exists as silver iodide (AgI) adsorbed by the silver doped alumina base sorbents. In this work solidification of iodine contaminated silver-sorbent within alumina matrix is studied using a hot isostatic press (HIP). The product is treated to form a dense solidified material, where 129I is physically confined in the form of AgI in the alumina based composite.This paper deals with the development of the production process. Silver-sorbents loaded with inactive iodine (I2) were prepared for HIP treatments. Although several types of alumina are originally present in the alumina based materials, they were found to be transformed to corundum after the HIP treatment. Optimization of the HIP process conditions was carried out. The effects of the major parameters on the process were investigated. Scanning electron microscope observations (SEM) confirmed that iodine was confined as AgI in the alumina matrix after the HIP treatments. A certain number of voids (void ratio: 10–15%) coexisted. Reduction of voids was further investigated and it was established that high temperature and vacuum pretreatment of iodine loaded silver-sorbents before the HIP treatment could significantly reduce void ratios to less than 5% in the solidified bodies. A simulation program for the HIP was developed to predict the size and relative density of the scale-up solidified body.

Influence of hot isostatic pressing on fatigue performance of K403 nickel-based superalloy

Low cycle fatigue experiments of K403 Nickel-based superalloy miniature specimens were carried out in the high temperature fatigue testing machine at 750 °C. These specimens were cut from turbine blades which were processed with hot isostatic pressing (HIP) under two different stresses, 135 MPa and 145 MPa, respectively. The geometric model of the K403 alloy was established based on the observation of its microscopic structure under the scanning electron microscopy (SEM), while its constitutive model was built based on the crystal plasticity theory. Both the fatigue experiments and the finite element analysis (FEA) indicated that the HIP process (especially 145 Mpa HIP treatment) could dramatically reduce the stress concentration and plastic deformation of K403 alloy by eliminating the internal casting defects effectively so as to extend its fatigue life at 750 °C. The SEM analysis demonstrated that the grain boundary carbides have been gradually refined. Moreover, the microstructure of γ and γ′ phase could be largely optimized, which guarantees the improvement of the alloy fatigue property.

Microstructure and Mechanical Properties of Al6061-31vol.% B4C Composites Prepared by Hot Isostatic Pressing

Fabrication of durable and usable composites with high content of B4C (up to 31vol.%) is quite challenging in several aspects including blending, cold isostatic pressing, and hot isostatic pressing (HIP), and especially the optimal HIP process is essential to achieve the metal matrix composite with desirable properties. The microstructure and mechanical properties of Al6061-31vol.% B4C with different particle sizes were investigated by scanning electron microscopy (SEM) and tensile testing, respectively. SEM analysis and quantitative measurements of the particle distribution reveal that B4C particles were uniformly distributed in the matrix without agglomeration when the HIP treatment temperature was about 580 °C, and x-ray diffraction also identified a dispersion of B4C particles as well as reaction products (AlB2 and Al3BC) in the composites. Microhardness of Al6061-31vol.% B4C composites was improved with B4C particle size, and the tensile strength of all the samples declined with an increase in B4C particle size. The contribution from different strengthening mechanisms was also discussed.

Enhancement of the densification and mechanical properties of aluminum-doped zinc oxide ceramics by hot isostatic pressing

The characteristics of sputtering targets used for transparent conductive oxide (TCO) films significantly affect the performances of TCO films produced by sputtering. The purpose of this study was to investigate the effect of hot isostatic pressing (HIP) on the densification, microstructure, electrical properties, and mechanical properties of Al-doped ZnO (AZO) and ZnO ceramic targets. The results showed that HIP treatment obviously improves the relative density, hardness, transverse rupture strength (TRS), and resistivity of AZO ceramics. AZO ceramics with relative densities of higher than 99.9% can be obtained after HIP at 1000 °C or 1250 °C. After HIP at 1250 °C, the resistivities of AZO ceramics are reduced from 6.0 × 10−2±1.1 × 10−2 Ω cm to 6.4 × 10−4±2.9 × 10−4 Ω cm. Furthermore, the hardness and TRS of AZO ceramics are raised from HV 261 ± 6 to HV 322 ± 5 and from 118 ± 3 MPa to 260 ± 3 MPa, respectively, after 1250 °C HIP. In contrast, for ZnO ceramics, the HIP process does not enhance the relative density or hardness, though the TRS and resistivity are improved.

The γ′ precipitate rafting and element distribution during hot isostatic pressing in a nickel-based superalloy

Abstract The γ′ precipitate rafting and the element distribution in the vicinity of creep cavities for a service-damaged nickel-based superalloy during hot isostatic pressing (HIP) were investigated. The concentrically oriented γ′ rafting-like structure near the creep cavities was formed under the HIP condition of 1150 °C/50 MPa/2 h, together with the primary γ′ denuded zone present between the creep cavity and the γ′ rafting zone. When increasing the hydrostatic pressure, the γ′ rafting structure became more and more remarkable. The wavelength-dispersive X-ray spectroscopy (WDX) results show that, the γ′-forming elements migrated from the primary γ′ denuded zone towards the γ′ rafting zone but the solutes in the γ matrix diffused in the opposite direction onto the creep cavity surface during HIP processing, With the increase of the hydrostatic pressure, the amount of γ′-forming elements which were driven by the atomic concentration gradient and diffused towards the γ′ rafting zone was continuously increased and the amount of solutes in the matrix that migrated in the opposite direction was also increased, indicating that the hydrostatic pressure can promote the atomic diffusion and heal creep cavities more effectively. It can be considered that the atomic diffusion mainly dominates pore closure.

Influence of Interfacial Oxidation on the High-Heat-Flux Performance of HIP-Manufactured Flat-Type W/Cu Plasma-Facing Components for EAST

A hot isostatic pressing (HIP) route has been developed by the Institute of Plasma Physics of the Chinese Academy of Sciences in collaboration with the Advanced Technology & Materials Co., Ltd. for bonding W/Cu tiles to Ni-electroplated CuCrZr heat sinks. During high-heat-flux testing, in the initial stage, Cu/Ni interfacial debonding was observed. Careful analyses indicated that interfacial oxidation during encapsulation for HIP processing using tungsten inert gas (TIG) welding was the main cause of the limited fatigue lifetime. Copper oxides formed during the TIG encapsulation do not decompose during HIP at 600°C. As a result, weak bonding and even some microcracks were generated, and unfortunately these microcracks could not be detected by current industrial ultrasonic probes. An oxidation-free encapsulation technique, suitable for batch processing, has been developed to achieve a thermal fatigue lifetime of more than 1000 cycles at a heat load of 5 MW/m2 for the components.

Microstructural characterization and high cycle fatigue behavior of investment cast A357 aluminum alloy

In order to observe the influence of strontium (Sr) modification and hot isostatic pressing (HIP) on an aluminum–silicon cast alloy A357 (AlSi7Mg0.6), the microstructure and the high cycle fatigue behavior of three batches of materials produced by investment casting (IC) were studied. The parts were produced by an advanced IC proprietary process. The main process innovation is to increase the solidification and cooling rate by immersing the mold in cool liquid. Its advantage is to produce finer microstructures. Microstructural characterization showed a dendrite arm spacing (DAS) refinement of 40% when compared with the same part produced by conventional investment casting. Fatigue tests were conducted on hourglass specimens heat treated to T6, under a stress ratio of R=0.1 and a frequency of 25Hz. One batch of material was unmodified but two batches were modified with 0.007% and 0.013% Sr addition, from which one batch was submitted to HIP after casting. Results reported in S–N diagrams show that the addition of Sr and the HIP process improve the 106cycles fatigue strength by 9% and 34% respectively. Scanning electron microscopy (SEM) observation of the fracture surfaces showed a variety of crack initiation mechanisms. In the unmodified alloy, decohesion between the coarse Si particles and the aluminum matrix was mostly observed. On the other hand, in the modified but non HIP-ed alloy, cracks initiated from pores. When the same alloy was subjected to HIP, a competition between crystallographic crack initiations (at persistent slip bands) and decohesion/failure of intermetallic phases was observed. When compared to fatigue strength reported for components produced by permanent mold casting, the studied material are more resistant to fatigue even in the unmodified and non HIP-ed states.

Experimental studies of prototype models of bimetallic blisks of a high-temperature turbine with cooled blades for advanced gas turbine engines

The traditional approach to designing turbine blisks based on the application of disk-blade pawl-coupling does not allow improving the design from the point of view of increasing the service life, reducing the wheel mass and improving the engine efficiency on the whole. This problem can be solved by using dissimilar materials in the integrated bimetallic wheel (blisk). Bimetallic blisk prototype models of a high-temperature turbine have been produced for strength durability research. The bimetallic blisk prototype model consists of one monocrystal cooled blade and a granulated Ni-based disk part. These elements are connected by the hot isostatic pressing (HIP) method. Capsular equipment is designed for producing the prototypes. It ensures the air tightness of the zone of joining of the blisk elements and preservation of the cooling lines in the blades during the HIP process. Investigations of micro- and macrostructures of prototype joining zones have been carried out. High-cycle fatigue tests of bimetallic blisk prototype models have been carried out. It has been found that fatigue cracks originate in the blade material, whereas the zone of diffusion bonding of the two alloys in test conditions proved to be stronger than the blade material.

Enhancement in the microstructure and neutron shielding efficiency of sandwich type of 6061Al–B4C composite material via hot isostatic pressing

Sandwich type of 6061Al–B4C composite plates, which are used as a thermal neutron absorber for spent nuclear fuel pool storage rack, were fabricated using two different consolidation ways as sintering and hot isostatic pressing (HIP) processes and their thermal neutron shielding efficiency was investigated as a function of B4C concentration ranging from 0 to 40wt.%. For this purpose, two respective inner core compaction parts of sintered and HIPped neutron absorbing composite materials were first produced and then cladded them between two outer plates by HIP process. The application of HIP process provided not only a lead of excellent interfacial adhesion due to the improved wettability but also an enhancement of thermal neutron shielding efficiency owing to the more uniform dispersion of B4C particles.

Effect of hot isostatic pressing on microstructure of cast gas-turbine vanes of K452 alloy

The effect of hot isostatic pressing (HIP) treatment on microstructure of gas-turbine vanes made of K452 alloy was investigated by OM, SEM and TEM. The results showed that HIP treatment played a great role in the porosity healing processing, where 80% of porosities were eliminated and the diameter of remnant porosities decreased to 10μm. The healing mechanism of the porosities was consistent with existing theories of porosity closure based on vacancy diffusion. According to the result of the tensile test, the plasticity of the alloy was improved as the result of the elimination of the porosities and the improvement of dendritic segregation, while there was not an obvious improvement in the tensile strength after the programmed HIP process. In addition, HIP had a positive effect on narrowing down the dispersion of tensile properties.

Mechanical and in vitro biological performance of graphene nanoplatelets reinforced calcium silicate composite.

Calcium silicate (CaSiO3, CS) ceramic composites reinforced with graphene nanoplatelets (GNP) were prepared using hot isostatic pressing (HIP) at 1150°C. Quantitative microstructural analysis suggests that GNP play a role in grain size and is responsible for the improved densification. Raman spectroscopy and scanning electron microscopy showed that GNP survived the harsh processing conditions of the selected HIP processing parameters. The uniform distribution of 1 wt.% GNP in the CS matrix, high densification and fine CS grain size help to improve the fracture toughness by ∼130%, hardness by ∼30% and brittleness index by ∼40% as compared to the CS matrix without GNP. The toughening mechanisms, such as crack bridging, pull-out, branching and deflection induced by GNP are observed and discussed. The GNP/CS composites exhibit good apatite-forming ability in the simulated body fluid (SBF). Our results indicate that the addition of GNP decreased pH value in SBF. Effect of addition of GNP on early adhesion and proliferation of human osteoblast cells (hFOB) was measured in vitro. The GNP/CS composites showed good biocompatibility and promoted cell viability and cell proliferation. The results indicated that the cell viability and proliferation are affected by time and concentration of GNP in the CS matrix.

Study on the mechanical properties, microstructure and corrosion behaviors of nano-WC–Co–Ni–Fe hard materials through HIP and hot-press sintering processes

Abstract This study aims to explore a series of Hot Isostatic Pressing (HIP) and hot-press sintering processes in order to examine the effects on the mechanical properties, microstructures and corrosion behaviors of micro- and nano-WC materials. The experimental results showed that the transverse rupture strength (TRS) values of micro- and nano-WC increased to 1627.3 and 1842.7 MPa after 1250 °C, 125 MPa, 100 min HIP treatments, respectively. Meanwhile, the porosity decreased slightly. The corrosion test results also showed that HIP-treated micro- and nano-WC effectively improved corrosion resistance in a 3.5 wt% NaCl solution. In addition, the lowest porosity (0.21%), highest hardness (91.7 HRA) and highest K IC (14.7 MPa√m) values appeared in nano-WC after 1250 °C, 15 MPa, 1 h hot-press sintering. Moreover, the hot-press sintering procedure significantly inhibited the grain growth of the tungsten carbide materials.

Microstructural evolution of MgAl2O4 oxide-dispersion-strengthened alloy by mechanical milling and hot isostatic pressing

Abstract

Simulation and verification of near-net shaping a complex-shaped turbine disc by hot isostatic pressing process

A new constitutive relation for powder materials used in finite element analysis (FEA) of hot isostatic pressing (HIP) complex-shaped parts was derived from Perzyna’s elastic-viscoplasticity equations, and the stick–slip boundary modelling and thermomechanical coupling solution were achieved. The temperature-dependent mechanical and thermal parameters were determined through experiments. A complex-shaped turbine disc from Inconel 625 alloy has been simulated and produced. The predicted dimensions and relative densities have been compared with those measured from the experiments, which shows a good agreement for most regions of the turbine disc. The reasons for local predicted discrepancies and physical defects were discussed, and future improvements for FEA simulation and HIP process were outlined.

Research on characteristics and deformation mechanism of Al2O3 inclusions with different forming processes in powder metallurgy superalloy

In this study, the defects of powder metallurgy superalloys, specifically, the characteristics of aluminium oxide (Al2O3) inclusions in the primal powder superalloy FGH96, were investigated. In addition, the deformation mechanism of Al2O3 inclusions from different forming processes, such as hot isostatic pressing (HIP), hot isostatic pressing and hot isothermal forging (HIP+HIF), hot isostatic pressing and hot extrusion (HIP+HEX) and hot isostatic pressing, hot extrusion and hot isothermal forging (HIP+HEX+HIF), was studied. The results showed that the major types of inclusions in primal powder were Al2O3 and silicon dioxide (SiO2). The Al2O3 inclusion showed purely mechanical bonding with the matrix, and it always ran through several grains. The HEX process played the most important role in crushing Al2O3 inclusion, which was elongated and broken into hundreds of tiny ones along the extrusion direction; there was no effect from the HIP process on the inclusion crushing, and the HIF process had a certain amount of effect in between the HIP and HEX processes.

HIP diffusion bonding of FGH96-DD6 dual alloys

Diffusion bonding of powder metallurgy superalloy FGH96 to single crystal superalloy DD6 by hot iso-static pressing (HIP) was studied. The microstructure and elements diffusion at FGH96-DD6 interface were discussed. The influence of HIP process on the microstructure and mechanical properties of FGH96 and DD6 was investigated. Tensile tests of FGH96-DD6 diffusion joints performed at 750°C showed that metallurgical diffusion bonding of FGH96 to DD6 could be achieved by the appropriate HIP process. The γ′ phase of DD6 grew up with increase of HIP temperature. The tensile mechanical properties of DD6 could also be maintained up to the desired levels with the appropriate HIP process. For FGH96, the variation of HIP temperature in the experimental range did not affect obviously the tensile mechanical property at 750°C.

Preparation and analysis of SiCf reinforced GH4738 composite

SiC fibre reinforced GH4738 composite, a new composite material with excellent elevated temperature mechanical properties and light weight, shows great potential to replace Ni based superalloys turbine disc for aerospace engines. Continuous Ti3Al coated SiC fibre reinforced GH4738 matrix composite was fabricated by hot isostatic pressing (HIP). Physical vapour deposition was used to deposit GH4738 on the surface of the Ti3Al coated SiC fibre. The elevated temperature tensile strength was established for the composite. The fracture surface, fibre surface, interfacial reaction zone and phase composition were analysed by scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. The composite shows higher elevated temperature tensile strength than GH4738 and the composite without coating, but only reaches 30% of its theoretical strength value, which can be explained by matrix diffused through the barrier coating and reacted with SiC fibre in HIP processing. The reaction was complicated, and the products were mainly Ni2Si and Cr23C6.

HIP processing of materials for offshore (energy) applications

The Particulate Engineering Committee (PEC) of IOM3 held its long anticipated workshop on hot isostatic pressing (HIP) of materials for offshore (energy) applications on 16 April in Aberdeen, UK. Hosted by TWI and supported by EPMA, the one day meeting attracted about 30 delegates that filled comfortably the premises to its capacity. It was an opportunity for end users from the oil and gas sector and those involved in powders, consumables, engineering services and other end user communities to come together to capture the latest developments in the field of PM-HIP for offshore and energy applications.

Inclusion of initial powder distribution in FEM modelling of near net shape PM hot isostatic pressed components

The final shape of powder metallurgy hot isostatic pressing (HIP) components is determined by many factors, including the shape and size of the capsule, the initial density distribution of the powder before HIP, and HIP process parameters. Current HIP simulation, which usually assumes that the powder inside the capsule is homogeneous, cannot predict non-uniform shrinkage. Therefore, the purpose of this work is to develop a methodology to quantitatively determine the initial powder density distribution inside HIP capsules, which were precompacted by different techniques. The relative density distribution obtained from experimental work is used as the initial condition for numerical simulations. The final shapes of the capsules produced by HIP are compared to simulation results. The paper shows the sensitivity of the final shape on the initial powder density distribution and illustrates the need to implement the initial powder distribution into the finite element model to improve the quality of the near net shape HIP simulation.