Use Of Hot Isostatic Pressing Research Articles

Pore tracing in additive manufactured and hot isostatic pressed components

Despite past scientific efforts and the increased use of hot isostatic pressing (HIP) in additive manufacturing applications, a complete understanding of the exact pore-closing behaviour has yet to be achieved. The present research focuses on laser powder bed fused (LPBF), hot isostatic pressed components made of AlSi10Mg, and process-related defects. The study shows the effect of HIPing in relation to various pore characteristics, such as pore shape, size, and type. A pore tracing method using X-ray data was developed to characterise the pores before and after HIP. The method is based on the k-nearest neighbours approach and allows to match leftover pores with the initial ones. Hence, the efficiency of the pore-closing behaviour for different HIP settings can be analysed. Moreover, the exact number of pore transformations can be tracked, providing a comprehensive insight into the change of pore characteristics during HIP. In this framework, eight different HIP settings and a total number of 274,886 pores were examined and discussed. The findings demonstrate that longer treatment times and higher pressure and temperature settings accelerated the pore transformation. Irregularly shaped and large pores close faster than spherically shaped and smaller ones. Furthermore, regardless of the initial pore type, all pores started transforming their shape towards irregular shapes and small pore diameters. Some pores remained after the HIP treatments, probably due to the inefficiency of HIP in closing pores connected with the component surface or the presence of oxide particles interfering with the diffusion bonding process.

HIP effect on microporosity value of large-sized working cast blades sections of IN-92-5A alloy

The formation of a dense cast billet is a basic requirement for products made of heat-resistant alloys. Based on the comparison of research results, the use of hot isostatic pressing (hereinafter – HIP) for castings made of IN-792-5A alloy. Work on selection of technological regimes to reduce the microporosity content in the body of cast billet has been carried out. The object of the research was a cast billet of the working blade of the fourth stage of a high-power gas turbine unit.

Rejuvenation of Nickel-Based Superalloy Experiencing Creep via Use of Hot Isostatic Pressing and Heat Treatment

Rejuvenation of Nickel-Based Superalloy Experiencing Creep via Use of Hot Isostatic Pressing and Heat Treatment

Comparison of Precursor Preparation Routes on Final Density of Y3Fe5O12 Garnets Prepared via Reactive Sintering.

Yttrium iron garnet was obtained using four methods of synthesis. A modified citrate method and a modified citrate method with YIG (yttrium iron garnet, Y3Fe5O12) nucleation were used. In two subsequent methods, YIP (yttrium iron perovskite, YFeO3) and α-Fe2O3 obtained in the first case by the citrate method and in the second by precipitation of precursors with an ammonia solution were used as the input precursors for reaction sintering. Differential scanning calorimetry (DSC) measurements of the output powders obtained by all methods allowed to identify the effects observed during the temperature increase. Dilatometric measurements allowed to determine the changes in linear dimensions at individual stages of reaction sintering. In the case of materials obtained by the citrate method, two effects occur with the increasing temperature, the first of which corresponds to the reaction of the formation of yttrium iron perovskite (YIP), and the second is responsible for the reaction of the garnet (YIG) formation. However, in the case of heat treatment of the mixture of YIP and α-Fe2O3, we observe only the effect responsible for the solid state reaction leading to the formation of yttrium iron garnet. The obtained materials were reaction sintered at temperatures of 1300 and 1400 °C. Only in the case of material obtained from a mixture of perovskite and iron(III) oxide obtained by ammonia precipitation at temperature of 1400 °C were densities achieved higher than 98% of the theoretical density. The use of Hot Isostatic Pressing (HIP) in the case of this material allowed to eliminate the remaining porosity and to obtain full density.

Structure and properties of EP741NP heat-resistant nickel alloy produced by selective laser melting

EP741NP alloy samples featuring various types of defects with the volume fraction varying from 0.31 to 0.65 % were produced by the method of selective laser melting (SLM) at various process conditions. The structure of SLM samples was investigated using optical and scanning electron microscopy, and mechanical properties were determined by tensile tests. All investigated SLM samples featured by low strength characteristics due to the metastable single-phase structure formation, as well as structural defects in the form of cracks. To improve mechanical properties, various types of post-processing were carried out including hot isostatic pressing (HIP), heat treatment according to the «solution + aging» (HT) type, and comprehensive processing combining HIP and HT. According to the research results, the influence of various post-processing types on the microstructure and properties of SLM samples were determined. It was established that the use of HIP contributes to a decrease in porosity to 0.04 %, structure recrystallization, and the precipitation of a strengthening intermetallic phase based on Ni3Al (γ ′-phase) in the form of large particles of different sizes forming agglomerates. HT leads to the structure recrystallization and precipitation of a finely dispersed γ ′-phase uniformly distributed in the alloy matrix. In this case, strength characteristics of samples after HIP and HT are approximately at the same level (σв ~ 1250÷1290 MPa), however, the ductility of samples after HT is significantly lower. This is associated with the retention of defects in the structure in the form of cracks and large pores. The maximum increase in mechanical characteristics (σ up to 1460 MPa, δ up to 21.3 %) was recorded during comprehensive post-processing (HIP + HT) that ensures defect elimination and optimal alloy structure formation.

Productivity enhancement of laser powder bed fusion using compensated shelled geometries and hot isostatic pressing

In laser powder bed fusion (L-PBF), the mechanical performance and especially fatigue properties of fabricated parts are significantly improved by hot isostatic pressing (HIP) as the density increases (pores are closed) and the microstructure improves. HIP ensures consistent and defect-free material, and consequently, this high temperature and high pressure process is often a requirement for safety-critical aerospace applications. The use of HIP to directly consolidate intentionally-unmelted interior powder in a L-PBF part was recently demonstrated. By confining the laser melting to only the outer shell (contour) of the structure, L-PBF production times can be dramatically reduced. A subsequent HIP cycle, which may be mandatory for reliability reasons, and therefore does not add additional costs, is then used to densify the entire structure. Production rates and energy efficiencies can therefore be improved in this way. This study explores the effect of relying on the HIP process to consolidate interior sections of test coupons, for which micro computed tomography (microCT), process simulation and tensile tests were conducted. MicroCT of coupons with varying shell thicknesses identify the minimum shell thickness required; and provide indications of the shrinkage ratio as a function of powder content relative to shell thickness. Preliminary results are included in which the shrinkage can be compensated for during design, by way of a “bloated cube” which collapses to a nominal cube geometry after HIP. The mechanical evaluation of the consolidated shelled parts indicates that their tensile performance is equivalent to those observed on fully dense printed parts. Up to an order of magnitude faster build rates are possible and any resulting shrinkage or distortion can be offset at design.

Investigating the hot isostatic pressing of an additively manufactured continuous carbon fiber reinforced PEEK composite

Abstract Additive manufacturing has recently begun to explore its role in the composites industry, utilizing the capability of complex fiber placement and part geometry to further reduce the weight of composite structures. Additively manufactured (AM) thermoplastic composites suffer weak interlayer bonding and high void contents. This study investigates the use of hot isostatic pressing (HIP) to post-process AM continuous carbon fiber reinforced polyetheretherketone (PEEK) composites to improve their flexural, interlaminar shear, tensile, and compressive properties. Isostatic pressure (200 psi) and elevated temperatures were used in combination to compress internal voids, promote PEEK crystallization, and enhance inter-filament polymer diffusion.Three different HIP temperatures of 200 °C, 250 °C, and 300 °C, between the glass transition and heat deflection temperatures of the composites, were considered. The post-processing was found to improve properties, with flexural strength and interlaminar shear strength improvements of up to 46% and 30%, respectively, and tensile strength and modulus reaching values as high as 1312 MPa and 92 GPa. The accompanying changes in void content and polymer structure for various HIP processing parameters were investigated to account for the changes in mechanical properties and failure mechanisms. Specifically, increasing the treatment temperature was found to monotonically reduce the void content. The polymer degree of crystallinity (DOC), however, was found to change appreciably only for the highest treatment temperature (300 °C), which negatively impacted the flexural and interlaminar composite properties. Treatment at 300 °C is understood to embrittle the polymer matrix, thereby increasing the stress concentration factors of the internal porosity. HIP demonstrates a fast and robust method to post-process AM composite parts, resulting in a significant improvement in their mechanical performance whereas a high crystallinity with void presence could degrade the performance of AM composites. The outcome of this study can be utilized to improve both the additive manufacturing process and post-HIP treatment to enhance the performance of AM composites.

Extremely dense microstructure and enhanced ionic conductivity in hot-isostatic pressing treated cubic garnet-type solid electrolyte of Ga2O3-doped Li7La3Zr2O12

A large number of pores and a low relative density that are frequently observed in solid electrolytes reduce severely their ionic conductivity and thus limit their applicability. Here, we report on the use of hot isostatic pressing (HIP) for ameliorating the garnet-type lithium-ion conducting solid electrolyte of Ga2O3-doped Li7La3Zr2O[Formula: see text] (Ga-LLZO) with nominal composition of Li[Formula: see text]Ga[Formula: see text]La3Zr2O[Formula: see text]. The Ga-LLZO pellets were conventionally sintered at 1075[Formula: see text]C for 12[Formula: see text]h, and then were followed by HIP treatment at 120[Formula: see text]MPa and 1160[Formula: see text]C under an Ar atmosphere. It is found that the HIP-treated Ga-LLZO shows an extremely dense microstructure and a significantly enhanced ionic conductivity. Coherent with the increase in relative density from 90.5% (untreated) to 97.5% (HIP-treated), the ionic conductivity of the HIP-treated Ga-LLZO reaches as high as [Formula: see text][Formula: see text]S/cm at room temperature (25[Formula: see text]C), being two times higher than that of [Formula: see text][Formula: see text]S/cm for the untreated one.

Effects of Hot Isostatic Pressing on Copper Parts Fabricated via Binder Jetting

Binder Jetting, an Additive Manufacturing process that fabricates parts via selective inkjet deposition of binder into a powder bed, is capable of cost-effectively producing complex metal and ceramic components without the need for support structures or anchors. Printed green parts are then sintered for added densification and strength. However, printed parts typically contain porosity due to the use of coarse powders and a loosely packed powder bed. While researchers have investigated many techniques (e.g., process parameter and powder morphology optimization) for achieving full theoretical density in binder jetted parts, 100% density is difficult to achieve without infiltration of a secondary lower melting point material. In this work, the authors investigate the use of Hot Isostatic Pressing (HIP) as a post-process heat treatment of sintered parts to evaluate its effect on density, porosity, and shrinkage of parts printed in Binder Jetting. The authors conduct this investigation in the context of copper. It is demonstrated that the use of HIP can improve the final part density from 92% (following sintering) to 99.7% of theoretical density.

Assessment of a controlled solidification aluminium investment casting technique for use in helicopter gearboxes

By using a combination of cast plates and a helicopter gearbox casting, the superiority of a controlled solidification investment casting process in terms of strength, ductility and fatigue resistance was observed, when compared to three sand casting processes (conventional, low pressure and low pressure with chills) and a conventional investment casting process was observed. The most important factors responsible for the high levels of tensile strength and ductility and fatigue life were a refined grain size, a fine distribution of particles, a low level of porosity and a reduction in the level of bifilm formation. When porosity levels were low, i.e. less than 0.6%, a refined grain size and microstructure have been shown to be the most important factors influencing strength and ductility. Further improvements in the fatigue life within the ‘as-cast’ controlled solidification investment process can be achieved by the use of hot isostatic pressing (HIPping). No statistically significant difference in the fatigue life between the ‘as-cast’ and machined surfaces was observed.A higher degree of mechanical property scatter, as measured by Weibull Modulus and the Coefficient of Variance (CV), was observed between the TGB casting and the cast plates inferring the design of the filling system used by the foundry had not been optimised resulting in higher metal flow and surface turbulence and a greater likelihood of bifilms occurring within the casting.

Manufacturing and testing of a ITER First Wall Semi-Prototype for EUDA pre-qualification

This paper describes the main activities carried out in the frame of EU-DA prequalification for the supply of Normal Heat Flux (NHF) First Wall (FW) panels to ITER. A key part of these activities is the manufacturing development, the fabrication and the factory acceptance tests of a reduced scale FW prototype (Semi-Prototype (SP)) of the NHF design. The SP has a dimension of 221mm×665mm, corresponding to about 1/6 of a full-scale panel, with six full-scale “fingers” and bearing a total of 84 beryllium tiles. It has been manufactured by the AREVA Company in France. The manufacturing process has made extensive use of Hot Isostatic Pressing, which was developed over more than a decade during the ITER Engineering Design Activity phase. The main manufacturing steps for the Semi-Prototype are recalled, with a summary of the lessons learned and the implications with regard to the design and manufacturing of the full-scale prototype and of the series fabrication of the EU-DA share of the ITER first wall (215 NHF panels).The fabricated SP is then tested under High Heat Flux (HHF) in the dedicated test facility of JUDITH-II in Forschungszentrum Jülich, Germany. The objective of the HHF testing is the demonstration of achieving the requested performance under thermal fatigue. The test protocol and facility qualification are presented and the behaviour of the fingers under the 7500 cycles at 2MW/m2 is described in detail.

Manufacturing of small-scale mock-ups and of a semi-prototype of the ITER Normal Heat Flux First Wall

This paper describes the manufacturing development and fabrication of reduced scale ITER First Wall (FW) mock-ups of the Normal Heat Flux (NHF) design, including a “semi-prototype” with a dimension of 305mm×660mm, corresponding to about 1/6 of a full-scale panel. The activity was carried out in the framework of the pre-qualification of the European Domestic Agency (EU-DA or F4E) for the supply of the European share of the ITER First Wall. The hardware consists of three Upgraded (2MW/m2) Normal Heat Flux (U-NHF) small-scale mock-ups, bearing 3 beryllium tiles each, and of one Semi-Prototype, representing six full-scale fingers and bearing a total of 84 beryllium tiles.The manufacturing process makes extensive use of Hot Isostatic Pressing, which was developed over more than a decade during ITER Engineering Design Activity phase. The main manufacturing steps for the semi-prototype are described, with special reference to the lessons learned and the implications impacting the future fabrication of the full-scale prototype and the series which consists of 218 panels plus spares.In addition, a “tile-size” mock-up was manufactured in order to assess the performance of larger tiles. The use of larger tiles would be highly beneficial since it would allow a significant reduction of the panel assembly time.

Reactions in the matrix and interface of the Fe–SiC metal matrix composite system

Abstract Fe–SiC metal matrix composite (MMC) was produced by the use of hot isostatic pressing (HIP) or sintering for consolidation. The SiC in the MMC was in the forms of particulates and chopped fibers. The effect of exposure of the MMC to high temperatures for long time, up to 1.4×10 4 s, was obtained by heat treatment of the HIPed or sintered specimens. A small reaction zone of ∼0.5–1 μm, composed of iron silicides, was observed in specimens HIPed at 1173 K at a pressure of 150 MPa. Cursory mechanical tests indicate an increase in the ultimate tensile strength and the yield strength of 33.1 and 12.6% of the as HIPed specimens, respectively, when the SiC content was 3% by volume. C, originating from the SiC and dissolved in Fe, induces changes in the matrix when the MMC is exposed to high temperatures, leading to the formation of the familiar transformation products. Strengthening by modification of the Fe matrix under controlled conditions is a unique feature of the Fe–SiC MMC system. The kinetics of the reaction zone formation was investigated and it was found that its growth is diffusion controlled and occurs with an activation energy of 205.4 kJ mol −1 . The reaction zone might act as a diffusion barrier preventing fiber degradation as long as the conditions of thermal effects are reasonable, but exposure of the MMC to high temperatures for extended time can result in severe fiber damage. A mechanism is suggested for the reaction zone formation.

Overview of advanced techniques for fabrication and testing of ITER multilayer plasma facing walls

The design of the ITER primary first wall incorporates a multi-layered structure consisting of a layer of beryllium bonded to a layer of copper alloy with embedded stainless steel tubes which in turn is bonded to a stainless steel structure. In this configuration, the stainless steel provides structural support, the copper alloy improved resistance to high heat loads, and the beryllium layer a low Z metal interface with plasma. Fabrication, testing and control of this multi-layered structure, and indeed the entire blanket shield module, calls for advanced methods. Several associations in the four home teams and their industrial partners have been involved in various fabrication and joining tasks now grouped under L4 blanket project. In this paper, an overview of the work done so far for joining stainless steel to stainless steel, stainless steel to copper alloy, copper alloy to copper alloy, and copper alloy to beryllium is presented. Specialised papers dealing with most of the topics treated here are scheduled in this symposium. The fabrication and joining methods presented here, other than the conventional welding and brazing, follow four main routes. Two of them make extensive use of hot-isostatic pressing (HIP); (a) solid to solid; (b) solid or powder to powder, with or without a prior cold or hot isostatic pressing of one of the products. The third combines advantages of casting and HIPping for fabricating large and complex parts. The fourth investigates the possibility of using explosive welding for joining copper alloys to stainless steel. Other methods, including friction welding, are investigated for specific parts. After a brief recall of considerations leading to selection of individual materials, specifications derived for wrought and powder products are presented. Optimised conditions for bonding steel to steel, copper to copper and steel to copper are tabulated and preliminary results obtained from tests on joints are compared with the values obtained for parent materials. Also presented in the paper are the results obtained from high heat flux testing of small scale mock-ups. Throughout the paper the collaboration with industry in defining specifications for reference products, fabrication routes, and construction of large scale mock-ups and their testing are referenced.

Aero Engine Test Experience With CMSX-4® Alloy Single-Crystal Turbine Blades

A team approach involving a turbine engine company (Rolls-Royce), its single-crystal casting facilities, and a superalloy developer and ingot manufacturer (Cannon-Muskegon), utilizing the concepts of simultaneous engineering, has been used to develop CMSX-4 alloy successfully for turbine blade applications. CMSX-4 alloy is a second-generation nickel-base single-crystal superalloy containing 3 percent (wt) rhenium (Re) and 70 percent volume fraction of the coherent γ′ precipitate strengthening phase. Its finely balanced composition offers an attractive range of properties for turbine airfoil applications. In particular the alloy’s combination of high strength in relation to creep-rupture, mechanical and thermal fatigue, good phase stability following extensive high temperature, stressed exposure and oxidation, hot corrosion and coating performance, are attractive for turbine engine applications where engine performance and turbine airfoil durability are of prime importance. The paper details the single-crystal casting process and heat treatment manufacturing development for turbine blades in CMSX-4 alloy. Competitive single-crystal casting yields are being achieved in production and extensive vacuum heat treatment experience confirms CMSX-4 alloy to have a practical production solution heat treat/homogenization “window.” The creep-rupture data-base on CMSX-4 alloy now includes 325 data points from 17 heats including 3630 kg (8000 lb) production size heats. An appreciable portion of this data was machined-from-blade (MFB) properties, which indicate turbine blade component capabilities based on single-crystal casting process, component configuration, and heat treatment. The use of hot isostatic pressing (HIP) has been shown to eliminate single-crystal casting micropores, which along with the essential absence of γ/γ′ eutectic phase, carbides, stable oxide, nitride and sulfide inclusions, results in remarkably high mechanical fatigue properties, with smooth and particularly notched specimens. The Re addition has been shown not only to benefit creep and mechanical fatigue strength (with and without HIP), but also bare oxidation, hot corrosion (sulfidation), and coating performance. The high level of balanced properties determined by extensive laboratory evaluation has been confirmed during engine testing of the Rolls-Royce Pegasus turbofan.

In-situ formation of the Ti 3AlSiC metal matrix composite system from its components

Ti 3AlSiC metal matrix composite (MMC) can be produced directly from its components by mechanical alloying and the use of hot isostatic pressing (HIP) for consolidation. A composite containing 5% SiC produced by this technique is of better quality than the unalloyed Ti 3Al. The progress of in-situ formation of Ti 3Al during sintering or HIP from its constituents, with and without SiC, was analyzed by X-ray diffraction (XRD), with Cu Kα radiation. Ti 3Al or a composite produced on the basis of this compound can also be obtained by sintering of the mechanically alloyed aggregate, but the composite so produced has low density and low specific strength and in general it is inferior to the monolithic base alloy itself. The poor quality is attributed to the formation of an interaction zone at the interface of the fiber and Ti 3Al. The evolution of the reaction zone was followed by optical microscopy. From measuring the interaction zone width it appears that the kinetics of the interface reaction proceeds by a parabolic law with an apparent activation energy of 75 kJ mole −1.

Parametric studies of the hot isostatic pressing of rapidly solidified 304 stainless steel powder

The increasing importance of powder materials fabrication by use of hot isostatic pressing (HIP) has led to recent emphasis on analytical techniques for describing and understanding the process. Understanding of particle consolidation during the HIP process has been attempted through the modelling of densification behavior by considering the deformation of a representative particle due to forces transmitted through the particle contacts. However, the properties of HIPed material have not been thoroughly investigated in terms of their deformation maps and HIP parameters. Mechanical properties of a compact can be quite different depending on the location of various deformation map boundaries. Diffusional creep is involved not only in densification but also in bonding at particle contacts. HIP pressure increases mechanical contact and enhances density but not particle bonding per se. Discrepancies between experimental and calculated data points for shorter HIP times may have been affected by oxide film layer on the original powder.

Farbication of Optically Transparent Lead Magnesium Niobate Polycrystalline Ceramics Using Hot Isostatic Pressing

The physical, dielectric, and optical properties of hot isostatically pressed lead magnesium niobate polycrystalline ceramics modified with 1/2 mol% La2O3, Pb1–3/2xLax□x/2‐(Mg1/3Nb2/3)O3, have been investigated. Methods used to characterize the ceramics included determination of the dielectric permittivity, optical transmittance, and refractive index dispersion. The materials exhibited relaxor ferroelectric type behavior with a peak dielectric constant K > 14000 and average Tc∼−35°C. Various sintering, hot isostatic pressing, and annealing conditions were examined to produce highly dense and optically transparent materials. Through the use of hot isostatic pressing, densities more than 99.5% theoretical and transmittance greater than 50% at 633‐nm wavelength were obtained. Hot isostatic pressing technique appears to be a good alternative to hot uniaxial pressing without the associated problem of PbO volatility, reactivity with the pressure vessel, and geometrical constraints.