Hot Isostatic Pressing Process Research Articles

The Characterization of Reinforced TiAl Intermetallic with Dispersed Cr Particles Consolidated by HIP

A Chromium (Cr) containing TiAl intermetallic has been consolidated by Hot Isostatic Pressing (HIP) process using high purity TiAl pre-alloyed powder as original material. Cr has been selected as an element which improves high temperature mechanical properties of HIPed TiAl intermetallic compound. Cr additions in TiAl powder were changed systematically and microstructure and mechanical properties at elevated temperatures were examined. This study determined the densification behavior of Cr containing TiAl intermetallic powder during HIP process conducted at 1273 K under the pressure of 200MPa. Microstructure of consolidated TiAl + xCr as well as high temperature mechanical properties are presented. Improvement of high temperature tensile strength of as-HIPed TiAl compound was achieved by the effect of Cr particles dispersion and reactive zone formation between Cr particles and TiAl matrix. From these results, it was concluded that tensile strength of HIPed TiAl-5Cr becomes 1.2-1.5 times high than that of HIPed and MIMed TiAl and machinability of TiAl at R.T. also was improved by high elongation of HIPing and Cr addition.

Characteristic evaluation of HIP bonded SS/DSCu joints for surface roughness

Bonding technologies of SS/DSCu, SS/SS and DSCu/DSCu using HIP method have been developed for the fabrication of the ITER shielding blanket first wall. In this study, the effect of the roughness of the HIP bonding surface has been studied for the 1–40 μm roughness from the view points of bondability of surfaces by HIPping and simplification of fabrication procedure. For the tensile properties, it has been found that the effect of the roughness within above range is negligibly small. On the other hand, it has been confirmed that the finer the surface roughness, the higher impact properties for the DSCu/DSCu joints. Significant differences are not found in the SS316L/DSCu and SS316L/SS316L joints with 1–40 μm, though the finer the surface roughness, the slightly higher the impact energy value. Also, it has been found that the HIP bonded joint with good bondability is obtained by using higher HIP pressure, i.e. 200 MPa even with coarser surface roughness, i.e. ∼10 μm, to reduce the machining requirement in the fabrication procedure. In the fabrication of the International Thermo-nuclear Experimental Reactor (ITER) shielding blanket, conditions of the surface roughness and the Hot Isostatic Pressing (HIP) pressure will be selected by taking into account the machining cost for surface preparation and the HIP process cost based on dimensions of the part to be HIP bonded.

Manufacturing routes for stainless steel first wall panels

Hot isostatic pressing (HIP) techniques are being considered in the European Home Team as one of the fabrication routes to produce ITER-FEAT primary first wall panels (PFWP). To demonstrate the potential and the availability of such techniques, material development, innovative mock-up fabrications and numerical modeling for the production of near-net shape components are currently been studied by CEA/CEREM in collaboration with the EFDA-CSU Garching. The aim of this work is to investigate the manufacturing feasibility of advanced PFWP concepts, with reduced pitch between FW cooling channels and reduced material thickness between the FW cooling channels and the front surface, in order to improve the thermal fatigue performance of these concepts. In order to select the best fabrication route, two different manufacturing methods based on the HIP process are being considered. The first one consists in manufacturing of the first wall panel by a HIP forming technique. Mock-ups are made of a serpentine tube expanded into a proper matrix. 2-D computer modeling has been performed to estimate the serpentine deformation. The second manufacturing route is based on the powder HIP technique. Mock-ups have been made of a serpentine embedded into SS powder. In both cases, the objective was to obtain the minimum pitch between the stainless steel (SS) tubes and between the SS tubes and the front face.

Effect of hot isostatic pressing on nanopore in glass-like carbon prepared from phenol–formaldehyde resin

The effect of a hot isostatic pressing (HIP) treatment on glass-like carbon (GC) was investigated by a small-angle X-ray scattering (SAXS) method. The sample was prepared from phenol–formaldehyde resin at 1700°C and then HIP-treated at 2500°C at 200 MPa in inert gas atmosphere. The structure change in pores was expected, because the bulk density of the HIP-treated GC is higher than those of untreated GCs. In order to contrast the HIP-treatment effect, SAXS measurements on untreated GCs were also carried out. The scattering intensity from the HIP-treated GC was weaker than that from the GC which was heat-treated only at the same temperature 2500°C. On the other hand, the distance distribution function (DDF) analysis showed that the sizes and shapes of nanopores for the both GCs are almost the same. It was proved that the HIP process contributes to not reducing the size but decreasing the number of nanopores in the GC. The facts suggest that the size of uncrushed nanopores will be the minimum one for each heat-treated GC.

Terahertz spectroscopic technique for characterizing the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 materials

We have measured the complex index of refraction of Ba(Mg 1/3 Ta 2/3 )O 3 , BMT, ceramics using coherent terahertz (THz) time domain spectroscopy. The dielectric properties of BMT ceramics, which were prepared via a two-step mixed oxide process or a hot isostatic press (HIP) process in 0.1–0.6 THz regime were studied. The real part of the index of refraction of BMT prepared via a two-step process was about 5.04, whereas that of BMT materials prepared via a HIP process was around 4.97. These values are similar to the real part of the index of BMT ceramics in the microwave range ( n =5.0). Hipped BMT materials exhibit much larger power loss and hence lower Q -factor than two-step mixed oxide processed BMT in 0.1–0.6 THz regime.

Indentation creep of nanocrystalline Cu-TiC alloys prepared by mechanical alloying

In recent years, nanocrystalline materials have attracted much attention in materials research because they behave differently from conventional materials. For example, the nanocrystalline materials exhibit enhanced mechanical properties, such as high strength and hardness. The present study was performed to investigate the indentation creep mechanism of nanocrystalline Cu-TiC alloys which were prepared by HIP (Hot Isostatic Press) processing of MA (Mechanical Alloying) powders and hot rolling afterwards. As these materials have high densities and high structural stability, the authors could investigate creep behavior at wide temperature ranges below 0.5Tm (Tm is the melting temperature of copper).

The Effect of Hot Isostatic Pressing on Crack Initiation, Fatigue, and Mechanical Properties of Two Cast Aluminum Alloys

This article presents the results of an experimental materials testing program on the effect of hot isostatic pressing (HIP) on the crack initiation, fatigue, and mechanical properties of two cast aluminum alloys: AMS 4220 and 4225. These alloys are often used in castings for high temperature applications. Standard tensile and instrumented Charpy impact tests were performed at room and elevated temperatures. The resulting data quantify improvements in ultimate tensile strength, ductility, and Charpy impact toughness from the HIP process while indicating little change in yield strength for both alloys. In addition standard fracture mechanics fatigue tests along with a set of unique fatigue crack initiation tests were performed on the alloys. Hot isostatic pressing was shown to produce a significant increase in cycles to crack initiation for AMS 4225, while no change was evident in traditional da/dN fatigue crack growth. The data permits comparisons of the two alloys both with and without the HIP process.

Processing of titanium net shapes by SLS/HIP

SLS/HIP is a hybrid direct laser fabrication method that combines the strengths of selective laser sintering (SLS) and hot isostatic pressing (HIP). SLS can produce complex shaped metal components with an integral, gas impermeable skin. These components can then be directly post-processed to full density by containerless HIP. SLS/HIP is envisioned as a rapid, low-cost replacement for conventional metal can HIP processing. The advantages of freeform fabrication combined with in situ HIP encapsulation include the ability to perform containerless HIP, no adverse container–powder interactions, reduced pre-processing time, and fewer post-processing steps compared to conventional HIP of canned parts. SLS/HIP is currently being developed for Inconel® 625 superalloy and Ti-6Al-4V. This paper focuses on microstructure and mechanical properties of SLS processed and HIP post-processed Ti-6Al-4V. SLS/HIP technology for Ti-6Al-4V was demonstrated by fabricating a subscale AIM-9 missile guidance section housing to specification. This work is funded jointly by DARPA and ONR under contract N00014-95-C-0139 titled `Low Cost Metal Processing Using SLS/HIP'.

硬質材料 カプセルＨＩＰ法により鋼と複合化したＭｏ‐Ｎｉ‐Ｂ系サーメットの特性

The Mo-Ni-B cermets were sintered in cans at various temperature by the hot isostatic pressing (HIP), to obtain the thick layers of the cermet securely bonded with steel. The bonding strength between cermet and steel HIPed at 1393-1523K was enough, but the mechanical properties of HIPed cermet were inferior to those of the vacuumsintered cermet. Especially, the fracture toughness (K1C value) was 65% of the latter.The gas evaporation from the cermet was investigated during the sintering in Ar, and evaporation of CO and boride gas at 1300K-was clarified. In HIP process, this evaporation could not occur sufficiently. The remained carbon reacted with Ta, W or Mo, and the brittle complex carbides were formed certainly. It is thought that the poorness in mechanical properties of HIPed cermet is due to the excess of carbon, oxygen and so on.

Application of HIP bonding to first wall panel fabrication made from reduced activation ferritic steel F82H

As a course of fabrication technology development of DEMO breeding blankets, fabrication of small-scaled first wall panels made from reduced activation ferritic steel F82H has been attempted by applying HIP (Hot Isostatic Pressing) method. By applying the conditions identified in the previous studies, two flat panels with ten cooling channels each have been fabricated. One of the fabricated panels was destructively tested to examine metallurgically sound HIP bonding and to characterize the change of the micro-structure of the F82H steel due to the HIP process. Destructive examination has confirmed sound bonding for all of the HIP interfaces and satisfactory dimensional tolerance, and applicability of HIP bonding to the complex component made from this steel has been demonstrated.

Structural materials by powder HIP for fusion reactors

Tokamak blankets have complex shapes and geometries with double curvature and embedded cooling channels. Usual manufacturing techniques such as forging, bending and welding generate very complex fabrication routes. Hot Isostatic Pressing (HIP) is a versatile and flexible fabrication technique that has a broad range of commercial applications. Powder HIP appears to be one of the most suitable techniques for the manufacturing of such complex shape components as fusion reactor modules. During the HIP cycle, consolidation of the powder is made and porosity in the material disappears. This involves a variation of 30% in volume of the component. These deformations are not isotropic due to temperature gradients in the part and the stiffness of the canister. This paper discusses the following points: (i) Availability of manufacturing process by powder HIP of 316LN stainless steel (ITER modules) and F82H martensitic steel (ITER Test Module and DEMO blanket) with properties equivalent to the forged one. (ii) Availability of powerful modelling techniques to simulate the densification of powder during the HIP cycle, and to control the deformation of components during consolidation by improving the canister design. (iii) Material data base needed for simulation of the HIP process, and the optimisation of canister geometry. (iv) Irradiation behaviour on powder HIP materials from preliminary results.

Hot isostatic pressing of plasma sprayed yttria-stabilized zirconia

Abstract The porosity in plasma sprayed ceramics is caused by the irregular splat formation of the lamellae structure as the molten droplets impact the substrate. This paper reports the influence of hot isostatic pressing (HIP) as a post-spray treatment of plasma sprayed coatings. Investigations are made on the physical properties, pore size distribution and thermo-physical properties, namely thermal diffusivity and thermal conductivity, of plasma sprayed yttria-stabilized zirconia (ZrO2–7.8 wt% Y2O3) coatings after HIP at 1000, 1100 and 1200°C for 1 h. Results show that HIP processing the plasma sprayed coatings reduced the porosity by ~2.5% and increased the microhardness by ~40%. Correspondingly, the thermal diffusivity and thermal conductivity of the coatings were found to be significantly changed after HIP treatment at 1200°C.

Dynamic behavior modeling for P/M superalloys during hot isostatic pressing

A method was developed for the dynamic behavior modeling of P/M superalloys during hot isostatic pressing (HIP). The power dissipative efficiency η during the HIP process was defined as a function of the relative density R and the strain-rate sensitivity index m. Based on the results of isothermal constant strain-rate tests, the microstructure evolution of P/M Rene95 alloy during the HIP process was predicted using the proposed method. The predicted results indicate that HIPing within the temperature range of 1100–1120°C and range of strain rate of 10−4–10−3) may eliminate the residual dendrite and ensure consistency in the microstructures and properties of HIP products, these indications being in good agreement with practical experience.

Aluminum-assisted joining of beryllium to copper for fusion applications

Five different brazing techniques were evaluated in the process of joining beryllium to copper. Aluminum-based filler metals were used in conjunction with aluminum coatings on both beryllium and copper substrates. This innovative approach was born out of the necessity to inhibit the formation of oxides and intermetallics on the aluminum and beryllium surfaces both before and during the joining process. Several bonding techniques, diffusion barriers, and oxide inhibitors were employed to reduce the bonding problem to that of joining aluminum to aluminum. The volume of aluminum in the joint was found to be an important factor in reducing the segregation of secondary alloying elements at the beryllium interface. Plasma sprayed aluminum coatings were too porous to use in the as-sprayed condition and were further processed using a hot isostatic press (HIP) to accomplish full density. The use of plasma sprayed aluminum coatings, Al-12%Si filler metal (Alloy 718), and the HIP process produced excellent bonds between the aluminum coated beryllium and 1100-Al alloy plate which was explosively bonded to a copper alloy. Bond strengths were measured at 100% of the strength of the 1100-Al plate strength (90 MPa). The ductility of the aluminum bond was sufficient to produce extensive necking prior to fracture.

Simulation of Hot Isostatic Pressing of a powder metal component with an internal core

This paper presents a finite element simulation of the thermomechanical phenomena occurring during Hot Isostatic Pressing (HIP) of a powder metal component which includes a graphite core. The thermomechanical coupling is achieved in a staggered step manner. The staggered step approach considers the coupled thermomechanical response of solids, including nonlinear effects in both the thermal and mechanical analyses. The creep behaviour of the powder material during densification is modelled using the constitutive equations of thermal elasto-viscoplastic type with compressibility. The various mechanical material properties are assumed to be functions of temperature and relative density. The mechanical solution also includes large deformation and strains. The thermal problem includes temperature and relative density dependent specific heat and thermal conductivity. The constitutive equations and relations for thermal characteristics are implemented into the implicit nonlinear finite element code, PALM2D. The simulation of the HIP process of a component with internal core is chosen as an application example. The component, injection molding tool, is produced of a hot isostatically pressed stainless tool steel with an internal cavity which is achieved by inserting a graphite core into the HIP container. To verify the result of the simulation, the geometry of the capsule and the coated core are measured both before and after pressing using a computer controlled measurement machine (CMM). The measured geometry is compared with the simulated final shapes of the container and internal core. A computer-aided concurrent engineering system (CACE) is used for the complete manufacturing process from the design of the component and finite element simulation to the inspection of the final geometry.

Forming of silicon nitride by the HIP process

The densification of silicon nitride was carried out by Hot Isostatic Press (HIP) sintering via glass-encapsulation method. The sintering performing techniques were studied in order to obtain high strength properties. α-Si 3N 4 raw powder was used as the starting material in addition with a composition of 3 wt% Al 2O 3 and 5 wt% Y 2O 3. That ratio corresponds to the liquid phase compositions at the lowest temperature in the system Al 2O 3 - Y 2O 3 - SiO 2 with having high strength at room temperature. Density, microstructure, hardness and fracture surface of specimens were measured. The experimental results showed that silicon nitride could have density nearly to theoretical density. X-ray Diffraction pattern indicated the transformation of α-phase to β-phase occurred in every sintered specimens and fully transformed to β phase after complete soaking for 2 hrs. The development of elongated grains was related to the formation of large nuclei during phase transformation. The SEM micrographs and fractograph also showed the β rodlike grain. For the specimens having density over than 95%, the calculated hardness was approximately between 14–16 GPa.

Sintering of partially-stabilized zirconia and partially-stabilized zirconia—hydroxyapatite composites by hot isostatic pressing and pressureless sintering

In this study two sintering techniques, pressureless sintering (PS) and hot isostatic pressing (HIP), were used for comparing the sinterability of two yttria-partially-stabilized zirconia/hydroxyapatite (PSZ/HA) composites. Virtually dense ceramics were obtained using HIP at a maximum pressure of 160 MPa for 1 h at 1225 °C for both PSZ powders and their HA composites. The ceramic bodies, produced using PS at the same temperature as in the HIP process and higher, had densities from 80% to 97% of theoretical density, depending on the properties of the PSZ powders. FTIR spectra of composites sintered by HIP and PS at 1225 °C were compared, indicating a degradation of HA by PS but no degradation by HIP. The bending strength of HIPed ceramics was measured and found to be high. It is concluded that it is possible to produce dense PSZ/HA composites by the HIP or PS processes. For the PS, the reactivity of powders is the key factor during the densification. The HIP technique is the preferable technique for producing stable and dense HA-containing composites.

Simulation of hot isostatic pressing of metal powder components to near net shape

Presents a finite element formulation of hot isostatic pressing (HIP) based on a continuum approach using thermal‐elastoviscoplastic constitutive equations with compressibility. The formulation takes into consideration dependence of the viscoplastic part on the porosity. Also takes into account the thermomechanical response, including nonlinear effects in both the thermal and mechanical analyses. Implements the material model in an implicit finite element code. Presents experimental procedures for evaluating the inelastic behaviour of metal powders during densification and experimental data. Chooses the simulation of the dilatometer measurement of a cylindrical component during HIP and manufacturing simulation of a turbine component to near net shape (NNS) as a demonstrator example. Both components are made of a hot isostatically pressed hot‐working martensitic steel. Compares the result of the simulation in the form of the final geometry of the container with the geometry of a real component produced by HIP. Makes a comparison between the calculated and measured deformations during the HIP process for the cylindrical component. Measures the final geometry of the turbine component by means of a computer controlled measuring machine (CMM). Performs the complete process from design and simulation to geometry verification within a computer‐aided concurrent engineering (CACE) system.

Microstructure-properties relationships in samarium modified lead titanate piezoceramics—I. Quantitative study of the microstructure

Samarium modified lead titanate piezoceramics prepared from hydrothermally synthesized powder are microstructurally characterized. The evolution of the ceramic microstructure of the ceramics during sintering and Hot Isostatic Pressing (HIP) as a post-sintering treatment is studied by a combination of optical and scanning electron microscopies with computerized image analysis. The obtained grain size and pore area distributions are studied through the use of probability plots. The analysis of the grain size distributions indicates that a process of normal grain growth takes place during sintering. The pore area distributions of some of the studied ceramics are bimodal, revealing a degradation of the microstructure, with the appearance of large area pores as sintering time or temperature increases. The post-sintering HIP process reduces drastically the ceramic porosity and acts mainly on the pores of large area, thus restoring the degraded microstructures.

Effect of Rising <i>R</i>-Curve Behavior on the High-Temperature Delayed-Failure Resistance of Si<sub>3</sub>N<sub>4</sub> Ceramics under Elastic Slow-Crack-Growth Regime

The effect of a rising R-curve behavior on the high-temperature lifetime and flaw-tolerance of Si3N4 ceramics has been systematically investigated. Extensive mechanical testing was pursued at 1400°C, typical temperature at which the selected materials fractured under the elastic slow-crack-growth (SCG) regime (i.e., with negligible plastic strain). Hot-isostatically pressed (HIP) Si3N4, its WC-platelet, SiC-platelet and SiC particulate composites were selected for this basic investigation. All the composites investigated contained the same volume fraction (i.e., 25%) of reinforcing phase and were fully dense after the HIP process without external addition of densification agents. This latter important processing circumstance has made available materials which, besides having the same grain-boundary structure and, hence, the same intrinsic thermo-mechanical response of the grain boundaries at high temperature, showed different R-curve behaviors. It was systematically found that the rising R-curve, especially pronounced in composites reinforced with high-aspect-ratio platelets, provided a positive effect on lifetime and flaw-tolerance. From the theoretical side, both the lifetime elongation and the improved flaw-tolerance were well explained by an algorithm incorporating into the mechanical driving force acting on the crack tip, the closure-field contribution due to the rising R-curve behavior of the material.