Cold Isostatic Pressing Pressure Research Articles

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.

Effect of Microstructural Change under Pressure during Isostatic Pressing on Mechanical and Electrical Properties of Isotropic Carbon Blocks.

In this study, carbon blocks were fabricated using isotropic coke and coal tar pitch as raw materials, with a variation in pressure during cold isostatic pressing (CIP). The CIP pressure was set to 50, 100, 150, and 200 MPa, and the effect of the CIP pressure on the mechanical and electrical properties of the resulting carbon blocks was analyzed. Microstructural observations confirmed that, after the kneading, the surface of isotropic coke was covered with the pitch components. Subsequently, after the CIP, granules, which were larger than isotropic coke and the kneaded particles, were observed. The formation of these granules was attributed to the coalescence of kneaded particles under the applied pressing pressure. This granule formation was accompanied by the development of pores, some remaining within the granules, while others were extruded, thereby existing externally. The increase in the applied pressing pressure facilitated the formation of granules, and this microstructural development contributed to enhanced mechanical and electrical properties. At a pressing pressure of 100 MPa, the maximum flexural strength was achieved at 33.3 MPa, and the minimum electrical resistivity was reached at 60.1 μΩm. The higher the pressing pressure, the larger the size of the granules. Pores around the granules tended to connect and grow larger, forming crack-like structures. This microstructural change led to degraded mechanical and electrical properties. The isotropic ratio of the carbon blocks obtained in this study was estimated based on the coefficient of thermal expansion (CTE). The results confirmed that all carbon blocks obtained proved to be isotropic. In this study, a specimen type named CIP-100 exhibited the best performance in every aspect as an isotropic carbon block.

High-strength and wave-transmitting Si3N4–Si2N2O-BN composites prepared using selective laser sintering

In this study, high-strength and wave-transmission silicon nitride (Si3N4) composites were successfully developed via selective laser sintering (SLS) with cold isostatic pressing (CIP) after debinding and before final sintering, and the optimal moulding process parameters for the SLS Si3N4 ceramics were determined. The effects of the sintering aids and secondary CIP on the bulk density, porosity, flexural strength, fracture toughness, and wave-transmitting properties of the Si3N4 composites were studied. The results showed that the increased CIP pressure was beneficial to the densification of SLS Si3N4 ceramics and improved their mechanical properties. However, the wave-transmitting performance decreased as the CIP pressure increased. The Si3N4 ceramics prepared by the moulding of sample S11 were more in line with the performance requirements of the radomes. To obtain good comprehensive performance, an additional 3% of interparticle Y2O3 was added to the pre-printed mixed powder of granulated Si3N4 particles and resin and the secondary CIP pressure was adjusted to 280 MPa. After sintering, the bending strength, fracture toughness, and dielectric constant of the Si3N4 ceramics were 651 MPa, 6.0 MPa m1/2, and 3.48 respectively. This study provides an important method for preparing of Si3N4 composite radomes using SLS process.

Magnetic performance enhancement in La-Ca-Co doped SrFe12O19 ferrite permanent magnets via cold isostatic pressing

The crystallographic alignment, microstructure and magnetic properties were studied for La0.6Ca0.6Sr0.1Fe12.4Co0.4O19 ferrite permanent magnets prepared with standard ceramic method. The effect of cold isostatic pressing (CIP) and sintering temperature on the structural and magnetic properties of the magnets were investigated. The CIP significantly improves the density of the green compact and final magnets, but undermines the crystallographic alignment of the magnets simultaneously. As a result, the remanence of the magnet achieves optimal value under the compromise between the increased density and the degraded alignment. Moreover, the coercivity of the magnet increases linearly with the increment of the CIP pressure due the fact that CIP processed samples bear more uniform and finer grains in favor of high coercivity. Under optimal CIP pressure and sintering temperature, the magnet obtains best magnetic properties of Br of 0.439 T, Hcj of 396 kA m−1, Hcb of 311 kA m−1, and (BH)maxof 35.8 kJ m−3.

Hierarchical macroporous–mesoporous γ-alumina monolithic green bodies with high strength

Hierarchical macroporous–mesoporous alumina (HMMA) and hierarchical mesoporous alumina (HMA) monolithic green bodies were fabricated by cold isostatic pressing (CIP) of mesoporous alumina (MA) powder, which was prepared by a quick, facile and very pure synthesis route that involved exploitation of the naturally self-driven aluminum nitride powder hydrolysis. The hierarchically self-assembled, nanocrystalline, yet micron-sized MA powder exhibited a controlled porosity, a fine crystallite size, a relatively large surface area and large pore volumes. The textural characteristics of the MA powder were analyzed, while the effect of the consolidation pressure on the pore size evolution, mechanical and permeability properties of the consolidated HMMA and HMA monoliths were investigated. At the lowest CIP pressures, the HMMA monoliths possessed favorable permeability characteristics with Darcian permeability constants up to 2 × 10−15 m2, also exhibiting a low thermal conductivity (≥0.185 W/mK), sufficient flexural strength (≥6 MPa) with an accessible porosity of ≤65%, a pore volume of ≤0.69 cm3/g and a macropore opening diameter of ≤370 nm at a constant mesopore opening diameter of about 4.5 nm. Increasing the CIP pressure resulted in the shrinkage of the macropores and a consequent suppression of the permeability characteristics; however, the flexural strength of the HMA monolith CIPed at 800 MPa increased to 51 MPa, which is the highest reported strength for a dry-pressed, binderless ceramic green body with an accessible porosity of 42% and a theoretical density of 44.3%.

Rapid heating of zirconia nanoparticle-powder compacts by infrared radiation heat transfer

Homogeneous rapid sintering of nanoparticle powder compacts of yttria-stabilized zirconia was achieved by the radiation heat transfer. Green bodies were prepared by cold isostatic pressing (CIP) at various pressures providing different porosity of samples before sintering. Pressure-less sintering was performed in air at a heating rate of 100°C/min up to the 1500°C/1 min. Scanning electron microscopy, mercury intrusion porosimetry, and Archimedes technique were used to characterize the microstructure and to determine the density of the green and sintered bodies. Contrary to expectations, our results reveal opposite dependence of the green- and sintered densities on the CIP pressure. Since the whole sintering process does not exceed 10min, to propose what processes are responsible for observed results, our attention is focused on the radiation heat transfer from furnace heating elements into the ceramics. Our arguments are supported by numerical calculations of the electromagnetic field enhancement in/between particles.

Stochastic analysis on ceramic granule collapse in powder compact during cold isostatic pressing

This paper proposes a stochastic model on ceramic granule collapse in a spherical powder compact during cold isostatic pressing (CIP). To estimate stress distribution in a compact during CIP, an ordinary differential equation for radial displacement is formulated when Young’s modulus is given as a function of radial coordinate. By solving the differential equation numerically, the stress distribution is actually estimated. Based on fracture location theory combined with the stress distribution, the joint probability density function of granule collapse and also its related functions are derived as functions of radial coordinate and applied CIP pressure. A numerical simulation is carried out for a given parameters, and it is shown that the collapse probability of granules is gradually increased with the CIP pressure and also becomes higher at the surface than inside the powder compact after CIP.

Mechanical and dielectric properties of SiCf/SiC composites fabricated by PIP combined with CIP process

2D KD-1 SiC fiber fabrics were employed to fabricate SiCf/SiC composites by an improved polymer infiltration and pyrolysis (PIP) process, combined with cold isostatic pressing (CIP). The effect of CIP process on the microstructure, mechanical and dielectric properties of SiCf/SiC composites was investigated. The infiltration efficiency was remarkably improved with the introduction of CIP process. Compared to vacuum infiltration, the CIP process can effectively increase the infiltrated precursor content and decrease the porosity resulting in a dense matrix. Thus SiCf/SiC composites with high density of 2.11gcm−3 and low porosity of 11.3% were obtained at 100MPa CIP pressure, together with an increase of the flexural strength of the composites from 89MPa to 213MPa. Real part (ε′) and the imaginary part (ε″) of complex permittivity of SiCf/SiC composites increase and vary from 11.7-i9.7 to 15.0-i12.8 when the CIP pressure reaches 100MPa.

CIP 成形体中の顆粒の崩壊確率の定式化

This paper proposes formulation how to calculate granule collapse probability in a spherical powder compact during cold isostatic pressing (CIP). To obtain the stress distribution in the compact, we solve a new ordinary differential equation for radial displacement, on a ground that Young's modulus is changed along radial coordinate. By substituting the stress distribution into fracture location theory, we derive the joint probability density function of granule collapse as a function of the radial coordinate and the applied CIP pressure. For a given parameters, we actually calculate the granule collapse probability in the powder compact during CIP.

Stochastic analysis on coordination number distribution of particles during powder compaction

This paper deals with the change in the coordination number distribution in spherical mono-sized silica powder compacts to discuss its particle-packing process during Cyclic CIP (Cold Isostatic Pressing) with increasing the number of cycles at the maximum CIP pressure of 100MPa. By measuring the distance between the first closest particles (viz. contact particles) to a center particle, the coordination number of the center particle is determined. The resultant coordination number distributions are analyzed with stationary Markov process. The transition probability matrix obtained by the data at the number of cycles from 1 to 10 gives sufficient predictions for the experimental data at the number of cycles of 100 and 1000.

Microstructures and Properties of Cu–AISI304 Parts Fabricated by Improved Selective Laser Sintering

For fabricating complex AISI304 parts with high performance by advanced powder/metallurgy technologies, cold isostatic pressing (CIP) is introduced into selective laser sintering (SLS) combined with hot isostatic pressing (HIP), which is abbreviated to selective laser sintering/isostatic pressed (SLS/IP). The effect of processing parameters on the densification of Cu–AISI304 parts is analyzed and then the influence of Cu on their relative densities, metallurgical structures, and mechanical performances are investigated. The results show that relative densities of Cu–AISI304 parts fabricated by SLS/IP are mainly influenced by CIP pressure and sintering temperature, and it is interesting to find that the formula 1−D=(1−D0)e−kP is testified by the CIP of SLS/IP. There is an antidensification phenomenon resulting from Cu and AISI304 in liquid sintering, but the relative densities of Cu–AISI304 parts can be gradually improved in HIP with Cu content increasing from 1 wt % to 3 wt %. After the above-mentioned Cu–AIS304 parts are finally hot isostatic pressed, their metallurgical structures consist of sosoloid (Cu,Ni) and (Fe,Ni) besides austenite (Fe,Cr,Ni,C), their best mechanical performances are close to those of solution treated compact AISI304 when Cu content is 3 wt %.

Manufacturing near dense metal parts via indirect selective laser sintering combined with isostatic pressing

To fabricate metal parts via indirect selective laser sintering (SLS), isostatic pressing technology, including hot isostatic pressing (HIP) and cold isostatic pressing (CIP), are exploited to reform SLS green parts and make them near dense. The processes of SLS/HIP and SLS/CIP/HIP technologies are investigated respectively and the densification of AISI304 stainless steel specimens is mainly discussed. It is indicated that green parts made by indirect SLS can be pressed into near dense parts with the relative densities of 67.3% and more than 80% in SLS/HIP and SLS/CIP/HIP routes, respectively, and their densities rise if much higher CIP pressure is employed. Compared with SLS/HIP, SLS/CIP/HIP technology is regarded as a better method to manufactured dense parts, and it enlarges the application domain of indirect SLS simultaneously.

Microstructural Characterization of Porous Silicon Carbide Membrane Support With and Without Alumina Additive

Porous silicon carbide (SiC) membrane supports sintered at 1500°–1800°C were prepared by cold isostatic pressing (CIP) under different pressures and using different amounts of alumina additive (0%–4%). The relationship between processing factors and pore size and microstructure was examined. Varying the sintering temperature, the CIP pressure and the amount of additive used were found to be effective for controlling pore size and microstructure. The pore size and particle size of the membrane support prepared without alumina were found to increase with increasing sintering temperature. This was attributed to surface diffusion. Densification of the undoped support did not occur, however, because of concurrent pore development. In the SiC membrane support containing 4% alumina, small particles and a pore size of around 100 nm were retained. This was because of the formation of a limited amount of SiO2–Al2O3 liquid phase during sintering.

Consolidation behavior of L12 phase (Al + 12.5 at.% Cu)3Zr powder with nanocrystalline structure during CIP and subsequent sintering

The mechanically alloyed (Al + 12.5 at.% Cu) 3 Zr powders were consolidated by cold isostatic pressing (CIP) and subsequent sintering. Effects of CIP pressure and sintering temperature on the stability of metastable L1 2 phase and nanocrystalline structure were investigated. Before sintering, the powders were CIPed at 138, 207, 276, and 414 MPa. The relative densities of the CIP compacts were not greatly affected by the CIP pressure. However, the L1 2 phase of the specimen CIPed at pressures greater than 276 MPa was partially transformed into D0 23 . The optimum consolidation conditions for maintaining L1 2 phase and nanocrystalline microstructure were determined to be CIP at 207 MPa and sintering at 800 °C for 1 h for which the grain size was 34.2 nm and the relative density was 93.8%. Full density specimens could be prepared by sintering above 900 °C, however, these specimens consisted of L1 2 and D0 23 phases. The grain sizes of all the specimens were confirmed by TEM and XRD, and were found to be less than 40 nm. This is one of the smallest grain sizes ever reported in trialuminide intermetallic compounds.

Cold isostatic compaction of nano-size powders: Surface densification and dimensional asymmetry

Cold isostatic pressing (CIP) is often used in the compaction of nano-sized powders. For technological reasons, however, uniaxial pressing prior to CIP takes place. This paper reveals the first quantitative measurements of density gradients within and the asymmetric sintering response of nanoscale zirconia compacts formed by (i) simple uniaxial compaction and (ii) specific ratios of uniaxial and CIP pressure. We find that CIP forms an exterior “skin” of higher but variable surface density and decreases the width of the density distribution. It does not eliminate density gradients; nonuniform shrinkage still occurs during sintering. The high- and low-density zones (the moving and fixed ram ends, respectively) that form during uniaxial compaction are reversed during CIP. Considering both density distribution width and spring-back cracking, the “best” uniaxial-CIP pressure combination is 1–20 ksi for this particular powder and an L/D of 1.0. The greater final compaction of the low-density zone during CIP causes relatively large variations in final dimensions (nearly 400 microns) in spite of the smaller density distribution width. The usually neglected uniaxial pressing step has definite technological impacts on the production of nanostructured components via compaction.

Effect of Hydroxide Calcination Temperature, Cold Isostatic Pressing (CIP) Pressure, and Sintering Temperature on Properties of ZrO2 + 3 mol.% Y2O3 Ceramic

ZrO2 + 3 mol.% Y2O3 ceramic specimens are prepared by sintering, at 1500 and 1600°C, preforms molded from calcined hydroxide powders at 850 and 750°C using a cold isostatic pressing (CIP) technique. Bending strength and density measured as a function of the CIP pressure is shown to be quite different for specimens sintered at the two temperatures. Implications of this different behavior are discussed.

Cold isostatic pressing as a method for fabricating ceramic products with high physicomechanical properties

The experimental results published by the author and his co-workers in 24 earlier works and novel original data are analyzed. It is shown that the process of cold isostatic pressing (CIP) occurs with mechanical activation of the powder particles due to their self-deformation with a simultaneous self-compaction of the semiproduct. The CIP process of powders or traditionally shaped preforms is shown to elevate their density and activate the sintering processes but diminish their sintering temperature and increase the density, strength and crack resistance of the ceramics. The use of surface-active substances (SAS) in CIP is shown to elevate the level of the physicomechanical properties of the ceramics. The basic concepts of controlling the properties of ceramics by choosing the appropriate dispersity of the powder, the CIP pressure, the SAS, and the sintering regime are presented.

Cold isostatic pressing as a method for fabricating high-strength ceramic materials based on ZrO2

High-strength ceramic materials fabricated with the use of cold isostatic pressing (CIP) at ≤0.8 GPa and sintering by different regimes from yttria-stabilized zirconia produced by leading foreign and Ukrainian firms are described. All the materials exhibit two peaks of mechanical properties, one at a low CIP pressure (0.1–0.3 GPa) attributable to destabilization of the press-powder and characterizing the stability of the material as a whole and the other at a high CIP pressure (above 0.6 GPa) attributable to attainment of close packing of the particles. In accordance with the set of standard properties the materials can be classified into two types, namely, intermediate-strength ones with an ultimate bending strength of 700–900 MPa,K1c ranging from 7 to 12 MPa·m1/2, a density of about 6 g/cm2, and an optimum CIP pressure of 0.2–0.3 GPa (the first peak) and high-strength materials with an ultimate bending strength of about 1200 MPa,KIc ranging from 6 to 9 MPa·m1/2, a density of about 6.1 g/cm3, and an optimum CIP pressure of 0.1 GPa. The intermediate type comprises the majority of domestic materials and some foreign ones and is characterized by higher stability and crack resistance. The high-strength type comprises mainly foreign materials with high strength and lower stability.

The Effect of Characteristics of Compressive Deformation of Ceramic Granules on CIP Compaction Behavior and Sinterability (Part 1)

Load-displacement curves and fracture behavior of individual ceramic granules were investigated by compression test. Three types of load-displacement curves were recognized for the granules: Granules of Al2O3 (A) showed elastic deformation and were ultimately broken, while no breaking of granules was observed for SiC and Si3N4 which showed elasto-plastic and plastic deformation, respectively. Surface and inner structures of green bodies prepared by cold isostatic pressing (CIP) were observed to relate data from mechanical characterization of individual granules and the macroscopic compaction behavior. No deformation of granules was observed in compacting some Al2O3 with a CIP pressure of 340MPa, while SiC and Si3N4 granules were deformed easily under a CIP pressure of 100MPa and 25MPa, respectively. It is discussed that load-displacement curves of individual granules in compression test can be closely related to the macroscopic compaction behavior of ceramics.

Mechanical properties of hydroxylapatite specimens obtained by cold isostatic pressing

The authors investigate how the density and mechanical properties of green and sintered hydroxylapatite specimens depend on the pressure of cold isostatic pressing (CIP). It is shown that as the CIP pressure grows, the density, the ultimate bending strength, and the fracture toughness in green specimens increase to reach 2.70 g/cm3, 50 MPa, and 0.8 MPa·m1/2, respectively, at 2.0 GPa. The maximum value of the ultimate bending strength of the sintered material is 120 MPa at a density of 3.02 g/cm3. A qualitative explanation of the observed phenomena is suggested.