Pseudo Hot Isostatic Pressing Research Articles

Prediction and fabrication of textured Si3N4 ceramics via grain rotation model

The grain preferential orientation has a significant influence on the mechanical properties of silicon nitride (Si3N4) ceramics. Based on the Jeffery’s theory, a grain rotation model under uniaxial compression is created to predict the texture evolution mechanism during sintering of Si3N4 ceramics. With deformation, the grain orientation was predicted to rotate towards the plane perpendicular to the pressure direction, and large strain was favorable for the formation of strong texture. According to guidance of the model, the weakly textured microstructure prepared by normal hot pressing is attributed to the limited strain, due to the constrains of graphite die. Therefore, a new PHIP (pseudo-hot isostatic pressing) process with the large deformation is guided to fabricate the strongly textured ceramics by promoting the grain rotation and dynamic grain growth. Generally, the experimental results are well accordance with the model prediction. Furthermore, this model could be applied to guide the design and fabrication of other isotropic and anisotropic ceramic materials.

Thermal shock behavior of Ti2AlC from 200°C to 1400°C

AbstractThe thermal shock behavior of Ti2AlC synthesized by means of self‐propagating high‐temperature combustion synthesis with pseudo hot isostatic pressing is investigated, with a focus on the effect of the quenching temperature and quenching times. In general, Ti2AlC exhibits a better thermal shock resistance than typical brittle ceramics like Al2O3. Although the flexural strength decreases quickly in the temperature range of 300°C‐500°C, no discontinuous decrease in the retained strength is observed in Ti2AlC which, as with other MAX phases, differs from the behavior of typical brittle ceramics. Overall, the initial strength (grain size) plays a determining role in the thermal shock behavior of Ti2AlC and other MAX phases. On increasing quench times to 5 cycles, the retained flexural strength decreases further, however with a lower rate of decrease compared with the first quench. Quenching at 300°C and above, voids after the pullout of grains and cracks are present, which however are absent in the un‐quenched samples, indicating the weakening of bonding among grains and the induced damage around the grain boundary during the thermal shock.

Growth morphology and microstructural characterization of nonstoichiometric Ti2AlC bulk synthesized by self-propagating high temperature combustion synthesis with pseudo hot isostatic pressing

Ti2AlC bulk pellets, Φ150×25mm2 in size, were fabricated by self-propagating high temperature combustion synthesis with pseudo hot isostatic pressing (SHS/PHIP). The growth morphology and microstructures were investigated in detail by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The used SHS/PHIP process results in some unusual microstructures. The relative density increases to over 98% when increasing the size of the used pellet. The as-fabricated Ti2AlC has many lattice defects, contributing to its low phonon thermal conductivity. Interestingly, many nanopores were present in Ti2AlC grains. Of much importance, a high density of vacancies contributes to the nonstoichiometry of Ti2AlC synthesized by the SHS/PHIP process. Ti2AlC synthesized by the SHS/PHIP process is deformed with high residual stress, due to fast cooling and grain growth.

Formation of M n+1AX n phases in Ti–Cr–Al–C systems by self-propagating high-temperature synthesis

In this paper, phase composition of the Mn+1AXn phases by self-propagating high-temperature synthesis (SHS) was determined using Ti, Cr, Al, and carbon black as raw materials. And, phase composition and microstructures of the Mn+1AXn phases-contained bulk by SHS with the pseudo-hot isostatic pressing (SHS/PHIP) were investigated in Ti–Cr–Al–C systems raw materials. Rietveld XRD refinement was introduced to study the lattice parameters and phase composition of the resultant phases from the SHSed and SHS/PHIPed samples. Ti2AlCx, Ti3AlC2x, and Cr2AlCx by SHS were detected in the Ti–Cr–Al–C systems, as well as the binary carbide of TiC and intermetallics. The mechanical properties of the synthesized bulk samples were determined, exhibiting a high strength and toughness compared with the typical monolithic Mn+1AXn phase ceramics. It is indicated that the samples prepared by SHS/PHIP are identified to be a strategy for improving the mechanical properties of monolithic Mn+1AXn phase.

Microstructures, Electrical, Thermal, and Mechanical Properties of Bulk Ti2AlC Synthesized by Self‐Propagating High‐Temperature Combustion Synthesis with Pseudo Hot Isostatic Pressing

The microstructure and the electrical, thermal, and mechanical properties of bulk Ti2AlC synthesized by self‐propagating high‐temperature combustion synthesis with pseudo hot isostatic pressing (SHS/PHIP) were investigated in detail. The plate‐like Ti2AlC grains distribute irregularly, with the grain size of around 6 μm in length and 1 μm in width. With increasing temperature, the electrical resistivity increases linearly from room temperature (RT) to 900°C, but the thermal conductivity decreases slightly. The RT electrical resistivity and thermal conductivity are 0.40 ± 0.03 μΩ·m and 27.0 W·(m·K)−1, respectively. The electronic component of the thermal conductivity is the dominant mechanism at all temperatures, and the phonon contribution almost can be neglected above 873 K. With increasing temperature, the flexural strength increases first, then decreases above 550°C, at which it reaches the maximum value of 539 ± 36 MPa. The brittle‐to‐plastic transition temperature falls in the temperature range of 750°C–950°C. The Ti2AlC synthesized by SHS/PHIP process exhibits an anisotropic compressive strength. The work of fracture of Ti2AlC is estimated to be 200 ± 7 J/m2, which is much higher than that of traditional ceramics.

Combustion Synthesis of TiC-TiB2-Based Cermets from Elemental Powders

TiC-TiB2-based cermets with Ni binder were fabricated using combustion synthesis assisted by pseudohot isostatic pressing by heating the compacted powder mixture to approximately 700°C. The effects of composition on microstructure and hardness of the synthesized samples were investigated. The samples exhibited finer microstructure and higher hardness as TiC/TiB2volume ratio increased and as Ni increased up to 30 vol%. A relatively high hardness value of 1950 HV was obtained for TiC-TiB2-Ni(52.5/17.5/30 vol%). However, the transverse rupture strength and the modulus of elasticity values were not very high. This may be due to weak bonding strength of the interface between hard phases and Ni binder and/or insufficient densification of the samples.

SHS/PHIP of ceramic composites using ilmenite concentrate

Self-propagating high-temperature synthesis (SHS) process in the mixture of ilmenite, boron carbide and aluminum combined with a pseudo hot isostatic pressing (PHIP) is used in this research to produce a compact multi-ceramic composite Al 2O 3/TiB 2/TiC with Fe as a binder. Several tests were performed to identify the optimum partial weight percent of the ilmenite, boron carbide and aluminum to produce a suitable amount of each components of the product. On the other hand, a number of tests were performed to measure the delay time, optimum compaction time and optimum compaction force to produce a compact high toughness samples. The results of phase analysis using XRD tests and microstructure using SEM and EDS show that the product is a multi-ceramic composite of the Al 2O 3/TiB 2/TiC with Fe as a binder. It was shown that there are no primary reactants in the product. In this work, the combustion characteristics (combustion wave propagation velocity and temperature) of the process, as well as density and hardness of the combustion product were measured. The fracture toughness of the product was measured using Vickers indenter and Brazilian test. This shows that the samples have a high toughness in comparison to conventional ceramics.

Wear-Resistant Properties of TiC/Fe Ceramic Composite Coating on Steel Plate via Combustion Synthesis

The highly dense TiC/Fe ceramic coating was fabricated on Q235 steel surface by self- propagating high-temperature synthesis combined with pseudo hot iso-static pressing. The wear-resistant properties were examined by means of ball-on-disk contact wear test. The microstructure of TiC/Fe cermets coating was investigated. The results show that TiC/Fe cermets coating has an excellent wear-resistant property. There is little mass loss after 1200s under 30N loading under the condition of dry sliding wear testing. The major wear mechanisms are described by the following stages: sticking friction, grain abrasion and stripping of hard phase.

Wear Resistance of TiC Ceramic Particulate-Reinforced Metal Matrix Cermets

To characterize wear behaviors of TiC ceramic particulate-reinforced metal matrix cermets in abominable condition, wear-resistance test was practiced in grain abrasive wear with the TiC-xNi cermets in-situ fabricated by self-propagating high-temperature synthesis method combined with pseudo hot iso-static pressing. Grain abrasion test was conducted with the MLS-225 type tester. Wear resistance was evaluated as weight loss obtained after each period of 10 minutes. Wear resistance of the cermets increased with the increase of TiC content in the composites. SEM was employed to analyze the wear process and wear mechanism. SEM examination of the wear tracks in the worn surface suggests that abrasive wear mechanisms of different binder content cermets are similar. The worn surface is characterized by long and deep parallel grooves. The fracturing of bigger carbide grains and carbide framework by a fatigue process under repeated abrasion is followed by weight loss of the material.

Oxidation Behavior of TiC/ Fe Ceramics Produced by Self-Propagating High-Temperature Synthesis

The key problem about the application of TiC/Fe composite ceramics in high temperature is the oxidation resistance. With an aim to investigate oxidation properties, the high density TiC/Fe ceramics was produced by self-propagating high-temperature synthesis method combined with pseudo hot iso-static pressing (SHS/PHIP). The oxidation kinetics of TiC/Fe ceramics were investigated by means of conducting the isothermal oxidation experiments in air at temperature of 550°C  900°C for up to 150 hours, and measuring the variations of the weight gains of the composites with the oxidation times. The microstructure evolution of the composites during the oxidation processing was studied by using SEM/EDS and XRD. Experimental results show that TiC/Fe ceramics basically follows a parabolic rule at high temperature. A detailed characterization of the microstructure and distribution of the phases within the scale following oxidation studies has been undertaken to suggest the possible mechanism for the oxidation of TiC/Fe ceramics.

Combustion Synthesis of Titanium-Based Cemented Carbides

TiC−Fe system cermets and TiC−SUS310L (TiC−SS) system cermets with fully relative density have been produced from elemental powders via self-propagating high-temperature synthesis (SHS) reaction combined with pseudo-hot isostatic pressing. X-ray diffraction (XRD) analysis showed that the SHS products consist of TiC and the binder phase of Fe or SS. Metallographic analysis revealed TiC particles of several micrometer size were homogeneously dispersed in the binder phase. Regardless of differences in the binders, both cermets have similar tendencies: their relative densities increased and their hardness and compressive strengths decreased with increases in the volume fraction of either Fe or SS. In addition, the cermets used stainless steel as the binder had twice superior corrosion resistance to those used iron and also their hardness and compressive strength showed excellent values.

Fabrication of Thermoelectric Module by A New Manufacturing Process and Its Performance

A new process for manufacturing thermoelectric modules was proposed, and thermoelectric performance of the modules were evaluated. Both powders of p-type FeCo3Sb12 and n-type Co0.92Ni0.08Sb2.96Te0.04 compounds were alternately filled into 4×4 square holes of an insulating mold. The powders in the holes were compacted and sintered simultaneously at 903 K in vacuum for 20 min under the pressure of 60 MPa by a pseudo hot isostatic pressing (pseudo HIP) method, in which one-directional load is transmitted isostatically to the sample through the alumina powder filled around the sample. The sixteen sintered elements (1.9 mm×1.9 mm×9.0 mm) in the mold were electrically connected in series using silver paste. Then, a thermoelectric module was constructed by parallel sandwiching the mold with glass plates of 0.5 mm in thickness. The thermoelectromotive force was 591 mV at the temperature gradient of 356 K, and the internal resistance in the module was 2.77 Ω. In this case, the output power of 31.5 mW was obtained and the power density of 576 W/m2 was estimated. The value of output power was less than that of the theoretical calculation.

Preparation of Ternary Layered Ti<sub>3</sub>SiC<sub>2</sub> Ceramic by SHS/PHIP

Ternary-layered Ti3SiC2 ceramic was prepared by self-propagation high temperature combustion synthesis with pseudo hot isostatic pressing (SHS/PHIP). The effect of Ti/C mol ratio, Si content and Al content on the phase composition of the products was investigated. Experimental results showed that the phase composition of SHS/PHIPed products was influenced greatly by Ti/C mol ratio and Si content in the raw material. When Ti/C mol ratio is 1.5, the main phase was TiC with only a little Ti3SiC2; the content of Ti3SiC2 increased greatly with increase of Si content. The main phase turned to Ti3SiC2 while TiC became the main impurity when the Ti/C mol ratio arrived at 2. With addition of aluminum, the content of Ti3SiC2 increased obviously and the distortion of lattice was caused in Ti3SiC2 crystals.

Thermal Shock Resistance and Ablation Behavior of TiB2-Cu-Ni Composite via Combustion Synthesis

TiB2-Cu-Ni cermet composite was fabricated by self-propagating high-temperature synthesis combined with Pseudo Hot Isostatic Pressing. The microstructure of the composite is fine and uniform. The thermal shock resistance and ablation behavior of the TiB2-Cu-Ni composite was investigated by heating it for twenty seconds using a plasma torch arc heater. Fatal breakup took place in the monolithic TiB2 ceramic once the plasma arc flow faced the surface of the ceramic. Only a small crack was found on the ablation surface of the TiB2-Cu-Ni composite. The thermal stress fracture resistance parameter, R, and the critical energy release rate GIC of TiB2-Cu-Ni composite are at the same order with that of the W/Cu alloy. It showed that the properties of thermal shock resistance and the ablation of the composite are good. The fraction of mass loss of the homogeneous composite was 2.32 %, which was similar to that of traditional W/Cu alloy. The volatilization of the metal binder and mechanical erosion was the main mechanisms of the ablation.

Large-Scale (Ti,Cr)B<sub>2</sub>-Cu Composite by Combustion Synthesis

Large-scale (Ti,Cr)B2-Cu composite from Ti, Cr, B and Cu powders was produced by combining combustion synthesis with Pseudo Hot Isostatic Pressing. The diameter of the synthesized product is 240 millimeter. The product was identified using X-ray diffraction and the result showed that only (Ti,Cr)B2 and Cu phases, without other phases, existed in the product. The analysis of the microstructure indicated that the skeletal structure had been formed in the (Ti,Cr)B2 solid solution phase. Fine (Ti,Cr)B2 reinforcement grew in near equivalent axis-like shape and some sintering neckings were found between the solid solution phases. The relative density of the synthesized product was 93.6% because the skeletal structure baffled the densification of the composite. The bending strength and fracture toughness of the product were 476 MPa and 6.8 MPa·m1/2 respectively.

Combustion Synthesis and Two-Time Densification of TiB<sub>2</sub>-Cu Composites

TiB2 -Cu cermet with the relative density of 92% was produced from titanium, boron and copper powders by combustion synthesis and subsequently pseudo hot isostatic pressing. To improve its mechanical and thermal physical properties, the two-time hot pressing sintering test was carried out at 1050°, 1090° and 1150°C respectively. The deformation behavior and variation of micro- structure and mechanical properties were investigated in detail. The results showed that the relative density and the flexural strength increase remarkably after two-time hot pressing. The relative density reaches 605.5MPa and the flexural strength reaches 96% when the two-time pressing temperature is at 1090°C, and the values increase 12% and 6% compared to that before two-time pressing.

Effect of Copper Content on the Microstructures and Properties of TiB<sub>2</sub> Based Cermets by SHS

TiB2 based cermets with different copper content were produced from titanium powder, boron powder and copper powder by Self-propagating High-temperature Synthesis under conditions of Pseudo Hot Isostatic Pressing (SHS/PHIP). In order to obtain the optimal copper content, the effect of copper content on the microstructures and properties of TiB2 based cermets was investigated. The size of the TiB2 particles in the products decreased with increasing amounts of copper. The hardness (HRA) and bend strength increased firstly, then decreased with copper increasing. Their maximum values appeared at 20 wt.% and 40 wt.% copper, respectively. The porosity of TiB2 based cermets decreased with the copper content increasing due to good fluidity of copper. With the addition of copper, the fracture toughness of TiB2 based cermets increased gradually. Crack-tip plastic blunting by a ductile metallic phase and crack deflection are the principal mechanisms of toughness improvement of TiB2 based cermets. The range of optimal copper content in the TiB2 based cermets is between 40 wt.% and 50 wt.%.

Self-propagating high temperature combustion synthesis of TiB/Ti composites

Dense TiB/Ti composites were fabricated by Self-propagating High Temperature Synthesis connected with Pseudo Hot Isostatic Pressing (SHS/PHIP). T ads, T c and combustion velocities of the TiB– xTi system decrease with increasing the amount of Ti. The synthesized TiB–Ti cermets mainly consisted of TiB and Ti phases, but TiB 2 phase existed in some products with lower content of metal. Needle-like, rod-like or plate-like TiB grains formed in the microstructure of synthesized TiB– xTi composites. The size of the TiB grains decreased with an increasing amount of metal addition. The hardness and relative density of the synthesized materials are all beyond HRA82 and 94%, respectively. The introduction of Ti into TiB– xTi cermets resulted in a drastic increase in the bending strength, tensile strength, compression strength, fracture toughness and the maximum values were obtained with the addition of 40 wt.%Ti.

Synthesis of near net shape high density TiB/Ti composite

TiB/Ti composite were produced by SHS (self propagating high temperature synthesis) under conditions of PHIP (pseudo-hot isostatic pressing). The synthesis conditions were optimized to produce highly dense materials conforming a high volume fraction of TiB. Self-propagating reaction of the Ti and B powders occurred above the α- to β-Ti transformation temperature (1155 K). The composites consist of Ti matrices with dispersed TiB reaction products of 2–30 μm size. Near fully dense composites with a TiB/Ti volume ratio of 33–44 vol.% were synthesized for B/Ti atomic ratios of 0.3–0.4 at pseudo isostatic pressures of 100 MPa. The Vickers hardness and fracture stress of the composites are 5.6–7.1 and 2.1–2.3 GPa, respectively, and the wear of the composite is approximately 7–9% of the Ti and Ti–6Al–4V.

Grain refinement of combustion-synthesized NiAl by addition of ceramic particles

Abstract A bulk material of NiAl has been combustion-synthesized from the mixture of nickel and aluminum powders by using a pseudo-hot-isostatic-pressing (PHIP) method, and the effects of the addition of Al 2 O 3 , SiC or NiAl particles on the microstructure, mechanical properties at roon temperature and oxidation resistance at a temperature of 1500 K have been investigated. The maximum volume fraction of the added particles is 10%, and the particle size is varied from 0.5 to 130 μm. The density and hardness of the combustion-synthesized NiAl significantly increase witl the PHIP pressure. The addition of each type of particles significantly reduces the grain size of the synthesized NiAl. The added Al 2 O 3 particles segregate at the grain boundary of the synthesized NiAl, while the added SiC particles decompose into silicon and carbon during the synthesis, and only silicon segregates at the grain boundary of the NiAl. The density of the synthesized NiAl slightly decreases with increasing volume fraction of the added particles, while the relative density remains more than 95%. The addition of the particles has no effect on the hardness of the NiAl. The increase in the volume fraction of the added Al 2 O 3 particles significantly degrades the oxidation resistance of the synthesized NiAl, while very little effect is brought about by the addition of SiC particles and no effect by the addition of NiAl particles.