Hot Pressing Deformation Research Articles

Hot-Pressing Deformation Yields Fine-Grained, Highly Dense and (002) Textured Ru Targets.

Ruthenium (Ru) is a refractory metal that has applications in the semiconductor industry as a sputtering target material. However, conventional powder metallurgy methods cannot produce dense and fine-grained Ru targets with preferred orientation. Here, we present a novel method of hot-pressing deformation to fabricate Ru targets with high relative density (98.8%), small grain size (~4.4 μm) and strong (002) texture. We demonstrate that applying pressures of 30-40 MPa at 1400 °C transforms cylindrical Ru samples into disk-shaped targets with nearly full densification in the central region. We also show that the hardness and the (002)/(101) peak intensity ratio of the targets increase with the pressure, indicating enhanced mechanical and crystallographic properties. Our study reveals the mechanisms of densification and texture formation of Ru targets by hot-pressing deformation.

Densification and grain orientation of ruthenium targets under hot-pressing deformation

This study presents a novel method for fabricating high-performance ruthenium (Ru) targets with high density, fine grain size and preferred grain orientation, which are challenging to achieve by conventional methods. The method involves hot-pressing deformation of Ru pre-sintered body at different temperatures and analyzing the resulting sintering and grain orientation behavior. The optimal Ru target is obtained at 1400 °C, exhibiting a relative density of 97.4%, a mean grain size of 4.4 μm and a dominant (002) texture. This method offers a significant contribution to the field of Ru target preparation and can be applied to other refractory metals and alloys that are difficult to process by conventional methods.

Fabrication of high-porosity open-cell aluminum foam via high-temperature deformation of CaCl2 space-holders

In this study, we found that porous CaCl2 granules can be easily deformed under certain pressure and temperature conditions. Based on this finding, a new infiltration process that employs CaCl2 granules as space-holders was developed to prepare aluminum (Al) foam with high porosity. In this process, porous CaCl2 granule preforms were first subjected to hot-pressing deformation, which provided two benefits: 1) the density of the preform was increased, thereby increasing the porosity of the final prepared open-cell Al foam (over 80%) and 2) the contact surface of the neighboring CaCl2 granules was increased. After hot-pressing, the sizes of the dissolution and removal channels of CaCl2 increased. Consequently, the space-holder particles could be completely removed, which is just the most difficult bottleneck problem in the traditional infiltration process applying salt particles as space-holders in which the salt removal is not enough and the porosity is lower than 65%.

Change in the Microstructure of Ni Alloy Disk Workpieces for Gas Turbine Engines Produced by the HIP + Deformation Method

Abstract—The changes in the microstructure during thermomechanical treatment under different regimes of a new granulated heat-resistant alloy based on VZh178P nickel obtained by the method of hot isostatic pressing and subsequent hot deformation (HIP + deformation) are studied. The change in the grain size of the γ matrix after the main operations of the technological conversion is shown; the dynamics of their growth in hardening below and above the temperature of total dissolution of the γ' phase and the microstructure after the total thermal treatment are shown.

Microstructural evolution and tensile properties of an in-situ TiZr-based bulk metallic glass matrix composite after hot-pressing deformation in its supercooled liquid region

Hot-pressing deformation treatment was carried out at different strain rates and temperatures to improve the microstructure homogeneity of the TiZr-based bulk metallic glass matrix composites (BMGMCs) after enlargement. At a compression strain rate of 0.001/s and temperature of 653 K, the TiZr-based BMGMCs exhibited good plastic rheological properties in supercooled liquid region. After work hardening to the peak stress, steady-state flow stress was rapidly obtained, resulting in a stress drop of 223 MPa. Moreover, during this period, no rapid stress drop and fracture phenomena were observed. Compared with those of the as-cast morphology, the distribution of dendrite and glass matrix was more homogeneous after 31% thickness reduction in hot-pressing deformation. Accompanied with viscous flow of the glass matrix, the dendrites markedly aggregated together after a thickness reduction ratio of 58%. Transmission electron microscopy analysis revealed that a large amount of dislocations formed in the dendrite, and a large amount of nanocrystals precipitated from the glass matrix after hot-pressing treatment. The amount of the nanoparticles continued to increase as the amount of deformation increased. TiZr-based BMGMCs with 31% compression deformation possessed both the distinguished plastic strain (εp) of 3.95% and ultimate strength (σmax) of 1595 MPa. The stress–strain curve demonstrated that the rate of stress drop considerably slowed down after tensile strength reached a maximum due to hot-pressing deformation. The rapid expansion of the shear band was efficiently hindered through the combined effect of partial nanocrystallization of the glass matrix and deformation hardening of the dendrite. This condition further improves the total coordinated deformation capacity of TiZr-based BMGMCs.

Investigation on hot deformation behavior of nanoscale TiC-strengthened Cu alloys fabricated by mechanical milling

In this work, ultrafine-grained (UFG) copper alloys dispersed with nanoscale TiC particles were produced by combination of mechanical milling and spark plasma sintering (SPS). Microstructure evolution during uniaxial compression to height reduction of 20–60% in the temperature range of 400–700°C was investigated systematically. The stress-strain curves in all conditions were characterized by a fast increase in stress at initial stage and a subsequent yield drop. No obvious microstructure change was observed with increasing reduction ratio. There exhibited a tendency in grain size refinement with increasing strain rate even the change in grain size is slight. A slight grain growth was found with the compression temperature high up to 700°C. The high temperature tensile tests results suggested that the yield stress showed a relatively weak dependence on strain rate with a strain rate sensitivity parameter of around 0.02, and a low degree of strain hardening was observed. In addition, the recrystallization behavior was found to be inhibited by the ultrafine grains and nanoscale TiC particles in starting microstructure, because the grain boundaries or junctions in initial structure act as the severe pinning points, limiting bowing, and the nanoscale TiC particles prevent the nuclei formation of recrystallization. The fracture morphologies occurred during the tensile test were closely related to the change in particles distribution from random to aligned distribution during the hot press deformation.

Effect of Deformation Temperature on Texture and Thermoelectric Properties of Bi0.5Sb1.5Te3 Prepared by Hot-Press Deformation

The effects of deformation temperature on texture and thermoelectric properties of p-type Bi0.5Sb1.5Te3 sintered materials were investigated. The sintered materials were prepared by mechanical alloying and hot-press sintering. The hot-press deformation was performed at 723 K and 823 K by applying mechanical pressure in a graphite die. Then, the materials were extruded in the direction opposite to the direction of applied pressure. X-ray diffraction and electron backscattered diffraction patterns showed that the hexagonal c-plane tended to align along the extruded direction when the samples were deformed at high temperatures. The thermoelectric power factor was increased by high-temperature hot-press deformation because of the low electrical resistivity that originated from the c-plane orientation.

Microstructure and Mechanical Properties of Commercial Purity HIPed and Crushed Aluminum

Ultrafine-grained aluminum microstructures were processed from commercial purity powder by combining hot isostatic pressing (HIP) and dynamic severe plastic deformation (DSPD). After the first step, the bulk consolidated material showed a random texture and homogeneous microstructure of equiaxed grains with an average size of 2µm. The material was then subsequently impacted, using a falling weight at a strain rate of 300s-1. The resulting material showed a microstructure having an average grain size of about 500 nm with a strong gradient of fiber-like crystallographic texture parallel to the impact direction. The mechanical properties of the impacted material were subsequently characterized under compressive tests at room temperature at a strain rate of 10-4s-1. The effect of the change of the deformation path on the mechanical response parallel (DN) and perpendicular (DT) to the impact direction was also investigated. These results are here discussed in relation with microstructure and texture evolution.

Correlation between Thermoelectric Properties and Plastic Deformation of p-Type Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> Thermoelectric Materials

A plastic deformation process and ratio study of p-type Bi 0.5 Sb 1.5 Te 3 was performed. The ingots were grown by the Bridgman method. Disks were cut from the ingots and deformed by either cold-pressing or by hot-pressing under pulse current heating. The plastic deformation ratio was controlled from 55 to 90%. The crystal structures of the deformed samples were identified by X-ray diffraction and pole figure analyses. The diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Thermoelectric properties change depending on not the plastic deformation ratio but the kind of plastic deformation process. The power factor for hot-press deformed samples exceeded those for the original ingots and cold-press deformed samples. The results suggest that the process of hot-press deformation enhances the thermoelectric properties of p-type Bi 0.5 Sb 1.5 Te 3 .

P-type Bi<sub>0.5</sub>Sb<sub>1.5</sub>Te<sub>3</sub>熱電材料の熱電特性と塑性加工度との相関関係

A plastic deformation process and ratio study of p-type Bi0.5Sb1.5Te3 was performed. The ingots were grown by the Bridgman method. Disks were cut from the ingots and deformed by either cold-pressing or hot-pressing under pulse current heating. The plastic deformation ratio was controlled in the range from 55 to 90%. The crystal structures of the deformed samples were identified by X-ray diffraction and pole figure analyses. The diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Thermoelectric properties change depending on not the plastic deformation ratio but the kind of plastic deformation process. The power factor for hot-press deformed samples exceeded those for the original ingots and cold-press deformed samples. The results suggest that the process of hot-press deformation enhances the thermoelectric properties of p-type Bi0.5Sb1.5Te3.

塑性加工によるＢｉ２Ｔｅ３系熱電材料の作製

Plastic deformation study of Bi2Te3-related materials was performed. The ingots were grown by the Bridgman method using the following source materials with the nominal compositions of Bi0.5Sb1.5Te3, Bi2Te2.85Se0.15 and Bi1.8Sb0.2Te2.85Se0.15. Disks were cut from the ingots, and then they were deformed by cold and hot-pressing under pulse-current heating. The crystal structures of the deformed samples were identified by X-ray diffraction. All diffraction peaks were assigned to Bi2Te3 structure and the diffraction patterns indicate that the surface and bottom of the samples were highly oriented in the hexagonal (00•l) plane. The Hall effect measurements show that carrier concentration of the samples is in the order of magnitude of 1025 m-3 at room temperature. The power factor for the samples after the hot-press deformation exceeded those for the original ingots. The results indicate that the hot press deformation can be expected to enhance thermoelectric properties of Bi2Te3-related materials.

Bi<SUB>2</SUB>Te<SUB>3</SUB>-Related Thermoelectric Samples with Aligned-Texture Prepared by Plastic Deformation

Plastic deformation study of Bi 2 Te 3 -related materials was performed. The ingots were grown by the Bridgman method using source materials with nominal compositions of Bi 0 . 5 Sb 1 . 5 Te 3 , Bi 2 Sb 2 . 8 5 Se 0 . 1 5 and Bi 1 . 8 Sb 0 . 2 Te 2 . 8 5 Se 0 . 1 5 . Disks were cut from the ingots, and were then deformed by either cold-pressing or by hot-pressing under pulse current heating. The crystal structures of the deformed samples were identified by X-ray diffraction. All diffraction peaks were assigned to the Bi 2 Te 3 structure, and the diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Hall effect measurements show the carrier concentration of the samples to be at an order of magnitude of 10 2 5 m - 3 at room temperature. The power factor for the samples after hot-press deformation exceeded that for the original ingots. The results suggest that hot-press deformation enhances the thermoelectric properties of Bi 2 Te 3 -related materials.

Hot‐Pressed Mica Glass‐Ceramics with High Strength and Toughness

A new type of mica glass‐ceramics has been prepared by hot pressing. X‐ray diffractometry (XRD) has confirmed that (001) planes of mica crystals are almost perpendicular to the direction of hot pressing. Flexural strength and fracture toughness of the materials increase with increasing hot‐pressing deformation. The orientation of the hot‐pressed materials is attributed to the combination of viscous flow of the residual glass phase and rotation of mica plates under pressure at high temperature.

Structure and mechanical properties of nanocrystalline Ag/MgO composites

Nanocrystalline Ag/MgO composites were prepared by the ultrafine-powder-compaction method. The structure was investigated for the first time by high-resolution electron microscopy. Nanometre-sized Ag grains and MgO grains in the composites bonded directly without any intermediate phase layer. Certain preferred orientation relationships were observed between the Ag and MgO grains. The nanocrystalline Ag/MgO composites retained their grain size during annealing up to 873 K. Vickers microhardness measurements were performed on the as-compacted and annealed specimens. Generation and propagation of cracks were less active in the nanocrystalline Ag/MgO composites than in a single-phase nanocrystalline MgO. The Vickers microhardness of the nanocrystalline Ag/MgO composites remained up to 1073 K. Hot-pressing deformation tests showed that the nanocrystalline Ag/MgO composites deformed plastically at 1073 K.