Hot-press Sintering Process Research Articles

Microstructure and bending behavior of Ti/Al laminated composites reinforced with high-entropy alloy particles

Ti/Al laminated composites embedded with Al0.5CoCrFeNi high entropy alloy particles were prepared by vacuum hot press sintering process at temperatures of 660 °C and 730 °C. The microstructure of the material was initially examined using XRD, SEM, EDS, EBSD, and TEM techniques. The results of microstructural characterisation show that Al3Ti is the only newly generated phase in the materials prepared at two temperatures. The Al3Ti generated at the temperature of 660 °C is concentrated at the Ti/Al interface position. The Al3Ti generated at a temperature of 730 °C is dispersed in the Al matrix, leading to the formation of numerous Al3Ti/Al interfaces. The residual HEA particles were observed at the sites of oxide aggregation, potentially enhancing the connectivity of the weak interfaces. Following that, the flexural strength and fracture toughness of the composites were evaluated. The results indicate that the materials prepared at a temperature of 730 °C exhibit superior properties. The flexural strength perpendicular to the layer direction reaches 515.89 MPa, while the flexural strength parallel to the layer direction reaches 487.1 MPa. These findings demonstrate clear anisotropy in the flexural performance. Additionally, the material exhibits excellent resistance to crack extension, with a fracture toughness of 32.67 MPa√m.

Influence of graphene content on the microstructure and properties of GNPs/2024Al composites

In this study, reinforced 2024Al-based composites with different graphene nanoplatelets (GNPs) contents (0 %, 0.25 wt%, 0.5 wt%, 1 wt%, 1.5 wt%) were prepared by the Hot Pressed Sintering process method. The impacts of graphene content on its microstructure, mechanical properties and corrosion resistance were investigated using hardness test, tensile property test and intergranular corrosion property test. Furthermore, the microscopic mechanism was explored by combining scanning electron microscopy (SEM), XRD analysis and electrochemical analysis. It was demonstrated that with the increase of GNPs content, the strengthening effect of the composite showed a trend of increasing and then decreasing, and the best strengthening effect of 0.5 wt% GNPs/2024Al composite was achieved. When the solution and aging was 12 h, the hardness was 161.74 HV0.2 and the tensile strength was 476 MPa. The GNPs could reduce the anti-intergranular corrosion performance of 2024Al. As the content of GNPs increases, the corrosion current density of the composite gradually increases and the anti-corrosion performance gradually decreases.

Mechanical, dielectric, and microwave absorption properties of rGO nanosheets and ZnO filled ZnAl2O4 composites with broad bandwidth and strong absorption

Reduced graphene oxide (rGO) nanosheets and ZnO filled ZnAl2O4 composites (rGO/ZnO/ZnAl2O4 composites) were fabricated by hot-pressing sintering process in-situ reactions for the purpose of microwave absorption applications. The effects of ZnO and rGO content on the mechanical, dielectric and microwave absorption properties were systemically investigated. The results show that the porosity and microhardness increase with increasing the absorbent content, while the flexural strength presents an opposite trend. In addition, the dielectric properties present an overall increase trend with increasing the absorbent content. Because of the favorable impedance matching and the optimal microwave attenuation, the rGO/ZnO/ZnAl2O4 composite with 1 vol% rGO and 8 vol% ZnO demonstrates minimum reflection loss of –44.5 dB at 10.1 GHz and effective absorption bandwidth of 3.8 GHz in 8.2–11.8 GHz and 12.2–12.4 GHz as the thickness is 2.2 mm. The synergistic effects of interfacial polarization, dipole polarization, conductance loss, and multiple scattering result in the outstanding microwave absorption properties for the investigated rGO/ZnO/ZnAl2O4 composite, which indicates their potential candidates for the microwave absorbing materials with broad bandwidth and strong absorption.

Development of Water-Soluble Composite Salt Sand Cores Made by a Hot-Pressed Sintering Process

Development of Water-Soluble Composite Salt Sand Cores Made by a Hot-Pressed Sintering Process

Study of the hot-pressing sintering process of diamond/copper composites and their thermal conductivity

Diamond/copper composites have been widely studied as high thermal conductivity (TC) materials for heat dissipation in electronic integrated devices. In this study, diamond/copper composites with fin structures were prepared by hot-pressing sintering. The relative density and TC of the composites were analyzed for different diamond particle sizes, diamond volume fractions, sintering temperatures and sintering pressures. The relative density of the composites decreases significantly with increasing diamond particle size and volume fraction. The TC of the composite was found to be a maximum of 564.2 W/m·K at 1400 N sintering pressure and 900 °C sintering temperature when the diamond particle size was 230 µm and the volume fraction was 60%. In addition, the coefficient of thermal expansion (CTE) of the diamond/copper composite was 7.01 × 10−6 K−1 at 1400 N sintering pressure and 900 °C sintering temperature, which meets the packaging requirements for electronic integrated devices. The heat dissipation experiment of the diamond/Cu microchannel heat sink (MCHS) showed that the surface temperature of the heat source can be controlled at 59.9 °C when the inlet velocity was 0.4 m/s, achieving a cooling of 40.1 °C.

Joining of p-type skutterudite and Cu electrodes with a laser patterned interfacial structure

p-type skutterudite (p-SKD) with laser patterned CoMo barrier layers were fabricated by a one-step hot press sintering process. Then the p-SKD coated by CoMo barriers layers with different patterned parameters were brazed with Cu electrodes. The shear strength increased by ∼1.5 times after the laser processing.

In situ reaction synthesis, microstructure and thermomechanical properties of novel medium-entropy (Ti,V,Nb,Ta)2AlC ceramics

High- and medium-entropy (HE and ME) materials have attracted considerable interest in recent years due to the advantages of designable components and tunable structures with modifiable physicochemical performances. Herein, a dense equiatomic quaternary (Ti,V,Nb,Ta)2AlC solid solution, or denoted as a medium-entropy MAX phase, was fabricated by in-situ reaction in hot-pressing sintering process using easily available elemental powders as raw materials. X-ray diffraction with its Rietveld refinement analysis, scanning electron microscope and high-resolution scanning transmission electron microscope equipped with energy-dispersed spectrometer analysis identify the phase composition and crystal structure of the novel ME-M2AlC (Ti,V,Nb,Ta)2AlC phase. Especially, the atomic-resolution HAADF images directly prove the mutual solution of four metallic elements of the ME (Ti,V,Nb,Ta)2AlC phase. Both the flexural strength and Vickers hardness are enhanced compared with the reported individual components, and the strengthening and hardening results largely benefit from solid-solution effect with lattice distortion in structure. The fracture toughness has not been enhanced due to the lack of effective toughening mechanism. Furthermore, the electrical conductivity of ME (Ti,V,Nb,Ta)2AlC ceramic is distinctly decreased as a result of the increasing carrier lattice scattering and point defect scattering, which is caused by severe lattice distortion. Similarly, the scattering effect of solid solutions is also responsible for the lower thermal conductivity. It is worth noting that size disorder parameter (δsize) is a more effective criterion to evaluate the reduced thermal conductivity than the ideal mixing configurational entropy itself. As a result, applying the medium- and high-entropy design to the MAX phases with chemical and structural diversity can provide a large compositional space with corresponding large range of unexpected performances, which is highly anticipated.

Study on Sliding Wear Characteristics of Tungsten Carbide Particle Reinforced Copper Matrix Composites Under Electrical Contact

Tungsten carbide (WC) particles reinforced copper (Cu) composites (1⁓5 wt.% WC/Cu) were fabricated by a hot-pressed sintering process and their mechanical, electrical properties and sliding wear behaviors were studied. The results show that the relative density and electrical conductivity of the sintered composites decrease whereas the microhardness increase, with increasing the mass fraction of WC reinforcements. During the sliding wear tests without electrical current, the wear rate of the WC/Cu composites decreases with an increase of WC reinforcement mass fraction. The increase in the normal load leads to the increase of wear rate. The wear rate under electrical contact increases with the increase of electrical current density. The dominant wear mechanism under electrical contact sliding conditions is the combination of the abrasive wear and oxidations resulted from electrical currents. The WC/Cu composites are promising electrical contact materials to restrain spark/arc discharge during the electrical contact sliding.

Effect of Ti on Characterization and Properties of CoCrFeNiTix High Entropy Alloy Prepared Via Electro-Deoxidization of the Metal Oxides and Vacuum Hot Pressing Sintering Process

The CoCrFeNi system is one of the most important high entropy alloys (HEAs) systems. By adding and adjusting the alloy element components and using different synthesis methods, different phases, organization and microstructure can be obtained, thus improving their properties. In this study, CoCrFeNiTix HEAs with various Ti contents (x in molar ratio, x = 0, 0.5, 1.0, 1.5) were fabricated by an electrochemical process by virtue of different oxides. The impacts of different Ti contents on the structure, distribution of elements, mechanical properties and corrosion behavior were researched using XRD, EDX and other testing methods. The bulk CoCrFeNiTix (x = 0, 0.5, 1.0, 1.5) HEAs could be obtained through vacuum hot pressing sintering process (VHPS), which had a single-phase FCC structure. The results of the study showed that the bulk CoCrFeNiTix exhibited superior ultimate tensile strength (UTS) and hardness, with the UTS of CoCrFeNiTi as high as 783 MPa and the hardness of CoCrFeNiTi1.5 reaching 669 HV. The corrosion behavior of CoCrFeNiTix (x = 0, 0.5, 1.0, 1.5) HEAs in 0.5 M H2SO4, 1 M KOH and 3.5 wt% NaCl was improved with addition of Ti. CoCrFeNiTix (x = 0, 0.5, 1.0, 1.5) HEAs have great potential for application in the fields of biomedical coating and aerospace, as well as extreme military industry, etc.

Effect of R2O3 (R=Y, La) on the microstructure, optical, and photoluminescent properties of MgAl2O4:Cr3+ transparent ceramics

MgAl2O4:Cr3+ transparent ceramics were prepared by a hot-pressed sintering process with Y2O3 and La2O3 as sintering aids, and the effects on the microstructure, densification, optical transmission, and photoluminescent properties were investigated. The sintering aids of Y2O3 and La2O3 enhanced the relative density, reaching 99.33% with 2.4 wt% Y2O3 and 99.24% with 0.8 wt% La2O3. La2O3 also inhibited abnormal grain growth and obtained ceramics with uniform grain size. In addition, the optical transmission was also improved with Y2O3 and La2O3 as sintering aids. The transmission of the ceramic with 2.4 wt% Y2O3 exceeded 78% in the region of 700–6000 nm and reached 83% at 1450 nm. Moreover, Y2O3 and La2O3 both contributed to improving the quantum yield of the ceramics, especially for Y2O3, and the quantum yield was about 0.354, which was approximately two times higher than that without R2O3. In summary, La2O3 was helpful for improving sintering process, inhibiting grain growth, and homogenizing the grain size, while Y2O3 was significant for enhancing the optical and photoluminescent properties.

Preparation of millimeter-scale hard layer on the surface of titanium alloy via self-propagating high temperature synthesis combined with hot pressing sintering process

A hard and thick surface strengthening layer with high interfacial bonding strength was innovatively prepared via self-propagating high temperature synthesis (SHS) combined with hot pressing sintering (HPS) process. The thickness of the surface layer reached 1.1 mm, far exceeding the strengthening layer prepared by the traditional surface modification methods of titanium alloy. The raw materials of the hard layer were carefully designed by mixing powders of Ti, C, B and Ni, and the raw material of the matrix was Ti–6Al–4V powder. During the HPS process (1100 °C, 40 MPa), the Ti–Ni reaction released a large amount of heat, which promoted the Ti–C reaction and Ti–B reaction. The test results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) suggested that a high amount of Ti6C3.75 and TiB were finally generated in the hard layer, and the Vickers hardness value was as high as 1800 HV. Furthermore, the energy dispersive spectrometer (EDS) test results indicated that most Ni atoms diffused to the Ti–6Al–4V side, and NiTi2 phase was mainly distributed at the interface. Obviously, metallurgical bonding was obtained, accounting for the high interfacial bonding strength of 162 MPa. The present work provided significant insights into the design of novel titanium alloy surface modification process.

Interface microstructure and mechanical properties of Ni–Co–P alloy coatings modified carbon fibres reinforced 7075Al matrix composites

To optimize interface microstructure between 7075Al matrix and CFs, Ni–Co–P multi-component alloy coatings coated carbon fibres were prepared by electroless plating firstly and then Ni–Co–P coated CFs reinforced 7075Al matrix composites (CF/Al(Ni–Co–P)) with high relative density were fabricated by hot pressing sintering process. After modification of Ni–Co–P coatings, Al–Co–Ni Intermetallic compounds were formed stably between matrix and reinforcement because of the smaller mixing enthalpy values of Al–Co, Al–Ni and Co–Ni, which not only restrained the generation of Al4C3 but also improved interfacial bonding strength. Yield strength and ultimate tensile strength of CF/Al(Ni–Co–P) composites with 30 vol% CFs had maximum improvement compared with CF/Al(U) composites than other composites reinforced by 10 vol%, 20 vol% and 30 vol%CFs, which is up to 305.8 MPa and 668.7 MPa respectively, and the fracture mode of composites from accumulation fracture to non-accumulation fracture as the existence of Ni–Co–P coatings.

Effects of Ba2+doping on microstructure and properties of PLMNT electro-optic ceramics fabricated by hot-pressed sintering process

A series of highly transparent electro-optic (EO) ceramics Pb0.975-xBaxLa0.025(Mg1/4Nb1/2Ti1/4)0.99375O3 with the Ba2+ content of 0, 0.005, 0.01, 0.02, 0.04 were fabricated through the vacuum/oxygen hot-press sintering process. The effects of the barium substitution on the material phase transition, transmittance, dielectric, ferroelectric and electro-optic properties have been investigated and analyzed. With the Ba2+ content increasing, the shape of the ferroelectric hysteresis loop changed from rectangular to slim, the values of remnant polarization (Pr) and coercive electric field (Ec) decreased obviously. The maximum reduction of Pr can reach up to ∼89.8%. All the samples present the high transparency of ∼68% in the near infrared wavelength. The quadratic EO coefficients declines slightly while the Ba2+ content increasing. When the x is 0.01, the sample shows a relatively larger quadratic EO coefficient of ∼30.42 × 10−16 (m/V)2 and a lower Pr value of ∼2.08 μC/cm2, which promise the material a hopeful application in EO modulator.

Preparation of Al2O3 coating on Nb fiber and the effect on interfacial microstructure of Nbf/TiAl composite

Continuous Nb fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. However, the premature cracking failure is resulted from the brittle reaction products formed at the interface between Nb fiber and TiAl matrix, which accelerates the structural failure of Nb f /TiAl composite. Fortunately, Al 2 O 3 coating could be introduced on the surface of Nb fiber to tackle the problem. In this study, Al 2 O 3 coating was prepared on the surface of Nb fiber by the cathodic plasma electrolytic deposition (CPED) technology, and then the Al 2 O 3 -coated Nb fibers were used to reinforce TiAl alloy by using vacuum hot-pressing sintering. Furthermore, the influence of the Al 2 O 3 coating on the interfacial microstructure of Nb f /TiAl composite after hot-pressing sintering and thermal exposure was studied. The results show that deposition voltage plays a key role in the microstructure of Al 2 O 3 coating on the Nb fiber. As the voltage increases from 200 V to 400 V, the thickness, density and Al 2 O 3 content of the coating increase. Meanwhile, the bonding between Nb fiber and Al 2 O 3 coating is better when the deposition voltage exceeds 350 V, and the components of Al 2 O 3 -coated Nb fibers prepared from fiber to coating are as follows: Nb/Nb 2 O 5 /Nb 2 O 5 + Al 2 O 3 /Al 2 O 3 . The Al 2 O 3 coating can restrain the formation of the interfacial brittle phases including σ-Nb 2 Al and α 2 -Ti 3 Al during hot-pressing sintering process of Nb f /TiAl composite. In addition, the introduction of Al 2 O 3 coating can reduce the defects in interface, as well as avoid the formation of the crisscrossed and deleterious oxides, which improves interfacial oxidation resistance of the Nb f /TiAl composite. • A uniform and dense Al 2 O 3 coating with a thickness of 4–6 μm can be obtained on Nb fiber surface by CPED technology. • Al 2 O 3 coating can prevent the formation of interfacial brittle phases during the preparation of Nb f /TiAl composite. • Al 2 O 3 coating with excellent thermal stability can avoid the formation of crisscross harmful oxides.

Influence of sintering temperature on heterogeneous-interface structural evolution and magnetic properties of Fe–Si soft magnetic powder cores

Ceramic oxides have attracted considerable research attention as ideal coating layers for novel Fe-based soft magnetic powder cores (SMPCs). However, maintenance of the integrity and uniformity of Fe-based/MOx core–shell heterostructures is challenging. The mechanism underlying the evolution of the core–shell heterostructure is a key determinant of the performance of Fe-based SMPCs. Herein, the laws governing the evolution of the core–shell structure of and heterogeneous interface in Fe–Si/SiO2 SMPCs with temperature and the influence of this evolution on SMPCs performance were investigated. The results revealed that at the sintering temperature of 1093–1183 K, the core–shell heterostructure gradually integrated, while SiO2 insulating coatings underwent amorphous-to-crystalline state transformation. When the sintering temperature was >1243 K, Fe–Si particles melted partially, and the core–shell heterostructure collapsed owing to the overheating induced by the gradient temperature field during the hot-pressing sintering process. When the sintering temperature was 1153 K, the core–shell heterostructure was intact, and the Fe–Si/SiO2 SMPCs had a saturation magnetisation of 245.5 emu/g, resistivity of 0.42 mΩ cm, and total loss of 923.2 kW/m3 at 10 mT and 100 kHz. When the core–shell heterostructure was destroyed, the resistivity dropped drastically, and the total loss increased by approximately 36.7% and 41.8%. Based on these results, the relationship among the core–shell heterostructure of Fe–Si/SiO2 SMPCs, sintering temperature, and magnetic properties was established, which is instrumental in achieving high power density, high efficiency, and miniaturisation in SMPCs.

Fabrication of Multiscale-Alumina Particles Reinforced Copper Matrix Composites with High-Energy Ball Milling and Hot Pressing

Cu-Al2O3 composite materials combining the good electrical of copper matrix and the high hardness of Al2O3 ceramic particles show great performance in electronics, electrical sliding contacts fields. However, the relationship of a dilemma between strength and ductility has become a limitation for the development of copper matrix composites. The previous works indicated that fine grain powders can improve interfacial bonding between the copper matrix and Al2O3 particles to further enhance strength while maintaining ductility. In the present work, the multiscale-alumina particles reinforced copper matrix composites were successfully fabricated by mixing high-energy ball milling and consolidation of hot-press sintering. SEM and TEM were used to observe the powder morphology and microstructure of Cu-Al2O3 composites. The results show that the reinforcing phase Al2O3 particles are uniformly dispersed in the copper matrix, which improves interfacial bonding between the copper matrix and Al2O3 particles. Especially, the micro Al2O3 particles play an important role in achieving an excellent tradeoff of strength and ductility in the Cu-Al2O3 composite. In addition, the microhardness of Cu-Al2O3 composites can be greatly improved by using the high-energy ball milling and hot-press sintering process. The research idea of this paper can provide a reference for other composite materials that need to improve mechanical properties.

Quasi-quantitative control of the properties at room temperature and 1000°C of NiAl-based composites prepared by hot press sintering

For high-temperature structural materials such as NiAl, the selection of appropriate mechanical properties to meet the room-temperature ductility and high-temperature strength required for practical engineering applications is a pressing issue. To address this issue, novel NiAl-based composites reinforced by 3-dimensional network structure were prepared using pre-alloyed powders sieved into five different particle size ranges. All composites in this paper had excellent mechanical properties as the 3-dimensional network structure could improve both room-temperature ductility and high-temperature strength. Due to almost each powders grew into one grain during the hot pressing sintering process and the grains did not grew further caused by the hindrance of the 3-dimensional network structure, the particle size of the original powders and the grain size of the composites showed an obvious linear relationship. The relationship among original powder particle size, grain size and mechanical properties of the NiAl-based composites was established by fitting method, and the fitted equations were validated with an average deviation of 2.45%, so that quasi-quantitative control of the mechanical properties could be achieved by designing the original powder particle size. This work allowed both room and high temperature mechanical properties of NiAl to be improved and quasi-quantitative control over them, which provided a new idea for the design of composites.

Effect of graphene on microstructure and properties of Gr/CuCr10 composites

Gr/CuCr10 alloys with graphene contents of 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, and 0.7 wt.% were prepared by a hot pressing sintering process. Compared with CuCr10 alloy, the relative density of CuCr10 composite with 0.3 wt.% addition of graphene remained constant, while the electrical conductivity increased from 62.2% (IACS) to 69.5% (IACS). The main reason for the increased electrical conductivity is that the addition of graphene leads to the size reduction of Cr phase and thus reduces the scattering of electrons. In addition, Brinell's hardness of 0.3 wt.% Gr/CuCr10 composite increased from HB 91.8 to HB 99.6 compared with that of CuCr10 alloy. The graphene was mainly distributed at the interface of Cu and Cr. A nano-Cr23C6 phase, which has been observed through HRTEM, is the main reason for the wettability enhancement at the interface of Cu and Cr, thus improving the hardness of the material.

Preparation Process and Quality Characterization of High Density Fine Grain Osmium Target for Coated Cathode

High quality osmium targets are the key influence in improving the emission performance, lifetime and reliability of M-type cathodes. In this experiment, oxidative distillation was used to prepare osmium powder with a purity greater than 99.99%. The effect of hydrogen sintering and hot pressing sintering processes on the densities and grain size of the targets was investigated. The results show that the oxidation distillation process can effectively separate Os from Si, Fe, Ni, Zn and other impurity elements, and the purity of osmium powder prepared by multiple oxidation distillation was not less than 99.99%. Both hydrogen sintering and hot pressing sintering processes can be used to obtain osmium targets with a density of not less than 95%. However, the sintering temperature and time used in the hot pressing sintering process under pressure assistance are significantly lower than those of hydrogen sintering, which is more conducive to inhibiting grain growth during the high densification sintering process. By optimizing the parameters of the hot pressing sintering process, the sintering temperature of 1500°C and the holding time of 1.5h resulted in an osmium target with a density of 99.11% and a grain size of ≤12. XPS analysis of the highly dense fine crystalline osmium targets prepared by hot pressing sintering showed that the C and O mass fractions on the surface of the targets were 0.85% and 4.43% respectively, and the C and O contents gradually decreased with increasing etching depth. The above highly dense and fine crystalline osmium targets can be used in the M-type cathode standard coating process to obtain high purity, dense and strong bonded osmium films.

Preparation of Millimeter-Scale Hard Layer on the Surface of Titanium Alloy Via Self-Propagating High Temperature Synthesis Combined with Hot Pressing Sintering Process

Preparation of Millimeter-Scale Hard Layer on the Surface of Titanium Alloy Via Self-Propagating High Temperature Synthesis Combined with Hot Pressing Sintering Process