Vacuum Hot-pressing Sintering Research Articles

The improved softening resistance and high electrical conductivity of the 3D graphene enhanced copper-based composite fabricated by liquid carbon source

A bulk Cu/Graphene composite with high electrical conductivity (98.2%IACS) and high hardness (61.2 HV) was fabricated by vacuum hot-press sintering. Cu powder with in-situ grown graphene was prepared by non-toxic, cheap liquid paraffin at lower temperature. The in-situ grown 3D graphene act as an electron transport channel and hinder the movement of the grain boundary. After cold rolling and annealing, the Cu/Graphene composite maintained a high tensile strength of 369.4 MPa, high electrical conductivity of 96.1%IACS and good ductility (6%). Comparing with the pure Cu, the existence of Graphene raised the recrystallization temperature of the composite, and made the composite possess excellent softening resistance.

Research on the inhomogeneity and joint interface of in situ oriented TiBw/TA15 composites fabricated by vacuum hot-pressing sintering and canned extrusion

Abstract TiBw/TA15 composite bars with in situ synthesized TiBw were successfully manufactured by the hot-pressing sintering and subsequent hot canned extrusion. Microstructure evolution and mechanical behavior of as-sintered and as-extruded composites had been systematically investigated. After extrusion, due to the large deformation degree, significant grain refinement occurred and the long axes of whiskers were almost parallel to the extrusion direction. Almost no micro-voids were caused by the fractured TiBw as a consequence of three-dimensional compressive stress during the extrusion process. The mechanical properties results demonstrated that the ultimate tensile strength, elongation and Vickers hardness of the as-extruded composites all increased compared with that of the as-sintered composites. Moreover, there was an inhomogeneous microstructure in the as-extruded composites. The edge part possessed stronger grain refinement and much weaker texture than that of the central part owing to the different deformation degree. The interface between the titanium matrix composites and the capsule (45# steel) was relatively flat with no interfacial reaction, which showed the superiority of the 45# steel as the capsule for hot canned extrusion. Oxygen content result illustrated that there was no significant oxidation of titanium matrix during the sintering and extrusion process.

Design and synthesis of a novel ceramic coating-like tool material

A novel ceramic coating-like (CCL) structure was proposed for preparing a potential ceramic cutting tool material. The influence of critical factors, including the material composition, composition content and surface layer thickness, on the residual stress was analyzed by the finite element method (FEM). Under the condition of the optimized parameters, the compressive stress generated on the surface layer of the CCL tool material ranged from −163 MPa to −248 MPa. Based on the obtained results, a (Ti,W)C/Al2O3+SiC CCL tool material was prepared by vacuum hot-pressing sintering, indicating the residual compressive stress (−122.3 MPa) of the surface layer. Compared with the performance of homogeneous cermet materials, the surface hardness and flexural strength of the CCL tool materials were increased by 46.58% and 37.76%, respectively. Moreover, the SEM imaging results of the sample surface and fracture morphology and the energy dispersive spectroscopy (EDS) analysis results showed that the dense ceramic surface and phase interfacial transition layer were formed with a uniform gradient distribution and without defects.

Effect of AlN on microstructure, mechanical and thermophysical properties of NiAl/Fe based alloys prepared by vacuum hot-pressing sintering

The effect of AlN content on the microstructure and mechanical properties of NiAl/Fe–x AlN (x = 0, 3, 5, 10, 15 wt%) alloys were investigated after mechanical alloying with subsequent vacuum hot-pressing sintering. The results showed that the AlN reinforced NiAl/Fe alloy contained B2-ordered NiAl phase, Fe phase and AlN phase. As the AlN content increased, the density of the material decreased gradually, and the hardness and thermal conductivity increased greatly. NiAl/Fe based alloys with 5 wt% AlN obtained higher compressive strength and Rockwell hardness. When the content of AlN was 15 wt%, the density was 5.42 g/cm3, which was 18.6% lower than that of NiAl/Fe alloy. When the content of AlN was 5 wt%, the hardness reached the maximum value of 59.5 HRC, which was 69.04% higher than that of NiAl/Fe alloy. The thermal conductivity of the material first increased and then decreased with the increasing AlN content. When AlN content was 10 wt%, its thermal conductivity was higher than others at each temperature, and the maximum was 34.75 W/(m·k) at 600 °C in the study.

Microstructure and mechanical behavior of in situ TiC reinforced Fe3Al(Fe–23Al–3Cr)matrix composites by mechanical alloying and vacuum hot-pressing sintering technology

In this paper, Fe3Al (Fe–23Al–3Cr) alloys reinforced with in-situ TiC precipitates were fabricated using a combination of high-energy ball milling and vacuum hot-pressing sintering technology. The experiment found that the 1 × 10−3 Pa vacuum was the optimal preparation conditions of composites. The results show that in-situ TiC ceramic is an efficient method to improve the mechanical properties of Fe3Al/TiC composites. The hardness and compressive strength of the composite significant increases with in-situ TiC. And note that in-situ 50% TiC composite has the highest compressive strength (2572 MPa). By comparison, the compressive strength and hardness of all the in-situ composites (15%–50%) are not much different from that of the same contents of ex-situ TiC composites. The bending strength decrease with in-situ TiC content increase except that of in-situ 15%TiC composite, and it exhibits the highest bending strength (1941 MPa). In addition, the fracture toughness of the composites decreases significantly with increasing TiC content. The main reason is that the brittle ceramic TiC particles could act as obstacles for the ductility of Fe3Al alloys. The bending fracture mode transforms from tough fracture mode to brittle cleavage facets crack mode.

ZCAS-assisting low-temperature hot-press sintering of SiC ceramic for immobilizing simulated radioactive graphite

The safe treatment and disposal of high-level radioactive graphite is an essential challenge in the governance of irradiated graphite. SiC has an insurmountable defect in densification sintering at low temperatures, although it is an ideal host material for immobilizing high-level radioactive graphite. To solve this issue, we employ ZCAS (short for ZnO–CaO–Al2O3–SiO2 glass) as a sintering aid to prepare SiC-ZCAS composite ceramic with the relative density up to 98% by vacuum hot-press sintering. For investigating the optimum formula and technological conditions of (1-x) SiC-x ZCAS composite ceramic, the effects of synthesis and sintering process on preparation (1-x) SiC-x ZCAS (x = 25-40 wt%) composites were investigated in detail. The results show that the SiC-ZCAS composite powder with x = 25-40 wt% can be synthesized at 1350 °C for 2 h when the Si/C mole ratio is 1.05:1. The relative density, Vickers hardness, and thermal conductivity of SiC-ZCAS composites ceramic increase rapidly by increasing sintering temperature and pressure. However, these properties will display different effects from the increase in the content of ZCAS, such as continuous elevation of the relative density and dramatic depression of thermal conductivity. the Vickers hardness starts to decline when the content of ZCAS is 30 wt%. Considering the above mentioned, we can conclude that the 0.7SiC-0.3ZCAS composite ceramic has choiceness comprehensive properties when sintered at 1550 °C and 60 MPa for 1 h, with the relative density, Vickers hardness and thermal conductivity of 95.5%, 1084 (HV 10) and 7.104 W/m·k, respectively.

Reinforcing effect of laminate structure on the fracture toughness of Al3Ti intermetallic

Metal/intermetallic laminate composites can improve the mechanical properties of intermetallic materials using metal layers. In recent years, titanium aluminide intermetallics have received increasing attention due to their excellent performance properties, such as high melting point, high specific strength and stiffness, and good corrosion resistance. However, the low fracture toughness of Al3Ti alloys at room temperature has greatly limited their application, and fiber or particle reinforcement has not shown a significant toughening effect. Research into the reinforcing effects of the interface and near-interface zone on the fracture behavior of Al3Ti is lacking. Ti/Al3Ti metal/intermetallic laminate composite was synthesized from titanium and aluminum foils using vacuum hot-pressed sintering technology. The microstructure of the prepared material was analyzed by scanning electron microscope and electron backscattered diffraction. Results illustrate that both Ti and Al3Ti were single-phase and there was a noticeable stress concentration on the interface. To obtain indentation and cracks, loads were applied to different locations of the composite by a microhardness tester. The growth path of the cracks was then observed under microscope, showing that crack propagation was prevented by the interface between the Ti and Al3Ti layers, and the cracks that propagated parallel to the laminate shifted to the interface. Fracture toughness of the different areas, including Al3Ti layers, interface, and near-interface zone, were measured by the indentation fracture method. The fracture toughness at and near the interface was 1.7 and 2 times that of the Al3Ti layers, respectively. Results indicate that crack blunting and crack front convolution by the laminate structure was primarily responsible for increased toughness.

Strengthening effects of in-situ synthetic nano-TiC particles on Ti64 based nanocomposites through adding graphene nanoplatelets

In-situ synthetic nano-TiC reinforced Ti64 composites (TiC/Ti64) through adding graphene nanoplatelets (GNPs) were successfully fabricated by vacuum hot-pressing sintering (HPS) and canned hot extrusion. The surface of Ti64 powders were coated by GNPs through low energy ball milling. During HPS, the agglomerate nano-TiC was distributed at the surface of Ti64 powders. During extrusion, the strip-like nano-TiC were broken into independent particles distributed along the extrusion direction. In addition, the TiC/Ti64 sintered at 1000 °C and extruded at 1000 °C achieved satisfactory mechanical properties based on nano-TiC particles and bi-modal microstructure, with an ultimate tensile strength of 1224 MPa, and a fracture elongation of 7.8%.

Copper matrix thermal conductive composites with low thermal expansion for electronic packaging

Reducing thermal expansion and improving thermal conductivity of copper based materials are particularly important for improving thermal stability of electronic packaging materials. Herein, Cu/Sc2W3O12/SiC composite with a moderate coefficient of thermal expansion (CTE) of 8.28 ppm/K and a high thermal conductivity of 287.2 W/m⋅K was successfully prepared by partial replacement of Sc2W3O12 by the nano SiC particles to compensate sacrificial thermal conductivity of the reported Cu/Sc2W3O12 composites using a hot-pressing method. Theoretical calculation and Ashby plot map suggests that this Cu/Sc2W3O12/SiC composite facilitate the best combination between tunable thermal expansion and high thermal conductivity, which may due to that SiC nanoparticles can strengthen the driving force of vacuum hot-pressing sintering and thus lead to more homogeneous microstructure accounting for improved thermal reliability. This work can provide useful insights into the design and synthesis of composites used as packaging material for various semiconductors.

In situ TEM observation of the microstructural characteristics and mechanical properties of vacuum hot-press sintered Co–30Cr–6Mo alloys

In this research, Co–30Cr–6Mo alloys were fabricated by vacuum hot-press sintering technique. The experiments utilized various hot-press sintering temperatures (1100 °C, 1150 °C, 1200 °C and 1250 °C) and hot-press pressures (20, 35 and 50 MPa) to find the optimal parameters for Co–30Cr–6Mo alloys, while simultaneously investigating the differences in microstructural characteristics and properties. The experimental results showed that the optimal hot-press sintering parameters of this sample were 1150 °C at 35 MPa for 1 h. Meanwhile, Co–30Cr–6Mo alloys possessed the optimal mechanical and electrical properties. Among them, the sintering density reached 8.13 ± 0.01 g cm−3, the hardness and TRS increased to 78.9 ± 0.2 HRA and 2672.2 ± 25.8 MPa, respectively, and the electrical conductivity was 3.11 ± 0.95 × 104 S m−1. TEM observation also identified the stacking faults, FCC and HCP structures of the Co phase, and the partial Cr23C6 carbides precipitated in the Co–30Cr–6Mo alloys, respectively. Consequently, the sintering characteristic of Co–30Cr–6Mo was effectively improved, and the mechanical properties were enhanced at a relatively lower sintering temperature by the vacuum hot-press sintering process.

Microstructures and mechanical properties of FeCoCrNi-Mo High entropy alloys prepared by spark plasma sintering and vacuum hot-pressed sintering

Fully dense FeCoCrNi-Mo high entropy alloy (HEA) was successfully prepared by two different sintering methods: spark plasma sintering (SPS) and vacuum hot-pressed sintering (VHP). The microstructures and mechanical properties of HEA prepared by both methods were systematically investigated and compared. The HEA powders were uniformly distributed at approximately 10 μm after 20 h of ball milling. The SPS sample maintained a single FCC structure and Multiple microstructures of σ phase, Mo2C and Cr23C6 carbides precipitated in the VHP samples. As a result of the precipitation of these hard and brittle phases, the VHP samples exhibited superior hardness and wear resistance but a lower flexural strength and toughness relative to the SPS samples. Considering the different microstructures and mechanical properties between SPS and VHP samples, the sintering method should be selected according to the specific working conditions, and the SPS process has potential in realizing rapid low-temperature sintering for HEAs compared with other sintering methods.

Microstructure and mechanical properties of Fe-ZTA cermet prepared by vacuum hot-pressed sintering

The cermet based on metallic iron with zirconia toughened alumina (ZTA) as the reinforcing phase was prepared by vacuum hot-pressed sintering. The ZTA particles were subjected to electroless nickel plating to improve the interfacial bonding ability of ZTA and Fe matrix. In this paper, after electroless nickel plating, the effects of different particle sizes and different contents of ZTA particles on the grinding properties of Fe-based ZTA (Fe-ZTA) cermets were investigated. The results show that the ZTA particles are tightly bound to the Fe matrix. An interface layer is formed between the ZTA particles and the Fe matrix and it can improve the grinding ability of the Fe-ZTA cermet. By reducing the particle size and the content of ZTA particles, the friction coefficient between Fe-based ZTA cermet and the machined surface can be increased, and the surface roughness of the machined surface will reduce. When the ZTA particle size is F14 and the iron binder content is 40%, the friction coefficient between the Fe-ZTA cermet and the steel bar is 0.4981, the surface roughness of steel bar is 40.164 μm, the grinding ratio is 685.952.

Characterization and Properties of CuZrAlTiNiSi High Entropy Alloy Coating Obtained By Mechanical Alloying and Vacuum Hot-Pressing Sintering

The CuZrAlTiNiSi high entropy alloy coating (HEAC) was synthesized on T10 substrate using mechanical alloying and vacuum hot-pressing sintering technique. The results show that the final product of as-milled powders is amorphous HEA phase with homogeneous component distribution. The sintered coating is composed of solid solutions and intermetallic compounds. No pores and defects appear in the HEAC surface, suggesting a good consolidation quality. In addition, the HEAC possesses a good interface bonding, mainly owing to the diffusion of Al atoms from coating to substrate. The average microhardness of the coating reaches 927 HV0.2, and is more than 3 times higher than the substrate (281 HV0.2). The high microhardness can be mainly explained by the second phase strengthening effect and solid-solution strengthening. Furthermore, compared with the substrate, the HEAC exhibits excellent wear resistance with lower friction coefficient, reduction of the wear groove depths and widths, fewer wear volumes, and minimum specific wear rate under the same conditions. Moreover, based on the wider passive region and uniform surface corrosion morphology, the HEAC presents a good pitting resistance in seawater solution.

Effect of c-BN surface modification on the microstructure and mechanical properties of (Ti,W)C-based cermet tool materials

Alumina-coated cubic boron nitride (c-BN) particles (c-BN@Al2O3) were prepared using a heterogeneous nucleation method. Then, they were added to a (Ti,W)C-based cermet tool material after synthesis via vacuum hot-press sintering. The microstructure and mechanical properties of the (Ti,W)C-based cermet tool material with varying c-BN@Al2O3 contents were recorded and analyzed. The results show that with increasing c-BN@Al2O3 concentration, the relative density, flexural strength, fracture toughness, and Vickers hardness all increase first and then decrease, and the average grain size first decreases and then increases. The introduction of Al2O3 into the c-BN particles used for surface modification can improve the wettability and interfacial bonding strength between the c-BN and matrix particles, restrain the grain growth of the matrix particles, and improve the flexural strength of cermet tool materials. The addition of c-BN@Al2O3 also alters the crack propagation mechanism of the cermet tool material and introduces multiple toughening mechanisms to improve the fracture toughness of the cermet tool material. The high hardness of c-BN and Al2O3 is the main reason for the increase in hardness; however, excessive addition of such material reduces the relative density, resulting in a decrease in hardness.

Phase transformation and mechanical properties of B4C/Al composites

Lamellar constituted with 5, 15, 25 vol.% B4C/Al composites and homogeneous (namely 5, 15, 25 vol.% B4C/Al) composites were fabricated at sintering temperature 680 °C, sintering pressure 30 MPa, and heat preservation period 90 min via vacuum hot-pressing sintering. Another sample constituted with the raw materials of Al sheet and B4C powders has been prepared by the same sintering process to discuss the interface reaction of Al and B4C. In-situ XRD of B4C/Al mixed powders illustrated that the reaction products between Al and B4C were AlB2, AlB12, Al3BC. EDS and EPMA tests have proved that there was an element diffusion existing at the interface of B4C and Al. After sintering, new generation phases AlB12, Al3BC have been detected by SAED analysis of TEM, additionally, the inner microstructure of the lamellar B4C/Al composites was also observed. The results of mechanical properties showed that the lamellar B4C/Al composites possessed the optimal performance of Vicker hardness 116.23 ± 5.25 Hv, bending strength 780.45 ± 12.35 MPa and fracture toughness 12.21 ± 0.23 MPa∙m1/2, which was better than these of homogeneous B4C/Al composites.

Study on the Sintered Characteristics and Properties of Co-30 mass% Cr Alloys under Various Vacuum Hot-Press Sintering Temperatures and Pressures

Study on the Sintered Characteristics and Properties of Co-30 mass% Cr Alloys under Various Vacuum Hot-Press Sintering Temperatures and Pressures

Study on microstructure of NiAl matrix high temperature lubricating composites containing BaO/TiO2 metallic oxide

The microstructure of NiAl matrix high temperature lubricating composites containing BaO/TiO2 metallic oxides were investigated. The NiAl-BaO/TiO2 composites were fabricated by vacuum hot-pressing sintering. The diffraction peaks of NiAl slightly shifted to the left with the addition of BaO/TiO2 metallic oxide. The crystal plane distance of NiAl phase in the composite was bigger than that in NiAl material according to the Bragg equation. Meanwhile, the lattice distortion and dislocation occurred in the composite structure, which is probably due to the Ti element dissolve in the NiAl matrix during sintering. The cohesive energy and formation enthalpy of NiAl were improved with the incremental of Ti solution contents through density functional theory calculations, which was indicated that the Ti element could dissolve in the NiAl and was in good accordance with the results of XRD and TEM.

Effect of shape-memory alloy NiTi fiber on microstructure and mechanical properties of continuous ceramic Al2O3 fiber-reinforced Ti/Al3Ti metal–intermetallic laminated composite

Shape-memory alloy titanium nickel (NiTi) fiber was introduced into continuous ceramic aluminum oxide (Al2O3) fiber-reinforced titanium–titanium trialuminide metal–intermetallic laminated (CSMAFR-MIL) composite using vacuum hot pressing (HP) sintering method to improve the microstructure and mechanical properties of the composite. Scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction techniques were employed to characterize the microstructure of the novel CSMAFR-MIL composite. Besides, the tensile tests were carried out on continuous Al2O3 fiber-reinforced Ti-Al metal–intermetallic laminated (CFR-MIL) composite and the CSMAFR-MIL composite to explore the influence of NiTi fiber additive on mechanical behavior of the CFR-MIL composite. The experimental results showed that the intermetallic layer including Al3Ti, Al3Ti0.8V0.2, Al3Ni intermetallics but without residual NiTi fiber was generated via the reactions of liquid Al with NiTi fiber and Ti foil during preparation. Moreover, owing to the addition of NiTi fiber, intermetallic centerline was prevented effectively to form in the CSMAFR-MIL composite. Moreover, the elemental diffusion occurred between the Al2O3 fiber and the intermetallic, revealing that the metallurgical bonding was formed during the fabrication process. Furthermore, the CSMAFR-MIL composite possessed higher strength and superior ductility than those of CFR-MIL composite attributed to the microstructure optimization.

Synthesis and Mechanical Characterization of a Ti(C,N)/Mo-Co-Ni/CaF2@Al2O3 Self-Lubricating Cermet.

In this paper, an Al2O3 coated CaF2 (CaF2@Al2O3) nanocomposite powder is used as the additive phase of a Ti(C,N)-based self-lubricating cermet material. A novel self-lubricating ceramic material with a multilayer core–shell microstructure was prepared using a vacuum hot-pressing sintering process. The results show that the surface of the CaF2 powder is coated with Al2O3, and when introduced into a Ti(C,N)–Mo–Co–Ni material system, it can utilize the high-temperature liquid phase diffusion mechanism of the metal Mo–Co–Ni phase in the sintering process. The CaF2@Al2O3@Mo–Co–Ni multilayer core–shell microstructure is formed in the material. Compared with the direct addition of CaF2 and Al2O3, the hardness and fracture toughness of the material are increased by 24.31% and 22.56%, reaching 23.93 GPa and 9.94 MPa·m1/2, respectively. The formation of the multilayer core–shell microstructure is the main reason for the improvement of the mechanical properties of the material.

In situ synthesis of high content graphene nanoplatelets reinforced Cu matrix composites with enhanced thermal conductivity and tensile strength

The difficulty of dispersing high content of graphene nanoplatelets (GNPs) in the metal matrix limits the strengthening efficiency of GNPs reinforcement. Herein, high content GNPs were synthesized on the surface of Cu powders using chemical vapor deposition with solid carbon source incorporating impregnation-reduction route, which made GNPs uniformly dispersed and improved the interfacial bonding between GNPs and Cu matrix. Then, the composites were densified by vacuum hot pressed sintering followed by multi-step hot rolling process, during which the orientation distribution of GNPs was achieved. After a rolling reduction of 70%, the composite materials containing 12 vol% GNPs were increased by 44% in yield strength (256 MPa) compared with that of pure Cu (178 MPa). Furthermore, the in-plane thermal conductivity was increased by 17% (441 W/mK) when the GNPs content is 15 vol%. This work sheds light on designing structural and functional integrated Cu matrix composites.