Mechanical,tribological and electrical properties of ZrB2 reinforced Cu processed via milling and high-pressure hot pressing

The present work investigates the effect of (0–10 wt%) ZrB₂ reinforcement on densification, mechanical, tribological and electrical properties of Cu. The consolidation of Cu–ZrB₂ samples was carried out using a hot press (temperature: 500 °C, pressure: 500 MPa, time: 30 min, vacuum pressure: 1.3 × 10^-2 mbar). The bulk density of the hot-pressed Cu composites decreased from 8.84 g/cc to 8.16 g/cc and the relative density of samples lowered from 98.6% to 92.1% with the addition of ZrB₂. The incorporation of hard ZrB₂ (up to 10 wt%) improved the hardness of Cu (1.32–2.55 GPa). However, the yield strength and compressive strength of Cu composites increased up to 5 wt% ZrB₂, and further addition of ZrB₂ lowered its strength. The yield strength of Cu samples varied from 602 to 672 MPa and the compressive strength between ~834 and 971 MPa. On the other hand, the coefficient of friction (COF) (from 0.49 to 0.18) and wear rate (from 49.3 × 10^-3 mm³/Nm to 9.1 × 10^-3 mm³/Nm) of Cu–ZrB₂ samples considerably decreased with the addition of ZrB₂. Significantly low wear was observed with Cu-10 wt% ZrB₂ (Cu-10Z) samples, which is 5.41 times less than pure Cu. As far as the wear mechanisms are concerned, in pure Cu, continuous chips (wear debris) were formed during sliding wear by plowing. Whereas the major amount of material loss was occurred due to the plowing mechanism with discontinuous and short chip formation for Cu–ZrB₂ composites. The electrical conductivity of Cu–ZrB₂ samples decreased from 75.7% IACS to 44.1% IACS. In particular, Cu with ZrB₂ (up to 3 wt%) could retain the conductivity of 66.8% IACS. This study reveals that the addition of ZrB₂ (up to 3 wt%) is advantageous to have a good combination of properties for Cu.     

Effect of ZrB2 content on the densification,microstructure, and mechanical properties of ZrC-SiC ceramics

ZrC ceramics containing 30 vol% SiC-ZrB₂ were produced by high-energy ball milling and reactive hot pressing. The effects of ZrB₂ content on the densification, microstructure, and mechanical properties of ceramics were investigated. Fully dense ceramics were achieved as ZrB₂ content increased to 10 and 15 vol%. The addition of ZrB₂ suppressed grain growth and promoted dispersion of the SiC particles, resulting in fine and homogeneous microstructures. Vickers hardness increased from 23.0 ± 0.5 GPa to 23.9 ± 0.5 GPa and Young’s modulus increased from 430 ± 3 GPa to 455 ± 3 GPa as ZrB₂ content increased from 0 to 15 vol%. The increases were attributed to a combination of the higher relative density of ceramics with higher ZrB₂ content and the higher Young’s modulus and hardness of ZrB₂ compared to ZrC. Indentation fracture toughness increased from 2.6 ± 0.2 MPa⋅m^1/2 to 3.3 ± 0.1 MPa⋅m^1/2 as ZrB₂ content increased from 0 to 15 vol% due to the increase in crack deflection by the uniformly dispersed SiC particles. Compared to binary ZrC-SiC ceramics, ternary ZrC-SiC-ZrB₂ ceramics with finer microstructure and higher relative densities were achieved by the addition of ZrB₂ particles.     

Densification,microstructure, and mechanical properties of V-substituted HfB2-based ceramics

This study firstly developed Hf_1-xV_xB₂ (x = 0, 0.01, 0.02, 0.05) powders, which were derived from borothermal reduction of HfO₂ and V₂O₅ with boron. The results revealed that significantly refined Hf_1-xV_xB₂ powders (0.51 μm) could be obtained by solid solution of VB₂, and x ≥ 0.05 was a premise. However, as the content of V-substitution for Hf increased, Hf_1-xV_xB₂ ceramics sintered by spark plasma sintering at 2000 °C only displayed a slight densification improvement, which was attributed to the grain coarsening effect induced by the solid solution of VB₂. By incorporating 20 vol% SiC, fully dense Hf_1-xV_xB₂-SiC ceramics were successfully fabricated using the same sintering parameters. Compared with HfB₂-SiC ceramics, Hf_0.95V_0.05B₂-20 vol% SiC ceramics exhibited an elevated and comparable value of Vickers hardness (23.64 GPa), but lower fracture toughness (4.09 MPa m^1/2).     

Influence of SiC ceramic reinforcement size in establishing wear mechanisms and wear maps of ultrafine grained AA6063 composites

This paper described the influence of varying sizes of SiC ceramic reinforcement (coarse (12 μm), fine (1 μm) and nano (45 nm)) in establishing the wear mechanisms and the wear mechanism maps of ultrafine grained (UFG) AA6063/4 wt%SiC composites. The UFG composites were developed by a hybrid manufacturing route of stir casting and cryorolling. The pin-on-disc machine under normal loads of 10–50 N and sliding speeds of 0.5–2 m/s was used to investigate wear behavior. The synergetic effect of cryorolling and varying ceramic reinforcement size has resulted in microstructural modification and has reducing effect on specific wear rate. Microstructural characterization revealed that, cryorolling has accumulated high dislocation density and arrested recovery and recrystallization at liquid nitrogen temperature. Frictional heat generated at wear surface with increase in sliding speed and load has activated the dynamic recovery, recrystallization and precipitation which further increased the hardness and reduced the specific wear rate. The wear mechanisms were established for UFG materials. The wear mechanism maps were constructed and correlated with the microstructures of worn surfaces of UFG materials to identify the dominant wear mechanism.     

MgO－ZrO_2材料的烧结、显微结构和性能

对会ＺｒＯ２５ｍｏｌ％～２５ｍｏｌ％的ＭｇＯ－ＺｒＯ２材料的烧结，显微结构和力学性能进行了研究。与纯ＭｇＯ材料相比，ＺｒＯ２的添加能起到促进烧结和提高材料强度和抗热震性的作用。１７８０℃烧结试样的显气孔率由１６％降至１％．常温抗折强度由５６ＭＰａ提高到９０ＭＰａ以上，１４００℃高温抗折强度由７．２ＭＰａ提高到４７ＭＰａ以上，热震稳定性也随着ＺｒＯ２含量的增加而提高。     

Microstructure and mechanical behaviors of 2D-Cf/ZrB2-SiC composites at elevated temperatures

Microstructure and mechanical behaviors of the 2D-C_f/ZrB₂-SiC composites at RT to 1800 ℃ were studied. It is indicated that the interface structure is critical, which affects the matrix phase composition and cracks deflection path in the intra-bundle area. It subsequently determines the load transmitting, cracks propagation behaviors and the mechanical properties of the composites. Flexural strength of the composites increases slightly at 1000 ℃ by the release of residual stress and self-healing of defects. Partial decomposition and crystallization of polycarbosilane (PCS) derived SiC result in the weakening of the SiC matrix at 1500 ℃. On the other hand, residual carbon reacts with ZrO₂ impurity above 1300 ℃. As a result, the matrix turns to porous structure at 1500 ℃, leading to the formation of short micro cracks. At higher temperature of 1800 ℃, quasi-creep mechanical behavior is presented in the composite.     

Effect of Y2O3-stabilized ZrO2 whiskers on the microstructure,mechanical and wear resistance properties of Al2O3 based ceramic composites

The aim of this study was to improve the mechanical properties of Al₂O₃ ceramics by the addition of Y₂O₃-stabilized ZrO₂ whiskers (designated as Al₂O₃/YSZ_W composite) through the flux method and hot-pressing technology. The effect of YSZ_W content on their microstructure, phase composition and transformability, mechanical properties, and wear resistance was systematically investigated. The Al₂O₃/YSZ_W composites containing 10 wt% YSZ_W exhibited the best mechanical performance, including the highest content of YSZ_W tetragonal phase and transformability as well as the largest values in their relative density (99.5%), hardness (1969 HV), fracture toughness (9.57 MPa m^1/2) and flexural strength (855 MPa). The strengthening and toughening of the Al₂O₃/YSZ_W composites were attributed to the YSZ_W tetragonal-monoclinic phase transformation as well as the whiskers reinforcing effect. Furthermore, the Al₂O₃/YSZ_W composites also showed the highest friction and wearing properties.     

Microstructures and mechanical properties of TiB2 composite ceramics with co-addition of Ti and TiC fabricated by SPS

TiB₂ composite ceramics containing different amounts of Ti and TiC were fabricated via spark plasma sintering (SPS), and effects of their addition contents on the microstructure and mechanical properties were discussed. The newly formed phases of TiB with a cubic lattice structure in the composite ceramics were observed. At a relatively low temperature of 1510 °C, pressure of 50 MPa, and holding time of 5 min, the TiB₂ composite ceramic with 30 wt% TiC and 10 wt% Ti additions acquired an excellent strength of 727 MPa and a high toughness of 7.62 MPa m^1/2. The improvement in strength and toughness was attributed to the mixed fracture mode, second phase strengthening, and increased energy consumption for crack propagation caused by the newly formed phases and fine TiC particles. In addition, the significant effects of the Ti and TiC addition contents on the densification temperature and mechanical properties of the composite ceramics were determined using analysis of variance (ANOVA).     

Influence of hBN content on mechanical and tribological properties of Si3N4/BN ceramic composites

Silicon nitride materials containing 1–5 wt% of hexagonal boron nitride (micro-sized or nano-sized) were prepared by hot-isostatic pressing at 1700 °C for 3 h. Effect of hBN content on microstructure, mechanical and tribological properties has been investigated. As expected, the increase of hBN content resulted in a sharp decrease of hardness, elastic modulus and bending strength of Si₃N₄/BN composites. In addition, the fracture toughness of Si₃N₄/micro BN composites was enhanced comparing to monolithic Si₃N₄ because of toughening mechanisms in the form of crack deflection, crack branching and pullout of large BN platelets. The friction coefficient was not influenced by BN addition to Si₃N₄/BN ceramics. An improvement of wear resistance (one order of magnitude) was observed when the micro hBN powder was added to Si₃N₄ matrix. Mechanical wear (micro-failure) and humidity-driven tribochemical reaction were found as main wear mechanisms in all studied materials.     

Effect of SiC whiskers and graphene nanosheets on the mechanical properties of ZrB2-SiCw-Graphene ceramic composites

Ultrahigh temperature ZrB₂-SiC_w-Graphene ceramic composites are fabricated by hot pressing ZrB₂-SiC_w-Graphene oxide powders at 1950 °C and 30 MPa for 1 h. The microstructures of the composites are characterized by Scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The results show that multilayer graphene nanosheets are achieved by thermal reduction of graphene oxide during sintering process. Compared with monolithic ZrB₂ materials, flexural strength and fracture toughness are both improved due to the synergistic effect of SiC whisker and graphene nanosheets. The toughening mechanisms mainly are the combination of SiC whisker and graphene nanosheets crack bridging, pulling out.     

Microstructure and mechanical properties of TiB2-reinforced 7075 aluminum matrix composites fabricated by laser melting deposition

In this study, we adopt laser-melting deposition (LMD) technology to fabricate TiB₂/7075 aluminum matrix composites (AMCs), and we investigate in detail the effect of the TiB₂ content on the microstructure, nano-hardness, compressive properties, and wear performance. We prepare experimental samples by using a laser power of 800?W and a velocity of 0.01?m/s, and the results are evaluated. It was observed that the reinforcement particles dispersed irregularly throughout the Al matrix as the TiB₂ contents increased. The grain size of the fine-grain zone decreased appreciably by 31.9% from 8.41?µm (LMD sample without TiB₂ reinforcement) to 5.73?µm. Furthermore, the AMCs with 4?wt% reinforcement exhibited impressive mechanical properties, i.e., nanohardness of 1.939 Gpa, compressive strength of 734.8?MPa, and a wear rate of 1.889?×?10^?4 mm³/Nm. The wear resistance improved and the wear mechanism changed from adhesive wear to debris wear with the addition of TiB₂ reinforcement.     

Improvement of sinterability and mechanical properties of ZrB2 ceramics by the modified borothermal reduction methods

Starting from ZrO₂ and boron (molar ratio: 1:4), four ZrB₂ powders were synthesized by borothermal reduction method, three of which were designed to introduce minor modifications by combining solid solution with Ti and/or water-washing. The sinterability, microstructures, mechanical properties and thermal conductivity were investigated. In comparison with the conventional borothermal reduction, the modified methods offered significant improvement in terms of densification of ZrB₂ ceramics, particularly the mixture that included water-washing. Owing to the refined particle size and boron residues, ZrB₂ ceramics from the modified borothermal reduction which included water-washing demonstrated nearly full densification, Vickers hardness of 14.0 GPa and thermal conductivity of 82.5 W/mK after spark plasma sintering at 2000 °C for 10 min. It was revealed that the properties of ZrB₂ ceramics could be enhanced utilizing the proposed minor modification, starting from the same raw materials and adopting the same sintering conditions.     

Influence of sol-gel derived ZrB2 additions on microstructure and mechanical properties of SiBCN composites

A simple method for introducing ZrB₂ using sol-gel processing into a SiBCN matrix is presented in this paper. Zirconium n-propoxide (ZNP), boric acid and furfuryl alcohol (C₅H₆O₂) (FA) were added as the precursors of zirconia, boron oxide and carbon forming ZrB₂ dispersed in a SiBCN matrix. SiBCN/ZrB₂ composites with different contents of ZrB₂ (5, 10, 15, and 20 wt%) were formed at 2000 °C for 5 min by spark plasma sintering (SPS). The microstructures were carefully studied. TEM analysis showed that the as formed ZrB₂ grains were typically 100–500 nm in size and had uniform distribution. HRTEM revealed clean grain boundaries between ZrB₂ and SiC, however, a separation of C near the SiC boundary was observed. The flexural strength, fracture toughness, Young's modulus and Vicker's hardness of composites all improved with the ZrB₂ contents and SiBCN matrix containing 20 wt% of ZrB₂ could reach 351±18 MPa, 4.5±0.2 MPa m^1/2, 172±8 GPa and 7.2±0.2 GPa, respectively. The improvement in fracture toughness can be attributed to the tortuous crack paths due to the presence of reinforcing particles.     

Effects of Ti2SnC on the mechanical properties and tribological properties of copper/graphite composites

Copper/graphite composites and copper/graphite/Ti₂SnC composites were fabricated through the process of ball-milling, pressing and sintering. The effects of Ti₂SnC as the second lubrication component on the mechanical properties, wear resistance and lubrication properties of copper/graphite composites were studied in this paper. The results showed that copper/graphite/Ti₂SnC composites had better hardness, impact toughness, wear resistance and lubrication performance than copper/graphite composites. The optimum values of hardness, impact toughness, friction coefficient and wear rate of copper/graphite/Ti₂SnC composites were, respectively, 56 HSD, 1.8J/cm², 0.15, 9.126 × 10^?6 mm³/N·m, while these were only 45 HSD, 1.2 J/cm², 0.17, 3.534 × 10^?4 mm³/N·m of copper/graphite composites.     

Densification,microstructure and properties of ultra-high temperature HfB2 ceramics by the spark plasma sintering without any additives

Ultra-high temperature HfB₂ ceramic with nearly full densification is achieved by using gradient sintering process of SPS without any additives. The effect of the sintering temperature on the densification behavior, relative density, microstructure, mechanical and thermionic properties is systematically investigated. The results show that the fast densification of HfB₂ ceramic occurs at the heating stage, and the highest relative density of 96.75% is obtained at T =1950 °C, P = 60 MPa and t =10min. As the temperature is increased from 1800 to 1950 °C, the grain size of HfB₂ increases from 6.12 ±1.33 to 10.99 ± 2.25 μm, and refined microstructure gives the excellently mechanical properties. The highest hardness of 26.34 ±2.1GPa, fracture toughness of 7.12 ± 1.33 MPa m^1/2 and bending strength of 501 ±10MPa belong to the HfB₂ ceramic obtained at T =1950°C. Moreover, both the Vickers hardness and fracture toughness obey the normal indentation size effect. HfB₂ ceramic also exhibits the thermionic emission characterization with the highest current density of 6.12 A/cm² and the lowest work function of 2.92 eV.     

Enhanced mechanical properties of Si3N4 ceramics with ZrB2-B binary additives prepared at low temperature

Phase composition, microstructures, and mechanical properties of silicon nitride (Si₃N₄) ceramics were investigated with ZrB₂ and B additives. Results showed that the addition of ZrB₂ and/or B in 2.5 and 5 vol.% promoted the phase transformation of α- to β-Si₃N₄ phase and the formation of bimodal microstructure after hot-pressing at 1500 °C. With the introduction of 2.5 vol.% (ZrB₂-B) binary additives, fracture toughness and strength of Si₃N₄ ceramics increased significantly from 5.2 MPa m^1/2 and 384 MPa to 7.2 MPa m^1/2 and 675 MPa, respectively. However, the hardness of ceramics decreased slightly from 23.5 GPa to 21.3 GPa, which was still higher than typical values reported on Si₃N₄ ceramics (15˜17 GPa).     

Fabrication and mechanical properties of metal matrix composite with homogeneously dispersed ceramic particles

Titanium carbide (TiC) particles were coated with nickel (Ni) to increase their compatibility with a metal matrix, leading to an improvement in the dispersibility of TiC particles in the molten matrix. TiC particles were dispersed into a basic aqueous solution of pH 12, and then nickel nitrate (Ni(NO₃)₂), as a Ni precursor, was added to the TiC suspension. The interaction between the TiC particles and the Ni precursor is driven by the attractive force between the Ni cations and the TiC particles with negative charge. An inoculant (ferrosilicon), which has been used in the foundry industry to improve crystal growth of graphite, was used as a core particle. The Ni-treated TiC particles were coated onto the surface of the inoculant using an inorganic binder converted into its glass phase by sol–gel reactions. The reinforcement particles prepared through the dual-coating process were then injected into the molten matrix based on iron at 1500 °C. The crystal phase of the graphite is more finely and shortly grown in the reinforced metal matrix than in that without the reinforcement particles. This means that the reinforcement particles are homogeneously and uniformly dispersed into the matrix without any aggregation of particles, implying that the mechanical properties of the reinforced matrix would be greater than those of a non-reinforced matrix. Consequently, metal matrix composites with reasonable properties can be fabricated successfully using the reinforcement particles prepared by the dual-coating process.     

Effect of preform architecture on the mechanical properties of 2D C/C composites prepared using rapid directional diffused CVI processes

The substrate architecture of carbon-carbon (C/C) composites has an effect on both the mechanical properties and the cost of the products. Four kinds of substrate materials, 1K and 3K plain carbon cloth, carbon paper, and carbon felt, were used in this study, and from them four different 2D preforms were produced, namely, 1K plain carbon cloth, carbon paper+1K plain carbon cloth, carbon felt+1K plain carbon cloth, 3K plain carbon cloth, using a spreading layer method. The preforms were densified using the rapid directional diffused CVI processes. A three-point bend test was used to investigate the influence of preform architecture on the flexural properties and microstructure of the C/C composites. The results show that all samples have an obvious pseudo-plastic fracture behaviour, and the macroscopic appearance of the bent fractured section shows as an Z shape. The samples prepared using 1K plain carbon cloth have a uniform microstructure, and consequently possess the highest flexural strength, while the composites produced from 3K plain carbon cloth possess the lowest value due to their poor microstructure and lower strength fibers. In general the flexural properties of the C/C composites are improved with an increase of the carbon fiber volume fraction in the preform. All the C/C composites manufactured from the four preforms fail by delamination when broken.     

Comparison of the homemade and commercial graphene in heightening mechanical properties of Al2O3 ceramic

Graphene has been successfully fabricated by a novel method, using graphite powder and NMP (N-Methyl Pyrrolidone) as the raw materials based on the principles of liquidoid exfoliation and mechanical milling. SEM, TEM and Raman spectrum were utilized to characterize the morphology of the homemade graphene, illustrating the few defects and rare layers were endowed in this study. Afterwards, the homemade and commercial graphene were doped into Al₂O₃ powder with the mass ratio of 0%, 1%, 2%, and 3% to reinforce the mechanical properties of the matrix. The composites were processed at 1600 °C, pressure of 30 MPa and soaking time of 1 h by vacuum hot pressing. The test results illustrated the bending strength and fracture toughness tended to be intensive at first and subdued afterwards, achieving the optimal performance of 625.4±18.2 MPa and 6.07±0.22 MPa m^1/2 at 2 wt% prepared graphene additive, and the commercial grapheme owned the best heighten effect in 3 wt% graphene/Al₂O₃ composites. Compared to the blank Al₂O₃ sintered samples, the graphene/Al₂O₃ specimens (both prepared and commercial additive) behaved evident increase in mechanical properties, even upon 30% enhanced in fracture toughness and bending strength generally by the prepared grapheme. Moreover, the prepared graphene had better improvement effect than commercial graphene in enhancing mechanical properties of Al₂O₃ ceramic.