Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Graphene-reinforced 7055 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering（SPS）. The structure and mechanical properties of the composites were investigated. Testing results show that the hardness, compressive strength, and yield strength of the composites are improved with the addition of 1wt% graphene. A clean, strong interface is formed between the metal matrix and graphene via metallurgical bonding on atomic scale. Harmful aluminum carbide（Al_4C_3） is not formed during SPS processing. Further addition of graphene（above 1wt%） results in the deterioration in mechanical properties of the composites. The agglomeration of graphene plates is exacerbated with increasing graphene content, which is the main reason for this deterioration.

Preparation and Ablation Properties of W/TaC Cermet via in-situ Reaction Sintering Process

An attractive way to prepare W/TaC based cermet at a relatively low temperature was proposed and confirmed experimentally. The thermodynamics calculations indicated that the reaction between WC and Ta2O5was feasible at as low a temperature as 1 400 ℃. The experimental results showed that W/TaC cermet could be fabricated by in-situ reaction sintering process at 1400 ℃ for 2 h in vacuum. The open porosity and bulk density of the W/TaC cermet were 15.3% and 13.4 g/cm3. Further, the microstructural features revealed that W, TaC, and Ta2WO8were identified to be the main constituents of the W/TaC cermet. The mass lose rate and linear recession rate of the W/TaC cermet during an oxyacetylene torch test were 0.0048 g/s and 0.0233 mm/s, respectively. The high porosity, the presence of Ta2WO8phases within W/TaC and evaporation of WO3on the surface of the composite contributed to the decrease of ablative property when comparing with pure W.

Effect of sintering on the relative density of Cr-coated diamond/Cu composites prepared by spark plasma sintering

Cr-coated diamond/Cu composites were prepared by spark plasma sintering. The effects of sintering pressure, sintering temperature, sintering duration, and Cu powder particle size on the relative density and thermal conductivity of the composites were investigated in this paper. The influence of these parameters on the properties and microstructures of the composites was also discussed. The results show that the relative density of Cr-coated diamond/Cu reaches ~100% when the composite is gradually compressed to 30 MPa during the heating process. The densification temperature increases from 880 to 915℃ when the diamond content is increased from 45vol% to 60vol%. The densification temperature does not increase further when the content reaches 65vol%. Cu powder particles in larger size are beneficial for increasing the relative density of the composite.

Microstructure and Mechanical Performance of Cu-SnO_2-rGO based Composites Prepared by Plasma Activated Sintering

A novel chemical technique combined with unique plasma activated sintering（PAS） was utilized to prepare consolidated copper matrix composites（CMCs） by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide（r GO）, SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2＋. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.

Fabrication of solid-phase-sintered Si C-based composites with short carbon fibers

Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

Research Progress on Preparation and Properties of Zirconium Carbide Matrix Composites

Zirconium carbide（ZrC） exhibits considerable potential for applications as aerospace thermal protection and the Generation-Ⅳ nuclear fuel inert materials due to its high melting point,exceptional hardness,good ablation resistance and low neutron absorption cross-section.Nevertheless,low sinterability of ZrC powders and poor fracture toughness and reliability of bulk ceramics limit their wide applications in extreme environments.This paper reviews the state of the art of preparation and properties of ZrC composites.Optimizing the sintering process and tailoring the chemical constituents of raw powders and sintering aids could improve sinterability to produce dense bulk ceramics.Different additives such as refractory metals,carbides,silicides,oxides,or carbon fibers are introduced into the ZrC matrix in order to improve fracture toughness,oxidation resistance or thermal shock resistance,etc.Further studies are needed to explore the effects of intrinsic defects（vacancies,dislocations,and grain or phase boundaries,etc.） and additives on microstructure and properties at elevated temperatures.

Comparative study of mechanical and wear behavior of Cu/WS_2 composites fabricated by spark plasma sintering and hot pressing

The mechanical and wear behavior of copper-tungsten disulfide（Cu/WS_2） composites fabricated by spark plasma sintering（SPS） and hot pressing（HP） was investigated, comparatively. Results indicated that the addition of lubricant WS_2 substantially reduced wear rate of the Cu matrix composites fabricated by SPS,and the optimum content of WS_2 is 20 wt% with regard to the wear behavior. However, it affected a little to the wear rate while dramatically decreased the friction coefficient of the composite fabricated by HP.This difference in friction behavior of the self-lubricating composites fabricated by the two techniques was closely related to their different mechanical properties. Severe interfacial reaction occurred during spark plasma sintering, leading to brittle phase formation at interface.

Fe/Cu gradient composite materials prepared by laser sintering

USLNG CO2 laser beam as a heat source to sinter whole P/M （powder metallurgy） green com-pact is a new technique. As reported in refs. [1--4], the advantages of the laser sintering ofCu-base and Fe-base green compact were characterized by rapid sintering rate, no contamina-tion, fine structure and good properties.

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina-fluorapatite composites with different titania additive amounts （0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%） have been investigated between 1200 and 1600℃. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500℃ for 1 h. Thus, the rupture strength of alumina-26.52 wt% Fap-1.4 wt% TiO2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO2 ,the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction （XRD） analysis of alumina-Fap-TiO2 composites shows the formation of aluminium titanate （Al2O3-TiO2：Al2TiO5 ）. The 27Al magic angle scanning nuclear magnetic resonance analysis of Al2O3-Fap-TiO2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.