Microstructure Evolution Of Composites Research Articles

Mechanical properties degradation and microstructure evolution of 2D-SiCf / SiC composites in combustion gas environment

Based on the turbine high-temperature combustion gas simulation test platform, the long-term combustion gas environment exposure test of the 2D plain woven SiCf/BN/SiC composites under two combustion conditions was carried out. Uniaxial tensile test, fracture morphology characterization and non-destructive testing analysis revealed the degradation and microstructure evolution of composites after exposure to combustion gas environment. The results show that the degradation of 2D-SiCf/SiC composites after exposure to combustion gas environment is manifested as a decrease in static toughness, and the interphase transition is the mesoscopic cause of the decrease in static toughness of the composite.

Microstructural evolution, strengthening and toughening mechanisms of AZ80 composite sheet reinforced by TiB2 with fiber-like distribution

In-situ TiB2/AZ80 composite was prepared by a simple casting method, and then hot-rolling. Effects of TiB2 reinforcements on the microstructural evolution of composite were investigated. In-situ TiB2 particles could refine the as-cast grains of AZ80 alloy, and promote recrystallization through particle stimulated nucleation (PSN) effect. Due to the grain refinement and the PSN effect of TiB2, the twin induced recrystallization mode in AZ80 alloy is transformed into grain boundary and particle dominated recrystallization process in the TiB2/AZ80 composite, which suppresses the generation of coarse shear bands during rolling and improves the rolling ability. At the same time, the morphology of TiB2 particle clusters was continuously modified with the increase of rolling passes, and finally formed fiber-like distribution characteristics. Fine grain strengthening and thermal mismatch strengthening are the main strengthening mechanisms of the composite sheet. Internal toughening mechanisms are texture weakening, the proliferation of more<c+a>dislocations, higher Schmidt factor and more uniform strain distribution induced by the PSN effect. In addition, external toughening ones should attribute to bending and deflection of cracks resulting from fiber-like particle distribution characteristics. Thus, the strength and toughness of the TiB2/AZ80 composite were simultaneously enhanced.

Microstructural evolution of hybrid aluminum matrix composites reinforced with SiC nanoparticles and graphene/graphite prepared by powder metallurgy

The dispersion of ceramic nanoparticles is of significance to the microstructure and properties of particulate reinforced metal matrix composites. In this study, two hybrid enhancers, SiC-graphite and SiC-graphene nanosheets (GNSs), were incorporated into aluminum matrix composites using powder metallurgy. The dispersion of the reinforcements and microstructural evolution of the composites were characterized by using Scanning Electron Microscopy, X-Ray Diffraction, Transmission Electron Microscopy, and Raman spectroscopy. The results show that thin GNSs accelerated the deformation of the aluminum particles, and defects were introduced into the carbonaceous phases during the ball milling process. Al4C3 needles generated during hot pressing, and were observed to bridge the aluminum grains. Compared with graphite, GNSs were more uniformly dispersed throughout the composite, which in turn restrained grain growth. As a result, a nanostructured composite (57.7 nm) was successfully produced upon the addition of SiC-GNSs.

Prediction of interfacial phase formation and mechanical properties of Ti6Al4V–Ti43Al9V laminate composites

Ti6Al4V–Ti43Al9V laminate composites were successfully fabricated by hot-pack rolling using as-forged Ti43Al9V alloy and as-rolled Ti6Al4V alloy. The microstructure evolution of composites was investigated by electron probe microanalysis (EPMA) equipped with energy dispersive X-ray spectrometry (EDS) and the electron back scattered diffraction (EBSD). In order to better control the properties of laminate composites, two models are established for better control the thickness and phase formation of interfacial region, respectively. The mechanical properties of composites show a negative correlation with rolling temperature. The composite fabricated at 1125 °C exhibits the highest tensile strength 805 MPa and fracture toughness 49.2 MPa•m1/2 which are much higher than Ti43Al9V alloy and other Ti–Al based laminate composites. The fracture features reveal that the increase of tensile strength is attributed to high density of dislocations and sub-structures stored in TiAl alloy and the crack propagation features show that the enhancement of toughness is associated with the aggravation of misorientation of α2 phase and the increase of the amount of γ/B2 boundaries.

Influence of ZnO nanoparticles on the microstructure of a CoCrFeMoNi matrix via powder metallurgy

In the last decade, extensive research has been carried out on the microstructural behavior of high-entropy alloys (HEA), for which the in-situ formation of nanoparticles has been reported. However, studies of the incorporation of nanoparticles in HEA have been rarely reported. In this work, the addition of zinc oxide nanoparticles (ZnO NP) as reinforcement in a CoCrFeMoNi high-entropy alloy matrix, as well as the morphological, structural, and microstructural evolution of composites synthesized via powder metallurgy, were studied. Scanning electron microscopy and X-ray diffraction analysis were performed in order to study the microstructural and phase characterization of the composites. After sintering, it was found that the ZnO NP addition (0.5wt%, 1wt% and 2wt%) had a significant influence on the micro-structure and hardness of the CoCrFeMoNi high-entropy alloy. Stronger bonding among metal particles was promoted with the additions of ZnO NP. A reduction in porosity as a function of ZnO NP content was also observed. The microhardness results showed that the composite reached its highest reinforcement in bulk samples with 1wt% ZnO NP (HV 870), which represented a 20% improvement over the unrein-forced HEA matrix.

Microstructure evolution of Cu-TiC composites with the change of Ti/C ratio

In this work, Cu-TiC composites have been successfully prepared by adding Ti and carbon black powder mixture into Cu melts. The microstructure evolution of the composites with the change of Ti/C ratio and its mechanism has been investigated. It is found that when Ti and carbon black powder mixture is added into Cu melts, Ti will react with carbon black to form TiC, which makes the carbon black be wetted. Then the unreacted Ti will be dissolved and further reacted with the wetted carbon black to form more TiC. However, the formed TiC particles are dispersed difficultly and tend to aggregate into agglomerations. Increasing the Ti/C ratio is an effective method to improve the distribution of TiC. It is found that, comparing with the Cu-4Ti-1C, non-stoichiometric TiCx with smaller x which has the better wettability with Cu melts can be synthesized in the Cu-5Ti-1C and Cu-6.67Ti-1C. As a result, TiC particles are more uniformly distributed in the prepared Cu-Ti-C composites with higher Ti/C ratio.

Formation of gradient microstructure and mechanical properties of hot-pressed W-20 wt% Cu composites after sliding friction severe deformation

W-based alloys are currently considered promising candidates for high heat flux components in future fusion reactors. In this paper, hot pressed W-20 wt%Cu composites were treated at room temperature using a sliding friction severe deformation (SFD) process, with a moving speed of 0.2 m/s and an applied load of 500 N. Microstructural evolution of composites after the SFD treatment was evaluated and compared with that of the untreated composites. Results showed that there was a gradient structure generated and an obvious refinement in tungsten particles size in the surface layer after the SFD process. The average particle size of tungsten in the SFD treated composites was 2.60 μm, whereas it was 4.5 μm for tungsten in the untreated composites. Fracture surfaces of the composites indicated that the SFD treatment destroyed the W skeleton and changed fracture mode from predominant inter-granular one to trans-granular one due to the decrease in contact area of W-W inter-particles. Yield strength and ultimate tensile strength of composites after the SFD treatment were 308 MPa and 553 MPa, respectively. The treated composites exhibited micro-hardness values with an average reading of about 308 HV. Analysis of the facture microstructures clearly suggested that the tungsten particles in the treated composites are consisted of dislocations and boundaries as well as dislocation tangles. The electrical conductivity of the composites was decreased from 33 IACS% to 28.5 IACS% after the SFD treatment, mainly due to loss or squeezing of copper into the inner surface.

Effects of mixing state of composite powders on sintering behavior of cathode for solid oxide fuel cells

Abstract For efficient development of high-performance composite electrodes for solid oxide fuel cells (SOFCs), it is crucial to precisely tailor the microstructural features of the electrodes, such as their grain size, phase connectivity, and pore structure. Herein, we report the effects of the mixing state of component powders of a composite cathode composed of Sr-doped LaMnO3 (LSM) and yttria-stabilized zirconia (YSZ) on its sintering behavior. LSM-YSZ composite powders were synthesized by a particle-dispersed glycine-nitrate process using YSZ particles as inclusions in the LSM precursor solution. The dispersion state of the YSZ particles in the solution was varied from a well-dispersed state to a highly flocculated state through adjustment of the amount of adsorbed polyethylene glycol. The dispersion state of the component powders was found to strongly impact the densification behavior of the composite, which was explained by the formation of a continuous network of the “slow-sintering” inclusion particles. A highly porous structure with phase connectivity and sufficient triple phase boundaries could be achieved by enhancing the mixing homogeneity and optimizing the mixing scale. The proposed concept provides new insights into the microstructural evolution of composites in constrained sintering, and it could potentially enable development of the ideal electrode structure for SOFCs.

Microstructure and mechanical properties of Al-Cu composite produced by accumulative roll bonding and folding (ARBF)

Aluminium-copper multilayered composite was successfully produced by a new technique of severe plastic deformation composed of accumulative roll bonding and folding (ARBF). Microstructure evolution of composites was verified by optical and scanning electron microscopy. Mechanical properties of the multilayered composite were evaluated using microhardness measurement and tensile testing. By increasing the cycles of process, strength, microhardness and elongation of these composites increased, and after a certain number of cycles, copper layers were necked and fractured. Fracture surfaces, after tensile tests, were examined by scanning electron microscopy. Fractography revealed evidence of a combination of failure mechanisms including cleavage, ductile failure and intergranular fracture.

Microstructure and Abrasive Wear Behavior of CuSn10–Graphite Composites Produced by Powder Metallurgy

In this study, CuSn10 metal-matrix composites (MMCs) reinforced with 0, 1, 3, and 5 vol.% graphite particulates were fabricated by powder metallurgy. The microstructure, relative density, hardness, and abrasive wear behavior of the composites were investigated. The abrasive wear tests were conducted on unreinforced matrix and CuSn10–graphite composites using a pin-on-disk-type machine. The effects of sliding distance, applied load, graphite particle content, and abrasive grit sizes on the abrasive wear properties of the composites have been evaluated. The microstructure evolution of composites and the main wear mechanisms were identified using a scanning electron microscope and an energy-dispersive X-ray spectrometer (EDS). The density and hardness of the sintered CuSn10–graphite composites decreased with increasing graphite content. The abrasive wear resistance increased with increasing graphite content, but the abrasive wear resistance decreased with increasing sliding distance, applied load, and abrasive grit size. Moreover, the wear resistance of the composite was found to be considerably higher than that of the CuSn10 matrix alloy and increased with increasing graphite particle content.

The effect of cation type, intergranular phase amount and cation mole ratios on z value and intergranular phase crystallization of SiAlON ceramics

The chemical resistance of SiAlONs is controlled by various factors such as z value, microstructure, type and amount of sintering additives, and intergranular phase nature (amorphous or crystalline). In this study, the relationship between z value and intergranular phase crystallization of αı:βı-SiAlON composites reinforced with TiN (17wt%) was investigated by using various dopant systems (Y:Sm:Ca, Yb:Sm:Ca, and Er:Sm:Ca) and various amounts of intergranular phase. The effect of TiN on densification, phase assemblage and microstructural evolution of composites was systematically investigated. Further, the effects of variations in the sintering aid amount and cation mole ratios on density, hardness and fracture toughness were determined in relation to z values. It was found that high z value (>0.5), crystalline intergranular phase and appropriate mechanical properties can be achieved by selecting the type of sintering additive, its amount and ratio.

Evolución microestructural de composites SiC/aleaciones CuSi obtenidos a través de infiltración reactiva

The microstructural evolution of composites of SiC/Cu-Si alloys obtained through process of reactive infiltration to 1400 °C was studied. Three zones were detected in the obtained composites: the reaction zone, the transition zone and the infiltrated zone. In the reaction zone and transition zone the resulting microstructure was composed of a metallic phase, graphite laminae and SiC particles. It was found that SiC decomposes into these areas because of the alloy Cu-Si, so the available Si forms a liquid solution that a room temperature consisted of a α solid solution and a γ phase (Cu 5 Si). The carbon resulting from the decomposition of SiC precipitated as graphite laminae. In addition, the SiC decomposition was decreasing as the initial amount of Si in the alloy increased.

Fabrication and microstructure evolution of niobium-niobium silicide composites by spark plasma sintering

By using Nb and Si elemental powders as raw materials, dense Nb/Nb5Si3 composites were successfully fabricated by a spark plasma sintering (SPS) technology. The microstructure of the fabricated composites was analyzed by OM, SEM, XRD and EPMA; the microstructure evolution of the composites was also investigated by a quenching test. The experimental results show that the prepared composites consist of Nb and Nb5Si3 phases; Nb particle uniformly distributes in the in-situ synthesized Nb5Si3 matrix. During the SPS process, an interfacial reaction occurs between Nb and Si particles to synthesize Nb5Si3 until reactant silicon has been completely depleted.