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The precipitation sequence of 6061Al has changed after introducing high amount SiC nanowires due to the serious segregation of Mg element. In the present work, 0.8 wt% Mg element was added into 6061Al matrix to compensate the segregation effect, and the 15 vol% SiCnw/6061Al+0.8Mg composite was prepared by pressure infiltration method. Regardless of aging time, the hardness of SiCnw/6061Al composite could be improved by the addition of Mg. MgAl 2 O 4 phase at SiC nanowire-Al matrix interface was found in SiCnw/6061Al+0.8Mg composite after solid solution treatment. The ultimate precipitate of Al matrix in SiCnw/6061Al+0.8Mg composite has been restored from B′ (MgSi >1 ) to β (Mg 2 Si). Moreover, the hardness of composites was improved 10% after addition of Mg in the over-aging status, implying that the strengthening effect of B′ phase might be inferior to that of β' and β phases. Due to early failure behavior, the tensile strength of the peak-aged composites was slightly decreased by the addition of Mg element. However, the yield strength of the composites was improved, which could be well explained by the modified shear-lag model. It is suggested that addition of extra alloying elements to compensate the segregation effect might be an effect method to improve the yield strength. However, for the application favor high tensile strength, design of performance matching in elastic-plastic behavior between matrix and reinforcement and the ability of Al matrix to relax the stress concentration might be the advisable choice. [ABSTRACT FROM AUTHOR]

In the present work, the effect of the W coatings prepared by the magnetron sputtering method on the stability of the thermal and mechanical properties of the Diamond/Al composites has been investigated. Due to the decomposition of the interfacial Al 4 C 3 phase, the thermal conductivity and bending strength of the Diamond/Al composites without W coating were decreased 23% and 33%, respectively. However, the variation of the normalized thermal conductivity (NTC) of the Diamond/Al composites has been changed from polynomial to linear relationships after the W-coating treatment, indicating the enhancement of the thermal conductivity and the bending strength stability. Diamond/Al composite with 45 nm W coating demonstrated the best thermal and mechanical stability with slight decrement of 3% after 720 h heat-moisture treatment (HMT). Due to the decomposition of the Al 4 C 3 phase and the corresponding weakened interfacial bonding, more “clean {111} planes” of the diamond particles were observed in the fracture surface of Diamond/Al composites without W coating after HMT. However, no significant difference was found in the fracture surface of the Diamond/Al composites with 45 nm and thicker W coatings before and after HMT. It is suggested that the continuous, stable and well bonded interfacial structure without the formation of the Al 4 C 3 phase is the key for the improvement of the stability of the Diamond/Al composites. [ABSTRACT FROM AUTHOR]

In the present work, the effect of W coatings prepared by the magnetron sputtering method on the mechanical performance of the Al matrix composites reinforced with diamond particles (Diamond/Al) has been explored. Since no debonding was observed between the diamond and the Al matrix in the composites with 45 nm and thicker W coatings while serious debonding was found in the composite without W coating, the interfacial bonding between the diamond particles (all the {100} and {111} facets) and the Al matrix has been improved. Further TEM observation indicated that the W coating has been well bonded with the diamond particle and the Al matrix, and no interfacial reaction product has been found. Furthermore, the fracture behaviors of the Diamond/Al composites were also affected by the W coatings. Compared to that of the Diamond/Al composite without W coating, the bending strength and the displacement of the bending failure of the Diamond/Al composites with 45 nm W coating have been improved 24% (from 245 to 304 MPa) and 120% (from 0.28 to 0.62 mm), respectively. Moreover, the summative results from the literatures and the present work indicate that the Diamond/Al composites have higher strength usually demonstrates higher thermal conductivity, which might be related to the interfacial performance of the composites. [ABSTRACT FROM AUTHOR]

In the present work, microstructure and mechanical behavior of the graphene nanoplates (GNPs) reinforced pure Al (GNPs/Al) composites prepared by the pressure infiltration method was investigated. No Al 4 C 3 phase was detected in the composites, while GNPs have been well bonded with the Al matrix. It is suggested that the reaction between pure Al matrix and graphene could also be inhibited by using graphene with fewer defects. It has been found that the mechanical properties of the composites could be significantly improved by the addition of graphene. After addition of 0.54 wt% GNPs, the improvement of the yield and tensile strength before the extrusion was 116% and 45%, respectively. However, after the extrusion treatment, the corresponding increment of the yield and tensile strength was increased to 228% and 93%, respectively. Moreover, the fracture surface of the GNPs/Al composites before and after the extrusion treatment was mainly characterized by the lamellar structure with bridging of GNPs and the fine equiaxed structure with the pulling-out of the GNPs, respectively. Based on the modified shear-lag model, the strengthening mechanism of the GNPs/Al composites has been discussed, and the effect of GNPs and the extrusion treatment on the yield strength of the composites have been analyzed. [ABSTRACT FROM AUTHOR]

In the present work, tungsten (W) coatings with thickness range of 35–130 nm on the diamond particles were prepared by magnetron sputtering method, and then the Diamond/Al composites were prepared by the vacuum infiltration method. The prepared W coatings were smooth and dense on all the facets of the diamond particles. Moreover, the presence of W-coatings inhibited the interfacial debonding phenomenon and improved the interfacial bonding between diamond particles and Al matrix. The Diamond/Al composite with the 45 nm W-coating achieved the maximum thermal conductivity (622 W/(m·K)). To the best of our knowledge, it is the highest thermal conductivity obtained in the Al matrix composites reinforced with 100 μm diamond particles with coatings. Based on the Hasselman and Johnson (H-J) model, the thermal conductivity behavior of the Diamond/Al composites has been discussed. It indicates that the magnetron sputtering is a feasible and successful method to prepare thin and reliable tungsten coatings for the Diamond/Al composites. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the characteristics of a friction and wear transition from the running-in stage to the steady-state stage for an Al-based composite containing TiB 2 particles and fabricated by a pressure infiltration technique. The dry sliding friction and wear behavior was investigated using a 3.98 mm diameter AISI 52100 steel ball-on-disk geometry under applied loads of 1 N and 3 N. Microstructural characterization and element distribution were carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). 3D surface topographies and roughness of the wear surfaces were measured using confocal laser scanning microscopy (CLSM). The results indicated that the formation of a transfer film and boric acid (H 3 BO 3 ) was the main reason for the low friction coefficient of about 0.16 at a load of 1 N. An increase of friction coefficient was caused by the abrasion of pulled-out TiB 2 particles. In the running-in stage at an applied load of 3 N, abrasive wear dominated and resulted in the formation of grooves and pulled-out TiB 2 particles. In addition, at a steady-stage friction coefficient of 0.6, severe three-body abrasive wear and oxidative wear were the dominant wear mechanisms. An excellent correlation was found between friction coefficient and surface roughness, as measured by 3D topography. [ABSTRACT FROM AUTHOR]