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Three contents of zinc oxide (2 wt %, 4 wt % and 6 wt %) were added into raw BaTiO 3 powders. The maximum relative permittivity value (ε r ) is in the range 230–406 and the dielectric loss (tanδ) varies between 0.18 and 0.09 for all ZnO modified BaTiO 3 coatings for frequency1 kHz at ambient temperature. The reasons for enhancing the relative permittivity are attributed to the elimination of micro-cracks and pores. The detail discussion was conducted on the characteristics morphologies (cross section, fracture surface and spreading behavior of BaTiO 3 +xwt. % ZnO composite powders) and phase. With the analysis, the addition of ZnO leads to the improvement in the melting state and increment in amorphous phase. Zn existed in the form of secondary phase (ZnO) and substitution in the BaTiO 3 lattice. The enhancement in structure and dielectric performance is highly discussed based on the phase equilibria and chemical defect. [ABSTRACT FROM AUTHOR]

Nanocrystallization is a promising way to increase the toughness of brittle materials. In this work, to obtain toughened Fe 2 B coating and overcome various limitations of boriding, electro-spark deposition (ESD) has been used to prepare nanocrystalline Fe 2 B coating. A coarse-grained Fe 2 B electrode was used as anode. The microstructure, microhardness, nanomechanical properties and fracture toughness of the coating and the electrode material were comparatively investigated. Results showed that a metallurgically fused nanocrystalline Fe 2 B coating with few defects is obtained by ESD. Compared to the anode, the coating contains more Fe 3 B phase and a new phase of martensite. Moreover, the coating consists of planar crystals, cellular crystals, cellular dendrites, columnar dendrites and equiaxed dendrites due to the solidification conditions, and the grain size of the cellular crystals and the dendrites ranges from few tens of nanometers to several hundred nanometers. The transition zone between the coating and the substrate is the molten zone of the substrate, and the microstructure of this zone is greatly refined. The nanocrystalline Fe 2 B coating has improved fracture toughness while it has reduced hardness and Young's modulus, and some structures of the coating are remarkably toughened. [ABSTRACT FROM AUTHOR]

1–9 wt% of ZrB 2 particles are added to Cu to produce ZrB 2 /Cu composites by a hot-pressed sintering process. Microstructures, mechanical and electrical properties of the prepared ZrB 2 /Cu composites are systematically investigated. The results indicated that the relative density and electrical conductivity of the composites decrease with increasing ZrB 2 content. However, the microhardness reaches a maximum value of 100.8 HV 0.2 as ZrB 2 content increases to 7 wt % and then decreases when ZrB 2 content further increases. TEM study reveals that the hexagonal ZrB 2 crystals in size of several micrometers are well embedded in Cu matrix. The interfacial zone consists of both sharp interfaces and amorphous transition layer. Grain refinement strengthening, Orowan strengthening and coefficients of thermal expansion mismatch strengthening contribute to the increment of microhardness and reduce the electrical conductivity. [ABSTRACT FROM AUTHOR]

• FeCrAlNbNi alloy zones were prepared on the surface of 304 stainless steel by laser surface alloying. • Nb segregated in the AZ and was mainly distributed in the interdendritic area. • In the process of oxidation at 900 °C for 100 h, the AZ had a slower oxidation rate than the substrate. • After oxidation at 900 °C for 100 h, the Al on the AZ surface did not appear depleted. To improve the high-temperature oxidation performance of 304 stainless steel and increase its service life, a FeCrAlNbNi alloyed zone (AZ) was prepared on the surface of 304 stainless steel through laser surface alloying, and the microstructure of the AZ was studied. The micromorphology of the AZ was mainly equiaxed dendrites, and the Nb element segregated in the interdendritic region. In addition, the AZ and substrate were subjected to isothermal oxidation experiments for 100 h at 900 °C. The AZ showed less weight gain and a lower oxidation rate, and it had better oxidation resistance than the substrate. In the early stage of oxidation, a less dense Al 2 O 3 oxide layer was formed on the surface of the AZ. As oxidation progressed, Al passed through the oxide layer to form aggregated Al 2 O 3 on the surface. In the middle of oxidation, the Al 2 O 3 oxide layer gradually became dense, and aggregated Al 2 O 3 began to scatter. In the late stage of oxidation, a stable, dense and continuous Al 2 O 3 layer was formed on the surface of the AZ with a thickness of approximately 1.2 µm. At the same time, energy dispersive spectroscopy showed that the Al under the oxide layer was not depleted, which indicates that the FeCrAINbNi AZ has excellent high-temperature protection performance. [ABSTRACT FROM AUTHOR]

This work attempted to strengthen the interfacial strength and mechanical properties of alumina whisker and graphene co-reinforced copper matrix composites by Cr matrix micro-alloying. Cr elements are observed to: (i) aggregate to form large particles rather than disperse uniformly in Cu matrix; (ii) disperse at interfaces between Cu matrix and reinforcements. The relative density, tensile strength, shear strength and compressive strength of the Cu-Cr composites were in direct proportional to Cr micro-alloying amount from 0 to 1.5 wt%. Increased Cr micro-alloying amount, on the one hand, can strengthen interfacial bonding between Cu matrix and reinforcements and thereby enhance the load transfer efficiency at interfaces; on the other hand, can yield obvious grain refinement, and thereby achieving grain boundary strengthening as well as twin boundary strengthening, which were considered as the dominant strengthening mechanisms of Cu-Cr composites. Besides, dislocation strengthening and solid-solution strengthening were also additional strengthening mechanisms of Cu-Cr composites. [Display omitted] • Cr micro-alloying can significantly improve the mechanical properties of Cu matrix composites. • Cr micro-alloying can strengthen interfacial bonding between Cu matrix and reinforcements. • Cr micro-alloying can yield grain refinement. • The strengthening mechanisms mediated by Cr micro-alloying were analyzed in detail. [ABSTRACT FROM AUTHOR]

The microstructures, mechanical properties and tribological behaviors in a wide temperature range of high velocity oxygen fuel sprayed CoMoCrSi coatings before and after 800 °C-annealed treatment were comparatively investigated. Particularly, the annealed CoMoCrSi coatings registered well crystallization, improved microstructures and enhanced properties compared to the as-sprayed coatings. Specially, the surface microhardness increased by 13.3%, and the adhesive strength increased by 12.5% after the annealed treatment. Moreover, a compact oxides layer comprising Cr 2 O 3 , Co 3 O 4 , MoO 3 and CoMoO 4 formed on the annealed coating surface, which could be account for the increased microhardness and excellent tribological behaviors of the annealed coatings. The annealed coatings registered lower friction coefficients and wear rates than the as-sprayed coatings in a wide temperature range. Consequently, the 800 °C-annealed treatment could significantly improve the microstructures and properties of the HVOF-sprayed CoMoCrSi coatings. Moreover, the annealed CoMoCrSi coatings could be a well candidate for the abrasion-resistant material in a wide temperature range. • The coating exhibited well crystallization and refined microstructure after the 800 °C-annealed treatment. • Tribological behaviors of annealed coatings were observably enhanced in a wide temperature range. • An oxides layer played synergistic effect of anti-wear and lubrication and could be responsible for the improved tribological performance of the annealed coatings. • CoMoO 4 was insitu formed by the oxidation of the Co 7 Mo 6 intermetallic (Co 7 Mo 6 + O 2 → CoMoO 4). [ABSTRACT FROM AUTHOR]