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The thermodynamic parameters for a series of Fe(100−x)/2Co(100−x)/2Cux (x from 10 to 90, at. pct) alloys including their characteristic temperatures, the enthalpy and entropy changes of three phase transformations were determined systematically using differential scanning calorimetry (DSC). The corresponding vertical section of ternary Fe-Co-Cu phase diagram was predicted, and the relationships of the enthalpy and entropy changes vs Cu content were described by polynomial expressions. Metastable phase separation took place in those liquid Fe-Co-Cu alloys with the Cu content 30 ≤ x ≤ 70. The liquid phase separation temperatures were determined to outline the metastable miscibility gap, and the critical undercoolings to initiate phase separation were measured as a range of 57 K to 98 K. After such a phase separation, the liquid phase (to γ(Fe, Co)) exhibited the strongest undercooling ability in the Fe-Co-Cu alloys with x ≤ 70, whereas the solid-state undercooling for the eutectoid transformation is comparatively higher in the alloys with x > 70. The nanomechanical properties of α(Fe, Co) and (Cu) phases were measured by nanoindentation technique. In the Fe20Co20Cu60 alloy, both phases had the lowest nanohardness and reduced elastic modulus, and displayed severe creep behaviors, resulting mainly from its conspicuous liquid phase separation.

In this study, amorphous Ni-P films were deposited by electroless plating under different pH values. Their mechanical properties and deformation behavior were then investigated by instrumented nano-indentation. With increasing pH value of the plating solution from 3.75 to 6.0, the hardness and elastic modulus of the obtained Ni-P films increased from 6.1 GPa and 146 GPa to 8.2 GPa and 168 GPa respectively. From the load-indentation depth curve, the Ni-P films were found to yield at an indentation depth of 8 nm. By microstructural examination around the indented regions, early-stage plastic deformation of the amorphous Ni-P films was verified through the formation and extension of shear bands with a spacing of several tens of nanometers. Within the shear bands, flow dilatation-induced intense shear localization was expected and resulted in crystallization in the amorphous matrix. The critical shear stress and energy release rate required for the initiation of early-stage plastic yielding of the Ni-P films were calculated to be about 1.4 GPa and 3.0 J/m2 respectively, both of which increased with pH values.

The interfacial shear strength of continuous silicon carbide fiber reinforced 7075 aluminum matrix composite (SiCf/7075Al) has been investigated in this research by pushout microindentation. The SiCf/7075Al composite specimens were processed by diffusion bonding alternate layers of SiC fibers and 7075Al alloy plates. From the measured stress-displacement curves of indentation tests, the interfacial shear strengths of the composite specimens were obtained, and the stress-displacement curves were basically divided into two regions: (1) elastic deformation and (2) interface decohesion and fiber sliding. With increasing aging time, the interfacial shear strength of the composite increased to 167 MPa for T6-treated specimens, and the variation of the interfacial shear strength well followed that of the ultimate tensile strength of 7075Al matrix alloy. With decreasing specimen thickness, the interfacial shear strength of the composite and the amplitude of stress fluctuation slightly decreased because of the stress relaxation effect near specimen surfaces. Under higher indentation velocities, both the interfacial shear strength and the amplitude of stress fluctuation became smaller.

The AlxCoCrCuFeNi alloys with multiprincipal elements (x=the aluminum content in molar ratio, from 0 to 3.0) were synthesized using a well-developed arc-melting and casting method, and their mechanical properties were investigated. These alloys exhibited promising mechanical properties, including excellent elevated-temperature strength and good wear resistance. With the addition of aluminum from x=0 to 3.0, the hardness of the alloys increased from HV 133 to 655, mainly attributed to the increased portion of strong bcc phase to ductile fcc phase, both of which were strengthened by the solid solution of aluminum atoms and the precipitation of nanophases. The alloys exhibited superior high-temperature strengths up to 800 °C, among which the Al0.5CoCrCuFeNi alloy, especially, had enhanced plasticity and a large strain-hardening capacity. Moreover, the wear resistance of these alloys was similar to that of ferrous alloys at the same hardness level, while the alloys with lower hardness exhibited relatively higher resistance because of their large strain-hardening capacity.

A new approach for the design of alloy systems with multiprincipal elements is presented in this research. The Al x CoCrCuFeNi alloys with different aluminum contents (i.e., x values in molar ratio, x=0 to 3.0) were synthesized using a well-developed arc-melting and casting method. These alloys possessed simple fcc/bcc structures, and their phase diagram was predicted by microstructure characterization and differential thermal analyses. With little aluminum addition, the alloys were composed of a simple fcc solid-solution structure. As the aluminum content reached x=0.8, a bcc structure appeared and constructed with mixed fcc and bcc eutectic phases. Spinodal decomposition occurred further on when the aluminum contents were higher than x=1.0, leading to the formation of modulated plate structures. A single ordered bcc structure was obtained for aluminum contents larger than x=2.8. The effects of high mixing entropy and sluggish cooperative diffusion enhance the formation of simple solid-solution phases and submicronic structures with nanoprecipitates in the alloys with multiprincipal elements rather than intermetallic compounds.

Silver matrix composites containing 10 to 40 vol pct ceramic reinforcements of different types, shapes, and sizes were processed by electroless silver plating and hot pressing. The thermal expansion behavior of the silver matrix composites has been studied from room temperature to 300 °C. The coefficients of thermal expansion (CTEs) of the composites are effectively lowered to below 10 × 10−6/°C by the addition of 40 vol pct reinforcements. The CTEs of composites decrease as the content of reinforcements increases due to the constraint effect provided by the ceramic reinforcements with low CTEs; this effect is more pronounced with the addition of whiskers and fibrous reinforcements. At the beginning of measurements, large residual thermal stresses existing in the water-quenched composites restrict the expansion of the silver matrix, resulting in lower CTEs than those of furnance-cooled composites. As the temperature increases, the residual thermal stresses are gradually released, and the CTEs of composites reach higher and stable values. At temperatures above 250 °C, the CTEs of composites increase at a higher rate due to the matrix yielding and interfacial debonding.

A simple process was developed to fabricate ceramic-reinforced copper and silver matrix composites by electroless plating and hot pressing at 873 K and 300 MPa, in air. Composites were produced containing 10 to 40 vol pct ceramic reinforcements of different sizes and shapes including silicon carbide whiskers (SiC w ), alumina particles (Al2O3p ), carbon short fibers (Carbon sf ), and Saffil short fibers (Saffil sf ) (3.8 pct SiO2-96.2 pct Al2O3) uniformly distributed within the matrix. The hardness and bending strength of the composites were much higher than those of the pure matrices. The electrical conductivity, measured by a four-point probe method, was similar to that of traditional CdO/Ag electrical contact materials. The surface morphologies and cross-sectional microstructures of the arc-eroded Al2O3p /Ag composites were similar to those of conventional CdO/Ag and SnO2/Ag and exhibited a good arc-erosion resistance. These composites combine the high strength and elevated-temperature stability of the ceramic reinforcements with the good electrical and thermal conductivity of the two metallic matrices.