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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.

We employ a sequential electrophoresis and electrodeposition approach to fabricate a large-area ordered macroporous Ni foam in 5 × 5 cm 2 via a template route. Images from scanning electron microscope exhibit hierarchical structures with hexagonally-arranged pores and interconnected pore channels. For as-prepared and annealed ordered macroporous Ni foams, the loading-depth profiles from nano indentation show typical elastic and plastic deformation. Upon annealing, moderate growth in grain size is observed, resulting in lower hardness and Young’s modulus. In contrast, for disordered macroporous Ni foam and solid Ni film, nano indentation results reveal larger hardness and undetermined Young’s modulus. The ordered macroporous foam reveals hardness that is 22% of that of solid Ni film, a value close to its theoretic packing density of 24%.

Cu with nanotwin (NT) possesses great electrical, mechanical, and thermal properties and has potential for electronic applications. Various studies have reported the effect of NT orientation on Cu mechanical properties. However, its effect on Cu stress-relaxation behavior has not been clarified, particularly in nano-scale. In this study, Cu nanopillars with various orientations were examined by a picoindenter under constant strain and observed by in situ TEM. The angles between the twin plane and the loading direction in the examined nanopillars were 0°, 60°, to 90°, and a benchmark pillar of single-crystal Cu without NT was examined. The stress drops were respectively 10%, 80%, 4%, and 50%. Owing to the interaction by NT, the dislocation behavior in nanopillars was different from that in bulk or in thin film samples. Especially, the rapid slip path of dislocations to go to the free surface of the nanopillar induced a dislocation-free zone in the 0° nanopillar, which led to work-softening. On the contrary, a high dislocation density was observed in the 90° nanopillar, which was generated by dislocation interaction and obstruction of dislocation slip by twin planes, and it led to work-hardening. The findings reveal the NT orientation in Cu nanopillars affected stress relaxation significantly.

Microanode-guided electroplating (MAGE) was performed to prepare cobalt-iron-nickel alloying micropillars. The electrolyte was prepared by fixing [Fe2+] at 0.040 M and varying [Co2+] in 0.040–0.100 M and [Ni2+] in 0.30–0.60 M. The effect of bath composition on the compositional, mechanical, and magnetic properties of the alloying micropillars was investigated. Resulting from FE-SEM and EDS, all the micropillars demonstrated a smooth morphology but in different compositions depending on the bath composition. Through XRD analysis, the micropillars were characterized in nanocrystals of Co-Ni and Co7Fe3. After nano-indentation testing, the reduced Young’s modulus of the pillars was estimated at 103.1–185 GPa and the hardness at 5.70–6.38 GPa. Investigation of all the specimens with VSM, Co61Fe27Ni12 and Co63Fe25Ni12 displayed the notable saturation magnetization (Ms = 180 and 175 emu/g) and the lowest coercive magnetic field (Hc = 2.1 and 1.4 Oe) among them. The mechanism of anomalous Co-Fe-Ni electrodeposition is proposed.

We show quasicrystal formation by annealing multilayers of Al, Cu and Fe. The mechanical and surface properties of quasicrystals are affected by the parameters of annealing process. Here, multilayer Al-Cu-Fe thin film samples with different compositions were sputtered on Si/SiO2 substrates and subjected to a two-step annealing process for different durations (5, 10 and 15 h). X-ray diffraction analyses indicated that the 15-h annealed sample had a sharper quasicrystal peak, which was more stable than any other phases. From the XRD data, the amount of each phase was calculated; the sample with longer annealing duration revealed a high amount of ψ-phase (84.3% crystallinity of quasicrystal) with a small amount of cubic Al50 (CuFe) 50 phase. Nanoindentation tests and contact angle measurements showed that this sample also had the greatest hardness (∼11 GPa) and the highest contact angle (127°), respectively.

The superior mechanical properties of high-entropy alloys (HEAs) have made an outstanding success in materials science and engineering. Studies to date have been devoted to what the severe lattice distortion induces. However, most researchers focus on its stimulation to plastic deformation instead of scrutinizing the variations on elasticity. Compared with conventional alloys, HEAs may perform disproportionate elasticity with uneven local lattice strain resulting from the severe lattice distortion. Therefore, it is necessary to survey its influence on the mechanical properties of HEAs systematically. In this study, the Lennard-Jones (LJ) potential, the embedded atom method (EAM) potential, and the modified embedded atom method (MEAM), are respectively conducted to investigate the lattice distortion effect on Young’s modulus E (hkl) and Poisson’s ratio ν (hkl, θ) along [100], [110], and [111] loading directions for several fcc metals composed of 1 ∼ 5 atomic types, including Ni, Ni98W2, Ni96W4, FeCrNi, and CoNiCrFeMn HEAs. Also, a method is used to analyze the performance of the individual element on the elastic properties in the HEA environment. As a result, it can be unveiled that the effect of electron density inconsistency is more dominant than the effect of lattice distortion associated with the atomic size difference. The electronic configuration in the HEA environment plays a major role in elastic anisotropy while the difference of the atomic radii does the minor one. The anisotropy of CoNiCrFeMn HEA analyzed by this work is also consistent with in-situ neutron diffraction measurements.

Texture evolution during tension test was investigated on three face-centered cubic (FCC) metals, namely, Ni (unary), equiatomic CrFeNi (ternary), and equiatomic CoCrFeMnNi (quinary) with small and large grain sizes of ~20 and ~100 μm, respectively. The microtextures for 18%, 36% and 54% engineering strains of a tension-interrupted specimen were characterized on the same area. The three metals exhibited a similar texture evolution, which the fraction of {001}//ND remains constant. However, the fraction of {011}//ND decreases, whereas that of {111}//ND increases. On the other hand, the fraction of //RD also remains constant, that of //RD decreases, and that of //RD increases. However, the several differences still were found during plastic deformation. Fine-grained Ni initiated a significantly crystallographic rotation (CRo) at the lower strain, increased with strain and then remained nearly unchanged as strain was higher than 18%. Coarse-grained Ni delayed this rotation and slowly developed the trend at large strains. As for CrFeNi, the comparison between fine-grained and coarse-grained structure does not have obvious difference. As for fine-grained CoCrFeMnNi, it can be seen that an obvious CRo develops under 36% strain, and maintains constant over 36% strain. But the coarse-grained CoCrFeMnNi reveals that the significant CRo develops continuously from 0% to 54% strain. The mechanisms for the effects of number of element and grain size in the present study are elucidated.

To minimize the room-temperature brittleness of AZ magnesium alloys (Mg–Al–Zn) and to inhibit grain growth at elevated temperatures for superplasticity optimization, AZ91−xSn alloys (x=0, 1, 2 and 3 wt%) were developed, processed by high-ratio hot extrusion for microstructure refinement. The mechanistic correlations of their superplasticity, from the perspectives of grain growth and boundary sliding, with the Sn content and the testing parameters were examined. With a higher Sn content, the activation energy of grain growth and diffusion-mediated boundary sliding, QG and QS, increased from 29.7 to 35.2 kJ/mol and from 114.1 to 126.5 kJ/mol, respectively. With an adequate Sn addition (2 wt%) and at a relevant strain rate and temperature, a compromise between competitive grain growth and boundary sliding was reached, and the superplasticity was optimized (elongation >1000%), following a proposed superplasticity parameter ( p Q G − Q S ) / 2.3 n G p R T + ( n G p − 1 ) log e .

Various (AlCrMoTaTi)-Six-N coatings were prepared on Si substrates through a reactive magnetron sputtering system to methodically investigate the effects of Si contents and free Si on oxidation behavior. The as-deposited Si-containing coating presented a relatively dense and compact structure compared with the Si-free coating. An oxide layer was formed on the coating surface and continued to thicken when the coatings were exposed to ambient air at elevated temperatures. At 1073 K, a two-layer structure, which consists of an amorphous Al2O3 layer with traces of other target elements followed by a rutile TiO2 + oxide of the target element mixed zone, was developed in the oxide layer. Oxidation resistance was gradually enhanced with the continued increase in Si concentration in the coatings. At 1173 K, the coatings with Si content of as low as 7.51 at.% exhibited a single order of magnitude lower oxidation rate than that of the Si-free coating. Nanohardness measurement of the coatings further confirmed the oxidation behavior. The significantly enhanced oxidation resistance may be attributed to the presence of Al and Si in the coatings.

This study demonstrates that simply by rolling at ambient temperature, FCC type high entropy alloy Al0.5CoCrCuFeNi can be refined to have nanocrystalline structure and exhibits outstanding combination of strength and ductility. The yield strength and ultimate tensile strength are 1284 and 1344 MPa, respectively, in combination with an elongation of 7.6%. After a short annealing at 900°C for 10 min, the elongation is doubled to 15.3% with a trade-off around 20% in strength. This excellent combination of strength and ductility is attributable to the activation of quasi-dynamic recrystallisation during cold work and the limited grain growth during 900°C annealing.

An Al 0.3 CrFe 1.5 MnNi 0.5 multi-component alloy with a very effective surface hardening ability attributed to intrinsic ρ phase precipitation and applicable to complex tool components was developed. Under a conventional aging treatment in a normal atmosphere at 550 °C for 2 h, the alloy with the surface precipitation hardening layer of 74 μm thick exhibited markedly enhanced surface hardness from HV 338 to HV 840 and efficiently improved wear resistance to 1.4 times the values of SUJ2 and SKD61 steels, while high fracture toughness close to that of ductile SKD61 steel was effectively retained. Precipitation thermodynamics and growth kinetics of the surface hardening layer were also investigated. The growth of the surface hardening layer was much faster than that of the precipitation in the bulk matrix; it did not follow typical long-distance diffusion kinetics but behaves more similar to a self-induced or reaction-accelerated short-range decomposition with a thickness increase proportional to the cube of aging time. On the surface, a lower heterogeneous nucleation energy and a reduced strain energy (total 55 kJ/mol) than the regular nucleation energy in the bulk matrix (78 kJ/mol) dominated the rapid formation and growth of the intrinsic surface precipitation with significant strain relaxations.

In this study, attempts were made to prepare and characterize TaN–(Cu,Ag) nanocomposite films by using a hybrid approach combining reactive co-sputtering and rapid thermal annealing at various temperatures to induce the formation of soft metal particles in the matrix or on the surface. The films’ properties and their antiwear and antibacteria behaviors were compared with those previously studied TaN–Cu and TaN–Ag films. All three types of TaN–(soft metal) films showed good tribological properties due to the lubricious Ag and/or Cu layers. It was also found that the antibacteria efficiency of TaN–(Ag,Cu) film against either Escherichia coli or Staphylococcus aureus could be much improved, comparing with that of TaN–Ag or TaN–Cu film. The synergistic effect due to the coexistence of Ag and Cu is obvious. The annealing temperature used to develop TaN–(Cu,Ag) films with good antibacterial and antiwear behaviors could be as low as 250 °C. The lowering of the annealing temperature made these films applicable onto low-melting-point materials, such as polymers.

Direct current electropulsing was used to improve the plasticity of (Zr53Cu30Ni9Al8)99.5Si0.5 bulk metallic glasses. After the electropulsing treatment, the specimen showed reductions in both the glass transition and the crystallization temperatures while retaining its amorphous structure, and both Young's modulus and the hardness decreased while the nanoindentation loading curve became more serrated. Using the bond-interface method and Vickers indentation, the treated specimen showed more branching of semi-circular shear bands and less radial shear bands compared to its as-cast counterpart. The possible plasticity enhancement mechanism of the electropulsing treatment was also discussed.

This work develops a multilayer structure of alternating (AlCrRuTaTiZr)N 0.5 senary nitride and AlCrRuTaTiZr senary alloy with a total thickness of only 4 nm as a diffusion barrier layer for application to Cu interconnects. Under annealing at a high temperature of 800 °C, the interdiffusion of Cu and Si through the multilayer structure was effectively retarded without the formation of any Cu silicides. Interdiffusion occurred only at 900 °C, and compounds that included Cu 3 Si were thus formed. This finding suggests that the high endurance temperature of the diffusion barrier is probably attributable to the stable amorphous solid-solution structure, the high packing factor, the severe lattice distortions that are caused by the incorporation of multiple components and the elongated diffusion path through the multilayer stacking structure.

The (TiVCr)N coatings were deposited on Si substrate via rf magnetron sputtering of a TiVCr alloy target under dc bias in a N 2 /Ar atmosphere. The deposition rate of the coatings gradually decreased with increasing N 2 -to-total (N 2 + Ar) flow ratio, R N . The TiVCr alloy and its nitride coatings exhibited a body-centered cubic (BCC) and a face-centered cubic (FCC) crystal structure, respectively. The preferred orientation of the (TiVCr)N coatings changed from (1 1 1) to (2 0 0) with increasing R N . In addition, the microstructure of the nitride coatings was also converted from a columnar structure with void boundaries and rough-faceted surface to a very dense structure with a smooth-domed surface. The grain size of the (TiVCr)N coatings decreased as the R N was increased. Accordingly, the hardness of the (TiVCr)N coatings was enhanced from 4.06 to 18.74 GPa as the R N was increased.

In this study, amorphous AlCrTaTiZr quinary alloy and 20 at.% Ru-incorporated AlCrTaTiZrRu senary alloy films were developed as diffusion barrier layers to inhibit Cu diffusion in interconnect structures. Under annealing at 700 °C, the interdiffusion of Cu and Si through the AlCrTaTiZr quinary alloy layer of 50 nm thick occurred, and compounds including Cu3Si consequently formed. In comparison, at 800 °C, the interdiffusion was still effectively retarded by the Ru-incorporated AlCrTaTiZrRu senary alloy layer of only 5 nm thick without obvious formation of silicides. It suggests the high diffusion resistance of the Ru-incorporated barrier layer possibly attributed to the large lattice distortions caused by the addition of extra-large-sized Ru atoms.

In this study, 96.5 Sn–3.0 Ag–0.5 Cu solder balls were joined to Au/Ni–P/Cu pads by a thermal reflow process. The interface reactions, solderablity and mechanical reliability of the solder joints were investigated. At the interfaces between the solder balls and pads, intermetallic compounds are formed. With increasing reflow temperature from 220 to 260 °C, the thickness of the intermetallic compound layer increased from 1.1 to 2.5 μm, and the wetting force of molten solder to the pads consequently increased from 0.4 to 0.5 mN. The shear strength of the solder joints decreased from 9.8 to 7.5 MPa because a thick intermetallic compound layer resulted in brittle fracture. The mechanical properties of constituent phases at the solder joints, including primary Sn, Sn–Ag3Sn eutectic phase, intermetallic compound layer and Ni–P underlayer, were measured by nanoindentation. The elastic modulus and hardness of the intermetallic compound layer were obtained as high as about 181 and 6.5 GPa, respectively. Cracks were formed around the indented regions and verified the brittleness of the intermetallic compound layer.

In this study, the mechanical properties of human dental structures have been investigated by using instrumented nanoindentation. Immersion in solutions containingStreptococcus mutans, which is the principal cause of dental caries, was applied to tooth specimens to clarify its effect on the microstructure and mechanical properties of the dental structures. With an extended time of up to 16 h, the pH value of theS. mutanssolutions dropped from 7.3 to 5.8. Therefore, after immersion in theS. mutanssolutions for 16 h, slight erosions of the dental structures began; after 64 h, severe tooth decay occurred with obviously etched dental features. After 128 h, the elastic modulus of enamel and dentine dropped to 85 and 67%, respectively, of the original values of untreated specimens, and the hardness dropped to 88 and 55%, respectively.

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 nanomechanical response and creep behavior of electroless plated copper (Cu) films have been investigated in this research by using a nanoindentation test. The hardness and elastic modulus of the nanostructural Cu films with a large amount of small grains in size of only 5 nm were measured as 1.5 and 120 GPa, respectively. The Cu films deformed elastically at first and then yielded at a stress of 3.3 GPa. Grain-boundary sliding and grain rotation were expected to dominate the deformation of the Cu films. The Cu films showed a creep strain rate of about 5 × 10 −5 s −1 under the nanoindentation test, and the creep strain rate–stress relation exhibited a typical power law expression with a stress exponent of 6.4. The high creep strain rate but low stress exponent of the Cu films implied a fixed creep behavior consisting of grain-boundary sliding and grain rotation by the fast diffusion of Cu atoms through the large amount of grain-boundary.

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.

The resistance of fibrous reinforced silver matrix composites to repeated make-break arc erosion has been investigated in this study. Three different types of short fibers were used as reinforcements, including graphite short fibers, Saffil short fibers, and silicon carbide whiskers. The weight losses of eroded composites increase with fiber content, applied current, and test number due to the worse thermal conductivity of the composites and the higher remained temperatures on contact surfaces. The composites reinforced with Saffil short fibers exhibit the best erosion resistance of all reinforcements in the study because of the small spacings between Saffil short fibers and the strengthening of strong short-fiber skeletons. The effective contribution of short fibers to arc erosion resistance depends on their sizes to construct small-spacing and deeply-embedded skeletons.

An electroless plating and hot-pressing process was developed to fabricate silver matrix composites reinforced with uniformly distributed graphite and Saffil short fibers (Graphitesf and Saffilsf). The hardness of the composites increases as the content of short fibers increase. Static-gap, single-spark erosion and repeated-collision, multiple-arc erosion tests were used to investigate the arc erosion behavior of the composites. The composites exhibited better arc erosion resistance when the contents of short fibers were increased in a static-gap, single-spark erosion test. However, the weight loss of the composites after 10,000 times repeated-collision, multiple-arc erosion operation shows that the composites with low volume percents of short fibers have a good arc erosion resistance. The Saffilsf/Ag composites show a better arc erosion resistance than Graphitesf/Ag because of the greater strengthening effect of the finer Saffil short fibers. The erosion behavior of the composites is dominated by the viscosity of composites in single-spark tests, while it depends on the competition of viscosity and thermal properties in multiple-arc tests.

Static-gap, single-spark tests were used to investigate the arc erosion behavior of newly developed silicon carbide and alumina particle reinforced silver matrix composites (SiCp/Ag, Al2O3p/Ag). Craters and hills exist on the surfaces of eroded silver matrix composites, and their depths and sizes decrease as the particle content increases and the particle size decreases. Obvious melting, flow, severe splash of molten silver, and the segregation of particles are present on the surfaces of eroded composites containing low volume percents of large particles. Easier silver flow results in smooth surfaces and reduces the total surface areas of the eroded composites containing large particles. The flow and splash of silver decreased with increasing particle content and decreasing particle size, exhibiting a better erosion resistance to single-spark tests. The static-gap, single-spark erosion behavior of silver matrix composites is dominated by the flow and splash of molten composites. A high viscosity of the liquids provides the composites a good arc erosion resistance.

Aluminum matrix composites reinforced with various contents and sizes of silicon carbide particles (SiCp) were fabricated by squeeze casting. A lower melting point AA A383 aluminum alloy (A383 Al) was squeezed into the higher melting point SiCp/pure aluminum (SiCp/pure Al) and SiCp/AA 6061 aluminum alloy (SiCp/6061 Al) preforms. The volume percents of the ceramic reinforcements were effectively lowered from traditional 50 to 8–25 vol% by the addition of pure Al and 6061 Al powders in the preforms. The SiC particles uniformly distributed within the matrices, and no pore was found in these composites. The growth of silicon precipitates in A383 Al alloys was limited by the addition of the aluminum alloy powders and SiC particles, and the tensile properties of the alloys were effectively enhanced by the refinement of the silicon precipitates. The tensile strengths and elongations of the SiCp/pure Al/A383 Al and SiCp/6061 Al/A383 Al composites were both better than those of the A383 Al alloy. The T6-treated 12-μm SiCp/6061 Al/A383 Al composite exhibited the highest tensile strength of 301 MPa.

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.

A vacuum infiltration process has been developed to fabricate the aluminum matrix composites reinforced with low volume fraction (p. Generally, it is difficult to fabricate low volume fraction particulate composites by traditional infiltration processes because the particles always pack up to about 50 vol% in the preforms or compacts. In this study, the powder compacts were prepared of the well-mixed Ni-coated SiCp and pure aluminum powders and then were packed in quartz tubes. An aluminum alloy (Al–8.7% Si–2.6% Cu) with a composition similar to AA 380.0 was used to infiltrate these compacts. Experimental results showed that the infiltration temperature of 640 °C is favorable for the fabrication of these composites. Infiltration behavior, microstructure, nickel distribution, bending test, and fractography of the composites were investigated.

In this study, aluminum-doped zinc oxide films were prepared by a sol–gel method, followed by thermal curing at 200–500 °C. Prior ultraviolet exposure resulted in the subsequent curing temperature required to produce films with obvious crystallinity being successfully lowered to 200 °C because of the early dissociation of diethanolamine ligands in the gel precursor. The crystalline films were constructed of nanosized grains without a preferred orientation. The grain size increased from 9 to 19 nm with curing temperature.

NiAl intermetallic is recently of considerable interest as the high temperature structure material because of its high melting point, high specific stiffness, better oxidation and creep resistance. However, the low-temperature brittleness of the NiAl intermetallic remained a main reason for its unpopularity for industrial applications. Composite ductile phase toughening approaches have been utilized by many researchers to improve the fracture toughness of intermetallics. In liquid metallurgy, pressure casting or infiltration of molten nickel aluminide into a preform is the usual method for the fabrication of nickel aluminide intermetallic composites. But generally, it is not useful for metallic reinforcements because of the drastic reactions between the molten nickel aluminide and the metallic preform, and the difficulty in sustaining the performance of the metallic preform at a high temperature. In solid metallurgy, this process is based on reactive powder metallurgy and hot pressing, hot extrusion and hot isostatic pressing (HIP). High processing temperature and pressure, generally at a temperature of at least 1,200 C, are necessary conditions for hot pressing, hot extrusion and HIP. Hence the processes require sophisticated manufacturing equipment and considerable energy and render the application of nickel aluminide intermetallic composites unpopular. Work on reactive hot pressing(RHP) at a lowmore » temperature near the melting point of aluminum is reconsidered again. Efforts indicated that by combining the spontaneous reaction of the electrically coated nickel film and the aluminum foils, and hot pressing at a temperature about 500 C lower than previously accomplished by HIP, would overcome the fabrication problem of NiAl intermetallic composites reinforced with the uniformly distributed metallic fibers.« less

Stainless steel fibres (SSF) were first wound and then plated with electrical nickel film. Alternative layers of these properly spaced Ni-coated stainless steel fibres (SSF–Ni) and aluminum foils were then stacked and diffusion bonded at 500 °C, 100 MPa in vacuum for 10 min to produce an SSF–Ni–Al precursor. Lower-temperature reactive hot pressing (RHP) at 700 °C, a process employed in this work, allowed the nickel and aluminum to react to form an NiAl matrix at a temperature approximately 500 °C lower than that accomplished by hot pressing, hot extrusion or hot isostatic pressing (HIP). RHP at 650 °C was also undertaken in order to investigate the mechanism leading to the formation of a nickel aluminide matrix composite. A dense specimen with complete NiAl reaction was obtained by hot pressing at 900 °C. The variance in microstructure that resulted from the different conditions of heat treatment and hot pressing was analysed by optical microscopy, scanning electron microscopy and X-ray diffraction (XRD).

Dispersion strengthened copper matrix composites, including Al{sub 2}O{sub 3}/Cu, TiC/Cu, Si{sub 3}N{sub 4}/Cu, SiC/Cu, B{sub 4}C/Cu and Gr./Cu, offer a unique combination of high strength and high electrical and thermal conductivities and, as such, would be worthwhile to develop in the future. Methods for the production of dispersion strengthened copper matrix composites involve traditional melting and casting techniques and powder metallurgy which ranges from simple mechanical mixing to complex processing such as coprecipitation from salt solution, mechanical alloying and internal oxidation of the reactive elements. Traditional melting and casting are not useful because of the poor wettability between ceramic particles and molten copper, which leads to flocculation of the dispersoids. In general, SiC{sub w} always clusters and can not be dispersed uniformly in the copper matrix. But application by means of electroless plating followed by hot pressing to fabricate the composite may easily solve the clustering problem. Hence, fabrication of copper matrix composites reinforced with a uniform distribution of SiC{sub w} using electroless plating and the study of their properties are the emphases of this research.

In this study, the bone structures, nanomechanical properties and fracture behaviors in different groups of female C57BL/6 mice (control, sham operated, ovariectomized, casein supplemented, and fermented milk supplemented) were examined by micro-computed tomography, scanning and transmission electron microscopy, and nanoindentation. The control and sham operated mice showed dense bone structures with high cortical bone mineral densities of 544 mg/cm(3) (average) and high hardness of 0.9-1.1 GPa; resistance to bone fracture was conferred by microcracking, crack deflections and ligament bridging attributed to aligned collagen fibers and densely packed hydroxyapatite crystals. Bone mineral density, hardness and fracture resistance in ovariectomized mice markedly dropped due to loose bone structure with randomly distributed collagens and hydroxyapatites. The acidic casein supplemented mice with blood acidosis exhibited poor mineral absorption and loose bone structure, whereas the neutralized casein or fermented milk supplemented mice were resistant to osteoporosis and had high bone mechanical properties.

In this study, the mechanical properties of bioactive coatings on Ti6Al4V substrates were investigated using instrumented nanoindentation. The aim was to observe the differences in the mechanical properties before and after immersion in collagen solution. The hydroxyapatite coatings were prepared through two processes: self-assembly in simulated body fluid and a hydrothermal method. Sintered hydroxyapatite disks were used as controls. The test samples were then incubated in a dilute collagen solution for 24 hours to produce composite coatings. The materials were investigated using XRD, SEM and nanoindentation. The results showed that the grain sizes of the hydroxyapatite coatings formed using two processes were 1 μm and 10 μm, respectively. The Young’s modulus of the pure hydroxyapatite, the disk and the coatings, was 3.6 GPa. After collagen incubation treatment, the composites had a Young’s modulus of 7.5 GPa. The results also showed that the strengthening phenomena of collagen were more obvious for homogeneous and small-grain hydroxyapatite coatings. These results suggest that there are similarities between these HAp/collagen composited and natural composite materials, such as teeth and bones.