Materials Science Forum Vols. 745-746

Abstract: SiC/Cu composites exhibit low density, low coefficient of thermal expansion and excellent mechanical properties. In this study, Zn of 2 wt. % was added as the sintering activator, and the high volume faction (60%) SiC/Cu composites was fabricated by hot pressing sintering technology. The phase composition and morphology of as-prepare samples were characterized by X-ray diffraction (XRD) system and scanning electron microscopy (SEM) equipped with an energy-dispersive spectroscopy (EDS) system. The as-prepared SiC/Cu composites were dense and uniform as well as void free. The results show that SiC/Cu composites can reach excellent mechanical properties of SiC/Cu composites. With the increase of sintering temperature, Vickers hardness and the bending strength of the samples increased obviously and the as-prepared SiC/Cu composites achieved a maximum Vickers hardness and bending strength respectively of 195MPa and 140MPa.

Abstract: The microstructure and Vickers hardness of the Al_xCrCuFeNi₂(x=0.5, 1.0, and 2.0 in molar ratio) high-entropy alloys with as-cast and heat-treated states were investigated. X-ray diffraction (XRD) patterns suggested that for the Al0.5 alloy annealed at 900,an incomplete phase transformation from FCC to BCC occurred, while for the Al2.0 alloy as heated at 500 and 700, a converse phase transformation from BCC to FCC was obtained. Compared with the as-cast dendrites, after heat treatment, the microstructure of the alloys was obviously coarsened or spheroidized or homogenized, whereas the resultant hardness has almost not decreased even at high heating temperatures, which indicated the probability of ordering for this alloy system and thus effectively compensating the stress and structural relaxations. The Al2.0 alloy reached the maximum hardness value of 610 HV by annealing at 1100, which might be ascribed to the worm-like nanoprecipitations and the enhanced fraction of B2-ordered precipitations. By cold rolling, the Al0.5 alloy is able to reach the yield strength of 1055 MPa and the fracture strength of 1179 MPa, which was a significant improvement in comparison with the as-cast alloy.

Abstract: Bulk nanocrystalline Fe-Al based alloys with 5, 10 and 15 wt. % Ni were prepared by aluminothermic reaction. The alloys were analyzed by electron probe microanalyzer, X-ray diffraction and transmission electron microscope. Compressive yield strength and hardness of the alloys were tested. The experimental results showed that all of the alloys consisted of Fe-Al-Ni matrix and small amount of Al₂O₃ sphere. The matrix phases of the alloys with 5 and 10 wt. % Ni had disordered α-Fe solid solution, while the matrix phases of the alloys with 15 wt. % Ni had disordered α-Fe solid solution, NiAl phase and Fe₃AlC_x phase. Average grain sizes of the matrix phases of the alloys were about 20 nm. The alloys with 5 wt.% Ni had the best plasticity, but the alloys with 15 wt. % Ni had the highest yield strength and hardness. Yield strength of those alloys is higher than that of coarse-grained Fe₃Al.

Abstract: In this paper, the effects of the processing parameters on the preparation of Nb₄₂Ni₄₀Co₁₈ amorphous alloy ribbons were analyzed in detail, including the property of the alloy, material and size of the injection nozzle, setting of the alloy ingots, the distance between the nozzle and the copper wheel, surface quality and velocity of the copper wheel, heating rate and time, injection pressure, injection time, etc. Finally key factors for preparing wide Nb₄₂Ni₄₀Co₁₈ amorphous alloy ribbon have been proposed.

Abstract: High entropy alloys are new alloys composed of over five principal elements with each having an atomic percentage in the range of 5%~35%, which break through the concept of traditional alloys design. In this paper, AlxFeCoNiCr (B) high entropy alloys were prepared in an vacuum arc induction melting furnace. The microstructure presents simple solid solution structure, and the fraction of FCC crystal structure decreased with increasing of Al content. Chromium tends to segregate at the inter-dendrite grain boundary. Electrochemical investigations indicated that AlxFeCoNiCr (B) high entropy alloys were more corrosion resistance than 316L stainless steel.

Abstract: The change in the internal states of Zr₅₆Co₂₈Al₁₆ bulk metallic glass (BMG) upon minor substitution of Co with Fe was investigated for alloys with different compositions of Zr₅₆Co_28-xAl₁₆Fe_x (x = 0, 1 and 2, respectively). Results exhibited that the ductile Zr-Co-Al-Fe BMGs were obtained and showed better glass-forming ability (GFA) via a small amount of Co partial replacement by Fe. In addition, the addition of a small amount of Fe enhanced the crystallization process and reduced the activation energy. The micro-alloying with Fe reduced the heat of mixing, which made the rearrangement of atoms easier during the crystallization process.

Abstract: Bulk nanocrystalline Fe₇₆Si₉B₁₀P₅ magnetic cores were sintered using spark-plasma technique through direct-nanocrystallizing method by Fe₇₆Si₉B₁₀P₅ amorphous alloy gas atomization powder. The saturated magnetic induction of magnetic cores was 1.5 T, and the maximum permeability was 1470. Coercive force was 38 A/m. X-ray analysis showed that the crystallization temperature of Fe₇₆Si₉B₁₀P₅ alloy decreased with the increase of the pulse current and sintering pressure. High resolution electron microscopic analysis results showed that the smaller nanograin size were obtained after spark-plasma sintering with the crystallization temperature decrease. In addition, the crystallization behaviour of the Fe₇₆Si₉B₁₀P₅ during sintering process was analyzed, and the influence of direct crystallization during spark-plasma sintering on the soft magnetic properties was discussed.

Abstract: A Zr-based amorphous composite coating was fabricated by laser cladding and remelting on plain carbon steel. The amorphous phase contents of coatings were tailored by controlling the power density. The effect of amorphous phase content along the depth direction on the microhardness and corrosion resistance of the coating was studied. The results showed that the content of amorphous phase significantly decreased from the remelted layer to the cladded layer. In addition, it was found that the maximum microhardness of the coating were about 1061 HV_0.1, observed 200 μm beneath the surface. Potentiodynamic polarization studies in 3.56 wt.% NaCl solution indicated that the remelted layer exhibited excellent corrosion resistance due to the high amount of amorphous phase.

Abstract: In this study, an in situ formed bulk metallic glass matrix composite (BMGMC) (Zr_58.5Ti_14.3Ni_4.9Cu_6.1Nb_5.2Be_11.0) was synthesized. Bulk metallic glass (BMG) (Zr5_2.5Cu_17.9Ni_14.6Al_10.0Ti_5.0) was also included in this work and a Ti-6Al-4V alloy was used as a reference material. Due to the glassy matrix that postpones the growth of corrosion pits, the BMGMC displays high positive corrosion potentials and low corrosion current densities. The BMGMC exhibited a higher improved corrosion resistance than the Ti alloys. Furthermore, the biocompatibility of this BMGMC was assessed by studying the cellular behavior of bone-forming mouse M3T3-E1 pre-osteoblast cells. The matrix did not significantly affect cell adhesion, proliferation and ALP activity. The general biosafety of Zr-based BMGMC for M3T3-E1 cells was revealed as normal cell responses. Zr-based BMGMC shows great potential for applications in the hard tissue implants.

Abstract: The Fe₇₆Si₉B₁₀P₅/Zn_0.5Ni_0.5Fe₂O₄/PVA composite film was fabricated by the spin-coating process. To improve the dispersibility and compatibility of Zn_0.5Ni_0.5Fe₂O₄ nanopaticles, Bis (P, P-bis-ethylhexyl diphosphato) ethanediolato titanate was used as the surface modifier to deal with Zn_0.5Ni_0.5Fe₂O₄ nanoparticles. The micro morphology and magnetic properties of the composites was observed respectively by 3D Measuring Laser Microscope OLS4000 and MATS type auto test system of magnetic materials. Several contrast groups using by the similar preparation process showed that surface modification on the Zn_0.5Ni_0.5Fe₂O₄ nanoparticles did not only improve the dispersibility of Fe₇₆Si₉B₁₀P₅ amorphous alloy particles presenting in the PVA, but also improve the softmagnetic properties of the composite films; the magnetic properties of the composite film containing Zn_0.5Ni_0.5Fe₂O₄ nanoparticles performed better than the one that not contain Zn_0.5Ni_0.5Fe₂O₄ nanoparticles; the permeability of the film increased with the increasing of the contents of Fe₇₆Si₉B₁₀P₅ amorphous alloy powder in the composites.