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The friction coefficients of CoCrMo sliding against UHMWPE and CoCrMo were measured in solutions of albumin and synovial fluid containing fluorescently labeled albumin. No fluorescence could be observed on the CoCrMo disc following incubation in labeled albumin or after sliding against CoCrMo. This was due to quenching of the fluorophore by the metal and indicated that a protein film thicker than 10 nm was not formed on the surface. A more complicated behavior was observed for UHMWPE sliding against CoCrMo. For each lubricating solution and at each load, a bimodal distribution of steady-state friction values was observed, the friction coefficient either remaining constant or decreasing during the early stages of the measurement. As no quenching of the fluorophores occurred on the UHMWPE surface, the fluorescence labeling method could be used to reveal polyethylene (PE) transfer and to show that it correlates with the friction coefficient: Low friction coefficients corresponded to a low density of PE spots on the CoCrMo surface. In addition, it was found that the friction coefficients for UHMWPE sliding against CoCrMo in synovial fluid were not significantly different from those in phosphate-buffered saline (PBS), but that the addition of albumin to PBS did cause a significant increase in the friction coefficient., (Copyright 2008 Wiley Periodicals, Inc.)

Abstract: Nanostructured Cr–xNi alloys were prepared by magnetron sputtering in low pressure argon gas, where x varied from 0 to 20at%. The structure and microhardness of the alloys were observed by TEM (microscopy) and Vickers hardness testing, respectively. The crystal structure of the sputtered alloys was BCC. The addition of nickel to chromium decreases the grain size of the Cr–Ni alloys and the grain sizes of the alloys changed from 88nm for Cr to 30nm for Cr-20at% Ni alloys. The microhardness of the Cr–Ni alloys showed the maximum around 5at% Ni. The increase in nickel content above 5 at% lowers the microhardness of the alloys, although the grain size of the Cr–Ni decreases. The abnormal tendency against grain size change was discussed in terms of the characteristics of the grain boundaries in the alloys. [Copyright &y& Elsevier]

Ultrasonic waves were applied during brazing of alumina to copper, The intensity of ultrasonic wave was 1 kW and 18 kHz and the aim of this work was to study the effect of the ultrasonic wave and brazing temperature on the properties of the braze joint between alumina and copper using Zn-Al alloys as filler metal. First the alumina was metallized by applying on ultrasonic wave in a Zn-Al braze bath. Then the metallized alumina was brazed with copper using the same filler alloy. The joining mechanism was investigated by measuring the joining strength and analyzing the microstructure at the interface of the joint. The ultrasonic waves improved the wetting in the molten Zn-Al bath by accelerating the removal of bubbles from the interface between alumina and the filler, and this was reflect in improved joint strength. [ABSTRACT FROM AUTHOR]

Vacuum diffusion bonding of SiC ceramic to Ni–25 at.-%Cr alloy was carried out at 1223–1323 K for 0.9–3.6 ks under a pressure of 7.2 MPa. The kinds of the reaction products and the interface structures of the joints were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD), and the kinetic parameters describing the growth of reaction layers were calculated. The experiment and analysis identify that four kinds of reaction products, namely Ni[sub 2]Si, graphite (G), Ni[sub 5]Cr[sub 3]Si[sub 2] and Cr[sub 3]Ni[sub 2]SiC, have formed during the diffusion bonding of SiC ceramic to Ni–25 at.-%Cr alloy. The interface structure of the SiC/Ni–Cr joints is SiC/(Ni[sub 2]Si+G)/(Cr[sub 3]Ni[sub 2]SiC + Ni[sub 5]Cr[sub 3]Si[sub 2])/Ni[sub 5]Cr[sub 3]Si[sub 2]/Ni- Cr, and each reaction layer in this structure grows according to a parabolic law. The activation energies for growth of (Ni[sub 2]Si+G), (Cr[sub 3]Ni[sub 2]SiC+Ni[sub 5]Cr[sub 3]Si[sub 2]), and Ni[sub 5]Cr[sub 3]Si[sub 2] are 217, 248, and 233 kJ mol ­ 1, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Si3N4 ceramic was self-jointed using a filler alloy of Cu–Pd–Ti, and the microstructure of the joint was analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15 (at.%), a high quality Si3N4/Si3N4 joint was obtained by brazing at 1100–1200°C for 30min under a pressure of 2×10−3 MPa. The microstructure of the Si3N4/Si3N4 joint which was observed by EPMA, XRD and TEM, and the results indicated that a reaction layer of TiN existed at the interface between Si3N4 ceramic and filler alloy. The center of the joint was Cu base solid solution containing Pd, and some reaction phases of TiN, PdTiSi and Pd2Si found in the Cu [Pd] solid solution. [Copyright &y& Elsevier]

Abstract: Si3N4 ceramic was jointed with itself by active brazing with a Cu–Pd–Ti filler alloy. Interfacial microstructure of the Si3N4/Si3N4 joint was analyzed by EPMA, TEM and X-ray diffract meter. The results indicate that a TiN reaction layer with a thickness about 5μm is formed at the interface between Si3N4 ceramic and filler alloy. The TiN reaction layer is composed of two zones: one next to the Si3N4 ceramic with grains of 100nm and the other zone that connects with the filler alloy and has grains of 1μm. The microstructure of the joint can be described as: Si3N4 ceramic/TiN layer with fine grains/TiN layer with coarsen grains/Cu[Pd] solid solution. Some new phases, such as Pd2Si, PdTiSi, Ti5Si3 and TiN, were formed in the Cu[Pd] solid solution interlayer. With increasing brazing temperature from 1100°C to 1200°C, the thickness of the TiN reaction layer is not changed. Meanwhile, the amount and size of the TiN and Pd2Si phases in the Cu[Pd] solid solution increase, while, the amount of the PdTiSi phase decreases. [Copyright &y& Elsevier]

Abstract: Si3N4 ceramic has been joined successfully to itself by brazing in a vacuum at 1373–1573K holding for 1.8ks using a Cu76.5Pd8.5Ti15 alloy filler. By observation and analysis of the microstructure of the joints, it is found that the joints comprise three parts: (1) a continuous reaction layer of TiN between Si3N4 and filler alloy, (2) a discontinuous reaction layer containing TiN, Pd2Si and Ti5Si3 connecting the continuous reaction layer, and (3) the Cu-based solid solution in the mid of the joint and some reaction products (TiN, Pd2Si, PdTiSi and Ti5Si3) in the solution. With increasing brazing temperature, both the thickness of the continuous reaction layer and amount of reaction phases increase, which improves the bending strength of the joints. When the brazing temperature surpasses 1473K, voids are formed in the joint because of the decomposition of the Si3N4 ceramic, leading to a decrease of the bond strength. The room-temperature bending strength of the joint brazed at 1423K reaches a maximum value of 155.8MPa. [Copyright &y& Elsevier]