Key Engineering Materials Vol. 616

Abstract: The wear mechanisms of conventional Ti–6Al–4V extra-low interstitial (Ti64) and the new Ti–29Nb–13Ta–4.6Zr (TNTZ) were studied to investigate the wear properties of Ti64/TNTZ for application in spinal fixation devices. Ti64 and TNTZ balls and discs were first prepared as wear-test specimens. A ball-on-disc frictional wear-testing machine was used in air to perform the frictional wear tests of the Ti64 and TNTZ discs mated against Ti64 and TNTZ balls. The wear mechanisms were investigated using a scanning electron microscopy to analyze the worn surfaces and wear debris. The volume losses for the TNTZ discs were larger than those for the Ti64 ones, regardless of the mating ball material. Furthermore, the morphologies of the wear tracks and the debris of the Ti64 and TNTZ discs were different, suggesting that the wear mechanisms for the Ti64 and TNTZ discs were abrasive and delamination wear caused by mild and severe subsurface deformations of the Ti64 and TNTZ, respectively, regardless of the mating ball material.

Abstract: LY12/TC4 joints have wide applications in many industrial areas such as aerospace, nuclear and chemical industries. In the present study, TC4 alloy and LY12 alloy with and without aluminum thin film was produced under low temperature of 380 ^oC. The microstructure and mechanical properties of the joints were investigated. The addition of the Al thin interlayer had largely improved the interfacial microstructure and shear strength of the joints. The average shear strength of LY12/Al/TC4 joints was 64.3 MPa which was 2.5 times larger than the LY12/TC4 joints’ strength. The shear fracture mainly occurred on the interface of LY12 and TC4 from the XRD result of fracture surfaces.

Abstract: Mg1 and 1060 Al were diffusion-bonded by using pure silver foil under different holding times (10 min~120 min). The interface of the joint consists of Mg-Ag diffusion zone, Ag foil interlayer and Ag-Al diffusion zone. The distributions of Mg, Ag and Al show ladder-like distributions at the interface of the joints. When the holding time is below 90 min, silver foil has impeded the inter-diffusion of Mg and Al. When the holding time is beyond 90 min, the brittle eutectic Mg-Al intermetallic compounds (IMCs) cannot be avoided. Mg₃Ag and MgAg intermetallic compounds formed on Mg base side. Ag₂Al intermetallic compound grew on Al base side. The thicknesses of Mg₃Ag, MgAg and Ag₂Al increased linearly with the increasing holding time, which is contrary to that of the silver foil. The growth rate relationship of the formed IMCs is MgAg > Ag₂Al > Mg₃Ag according the slope values of the fitted lines. The hardness sharply increased at the interface because of the formation of IMCs. The maximum hardness values of three IMCs Mg₃Ag, MgAg and Ag₂Al are 287.5 HV, 196.5 HV and 175.7 HV respectively. The hardness of each IMC layer increased with the extension of holding time. The shear strength of the joints decreased from 10.5 MPa to 4.6 MPa with the rising holding time.

Abstract: Mg and Al were bonded successfully by means of diffusion bonding using Ni interlayer. The microstructure, diffusion mechanism and regulation of atom diffusion were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron probe microanalysis analysis (EPMA). The results showed that the joints consisted of Mg-Ni interface and Al-Ni interface, and there were Mg₂Ni formed in the Mg-Ni interface and Al₃Ni formed in the Al-Ni interface, respectively. Diffusion activation energy of Mg and Al were lower than that of Ni in the Mg-Ni and Al-Ni interface. The thickness (x) of Mg₂Ni and Al₃Ni can be expressed as x²=3.97×10^-4 exp (-139600/RT) (t-t₀) and x²=8.62×10^-3 exp (-174200/RT) (t-t₀) with heating temperature (T) and holding time (t).

Abstract: We have performed inelastic neutron scattering measurement on high-transition temperature superconductor La_1.90Sr_0.10CuO₄ with utilizing a Fermi chopper spectrometer. We succeeded in converting the observed neutron scattering intensity into a dynamical structure factor in the absolute unit by attempting two methods with analyzing (i) incoherent scattering intensity from the sample itself and (ii) that from vanadium standard. The total squared moment <M²> was evaluated to be 0.176 μ_B²/Cu, which is much smaller than the value for the parent compound, indicating a markedly change of electronic state by hole-doping.

Abstract: Zero-field muon spin rotation/relaxation (μSR) measurements were performed in order to clarify the effect of oxygen reduction and Ce-substitution on magnetic properties in T’-structured Pr_1.40-xLa_0.60Ce_xCuO_4+δ−α. At 75 K, a clear rotation signal was observed in the three samples; as-sintered x = 0 and annealed x = 0, and as-sintered x = 0.16 samples. From the qualitative analysis of μSR time spectrum measured at various temperatures, the magnetic ordering (Néel) temperature T_N for these samples was evaluated. It was found that both oxygen reduction and Ce-doping reduce T_N, however, the suppression of the order occurs in a different manner in the oxygen reduced and Ce-doped samples.

Abstract: The excitation mechanism of Cu II lines under an Ar and Ne glow discharge plasmas were investigated. Charge transfer collision is the domain excitation mechanism which resulting into the intensive emission of Cu II lines at particular wavelength. Under Ne glow discharge plasma, charge transfer collision and Penning type collision makes great contribution to the violently emission of particular Cu II lines.

Abstract: Boron (B) has great potential to be the primary fuel in energetic systems for its high heating values per unit volume and mass. The existence of B₂O₃ layer on its surface holding the combustion of B back has limited its extensive utilization. Adding magnesium (Mg) into B can improve its poor combustion performance according to the previous research. A new technique, cryomilling, was employed to prepare Mg and B (Mg/B) composite powders. The powders were cryomilled with a ball-to-powder ratio (BPR) of 80: 1(w/w) and an impeller rotation speed of 400 rpm, 500 rpm and 600 rpm. The cryomilling time is 5 h, 6 h and 7 h. A small amount of ferrum (Fe) is introduced into the powders in spite that the main phases are Mg and B. The effects of cryomilling parameters, such as cryomilling time and rotation speed on Mg/B composite powders were investigated. The results show the amount of active Mg and B is over 80%. The bonding mechanism during the process is analogous to mechanical alloy.

Abstract: In this study, pure boron-containing phenol-formaldehyde resin (BPFR) and boron oxide (B₂O₃) modified BPFR have been pyrolyzed at elevated temperatures in air and their thermal decomposition behavior is mainly explored. The structural evolution and chemical composition change during pyrolysis are characterized by thermal gravity (TG), Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). It is shown that the mass residues of pure BPFR are 27.1 and 8.7 wt.% after being pyrolyzed at 600 and 1000 °C for 2 h, respectively. In comparison with the pure BPFR, the mass residue of B₂O₃ modified BPFR is obviously higher, with the values of 72.9 and 39.7 wt.% at 600 °C and 1000 °C, respectively. The results of FT-IR prove the degradation and failure of the resin matrix are mainly resulted from the fracture of methylene and the release of small molecules. The XRD characterization shows the residues are amorphous carbon and B₂O₃. FE-SEM exhibits the melting B₂O₃ layer formed on the surface of the samples which could prevent oxygen from diffusing into composites during oxidation to some extent.