Multi wall carbon nanotube (MWNT) is an attractive material with excellent thermal conductivity and mechanical properties. However, the report to which thermal conductivity improves by combining it to the metal matrix is very few. In the aim of improving the thermal conductivity, nickel-matrix composite with MWNT was prepared by slurry mixing process where ethanol was used as solvent. Using spark plasma sintering (SPS), MWNT/Nickel nanocomposite were fabricated and the fabricating conditions were investigated. The sintered relative densities of the composites containing up to 5 vol% of MWNT were above 99%. The thermal and electrical behaviors of MWNT/Nickel composite were determined using laser flash and van der Pauw methods and were found to be anisotropic, respectively. The thermal conductivity is found to increase 10% for composition with 3 vol% MWNT.
Significant phase refinement and dispersion were achieved in a cast Mg-8 mass%Li alloy through processing by equal-channel angular pressing (ECAP) using a die having an internal channel angle of 110° and a pressing temperature of 473 K. Following extrusion and subsequent ECAP through 2 passes, the alloy exhibited superplasticity over the temperature range from 423 to 473 K. A maximum fracture elongation of >950% was attained at 473 K with an initial strain rate of 1.0×10-4 s-1. The measured strain rate sensitivity was of the order of 0.6. The maximum elongation is high in comparison with other Mg alloys tested in tension at the same temperature and strain rate. The activation energy for superplastic flow was essentially equal to the value for grain boundary diffusion of Mg. The use of ECAP gives a significant improvement in strength and ductility at room temperature.
In order to investigate the strength and the deformation properties of metals in nearly perfect crystal, nanoindentation test is performed on aluminum samples with the various purities: 99.9999%(6N), 99.99%(4N) and 99%(2N). It is widely known that the strength decreases with increasing the purity of metals. In nanoscale, however, the strength has been revealed to close the ideal shear strength, because the area in nanoscale is expected to behave as a perfect crystal. In this study, the nanoindentation system that is able to obtain indentation load vs. penetration depth curves is employed. The experiment is performed on ultrahigh-purity aluminum (99.9999%), and on high-purity aluminum (99.99%) and purity aluminum (99%) so as to discuss the relationship between the purity level and the mechanical properties at room temperature. It is revealed that penetration depth decreases with increasing purity, and the critical shear stress estimated from the experimental results indicates the value close to the ideal shear strength. These results suggest that a perfect crystal is harder than an imperfect crystal. Furthermore, the indentation load vs. penetration depth curves indicate the discontinuous deformation of the metals. It is considered that these discontinuities are caused by the existence of impurities or the initiation and the multiplication of dislocations in these samples.
A thermodynamic study of phase equilibria in the Nb-Ni-Zr system has been carried out experimentally and using CALPHAD method. To enable the thermodynamic description of the constituent binary systems, the results from a previous evaluation were adopted for the Nb-Ni, Ni-Zr and Nb-Zr systems. However, some modifications of thermodynamic parameters of the Ni-Zr system were made based on the recent experimental data on binary and ternary phase equilibria. The phase boundaries involving the liquid phase in the Nb-Ni-Zr ternary system at a constant 60 mol%Ni and 20 mol%Zr were determined experimentally by differential scanning calorimetry (DSC). Thermodynamic parameters of the Nb-Ni-Zr ternary system were evaluated by combining the experimental results from DSC with the reported phase boundaries of the isothermal sections at 773 and 1073 K. The calculated results reproduced the present DSC results as well as the experimental isothermal sections. Furthermore, the amorphous-forming ability of Nb-Ni-Zr ternary alloys has been evaluated by incorporating the thermodynamic properties from the phase diagram calculations into the Davies-Uhlmann kinetic formulations. The calculated critical cooling rates in the observed metallic glass forming compositional range were found to be lower than those in the observed amorphous forming range by one or more orders of magnitude.
The effects of microstructure on the bend formability of an age-hardenable Cu-4 mass%Ni-1 mass%Si-0.02 mass%P alloy have been investigated. A number of micro necks first arise along grain boundaries, and part of them grows, resulting in surface wrinkles, which finally lead to surface cracking. The wrinkles occur by shearing in the vicinity of grain boundaries. The width of precipitate-free zones has been found to be one of the factors affecting the bend formability. The grain-boundary shearing takes place more easily, resulting in worse bend formability as the width of precipitate-free zones increases. The bend formability is improved by two-step aging.
Isobaric heat capacities, Cp, of LaXSr1-XFeO3-δ solid solutions from near absolute zero Kelvin (2 K) to high temperature (1340 K) were measured by a relaxation method and differential scanning calorimetry. Also, their Debye temperatures, ΘD, were determined from the measured Cp values below 10 K and isochoric heat capacities, CV, were calculated by inserting the ΘD values into Debye functions, followed by calculating the isochoric entropies of vibration, Δ0TSV. From the measured Cp values, it was found that oxygen vacancy (Vo) formed by a self-compensating reaction by doping of Sr′La decreased the onset temperatures of the magnetic and structure phase transitions, broadening the temperature ranges of such phase transitions. The entropies of vibration of oxygen vacancy, ΔfSTvib.V(Vo), estimated by differentiation of Δ0TSV with the Vo content at 298 K and 800 K were 58.65 J•K-1•mol-1 and 64.59 J•K-1•mol-1, respectively. Such a large ΔfSTvib.V(Vo) appears to be one of important reason for foming Vo.
Metallic manganese nitrides Mn3AN (A=Zn, Ga, etc) are well known for their large magnetovolume effect (MVE), a discontinuous volume expansion at the magnetic transition. However, MVE is exceptionally absent in Mn3CuN. We found that MVE is induced by a small amount of Ge in the Cu site. This seems to coincide with recovery of the cubic structure. By further Ge doping, the volume expansion becomes gradual (ΔT~100 K) and large negative thermal expansion (NTE) is exhibited around room temperature [α=-12×10-6 K-1 (α: coefficient of linear thermal expansion) for Mn3(Cu0.5Ge0.5)N]. Such a large, isotropic and non-hysteretic NTE is desirable for practical applications.
Recently, the use of soldering tips using Pb-free solder has caused problems because the Nickel- or Iron-plating layer on the soldering tip is easily eroded by the Pb-free solder. Therefore, solder tips with higher solder erosion resistance and wettability are required. In this study, Al2O3 ceramic soldering tips with various additional components were fabricated by hot press sintering and their properties were investigated with the aim of developing soldering tips with higher solder wettability and erosion resistance. The solder wettability of Al2O3/metal composite could be improved by added nickel or iron at about 80 mass%. However, the Vickers hardness (Hv) of Al2O3/metal composite decreased to about 400 with the addition of Ni at about 80 mass%.
Microstructural change of a Mg-8 mass%Li alloy processed by a deformation combining the extrusion and equal-channel angular pressing (ECAP) during superplastic deformation has been investigated by optical microscopic observation and SEM/EBSP analysis. The maximum tensile elongation to failure of up to about 970% was attained at a temperature of 473 K and with a strain rate of 1.0×10-4 s-1. The elongated α phase in the cross section of tensile specimens was observed to change an equiaxed shape during superplastic deformation. Twinning was observed in the α phase in the initial stages of superplastic deformation. The frequency of high angle boundaries defined as above 15° misorientation increased with increasing the elongation to failure in order to advance a dynamic recrystallization during superplastic deformation. Cavities were formed in the boundaries between α and β phases from elongations of about 600%. The area fraction of cavities in the cast+extrude+ECAP condition was smaller than in the cast+extrude condition. These microstructural changes play an important role for superplastic deformation of the Mg-8 mass%Li alloy.
Many types of cyclic corrosion test devices have been developed for simulating the atmospheric corrosion near seashore environment and most of test methods are doing dry/wet process after spraying NaCl solution or artificial seawater. In real environment, it has been observed that the corrosion rate is the highest where seasalt particles continuously attached on the surface of the metal and no cleaning process occurred by rainfall. In order to simulate this environment, we have developed a new atmospheric corrosion test device. Using this test device, long term atmospheric corrosion tests have been done under various seasalt deposition rates. The corrosion behaviour of steels in 0.2 mdd was similar to that in 1 mdd, so acclerating test can be done using this test device.