No abstract

The aim of this study is to investigate the structure development and growth kinetics of the interfacial structure of cold roll bonded Al/Cu bimetal sheet. An interfacial structure is developed during the annealing process. The characteristics of the constituent phases at the interface of Al/Cu bimetal are studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that an obvious multi-layers interdiffusion structure is developed at the Al/Cu interface. The diffusion layer is consisted of four intermetallic compounds; Al 2 Cu, AlCu, Al 3 Cu 4 and Al 4 Cu 9 . The growth of these intermetallics during annealing can be achieved by the diffusion process. The activation energies of Al 2 Cu, AlCu + Al 3 Cu 4 , Al 4 Cu 9 and the total intermetallic layer are found to be 97.504, 107.46, 117.52 and 107.85 kJ/mol, respectively. These intermetallics generally possess higher hardness values than those of the corresponding base metals. AlCu and Al 3 Cu 4 exhibit much higher hardness than that of Al 2 Cu and Al 4 Cu 9 , which implies lower fracture toughness. The observation of crack propagation paths shows that fracture mainly occurs in the intermetallic compound layers of AlCu and Al 3 Cu 4 , which are located between Al 2 Cu and Al 4 Cu 9 .

The dominant point defects in p-type NiO films were determined by analyzing the coordination number (CN) change with various annealing temperatures and the composition profile of double-layer films deposited individually in oxygen and in argon atmospheres. The results show that the nonstoichiometry of sputtered NiO film is determined by the number of nickel atoms rather than by the number of oxygen atoms. It is concluded that nickel vacancies are the dominant point defects that result in the electrical conductivity of NiO films.

The aim of this article is to study the influence of interfacial structure development at interface on the fracture mechanism and the bond strength of cold roll bonded Al/Cu bimetal plate. The Al/Cu bimetal plates are produced by cold roll bonding and then sintered at different conditions. The bond strength of the Al/Cu bimetal plate increases generally to maximum values and then decreases to low values with increasing sintering temperature and time. Interfacial structures develop with increasing sintering temperature and time. The main interfacial layers are Al 2 Cu, AlCu, Al 3 Cu 4 and Al 4 Cu 9 . The formation and thickening of those intermetallic compounds promotes cracks propagation and weakens the bond strength of the bimetal plates. The fracture mechanism transforms from ductile to brittle cleavage with the development of interfacial structures. While the bond strength of the material starts to decrease, no obvious Kirkendall effect of void formation is observed in the present study.

No abstract

Inkjet printing of a liquid suspension prepared by dispersing silver powders of size around 4 nm in deionized (DI) water at 30 wt% was investigated in this study. By comparing with the results of pure DI water, the effects of nanoparticles on droplet formation between the nozzle and the substrate were also studied. A bipolar pulse waveform was employed in driving the piezoelectric printhead with pulse voltage set as the primary variable of this study. Observations showed that a higher driving pulse voltage was required for the silver suspension to form droplets than DI water. The liquid column broke up at the nozzle orifice for DI water while the silver suspension broke up further away below the nozzle office. It was also observed that the droplet size of the silver suspension was smaller than that of DI water. For the silver suspension the liquid column formed was thinner and longer and the pinch-off time of the liquid column to form droplets was also longer. However, the characteristic adjustment time for droplet recombination was shorter for the silver suspension than for DI water.

No abstract

There are serious questions about the grain structure of metals after laser melting and the ways that it can be controlled. In this regard, the current paper explains the grain structure of metals after laser melting using a new model based on combination of 3D finite element (FE) and cellular automaton (CA) models validated by experimental observation. Competitive grain growth, relation between heat flows and grain orientation and the effect of laser scanning speed on final micro structure are discussed with details. Grains structure after laser melting is founded to be columnar with a tilt angle toward the direction of the laser movement. Furthermore, this investigation shows that the grain orientation is a function of conduction heat flux at molten pool boundary. Moreover, using the secondary laser heat source (SLHS) as a new approach to control the grain structure during the laser melting is presented. The results proved that the grain structure can be controlled and improved significantly using SLHS. Using SLHS, the grain orientation and uniformity can be change easily. In fact, this method can help us to produce materials with different local mechanical properties during laser processing according to their application requirements.