Jiayun Zhang

Microstructural characterization of in situ TiC/Al and TiC/Al–20Si–5Fe–3Cu–1Mg composites prepared by spray deposition

An innovative spray-deposition technique has been applied to produce in situ TiC/Al and TiC/Al-20Si-5Fe-3Cu-1Mg composites. This technique provides a new route to solve the problems of losses and agglomeration of the reinforcement particles when they are injected into the spray cone of molten droplets during spray forming process. Experimental results have shown that the presence of needle-like Al3Ti and Al-Si-Fe compounds, which are detrimental not only to the fracture toughness, but also to the stability of the microstructure, can be eliminated completely from the final product by using a proper Ti:C molar ratio of 1:1.3 in the Ti-C-Al preforms and adding 5 wt% TiC particles to Al-20Si-5Fe-3Cu-1Mg alloy. Moreover, another major problem of coarsening of silicon particles usually encountered in the hypereutectic A1-Si alloys has also been solved by the technique. The silicon particles in the spray-deposited 5 wt% TiC/Al-20Si-5Fe-3Cu-1Mg composite were much refined (similar to2 mum) compared to those (-5 pm) obtained in the matrix alloy without TiC addition. The formation and elimination mechanisms of Al3Ti phase in TiC/Al composites can be explained based on thermodynamic theory. The modification of the microstructures in the spray-deposited Al-20Si-5Fe-3Cu-1Mg alloy can be interpreted in the light of the knowledge of atomic diffusion. The experimental results also showed that the ultimate tensile strength of the TiC/Al composites was improved over that of the unreinforced Al matrix

Low-temperature hydrothermal synthesis and structure control of nano-sized CePO4

The nanostructured CePO4 with hexagonal and monoclinic phases were controllably synthesized through a hydrothermal route at a low temperature of 100 °C by simply varying the reactant PO4/Ce molar ratio. By analyzing the synthesis procedure and product structures, the formation mechanism of the CePO4nanostructures was proposed. The luminescent properties of CePO4 with different structures and morphologies have been studied and compared. The obvious blue shift of the strongest excitation peak of the monoclinic CePO4 compared with the hexagonal CePO4 could be observed in their luminescence spectra. With the cycling use of phosphoric acid, the low-cost preparation of CePO4 could be achieved. Furthermore, this synthesis strategy will open a novel approach to rare earth phosphates with multiple structures.

Ageing behaviour of spray-deposited 18Ni(250) maraging steel + 10 vol.% Al2O3 particulate-reinforced metal matrix composites

Abstract The ageing behaviour of spray-deposited 18Ni(250) maraging steel+10 vol.% Al2O3 particulate-reinforced metal matrix composites (MMCs) was investigated by microhardness and nanoindentation techniques. Compared to the control steel, the composite material showed an accelerated ageing kinetics. Nanoindentation investigation revealed observable gradient distribution of elastic modulus and hardness around Al2O3 particulates inside the plastic zone in the matrix. Around a reinforcement particulate, the gradient distribution of the properties is steeper at the sharp corner than that at the flat interface. Theoretical Avrami-type precipitation model was successfully modified to calculate the distribution of precipitates around an Al2O3 particulate. The calculation results showed a gradient distribution of precipitates similar to the experimentally measured distribution of elastic modulus and hardness, which can attributed to the gradient distribution of dislocations within the plastic zones around the reinforcements.