Microstructure and Nanoindentation Behavior of Ti40Zr40Ni20 Quasicrystal Alloy by Casting and Rapid Solidification

A Ti40Zr40Ni20 quasicrystal (QCs) rod and ribbons were prepared by conventional casting and rapid solidification. The X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC) techniques were used to investigate the microtissue, phase composition, and solidification features of the samples; the nano-indentation test was carried out at room temperature. The results show that a mixture of the α-Ti(Zr) phase and the icosahedral quasicrystal (I-phase) was formed in the Ti40Zr40Ni20 rod; the microstructure of Ti40Zr40Ni20 ribbons mainly consisted of the I-phase. The solidification mechanism of the I-phase was different in the two alloys. The I-phase in the quasicrystalline rod was formed by packet reaction while in the ribbons it was generated directly from the liquid. At room temperature, both samples had relatively high hardness and elastic modulus; the elastic modulus of the ribbons is 76 GPa, higher than the 45 GPa of the rod. The hardness of the ribbons was more than twice that of the rod.

Microstructural Investigations of Ni-Based Superalloys by Directional Solidification Quenching Technique

The improvement of the mechanical properties of Ni-based superalloys is achieved in most cases by modifying the chemical composition. Besides that, the processing can be modified to optimize the as-cast microstructure with regard to the mechanical properties. In this context, the present study highlights the solidification mechanism of several Ni-based superalloys by conducting experiments using a modified, laboratory-scale Bridgman-Stockbarger furnace. In that context, the single-crystal rods are partially melted, directionally solidified and quenched sequentially. Several characterization methods are applied to further analyze the influence of the alloying elements and the variation of the withdrawal rate on the as-cast microstructure. Four stages of solidification are distinguished whereby the morphology observed in the different stages mainly depends on the cooling rate and the local concentration of the carbide forming elements. The effect of carbide precipitation and the effect on the as-cast microstructure is investigated by employing energy dispersive X-ray spectrometry (EDX) and electron backscatter diffraction (EBSD) analysis techniques. A local polycrystalline structure is observed in the single-crystal system as consequence of the influence of the carbon content and the cooling rate. The present work aims to develop strategies to suppress the formation of the polycrystalline structure to maintain the single-crystal microstructure.

Strength and Solidification Mechanism of Silt Solidified by Polyurethane

To determine the mechanism and strength characteristics of solidification of silt by a permeable polyurethane grouting material, the effects of polymer content, soil moisture, and immersion time on the unconfined compressive strength (UCS) of the silt have been studied. The results showed that the permeable polymer grouting material can significantly improve the performance of silt: (1) A higher amount of polymer produced a greater strength in the solidified soil. (2) The strength of the solidified soil increased as the immersion time was increased. (3) Moisture in the soil was not conducive to improving the strength of the solidified soil. The X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) have proven that polyurethane does not react with the silt, but they could improve the strength of the silt through physical action. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were performed to find that polymers can reduce soil porosity, and the addition of polyurethane improved the strength of the silt mainly through adhesion, wrapping, filling, and bridging.