High Pressure Solidification Research Articles

High pressure solidification process and effect on nanohardness of Ti–48 at-%Al alloy

In this work a tungsten carbide six-anvil apparatus was introduced to investigate the high pressure solidification effect on Ti–48 at-%Al alloy. The experimental processes of Ti–48 at-%Al alloy solidified under different pressures were presented in detail. The mechanical properties of Ti–48 at-%Al alloy solidified under different pressures were examined by a Nanoindentor XP tester. It shows a certain increase in the nanohardness of the lamellar structure as the pressure increases from normal pressure to 4 GPa. When the pressure is 4 GPa, the nanohardness increases by 50·2% compared with that of normal pressure.

High Pressure Solidification: An Effective Approach to Improve the Corrosion Properties of Mg-Y Based Implants

High Pressure Solidification: An Effective Approach to Improve the Corrosion Properties of Mg-Y Based Implants

Effects of High Pressure on the Solidification Microstructure of Al-Si Alloy

The microstructure of the aluminum-silicon (Al-Si) alloy solidified under high pressure was compared with that solidified under normal pressure. High-pressure solidification was performed at 4.0 and 5.0 GPa. The microstructures of the samples were observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The effects of pressure were analyzed by examining the microstructure of the alloy. The observed microstructures show an additional amount of primary a(Al) phase in the Al-13at%Si alloy solidified under high pressure; this indicates the existence of a eutectic point moving toward the silicon direction with increasing pressure. The eutectic cells of the Al-Si alloy solidified under high pressure are evident, and the eutectic silicon phases are presented as curved and near-parallel lamellar crystals, signifying that the growth mechanism of the eutectic silicon phase changed from faceted to non-faceted. The eutectic silicon lamellar phase and the primary b(Si) phase were refined by the applied pressure.

Theory and application research development of semi-solid forming in China

In order to adapt to the trend of “energy saving and emission reduction” and impel the practical application of semi solid processing (SSP) in China, the progress and application of semi-solid theory in China have been reviewed briefly and systematically. It was emphasized on basic theories, such as formation of globular grains, rheology, high pressure solidification and plastic deformation and applications, such as material design, preparation of semi-solid billets (slurries), thixoforming and application status, which are based on the advantage of semi-solid processing. The results show that the gap of SSP between world level and China exists, especially in application technologies, including market recognition, application fields exploiting, developing of billets (slurries) preparation technologies with low cost and special equipments. The prospect of semi-solid forming development path in China is presented. And we hope that application of SSP has great new breakthrough and development and China will be changed from a large metal processing country to a powerful metal processing country.

Superior in vitro biological response and mechanical properties of an implantable nanostructured biomaterial: Nanohydroxyapatite–silicone rubber composite

A potential approach to achieving the objective of favorably modulating the biological response of implantable biopolymers combined with good mechanical properties is to consider compounding the biopolymer with a bioactive nanocrystalline ceramic biomimetic material with high surface area. The processing of silicone rubber (SR)–nanohydroxyapatite (nHA) composite involved uniform dispersion of nHA via shear mixing and ultrasonication, followed by compounding at sub-ambient temperature, and high-pressure solidification when the final curing reaction occurs. The high-pressure solidification approach enabled the elastomer to retain the high elongation of SR even in the presence of the reinforcement material, nHA. The biological response of the nanostructured composite in terms of initial cell attachment, cell viability and proliferation was consistently greater on SR–5 wt.% nHA composite surface compared to pure SR. Furthermore, in the nanocomposite, cell spreading, morphology and density were distinctly different from that of pure SR. Pre-osteoblasts grown on SR–nHA were well spread, flat, large in size with a rough cell surface, and appeared as a group. In contrast, these features were less pronounced in SR (e.g. smooth cell surface, not well spread). Interestingly, an immunofluorescence study illustrated distinct fibronectin expression level, and stronger vinculin focal adhesion contacts associated with abundant actin stress fibers in pre-osteoblasts grown on the nanocomposite compared to SR, implying enhanced cell–substrate interaction. This finding was consistent with the total protein content and SDS–PAGE analysis. The study leads us to believe that further increase in nHA content in the SR matrix beyond 5 wt.% will encourage even greater cellular response. The integration of cellular and molecular biology with materials science and engineering described herein provides a direction for the development of a new generation of nanostructured materials.

Mechanical Analysis of Semi-Solid Metals Shear Deformation during Compression

Rheological behavior of semi-solid metals during isothermal compression is the most basic forming way for semi-solid die forging. In this paper, based on the metal plastic deformation and high pressure solidification theory, the shear deformation mechanisms of semi-solid metals were analyzed during isothermal compression. Experimental observations and theoretical analyses for AZ91D and composite Al/Al2O3 in the semi-solid state were performed with thermal simulation tests. The results for theoretical analyses and experimental observations show that the shear deformation of semi-solid metals has been realized by metal inhomogeneous flowing from macroscopic view and by grain boundary inhomogeneous migrating from microscopic view respectively during compression.

Effect of applied pressure during solidification on the microstructural refinement in an AlCu alloy

The solidification microstructure can be refined by increasing the cooling rate during solidification. Applying high pressure during solidification can promote the solidification rate by increasing the heat transfer coefficient at the metal/mold interface and changing thermodynamic properties such as solid-liquid transition temperature. Based upon these advantages of high pressure solidification, various investigators have reported substantial refinement of microstructures and improvement of mechanical properties. However, the cooling rate and the degree of the microstructural refinement have not been reported consistently. The purpose of the present study is to investigate the effects of pressure up to 1.7GPa during solidification of an hypoeutectic Al-Cu alloy. Experimental observation of the microstructural refinement in high pressure solidified Al-5.4wt%Cu was compared with the mathematical simulation of the heat transfer behavior during high pressure solidification.

Transient, high-pressure solidification associated with cavitation in water.

The very high pressures (≳1 GPa) that occur during the final stages of collapse of a cavitation bubble force the water in the vicinity of the bubble wall briefly (∼1 ns) into a metastable state of subcooling, relative to the equilibrium phase diagram. Estimates show that the subcooling can fall below the critical temperature for homogeneous nucleation of freezing and that high‐pressure ice particles form at a sufficient rate to affect the collapse. Because of the greater density of high‐pressure ice, a sudden drop in pressure occurs that triggers a shock wave that converges at the center of the compressed gas in the bubble. Such microshocks are believed to be the cause of the extremely short duration of the flashes of sonoluminescence (<50 ps) that have been observed from single cavitation bubbles. The occurrence of transient, high‐pressure solidification can explain different phenomena associated with cavitation, specifically the decrease in cavitation erosion and the increase in sonoluminescence as the ...

Transient, high-pressure solidification associated with cavitation in water

The very high pressures (≳1 GPa) that occur during the final stages of collapse of a cavitation bubble force the water in the vicinity of the bubble wall briefly (∼1 ns) into a metastable state of subcooling, relative to the equilibrium phase diagram. Estimates show that the subcooling can fall below the critical temperature for homogeneous nucleation of freezing and that high-pressure ice particles form at a sufficient rate to affect the collapse. Because of the greater density of high-pressure ice, a sudden drop in pressure occurs that triggers a shock wave that converges at the center of the compressed gas in the bubble. Such microshocks are believed to be the cause of the extremely short duration of the flashes of sonoluminescence (&amp;lt;50 ps) that have been observed from single cavitation bubbles. The occurrence of transient, high-pressure solidification can explain different phenomena associated with cavitation, specifically the decrease in cavitation erosion and the increase in sonoluminescence as the overall water temperature approaches 0 °C, together with the nucleation of freezing by cavitation in subcooled liquids. A single explanation for such diverse effects provides strong support for the solidification hypothesis.

55 T long pulse magnet reinforced by ice and woven-glass cloths

A simple method of constructing a multilayer wire-wound pulse magnet was developed by using ice with woven-glass cloth as a reinforcement spacer. Employing strong copper-wire embedded with Nb-Ti filaments, magnetic fields up to 58 T were generated within an 18 mm bore-diameter with a pulse duration of about 8 ms. Even with soft copper-wire, magnetic fields of over 45 T were produced. The advantages of this method are: easy construction of the magnet, without any troublesome processes such as epoxy impregnation or high-pressure solidification; fast cooling time after a large current discharge; recovery from fatigued insulation after multiple use by a process of warming up the magnet once to room temperature and cooling it again to liquid nitrogen temperature, forming a new ice binder for the woven-glass fibre.

Fatigue strength of aluminum and aluminum alloys

The effect of high pressure solidification on the fatigue strength of cast aluminum and aluminum alloys was studied.(1) The fatigue limit of pure aluminum is hardly influenced by high pressure solidification.(2) High pressure casting of an eutectic Al-Si alloy (JIS AC3A and AC4C)(3) The fatigue limit of an Al-Cu alloy (AC1A), T-6 treated, is increased by approximately 10% by casting under high pressure.(4) High pressure casting produces an increase of the fatigue limit of an Al-Mg alloy (AC7A), although the pressure larger than 2, 000kg/cm2 has an inverse effect caused by pronounced segregation.