High Pressure Solidification Research Articles

Optimization of mechanical, corrosion properties and cytotoxicity of biodegradable Zn-Mn alloys by synergy of high-pressure solidification and cold rolling process

Zinc (Zn) and Zn-based alloys are biodegradable materials, that have recently gained significant research attention due to their moderate degradation rate and good biocompatibility. However, their clinical applications are limited by their inferior mechanical properties. In this study, Zn-0.5Mn, Zn-1.0Mn, and Zn-1.5Mn (wt%) alloys were prepared via high-pressure solidification (HPS) and cold rolling (CR) procedures. Further, the microstructure, mechanical properties, corrosion behavior, and in-vitro cytotoxicity of these Zn-Mn alloys were systematically investigated. The results revealed that their yield strength (σys) and ultimate tensile strength (σUTS) enhanced significantly after synergy of HPS-CR treatment compared to CR alone. Notably, among these alloys, the Zn-1.5Mn alloy exhibited the highest σys and σUTS after HPS-CR, at 296.4±5.4 MPa and 322.6±3.5 MPa, respectively. The primary reason for this phenomenon is attributed to the combination of grain refinement and solid solution strengthening performance. Furthermore, these newly designed biodegradable Zn-Mn alloys exhibited appropriate in-vitro degradation rates and acceptable in vitro cytocompatibility when tested in Hanks' solution.

Liquid to solid phase transition detection by using a vibrating tube densimeter along with densities up to 137 MPa of beef tallow fatty acid alkyl esters

Phase behavior and thermophysical properties of biodiesel at high pressure and high temperature are limited in the literature. These are useful to develop models and to understand their behavior having in mind the use of biodiesel in engines. Liquid to solid phase transitions, by using a vibrating tube densimeter, along with densities of three beef tallow fatty acid alkyl esters were studied in this work. Measurements of the oscillating period for each biofuel were carried out in a modular array constituted by two vibrating tube densimeters coupled in series and connected to a single loading cell. The oscillating period was converted to density by the forced path mechanical calibration (FPMC) method. Experimental liquid density sets for three beef tallow biodiesel samples based on fatty acid alkyl esters (FAAEs) are reported for the first time for pressures up to 137 MPa. These biofuels, named fatty acid methyl esters (FAMEs), fatty acid ethyl esters (FAEEs) and fatty acid butyl esters (FABEs), were measured in the temperature range of 286–393 K. The detection procedure for the beginning of the high-pressure solidification was focused on the beef tallow FABEs sample based upon its lower cloud point (CPFABEs = 281.15 K) in comparison with the reported property for the other esters (CPFAEEs = 289.15 K, CPFAMEs = 291 K) with the same feedstock; therefore, the conditions for the metastable liquid to solid phase transition associated to the effect of high pressure was detailed for waste beef tallow butyl ester biodiesel by performing step-by-step compressions in the interval of 286.20–298.13 K and with the help of the vibrating tube densimeters. FABEs had the lower density in contrast with FAEEs and FAMEs, this one being the denser biofuel. Modeling of liquid density data was performed by the perturbed-chain statistical associating fluid theory (PC-SAFT) Equation of State and the Tammann-Tait equation with maximum absolute average deviations of 0.15 % and 0.05 %, respectively. Both models were applied for correlating the thermodynamic derived properties of the fluid phase: isobaric thermal expansivity and isothermal compressibility.

Spinodal decomposition, ordering, and precipitation transformation in CoCrFeNiAl HEAs under GPa pressure

Pressure is a critical component of preparation processes regardless of its magnitude, whether it is a few megapascals, such as in metal squeeze casting, or thousands of megapascals, such as in the experimental preparation of amorphous materials, quasicrystals and nanocrystals. Spinodal decomposition and ordering are two common forms of unstable phase transformation in solid solutions. Reasonable regulation of these two transformations can effectively control microstructures and improve properties. Therefore, the study of solid solution instability under the effect of ultrahigh pressure is of great significance for regulating the properties of high-entropy alloys (HEAs). From this perspective, CoCrFeNiAl HEAs were prepared under pressures of ambient pressure, 4 GPa and 7 GPa. Both solid spinodal decomposition and ordering of the BCC structure were detected when CoCrFeNiAl HEAs are solidified at ambient pressure. Nevertheless, after high-pressure solidification, liquid‒liquid phase spinodal decomposition occurred. One phase was rich in (Fe, Cr), and the other phase was rich in (Ni, Al). Both phases experienced solid spinodal decomposition during cooling. Discontinuous precipitates were generated in the (Ni, Al)-rich solid phase, each with a size of approximately 1.4 μm. Furthermore, a graphic thermodynamic model was established to reveal the solidification behavior. After solidification at 7 GPa, the corrosion rate of the alloy decreased by 98.3 %; that is, the high pressure greatly improved the corrosion resistance of the alloy. This improvement was attributed to the influences of high pressures on the dynamics of spinodal decomposition processes.

Development of in-situ Zn–3Cu–10ZnO composite prepared by high-pressure solidification for orthopedic applications

Biodegradable zinc (Zn)-based composites are considered to be the next generation of promising orthopedic implant materials due to their degradability and the multiple functionality of combining metal and ceramic phases. However, its clinical bone-implant application is seriously limited due to their poor interface binding ability and mechanical properties. Herein, we developed the biodegradable in-situ Zn–3Cu–10ZnO composite through powder metallurgy using Zn and copper (Cu) powder combined with hot forging, followed by the high-pressure solidification (HPS) process for bone-implant application. Microstructural characterization showed that the HPS process can densify composite, form a uniform distribution of fine ZnO particle, and increase Cu atom solid solubility in the Zn matrix. Mechanical test revealed that the HPS composite exhibited a high compression performance with a compressive yield strength of 340.8 MPa, an ultimate compressive strength of 514.2 MPa, and a failure strain of ≥70%. The HPS composite exhibited the lowest corrosion rate of 25.8 μm/y and 44.3 μm/y measured by electrochemical corrosion and immersion tests, respectively, among these composites. Moreover, the diluted extracts of HPS composite with a concentration of ent% showed a higher cytocompatibility among these composites and better antimicrobial capability than those of the as-cast pure Zn. Accordingly, the HPS Zn–3Cu–10ZnO composite is expected to be a potential biodegradable material for orthopedic applications.

Microstructural Evolution and Mechanical Properties of SiC/Al-40Si Composites Fabricated by High Pressure Solidification.

The microstructure and mechanical properties of SiC/Al-40Si composites prepared under high pressure were studied. As the pressure increases from 1 atm to 3 GPa, the primary Si phase in the Al-40Si alloy is refined. With increasing pressure, the composition of the eutectic point increases, the solute diffusion coefficient decreases exponentially, and the concentration of Si solute at the front of the solid-liquid interface of the primary Si is low, which contributes to the refining of the primary Si and inhibiting its faceted growth. The bending strength of SiC/Al-40Si composite prepared under 3 GPa was 334 MPa, which was 66% higher compared to the Al-40Si alloy prepared under the same pressure.

Nano-Phase and SiC-Si Spherical Microstructure in SiC/Al-50Si Composites Solidified under High Pressure.

The formation of coarse primary Si is the main scientific challenge faced in the preparation of high-Si Al matrix composites. The SiC/Al-50Si composites are prepared by high pressure solidification, which allows the primary Si to form a SiC-Si spherical microstructure with SiC, while the solubility of Si in Al is increased by high pressure to reduce the proportion of primary Si, thus enhancing the strength of the composites. The results show that the high melt viscosity under high pressure makes the SiC particles almost "fixed" in situ. The SEM analysis shows that the presence of SiC in the growth front of the primary Si will hinder its continued growth and eventually form SiC-Si spherical microstructure. Through aging treatment, a large number of dispersed nanoscale Si phases are precipitated in the α-Al supersaturated solid solution. The TEM analysis shows that a semi-coherent interface is formed between the α-Al matrix and the nanoscale Si precipitates. The three-point bending tests shows that the bending strength of the aged SiC/Al-50Si composites prepared at 3 GPa is 387.6 MPa, which is 18.6% higher than that of the unaged composites.

Enhanced corrosion resistance and hardness of CoCrCuFeNi alloy under high-pressure solidification

This study adopts a high-pressure method to prepare a CoCrCuFeNi high-entropy alloy (HEA). The effects of high pressure on the microstructure, phase composition, hardness, and corrosion resistance of the alloy are studied. The Vickers hardness of the CoCrCuFeNi HEA solidified under ambient pressure and 4 GPa is determined to be 203.4 HV and 822.4 HV, respectively. This presents an approximately three-fold increase in hardness. The nanohardness of the matrix is also increased three-fold, and the value of the intergranular phase is increased by 0.2 times, which is attributed to the precipitation of a finer nano Cu-rich phase and nano Fe–Cr phase under high pressure. A more complete, dense, and uniform CoCrCuFeNi HEA passive film is obtained under high pressure, and the passivation film resistance (Rpass) is increased by 1.3 times. From a polarization curve test, the corrosion rates of the CoCrCuFeNi HEA solidified under ambient pressure and 4 GPa are 0.0209 mm/a and 0.0076 mm/a, respectively. Thus, the corrosion rate is reduced by 64%.

Property manipulation of CoCrFeNiAlCu high-entropy alloy under GPa high pressure

In this study, we investigated the corrosion resistance and mechanical properties of a CoCrFeNiAl0.2Cu0.8 high-entropy alloy (HEA) that was subjected to high-pressure solidification at 4 and 7 GPa. In addition, the mechanism of the effect of Cu segregation regulation on the properties was described. Results indicated that the volume fraction of the Cu-enriched FCC2 phase segregated at the grain boundary decreased from 8.17 % to 5.42 % under high pressure. We also observed that high-pressure solidification can lead to the formation of nano-precipitates in the FCC2 phase with better refinement and distribution uniformity. The reduction in the Cu-enriched FCC2 phase led to a decrease in the corrosion rate by approximately 85.6 % with an increased solidification pressure of 7 GPa, thereby improving corrosion resistance. Finally, we achieved a superior hardness and yield strength combination via fine-scale nano-precipitates and solution strengthening.

High pressure solidification of alloying substitution and promotion of hydrogen storage properties in AB2-type Y-Zr-Ti-Fe based alloys

Metastable phase has great potential in searching hydrogen storage alloys. In this work, high pressure solidification has been successfully used to realize the supersaturation of Ti in YFe2 based C15 Laves phase to obtain a metastable Y0.7Zr0.24Ti0.06Fe2 alloy. The segregation of Ti, Y, Zr and related multi-phase formation were substantially suppressed and the obtained HPS alloy contained a primary C15 phase(C15–1) and a secondary C15 phase(C15–2) with 77.1% and 22.9% of the total content, respectively. Meanwhile, the hydrogen absorption and desorption capacities increased substantially. This study proves that the combination of high-pressure solidification and alloying is a very effective method for exploring new hydrogen storage materials with metastable structure and high performance.

The evolution of microstructure, micromechanical and magnetic properties of FeCoNiAlSi alloys with peritectic structure processed by high-pressure solidification

In this work, we examined the microstructure evolution, as well as the micromechanical and magnetic properties of FeCoNiAlSi high-entropy alloys (HEAs) under high pressure solidification (HPS). According to the results, FeCoNiAlSi alloy solidified at 0.1 MPa (atmospheric pressure) contains three kinds of phases: grain boundary (GB)phases, peritectic phases, and primary phases. As the solidification pressure increases to 7 GPa, the volume fraction of GB phases and peritectic phases decreases, while the volume fraction of primary phase increases by 82.8%. In addition, the Fe of the primary phase increases by 63.6 %, which enhances the ferromagnetism and exchange coupling properties of the alloy. Furthermore, HPS also reduces the magneto-crystal anisotropy of the GB phases and the pinning effect of boundaries on domain movement. Additionally, with the increasing solidification pressure, the FeCoNiAlSi HEAs shows stronger ferromagnetic. When solidified at 7Gpa, a reduction of 51.5 % in intrinsic coercivity(H MC ) was observed, as was an increase of 106 % in magnetic polarization strength (Js). As well, HPS significantly increased the high temperature magnetic properties of FeCoNiAlSi alloy as well as the microhardness(i.e. from 8.25 GPa to 10.15 GPa). According to these results, HPS is an effective method for developing new functional applications for FeCoNiAlSi HEAs. • The Js (HMC)of the FeCoNiAlSi HEAs increased (decreased) by 106% (51.5%) after HPS at 7Gpa, The Tc are also improved. • The pinning effect of boundary on magnetic domain movement were reduced after HPS and exchange coupling was enhanced. • The volume fraction of primary phase and the content of Fe in primary phase increased when solidified under 7GPa. • The promoted solution strengthening after HPS significantly improved the microhardness (i.e. from 8.25GPa to 10.15GPa).

High-Pressure Solidification of Ternary Al-Ni-Sn Alloy

The microstructure, phase composition and mechanical properties of ternary Al-5.4Ni-2Sn (mass fraction) alloy solidified under different high pressures were researched. The results show that the phase composition of the alloy solidified at different pressures is Al, Al3Ni and β-Sn. The thermodynamic phase diagram of the ternary alloy Al-5.4Ni-2Sn was calculated under the equilibrium condition. The results demonstrate that the solidification process is as follows: L→Al3Ni→(α-Al + Al3Ni)eutectic→(α-Al + Al3Ni + β-Sn)eutectic. The hardness values of α-Al phase at ambient pressure, 2 GPa and 4 GPa are 1.5 GPa, 1.62 GPa and 1.99 GPa, respectively. This is an increase of 8% and 32.7%, respectively. The hardness of β-Sn phase decreases by about 31.2% at 4 GPa. When the deformation is 30%, the compressive strength at ambient pressure, 2 GPa and 4 GPa is 538.1 MPa, 1403.2 MPa and 1547.9 MPa, respectively. The compressive strength under high pressure increased by 160.85% and 187.7%, respectively.

Microstructure control and strengthening mechanism of fine-grained cast Mg alloys based on grain boundary segregation of Al solute

Mg-xAl alloys (x = 3–12 wt%) were prepared by high pressure solidification. The microstructure of the alloys was studied using Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD), and the strengthening mechanism was analyzed in combination with the compressive properties of the experimental alloys. Furthermore, the grain boundary segregation of Al solute was investigated by experiments and first-principles calculations. For the Mg-xAl alloys solidified under atmospheric pressure, the microstructure will be a single solid solution when the Al content of the alloy is less than 5 wt%. However, for the Mg-xAl alloys solidified under 4 GPa pressure, the microstructure will always ba e single solid solution when the Al content of the alloy is less than 12 wt%. Moreover, the segregation of Al solute with a high concentration gradient can be observed at plenty of grain boundaries (area fraction is as high as 46%), because α-Mg dendrites are significantly refined under high pressure. In addition, many Al atoms are dissolved in the α-Mg matrix owing to high pressure. On this basis, it is found that grain boundary segregation of Al solute can decrease the grain boundary energy, and increase the bonding strength of grain boundaries. As a result, the Mg–Al alloys solidified under high pressure have superior compression properties. The compression strength of the Mg–9%Al alloy and the Mg–12%Al alloy solidified under 4 GPa is as high as 458 MPa and 490 MPa respectively, the alloys retain superior plasticity simultaneously.

The evolution of microstructure, micromechanical and magnetic properties of FeCoNiSi alloys solidified under high pressure

A comprehensive study has been conducted on the effects of high-pressure solidification (HPS) on the evolution of microstructures, micromechanical properties, and magnetic properties of FeCoNiSi alloys. As solidification pressure increases(up to 7GPa), FeCoNiSi alloy's columnar grain changes into an equiaxed grain, and the grain size and Ni-rich precipitates are significantly refined. Furthermore, HPS facilitates the conversion of in-coherent matrix/precipitates interface of alloy solidified under atmospheric pressure into semi-coherent, which reduces the pinning effect of phase boundaries on the motion of the magnetic domains and enhances the exchange coupling between matrix and precipitates. As FeCoNiSi alloy solidifying under 7GPa, the maximum magnetic permeability (μ m ) is significantly increased (from 52,600 to 113,000), the inherent coercivity is decreased by 29.5%, and the saturation magnetic polarization( Js ) is increased by 21%. In addition, the high temperature magnetic properties of FeCoNiSi alloys are improved by HPS. Furthermore, HPS produces compressive stress in both the precipitates and matrix, which significantly improved the modulus of precipitates and matrix (i.e. from 171GPa to 215 GPa in matrix),as well as microhardness (i.e. from 5.46 GPa to 10.65 GPa in matrix). Based on the results of these studies, HPS is capable to improve the comprehensive properties of magnetic alloys significantly. • The J s and μ max (H MC ) of FeCoNiSi alloy are increased (decreased) by 21% and 114% (29.5%) after solidified under 7GPa. • HPS produces compressive stress in the precipitates and matrix and significantly improved the modulus and microhardness. • HPS refine the microstructure of FeCoNSi alloy and result in the semi-coherent interface. • The semi-coherent interface enhances the exchange coupling effect between precipitates and matrix.

Critical structural invariant during high-pressure solidification of copper

Critical structural invariant during high-pressure solidification of copper

Microstructure and magnetic behaviors of FeCoNi (Al) alloys with incoherent nanoprecipitates prepared by high-pressure solidification

In this work, we investigated the microstructure and magnetic properties of FeCoNi (Al) high-entropy alloys (HEAs) prepared by high-pressure solidification (HPS). The results show that incoherent nanoprecipitates distributed in uniaxial grain uniformly, which significantly reduces the average magnetic anisotropy of the alloys. The maximum permeability (μm) of alloys increased prominently (i.e. from 47800 to 169000 in FeCoNi alloy and 78000–205000 in FeCoNiAl alloy) and the intrinsic coercivity decreased by 43% in FeCoNiAl alloy after HPS. Nanoprecipitates were related with the double sluggish diffusion effect (DSDE), which is caused by the coupling of high-entropy and high-pressure during solidification process. DSDE not only ensures the retention of short-range ordering (SRO) structures in the liquid metal, but also inhibits the SRO structures’ growth during the solidification process. These SRO structures provide structural conditions to the nanoprecipitates. The molecular dynamics simulation results provide support to the crucial role of DSDE on short-range ordering structures. HPS can effectively reduce the volume fraction of grain boundary precipitates also due to DSDE. Thus, DSDE exhibited the great significance to understand the microstructure of FeCoNi (Al) HEAs by HPS. The perspective also provides a paradigm to enhance the magnetic property of soft magnetic alloys significantly.

In situ formation of SiC in Al–40Si alloy during high-pressure solidification

The in situ formation of SiC in Al–40Si alloys during the fabrication of SiC/Al–Si composites by high-pressure solidification were investigated. The results demonstrate that the in situ formation of SiC occurs by a gradual conversion of Al4C3 and Al4SiC4 to SiC. In situ SiC can be formed in an Al–40Si alloy solidified under a pressure of 3 GPa at a temperature of 1373 K. The SiC particles (SiCp) formed in situ was compatible with the α-Al matrix and the Si phases. The relative density of the SiC/Al-38.6Si composite was 99.9%. The bending strengths of the Al–40Si alloy and the SiC/Al-38.6Si composite obtained by solidification under a pressure of 3 GPa were 200.8 MPa and 322 MPa, respectively, which represents an enhancement of 60.3% as a result of reinforcement by the in situ-formed SiC.

Evolution of Primary and Eutectic Si Phase and Mechanical Properties of Al2O3/Al-20Si Composites under High Pressure

To further improve the mechanical properties of Al-Si alloys. The phase, microstructure and mechanical properties of Al2O3/Al-20Si composites under different pressures were studied. The results show that the phase of Al2O3/Al-20Si composites are composed of α-Al phase, β-Si phase and Al2O3. Under the condition of hot-pressing sintering (0.02 GPa), a large number of Si phases with irregular shape and sharp angle are distributed on the α-Al matrix. Under high pressure solidification, the growth of primary Si phase is inhibited and the eutectic Si is spheroidized obviously. The microhardness of Al2O3/Al-20Si composite increases from 102.5 HV0.05 at 0.02 GPa to 156.4 HV0.05 at 4 GPa, which increases by 52.6%. The compressive strength increased from 381.5 MPa at 0.02 GPa to 469.1 MPa at 4 GPa, increasing by 23%. With the increase of solidification pressure, the fracture mechanism changes from cleavage fracture to quasi cleavage fracture.

Biodegradable Zn−3Mg−0.7Mg2Si composite fabricated by high-pressure solidification for bone implant applications

Zinc (Zn)-based alloys have been considered potential biodegradable materials for medical applications due to their good biodegradability and biocompatibility. However, the insufficient mechanical properties of pure Zn do not meet the requirements of biodegradable implants. In this study, we have developed a biodegradable Zn−3Mg−0.7Mg2Si composite fabricated by high-pressure solidification. Microstructural characterization revealed that the high-pressure solidified (HPS) composite exhibited uniformly distributed fine MgZn2 granules in an α-Zn matrix. Comprehensive tests indicated that the HPS composite exhibited exceptionally high compression properties including a compressive yield strength of 406.2 MPa, an ultimate compressive strength of 1181.2 MPa, and plastic deformation up to 60% strain without cracking or fracturing. Potentiodynamic polarization tests revealed that the HPS composite showed a corrosion potential of −0.930 V, a corrosion current density of 3.5 μA/cm2, and a corrosion rate of 46.2 μm/y. Immersion tests revealed that the degradation rate of the HPS composite after immersion in Hanks’ solution for 1 month and 3 months was 42.8 μm/y and 37.8 μm/y, respectively. Furthermore, an extract of the HPS composite exhibited good cytocompatibility compared with as-cast (AC) pure Zn and an AC composite at a concentration of ≤25%. These results suggest that the HPS Zn−3Mg−0.7Mg2Si composite can be anticipated as a promising biodegradable material for orthopedic applications.

Interconnected SiC–Si network reinforced Al–20Si composites fabricated by high pressure solidification

The microstructures and mechanical properties of the interconnected SiC–Si network reinforced Al–20Si composites solidified under high pressures were investigated. The results demonstrate that the complete interconnected SiC–Si network can be obtained by high pressure solidification, and the connected micron-sized pores are uniformly distributed in the interconnected SiC–Si network. The compressive strength and microhardness of the SiC/Al–20Si composites solidified under 3 GPa were 723 MPa and 229 HV0.05, respectively. Furthermore, the fracture process of SiC/Al–20Si composites was studied by in situ TEM tensile testing. The result shows that the crack first initiated and propagated at the Al/Si interface under an external load, and the SiC particles in the interconnected SiC–Si network can effectively hinder the crack propagation, thus enhancing the strength.

Microstructure and Nanohardness of Ti-48Al-2Cr Alloy Solidified under High Pressure

In this work, the Ti-48Al-2Cr alloy, solidified under different pressures and temperatures, was investigated in detail. The effect of high pressure on the microstructure and nanohardness of the Ti-48Al-2Cr alloy was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and a nanoindenter XP testing machine. The results showed that the B2 phase disappeared after high-pressure solidification. Compared with ambient pressure solidification, high pressure led to the increase of (α2 + γ) lamellar structure and the decrease of γ phase. The nanohardness of the lamellar structure was discussed based on the microstructure observation. When solidified at 5 GPa/1873 K, the hardness rose to 5.54 GPa, an increase of 60.5% compared with that solidified at ambient pressure. However, the increased holding temperature of 1973 K made the dislocation density in the lamellar structures greatly decrease, and reduced the structure’s hardness to 4.48 GPa.