High-performance hot-warm rolled Zn-0.8Li alloy with nano-sized metastable precipitates and sub-micron grains for biodegradable stents

Fabricated through a newly developed hot-warm rolling process,Zn-0.8 Li(wt%) alloy has ideal strength and ductility far beyond the mechanical benchmark of materials for biodegradable stents.Precipitation of needle-like Zn in primary p-LiZn_4 phase is observed in Zn-Li alloy for the first time.Orientation relationship between them can be described as [1-213]_β//[2-1-10]_(Zn),(10-10)_β about 4.5° from(0002)_(Zn).Zn grains with an average size of 640 nm exhibit strong basal texture,detected by transmission electron back-scatter diffraction.Li distribution is determined by three-dimensional atom probe,which reveals the formation of nano-sized metastable α-Li_2Zn_3 precipitates with a number density of 7.16 x 10~(22) m~(-3).The fine lamellar Zn+β-LiZn_4 structure,sub-micron grains and the nano-sized precipitates contribute to the superior mechanical properties.     

Influence of size and distribution of W phase on strength and ductility of high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca alloy processed by indirect extrusion

A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca(wt%) alloy containing W phase(Mg_3Y_2Zn_3) prepared by permanent mold direct-chill casting is indirectly extruded at 350?C and 400?C, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized(DRXed) grains and unrecrystallized coarse regions containing fine W phase and β2' precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350?C exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400?C shows lower yield strength of 332 MPa,ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400?C, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the un DRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of un DRXed regions which contributes to higher strength of the alloy extruded at 350?C.     

Development of extruded Mg-6Er-3Y-1.5Zn-0.4Mn (wt.%) alloy with high strength at elevated temperature

A new Mg-6Er-3Y-1.5Zn-0.4 Mn (wt.%) alloy with high strength at high temperature was designed and extruded at 350 °C. The as-extruded alloy exhibits ultimate tensile strength of 301 MPa, yield strength (along ED) of 274 MPa and thermal conductivity of 73 W/m⋅K at 300 °C. Such outstanding high-temperature strength is mainly attributed to the formation of nano-spaced solute-segregated basal plane stacking faults (SFs) with a large aspect ratio throughout the entire Mg matrix, fine dynamically recrystallized (DRXed) grains of 1–2 μm and strongly textured un-DRXed grains with numerous sub-structures. Microstructural examination unveils that long period stacking ordered (LPSO) phases are formed in Mg matrix of the as-cast alloy when rational design of alloy composition was employed, i.e. (Er + Y): Zn = 3: 1 and Er: Y = 1: 1 (at.%). It is worth mentioning that it is the first report regarding the formation of nano-spaced basal plane SFs throughout both DRXed and un-DRXed grains in as-extruded alloy with well-designed compositions and processing parameters. The results provide new opportunities to the development of deformed Mg alloys with satisfactory mechanical performance for high-temperature services.     

Origins of high ductility exhibited by an extruded magnesium alloy Mg-1.8Zn-0.2Ca:Experiments and crystal plasticity modeling

Low ductility and strength are major bottlenecks against Mg alloys'wide applications.In this work,we systematically design the composition and fabrication process for a low-alloyed Mg-Zn-Ca alloy,showing that it can be extruded at low temperatures(～250℃)and high speeds(～2 mm/s).After the extrusion,this alloy exhibits a substantially weakened basal texture,relatively small grain size,very high tensile elongation(～30％),and good strength.The origin of the considerably improved ductility was studied using a combination of three-dimensional atom probe tomography(3D-APT),transmission electron microscopy(TEM),electron backscattered diffraction(EBSD)in conjunction with surface slip trace analysis,in-situ synchrotron X-ray diffraction,and elasto-plastic self-consistent(EPSC)modeling.Co-segregation of Zn and Ca atoms at a grain boundary is observed and associated with texture weakening and grain boundary mediated plasticity,both improving the ductility.While basal slip and prismatic slip are identified as the dominant deformation systems in the alloy,the ratio between their slip resistances is substantially reduced relative to pure Mg and most other Mg alloys,significantly contributing to the improved ductility of the alloy.This Mg-Zn-Ca alloy exhibiting excellent mechanical properties and low fabrication cost is a promising candidate for industrial productions.     

Role of macropore size in the mechanical properties and in vitro degradation of porous calcium phosphate cements

The goal of the present study was to investigate the effect of macropore size on the compressive strength and in vitro degradation of porous calcium phosphate cements (CPCs). For this purpose, a series of porous CPCs with three different macropore sizes (200-300 μm, 300-450 μm and 450-600 μm) and comparable porosity were prepared by salting-out method, and the study of in vitro degradation behavior was carried out under a constant fluid flow environment. The results showed that the increase in macropore size of CPCs with invariant porosity resulted in a decrease in the compressive strength but an increase in the degradation rate of CPCs significantly, suggesting the possibility that the degradation rate and compressive strength of biomaterials can be regulated by varying the macropore size while maintaining the porosity unchanged.     

Characteristics and in vitro biological assessment of (Ti, O, N)/Ti composite coating formed on NiTi shape memory alloy

In this investigation, plasma immersion ion implantation and deposition (PIIID) was used to fabricate a (Ti, O, N)/Ti coating on NiTi shape memory alloy (SMA) to improve its long-term biocompatibility and wear resistance. The surface morphology, composition and roughness of uncoated and coated NiTi SMA samples were examined. Energy dispersive X-ray elemental mapping of cross-sections of (Ti, O, N)/Ti coated NiTi SMA revealed that Ni was depleted from the surface of coated samples. No Ni was detected by X-ray photoelectron spectroscopy on the surface of coated samples. Furthermore, three-point bending tests showed that the composite coating could undergo large deformation without cracking or delamination. After 1 day cell culture, SaOS-2 cells on coated samples spread better than those on uncoated NiTi SMA samples. The proliferation of SaOS-2 cells on coated samples was significantly higher at day 3 and day 7 of cell culture.     

Effect of forced-air cooling on the microstructure and age-hardening response of extruded Mg-Gd-Y-Zn-Zr alloy full with LPSO lamella

The homogenized Mg-8.2Gd-3.8Y-1.0Zn-0.4 Zr (wt.％) alloy full of plate-shaped long period stacking ordered (LPSO) phases was hot extruded in the atmosphere and cooled by the forced-air,then the effect of forced-air cooling on the microstructure and age-hardening response of the alloy was investigated in this work.The results show that in comparison with the extruded sample cooling in the atmosphere,the forced-air cooling restricts dynamic recrystallization (DRX) and brings about finer dynamic recrystallized (DRXed) grain size,stronger basal texture and higher dislocation density.Furthermore,the forced-air cooling promotes the dynamic precipitation in the DRXed regions and facilitates formation of plate-shaped LPSO phases and γ'phases with smaller interspacing in the unrecrystallized (unDRXed) regions,then slightly restricts the precipitation of β'phases during aging.After peak-ageing treatment,the extruded sample with forced-air cooling shows superior tensile properties with a tensile yield strength of 439 MPa,an ultimate tensile strength of 493 MPa,and elongation to failure of 18.6 ％.     

PET in situ composites improved both flame retardancy and mechanical properties by phosphorus-containing thermotropic liquid crystalline copolyester with aromatic ether moiety

A novel phosphorus-containing thermotropic liquid crystalline copolyester with aromatic ether moiety (TLCP-AE) was used to prepare the in situ composites of poly(ethylene terephthalate) (PET)/liquid crystalline polymer. The morphological structure and properties of PET/TLCP-AE in situ composites were investigated using scanning electron microscopy (SEM), capillary rheometer, tensile tests, limiting oxygen index tests (LOI), cone calorimeter and thermogravimetric analysis (TGA). The rheological measurements show that the viscosity ratio of TLCP-AE to PET at 260 °C is less than 1, which meets a precondition for TLCP-AE to form fibrils in PET matrix during processing. The mechanical, LOI and cone tests prove that TLCP-AE can improve the mechanical properties and flame retardancy of PET synchronously. Moreover, TGA results exhibit that the initial decomposition temperatures and the final residues of PET/TLCP-AE composites increase with increasing TLCP-AE content.     

In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering

Fe alloy composites reinforced with in-situ titanium carbide(Ti C) particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8,0.9,1 and 1.1 to investigate the microstructure and mechanical properties of in-situ Ti C/Fe alloy composites.The microstructure showed that the in-situ synthesized Ti C particles were spherical with a size of 1–3 μm,irrespective of C/Ti ratio.The stoichiometry of in-situ Ti C increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9,but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in Ti Cxat the common sintering temperature.The in-situ Ti C/Fe alloy composite with C/Ti = 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon(C/Ti = 1 and 1.1) resulted in unreacted carbon within the Fe alloy matrix,while insufficient carbon(C/Ti = 0.8)caused the depletion of carbon from the Fe alloy matrix,leading to a significant decrease in hardness.This study presents that the maximized hardness and superior strength of in-situ Ti C/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized Ti C particles,while maintaining the ductility of the composites,compared to those of the unreinforced Fe alloy.Therefore,we anticipate that the in-situ synthesized Ti C/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool,mold and roller material applications.     

In situ polymerized nanocomposites: Polystyrene/CNT and Poly(methyl methacrylate)/CNT composites

Carbon nanotubes (CNTs) were incorporated into polystyrene (PS) and poly(methyl methacrylate) (PMMA) matrices via in situ emulsion and emulsion/suspension polymerization methods. The polymerizations were carried out using various initiators, surfactants, and carbon nanotubes to determine their influence on polymerization and on the properties of the composites. The loading of CNTs in the composites varied from 0 to 15 wt.%, depending on the CNTs used. Morphology and dispersion of the CNTs were analyzed by transmission and scanning electron microscopy techniques. The dispersion of multi-walled carbon nanotubes (MWCNT) in the composites was excellent, even at high CNT loading. The mechanical properties, and electrical and thermal conductivities, of the composites were also analyzed. Both electrical and thermal conductivities were improved.     

Material processing of hydroxyapatite and titanium alloy (HA/Ti) composite as implant materials using powder metallurgy: A review

The bio-active and biodegradable properties of hydroxyapatite (HA) make this material a preferred candidate for implants such as bone replacement in replacing natural tissues damaged by diseases and accidents. However, the low mechanical strength of HA hinders its application. Combining HA with a biocompatible material with a higher mechanical strength, such as a titanium (Ti) alloy, to form a composite has been of interest to researchers. A HA/Ti composite would possess characteristics essential to modern implant materials, such as bio-inertness, a low Young’s modulus, and high biocompatibility. However, there are issues in the material processing, such as the rheological behavior, stress-shielding, diffusion mechanism and compatibility between the two phases. This paper reviews the HA and Ti alloy interactions under various conditions, in vitro and in vivo tests for HA/Ti composites, and common powder metallurgy processes for HA/Ti composites (e.g., pressing and sintering, isostatic pressing, plasma spraying, and metal injection molding).     

Preparation and characterization of novel gelatin/cerium (III) fiber with antibacterial activity

Gelatin/Cerium (III) fibers with high tensile strength and good antibacterial activity were prepared by wet spinning method. The fiber structure and properties were investigated. The optical microscope (OPM) results showed that the fiber had a smooth surface and the fiber diameter was in the range of 60-90 µm. The mechanical properties tests showed that the tensile strength of gelatin/cerium (III) fibers increased greatly compared with the pure gelatin fibers. Furthermore, it was found that the gelatin/Ce (III) fibers have the antibacterial activity for Escherichia coli and Staphylococcus aureus.     

New glass fiber/bismaleimide composites with significantly improved flame retardancy,higher mechanical strength and lower dielectric loss

Novel glass fiber (GF)/bismaleimide composites with significantly improved flame retardancy, higher mechanical strength and lower dielectric loss were developed, of which the resin matrix is a new flame retarding resin system (BDDP) based on 4,4′-bismaleimidodiphenyl methane (BDM), 2,2′-diallyl bisphenol A (DBA) and [(6-oxido-6H-dibenz [c,e] [1,2] oxaphosphorin-6-yl)-methyl]-butanedioic acid (DDP). The influence of the loading of DDP in the matrix on the integrated performances of composites was intensively studied. Results show that GF/BDDP composites not only have significantly improved mechanical and dielectric properties, but also possess excellent flame retardancy. The main flame retarding mechanism of GF/BDDP composites is the condensed phase mechanism. The introduction of DDP significantly strengthens the interfacial adhesion between GF and the resin matrix, this is responsible for the attractive performances of GF/BDDP composites.     

Biocomposites from Musa textilis and polypropylene: Evaluation of flexural properties and impact strength

Abaca (Musa textilis)-reinforced polypropylene composites have been prepared and their flexural mechanical properties studied. Due to their characteristic properties, M. textilis has a great economic importance and its fibers are used for specialty papers. Due to its high price and despite possessing very distinctive mechanical properties, to date abaca fibers had not been tested in fiber-reinforced composites. Analysis of materials prepared showed that, in spite of reduced interface adhesion, flexural properties of the PP composites increased linearly with fiber content up to 50 wt.%. Addition of a maleated polypropylene coupling agent still enhanced the stress transfer from the matrix to the reinforcement fiber. As a result, composites with improved flexural properties were obtained. The mechanical properties of matrix and reinforcing fiber were evaluated and used for modelling both the flexural strength and modulus of its composites. In addition, the impact strength of materials was evaluated. Comparison with mechanical properties of composites reinforced with fiberglass points out the potentiality of abaca-reinforced polypropylene composites as suitable substitutes in applications with low impact strength demands.     

Microstructure effect on mechanical properties of in situ synthesized titanium matrix composites reinforced with TiB and La2O3

High temperature titanium matrix composites (TMCs) with different volume fraction of reinforcements were insitu synthesized by casting and hot forging. An effort was made to investigate the mechanical properties as a function of the microstructure of composites. Tensile tests were performed at room temperature, 600 °C, 650 °C and 700 °C respectively. Creep behavior at 650 °C was characterized in the stress range of 200-300 MPa. Results indicated that the composite with 2.11 vol.% reinforcements had the highest tensile strength and lowest steady state creep rate. Morphology of TiB whiskers was critical to mechanical properties of TMCs. TiB whiskers fracture and debonding acted as the dominant failure modes.     

Bending strength of silica gel with bimodal pores: II. Effect of variations in morphology and porosity

The bending strength of amorphous silica gels with bimodal pore structure was evaluated by changing macropore morphology and porosity, where the macropore morphology was controlled by inducing phase separation during gelation of silicate solution and the porosity was controlled by changing aging conditions and calcination temperature. At the same porosity, the bending strength was decreased for gels with larger macropores. In this preparation of bimodal porous silica gels, however, samples with large macropores also had many small particles in the macropores. Therefore, the decrease in bending strength with increasing macropore size was attributed to the presence of the particles that contributed to increasing bulk density but not bending strength. A power law applies to the bending strength and the bulk density of gels with the same macropore morphology, where the exponent depends on the morphology.