Interconnected microstructure and flexural behavior of Ti_(2)C-Ti composites with superior Young’s modulus

To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ reaction yielded an interconnected microstructure composed of Ti_(2)C particles when the Ti_(2)C content reached 50vol%.With widths of 10 and 230 nm,the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti_(2)C particles.The composites with interconnected microstructure attained superior properties,including E of 174.3 GPa and ultimate flexural strength of 1014 GPa.Compared with that of pure Ti,the E of the composite was increased by 55% due to the high Ti_(2)C content and interconnected microstructure.The outstanding strength resulted from the strong interfacial bonding,load-bearing capacity of interconnected Ti_(2)C particles,and bimodal intraparticle Ti lamellae,which minimized the average crack driving force.Interrupted flexural tests revealed preferential crack initiation along the{001}cleavage plane and grain boundary of Ti_(2)C in the region with the highest tensile stress.In addition,the propagation can be efficiently inhibited by interparticle Ti grains,which prevented the brittle fracture of the composites.

Microstructural characterization and mechanical properties of(TiC+TiB)/TA15 composites prepared by an in-situ synthesis method

Titanium matrix composites reinforced with ceramic particles are considered a promising engineering material due to their combination of high specific strength,low density,and high modulus.In this study,the TA15-based composites reinforced with a volume fraction of 10% to 25%(TiB+TiC)were prepared using powder metallurgy and casting technique.Microstructural characterization and phase constitution were examined using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray diffraction(XRD).In addition,the microhardness,room temperature(RT)and high temperature(HT)tensile properties of the composites were evaluated.Results revealed that the reinforcements are distributed uniformly even in the composites with a high volume of TiB and TiC.However,as the volume fraction exceeds 15%,TiB and TiC particles become coarsening and exhibit rod-like and dendritic-like morphology.Microhardness increases gradually from 321.2 HV for the base alloy to a maximum of 473.3 HV as the reinforcement increases to 25vol.%.Tensile test results indicate that a reinforcement volume fraction above 20% is beneficial for enhancing tensile strength and yield strength at high temperatures,but it has an adverse effect on room temperature elongation.Conversely,if the reinforcement volume fraction is below 20%,it can improve high-temperature elongation when the temperature exceeds 600℃.

Corrosion behavior of composite coatings containing hydroxyapatite particles on Mg alloys by plasma electrolytic oxidation: A review

Mg and its alloys have been introduced as promising biodegradable materials for biomedical implant applications due to their excellent biocompatibility, mechanical behavior, and biodegradability. However, their susceptibility to rapid corrosion within the body poses a significant challenge and restricts their applications. To overcome this issue, various surface modification techniques have been developed to enhance the corrosion resistance and bioactivity of Mg-based implants. PEO is a potent technique for producing an oxide film on a surface that significantly minimizes the tendency to corrode. However, the inevitable defects due to discharges and poor biological activity during the coating process remain a concern. Therefore, adding suitable particles during the coating process is a suitable solution. Hydroxyapatite(HAp)has attracted much attention in the development of biomedical applications in the scientific community. HAp shows excellent biocompatibility due to its similarity in chemical composition to the mineral portion of bone. Therefore, its combination with Mg-based implants through PEO has shown significant improvements in their corrosion resistance and bioactivity. This review paper provides a comprehensive overview of the recent advances in the preparation, characterization, corrosion behavior and bioactivity applications of HAp particles on Mg-based implants by PEO.

Synthesis of Chitosan-Hydroxyapatite Composites and Its Effect on the Properties of Bioglass Bone Cement

Chitosan-hydroxyapatite （CS-HA） composite powders were synthesized via in situ co-precipitation method, through the reaction of Ca（NO3）2 and H3PO4 in the simulated body fluid （SBF） containing appropri- ate amount of chitosan. The thermal evolution, microstructure and morphology were studied by TG-DTA （thermogravimetry-differential thermal analysis）, XRD （X-ray diffraction）, FTIR （Fourier transform infrared spectroscopy） and TEM （transmission electron microscopy）. The in vitro bioactivity test showed that the obtained CS-HA composites had higher capability of inducing calcium ions deposition. Effects of CS-HA com- posites on the bioactivity and compressive strength of bioglass bone cement were investigated. The results indicated that the bioactivity of bioglass bone cement could be improved further when CS-HA composite pow- ders were added into the cement, and appropriate amount of CS-HA additive was favorable for compressive strength improvement of bioglass bone cement.

Effect of ball milling process on the microstructure of titanium-nanohydroxyapatite composite powder

Titaninm-nanohydroxyapatite （Ti-nHA） composite powders, composed of titanium with 10 vol.% and 20 vol.% of nano-hydroxyapatite, were milled in a planetary ball mill using alcohol media to avoid excessive heat. XRD and SEM were performed for characterization of the microstructure, and the homogeneity of Ti/HA nanocomposite powder was evaluated by EPMA with prolonged ball milling time. The results show that under the condition of wet milling, the grain size of Ti-nHA composite powders is decreased with the increase in ball milling time and the amount of the addition of nHA. While for milling of 30 h, the nanocomposite powder with free structure, which consists of the nano-hydroxyapatite （nHA） particles and titanium （Ti） phase, is obtained. Three stages of milling can be observed from the dement mapping of Ti, Ca, and P by EPMA; meanwhile, it is found that the nHA would be more homogenously distributed after milling for 30 h.

Biotribological behavior of ultra high molecular weight polyethylene composites containing bovine bone hydroxyapatite

Wear particles of ultrahigh molecular weight polyethylene （UHMWPE） are the main cause of long-term failure of total joint replacements. Therefore, increasing its wear resistance or bioactivity will be very useful in order to obtain high quality artificial joints. In our study, UHMWPE composites filled with the bovine bone hydroxyapatite （BHA） were prepared by the method of compression moulding. A ball-on-disc wear test was carried out with a Universal Micro-Tribometer to investigate the friction and wear behavior of a Si3N4 ceramic ball, cross-sliding against the UHMWPE/BHA composites with human plasma lubrication. At the same time, the profiles of the worn grooves on the UHMWPE/BHA surface were scanned. The experimental results indicate that the addition of BHA to UHMWPE had a significant effect on the biotribological behavior of UHMWPE cross-sliding against the Si3N4 ceramic ball. The addition of BHA powder enhanced the hardness and modulus of elasticity of these composites and decreased the friction coefficients and wear rates under conditions of human plasma lubrication. When the added amount of BHA powders was up to 20%-30%, UHMWPE/BHA composites demonstrated the designed performance of the mechanical properties and biotribological behavior.

Osteogenic composite nanocoating based on nanohydroxyapatite, strontium ranelate and polycaprolactone for titanium implants

Titanium and its alloys are commonly used as dental and bone implant materials.Biomimetic coating of titanium surfaces could improve their osteoinductive properties.In this work,we have developed a novel osteogenic composite nanocoating for titanium surfaces,which provides a natural environment for facilitating adhesion,proliferation,and osteogenic differentiation of bone marrow mesenchymal stem cells(MSCs).Electrospinning was used to produce composite nanofiber coatings based on polycaprolactone(PCL),nano-hydroxyapatite(nHAp)and strontium ranelate(SrRan).Thus,four types of coatings,i.e.,PCL,PCL/nHAp,PCL/SrRan,and PCL/nHAp/SrRan,were applied on titanium surfaces.To assess chemical,morphological and biological properties of the developed coatings,EDS,FTIR,XRD,XRF,SEM,AFM,in-vitro cytotoxicity and in-vitro hemocompatibility analyses were performed.Our findings have revealed that the composite nanocoatings were both cytocompatible and hemocompatible;thus PCL/HAp/SrRan composite nanofiber coating led to the highest cell viability.Osteogenic culture of MSCs on the nanocoatings led to the osteogenic differentiation of stem cells,confirmed by alkaline phosphatase activity and mineralization measurements.The findings support the notion that the proposed composite nanocoatings have the potential to promote new bone formation and enhance bone-implant integration.

Electrophoretic deposition of titanium/silicon-substituted hydroxyapatite composite coating and its interaction with bovine serum albumin

Silicon-substituted hydroxyapatite (Ca10(PO4)6-x(SiO4)x(OH)2-x, Si-HA) composite coatings on a bioactive titanium substrate were prepared by electrophoretic deposition technique with the addition of triethanolamine (TEA) to enhance the ionization degree of Si-HA suspension. The surface structure was characterized by XRD, SEM, XRF, EDS and FTIR. The bond strength of the coating was investigated. The results show that the depositing thickness and the images of Si-HA coating can be changed with the variation of deposition time. The XRD spectra of Ti/Si-HA coatings show the characteristic diffraction peaks of HA, and the incorporation of silicon changes the lattice parameter of the crystal. The FTIR spectra shows that the most notable effect of silicon substitution is the decrease of intensities of —OH and PO43- groups with the silicon contents increasing. XRD and EDS element analyses present that the content of silicon in the coating increases with increasing silicon concentration in the suspension. The bioactive TiO2 coating formed may improve the bond strength of the coatings. The interaction of Ti/Si-HA coating with BSA is much greater than that of Ti/HA coating, suggesting that the incorporation of silicon in HA is significant to improve the bioactive performance of HA.

Hydroxyapatite/β-tricalcium Phosphate Composite for Guiding Bone Tissue Growth into a Titanium Tube in 8 mm Dog Tibia Cavity Defects

We developed a fixation method and evaluate bone regrowth in the cavities of a Ф4 mm× 8 mm titanium（Ti）tube through porous hydroxyapatite（HAP）/β-tricalcium phosphate（β-TCP）composite filling（group A）,chitosan/calcium phosphate composite filling（group B）,and HAP particle modification（group C）.After 2 and 5 months of implantation in dog tibia defects,new bone formation in the three groups was studied by histology and histomorphometry.Group A displayed the most bone regenerated area in both 2 and 5 months post-operation.The chitosan/calcium phosphate composite in group B mostly degraded 2 months after implantation,leading to fibrous tissue invasion after 5 months.By contrast,less bone formation was observed in group C.These results indicated that filling the cavities of metalprostheses with a porous HAP/β-TCP composite can be used for stable long-term fixation in clinicalsettings.

Preparation of Hydroxyapatite/Polylactide Bicomposites by Absorption Process in Liquid Phase

The hydroxyapatite/polylactide biocomposites were prepared by absorption process in liquid phase. The method avoided many disadvantages, such as inaterfusion of chemical impurity substances, nonuniformity dispersal of HA in PLA, low molecular weight of PLA . HA particles were uniformly dispersed in PLA matrix, and showed well ndhesion with PLA matrix. The biocomposites have the higher mechanical properties and suitable decomposable capability.

In Vitro Immersion Behavior of Cold Sprayed Hydroxyapatite/Titanium Composite Coatings

In previous study, dense and homogenous 20wt% HAP/Ti composite coatings were successfully deposited on Ti substrates by cold gas dynamic spray technique. The results revealed that the phase composition of the HAP in the deposit is identical to that of the precursor powder and the bonding strength of the deposit is comparable/better to that of the plasma sprayed HAP. A relatively higher corrosion current of HAP/Ti composite than that of pure Ti coating in simulated body fluid indicates a good bioactivity for composite coating. In the present study, in vitro immersion test is carried out for various period of time and the formation of apatite layer on surface of composite coating proves the good bioactivity of the composite coating further. The cold sprayed HAP/Ti composite can be anticipated to be a promising load-bearing implant material for biomedical applications.

Hybrid Composites of Phosphate Glass Fibre/Nano-Hydroxyapatite/Polylactide: Effects of Nano-Hydroxyapatite on Mechanical Properties and Degradation Behaviour

Hydroxyapatite/polylactide (HA/PLA) composites have been intensively investigated for their potential as biodegradable fixation devices to heal bone fractures. However, most of these composites failed to achieve a bone-mimicking level of mechanical properties, which is an essential demand of the targeted application. In this study, the nano-hydroxyapatite/polylactide composites were used as the matrix and continuous phosphate glass fibres (PGF) served as the major reinforcement to obtain the nano-HA/PGF/PLA hybrid composites. While the PGF volume fraction remained constant (25%), the nano-HA content (in weight) varied from 0% to 20%. As nano-HA loading increased, the flexural modulus of the composites increased from 8.70 ± 0.35 GPa to 14.97 ± 1.30 GPa, and the flexural strengths were enhanced from 236.31 ± 10.83 MPa to 310.55 ± 22.88 MPa. However, it is found that the degradation rates are higher with more nano-HA loaded. Enhanced water absorption ability, as well as increased voids in the composites is possible reasons for the accelerated degradation of composites with higher nano-HA loading. The hybrid composites possess mechanical properties that are superior to most of the HA/PLA composites in previous research while maintaining the biodegradability. With a proper loading of nano-HA in composites of 10 weight percent, the composites are also found with improved mechanical properties without catastrophic degradation. The composites developed in this study have great potential as biodegradable bone fixation device with enhanced load-bearing ability as confirmed and superior bioactivity as anticipated.

Hydroxyapatite-Bioglass-Titanium Biomaterials Used as Dense Bulk in Double-layer Biomimetic Composite

Sintering shrinkage, compressive strength, bending strength, chemical composition and their relationships with mi-crostructure of HA-Ti and HA-BG-Ti biomaterials were studied. The results show that sintering shrinkage curve of HA-BG-Ti composite changes just like S shape (23.1%-16.2%-21.8%-17.1%) with increase of Ti content, and sintering shrinkage of HA-BG-Ti composite is always higher than that of HA-Ti composite. The approach also indicates that compressive strength and bending strength of HA-BG-Ti composite are always higher than that of HA-Ti composite. Basically, with its compressive strength and bending strength equaling to 211.5 MPa and 132.1 MPa respectively, HA-10 vol. pct BG-60 vol. pct Ti composite can meet the mechanical properties requirements of the outer dense bulk. Furthermore, microstructure analysis shows that interfacial integration of HA-BG-Ti composite is better than that of HA-Ti composite. From X-ray diffraction (XRD) and SEM-EDAX analysis, brittle new phases including calcium titanate and calcium carbonate are detected in HA-Ti composite. New phases in HA-Ti composite and complex strong binding force accompanied by elemental diffusion of Si, Ti in HA-BG-Ti composite can explain theoretically the great difference of mechanical properties of HA-Ti and HA-BG-Ti composites.

Microstructure and mechanical properties of GTA weldments of titanium matrix composites prepared with or without current pulsing

The effects of current pulsing on the microstructure, hardness and tensile properties at different temperatures of gas tungsten arc （GTA） weldments of titanium matrix composites were studied. Full-penetration butt joints were made with or without current pulsing. Optical microscopy, hardness test and scanning electron microscopy were employed to evaluate the metallurgical characteristics of welded joints. Tensile properties of weldments at different temperatures were studied and correlated with the microstructure. The results exhibit that current pulsing leads to the refinement of the weld microstrucmre and TiB whisker and the redistribution of reinforcements resulting in higher hardness, tensile strength and ductility of weldments in the as-welded condition.

Effect of heat treatment on microstructure,mechanical and tribological properties of in-situ (TiC+TiB)/TC4 composites by casting

To enhance the performance of in-situ synthesized 6vol.%(Ti C+Ti B)/TC4 titanium matrix composites fabricated by casting,a variety of heat treatment processes were carried out.Upon conducting microstructure observations following various heat treatments,it was found that the composites exhibit a basketweave microstructure,consisting of an α phase and a transformed β phase.The sizes of(α+β) phases were found to be refined to varying degrees after the heat treatment processes,while the morphology of Ti B remains largely unchanged and Ti C becomes granulated.Compressive testing revealed that all composites subjected to different heat treatments demonstrate a notable increase in ultimate compressive strength as well as a slight improvement in plasticity compared to the as-cast state.The results of the tribological performance test indicated that the heat-treated composites exhibit lower average friction coefficient,specific wear rate,and worn surface roughness compared to the as-cast composite.Among the heat treatment processes studied,the composite solution heated at 1,150 °C/1 h followed by air cooling,then 950 °C/1 h followed by air cooling,and finally 500 °C/4 h followed by air cooling,demonstrates the highest levels of hardness,compressive strength,and wear resistance.These improvements are attributed to the combined effects of solid solution strengthening,grain refinement,and the pinning of dislocation slip.

Comparative Assessment on Microstructure and Properties of in-situ TiC+Ti_(5)Si_(3)Reinforced TiAl-Sn-Zr Matrix Composites by Spark Plasma Sintering and Argon Protected Sintering

The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium matrix composites were prepared by discharge plasma sintering(SPS)and argon protective sintering(APS).The results show that the two processes have a negligible effect on the composition and hardness of the samples,but the hardness of the two samples is significantly improved by adding SiCp.The apparent porosity of SPS process is obviously smaller than that of APS process,whereas,the apparent porosity increases slightly with the addition of SiCp.The oxide layer thickness and mass gain of the samples obtained by SPS process are smaller than those obtained by APS process.The oxide thickness and mass gain of both processes are further reduced by adding SiCp.The SPS composites showed the best high temperature oxidation resistance.Therefore,TMCs with Si Cp by SPS can effectively improve the high-temperature oxidation behavior of the materials.

Microstructure and formation mechanism of titanium matrix composites coating on Ti-6Al-4V by laser cladding

Laser cladding experiments were done on a 5-kW continuous wave CO2 laser to synthesize TiC and TiB rein- fowed titanium matrix composite coatings on Ti-6AI-4V alloy with a mixture of Ti and B4C precursor powder. The ther- modynamics of the reactions were calculated and analyzed. The microstructure and phase evolution of TiB and TiC com- posites were investigated. The results showed that the chemical reaction between Ti and B4C would release much heat, and these compounds, TiC, TiB, and small amount of TiB2, can be formed on the surface of Ti-6AI-4V alloy if the supplied en- ergy is sufficient to excite the reaction among the initial products. A good metallurgical bond between the coating and the substrate can be achieved. The microhardness of coating was irregular and the maximum value was approximately HV600.

Microstructure and thermal properties of copper matrix composites reinforced with titanium-coated graphite fibers

Milled form of mesophase pitch-based graphite fibers were coated with a titanium layer using chemical vapor deposition technique and Ti-coated graphite fiber/Cu composites were fabricated by hot-pressing sintering. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopies, and by mea- suring thermal properties, including thermal conductivity and coefficient of thermal expansion （CTE）. The results show that the milled fibers are preferentially oriented in a plane perpendicular to the pressing direction, leading to anisotropic thermal properties of the composites. The Ti coating reacted with graphite fiber and formed a continuous and uniform TiC layer. This carbide layer establishes a good metallurgical interracial bonding in the composites, which can improve the thermal properties effectively. When the fiber content ranges from 35 vol% to 50 vol%, the in-plane thermal conductivities of the composites increase from 383 to 407 W.（m.K）-~, and the in-plane CTEs decrease from 9.5 x 10-6 to 6.3 10-6 K-1.

Morphology and Phase Compositions of Hydroxyapatite Powder Particles Plasma-sprayed into Water

Hydroxyapatite powder particles were plasma sprayed into water, their inner structures and phase compositions were studied by using scanning electron microscope(SEM) and X-ray diffractometer. The results show that the molten HA particles have a central hollow morphology and high crystallinity. The hollow morphology was caused by sublimated P2O5 and H2O, which will have an effect on surface morphology, cohesive and adhesive strength as well as dissolution and degradation of coating. The high crystallinity is attributed to lower cooling speed in water.

Preparation and properties of a cerium-containing hydroxyapatite coating on commercially pure titanium by micro-arc oxidation

A porous cerium-containing hydroxyapatite coating on commercially pure titanium was prepared by micro-arc oxidation （MAO） in an electrolytic solution containing calcium acetate, p-glycerol phosphate disodium salt pentahydrate （β-GP）, and cerium nitrate. The thickness, phase, composition morphology, and biocompatibility of the oxide coating were characterized by X-ray diffraction （XRD）, electron probe microanalysis （EPMA）, scanning electron microscopy （SEM） with energy dispersive X-ray spectrometer （EDS）, and cell culture. The thickness of the MAO film is about 15-25 ~tm, and the coating is porous and uneven, without any apparent interface to the titanium substrates. The results of XRD and EDS show that the porous coating is made up of hydroxyapatite （HA） film containing Ce. The favorable osteoblast cell affinity makes the Ce-HA film have a good biocompatibility. The Ce-HA film is expected to have significant medical applications as dental implants and artificial bone joints.