Ti-based Alloys Research Articles

Optimizing mechanical properties and Ag ion release rate of silver coatings deposited on Ti-based high entropy alloys

This paper details the characterization of microstructure, texture, mechanical properties, and ion release behavior of antibacterial Ag thin films sputtered on two novel biomedical high entropy alloys (HEAs), namely the Ti23Ta10Hf27Nb12Zr28 (HEATi23) and Ti28Ta10Hf30Nb14Zr18 (HEATi28) alloys. Specifically, the influences of varying deposition time and Ar flow rate were investigated to reveal the mechanisms dictating the microstructure, texture, and mechanical properties of the coatings. In addition, static immersion experiments were carried out in simulated body fluid (SBF) for 28 days to establish the relationship between ion release from the coatings and the deposition parameters, microstructure, and surface texture. It was shown that texture evolution in Ag thin films depends on both film thickness and Ar flow rate, such that there exists a critical thickness at which the energy minimization mechanism is altered. A very good correlation was also observed between an increase in (111) peak intensity and a decrease in released Ag ion fraction. Overall, the findings of the work presented herein suggest that the alterations in Ag deposition parameters could be optimized to obtain the desired mechanical properties while enhancing the biocompatibility of the HEA substrates by coating them with antibacterial Ag films.

Analysis of tribological behaviors and regulating functions at elevated temperatures of microchannel interfaces prepared in Ti-base alloys.

For improving the tribological behaviors of traditional Ti alloys, high-nickel Ti alloy with sinusoidal micropores was prepared by laser additive manufacturing (LAM). MgAl (MA), MA-graphite (MA-GRa), MA-graphenes (MA-GNs), and MA-carbon nanotubes (MA-CNTs) were respectively filled into the Ti-alloy micropores to prepare interface microchannels through high-temperature infiltration. In a ball-on-disk tribopair system, the tribological and regulating behaviors of the microchannels in Ti-base composites were elucidated. The results showed that the regulation functions of MA were noticeably improved at 420 °C, resulting in their superior tribological behaviors than those at other temperatures. It could be concluded that GRa, GNs, and CNTs combined with MA further enhanced the regulation behaviors compared to individual MA lubrication. The following regulation factors were responsible for the excellent tribological properties: the interlayer separation of graphite, which accelerated the plastic flow of MA, improved the interface crack self-healing of Ti-MA-GRa, and regulated the friction and wear resistance abilities. Compared with GRa, GNs were easier to slide, and helped to produce a greater deformation of MA, facilitating a good self-healing of cracks, and further enhancing the wear regulation of Ti-MA-GNs. CNTs showed good synergism with MA to allow the rolling friction, which effectively repaired the cracks to improve interface self-healing, resulting in a better tribological performance of Ti-MA-CNTs compared to Ti-MA-GRa and Ti-MA-GNs.

Effect of Cu content on the corrosion behavior of Ti-based bulk amorphous alloys in HCl solution

In this study, the effect of Cu content on the corrosion behavior of (Ti36.1Zr33.2Ni5.8Be24.9)100−xCux (x = 5, 7, and 9 at.%) amorphous alloys in an HCl solution was systematically investigated. The results demonstrate that three materials exhibited pitting corrosion in the HCl solution. The stability of the passivation film suffered with an increase in Cu content and the corresponding decrease of the TiO2 content, thus decreasing the pitting potential. Furthermore, the increase in Cu content enhanced the adsorption of Cl− ions on the alloys surface, producing additional sites for pitting. Thus, the number of corrosion pits and the corrosion rate increased. The corrosion resistance of the amorphous alloy was optimal at x = 5.

3D Modeling of the Solidification Structure Evolution and of the Inter Layer/Track Voids Formation in Metallic Alloys Processed by Powder Bed Fusion Additive Manufacturing.

A fully transient discrete-source 3D Additive Manufacturing (AM) process model was coupled with a 3D stochastic solidification structure model to simulate the grain structure evolution quickly and efficiently in metallic alloys processed through Electron Beam Powder Bed Fusion (EBPBF) and Laser Powder Bed Fusion (LPBF) processes. The stochastic model was adapted to rapid solidification conditions of multicomponent alloys processed via multi-layer multi-track AM processes. The capabilities of the coupled model include studying the effects of process parameters (power input, speed, beam shape) and part geometry on solidification conditions and their impact on the resulting solidification structure and on the formation of inter layer/track voids. The multi-scale model assumes that the complex combination of the crystallographic requirements, isomorphism, epitaxy, changing direction of the melt pool motion and thermal gradient direction will produce the observed texture and grain morphology. Thus, grain size, morphology, and crystallographic orientation can be assessed, and the model can assist in achieving better control of the solidification microstructures and to establish trends in the solidification behavior in AM components. The coupled model was previously validated against single-layer laser remelting IN625 experiments performed and analyzed at National Institute of Standards and Technology (NIST) using LPBF systems. In this study, the model was applied to predict the solidification structure and inter layer/track voids formation in IN718 alloys processed by LPBF processes. This 3D modeling approach can also be used to predict the solidification structure of Ti-based alloys processes by EBPBF.

Excellent mechanical properties of a Ti-based alloy via optimizing grain boundary α phase

In this paper, the continuous grain boundary α phase of a Ti-based alloy is optimized by the combined process of deformation and heat treatment, the equiaxial discontinuous grain boundary α phase is obtained, and the ductility is greatly improved while the strength still keep high (strength of 1280 MPa and elongation of 10 %). Firstly, continuous grain boundary α phase is obtained by solid solution-short time aging, then the continuous grain boundary α phase is sheared and broken by 30 % hot rolling deformation, and finally recrystallized by recrystallization annealing, the near duplex microstructure with equiaxial grain boundary α phase and lamellar secondary α phase is obtained, and the comprehensive mechanical properties of this near duplex microstructure are obviously better than that of the traditional lamellar, duplex or equiaxial microstructure. This paper provides a new idea for strengthening and toughening design of metal materials and thus should be of interest.

Surface tension of liquid Ti, V and their binary alloys measured by electromagnetic levitation

AbstractThe surface tension of the liquid Ti-V system is systematically measured using the oscillating drop technique during electromagnetic levitation. Temperature- and compositional dependence are both investigated. The entire compositional range is covered. A linear decrease with increasing temperature is found for the pure elements as well as for all investigated alloys. The surface tension generally increases with increasing V-content. The obtained data are in good agreement with the Butler model for the ideal solution. Additionally, the Butler model for the regular solution was evaluated in the context of the obtained surface tension data. In contrast to many other Ti-based alloys, the Butler model for the regular solution yields no additional benefit for Ti-V, since there is only a neglectable small deviation between the calculations for the ideal and regular solution. Segregation effects are modeled using the Butler equation for an ideal solution. The findings are discussed considering already existing trends for the mixing behavior of liquid Ti-alloys. The results strongly suggest, that the Ti-V system obeys in general the ideal solution law.

Enhancing the corrosion behavior of Ti–6Al–4V and Nitinol alloys by simple chemical oxidation in H2O2

This study investigated the effect of hydrogen peroxide treatment on the corrosion behavior of two Ti biomaterial alloys (Ti–6Al–4V and Nitinol (NiTi)). The obtained oxides were characterized by a scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Even though both oxidized alloys are constituted mostly by TiO2 oxide on their surfaces, different topographies were obtained: a non-porous film with mud-cracked structure type was formed on Ti–6Al–4V while some micropores were observed on the NiTi surface. Oxidized NiTi samples also exhibited Ni species present as oxides and hydroxides in the form of Ni2+ and Ni3+. The ICP-AES analysis demonstrated that the presence of the oxides reduced the amount of alloying ions released to the simulated physiological environment after the electrochemical tests. The results show that this simple technique without the need for thermal post-treatment is enough to reduce the corrosion current density (icorr) and shift the corrosion potential (Ecorr) to more noble values enhancing the anticorrosive properties of both Ti-based alloys in Ringer solution. Moreover, the hydrophilicity of the surfaces was increased after the treatment.

Characterization of Martensitic Transformation, Microstructure and a Kinetic Study of Ti-based High Temperature Shape Memory Alloy

High temperature shape memory alloys (HTSMAs) are widely used in many fiels such as industry, biomedical, aerospace, etc. In order to expand the usage areas of these alloys, it is necessary to improve the materials, especially the martensitic transformation temperatures should be controlled. Third elements are often added to the material to control the martensitic transformation temperature. Ti-12V-8Al (wt. %) alloy, which is prepared for use in aircraft engines in the aviation industry, is a good choice due to its low density. In this study, Ti-12V-8Al (wt. %) alloy was prepared with the help of arc-melting technique. The martensite-austenite transformation temperatures, phase formations, microstructure of Ti-12V-8Al (wt. %) alloy were examined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM) respectively. In the DSC test, it was determined that the martensitic transformation temperature reduced according as the heating rate of the alloy. In XRD and SEM measurements, it was observed that the alloy has α″ martensitic phases as well as some β austenite phases. Thermal activation energies of the alloy were founded by Kissinger and Ozawa techniques. It was concluded that the activation energy amounts computed by these two techniques are parallel to each other.

Scientific Advancements in Composite Materials for Aircraft Applications: A Review.

Recent advances in aircraft materials and their manufacturing technologies have enabled progressive growth in innovative materials such as composites. Al-based, Mg-based, Ti-based alloys, ceramic-based, and polymer-based composites have been developed for the aerospace industry with outstanding properties. However, these materials still have some limitations such as insufficient mechanical properties, stress corrosion cracking, fretting wear, and corrosion. Subsequently, extensive studies have been conducted to develop aerospace materials that possess superior mechanical performance and are corrosion-resistant. Such materials can improve the performance as well as the life cycle cost. This review introduces the recent advancements in the development of composites for aircraft applications. Then it focuses on the studies conducted on composite materials developed for aircraft structures, followed by various fabrication techniques and then their applications in the aircraft industry. Finally, it summarizes the efforts made by the researchers so far and the challenges faced by them, followed by the future trends in aircraft materials.

Constructing a bimodal microstructure via cyclic thermal treatment in selective laser melted Ti6Al4V-5vol%TiB composite

Titanium matrix composites are considered promising materials in engineering fields that demand high strength and wear-resistant materials in combination with lightweight. Selective laser melting (SLM) recently has been used to fabricate TMCs, but their plasticity is generally poor as reported. Bimodal microstructures consisting of globular α are known to possess excellent comprehensive mechanical properties in Ti-based alloys. Heat treatment for the transformation of lamellar to globular microstructures is usually preceded by thermomechanical processing. This work reports a cyclic thermal treatment (CTT) for constructing a bimodal microstructure in SLM-processed Ti6Al4V-5vol%TiB composite without the need for predeformation. The CTT process involves repeated thermal cycling between 875 and 975 °C to induce notable changes in the fractions of α and β. Additionally, a β-region annealing process (1050 °C, 1 h) was designed and implemented before CTT to accelerate the globularization process. After a CTT of 10 cycles, a typical bimodal microstructure with highly spherical αp was successfully prepared. Meanwhile, the segregated TiB whisker clusters were significantly replaced by uniformly distributed individual TiB whiskers. Boundary splitting and termination migration are two competing mechanisms in the globularization process. TiB whiskers promote the globularization process through repeated heterogeneous nucleation in the cooling part. Compressive testing suggested that the sample with a bimodal microstructure (54.5% αp) exhibited improved plasticity (12.3%–27.3%) at the cost of acceptable yield strength reduction (1743 MPa–1392 MPa), which is desirable for structural applications.

Corrosion behaviour of aluminide coatings on Ti-based alloy in the marine environment at high temperature

Ni-Al aluminide coating was deposited by electroplating of Ni and subsequent aluminisation while Ti-Al aluminide coating was deposited by aluminisation directly on Ti-based alloy. The corrosion performance of two coated samples with uncoated sample in marine environment in the presence of NaCl and water vapour at 700 °C were studied. Ni-Al coated sample showed the best corrosion resistance. Ti-Al coated sample showed severer corrosion in marine environment compared with that in static air due to self-sustainable oxychlorination process. The detrimental effect of Ti and beneficial effect of Ni-plating on self-sustainable oxychlorination in marine environment are discussed.

Glass-Forming Ability and Corrosion Behavior of Ti-Based Amorphous Alloy Ti-Zr-Si-Fe.

Ti-based alloy Ti75Zr11Si9Fe5 (At %) and Ti66Zr11Si15Fe5Mo3 (At %) ribbons are fabricated by a single roller spun-melt technique, according to the three empirical rules. Both alloys are found to have a large, supercooled liquid region (ΔTx) before crystallization that reaches 80–90 K. The results show that both alloys possess excellent glass-forming abilities. The electrochemical measurement proves both amorphous alloys possess relatively high corrosion resistance in 3 mass% NaCl solution.

Achieving superior strength-ductility synergy by constructing network microstructure in Ti-based high-entropy alloy matrix composites

In-situ (Ti,Nb)B whiskers ((Ti,Nb)Bw) reinforced Ti-based high-entropy alloy (HEA) matrix composites ((Ti,Nb)Bw/Ti1.5ZrNbAl0.3) with a quasi-continuous network microstructure were successfully fabricated via low energy milling (LEM) and hot-pressed sintering (HPS). The results show that the in-situ (Ti,Nb)Bw reinforcements were distributed around Ti1.5ZrNbAl0.3 matrix particle forming a special network architecture. This microstructure resulted in remarkable grain refinement of Ti-based HEA matrix, which contributed to the superior strength-ductility synergy. Consequently, the as-sintered (Ti,Nb)Bw/Ti1.5ZrNbAl0.3 composites exhibited a high yield strength (σYS = 1015 MPa) while maintaining superior ductility (ϵe = 17.5%), which were simultaneously increased by 11.5% and 96.6% compared with the monolithic Ti1.5ZrNbAl0.3 alloy. The network microstructure design of HEA-based composites could be therefore exploited to overcome the strength-ductility trade-off.

Identification of prior β grains of additive manufactured Ti-6Al-4V alloy using electron backscatter diffraction

• Prior columnar β grains were identified by theoretical and experimental means. • The OR between the α and β phases is close to the Burgers OR but not rational. • The inheritance between prior β phase and reversed β phase was validated. • Specific α boundaries are nearly identical to the HAGBs of prior β phase. Prior columnar β grains are an important microstructural feature of laser powder bed fusion (LPBF) Ti-based alloys and affect the properties. The objective of this study was to reconstruct the prior β grains of heat-treated LPBF Ti-6Al-4V alloy using crystallography data of α grains from electron backscatter diffraction. The reconstruction shows that the orientation relationship in β to α transformation is close to the Burgers orientation relationship but not rational. Besides, the results clearly confirm the orientation inheritance between the reversed β phase and the prior β phase. An accidental finding is that the α boundaries, having with misorientation ranges of 15°–56° and 67°–88°, are nearly identical to the high-angle grain boundaries of prior β phase. This can be a simple approach to identify high-angle grain boundaries of prior β phase when reconstruction algorithm cannot be obtained.

High power arc ion plating of thick Cr2N hard coating on Ti-based alloys: Oxidation and wear behaviors

Thick Cr2N hard coating was obtained at a high rate of around 15 μm/h by high power arc ion plating to improve the oxidation and wear resistance of Ti6Al4V at medium high temperatures. The coating grew only about 1 μm thick Cr2O3 scale after oxidation for 500 h at 600 °C accompanied by a slight interfacial diffusion, whereas a non-protective TiO2-based scale of around 8 μm in thickness was formed on the Ti6Al4V after oxidation at the same condition. The wear rate of Cr2N-coated Ti6Al4V was significantly reduced by about 99.6 % and 86 % at 25 °C and 600 °C, respectively. In addition, the Cr2N coating maintained excellent structural integrity after oxidation and wear, demonstrating that the Cr2N coating is a promising candidate for protecting Ti-based alloys against oxidation and wear.

Electrical resistivity and oxidation behavior of Cu and Ti doped laser deposited high entropy alloys

PurposeIn this study, AlCoCrFeNi–Cu (Cu-based) and AlCoCrFeNi–Ti (Ti-based) high entropy alloys (HEAs) were fabricated using a direct blown powder technique via laser additive manufacturing on an A301 steel baseplate for aerospace applications. The purpose of this research is to investigate the electrical resistivity and oxidation behavior of the as-built copper (Cu)- and titanium (Ti)-based alloys and to understand the alloying effect, the HEAs core effects and the influence of laser parameters on the physical properties of the alloys.Design/methodology/approachThe as-received AlCoCrFeNiCu and AlCoCrFeNiTi powders were used to fabricate HEA clads on an A301 steel baseplate preheated at 400°C using a 3 kW Rofin Sinar dY044 continuous-wave laser-deposition system fitted with a KUKA robotic arm. The deposits were sectioned using an electric cutting machine and prepared by standard metallographic methods to investigate the electrical and oxidation properties of the alloys.FindingsThe results showed that the laser power had the most influence on the physical properties of the alloys. The Ti-based alloy had better resistivity than the Cu-based alloy, whereas the Cu-based alloy had better oxidation residence than the Ti-based alloy which attributed to the compositional alloying effect (Cu, aluminum and nickel) and the orderliness of the lattice, which is significantly associated with the electron transportation; consequently, the more distorted the lattice, the easier the transportation of electrons and the better the properties of the HEAs.Originality/valueIt is evident from the studies that the composition of HEAs and the laser processing parameters are two significant factors that influence the physical properties of laser deposited HEAs for aerospace applications.

New-generation biocompatible Ti-based metallic glass ribbons for flexible implants

We introduce five new biocompatible Ti-based metallic glass (MG) compositions with different metalloid and soft metal content for a synergistic improvement in corrosion properties. Without any potentially harmful elements such as Cu, Ni or Be, these novel alloys can eliminate the risk of inflammatory reaction when utilized for permanent medical implants. Excluding Cu, Ni or Be, which are essential for Ti-based bulk MG production, on the other hand, confines the glass-forming ability of novel alloys to a moderate level. In this study, toxic-element free MG alloys with significant metalloid (Si–Ge–B, 15–18 at.%) and minor soft element (Sn, 2–5 at.%) additions are produced in ribbon form using conventional single-roller melt spinning technique. Their glass-forming abilities and their structural and thermal properties are comparatively investigated using X-ray diffraction (XRD), synchrotron XRD and differential scanning calorimetry. Their corrosion resistance is ascertained in a biological solution to analyze their biocorrosion properties and compare them with other Ti-based bulk MGs along with energy dispersive X-ray. Ti60Zr20Si8Ge7B3Sn2 and Ti50Zr30Si8Ge7B3Sn2 MG ribbons present a higher pitting potential and passivation domain compared with other Ti-based MG alloys tested in similar conditions. Human mesenchymal stem cell metabolic activity and cytocompatibility tests confirm their outstanding cytocompatibility, outperforming Ti-Al6-V4.

Design and Characterization of New Ti-Zr-Nb-(Mn) Medium Entropy Alloys for Biomedical Applications

β titanium alloys have been widely used as implantation inside the human body. Based on this, two β Ti-based medium entropy alloys (namely; Ti45Zr33Nb22 and Ti40Zr33Nb22Mn5, at. %) were designed using mean bond order (Bo) and mean d-orbital energy level (Md) diagram along with the CALPHAD approaches. The two alloys showed single β phase composed of a dendritic structure. When 5 at. % of Ti was replaced by Mn in Ti45Zr33Nb22alloy, the compressive yield strength has increased. Furthermore, the hardness was increased upon the addition of Mn. Finally, Ti45Zr33Nb22alloy showed good cold workability and slight hardness increase upon cold rolling up to 90% reduction.

Screening and analysis of key genes in the biological behavior of bone mesenchymal stem cells seeded on gradient nanostructured titanium compared with native pure Ti.

Titanium (Ti) and Ti-based alloy materials are ideal brackets that restore bone defect, and the mechanism of related genes inducing bone mesenchymal stem cells (BMSCs) to osteogenic differentiation is currently a hot research topic. In order to screen key genes of BMSCs during the osteogenic expression process, we acquired data sets (GSE37237 and GSE84500) which were in the database Gene Expression Omnibus (GEO). Investigations on differentially expressed genes (DEGs) and their enrichment of functions were conducted. We constructed relative protein-protein interaction (PPI) network by using Search Tool for the Retrieval of Interacting Genes (STRING) and visualized the expression of DEGs with Cytoscape. A total of 279 DEGs were discerned, which could be divided into 177 down regulated genes and 102 up regulated genes. In addition, the DEGs' enrichment and pathways included regulation of actin cytoskeleton, inflammatory mediator regulation of transient receptor potential (TRP) channels, peroxisome proliferator-activated receptors (PPAR) pathway, cell cycle, Rheumatoid arthritis, mitogen-activated protein kinases (MAPK) signaling pathway and Ras signaling pathway ect. It showed that 10 notable up regulated genes were mainly in AMP-activated protein kinase (AMPK) pathway. Then we used a technology named surface mechanical attrition treatment (SMAT) to prepare gradient nanostructured (GNS) surface Ti and seeded well-growing BMSCs on the surface of SMAT Ti and native pure Ti. Cell Counting Kits-8 (CCK-8), apoptosis experiment, immunofluorescence technology and staining experiments for alka-line phosphatase (ALP) and alizarin red staining (ARS) were used to research the proliferation, adhesion and differentiation ability of BMSCs seeded on SMAT Ti compared with native pure Ti. We used quantitative real-time PCR (qRT-PCR) technology so as to verify the expression of the most significant 5 genes. In summary, these results indicated novel point of views into candidate genes and potential mechanism for the further study of BMSCs' behaviors seeded on SMAT Ti.

The promoting effect of the TiO2 nano-porous arrays after polydopamine-based modification and Arg-Gly-Asp peptide immobilization on biomineralization and osteogenesis

TiO2 nano-porous arrays with appropriate structural parameters, roughness and wettability have application potential in implantable titanium-based (Ti-based) alloys. In this research, the polydopamine (PDA) and Arg-Gly-Asp (RGD) peptide are adopted to construct a favorable osteogenic microenvironment on the anodized TiO2 nano-porous arrays before and after heat treatment. The characterization of surface morphologies and chemical compositions has been conducted to confirm the feasibility of the PDA-based modification and RGD peptide immobilization. Via immersion in the modified-simulated body fluid (m-SBF) for 7 days, the PDA-based modified samples have represented enhanced biomineralization performance. Moreover, the cell adhesion and proliferation assay, alkaline phosphatase (ALP) activity assay and quantitative real-time polymerase chain reaction (qRT-PCR) assay in vitro have indicated that the heat-treated TiO2 nano-porous arrays modified with PDA and RGD peptide have endowed the seeded MC3T3-E1 mouse pre-osteoblasts with excellent osteogenic performance. Such modified TiO2 nano-porous arrays have great latent capacity in implantable materials for biomineralization and osteogenesis.