Structure Of Titanium Alloys Research Articles

Structure and properties of Ti-6Al-4V titanium alloy products obtained by direct laser deposition and subsequent heat treatment

A large number of studies have been carried out the effect on the structure and properties of titanium alloys produced by the DLD technology. Part of the research is devoted to the special features of the influence of various process parameters on the properties and quality of final products [1, 2]. Thus, obtaining products from Ti-6Al-4V using DLD technology has attracted increasing attention in recent years. But the technology of direct laser deposition is constantly being modernized and improved. The quality of laser radiation improves, as well as new laser heads are designed to increase the productivity of the process and improve the properties of the finished product. In this work will be studied structure and properties of Ti-6Al-4V titanium alloy products obtained by direct laser deposition and subsequent heat treatment

Analysis of the effect of fretting wear on key structural components of TB6 titanium alloy with actual failure cases

As the main metal structure materials, titanium alloys have been widely applied in aerospace and other military industries. Titanium alloy develops on the way of high performance and functionalization. Compared with other materials, titanium alloy has high surface integrity and high fretting damage sensitivity. In this paper, the failure case of TB6 high strength titanium alloy key structural parts is taken as the breakthrough point to analyze the effect of surface fretting wear damage on its performance. The appearance inspection, macro and micro morphology observation and energy spectrum analysis were carried out, and the microstructure examination and hardness test were also adopted. The results showed that the fracture property of lug of TB6 high strength titanium alloy was fatigue fracture, and the fretting wear damage of the inner surface of lug hole was the main reason for the fatigue crack initiation. This case is a typical example of titanium alloy structure failure due to fretting wear, which provides reference for the prevention of the recurrence of such faults.

Determining the porous structure for optimal soft-tissue ingrowth: An in vivo histological study.

The success of osseointegrated transcutaneous prostheses depends on a soft-tissue seal forming at the skin-implant interface in order to prevent infection. Current designs include a flange with drilled holes or a subdermal barrier with a porous coating in an attempt to promote soft-tissue attachment. However, the soft-tissue seal is not reliably achieved despite these designs and infection remains a significant problem. This study investigated soft-tissue integration into fully porous titanium alloy structures with interconnected pores. The study aimed to determine the effect of altering pore and strut size combinations on soft-tissue ingrowth into porous titanium alloy structures in vivo. It was hypothesized that implants with a more open porous structure with larger pore sizes would increase soft-tissue ingrowth more than less open porous structures. Porous titanium alloy cylinders were inserted into sheep paparaspinal muscles (n = 6) and left in situ for four weeks. A histological assessment of soft-tissue ingrowth was performed. Percentage soft-tissue pore fill, cell nuclei density and blood vessel density were quantified. The results showed that larger pore sizes were supportive of soft-tissue ingrowth. A structure with a pore size of 700μm and a strut size of 300μm supported revascularisation to the greatest degree. A flange with this structure may be used in future studies of osseointegrated transcutaneous prostheses in order to enhance the soft-tissue seal.

Buckling and post-buckling behavior of titanium alloy stiffened panels under shear load

Titanium alloy has been increasingly applied in aviation industry due to its superior performance. However, the titanium alloy structures are less studied. This work investigates the structural behavior of Ti6Al4V titanium alloy stiffened panels under in-plane shear load by experiments and numerical analysis. After the shear tests, the buckling instability, the post-buckling process and the failure mechanism of the specimen were obtained. The Finite Element (FE) models were established with the subsequent validation verification. A parametric analysis was implemented to study the influence of stringer thickness and stringer height on the behavior of the stiffened panels. The results show that after the initial local buckling on the skin, the buckling mode jumps several times with the increase of load. The stringers twist when the load reaches a certain level, and finally the structure damages due to the plastic deformation and the global buckling. The shear clip has little effect on the buckling and failure loads. Compared to the relatively large effect on the buckling load, the influence of the stringer thickness and stringer height on the failure load is neglectable. According to the parametric analysis, the stringer thickness influences the final buckling mode and failure mode, while the stringer height affects the buckling mode transformation.

High temperature deformation and microstructural evolution of core-shell structured titanium alloy

The hot deformation behavior and microstructural evolution of a core-shell (soft coarse-grained Ti cores and hard Ti-N solid solution shells) structured titanium alloy were investigated under 800–950 °C at a strain rate range of 0.001–1 s−1. The core-shell structured titanium alloys exhibit a higher flow stress (195 MPa deformed at 800 °C/0.1 s−1) compared with that of pure Ti (48 MPa deformed at 800 °C/0.1 s−1), suggesting that core-shell structure promotes a strengthening effect of titanium alloys. The nitrogen solution strengthened hard shells squash along compression direction playing a roll of skeleton and the soft cores accommodate the deformation, leading to inhomogeneous deformation. Dynamic recrystallization takes place mainly adjacent to the shells due to stress and strain concentration. The improvement compression stress of core-shell structured titanium alloys is attributed to the nitrogen-induced solution strengthening and core-shell structure itself, together with the inhabited plastic deformation and dynamic recrystallization by core-shell structure.

Effect of Vacuum Ion-Plasma Treatment on Surface Layer Structure, Corrosion and Erosion Resistance of Titanium Alloy with Intermetallic a2-Phase

Results are provided for a study of the effect of vacuum ion-plasma nitriding on the phase composition, structure, microhardness, salt corrosion resistance, and erosion resistance of alloy Ti – 14Al – 3Nb – 3V – 0.5Zr with an original bimodal structure and different surface microgeometry. It is shown that with an increase in nitriding temperature from 550 to 650°C the content of Ti2N nitrides in the surface layer increases and Ti3AlN nitride in formed, which raises the microhardness but reduces the thickness of the hardened diffusion zone; pores appear in the surface at 650°C. Vacuum ion-plasma nitriding is shown to raise substantially the resistance of specimens of alloy Ti – 14Al – 3Nb – 3V – 0.5Zr with a polished surface to salt corrosion. Additional nitriding after deposition of a TiN coating improves ground specimens salt corrosion resistance. Vacuum ion-plasma nitriding with additional deposition of a TiN coating increases the resistance of specimens with polished and ground surfaces to erosive action.

Effect of Annealing on the Structure and Properties of Titanium Alloy with Cellular Architecture for Medical Applications

The methods of optical metallography, SEM, x-ray fluorescence analysis, microindentation and compression testing were used to study the effect of annealing of Ti – 6%Al – 4%V alloy produced by direct laser sintering of the powder on structure, phase composition and mechanical properties of the samples with cellular architecture intended for use as bone replacement implants. Annealing of the cellular samples having a relative density of 45% was conducted in the temperature range of 720 – 1000°C for 1 h under high vacuum. Mechanical properties were determined according to ISO 13314 for compression testing of porous metallic materials.

Numerical and Experimental Study on TC4-DT Titanium Alloy Structure after Double Cold Expansion

Cold Expansion and Interference Fit are two well-known techniques in hole strengthening, having been widely used in aviation industry. Double cold expansion is a new strengthening process which effectively combined with the two techniques. A modelling method based on ABAQUS finite element method is proposed in order to study the effect of double cold expansion, which will include cold expansion, reaming process, interference fit and springback after that, the influence of edge distance ratio (EDR) on the stress-strain distribution has been studied. Proto-LXRD device has been used to measure the residual stress distribution in the surface of the specimens. Simulation and experimental results show that the stress distribution of the simulation is in an higher level than that of experimental, but the trends of the stress distribution are in a good agreement.

Influence of Cobalt and Molybdenum Additives on the Structure and Shape Memory Parameters of Reaction-Sintered Porous Nickel Titanium Alloys

We have studied the structure and properties of porous nickel titanium (TiNi) alloys obtained upon reaction sintering of Ti and Ni powders with Co and Mo additives. It is established that Co and Mo doping additives retain the compaction of Ni powder achieved at the initial stage of sintering. The maximum deformation of porous samples loaded in the austenite state was observed upon adding Co, while the addition of Mo resulted in minimum deformation. The addition of Co leads to single-stage martensitic transformation in TiNi phase, while the addition of Mo leads to the two-stage transformation that is more homogeneous over the volume. Both Co and Mo additives lead to increase in the maximum accumulated strain due to the formation of favorably oriented stress-induced martensite and reoriented quench-induced martensite.

Surface modification of Ti6Al4V based on ultrasonic surface rolling processing and plasma nitriding for enhanced bone regeneration

Titanium alloy has been widely used in dentistry, orthopedic surgery and other medical fields. Surface morphology and structure of titanium alloy play an important role in cell adhesion and proliferation. The main purpose of this study is to investigate the biocompatibility and osteogenesis performance of Ti6Al4V modified using ultrasonic surface rolling processing (USRP) and plasma nitriding (PN). The raw materials were nominated as untreated, and the Ti6Al4V samples treated by USRP (with a processing duration of 1 h and 3 h) and PN were named as USRP1, USRP2, USRP1+PN, and USRP2+PN, respectively. The Ti6Al4V samples were characterized by SEM, AFM, and surface profilometer for surface morphology and 3D surface topography, and USRP1+PN showed the highest surface roughness (268 nm). The water contact angle measurements demonstrated that USRP2 had more favorite wettability (75.7°). The XRD analysis indicated the enhancement of nanocrystallization for the samples treated by USRP and the formation of a nitride layer for the samples treated by USRP and PN. The interactions between the Ti6Al4V samples and MC3T3-E1 cells were investigated in vitro by SEM, CCK-8 test, alkaline phosphatase (ALP) activity assay, and Alizarin Red S staining. The SEM images and CCK-8 tests revealed that all the Ti6Al4V samples were biocompatible to MC3T3-E1 cells, and the results of ALP activity assay and Alizarin Red S staining showed a better osteogenesis performance for the samples treated by USRP and PN. The present study indicates that USRP and PN may act as an effective method for Ti6Al4V to induce bone regeneration.

Analysis of the Possibilities of Transformation of Lamellar Structures of Titanium and Zirconium Alloys by Methods of Thermohydrogen Treatment

Comparative analysis of the possibilities of transformation of the structure of titanium and zirconium alloys by thermohydrogen treatment is performed. The mechanisms of phase transformation and structure formation in zirconium alloy Zr – 2.5% Nb under reversible alloying with hydrogen are described. Phase diagram of the (alloy Zr – 2.5% Nb) – hydrogen system is plotted using the methods of metallographic and x-ray diffraction analysis and differential scanning calorimetry. The diagram is compared to that of a titanium alloy. The hydride phases in the zirconium alloy are shown to exhibit much higher temperature and concentration (with respect to hydrogen) stability than those of the titanium alloy. It is shown that the original lamellar structure of the zirconium alloy can be globularized by thermohydrogen treatment.

Influence of phase composition and microstructure on mechanical properties of hot-rolled Ti-χZr-4Al-0.005B alloys

The effects of phase composition and microstructure evolution on mechanical properties of hot-rolled Ti-χZr-4Al-0.005B alloys (abbreviated as, TχZAB with χ = 0, 10, 20, 30, and 40 wt%) were investigated by means of theoretical calculations, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The as-prepared TχZAB alloys showed an excellent combination of the tensile strength and ductility features. For example, the hot-rolled T40ZAB alloy displayed the ultrahigh tensile strength of 1535 MPa at 6.06% elongation. As Zr content increased, the fracture morphologies revealed typical transitional processes from dimple to quasi-cleavage fracture surfaces. The theoretical calculations agreed well with results from X-ray diffraction, where examined alloys showed only α/α′ crystal phases. Under the same hot-rolled condition, the microstructure evolved from distorted (or broken) lamellar α phase to crisscross acicular α′ martensite phase as the Zr content increased. Finally, in search for ideal structural titanium alloys, phase composition and microstructure and relationship with mechanical properties were examined and discussed.

Control of high-modulus titanium alloy phase composition, structure and complex of properties using thermohydrogen processing methods

This paper considers the possibility and efficiency of thermohydrogen processing of the high-modulus Ti–8,7Al–1,5Zr–2,0Mo titanium alloy with aluminum content exceeding its solubility limit in α-titanium. Experimental data on the effect of hydrogen on the alloy phase composition and structure are obtained. Regularities of phase transformations in the hydrogen-containing alloy are analyzed under different thermal effects. An alloy–hydrogen system is diagramed in the hydrogen concentration range from the initial content up to 1,0 wt.% and temperature range from 20 up to 1100 °C. It is shown that a β single-phase structure forms in the alloy via quenching from the temperatures of β range at a hydrogen content of 0,6 wt.% or more. Hydrogen saturation up to 0,8–1,0 wt.% causes β → δ hydride shear transformation during quenching from the temperatures below 750 °C and results in partial eutectoidal β phase transformation at slow cooling. It is stated that hydrogen extends the region of β phase stability by decreasing the temperature of β / (α + β) transition by 210 °C (at 1,0 wt.% of hydrogen) and increases the temperature of α2 phase stability by 50 °C. Technological schemes and modes of thermohydrogen processing are developed and tested using the alloy specimens in order to form the two types of structure – submicrocrystalline and bimodal, and formation mechanisms of these structures under thermohydrogen processing are analyzed as well. Mechanical properties of the alloy specimens are determined. It is stated that thermohydrogen processing results in growth of strength and hardness as compared with the initial state. The thermohydrogen processing forming submicrocrystalline structure leads to decrease of plasticity characteristics at maximum hardness.

Selecting Clinical and Laboratory Methods of Manufacture of Orthopaedic Titanium Alloy Structures Using a Biopotentiometer

Selecting Clinical and Laboratory Methods of Manufacture of Orthopaedic Titanium Alloy Structures Using a Biopotentiometer

Mass Optimisation of Turbofan Engine Casing Made of Sandwich Structure

Materials of a high specific strength and stiffness are used in the aerospace industry to obtain the lowest possible aircraft mass. The object of analysis is the casing of the F124 turbofan engine. The axially compressed cylindrical part of this casing is considered. The aim of the paper is to analyse possible benefits of replacing the original ribbed metal casing with a sandwich structure. The sandwich structure (metal-fibre laminate) of titanium alloy faces and a flax fibre laminate core is proposed. Semi-analytical optimisation of a sandwich structure was performed including a polynomial approximation of the critical load with correction obtained based on numerical analysis. The best mass efficiency was obtained for a core to faces thickness ratio equal to about 4.

Влияние легирующих добавок кобальта и молибдена на структуру и параметры памяти формы пористого реакционно-спеченного никелида титана

AbstractWe have studied the structure and properties of porous nickel titanium (TiNi) alloys obtained upon reaction sintering of Ti and Ni powders with Co and Mo additives. It is established that Co and Mo doping additives retain the compaction of Ni powder achieved at the initial stage of sintering. The maximum deformation of porous samples loaded in the austenite state was observed upon adding Co, while the addition of Mo resulted in minimum deformation. The addition of Co leads to single-stage martensitic transformation in TiNi phase, while the addition of Mo leads to the two-stage transformation that is more homogeneous over the volume. Both Co and Mo additives lead to increase in the maximum accumulated strain due to the formation of favorably oriented stress-induced martensite and reoriented quench-induced martensite.

Statistical fatigue properties and small fatigue crack propagation in bimodal harmonic structured Ti-6Al-4V alloy under four-point bending

Small fatigue crack propagation in bimodal harmonic structured titanium alloy (Ti-6Al-4V) with high strength and ductility was examined under four-point bending at a stress ratio of 0.1 in the ambient laboratory atmosphere. The crack profiles were observed using optical microscopy and scanning electron microscopy, and analyzed using an electron backscattered diffraction to examine the mechanism of small fatigue crack propagation. Fatigue crack paths were not influenced by the bimodal harmonic structure, and the crack growth rates, da/dN, in the harmonic structured Ti-6Al-4V were almost the same as those in a material with coarse acicular microstructure for comparable values of stress intensity range, ΔK. In contrast, the harmonic structured Ti-6Al-4V had a higher resistance of fatigue crack initiation due to the grain refinement induced by mechanical milling, which resulted in an increase of the fatigue life and fatigue limit. Furthermore, the statistical fatigue properties of Ti-6Al-4V alloy were analyzed using the stress dependence of Weibull parameters to quantitatively examine the effects of the bimodal harmonic structure on its fatigue life.

Backscattered electron imaging and electron backscattered diffraction in the study of bacterial attachment to titanium alloy structure.

The application of secondary electron (SE) imaging, backscattered electron imaging (BSE) and electron backscattered diffraction (EBSD) was investigated in this work to study the bacterial adhesion and proliferation on a commercially pure titanium (cp Ti) and a Ti6Al4V alloy (Ti64) with respect to substrate microstructure and chemical composition. Adherence of Gram-positive Staphylococcus epidermidis 11047 and Streptococcus sanguinis GW2, and Gram-negative Serratia sp. NCIMB 40259 and Escherichia coli 10418 was compared on cp Ti, Ti64, pure aluminium (Al) and vanadium (V). The substrate microstructure and the bacterial distribution on these metals were characterised using SE, BSE and EBSD imaging. It was observed that titanium alloy-phase structure, grain boundaries and grain orientation did not influence bacterial adherence or proliferation at microscale. Adherence of all four strains was similar on cp Ti and Ti64 surfaces whilst inhibited on pure Al. This work establishes a nondestructive and straight-forward statistical method to analyse the relationship between microbial distribution and metal alloy structure.

Quantitative Analysis of Weld-Pore Size and Depth and Effect on Fatigue Life of Ti-6Al-2Zr-1Mo-1V Alloy Weldments

Titanium-alloy weldments have been extensively used in engineering structures, and accurate estimation of the fatigue life is beneficial for avoiding catastrophic failures in titanium-alloy structures. The weld pore is a common defect in these weldments that significantly influences the fatigue process. In this study, the weld-pore size and depth and its effect on the fatigue life of Ti-6Al-2Zr-1Mo-1V (TA15) alloy weldments are investigated by adopting fatigue tests and fracture observations. The results show that fatigue crack initiations occurred at the weld pores for all specimens. The diameter and depth of all weld pores on fracture surfaces were then measured, and an indicator, P, was proposed, defined as a combination of pore diameter and depth. It was found that all the fatigue cracks initiated from the pore have the smallest P indicator, which suggests that P can be used to judge the location of crack initiation in an individual sample. Moreover, a model was developed based on P to estimate the fatigue life of weldments, considering the effects of weld-pore size and depth. Finally, analogous fatigue tests were carried out for model verification, and results show that the proposed model has a higher accuracy compared with several typical models. The findings of this study can be helpful in estimating the fatigue life and fatigue design of titanium-alloy weldments.

ВЛИЯНИЕ СКОРОСТИ ОХЛАЖДЕНИЯ НА ФАЗОВЫЙ СОСТАВ И СТРУКТУРУ ТИТАНОВОГО СПЛАВА ВТ6 ПОСЛЕ НАВОДОРОЖИВАЮЩЕГО ОТЖИГА

ВЛИЯНИЕ СКОРОСТИ ОХЛАЖДЕНИЯ НА ФАЗОВЫЙ СОСТАВ И СТРУКТУРУ ТИТАНОВОГО СПЛАВА ВТ6 ПОСЛЕ НАВОДОРОЖИВАЮЩЕГО ОТЖИГА