Toughening High Strength Titanium Alloys Through Fine Tuning Phase Composition and Refining Microstructure

High strength titanium alloys suffer from a limited combination of strength and ductility. Considering their microstructure, the coarse β grain is a detrimental factor. In the present study, the effects of hot deformation and annealing treatment on the β grain refinement of Ti–5Al–5Mo–5V–1Cr–1Fe (TC18) titanium alloy have been investigated by using electronic backscattered diffraction (EBSD) and transmission electric microscopy (TEM). Hot compression tests of TC18 alloy were performed between 1073 and 1223 K at strain rates of 0.01 and 0.10 s −1 . Subsequent annealing treatments were conducted to investigate the effect of deformation microstructure on the recrystallization behavior of β grains. The results indicate that dynamic recovery (DRV) is the dominant restoration mechanism during hot deformation. Discontinuous dynamic recrystallization (dDRX) is significantly limited at a higher temperature in the β region, whereas continuous dynamic recrystallization (cDRX) of the β phase is observed at a higher strain rate in the (α + β) region. The final annealing microstructure is highly dependent on the deformation microstructure. Limited dDRX during hot deformation could not effectively refine the β grains. The refined and uniform β grains with an average grain size of 12 μm are achieved by combining hot deformation and subsequent annealing in the (α + β) region. This study provides a guide for the β grain refinement of high strength titanium alloys.

Microstructure and mechanical properties of a high nitrogen titanium alloy

A CPFEM based study to understand the void growth in high strength dual-phase titanium alloy (Ti-10V-2Fe-3Al)

ABSTRACTThis article aims to prepare by injection molding recycled polymeric composites based on PA66 reinforced with short carbon fibers after artificial aging for applications in the automotive field. The aging cycles involves the combined action of UV radiation, moisture, and temperature in order to simulate the common outdoor conditions. The 100% recycled composites are obtained by the regranulation of the aged specimens followed by the remelting and re‐injection molding. The study is focused on the comparison between the mechanical behavior and the microstructure of the composites before and after mechanical recycling. The results of mechanical, thermal, and morphological investigations reveal that the recycling process had no significant effect on the final properties and microstructure of the recycled composites. Therefore the recycled PA66CF30 composites could be successfully used for structural or semi‐structural automotive applications guaranteeing good final performances and advantages from the environmental point of view. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42275.

Enhanced comprehensive mechanical properties of laser additive manufactured TC17 by design of new heat treatment based on continuous cooling transition

Titanium alloys are widely used in aerospace industry in the areas of pressure vessels, airframe structures, landing gears, aeroengine compressor blades etc. The principal qualities of titanium alloys required for these applications are high specific strength, low density and high specific modulus. Among the families of Ti alloys, high strength titanium alloys come under martensitic α + β and metastable β alloys. Titanium alloy Ti-5Al-5V-2Mo (BT-23) is an important example of martensitic α + β alloy similar to the work horse Ti6Al4V alloy which exhibits good combination of strength and ductility in solution treated and aged conditions. But due to quenching from solution treatment temperature, the alloy tends to retain good amount of residual stresses. The severity of residual stress increases with increase in solution treatment temperature as well as severity of quench. An attempt has been made to study the effect of air cooling subsequent to solution treatment to compare the strength of the alloy vis-à-vis that achievable during water quenching. An attempt has also been made to correlate the microstructure evolution, hardness with variation in solution treatment temperature and quench severity in titanium alloy Ti-5Al-2Mo-5V. Samples subjected to air cooling subsequent to solution treatment exhibited higher microhardness when compared to water quenched samples. It is proposed that dynamic aging and/ or stress relieving occurs during air cooling from solution treatment temperature down to room temperature. Also the fine α precipitates formed during air cooling may be resulting in higher hardness compared to the α’’/α’ formed during water quenching. The same has been supported by thermal analysis of air cooling and water quenching processes employed subsequent to solution treatment.

As intensive work is underway in leading material science centers in the USA, EU, Russia, and China, both to modernize existing titanium alloys and to create new ones, the E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine developed titanium alloys T110 (Ti-5.5Al-1.2Mo-1.2V-4Nb-2Fe-0.5Zr system) and T120 (Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr system), which according to their characteristics, belong to the group of modern two-phase high-alloyed alloys characterized by high strength and good ductility. With more and more attention is being paid to the expansion in the usage of welded structures and assemblies of high strength titanium alloys with UTS ≥ 1100 MPa, there’s urgent need in studying best ways to obtain welded joints from such alloys. The weldability of two-phase high-alloyed titanium alloys, the use of which can give big reduction in structural weight, is significantly worse than low-alloyed alloys, therefore for a new alloy it is necessary to ensure the possibility of obtaining welded joints with a strength of at least 90% compared to the strength of base material. The aim of this work is to study the influence of the welding thermal cycle and reducing of weld metal alloying degree on the structure and mechanical properties of welded joints of high-strength titanium alloy Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr with tensile strength more than 1200 MPa, as well as assessment of it welded joints properties in comparison with other high-strength titanium alloys.

TC21 is a first high strength and damage-tolerant titanium alloy self-developed in China, which has independent intellectual property. As it is known to all, titanium alloy TC21 is one of the most widely used materials in aerospace. The improvement of cutting quality of titanium alloy is an urgent problem. In this paper, the orthogonal experiment were carried out to study surface roughness of turning TC21. The predictive model of surface roughness in turning TC21 was built by analysis of multivariable linear regression on the basis of experiment. Statistical test results indicated the established predictive model were in highly notable test status and had high reliability. These works provide references for machining TC21.

Riveting is still one of the main joining methods of thin-walled aircraft structures. Such features as: simplicity of implementation, possibility of two different material connection (e.g. metallic with non-metallic ones) and the fact that is it a well-known (reliable) method causes popularity of riveting. The never-ending attempt to obtain as low mass as possible (mainly to reduce fuel consumption) is the reason for using material of high specific strength in the aerospace industry. High strength titanium or aluminium alloys (e.g. 2024T3) and composite laminates (e.g. CFRP or Glare) are examples of such materials. The article deals with methods of connecting various materials. The paper presents advantages and disadvantages of different/selected connection types. Strength prediction and failure modes of mechanical joints are described for metallic as well as for composite components. Composites are complex materials having an anisotropic structure (and anisotropic mechanical properties) leading to various failure mechanisms. Main principles for appropriate joint design of composite laminate panels (laminate configuration and typical/specific geometrical dimensions) are indicated/specified. The bearing failure mechanism is accepted to be a safe progressive one. Mechanism of bearing (generally compressive) load transfer into composite laminates by shear of the matrix is analysed. Some examples of improvement bearing strength of laminates are presented/shown according to literature. On the base of presented examples and bearing load transfer analysis, some conclusions for an appropriate solution of this problem are drawn.

Specimen geometry and loading condition usually have a great influence on the fatigue strength of metallic materials, which is an important issue in evaluating the reliability of component parts. In this paper, a rotating bending fatigue test is performed at first on an hourglass specimen and a notch specimen of a high strength titanium alloy. Experimental results indicate that, in terms of local stress, the notch specimen endures higher fatigue strength in comparison with the hourglass specimen due to its relatively smaller control volume. Then, a probabilistic control volume method is proposed for correlating the effects of specimen geometry and loading condition on the fatigue strength based on Weibull distribution and the concept of control volume. A simple formula is obtained for the fatigue strength in relation to control volumes, in which the parameter is the shape parameter of Weibull distribution of fatigue strength. The predicted results are in good agreement with the present experimental data for high strength titanium alloy and the data for the high strength steel and the full scale EA4T axle in the literature.

Effect of aging heat treatment on microstructure and tensile properties of a new β high strength titanium alloy

Transmission electron microscopy, X-ray diffraction analysis, durometry, and mechanical tensile and impact toughness tests were used to study changes in the structure, phase composition, and mechanical properties in a high-strength VT22I titanium alloy (Ti–3Al–5Mo–5V–1Cr–1Fe) upon isothermal and thermomechanical treatments, including warm rolling and aging. It has been found that the decomposition of the β solid solution in an alloy preliminarily heated in the β region (Тpt + 50°C) after isothermal treatment at 650°C for 1 and 4 min is accompanied by the formation of an intermediate α'' phase; upon holding for 20 min, an equilibrium α phase precipitates. The А7В-type ordering processes, where β stabilizers and aluminum can serve as a B element, are possible and, upon final cooling, in water, the formation of an athermal ω phase can take place at the initial stages of decomposition. It has been shown that the warm rolling of the alloy at 650°C accelerates the processes of the decomposition of the metastable β solid solution, contributes to the refinement of the arising α precipitates, and suppresses the formation of the athermal ω phase upon cooling compared to the similar isothermal treatment without deformation. A regime of a thermomechanical treatment that provides the high mechanical properties required to fabricate elastic structural components has been proposed for this alloy.

Titanium alloys have been found to provide substantial cost and operational benefits in offshore production and drilling systems. Properties such as high strength, low density, exceptional corrosion resistance, and inherent flexibility have made the alloys a viable choice for equipment including drilling risers, drill pipe, and tapered stress joints. In most cases the most successful applications will marry titanium and steel together in a hybrid fashion. This paper provides an overview of known and potential benefits of certain high strength titanium alloys in a variety of offshore applications.

A comparison of fracture toughness parameters for titanium alloys

TC21 is a first high strength and damage-tolerant titanium alloy self-developed in China, which has independent intellectual property. As it is known to all, titanium alloy TC21 is widely used in aviation and aerospace fields. The experimental study of cutting force is a important content of machining mechanism about TC21. In this paper, the orthogonal experiment were carried out to study. The predictive model of milling force in milling TC21 was built by analysis of multivariable linear regression on the basis of experiment. Statistical test results indicated the established predictive model were in highly notable test status and had high reliability.