Titanium Alloyed with Boron

Small additions of boron to conventional titanium alloys have been found to produce significant changes to the microstructures and associated properties. Grain refinement and improved strength and stiffness are first-order effects, which lead to possibilities for developing novel and affordable processing methodologies and to enhance performance over conventional titanium alloys. In this article, we introduce this new class of titanium alloys and describe unique formability benefits achieved via engineering microstructures

Microstructure and Porosity of Laser Welds in Cast Ti-6Al-4V with Addition of Boron

Addition of small amounts of boron to cast Ti-6Al-4V alloy has shown to render a finer microstructure and improved mechanical properties. For such an improved alloy to be widely applicable for large aerospace structural components, successful welding of such castings is essential. In the present work, the microstructure and porosity of laser welds in a standard grade cast Ti-6Al-4V alloy as well as two modified alloy versions with different boron concentrations have been investigated. Prior-β grain reconstruction revealed the prior-β grain structure in the weld zones. In fusion zones of the welds, boron was found to refine the grain size significantly and rendered narrow elongated grains. TiB particles in the prior-β grain boundaries in the cast base material restricted grain growth in the heat-affected zone. The TiB particles that existed in the as cast alloys decreased in size in the fusion zones of welds. The hardness in the weld zones was higher than in the base material and boron did not have a significant effect on hardness of the weld zones. The fusion zones were smaller in the boron-modified alloys as compared with Ti-6Al-4V without boron. Computed tomography X-ray investigations of the laser welds showed that pores in the FZ of the boron modified alloys were confined to the lower part of the welds, suggesting that boron addition influences melt pool flow

Solidification of Al alloys under electromagnetic pulses and characterization of the 3D microstructures under synchrotron x-ray tomography

A novel programmable electromagnetic pulse device was developed and used to study the solidification of Al-15 pct Cu and Al-35 pct Cu alloys. The pulsed magnetic fluxes and Lorentz forces generated inside the solidifying melts were simulated using finite element methods, and their effects on the solidification microstructures were characterized using electron microscopy and synchrotron X-ray tomography. Using a discharging voltage of 120 V, a pulsed magnetic field with the peak Lorentz force of ~1.6 N was generated inside the solidifying Al-Cu melts which were showed sufficiently enough to disrupt the growth of the primary Al dendrites and the Al2Cu intermetallic phases. The microstructures exhibit a strong correlation to the characteristics of the applied pulse, forming a periodical pattern that resonates the frequency of the applied electromagnetic field

Integrated Computational Materials Engineering of Gamma Titanium Aluminides for Aerospace Applications

Although the benefits of titanium aluminides for intermediate service temperature applications were well conceived and significant research and development activities were conducted in the past four decades, they remained as developmental materials due to barriers associated with melting, processing, scale-up, and cost. Demanding requirements of efficient aero-engines and extensive risk reduction demonstrations paved the path for commercial introduction of gamma titanium aluminides. The single most attractive current application is for low pressure turbine blades (LPTBs) in advanced aero-engines replacing conventionally cast nickel superalloys. This paper provides an overview of recent progress, producibility challenges, and opportunities. The successful journey of gamma (γ) TiAl LPTB development from laboratory demonstrations to production insertions in mass-produced commercial jet engines will be described. Collaboration and integrated product development were identified as the most critical needs for rapid maturation and implementation of γ-TiAl into aerospace applications. An integrated computational materials engineering modeling framework and toolsets developed under a collaborative US Air Force Metals Affordability Initiative project between industry, government, and academia will be illustrated. Model-based optimization of material and processing for achieving desired performance goals will be highlighted

Superplastic Behavior of Ti–6Al–4V–0.1B Alloy

The superplastic behavior of Ti–6Al–4V–0.1B sheet was evaluated. The strain rate sensitivity (m) is ≥0.47 in the temperature range 775–900 °C and at strain rate, ε˙ = 10−5 to 10−3 s−1. The material exhibits tensile elongations \u3e 200% in the temperature range 725–950 °C at ε˙ = 3 × 10−4 s−1. The optimum superplastic forming temperature is 900 °C, which is similar to conventional Ti–6Al–4V. However, a lower flow stress is needed in the case of Ti–6Al–4V–0.1B. The superplastic deformation mechanism is suggested from estimates of activation energy to be grain boundary sliding (GBS) accommodated by dislocation motion along grain boundaries at ε˙ = 10−4 s−1 and is diffusion-controlled dislocation climb at ε˙ = 10−3 s−1. Microstructural observations also confirm that GBS is the operating deformation mechanism at 900 °C and ε˙ = 3 × 10−4 s−1

Integrated Computational Materials Engineering of Gamma Titanium Aluminides for Aerospace Applications

Although the benefits of titanium aluminides for intermediate service temperature applications were well conceived and significant research and development activities were conducted in the past four decades, they remained as developmental materials due to barriers associated with melting, processing, scale-up, and cost. Demanding requirements of efficient aero-engines and extensive risk reduction demonstrations paved the path for commercial introduction of gamma titanium aluminides. The single most attractive current application is for low pressure turbine blades (LPTBs) in advanced aero-engines replacing conventionally cast nickel superalloys. This paper provides an overview of recent progress, producibility challenges, and opportunities. The successful journey of gamma (γ) TiAl LPTB development from laboratory demonstrations to production insertions in mass-produced commercial jet engines will be described. Collaboration and integrated product development were identified as the most critical needs for rapid maturation and implementation of γ-TiAl into aerospace applications. An integrated computational materials engineering modeling framework and toolsets developed under a collaborative US Air Force Metals Affordability Initiative project between industry, government, and academia will be illustrated. Model-based optimization of material and processing for achieving desired performance goals will be highlighted

Microstructural effects on the mechanical behavior of B-modified Ti–6Al–4V alloys

Small additions of B $(\leq0.4 wt.\%)$ to Ti alloys refine the as-cast microstructure significantly and improve the alloys’ mechanical performance. In this work, tensile, fracture and fatigue properties of the as-cast and hot isostatically pressed Ti–6Al–4V alloy with 0, 0.05, 0.10 and 0.40 wt.% B additions have been examined, with particular emphasis on identifying the microstructural length scale (grain size vs. lath size) that controls the mechanical properties of these alloys. Microstructural observations indicate an order of magnitude reduction in the prior \beta grain size, d, as well as a significant reduction in the \alpha lath size, \lambda, with B additions. It was observed that d and \lambda are correlated. With the refinement in the microstructure, the yield and ultimate tensile strengths, $\sigma_y$ and $\sigma_u$ respectively, increase whereas the fracture toughness, $K_{IC}$, decreases. Application of the Rice–Knott–Ritchie model for quasi-brittle cleavage fracture indicates that the reduction in $K_{IC}$, with increasing B content is due primarily to the reduced \lambda. Fatigue crack growth measurements show a gradual reduction in the threshold for fatigue crack propagation with $\sigma_y \sqrt\lambda$ dependence

Assessment of in situ TiB whisker tensile strength and optimization of TiB-reinforced titanium alloy design

A statistical model for fracture of aligned-whisker-reinforced metals was used to interpret tensile data of a TiB-reinforced titanium alloy. From this analysis, a TiB whisker strength of 8.0 GPa with a Weibull modulus of 2 was predicted. The analysis is consistent with observations of the whisker fragmentation process. Moreover, the analysis rationalizes why high tensile elongation was maintained in this reinforced alloy and identifies the constraints on material properties that are necessary to obtain both high elongation and high strength. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All. rights reserved