Structure and mechanical properties of Ti–6Al–4V alloy after zirconium addition
Highlights
► The mechanical properties of alloys have been greatly improved. ► The phase compositions change significantly with the zirconium content. ► The ductile–brittle transfer of alloys is evidently related to the zirconium content.
Introduction
Titanium (Ti) alloys are widely used in automotive applications and the aerospace industry because of their very attractive properties, such as exceptional strength-to-weight ratio, good hardenability, good elevated temperature performance, excellent fatigue/crack-propagation behavior, and corrosion resistance [1], [2]. Among various Ti alloys, Ti–6Al–4V alloy is the most widely used because of its better physical and mechanical properties than commercial purity (c.p.) Ti and other Ti alloys [3], [4], [5], [6]. However, this alloy has a low hardness value [7]. These problems can be overcome by changing the alloy matrix components using additional alloying elements to improve mechanical properties. Hence, a new alloy system that satisfies the requirements of the new environment needs to be designed.
Zirconium (Zr) is well known to have a small capture cross-section for thermal neutrons, which leads to excellent anti-neutron irradiation, relatively good high-temperature strength, and pre-eminent corrosion resistance in nuclear reactors. Hence, Zr and Zr-rich alloys, to which zircaloy belongs, are employed in nuclear reactors specifically for the fuel element cladding tubes of light-water reactors [8], [9], [10], [11], [12]. Many studies have been conducted on nuclear structural materials, such as Zr–Sn, Zr–Nb, Zr–Nb–Sn [13], [14], [15], [16]. However, these Zr-based alloys do not possess high strength and low density, which increase aerospace industry costs. The chemical properties of pure Zr and pure Ti are similar, and both belong to the same main group (IVB) in the periodic table. The Ti–Zr system also forms a completely solid solution for both high-temperature β-phase [body-centered cubic (bcc) structure] and low-temperature α-phase [hexagonal close-packed (hcp) structure] (Fig. 1) [17]. Numerous alloy designs are available, and large quantities of solid solution hardening must be possible.
Accordingly, Zr can be a partial substitution element for Ti. The aim of this paper is to find the appropriate Zr concentration to displace partial Ti, and investigate the mechanical properties and microstructure of TiZrAlV alloys.
Section snippets
Experiments
All ingots of TiZrAlV quaternary alloys are prepared by arc-melting the mixture of Ti wire (99.9 mass% purity), Zr (99.7 mass% purity), Al (99.9 mass% purity), and V (99.9 mass% purity) in an argon atmosphere purified with a Ti getter. All ingots are turned and re-melted five times to ensure compositional homogeneity. The compositional analysis of as-cast alloys is presented in Table 1. All ingots used in the experiment are subjected to homogenization at 1273 K for 2 h. The ingots are held at 1123 K
Results and discussion
The XRD patterns of hot-rolled TC4 and the series of TxZ alloys are shown in Fig. 3. The experimental results indicate that the crystal structures of TiZrAlV alloys are affected by the addition of Zr. For the TC4 alloys, all diffraction peaks well match those of the α- and β-phases (Fig. 3(a)). The XRD patterns of T5Z are mainly α-phase peaks as well as a small a mount β-phase peak (2 0 0), and the intensity of the peak 2θ = 38.4° of β-phase is lower than TC4 alloy. With the Zr contents further
Conclusions
In the current study, the microstructure and mechanical properties of Ti–xZr–6Al–4V alloys have been investigated. The main conclusions are as follows:
- (1)
Based on the results of XRD patterns, the phases of the studied alloys suffer a series of changes, especially, the intensity of the peak (2 0 0) of the β phase increases with the increase of Zr content. And with the Zr content increase, the β transus temperature gradually decreases.
- (2)
With increased Zr content, the tensile strength of TxZ alloys
Acknowledgments
This work was supported by the SKPBRC (Grant No. 2010CB731600), NSFC (Grant No. 51121061/51171160/51171163), NSF of Hebei (Grant No. E2010001176), and DFME of China (Grant No. 20101333110004).
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