Influence of annealing on the microstructure and mechanical properties of Ti/steel clad plates fabricated via cold spray additive manufacturing and hot-rolling
Introduction
In the recent years, Ti and its alloys have been widely used in aerospace and nuclear industries because of their excellent corrosion resistance and high specific strength [1,2]. However, the high cost and limited resources of Ti hamper their widespread applications for engineering structures [3,4]. In order to address this issue, Ti/steel clad plates have been developed and are being widely used in ocean engineering, petrochemical and other industries [5,6]. Ti/steel clad plates synergize the advantages of Ti alloys and carbon steel thereby exhibiting superb corrosion resistance and excellent mechanical properties [5,7]. Currently, roll bonding [8,9], explosive bonding [10,11], and diffusion bonding [12,13] are the main industrial techniques to manufacture clad plates. However, all these methods have their own shortcomings. For example, in roll bonding process, it is difficult to avoid formation of cracks and pores due to interface oxidation. Consequently, the mechanical properties of the clad plates are degraded [14]. Explosive bonding has a problem of uneven interfacial shear strength which originates from inhomogeneous deformation induced by an uncontrollable explosion wave [15]. Likewise, diffusion bonding is not a suitable choice for the mass scale industrial production due to prolonged process time and size limitation [3]. Therefore, in order to cope with the above-mentioned challenges, it is necessary to develop a new and viable technique to fabricate clad plates.
In the recent years, cold spraying additive manufacturing (CSAM) has emerged as a potential material processing technology, which can directly process powders of pure metals and their alloys (such as Ti, Al, Cu, steel, Ti6Al4V, 6061Al, etc.) into structural components [[16], [17], [18], [19], [20]]. In CSAM, the raw feedstock powder is accelerated by pre-heated high-pressure gas while passing through a converging-diverging nozzle. Wherein, the thermal energy of the accelerating gas is converted into kinetic energy to form a supersonic solid/gas stream which is layer by layer deposited on a substrate to achieve a thick metallic deposit [[21], [22], [23]]. Due to the unique feature of CSAM, i.e. low process temperature, there is a limited chance for thermal residual stresses or oxidation in the deposited layer. This makes CSAM an attractive industrial prospect [24,25].
However, weak mechanically interlocked (coating/substrate) interface, formed in CSAM, does not meet the required strength criteria for the clad plates [26]. Therefore, post-spray treatment is essential for CSAM samples. For instance, hot-rolling facilitates metallurgical bonding at the coating/substrate interface [27]. Similarly, annealing has been proved to be a simple and effective way to modify the microstructure as well as to improve the mechanical properties of clad plates [[28], [29], [30]]. Literature suggests that selection of annealing temperature plays a pivotal role in modifying the microstructure and resulting mechanical properties, since, the atomic diffusion coefficient is a function of temperature [31]. The atomic diffusion at the interface leads to metallurgical bonding and greatly improves the shear strength of the clad plates [32]. Appropriate annealing temperature activates recovery and recrystallization mechanisms, which improve the plasticity of the clad plates. However, if the annealing temperature is on the higher side, it may lead to the growth of brittle intermetallic compounds at the interface which adversely affect the shear strength of the clad plates [33,34].
Therefore, we recently developed an innovative approach, based on CSAM and hot-rolling, to fabricate Ti/steel clad plates with excellent properties. In our previous work [35], Ti powder was initially deposited on steel sheets via CSAM and subsequently hot-rolling was performed to achieve metallurgical bonding between Ti/Ti particles as well as Ti/steel interface. In this work, the Ti/steel clad plates were subjected to a series of annealing treatments with the aim to further improve their mechanical properties. Evolution of microstructure and formation of interfacial compounds in the annealed samples were systematically investigated by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) techniques. The mechanical properties were evaluated by performing tensile test, tensile shear test and microhardness test. The influence of annealing temperature on the microstructure and mechanical properties of Ti/steel clad plates was discussed.
Section snippets
Materials
Commercial grade, 99.8% pure Ti powder (d50 ~ 28 μm) and cold-rolled mild steel sheets (chemical composition in wt%: 0.173 C, 0.465 Mn, 0.287 Si, 0.036 S, 0.027 P and balance Fe) were used as the feedstock and substrate materials, respectively. The as-received mild steel sheets were cut into the size of 100 × 100 × 1.5 mm3. Before the deposition, the steel sheets were ground with sandpaper followed by cleaning with acetone and alcohol.
Fabrication of Ti/steel clad plates
The whole process for fabricating Ti/steel clad plates is
Microstructure
Fig. 2(a) shows that the morphology of the as-received Ti powder is irregular, which causes higher drag coefficient and promotes higher speed during the spraying process [37]. Fig. 2(b) presents the result of EDS analysis (in wt%) performed at the location ‘b’ marked in Fig. 2(a), indicating that the chemical composition of the as-received powder is 99.8% Ti and 0.2% V. Fig. 2(c) shows that the size distribution of the Ti powder lies in the range 10–60 μm with d10, d50 and d90 values of 18, 28,
The effect of annealing temperature on microstructure of the Ti/steel clad plates
After hot-rolling treatment, a transition layer (chiefly composed of FeTi) is formed through inter-diffusion of Ti and Fe at the Ti/steel interface. Consequently, metallurgical bonding at Ti/Ti and Ti/steel interfaces is achieved (Fig. 3(a, d)). Owing to the large plastic deformation, induced by the rolling process, the Ti layer in the As-Rolled sample accumulated abundant dislocations and local strain (Fig. 5(i)). Moreover, the severe plastic deformation (during the rolling process) resulted
Conclusions
Ti/steel clad plates were successfully fabricated by CSAM followed by hot-rolling. To study the effect of annealing temperature on the microstructure and mechanical properties of the Ti/steel clad plates, three different temperatures (i.e. 450, 550 and 650 °C) were selected. After analyzing all the experimental results, following conclusions are drawn:
- (1)
Annealing promotes the recovery and recrystallization mechanisms in the Ti/steel clad plates. The hot-rolled sample was completely recovered
CRediT authorship contribution statement
Zhipo Zhao: Investigation, Methodology, Formal analysis, Writing - original draft. Naeem ul Haq Tariq: Writing - review & editing. Junrong Tang: Investigation, Formal analysis. Yupeng Ren: Data curation. Hanhui Liu: Data curation. Min Tong: Resources. Lisong Yin: Writing - review & editing. Hao Du: Writing - review & editing, Formal analysis. Jiqiang Wang: Supervision, Project administration. Tianying Xiong: Supervision, Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The financial support of National Natural Science Foundation of China (No. 51671205) is gratefully acknowledged.
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2023, Defence TechnologyCitation Excerpt :Explosive welding is an important processing method for Ti/Fe clad plate, which converts chemical energy released by explosive detonation into kinetic energy of flyer layer to achieve metallurgical bonding between the two metallic plates [8–11]. Flyer layer for explosive welding needs to collide with base layer at high speed, thus the thickness of flyer layer is generally more than 2 mm to withstand explosion load [12–15]. However, titanium layer with a thickness of 400 nm could play a corrosion resistance effect [1,2,16].