Effects of Interlayer Materials Fe and Nb on Interfacial Shear Strength of Hot Extruded High-Strength Titanium-Steel Composite Pipe
CHENG Lei(), ZHANG Xuhang, HAN Ying, CHENG Zhicheng, YU Wei
Institute of Engineering Technology, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
CHENG Lei, ZHANG Xuhang, HAN Ying, CHENG Zhicheng, YU Wei. Effects of Interlayer Materials Fe and Nb on Interfacial Shear Strength of Hot Extruded High-Strength Titanium-Steel Composite Pipe. Acta Metall Sin, 2024, 60(1): 117-128.
The production of metallic composites is an effective way to combine the advantages of different metals. Specifically, the combination of titanium and CrMo steel in a composite pipe can yield good corrosion resistance and excellent abrasion performance, rendering it highly promising for use in the petroleum industry. However, the interfacial reactions between the two metals during the manufacturing process can lead to the precipitation of brittle carbides or intermetallic compounds, resulting in substantial weakening of the combining strength. This is particularly problematic for the TC11 titanium and CrMo steel matrix due to their higher alloy content. Thus, to improve the bonding properties of titanium-steel composites, an interlayer is added between the matrixes. In this study, the effects of interlayer materials (Fe and Nb), extruding temperatures (920 and 970oC), and heat treatment on the bonding strength of high-strength CrMo steel and TC11 titanium matrixes were investigated. The results revealed that for the titanium-steel composite pipe, the bonding strength of the Fe-titanium interface dominates the shear stress (185 MPa) due to the locking effects of unevenly deformed grains. However, after heat treatment, M23C6 heavily precipitates in the Fe interlayer causing it to become hard and brittle, weakening the locking effects, and resulting in a significant decrease in shear stress (70 MPa). Conversely, the Nb-interlayer samples extruded at 920oC mainly cracked along the steel-Nb interface, while those extruded at 970oC mainly cracked along the Nb-titanium interface. Thus, the two interfaces respectively dominated the shear stress of the two Nb-interlayer samples, and this feature persisted after heat treatment. Moreover, the different cracking routes were found to be caused by the formation of a new NbC layer and a β-titanium layer, respectively. As the fractured NbC layer recovered during the heat treatment, the shear stress of the 920oC extruded sample increased to 170 MPa and that of the 970oC extruded sample decreased due to the solution of Ti0.86Al0.11Nb0.03 particles and the discontinuous β-titanium layer induced by it. Thus, the comparative study of interlayer materials and different processing parameters on the interfacial shear stress can effectively improve the production of hot-extruded high-strength titanium-steel pipe.
Fig1 Schematics of the extrusion billet (a), tensile shear and compressive shear samples (b) and hardness testing method (c), and cross section and length features of the extruded compound pipe (d)
Fig.2 Interfacial characteristics (a) and related phase distribution features (c) of the 920oC extruded sample with a Fe interlayer (Fe-920oC), and interfacial characteristics (b) and EDS mappings (d) of the 970oC extruded sample with a Fe interlayer (Fe-970oC)
Fig.3 Linear distributions of alloying elements (a, b, d, e) and interfacial microstructures (c, f) of samples with a Fe interlayer (a) Fe-920oC (b, c) Fe-920oC-H (H means the sample with heat treatment, the same below) (d) Fe-970oC (e, f) Fe-970oC-H
Fig.4 Interfacial characteristics of the 920oC extruded sample (Nb-920oC) (a) and 970oC extruded sample (Nb-970oC) (b) with a Nb interlayer, EDS mappings corresponding to Fig.4a (c), and the enlarged views of rectangle regions marked in Figs.4a and b (d1-d3)
Fig.5 Linear distributions of alloying elements (a, b, d, e) and interfacial microstructures (c, f) of samples with a Nb interlayer (a) Nb-920oC (b, c) Nb-920oC-H (d) Nb-970oC (e, f) Nb-970oC-H
Interlayer
T / oC
Shear stress 1 / MPa
Fracture interface
Shear stress 2 / MPa
Shear stress 3 / MPa
Fracture interface
Fe
920
185
Fe-TC11
70
75
Fe-TC11
970
163
Fe-TC11
73
89
Fe-TC11
Nb
920
131
Steel-Nb
170
140
Steel-Nb
970
135
Nb-TC11
98
68
Nb-TC11
Table 1 Shear stresses of different bonding interfaces and corresponding fracture features
Fig.6 Hardness distributions of Fe-970oC and Fe-970oC-H (a), Nb-920oC and Nb-920oC-H (b), Nb-920oC and Nb-970oC (c), and β-Ti layer in Nb-920oC-H (d)
Fig.7 Isothermal sections (1000oC) of typical ternary phase diagrams (The marked numbers and symbols indicate the EDS indexed compositions of the five compounds formed in the interface of sample Fe-920oC in Fig.2c; the content of each element in the figures is the atomic fraction, %) (a) C-Cr-Fe (b) C-Ti-Fe (c) C-Ti-Al (d) Fe-Ti-Nb (The shaded green region presents the infinite solid solution relationship between Nb and β-titanium)
Fig.8 Microstructures of Fe-920oC (a) and Fe-970oC (b) samples, and microstructure of Fe-970oC-H (c) and corresponding precipitation state (d) (Arrows with green, blue, and red colors indicate the β-Ti grains, the original steel-Fe interface, and the newly formed zigzag interface after the hot extrusion process, respectively)
Fig.9 Shear fractures of Fe-920oC (a), Fe-970oC (b), Nb-920oC (c), Nb-920oC-H (d), Nb-970oC (e), and Nb-970oC-H (f)
Fig.10 Schematics of interfacial microstructures of Fe-920oC (a), Fe-970oC (b), Fe-970oC-H (c), Nb-920oC (d), Nb-970oC (e), and Nb-920oC-H (f) samples (Red arrows indicate the interface reliefs caused by the inhomogeneous deformation of grains)
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