Investigation of Microstructure and Mechanical Properties of Fe-V Dissimilar Welds
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INTRODUCTION
VANADIUM alloys have many desirable properties that make them suitable for a number of demanding engineering applications.[1] There is considerable interest in joining of vanadium with steels to exploit their excellent performance as well as reduce the cost. Fe-V system shows large regions of continuous (aFe, V) solid solution phase, but it also contains brittle r-phase (r-FeV) which is formed congruently from (aFe,V) solid solution near the equiatomic composition in the temperature range of 650 C to 1219 C.[2] Several research workers[3–5] have proved that this brittle r-phase can be inhibited under high cooling rates. However, the zones whose compositions correspond to r-phase homogeneity range are crack-susceptible.[6] The exact reason behind this remains unclear. Metallurgical incompatibilities are the principal factors that restricted the dissimilar bonding.[7–9] However, the mechanical properties of such welds can be enhanced by the addition of an intermediate that modifies the final phase compositions.[10,11] Due to their high ductility and relatively low cost, Cu and its alloys are widely used as
intermediate materials in dissimilar couples that are confronted with brittle phases.[12,13] Moreover, there are no intermetallic phases in Cu-V and Cu-Fe systems.[14,15] The assumption of using Cu as an intermediate is further supported by Wang et al.[16] where sound joints are obtained with the composite Cu33V filler during steel and titanium dissimilar joining. Therefore, the aim of this study is to further investigate the phase formation in Fe-V weld metal. Effort on improving the phase constitutions has also been made by the addition of a Cu intermediate. Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) were used to characterize the microstructures. Nanoindentation was employed to identify the mechanical properties. Based on the phase diagrams and welding thermal cycles, a simple model was developed to elaborate the possible phase formation mechanism in Fe-V and Cu-Fe-V systems. This is a preliminary research for further manufacturing of Fe-V dissimilar welded structures.
II. QIAOLING CHU is with the College of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China and also with the School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology(QUT), Brisbane, QLD 4001, Australia. MIN ZHANG and JIHONG LI are with the College of Materials Science and Engineering, Xi’an University of Technology. Contact e-mail: [email protected] NING HU is with the College of Aerospace Engineering, Chongqing University, Chongqing 400044, China. CHENG YAN is with the School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT). Contact e-mail: [email protected] Manuscript submitted November 23, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
EXPERIMENTAL PROCEDURES
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