توصيفگر ها :
آلياژ هاي آنتروپي بالا , فولادهاي زنگ نزن آستنيتي , فرايند جوشكاري قوسي تنگستن-گاز محافظ , آزمون پراش پرتو ايكس , آزمون سختي وريزسختي , آزمون كشش , شكست نگاري
چكيده انگليسي :
The purpose of this research is to investigate the microstructural and mechanical properties of dissimilar joint between CuFeNiMnTi cast high entropy alloy (HEA) and 316Ti cold rolled austenitic stainless steel(SS). In this regard, similar and dissimilar joints of HEA and SS were conducted using gas tungsten arc welding process without using filler metal, and their microstructural and mechanical properties were investigated. The microstructure of different areas of weldments was investigated using X-ray diffraction analysis, optical microscope and scanning electron microscope equipped with X-ray energy dispersive spectrometer. In order to investigate the mechanical behavior of base metals and weld sections, hardness and microhardness tests and uniaxial tensile tests were carried out. Also, fracture surfaces were investigated using scanning electron microscope after tensile testing. The results of this research showed that the microstructure of the weld metal in similar joint of SS, includes 10% delta ferrite phase with skeletal morphology in the matrix of austenite phase, which well reduces the sensitivity to solidification cracking of the weld metal. The microstructure of the weld metal in similar joint of HEA, is similar to the base metal of this alloy, but it has a finer structure and includes two FCC phases rich in copper and nickel, a Fe2Ti lava phase, a BCC(β) phase, and FeTi and NiTi intermetallic phases. The microstructure of dissimilar weld metal between HEA and SS includes austenite, Fe2Ti lave, BCC(β) and FCC phases. Investigations showed that the microstructure of the dissimilar joint weld metal, is not similar to the conventional solidification structures, and during cooling between solidus temperature and room temperature, it underwent a phase transformation of the spinodal decomposition type and creates a modulated structure in the core of the dendrites of the austenite phase. This event is while the inter-dendritic regions that constitute the lave phase have remained unchanged. Average microhardness values in; base metal, heat-affected zone and weld metal in the similar joint of HEA weldment, are 438, 475, 515 Vickers and in; base metal, heat-affected zone and weld metal in the similar joint of SS weldment, are 360, 174, 170 Vickers and in; heat affected zone of HEA, weld metal and heat affected zone of SS in dissimilar joint weldment are 459, 363, 180 Vickers, respectively. Also Average hardness values in; base metal, heat-affected zone and weld metal in the similar joint of HEA weldment, are 398, 406, 427 Vickers and in; base metal, heat-affected zone and weld metal in the similar joint of SS weldment, are 300,164, 157 Vickers and in; heat affected zone of HEA, weld metal and heat affected zone of SS in dissimilar joint weldment are 413, 354,166 Vickers, respectively. The ultimate tensile strength of HEA base metal, SS base metal, similar joint of HEA weldment, similar joint of SS weldment, and dissimilar joint weldment are 380, 586, 440, 520 and 603 MPa and their elongation values are 5, 41, 6, 42 and 6.5 percent, respectively. Also, the tensile test results showed that the strength of the dissimilar joint weldment has increased in comparison with the strength of the similar joints and base metals, while its elongation in comparison with the the tensile samples of base metal and similar weldment of SS has decreased and it behaves as same as the base metal and similar joint of HEA weldment. The results of the fractography analysis of the weldments showed that the similar joint of SS weldment had a mostly soft fracture mechanism, while the weldment in similar joint of HEA had a completely brittle fracture mechanism and the weldment in dissimilar joint of SS to HEA had a mostly brittle fracture mechanism. Also, the failure of the weldments of SS similar joint, HEA similar joint, and dissimilar joint occurred in the base metal, weld metal, and weld metal, respectively.
