MICROSTRUCTURE CHARACTERIZATION AND MECHANICAL PROPERTIES OF CP-TI & SS-316L DISSIMILAR METAL JOINING USING GTAW

• Main Author: Ade Anugra, Binar
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/87471
• Institution: Institut Teknologi Bandung

This study was conducted to determine the optimal joining between dissimilar metals, Commercial Pure Titanium (CP-Ti) and Stainless Steel 316L (SS-316L). The selection of filler materials, including Al4043, ErTi3, and Tin Babbitt, executed using the fillet welding technique, was evaluated through dye penetrant tests, metallographic tests, hardness tests, and tensile tests. Tin Babbitt filler rod successfully produced a good bond between the two substrates, which was then further tested using butt welding techniques, varied with the use of a 1 mm thick SS-316L backing plate and different welding currents (185A, 195A, and 205A). The tests included dye penetrant, metallographic analysis, SEM-EDS, hardness, and tensile testing. The results showed metallurgical bonding at a low level due to minimal diffusion between the substrate and weld metal, with a UTS value below that of each substrate. The highest UTS achieved was 50.91 MPa using a 205A current and without a backing plate. Sensitization occurred but at a very minor level. Brittle behavior was observed in the HAZ, where hardness increased proportionally with welding current for welds without a backing plate, while the opposite trend occurred when using a backing plate. There were indications of brittle compounds, such as Fe-Ti or other compounds like carbides or oxides, due to the presence of C, O, Fe, and Ti in the weld metal area. A significant increase in Fe and Ti was observed in discontinuities (porosity), accompanied by a reduction in Sn and Sb, forming metallurgical porosity during the welding process. The addition of Cu as a filler rod alongside Tin Babbitt negatively impacted the welding integrity. This was evidenced by the behavior of Cu forming its own Cu-rich colonies and diffusing with other elements in the weld metal. Another contributing factor was the increased porosity compared to using only Tin Babbitt. The abundance of porosity was further confirmed by lower tensile test results (low-level metallurgical bonding), which tended to decrease as welding current increased. However, the use of a backing plate produced higher values compared to welding without a backing plate, as the backing plate helped distribute heat during rapid cooling, resulting in a more uniform and stable microstructure. The broader hardness distribution in the HAZ, accompanied by an increased Cu concentration in the HAZ of each substrate, indicated embrittlement, although it did not lead to cracking (cold cracks). The presence of C, O, Fe, and Ti, along with the reduction of Sn, Sb, and Cu in the weld metal, posed similar risks to those observed when only Tin Babbitt was used as the filler rod. The use of Cu as a backing plate further exacerbated the situation due to its high thermal conductivity and coefficient of thermal expansion (CTE), which caused distortion in the weld metal. This was evidenced by cracks initiated from the backing plate. The UTS values were also worse compared to welding without a backing plate under the same welding current. This study presents potential advancements by optimizing filler rods with high thermal conductivity, lower melting points, and Fe content between 5-10%. Focusing on conventional GTAW techniques can support field applications involving titanium and stainless steel, providing a cost-effective solution. This research is highly applicable in fabrication processes, enabling high-quality joints that meet industrial standards.