Issue 48

H. S. Patil et alii, Frattura ed Integrità Strutturale, 48 (2019) 377-384; DOI: 10.3221/IGF-ESIS.48.36 381 Figure 2: Tensile test specimens for welded samples The tensile properties of welded titanium for different joints were measured at room temperature. The welded joints have mechanical properties like in the range of yielding strength of 190-339.23 MPa, ultimate tensile strength of 318.46- 429MPa and percentage elongation of 6.66 %-26.66%. The stress-strain curves for weld samples with various weld process parameters have been shown in figure-3. The weld sample-5 exhibited good mechanical properties than other weld samples. These results indicate that the ultimate tensile strength of welded joints is higher than the yield strength, which indicates a noticeable work hardening beyond the yielding. Figure 3: Tensile test specimens for welded samples W ELD M ICROSTRUCTURE A NALYSIS The samples for optical microscopy were cut into the size of 30mmx25mmx3mm and pieces were polished using 100, 150, 220, 400, 600 grit silicon carbide paper. Etching procedures were used to expose the underlying microstructural features. Solutions used for etching titanium include a fresh Keller etchant with composition 5ml HNO 3 , 3ml HCL, 2ml HF and 190ml distilled water. The polished metallographic mount was etched in the solution from 40 to 50 seconds to reveal the microstructural features. The variation of microstructures/grain structures of various welded samples and C.P titanium has been shown in figure 4. Figure 5(a) shows the optical micrographs weld jointed commercially pure titanium moving from the base metal (BM) to the fusion zone (FZ) through the heat affected zone (HAZ). It has observed from the figure-5(b) that the BM microstructure of commercial pure titanium consists of equi-axed α-phase grains with the presence of fine and disperses precipitation of β-phase. Inside the grains structure and in the grain boundary, the fine and disperse precipitation of beta phase has noticed. The interface between the BM and the heat HAZ clearly indicates that the region from where the thermal cycles occurred during the welding process operate originally and usually on the change in microstructure. Due to this complex thermal cycle, the equiaxed grains had grown in larger size in the HAZ and it has noticed in the figure-5(c). As a result of the welding thermal cycles with a peak temperature, a significant grain coarsening is noticed in the FZ which consists of α-phase in different direction bounded by β-phase as depicted in figure 5(d). In comparison to the microstructure of the heat affected zone, an inhomogeneous growth of microstructure at the fusion zone has