Investigating Nanoindentation Creep Behavior of Pulsed-TIG Welded Inconel 718 and Commercially Pure Titanium Using a Vanadium Interlayer

Abstract

In a dissimilar welded joint between Ni base alloys and titanium, creep failure is a potential concern as it could threaten to undermine the integrity of the joint. In this research, the mechanical heterogeneity of a Pulsed TIG welded joint between commercially pure titanium (CpTi) and Inconel 718 (IN718) with a vanadium (V) interlayer was studied through a nanoindentation technique with respect to hardness, elastic modulus, and ambient temperature creep deformation across all regions (fusion zones and interfaces, mainly composed of a dendritic morphology). According to the experimental results, a nanohardness of approximately 10 GPa was observed at the V/IN718 interface, which was almost 70% higher than that at the V/CpTi interface. This happened due to the formation of intermetallic compounds (IMCs) (e.g., Ti2Ni, NiV3, NiTi) and a (Ti, V) solid solution at the V/IN718 and V/CpTi interfaces, respectively. In addition, nanohardness at the V/IN718 interface was inhomogeneous as compared to that at the V/CpTi interface. Creep deformation behavior at the IN718 side was relatively higher than that at different regions on the CpTi side. The decreased plastic deformation or creep effect of the IMCs could be attributed to their higher hardness value. Compared to the base metals (CpTi and IN718), the IMCs exhibited a strain hardening effect. The calculated values of the creep stress exponent were found in the range of 1.51–3.52 and 2.52–4.15 in the V/CpTi and V/IN718 interfaces, respectively. Furthermore, the results indicated that the creep mechanism could have been due to diffusional creep and dislocation climb.

Influence of pulsed Nd:YAG laser welding power on the microstructures and nano creep behaviour of Ti5Al2.5Sn beads

“…Using the same methodology, the measured stress component of all the beads, except the one produced that formed at 360 W, was calculated to be less than 2 as presented in Figure 11 (b), indicating the activation of the diffusional creep mechanism, the material deforms plastically over time. 61 The 360 W specimen had the creep stress exponent greater than 2 (2.06), suggesting grain boundary sliding as the creep deformation mechanism. 61 However, better mechanical properties were obtained from the 440 W bead, since the nanohardness and elastic moduli were almost the same as the BA as shown in Table 3.…”

“…61 The 360 W specimen had the creep stress exponent greater than 2 (2.06), suggesting grain boundary sliding as the creep deformation mechanism. 61 However, better mechanical properties were obtained from the 440 W bead, since the nanohardness and elastic moduli were almost the same as the BA as shown in Table 3.…”

“…Higher values of the creep stress exponent are indicative of better creep resistance. 60 Shehbaz et al 61 measured the creep stress exponent of P-TIG welded CpTi with Inconel using V as an interlayer. Using the same methodology, the measured stress component of all the beads, except the one produced that formed at 360 W, was calculated to be less than 2 as presented in Figure 11 (b), indicating the activation of the diffusional creep mechanism, the material deforms plastically over time.…”

Combined titanium-steel structures formation by directed energy deposition using vanadium and nickel interlayers

“…Pure vanadium is often applied as an interlayer between titanium alloy and steel [16][17][18][19][21][22][23][24]. When fusing vanadium and iron-based alloys, the possibility of σ-phase brittle layer formation on the fusion line has existed.…”

Obtaining of combined titanium-steel structures by electron beam freeform fabrication using niobium and copper interlayers

“…Considering that niobium is not metallurgically compatible with iron, it is essential to use the second interlayer, namely nickel [17,[26][27][28][29][30][31], copper [2, 6, 8,9, 16,19,[21][22][23] or alloys based on them. Based on the analysis of the nickel interaction with vanadium [26,27, 28] and niobium [17,[29][30][31] the formation of brittle phases is noted in both systems [26,[29][30][31]. Hardness varies from 723 [31] to 2450 HV [26].…”