Mirza Nadeem Baig

Dissimilar welding of Nickel and Titanium alloys is crucial for high performance applications, yet possess several challenges because of disparate metallurgical properties. This paper explores autogenous Electron Beam Welding (EBW) of Nitinol with Ti6Al4V in a butt joint configuration. Unlike, other autogenous dissimilar fusion welding of titanium and nickel alloys, no macroscopic cracks were observed during or after solidification. Optical microscopy and Scanning Electron Microscopy revealed distinct microstructures at the titanium and nickel interfaces, and within the weld zone. Microstructure at the interface of titanium was markedly different from the microstructure at nickel alloy interface. Composition analysis via Energy Dispersive X-Ray Spectroscopy and X-Ray Diffraction detected Ti2Ni and NiTi intermetallic compounds, with higher Ti2Ni concentrations near the titanium interface. Tensile test yielded an average strength of 160 ± 5 MPa and 0.92% percent elongation, with fracture occurring at the titanium interface in regions of high Ti2Ni concentration. Fracture surface of the tensile test specimen mostly highlighted brittle failure mode. The peak hardness value was also observed near the titanium interface. This study demonstrates the feasibility of autogenous EBW for dissimilar nickel-titanium alloy joints without interlayers, providing a foundation for future research and potential improvements through interlayer applications.

Corrosion and heat treatment studies are essential to predict the performance and sustainability of the coatings in harsh environments, such as the oil and gas industries. In this study, nickel phosphorus (NiP)–titanium (Ti) nanocomposite coatings (NiP-Ti nanoparticles (TNPs)), containing various concentrations of Ti nanoparticles (TNPs) were deposited on high strength low alloy (HSLA) steel through electroless deposition processing. The concentrations of 0.25, 0.50 and 1.0 g/L TNPs were dispersed in the electroless bath, to obtain NiP-TNPs nanocomposite coatings comprising different Ti contents. Further, the effect of TNPs on the structural, mechanical, corrosion, and heat treatment performance of NiP coatings was thoroughly studied to illustrate the role of TNPs into the NiP matrix. Field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDX) results confirm the successful incorporation of TNPs into the NiP matrix. A substantial improvement in the mechanical response of the NiP matrix was noticed with an increasing amount of TNPs, which reached to its ultimate values (hardness 675 Hv, modulus of elasticity 18.26 GPa, and stiffness 9.02 kN/m) at NiP-0.5TNPs coatings composition. Likewise, the electrochemical impedance spectroscopy measurements confirmed a tremendous increase in the corrosion inhibition efficiency of the NiP coatings with an increasing amount of TNPs, reaching ~96.4% at a composition of NiP-0.5TNPs. In addition, the NiP-TNPs nanocomposite coatings also unveiled better performance after heat treatment than NiP coatings, due to the presence of TNPs into the NiP matrix and the formation of more stable (heat resistant) phases, such as Ni₃P, Ni₃Ti, NiO, etc., during the subsequent processing.