Fahd Nawaz Khan

Electroless coatings mark a significant improvement in surface engineering by providing superior uniformity, precision, and functional properties compared with traditional plating processes. Electroless Ni-P-Al₂O₃ composite coatings were successfully deposited on Ti-6Al-4V, forming a Ni-Ti intermediate (~14–16 µm) that ensured strong interfacial bonding. Al₂O₃ concentration (0.2–1.4 g/L) strongly influenced microstructure and performance, with 0.4 g/L yielding the most refined coating. AFM revealed a dense, uniform surface with the lowest roughness (~23.4 nm). This composition achieved the highest hardness (464.6 HV_0.1), ~157% higher than the substrate and ~53% higher than Ni-P. It also showed superior tribological behavior, reducing wear volume to ~4.46 × 10⁻⁷ mm³ and friction coefficient to ~0.32 (~85% and ~50% reductions vs. substrate). Corrosion resistance was maximized at 0.4 g/L, with the lowest corrosion current (2.45 × 10⁻⁶ A/cm²) and rate (0.0053 mpy), outperforming both Ni-P and uncoated Ti-6Al-4V due to the compact composite matrix and stable passive film.

Titanium is widely used in aerospace and medical industries for its high strength-to-weight ratio and corrosion resistance, while Inconel 718 is favored in aerospace and power generation for its exceptional mechanical strength and oxidation resistance at high temperatures. It’s challenging to directly combine the Inconel 718 and the titanium, so the interlayer of vanadium is used which causes the strengthening of the bond by the formation of inter-metallics (TiaNib, NixVy). In this study, the RVE model was developed in order to examine the mechanical properties (i.e. Modulus, Poisson ratio) of the inter-metallics, by examining their microstructures. Furthermore, nanoindentation techniques are employed across different zones of the weldment to determine the modulus and hardness values. At the vanadium-Inconel interface, hardness and modulus values were observed to range from 2 to 8.5GPa and 130 to 205GPa respectively. The maximum error in hardness between the experimental and simulation was 3.75%. The pile up behavior was also examined in the simulation setup to determine the amount of plastic zone in the indent.

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.

A void closure analytic model for the diffusion bonding of titanium TC4 alloy is developed in this study, in which an FEA-based deformation mechanism is coupled with a numerical analysis for diffusion. The focus was to evaluate the effect of pressure and the temperature on the bonded ratio. As the value of bonding pressure or the bonding temperature increased, the bonding time decreased. The dependence of bonded ratio and time was modeled as an exponential curve. The geometrical model for the mechanism was utilized so that it can incorporate the void division aspect in the process of diffusion bonding.

The component’s strength and reliability are greatly influenced by the occurrence of cracks and flaws. Material surfaces or internal defects can create stress concentration, which causes failure of the materials. To quantify the stress intensity factor (SIF) and strain energy release rate (SERR) around the tips of the crack, numerical simulation has been performed on a plate of central crack with Comsol Multiphysics. The SIF and SERR with varying uniaxial stress loading (5, 10, 15, 20, 25 MPa) and crack’s angle (0°–180°) were determined using the J-integral method. The results show that the crack’s maximum opening and sliding displacement occurred at an angle of 90° and 45° respectively. For mode I, the SIFs were maximum at the crack’s inclination of 90° and for mode II, it was maximum at an angle of 45°. Similarly, the SERR was also found to be maximum when the crack was normal to the applied stress and observed to increase with the increase in applied stress.

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.