PhD Defence Hadi Moutablaleh | Multimaterial Laser Powder Bed Fusion of Ti6Al4V and NiTi Shape Memory Alloys

Multimaterial Laser Powder Bed Fusion of Ti6Al4V and NiTi Shape Memory Alloys

Hadi Moutablaleh is a PhD student in the Department of Advanced Manufacturing, Sustainable products & Energy systems. (Co)Promotors are dr.ir. T.H.J. Vaneker, prof.dr. I. Gibson and dr.ir. M. Mehrpouya from the Faculty of Engineering Technology.

The evolution of metal additive manufacturing from single material to multimaterial systems enables the production of next-generation components with site-specific functionality. In the medical field, traditional orthopedic implants manufactured from single alloys like Ti6Al4V often fail due to a mechanical mismatch with natural bone (~110 GPa vs. ~20 GPa), leading to stress shielding and aseptic loosening. This thesis presents a manufacturing-led strategy to address these challenges by developing the fundamental metallurgical and process knowledge required for multimaterial Laser Powder Bed Fusion (LPBF), specifically investigating the integration of high-strength Ti6Al4V with superelastic, low-modulus Nickel-Titanium (NiTi).

The research first establishes a baseline for LPBF-processed NiTi. Through a comparative functional analysis of architected metastructures, it demonstrates that NiTi’s superior energy dissipation and damping capacity are driven primarily by its intrinsic superelastic hysteresis rather than structural design alone. To ensure precise process control, a high-fidelity, temperature-dependent laser absorptivity coefficient for NiTi was determined and validated.

The core of this work explores the fabrication of uninterrupted Ti6Al4V–NiTi interfaces using an advanced Aerosint Selective Powder Deposition system. While this technology overcomes multimaterial deposition constraints, metallurgical investigation reveals a failure mechanism dominated by brittle intermetallic compounds (IMCs), specifically Ti2Ni and Ni3Ti. Systematic analysis of Volumetric Energy Density (VED) shows that increasing energy input encourages elemental intermixing and promotes interfacial cracking, proving that direct fusion without an interlayer is insufficient for load-bearing applications.

The thesis concludes by proposing a framework for next-generation biomimetic orthopedics. The results justify a hybrid architectural concept: a Ti6Al4V core providing the 860 MPa yield strength required for structural integrity, integrated with NiTi functional zones for modulus matching. Future work outlines a third-element interlayer (CuCrZr) to suppress IMC formation, enabling functional, multimaterial bone implants with long-term mechanical stability.

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