Microstructure and phase evolution of functionally graded multi-materials of Ni–Ti alloy fabricated by laser powder bed fusion process

Abstract

The layer-by-layer laser powder bed fusion (L-PBF) process was applied to fabricate functionally graded multi-materials (FGMs) of nickel-titanium alloy. The FGMs Ni–Ti alloy was built with composition transitioning from pure Ni incrementally graded to pure Ti by different composition gradients. The microstructure, chemical composition, and phase evolution were characterized using SEM, EDS, XRD, and EBSD along the build direction. By varying the proportions of Ni and Ti, the microstructure and phases were changed gradually across the build direction. Several phase transformations, γ-Ni → NiTi B2 + intermetallic phases → α-Ti, appeared through the compositional gradient. Cracks were found in the gradient zone, and the results were explained in terms of the various phases present. The potential to accomplish such a completely deposited FGMs Ni–Ti alloy and considerable changes in composition are made possible by a new strategy to make innovative FGMs Ni–Ti alloys together with 3D components using L-PBF additive manufacturing.

Keywords

• Laser powder bed fusion process
• Functionally graded materials
• Ni-Ti alloy
• Microstructure
• Compositional gradient