Investigations on phase transformation and mechanical characteristics of laser additive manufactured TiNiCu shape memory alloy structures

Abstract

This paper reports laser additive manufacturing (LAM) of shape memory alloyed (SMA) structures using three premixed compositions of TiNiCu (Ti50Ni (50−x)Cux(x = 5,15 and 25)). A 2 kW fiber laser based additive manufacturing system was used. First, the processing parameters were optimized for defect free deposition, subsequently the optimized parameters were used for the LAM of the structures. These fabricated structures were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), micro-hardness measurement and compression testing. SEM and AFM revealed the fine grain structures with good surface morphological characteristics (<5 μm Ra value) for TiNiCu5. The ultimate compressive strength, modulus of elasticity and micro-hardness values for this sample was 451 ± 15 MPa, modulus of 28 ± 2 GPa and 237 ± 12 VHN, respectively. XRD confirmed the presence of two phases austenite and martensite in the LAM samples and DSC demonstrated low hysteresis between 22 °C and 25 °C, a prime requirement of SMA. The study paved a way for LAM of complex shapes using TiNiCu with all the prerequisite properties of SMA. © 2016 Elsevier B.V.