Thermo-mechanical analysis of functionally graded nickel/titanium alloys under different process parameters of directed energy deposition

Abstract

The build-up of residual stress and porosity plays an important role in the mechanical properties of as-built parts during directed energy deposition (DED). However, the thermo-mechanical behavior of functionally graded nickel/titanium alloys (FGNTAs) in the DED process remains unclear. In this study, a computationally efficient thermo-mechanical coupled model of DED-printed FGNTAs with different porosities is developed. The temperature-dependent effective material properties of FGNTAs are first determined based on the rule of mixture. Subsequently, the temperature, residual stress, and deformation fields within as-built FGNTAs are predicted using the differential quadrature method. The predicted results show excellent agreement with the predictions and experimental data in the literature. Furthermore, the effect of key parameters on the thermo-mechanical responses of DED-printed FGNTAs is investigated, including energy density, porosity distributions, part dimensions, temperature settings, and structural modes. The results show that the residual stress and vertical deflection increase with the higher energy input, length-to-width ratio, and evener porosity distributions, while decreasing with larger porosity, preheating as well environment temperatures, external loads, and power index. These results can provide a useful guideline for the design and manufacturing of high-quality FGNTAs during DED.