Caracterização microestrutural e mecânica da liga Ti-35Nb-7Zr-5Ta produzida por fusão seletiva à laser

Abstract

Selective Laser Melting (SLM) is an additive manufacturing technique that consists of a layer-by-layer fusion of a powder bed by scanning a laser enabling the production of full density parts accordingly to a 3D CAD model with complex geometry. Biocompatible beta-TiNb alloys have been specially considered as promising to replace the more conventional Ni-Ti and Ti-6Al-4V alloys to be used in prostheses because their low Young’s modulus and their excellent biocompatibility. In this study, the main objective is to investigate and compare the microstructure and mechanical properties of a beta Ti-35Nb-7Zr-5Ta (TNZT) alloy processed by SLM using three different scanning strategies: unidirectional (Y); bi-directional, 79° rotating between layers (R79°); and checkboard (CHB). We produced samples in a SLM Realizer 50 with a laser power of 129W, scanning speed of 0,57 m/s, layer thickness of 40μm, in argon atmosphere, using those three different strategies. We analyzed these samples in terms of density and porosity using Archimedes’ principle and micro X-ray computerized tomography. Moreover, we characterized the samples by X-ray diffraction, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattered diffraction, and compression and microhardness tests. All samples presented columnar dendritic and equiaxial grains of beta Ti phase, preferably oriented in the building direction. The oxygen percentage increased in relation to the starting powder, indicating oxygen absorption during the process. The samples showed greater than 99.5% relative density with pores of different shapes, sizes and distribution among the strategies. The EBSD showed samples with different textures. The samples showed high ductility under compression, without premature failure. The yield limit ranged between σ = 436 and 466 MPa and elastic modulus between E = 47 and 50 GPa. The Vickers microhardness values kept constant along the building direction (190 HV) for both samples.