Avaliação da dureza e do módulo de elasticidade de ligas Ti-Si-B e Ti-Zr-Si-B pela técnica de nanoindentação

Abstract

Ti-Si-B alloys based on Ti6Si2B have been considered with potential for structural applications in the areas of health and automotive / aeronautics / aerospace, because of their good characteristics of biocompatibility and resistance to corrosion. However, information about its mechanical properties is still limited in the literature. The titanium-rich Ti-Si-B alloys may present the eutectic formation of Ti + TiB, Ti + Ti6Si2B and Ti + Ti6Si2B + Ti5Si3 during solidification, depending on the chemical composition adopted. In Ti-Zr-Si-B alloys with 6% -at. Zr, the Ti6Si2B phase is not formed during solidification. In this regard, the present work aimed to evaluate the hardness and the modulus of elasticity of the 97Ti-2Si-1B, 91Ti-6Si-3B, 85Ti-10Si-5B, 95Ti-2Zr-2Si-1B, 89Ti-2Zr-6Si- alloys 3B and 83Ti-2Zr-10Si-5B (% -at.), as-cast and heat-treated, using the dynamic nanoindentation technique. Such information about the phases present in the microstructures of these alloys was also obtained. To obtain equilibrium microstructures, the alloys produced by arc melting were heat treated at 1200ºC for 16 h, under argon atmosphere. The microstructural characterization of as-cast and heat-treated Ti-Si-B and Ti-Zr-Si-B alloys were conducted by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry and dynamic nanoindentation tests. For the hardness and elastic module of phases in Ti-Si-B and Ti-Zr-Si-B alloys, the samples were carefully prepared following the conventional metallographic techniques and were subjected to nanoindentation tests. The results showed the microstructures of the as-cast ternary alloys were formed by the primary Ti-α precipitation and different eutectic regions formed by the TiB and Ti6Si2B phases. In as-cast quaternary Ti-Zr-Si-B alloys, the Ti3Si was preferentially formed instead the Ti6Si2B. After heat treatment, it was noted that the phases were coalesced and had the the preferential formation of the Ti-α and Ti6Si2B phases. As-cast ternary alloys presented the hardness values varying from 5.6±0.3 to 11.6±0.5, which have varied between 5.5±0.3 to 10.2±0.7 GPa after heat treatment. The quaternary alloys exhibited the values of 6.3±0.3 – 10.5±0.7 GPa and 4.8±0.4 – 12.4±0.7,GPa, respectively. Elastic module of the as-cast and heat-treated ternary alloys were varied between 163±9 – 222±16 GPa and 149±5 – 199±19 GPa, respectively. The as-cast and heat-treated quaternary alloys present similar results; i.e., their elastic module values were 174±11 – 224±15 GPa and 153±13 – 204±14 GPa, respectively. The results of the hardness and the reduced modulus of elasticity indicate that the addition of Zr did not result in any variation of these mechanical properties, regardless of the process condition. The addition of B and Si resulted in a significant increase in the hardness and reduced module of elasticity of the material, because of the greater amount of precipitates that are formed in the microstructure of these alloys during solidification and subsequent heat treatment.