Processamento, caracterização microestrutural e avaliação das propriedades mecânicas de compressão de ligas de Ti-6Zr-2Si-1B, Ti-6Zr-6Si-3B e Ti-6Zr-10Si-5B tratadas termicamente

Abstract

Titanium alloys are widely used for medical implant devices and high-temperature structural components due to their physical, chemical, mechanical and biological properties. For bearing articular orthopedic components, the Co-Cr-Mo alloys with metal matrix and intermetallic precipitates have presented superior wear resistance whereas the Ti alloys exhibit better biocompatibility. The Ti-Si-B and Ti-Zr-Si-B alloys with similar microstructures and superior bone integration than pure Ti can be produced by conventional arc melting and subsequent heat treatment. Previous works have indicated that the Zr addition can contribute to increase the oxidation resistance of Ti-Si-B alloys and, depending on its added amount the Ti6Si2B or Ti3Si is preferentially formed in these heat-treated alloys. However, limited information on mechanical properties of these materials are found in literature. In this sense, the aim of this work was the microstrutural characterization and evaluation on compression mechanical properties of the Ti-6Zr-2Si-1B, Ti-6Zr-6Si-3B and Ti-6Zr-10Si-5B (%-at.) alloys produced by arc melting and subsequent heat treatment. The following staring materials were used to produce the Ti-Zr-Si-B alloys: Ti (min. 99.7 wt-%), Zr (min. 95 wt.-%, with up to 4.5 wt.-% Hf), Si (99.999 wt.-%) and B (99.5 wt.-%). Ti-Zr-Si-B ingots weighting close to 40 g were produced in a furnace under Ar atmosphere using water-cooled copper crucible, non-consumable W electrode and Ti getter. In the sequence, the ingots were heat treated under Ar atmosphere at 1100oC for 4h, and cylinder bodies were successfully machined. The microstructural characterization of as-cast and heat-treated Ti-Zr-Si-B alloys were conducted by means of X-ray diffraction, optical microscopy, scanning eléctron microscopy and energy dispersive spectrometry techniques. The microhardness and compression mechanical properties were determined in accordance with ASTM E384 and ASTM E9 standards, respectively. To identify the fracture type and mechanism, the fracture surfaces of Ti-Zr-Si-B were investigated by SEM analysis. Results have indicated that the heat-treated Ti-6Zr-2Si-B and Ti-6Zr-6Si-3B alloys were formed by Ti-α as matrix and the disperses TiB and Ti3Si precipitates, whereas the Ti-6Zr-10Si-5B alloy with two-phase Ti-α and Ti3Si matrix besides the disperse TiB precipitates. In detrimental to the Ti6Si2B, the Zr was prefferentially dissolved into the Ti3Si lattice. It was noted that the values of Vickers microhardness, yield stress, ultimate compression stress, and fracture stress of Ti-Zr-Si-B alloys have increased whereas their total deformation reduced for the Si- and B-richer alloys, due to occurrence of strengthening mechanisms by substitutional (Zr in α-Ti and Ti3Si, and Si in α-Ti) and interstitial (B in -Ti) solid solutions, precipitation (TiB) and deformation mechanisms during plastic deformation. The fracture surfaces indicated the presence of dimples, which were reduced for the Si- and B-richer alloys, indicating that the fracture behavior from ductile to quasi-cleavage was achieved. Transgranular and intergranular fractures were identified close to the -Ti and TiB (and Ti3Si) regions. TiB and Ti3Si were efficient to difficult and change the crack path during plastic deformation.