Abstract
The comparisons of mechanical properties and fracture behaviour between as-consolidated PM Ti-5553 alloy and as-cast IM Ti-5553 alloy were investigated through tensile, fracture toughness and impact toughness tests in this research. The slightly higher strength but much higher ductility and toughness can be identified in IM alloy specimens, which is also confirmed by the fracture behaviour of the specimens after mechanical tests. IM alloy specimens always exhibit the ductile dimple fracture mechanism in the different tests, while the fracture mechanism of PM alloy specimens indicates a high loading rate sensitivity, changing from the mixed ductile-brittle quasi-cleavage fracture into the brittle cleavage fracture mechanism accompanied by the remarkable decrease of impact toughness. The relatively low mechanical properties, especially the ductility and the brittle fracture behaviour of as-consolidated PM Ti-5553 alloy, are mainly explained by the differences in the initial microstructures between these two alloys.
Highlights
Titanium and its alloys are very promising materials in high-performance engineering applications due to their excellent properties, such as high specific strength, excellent corrosion resistance and biocompatibility 1-3
The mechanical properties of the Ti-based parts prepared through HIP 10, PS 11, BE and SLM routes are examined to meet the ASTM standard, It was reported that Powder metallurgy (PM) parts are still suffering from some shortages in mechanical properties compared with ingot metallurgy (IM) products including low ductility, low fatigue resistance and insufficient fracture toughness
A relative flat fracture surface composed by continuous small fracture facets and tear ridges can be observed in the macroscopical images of PM alloy (Fig. 2a), the detailed fracture surface morphologies can be revealed in Fig. 2b and 2c, typical cleavage fracture facets with river-like patterns divided by tear ridges, some ununiformly distributed shallow and small dimples can be clearly identified
Summary
Titanium and its alloys are very promising materials in high-performance engineering applications due to their excellent properties, such as high specific strength, excellent corrosion resistance and biocompatibility 1-3. There were significant efforts to study the mechanical properties and fracture behaviour of IM metastable β titanium alloys including Ti-5553 alloys during tensile, fracture toughness and impact tests. The relationship between the fracture behaviour and residual porosity of powder metallurgy (Pressing-Sintering) Ti-6Al-7Nb biomedical titanium alloy obtained by different sintering temperature was explored by Bolzoni et al 20. In these related works, the mechanical properties and fracture behaviour of IM and PM titanium alloys were studied and discussed, but there is no work compared the mechanical properties directly between PM and IM alloys comprehensively, nor the comparisons of fracture behaviour were referred. The microstructure, mechanical properties, fractographic characterization and fracture mechanisms of PM and IM Ti-5553 alloys are investigated and discussed
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