Effect of Mn on the Properties of Powder Metallurgy Ti-2.5Al-xMn Alloys.

Titanium alloys are the ideal material for a wide range of structural applications, but their high cost compared to other metals hinders their adoption. Powder metallurgy and cheap alloying elements can be used to create new Ti alloys. In this study, the simultaneous addition of Al and Mn is considered to manufacture and characterise ternary Ti-2.5Al-Mn alloys obtained via pressing and sintering by varying the Mn content (1-10 wt.%). It is found that the addition of the alloying elements reduces compressibility. Consequently, the amount of porosity increases (8.5 → 10.8%) with the amount of Mn as the alloys were processed under the same conditions. The progressive addition of Mn refines the classical lamellar microstructure and, eventually, transforms it into an equiaxed ß-grain structure with acicular α grains. The microstructural changes lead to continuous increases in strength (ultimate tensile strength: 694 → 851 MPa) and hardness (225 → 325 HV30) with an associated loss of ductility (elongation to failure: 13.9 → 1.0%). However, the obtained ternary Ti-2.5Al-Mn alloys have similar or better overall mechanical behaviour than most of the binary Ti-Mn alloys obtained through a variety of manufacturing methods.

Antibacterial Ti-Mn-Cu alloys for biomedical applications.

Titanium alloys are common biomedical materials due to their biocompatibility and mechanical performance. However, titanium alloys are expensive and, unless surface treated, generally cannot prevent surgical infections related to bacteria which can damage the integrity of the implant. In this study, new titanium alloys were developed via powder metallurgy and the addition of manganese and copper, respectively, aiming to limit the manufacturing costs and induce new functionality on the materials including antibacterial response. The addition of manganese and copper to titanium significantly changes the behaviour of the Ti-Mn-Cu alloys leading to the successful stabilization of the beta titanium phase, great refinement of the typical lamellar structure, and achievement of materials with low level of porosity. Consequently, it is found that the mechanical performance and the antibacterial efficacy are enhanced by the addition of a higher amount of alloying elements. The manufactured Ti-Mn-Cu alloys fulfil the requirements for structural biomedical implants and have antibacterial response making them potential candidates for permanent medical implants.

Comparison of the Cracking Behavior of Powder Metallurgy and Ingot Metallurgy Ti-5Al-5Mo-5V-3Cr Alloys during Hot Deformation.

The hot workability of metallic materials is significantly dependent on its ability to form plastic without cracking and fracturing. In this work, the cracking behavior of powder metallurgy (PM) Ti-5Al-5Mo-5V-3Cr (Ti-5553) alloy, consolidated from powder mixture, at a deformation temperature range of 600 °C⁻850 °C and strain rate of 0.1 s-1⁻10 s-1, was investigated through isothermal compression tests. The cracking behavior of the as-cast ingot metallurgy (IM) Ti-5553 alloy, at a deformation temperature of 700 °C was also investigated for comparison. Results suggested that the PM Ti-5553 alloy had a better hot workability, with a larger cracking-free processing window, and a lower deformation resistance than the IM counterpart. 45° shear fracture occurred in the PM alloy, compressed at the condition of 600 °C/10 s-1, and edge cracking was observed at the 700 °C/10 s-1. 45° shear fracture was also significant in the IM alloy specimen tested at 700 °C/10 s-1, and all the other IM alloy specimens compressed at 700 °C displayed longitudinal cracking. Moreover, the microscopic cracking observation showed that ductile dimple cracking can be found in the IM alloy, but brittle cleavage fracture was dominant in the cracking surface of PM alloy with a relatively low cracking ductility.

Formation of equiaxed crystal structures in directionally solidified Al-Si alloys using Nb-based heterogeneous nuclei.

The design of chemical compositions containing potent nuclei for the enhancement of heterogeneous nucleation in aluminium, especially cast alloys such as Al-Si alloys, is a matter of importance in order to achieve homogeneous properties in castings with complex geometries. We identified that Al3Nb/NbB2 compounds are effective heterogeneous nuclei and are successfully produced in the form of Al-2Nb-xB (x = 0.5, 1 and 2) master alloys. Our study shows that the inoculation of Al-10Si braze alloy with these compounds effectively promotes the heterogeneous nucleation of primary α-Al crystals and reduces the undercooling needed for solidification to take place. Moreover, we present evidences that these Nb-based compounds prevent the growth of columnar crystals and permit to obtain, for the first time, fine and equiaxed crystals in directionally solidified Al-10Si braze alloy. As a consequence of the potent heterogeneous particles, the size of the α-Al crystals was found to be less dependent on the processing conditions, especially the thermal gradient. Finally, we also demonstrate that the enhanced nucleation leads to the refinement of secondary phases such as eutectic silicon and primary silicon particles.