Low-Cost α+β PM Ti Alloys by Fe/Ni Addition to Pure Ti

Ti and its alloys can deliver a very interesting combination of properties such as low density, high strength, corrosion resistance and biocompatibility and, therefore, are very flexible materials which can be adapted to various applications. Nonetheless, Ti and Ti alloys are only employed in critical applications (i.e. aeronautical and aerospace, nautical, medical, etc.) or in products for leisure. In both of these cases the higher fabrication costs of Ti in comparison to its competitors (i.e. steel and aluminium) is not the limiting factor as it is for many structural applications, especially for mass production (i.e. automotive sector). The use of creative techniques and the decrement of the starting price of Ti have been identified as the two main routes to follow to decrease the fabrication costs. In this study, the production of low-cost α+β Ti alloys has been assessed by combining the addition of cheap alloying elements (in particular a Fe/Ni powder) with the classical powder metallurgy route (pressing and sintering). Physical and mechanical properties as well as microstructural analysis of these low-cost alloys were measured and correlated to the processing parameters used to sinter them. It is found that the low-cost Ti alloys show similar behaviour to conventional α+β Ti alloys and, thus, have the potential to be used for non-critical applications

Investigation of the factors influencing the tensile behaviour of PM Ti-3Al-2.5V alloy

Titanium, a relatively new engineering metal, has been employed principally in high demanding industries due to its high final cost and it is well known for its biocompatibility. Powder metallurgy (PM) techniques could offer the possibility to reduce the production cost without paying it in terms of mechanical properties, thanks to their intrinsic advantages. In this study the Ti-3Al-2.5V titanium alloy was produced considering two powder production routes and sintered under different temperatures in order to address their feasibility as alternative to the wrought alloy. The results indicate that PM Ti-3Al-2.5V alloys studied have comparable mechanical behaviour as their counterpart obtained by conventional metallurgy and, therefore, are potential candidates to fabricate cheaper titanium products for structural applications as well as biomedical devices. © 2014 Elsevier B.V.The authors want to acknowledge the financial support from the Spanish Ministry of Science through the R&D Projects MAT2009-14448-C02-02 and MAT2009-14547-C02-02, and from Regional Government of Madrid through the ESTRUMAT (S2009/ MAT-1585) projectPublicad

Influence of vacuum hot-pressing temperature on the microstructure and mechanical properties of Ti—2.5V alloy obtained by blended elemental and master alloy addition powders

This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti–3Al–2.5V components using vacuum hot-pressing. Two Ti–3Al–2.5V starting powders were considered. On one side, hydride-dehydride (HDH) elemental titanium was blended with an HDH Ti–6Al–4V prealloyed powder. On the other side, an Al:V master alloy was added to the HDH elemental titanium powder. The powders were processed applying a uniaxial pressure of 30 MPa. The sintering temperatures studied varied between 900 degrees C and 1300 degrees C. The relative density of the samples increased with processing temperature and almost fully dense materials were obtained. The increase of the sintering temperature led also to a strong reaction between the titanium powders and the processing tools. This phenomenon occurred particularly with boron nitride (BN) coating, which was used to prevent the direct contact between titanium and graphite tools. The flexural properties of the Ti–3Al–2.5V samples increased with vacuum hot-pressing temperature and are comparable to those specified for wrought titanium medical devices. Therefore, the produced materials are promising candidates for load bearing applications as implant materials.Financial support from Comunidad de Madrid through the ESTRUMAT (S-2009/MAT-1585) project and from the Spanish Ministry of Education through the R&D MAT2009-14448-C02-02 and MAT2009-14547-C02-02 Projects

Flexural Properties, Thermal Conductivity and Electrical Resistivity of Prealloyed and Master Alloy Addition Powder Metallurgy Ti-6Al-4V

A comparison between the properties achievable by processing the Ti&-6Al&-4V alloys by means of two powder metallurgy approaches, precisely prealloyed and master alloy addition, was carried out. Prealloyed and master alloy addition hydride&-dehydride powders characterised by an irregular morphology were shaped by means of cold uniaxial pressing and high vacuum sintered considering the effect of the variation of the sintering temperature and of the dwell time. Generally, the higher the temperature and the longer the dwell time, the higher the relative density and, consequently, the better the mechanical performances. Nevertheless, a higher processing temperature or a longer time leads also to some interstitials pick-up, especially oxygen, which affects the mechanical behaviour and, in particular, lowers the ductility. Although some residual porosity is left by the pressing and sintering route, mechanical properties, thermal conductivity and electrical resistivity values comparable to those of the wrought alloy are obtained.The authors want to acknowledge the financial support from Regional Government of Madrid through the ESTRUMAT (S2009/ MAT-1585) project and from the Spanish Ministry of Science through the R&D Projects MAT2009-14547-C02-02 and MAT2009-14448-C02-02. The authors want also to thanks the Fraunhofer IFAM-Dresden Institute for the measurements of the thermal conductivity and electrical resistivityPublicad

Powder metallurgy CP-Ti performances: hydride-dehydride vs. sponge

Titanium is characterised by two contrasting aspects: outstanding combination of properties and high production costs which confine its application to high demanding sectors. The employment of powder metallurgy (P/M) techniques is one creative alternative to lower the final costs of titanium products due to some intrinsic advantages of P/M such as high yield of material and limited machining requirement. In this work the performances of hydride&-dehydride (HDH) and sponge elemental titanium products obtained by cold uniaxial pressing and sintering are compared. It is found that the two materials achieved similar relative density values but HDH shows much better mechanical performances.The authors want to acknowledge the financial support from the Spanish Ministry of Science through the R&D Projects MAT2012-38650-C02-01, and from Regional Government of Madrid through the ESTRUMAT (S2009/MAT-1585) projec

Influence of Sintering Parameters on the Properties of Powder Metallurgy Ti-3Al-2.5V Alloy

The processing of near net shape Ti-3Al-2.5V components using the conventional pressing and sintering route is addressed in this study. The Ti-3Al-2.5V starting powder was obtained considering both the blending elemental and the master alloy addition methods. The powders were uniaxially pressed and sintered in a high-vacuum furnace under various temperature-time combinations. The influence of the processing parameters on the relative density, microstructural features, amount of interstitials, mechanical behaviour, thermal conductivity and electrical resistivity of the sintered materials was evaluated. It was found that the relative density of the samples increases with processing temperature and time, and almost fully dense materials were obtained. The mechanical performance of the Ti&-3Al&-2.5V improves due to the reduction of the residual porosity and are, generally, of the same order of magnitude of those required for titanium biomedical products. Furthermore, the temperatures&-times selected permit to obtain thermal and electrical properties similar to the wrought alloy.The financial support from the Spanish Ministry of Science through the R&D Projects MAT2009-14448-C02-02 and MAT2009-14547-C02-02, and from the Regional Government of Madrid through the ESTRUMAT (S2009/MAT-1585) project is acknowledged. The possibility to perform the measurements of the thermal conductivity and electrical resistivity in the Fraunhofer IFAM-Dresden Institute is really appreciated.Publicad

Evaluation of the mechanical properties of powder metallurgy Ti-6Al-7Nb alloy

Titanium and its alloys are common biomedical materials owing to their combination ofmechanical properties, corrosion resistance and biocompatibility. Powder metallurgy (PM) techniques can be used to fabricate biomaterials with tailored properties because changing theprocessing parameters, such as the sintering temperature, products with different level ofporosity and mechanical performances can be obtained. This study addresses the productionof the biomedical Ti-6Al-7Nb alloy by means of the master alloy addition variant of the PMblending elemental approach. The sintering parameters investigated guarantee that thecomplete diffusion of the alloying elements and the homogenization of the microstructure isachieved. The sintering of the Ti-6Al-7Nb alloy induces a total shrinkage between 7.4% and10.7% and the level of porosity decreases from 6.2% to 4.7% with the increment of thesintering temperature. Vickers hardness (280-300 HV30) and tensile properties (differentcombination of strength and elongation around 900 MPa and 3%) are achieved.The authors want to acknowledge the financial support from New Zealand Ministry of Business, Innovation and Employment (MBIE) through the UOWX1402 research contract (TiTeNZ - Titanium Technologies New Zealand)

Inductive hot-pressing of titanium and titanium alloy powders

Inductive hot-pressing is a field-assisted sintering process (FAST) in which an electrical current is used to enhance the densification of the powder. Inductive hot-pressing could be employed to enable titanium powder to reach a higher density in less time than the pressing and sintering process. In this study, titanium and titanium alloy powders with different features were processed by means of inductive hot-pressing. The influence of processing temperature on density, microstructure, quantity of interstitial elements and hardness was investigated. Generally, practically fully dense materials were obtained without any carbon pick-up, even if the materials were in contact with the graphite matrix during processing. Nevertheless, there was an increment of the nitrogen content and some oxygen pick-up, especially for the powders with smaller particle size. Hardness is not significantly affected by the pressing temperature, but it strongly depends on the amount of interstitials.The authors are thankful for the financial support from Comunidad de Madrid through the ESTRUMAT (S-2009/MAT-1585) project and from the Spanish Ministry of Education through the R&D MAT2009-14448 ProjectPublicad

PM processing and characterisation of Ti–7Fe low cost titanium alloys

This work studies a set of low cost beta alloys with the composition Ti-7Fe, processed by conventional powder metallurgy (PM). The materials were prepared by conventional blending of elemental Ti hydride-dehydride powder with three different Fe powder additions: water atomised Fe, Fe carbonyl and master alloy Fe-25Ti. The optimal sintering behaviour and the best mechanical properties were attained with the use of Fe carbonyl powder, which reached a sintered density of up to 93% of the theoretical density, with UTS values of 800 MPa in the 'as sintered' condition. Coarse water atomised powder particles promoted reactive sintering, and coarse porosity was found due to the coalescence of Kirkendall porosity and by the pores generated during the exothermic reaction between Ti and Fe. The addition of Fe-25Ti produced brittle materials, as its low purity (91·5%) was found to be unsuitable for formulating Ti alloysThe authors would like to acknowledge financial support from the Comunidad de Madrid to carry out this research through the programme ESTRUMAT-CM (reference MAT/77), and from the Ministry of Education through the R&D Project MAT2006-02458.Publicad

Influence of powder characteristics on sintering behaviour and properties of PM Ti alloys produced from prealloyed powder and master alloy

The use and development of titanium and titanium alloys have been strongly correlated to high technology industries where costs are not the most important aspect. Titanium could see its market grow by the application of lower cost and more efficient processing methods such as powder metallurgy. This work deals with the characterisation of two types of powders: commercial prealloyed powder and powder produced from master alloy combining mechanical milling and conventional blending to adjust the particle size. The characteristics of the powders, sintering behaviour and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sintering. The most important result is that it is possible to obtain Ti alloys with properties similar to or better than alloys from prealloyed powders and to obtain homogeneous microstructures, which allows the composition to be adjusted to requirements.The authors would like to acknowledge the financial support from the Spanish Ministry of Education through R&D projects nos. MAT2009-14448 and MAT2009-14547 and from Comunidad de Madrid through the ESTRUMAT (grant no. S2009/MAT-1585) project.Publicad