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The β titanium alloys are key materials in lightweight and biomedical applications, due to the combination of excellent biocompatibility and mechanical properties. However, the Binder-based Powder Technologies such as Metal-Injection-Molding (MIM), Binder-Jetting and Fused-Filament-Fabrication, normally introduce three major processing-related defects in the as-sintered Ti-parts: (i) residual porosity, (ii) high impurity level and (iii) coarse-grained structure. The previous studies revealed that these processing defects invariably tend to be even more severe in β titanium alloys than in α/β Ti-6Al-4V alloy, all fabricated by powder metallurgical route. In this work, these processing defects and their likely origins in MIM β titanium alloys are analysed. Furthermore, the influence of these defects on damage tolerance and fracture mechanisms of MIM β titanium alloys under either static or dynamic loading is investigated. Based on the studies, strategic technical improvements in the processing to improve the reliability of MIM β titanium alloys products are proposed. [ABSTRACT FROM AUTHOR]

Several material parameters affect degradation characteristics of Mg and its alloys under physiological conditions. Porous Mg materials are interesting for their simultaneous degradation and drug delivery capabilities. However, an increase in pore surface area is detrimental to both degradation resistance and subsequent mechanical properties. The present work aims at determining the threshold porosity value in Mg–0.6Ca specimens produced by powder metallurgy (PM) below which low degradation rates persist with acceptable mechanical properties. Seven different porous Mg–0.6Ca specimens containing both closed and open pore structures were fabricated with porosities ranging from 3% to 21%. Degradation profiles were obtained via a semi static immersion test over 16 days under physiological conditions using Dulbecco's modified Eagle's medium with Glutamax and 10% fetal bovine serum as supplements. The results are related to morphological pore parameters like pore size distribution, pore interconnectivity and pore curvatures that were quantified using an ex situ µCT analysis. In general, with decreasing porosity a decrease in pore interconnectivity is seen followed by rounding of the pores. Low degradation rates (MDR < 0.3 mm/year) are observed in specimens until 10% porosity, however, the upper bound for reproducible degradation is observed to be in specimens until 12% porosity. This porosity level also marks the transition from closed to open pore nature with a simultaneous change in pore interconnectivity from less than 10% to greater than 95%, below and above this porosity level, respectively. The tensile strength and elongation to failure recorded for specimens with 10% porosity were 70 MPa and 2%, respectively displaying positive traits of both homogenous degradation and mechanical properties. The results suggest that high pore interconnectivity is the dominant factor controlling degradation and mechanical properties in porous Mg-0.6Ca specimens. The results also indicate a good sintering response of Mg-0.6Ca specimens providing further material development towards biomaterial applications. [ABSTRACT FROM AUTHOR]

The effect of Al variations in the sintering behavior and creep resistance is investigated in powder‐metallurgy‐processed titanium aluminides based on the alloy TNB‐V5 (Ti‐45Al‐5Nb‐0.2B‐0.2C at%). Two compositions are prepared with Al‐contents of 43 and 47 at%, varying Al‐content by ±2 at% relative to the reference material TNB‐V5. Specimen preparation is conducted by metal injection molding using feedstock prepared with mixtures of prealloyed and elemental powders. The sinterability of alloys with addition of elemental powders decreases in comparison to the reference material, according to dilatometry experiments. However, in experiments with the sintering furnace, it is possible to obtain porosity with values of ≈10% by sintering at 1450 °C, whereas sintering at 1500 °C decreases the porosity to less than 1% in case of 43 at% and 45 at% of Al. Even though the alloy containing 47 at% Al shows higher porosity of about 7%, the creep resistance is superior to 43 at% Al, which can be attributed to a larger colony size. In tensile tests at room temperature, the effect of porosity is very detrimental leading to significantly reduced tensile strength and total elongation. Nevertheless, in compressive creep tests, the effect of porosity is secondary to colony size. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) is an attractive technology for manufacturing net-shape titanium-based components. However, it is challenging to make PM titanium products competitive in terms of mechanical properties. This article gives an overview of the current challenges in PM titanium and the best strategies to overcome them by alloying. By adding suitable alloying elements the properties of PM titanium components can be enhanced. The use of sintering aids helps to control the typical residual porosity of PM titanium alloys. Furthermore, controlling microstructure by alloying offers the possibility to go for high performance applications. Moreover, ductility is improved by adding elements that scavenge oxygen. A favorable selection of alloying elements offers a practical and competitive approach to meet the mechanical requirements in future PM titanium applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Ongoing research has proven that Mg alloys can be introduced into the metal injection moulding process for the production of small parts in high quantities and of complex shape for medical as well as lightweight applications. Previously, development studies have been conducted using Mg and Mg-Ca alloys intended for medical application. However, progress towards the implementation of a process for technical and lightweight applications alloys with higher strength is needed. Therefore, in this study processing of conventional AZ81 alloy by MIM was successfully developed. Using this alloy, a yield strength of approximately 120 MPa and an ultimate tensile strength of approximately 255 MPa with elongation at fracture of approximately 7% was achieved. T4 heat treatment at 420 °C for 10 h does not reveal a positive influence on the mechanical properties this could be caused by an observed grain growth effect. This is in contrast to conventional material for example as cast, where T4 heat treatment is known to improve the mechanical properties especially elongation at fracture. [ABSTRACT FROM AUTHOR]

Since the presence of retained β phase might be detrimental for the creep properties of titanium aluminides, elements that stabilize the β phase, e.g. Nb and Mo, can only be used within a limited range. In this work, additions of the neutral element Zr to the alloy Ti-45Al-5Nb-0.2B-0.2C (in at.%) through elemental powder metallurgy were investigated. A powder-metallurgical processing route has been selected for this study, as it appears attractive with respect to microstructural homogeneity and manufacturing costs of complex parts. Different alloys with Zr content varying from 1 to 5 at.% were prepared by uniaxial pressing of a mix of elemental and pre-alloyed powders together with a binder system. The mechanical properties were evaluated by hardness and compression creep tests. The results indicate that Zr significantly decreases the melting point of the base alloy, which directly influences the sintering behaviour and with increasing Zr content the optimum sintering temperature decreases. The creep resistance showed a general improvement with increasing Zr content. The Zr additions resulted in the formation of γ phase enriched with Zr at the colony boundaries, the implications of which are discussed in the paper. [ABSTRACT FROM AUTHOR]