Discontinuous reinforced titanium matrix composites have generated significant interest due to their compelling properties such as their specific strength and wear resistance at room and elevated temperatures. For these reasons, these materials have been considered in various applications such as automotive (valve components), aerospace (engine components) and medical devices (implants). Metal injection molding (MIM) has proven to be an efficient near net-shape technology suitable for high volume manufacturing of parts having complex geometries. The MIM technology is particularly attractive for producing composites as the metallic matrix does not go through the liquid state. This helps minimizing the segregation of the hard particles. MIM also reduces the needs for machining. However, the production of titanium components with the MIM process has its own challenges and limitations, such as presence of porosities and coarser microstructures compared to wrought products. The present work introduces the results obtained during the development of a MIM route for producing Ti6Al4V-5wt%TiC composites. The feedstock developed is wax-based and incorporates a pre-alloyed metal powder. The microstructure, mechanical properties at room and elevated temperatures, the wear resistance and the thermal diffusivity of the composites have been characterised. Properties are compared with those of a Ti6Al4V MIM material produced with the same feedstock and process but without TiC as well as with those of wrought Ti6Al4V reported in the literature. The presence of a small amount of TiC promotes densification and grain size refinement and affects the surface finish of the sintered components. Tensile properties of the composites are comparable or better than those of wrought Ti6Al4V (ASTM F1472). Improved mechanical properties compared to unreinforced material are associated to the higher density, finer grain size as well as solution strengthening of the titanium matrix.
With the constant evolution of additive manufacturing (AM) processes, there is a need to adapt current characterization methods to better understand metallic powder behavior. Accurate and quantifiable characterization of powder particles is essential for qualification, certification, and quality control of AM manufactured parts. Particle morphology is often stated as an important parameter that affects powder flowability, layer density/uniformity, and—ultimately—part quality. However, work still needs to be accomplished to correlate particle characteristics to their impact on AM processes and manufactured parts. This study presents the sensitivity of various shape descriptors used in two-dimensional image analysis to particle morphologies commonly observed in AM. The objective was to determine which standard descriptors could adequately differentiate powder characteristic features such as elongation, facets, number, and size of satellites. To do so, a library of schematized particles containing various shapes was used and a sequential methodology capable of adequately classifying and quantifying particle shapes was developed. The methodology was then validated on metallographic cross sections of powders. The proposed approach could serve as a guide when selecting the most appropriate shape descriptors to monitor various powder characteristics and also provide a more complete characterization of particle morphologies.
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