Additive Manufacturing of Ti-6Al-4V with Added Boron: Microstructure and Hardness Modification

Titanium alloy composites with titanium boride (TiB) discontinuous reinforcement have shown improved performance in terms of strength, stiffness, and hardness. Producing this composite through selective laser melting (SLM) can combine the advantages of freeform design with the ability to produce TiB reinforcement in-situ. In this study, SLM was used to consolidate a pre-alloyed Ti-6Al-4V (Ti64) and amorphous boron (B) powder mixture with the intent of producing 1.5wt% TiB reinforcement in a Ti64 matrix. The processing parameters of laser power and scanning speed were investigated for their effect on the density, microstructures, and hardness of the composite material. The results showed that the boron and Ti64 composite could achieve a density greater than 99.4%. Furthermore, it was found that processing parameters changed the microstructural features of the material. The higher the energy density employed the more homogenous the distribution of boron modified material. Macro features were also observed with laser paths being clearly evident in the subsurface microstructure. Micro-hardness testing and density measurement also showed a corresponding increase with increasing energy density. Maximum hardness of 392.4HV was achieved in the composite compared to 354.2HV in SLM fabricated Ti64.

Effect of Cast Geometries on Particle Dispersion in Metal Matrix Composites

Metal composite materials are not being extensively used because of their complex processing, agglomeration and dispersion of particles in case of discontinuous reinforcement. Significant amount of research work has been carried to understand and improve primary processing of metal composites using liquid processing route. Most of the research revealed the fact that composites were cast either in plate geometry or geometry of crucible. Present work mainly focuses to examine effect of mold cavity geometries on dispersion of particles in solidifying composite slurries. Aluminium alloy composites using silicon carbide (SiC) particles were manufactured using stir casting technique. ‘T’ shape and plus shape geometries were cast in the present work. Critical velocity and solidification front velocity was analyzed to investigate effect of cast geometries on particle dispersion. Microstructural examination revealed that cast geometries have significant effect on dispersion of particles.

Electrical Conductivity of Discontinuous Filament–reinforced Unidirectional Composites

The electrical conductivity of discontinuous filament–reinforced unidirectional composites was investigated. The discontinuous reinforcement used was copper filament, and the matrix materials included solder and epoxy. It was found that the composite conductivity increases with filament length and eventually becomes a constant. Such behavior is described by introducing an interface impedance and the principle of rule of mixture. It was found both experimentally and theoretically that there exists a critical filament length that must be exceeded so the composites will exhibit conductivity as composites having continuous reinforcing filaments.