A counter-gravity casting system for in situ high-speed synchrotron x-ray imaging characterization.

Counter-gravity casting (CGC) aims to eliminate turbulent melt flow and defect formation during filling and subsequent solidification by pushing high-temperature melt into the mold cavity against gravity with regulated pressure. However, limited by the opaqueness of molten metals and the complexity of the CGC apparatus, it is extremely difficult to directly quantify the high-velocity mold filling and pressurized solidification in real-time. Here, we report the design and characterization of a CGC system capable of in situ monitoring of mold filling and subsequent solidification processes in the synchrotron beamlines by deploying a high-energy, high-speed synchrotron x-ray imaging technique. The high-velocity melt flow and dendrite growth during pressurized solidification have been quantified for systematical process parameter analysis by investigating time-resolved x-ray images of an exemplary Al-Cu alloy. The high-speed imaging results demonstrate that the in situ CGC system provides a useful way to better understand the fundamentals of mold filling, pressurized solidification, and experimental inputs for high-fidelity modeling in scientific and industrial applications.

Microstructure and properties of TC4/TNTZO multi-layered composite by direct laser deposition.

In this work, TC4/TNTZO multi-layered composite as well as TNTZO and TC4 alloys were prepared by direct laser deposition (DLD) to investigate the microstructure, mechanical properties and in vitro bioactivity. The microstructure characterization shows that the multi-layered material is free of cracks and intermetallics while the interface is metallurgically bonded. The fine microstructure was observed in TC4 layer of the TC4/TNTZO multi-layered material, and a large amount of α' martensite exists in the transition zone. Different from the single ß phase cellular arrays in the DLD-ed TNTZO alloy, α″ martensite with high volume content formed at the cellular grain boundary in TNTZO zone of DLD-ed TC4/TNTZO. The elastic modulus of the DLD-ed TC4/TNTZO is 64 GPa, decreased about 45% compared to the DLD-ed TC4. The tensile yield strength and elongation along the printing direction are up to 789 MPa and 7%, which are 12% higher than the tensile yield strength of DLD-ed TNTZO and 61% higher than the elongation of DLD-ed TC4 respectively. Moreover, the DLD-ed TC4/TNTZO shows good in vitro bioactivity. The TC4/TNTZO multi-layered composite fabricated by DLD can be regarded as a potential candidate to integrate the advantages of the two Ti-base alloys for application in the biomedical field.

Formation Mechanism of Spherical TiC in Ni-Ti-C System during Combustion Synthesis.

The formation mechanism of TiC particles in a Ni-Ti-C system were revealed by using differential thermal analysis (DTA), XRD, and SEM to identify the reaction products in different temperature ranges. The results indicated that the synthesis mechanism of TiC in Ni-Ti-C system was complex; several reactions were involved in the combustion synthesis of TiC-Ni composite. The Ni-Ti intermediate phases play important roles during the formation of TiC. Moreover, the influence of heating rate on the size range of TiC was also discussed.