R.K. Shiue

Transmission Electron Microscopy Study of the Infrared Brazed High-strength Titanium Alloy

The transmission electron microscopy was employed to investigate the microstructure of infrared brazed high-strength Ti alloy using the Ti-15Cu-15Ni filler metal. Coarse primary Ti 2 Ni and transformed β-Ti are observed in the 300 s brazed specimen. Blocky Ti 2 Ni and eutectoid Ti 2 Cu intermetallics are disappeared from the joint with increasing the brazing time to 1800 s. Both acicular α-Ti and retained β-Ti dominate the entire brazed joint.

Microstructural Evolution of Infrared Brazed CP-Ti Using Ti-Cu-Ni Brazes

Microstructural evolution of infrared vacuum brazed CP-Ti using two Ti-based braze alloys, Ti-15Cu-15Ni and Ti-15Cu-25Ni, has been investigated. The infrared brazed joint consisted of eutectic Ti2Cu/Ti2Ni intermetallic compounds and Ti-rich matrix. The eutectic Ti2Cu/Ti2Ni intermetallic compounds disappeared from the joint after being annealed at 900°C for 1 h. In contrast, the depletion rate of both Cu and Ni from the braze alloy into CP-Ti substrate at 750°C annealing was greatly decreased as compared with that annealed at 900°C. Blocky Ti2Cu/Ti2 Ni phases were observed even if the specimen was annealed at 750°C for 15 h. Because the Ni content of the Ti-15Cu-25Ni braze alloy is much higher than that of the Ti-15Cu-15Ni alloy, the amount of eutectic Ti2Cu/Ti2Ni phases in Ti-15Cu-25Ni brazed joint is more than that in Ti-15Ci-15Ni brazed joint. However, similar microstructural evolution can be obtained from the infrared brazed joint annealed at various temperatures and/or time for both filler metals.

Developing Corrosion-Resistant Joints Applied in the Plate Heat Exchanger

The manufacturing of plate heat exchangers is much more difficult than that of making traditional heat exchangers. The demand of increased corrosion resistance, avoiding Cu ion contamination, resisting to high-temperature resulting from various applied environments makes the traditional Cu brazed 316 stainless steel (316SS) plate heat exchanger fail to satisfy certain applications. Corrosion-resistant brazed 316SS plate heat exchangers are successfully developed using two commercially available Ni-based brazing foils, and they are valuable for industrial applications.

Infrared Heating Applied in Titanium Brazing

Infrared heating is featured with a high heating rate up to 50oC/s. It is a very powerful tool applied in brazing application, so infrared heating has been used to study the kinetics of brazing process in recent years. The importance of brazing Ti alloys has been increased in past twenty years due to the strong demand from chemical and aerospace industry. Based on the previous studies, the use of Ti-based brazes alloyed with Cu and Ni contents is considered as one of the best alloys in brazing Ti and its alloys due to their high bonding strength. However, the presence of Ti-Cu-Ni intermetallics in the brazed joint has a strong effect on the joint strength, and the reaction kinetics of the joint is still unclear. The purpose of this investigation is concentrated on transmission electron microscopy (TEM) study of the infrared brazed CP-Ti using Ti-15Cu-15Ni filler, and microstructural evolution of the infrared brazed joint is unveiled. It is helpful for industrial applications of Ti-based alloys.