Application of energy,electronic and interface bonding properties in highly reliable brazing joints between dissimilar materials

Brazing,an important welding and joining technology,can achieve precision joining of materials in advanced manufacturing.And the first principle calculation is a new material simulation method in high-throughput computing.It can calculate the interfacial structure,band structure,electronic structure,and other properties between dissimilar materials,predicting various properties.It plays an important role in assisting practical research and guiding experimental designs by predicting material properties.It can largely improve the quality of welded components and joining efficiency.The relevant theoretical foundation is reviewed,including the first principle and density functional theory.Exchange-correlation functional and pseudopotential plane wave approach was also introduced.Then,the latest research progress of the first principle in brazing was also summarized.The application of first principle calculation mainly includes formation energy,adsorption energy,surface energy,adhesion work,interfacial energy,interfacial contact angle,charge density differences,density of states,and mulliken population.The energy,mechanical,and electronic properties were discussed.Finally,the limitations and shortcomings of the research in the first principle calculation of brazed interface were pointed out.Future developmental directions were presented to provide reference and theoretical basis for realizing high-throughput calculations of brazed joint interfaces.

Wetting Behavior of Graphite and CFC Composites by Cu-Ti Compacts

The wetting behavior of Cu-Ti powder compacts with 22 wt %Ti and 50 wt %Ti on carbon materials, including graphite and carbon fiber reinforced carbon composites（CFC）, has been investigated in a vacuum using the sessile drop method. The equilibrium contact angles of Cu-22Ti（containing 22 wt%Ti） on the graphite and the CFC substrates at 1 253 K are 32 o and 26 o, respectively, whereas the equilibrium contact angle of 9° is obtained for Cu-50Ti（containing 50 wt%Ti） on both the graphite and the CFC substrates at 1 303 K.Microstructural analysis of the wetting samples shows that a thin TiC reaction layer is developed at the interfacial area and Ti-Cu intermetallic compounds are formed over the reaction layer. The investigation on the spreading kinetics of Cu-Ti compacts on carbon materials substrates at fixed temperatures reveals that the spreading is controlled by the interfacial reactions in the first stage and then by the diffusion of the active Ti from the drop bulk to the triple line in the later stage. The spreading is promoted by the intense reaction at higher Ti concentrations.