A First Principle Calculation Of Al Based And Sn Based Solder With SiC Ceramic Interfacial Bonding

SiC has a wide application in opto-mechanical structure of space optical remote sensor, residual stress need to be considered when brazing complex-shaped silicon carbide ceramic parts. The objective of this study was to decrease the wetting temperature of SiC ceramic using a metal or alloy, which helps to relax the thermal stresses in the SiC brazed joints. Tin based solder is a common solder, but Sn element is a non-active elements for SiC. Al, as an active element for SiC ceramics, can react with SiC. This main idea of this paper is that adding some active element Al element into pure tin solder. The interfacial characteristics and the function of Al element at the interface were investigated.In this arcitle, I used first-principle calculation to study the interfacial bonding character of solder/SiC systems. The interfacial bonding strength is evaluated by the number of work of separation and the interfacial electronic structure is used to reveal the nature of interfacial bonding. The results are as follows:The results of Al/SiC interface system: Top site interface has the biggest work of separation（Wsep）, is the most stable atomic configuration among three interfaces. Electronic bonding analysis show: Al/SiC interface are formed by Al-C and Al-Si bonding, mainly from the Al-C covalent-ionic bond, and is likely to generate a new phase of Al₄C₃.For the Al-12Si/SiC system, the results show: Top site interface has a maximum Wsep, namely top stacking is the most thermo-dynamically stable atomic configuration; Electronic structure analysis show: interface bonding are formed by Al-C covalent-ionic bond and Si-C covalent ionic bonding which makes main effect. Electronic bonding analysis show: Al atom’s activity is inhibited and Si atom’s activity is promoted in the Al-12Si/SiC interface, Al-C is bonded but not enough to form Al₄C₃. The bond length of C–Al bonding is 1.99?.Six Sn/SiC interfaces’ results show: in the two terminated interfaces, the most stable site of is top site which has a maximum Wsep. Besides, Wsep of C-terminated interfeces are higher than correspongding Wsep of Si-terminated. Electronic bonding analysis show: interface’s bonding mainly depends on Sn-C ionic covalent bonds and Sn-C bond length is 2.30?.Sn1.0Al/SiC interfaces’ results show: C terminated interface’s Wsep is 4.40J/m2, Si-terminated is 3.30J/m2, both of them are higher than corresponding Sn/SiC interfaces’ Wsep, this show that the addition of Al element has the ability to improve the interfacial bond strength. Electronic structure analysis show: C-Al and C-Sn bond both has ionic covalent character and ionic bond is relatively weak, in the interlayer;.The difference between Sn-C and Al-C is that the coavelent strength of Al-C stronger than Sn-C, The bond length of Al–C is smaller than that of Sn–C bond. All of this show that the interaction between Al and C atom play a major role in the formation of interlayer. Al element will enrich in the near interface, but don’t from Al₄C₃ phase.After the calculation of Sn/SiC, Sn-1.0Al/SiC interface, I used ultrasonic-assisted brazed joint of SiC ceramics with Sn、Sn-1.0Al filler metals in air, results show that: there are no obvious interface reaction layer, diffusion layer, and dissolved layer in Sn/SiC, Sn-1.0Al/SiC interface. Shear test results show: Sn-1.0Al/SiC joint shear strength is higher than Sn/SiC joint strength. TEM of Sn-1.0Al/SiC joint result show: the interface exist an Al-rich region which is in the form of Al-O amorphous layer under this experiment air conditions. All of test results are consistent with the simulation results.