Analysis of melting behaviour during the equilibration stage of wide-gap brazing
- PDF / 6,760,715 Bytes
- 10 Pages / 595.276 x 790.866 pts Page_size
- 105 Downloads / 188 Views
ORIGINAL ARTICLE
Analysis of melting behaviour during the equilibration stage of wide-gap brazing Oluwadara C. Afolabi 1 & Olanrewaju A. Ojo 1 Received: 9 January 2020 / Accepted: 21 August 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract A hybrid explicit-fully-implicit numerical simulation model that conserves solutes is used to study the dissolution process during the equilibration stage of wide-gap brazing, and the numerical simulation results are validated with experimental data. In contrast to what has been commonly reported, the study shows that notwithstanding the high solute diffusivity in the liquid-phase, instead of seconds and few minutes, the dissolution stage can take hours to attain completion, depending on the gap size. This is attributable to the occurrence of rapid and large reduction in the solute concentration gradient in the liquid during the early stage of the dissolution process. Moreover, by keeping the two key factors that are generally known to influence the extent of isothermal solidification during brazing, temperature, and time, constant, it is found that initial gap size can also alter the extent of isothermal solidification, due to its influence on the dissolution process. The study further confirms that it is possible to use powder mixture that contains base-alloy additive powder, as interlayer material during wide-gap brazing, without partial melting of the additive powder particles, which can be crucial to the properties of brazed single-crystal and polycrystalline alloys. Keywords Brazing . Wide-gap . Repair . Diffusion . Dissolution . Powder mixture
1 Introduction Superalloys are used in the hot sections of aero-engines and land-based gas turbines due to their attractive properties such as high hot corrosion resistance, fatigue resistance and creep resistance. These advanced materials often encounter damage during service [1, 2]. Since the manufacture of components with these materials is very costly, it is often desirable to repair rather than replace [3–5]. Due to shape complexities and a very high possibility of hot cracking, a lot of these materials are difficult to repair-weld by conventional welding techniques [5, 6]. Diffusion brazing has emerged as an attractive alternative [6–8]. Diffusion brazing involves the use of an interlayer containing melting point depressant (MPD) elements such
* Oluwadara C. Afolabi [email protected] * Olanrewaju A. Ojo [email protected] 1
Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada
as phosphorus, silicon and boron. The melting of the interlayer between the base materials produces a liquid phase which is in contact with the solid base materials. This liquid is initially not in equilibrium with the base metal; hence, the system tries to attain thermodynamic equilibrium at the liquid-solid interface by inter-diffusion between the liquid and solid phases. This stage is the dissolution stage and is typified by the melting-back of the base-metal. By the end
Data Loading...
