Steady and oscillatory cellular morphologies in rapid solidification

Weldability and weld performance of candidate austenitic alloys for advanced ultrasupercritical fossil power plants

“…David and Vitek 31 observed a fully austenitic microstructure in type 308 stainless steel laser welded at very high speeds that would normally have a γ+δ duplex microstructure. At the same time, Kelly et al 32 made a similar observation in rapidly solidified austenitic stainless steel powders. Since then, a number of other investigators have observed similar changes in the microstructures of welds cooled at very rapid cooling rates.…”

“…Austenitic stainless steels are considered to be critical materials in the construction of AUSC boiler components in coal fired power plants. They are expected to perform satisfactorily in an AUSC power plant operating environment of high temperatures (700-760uC) and high pressures (27)(28)(29)(30)(31)(32)(33)(34). In spite of extensive studies related to austenitic stainless steels and their welds, it is only since the 1970s that significant advances have been made in the understanding of the properties of austenitic stainless steels or the solidification behaviour, segregation and phase stability of the welds.…”

“…Since then, a number of other investigators have observed similar changes in the microstructures of welds cooled at very rapid cooling rates. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Such a change in the microstructure has a significant effect on the ferrite content in the weld and on the hot cracking susceptibility of the weld metal. The fully austenitic weld produced by rapid solidification is as susceptible to hot cracking 33,34 as a conventional fully austenitic weld.…”

“…[40][41][42][43] The second model is based on a change in the mode of solidification from primary d ferrite to metastable c during rapid solidification. 32 This is thermodynamically rationalised for rapid cooling conditions when the liquid may undercool below the extended metastable c liquidus temperature, 32 and is easiest for compositions close to the eutectic or peritectic temperature.…”

The oscillatory instability in rapid solidification

“…As in [8] we go into the frame moving with the pulling velocity uo and measure length in units of A /2 (the wavelength of the cell), In this section we will review linear perturbation theory for the set of equations (6) as described by Merchant and Davis [7] and apply the results to an actual system. As our system we will choose the Sisb system described in [3]. We will see that for this system we will not To find the neutral stability curve we set w = 0.…”