I'm a materials engineering student in the Philippines and I've produced a powder metal SS304L matrix with a 7% by volume (max) tungsten carbide reinforcement in the form of particulates. The trouble is, we have been unable to find the necessary etchant for metallographic anyalsis. the samples have undergone pressing at 60 Tsi, heat treatment at 1100 celsius for a max of 2 hours. we have tried glyceria, villela' reagent, and kahling'solution. None of these have produced a satisfactory grain boundary etch. we have reached etch times of up to 30 minutes and have endded up with nothing other than a unformly corroded sample. can anyone suggest a suitable ecthant? we are looking for grain boundaries in this particular study.