Particle strengthened alloys for high temperature applications: strengthening mechanisms and fundamentals of design

Particle strengthening of metallic alloys, subjected to high temperatures, is reviewed in this article. Distinction is made between nanometer-size dispersoids and discontinuous reinforcements with meso- or macroscopic dimensions. Dislocation climb and detachment are considered in conjunction with the first particle type, demonstrating that creep behaviour is dominated by the thermally activated detachment process. A number of implications resulting from that finding, such as the existence of an optimum dispersoid size, are discussed in this context. Reinforcement strengthening is reviewed, discussing load transfer strengthening, generation of geometrically necessary dislocations, relaxation of load transfer by diffusion, dislocation climb and fiber failure as key mechanisms. Finally, dual scale particle strengthening is addressed. The basic idea is to purposefully combine dispersoids and reinforcements, i.e., particles of two different size scales. The interesting point here is that a synergistic interaction between both particle types, leading to superior elevated temperature strength, is predicted by theoretical analysis.