Quantification of Precipitation Hardening and Evolution of Precipitates

Abstract

Quantification of precipitation hardening is a challenging subject as it demands combined knowledge of precipitation strengthening mechanism and precipitate growth/coarsening kinetics. Having not seen many attempts on developing new theories in recent years, the authors are aware of the fact that many existing concepts and developed theories are sometimes even neglected or misused. This article therefore aims to describe overview on some aspects which have not been fully addressed and/or misused. Recent developments in this subject include an accurate determination of the equilibrium precipitate fraction and interparticle spacing. The influence from precipitation fraction on precipitate coarsening and hardening kinetics was accounted for quantitatively, which allows the hardening quantification to be carried out in a more accurate manner. In addition, difficulties in quantification of precipitation strengthening effects in commercial systems are discussed. Advanced theories on dislocation precipitate interaction mechanisms are required to improve the accuracy in quantification of precipitation hardening to a high level.

Design of Heusler Precipitation Strengthened NiTi- and PdTi-Base SMAs for Cyclic Performance

“…Additionally, large coherency strains can be an obstacle for martensite interface motion during phase transformation, increasing interfacial frictional work and transformation hysteresis [10], which is detrimental to actuator applications with narrow temperature ranges. Lastly, early coherency loss during particle growth and coarsening would prohibit dislocation cutting and cause premature bypass, leading to non-optimal peak strength values [11]. For these reasons, the objective is set to reduce lattice misfit from d = -2.57 % in the NiTiAl system to |d| \ 1 % in quaternary and higher-order system designs.…”

A Review on Nano-Scale Precipitation in Steels

“…Precipitate shearing mechanism occurs when the precipitates are small in size so that dislocations can cut through (shearable or penetrable) the precipitates easily, while the Orowan looping mechanism takes place when the precipitates are large and impenetrable by dislocations [42][43][44][45][46][47]. In other words, precipitation strengthening depends on how dislocations interact with precipitates [46].…”

Um estudo cinético da precipitação de compostos intermetálicos e da reversão da martensita em aços maraging 300 e 350.

“…Em ambos os mecanismos, quando a fração volumétrica e o raio do precipitado crescem, também aumenta a tensão crítica de cisalhamento necessária para cortar o precipitado, o que está de acordo com o comportamento do primeiro estágio da curva de envelhecimento mostrada na figura 44 (MARTIN, 1998;SHA, 2002).…”

“…As medidas de microdureza têm sido usadas tanto para a avaliação da cinética de precipitação de amostras envelhecidas quanto para o estudo das mudanças de mecanismo de endurecimento durante o envelhecimento em aços maraging (GUO, SHA, 2002;PARDAL et al, 2006;SHA, 2000;WILSON, 1996;VISWANATHAN, DEY, ASUNDI,1993a;FLOREEN, DECKER, 1962;SINHA et al, 1998 …”

“…Caso uma diferença de temperatura seja detectada entre a amostra analisada e a amostra de referência, o fluxo de calor gerado pela transformação de fase pode ser estimado (BERNAL et al;2002, GUO;SHA, 2004). …”