Random Grain Boundary Network Research Articles

Suppression of liquid-metal-embrittlement by twin-induced grain boundary engineering approach

Grain boundary engineering (GBE) has lately been recognized as a viable approach to manipulate grain boundary characteristics to improve resistance against intergranular degradation. One of the most challenging intergranular degradation phenomena is liquid-metal-embrittlement (LME), where a reactive liquid metal penetrates along random grain boundary network. In contrast to random grain boundaries, special coincidence site lattice (CSL) boundaries has been shown to be resistant against the embrittlement. The present study investigates the feasibility of using a GBE technique to arrest LME in a Fe (FCC)-Zn couple. Two sets of low-strain-heat-treatment processing routes were used to optimize grain boundary characteristics based on: (a) Σ3 and Σ3n boundaries frequency, and (b) the material's texture and grain size evolution. The optimum characteristics resulted in significantly improved resistance against LME. The mechanism of the embrittlement arrest is discussed based on the random-grain boundary network continuity and the grain boundary triple junctions distributione.

Grain boundary engineering of austenitic steel PNC316 for use in nuclear reactors

Austenitic stainless steel PNC316 was subjected to grain boundary engineering (GBE). It was found that the grain boundary engineered PNC316 (PNC316-GBEM) had a coincidence site lattice (CSL) fraction of 86% and that the network of random grain boundaries was perfectly divided by the CSL boundaries. The thermal stability and the void swelling behavior of PNC316-GBEM were investigated by means of SEM and TEM analyses. After thermal aging at 973 K for 100 h, structural changes were observed neither in the grain boundary networks of PNC316-GBEM nor in another sample of PNC316-GBEM subjected to 20% additional cold rolling, PNC316-GBEM20%CW. PNC316-GBEM showed a higher void swelling rate than as-received PNC316 (PNC316-AS). However, with additional 20% cold rolling after GBE, the void swelling rate decreased to as low as that of PNC316-AS.

Characterisation of grain boundary cluster compactness in austenitic stainless steel

The distribution of grain boundaries of particular crystallographic character can provide descriptive information on the properties of engineering materials. For example, the fraction and connectivity of corrosion susceptible grain boundaries typically correlates with the extent of intergranular corrosion and stress corrosion cracking resistance in sensitised austenitic stainless steels. A parameter defining the cluster compactness is proposed to describe the breakup of the network of corrosion susceptible grain boundaries. It may therefore provide a measure of intergranular stress corrosion cracking resistance. The cluster compactness of the network of random grain boundaries (>Σ29) in electron backscatter diffraction assessments of microstructure is shown to decrease with increasing fraction of Σ3 boundaries. However, the cluster compactness of the network of corroded grain boundaries identified after electrochemical testing is less sensitive to changes in microstructure obtained by thermomechanical processing.

Influence of processing method on the network of grain boundaries

Abstract Improved properties are realized in certain materials by modification of the grain boundary character distribution (GBCD) through thermomechanical processing. Here, we evaluate the influence of different processing paths on the resulting GBCD and demonstrate that the primary effect is to reduce or break the connectivity of the network of random grain boundaries.

Effect of Grain Boundary Character Distribution on Stress Corrosion Cracking Behavior in Austenitic Stainless Steels

The effect of grain boundary character distribution (GBCD) on intergranular stress corrosion cracking (IGSCC) in austenitic stainless steels in high temperature water was verified experimentally. GBCD control using the strain annealing method increased the fraction of low- S coincidence site lattice (CSL) boundaries and the segmentalized network of random grain boundaries in austenitic stainless steels. The fractions of low- S CSL boundaries of GBCD controlled steels were 75–85%, while those of uncontrolled steels were 60–70%. Creviced bent beam tests were conducted at 561 K in pure water containing 8 ppm dissolved oxygen for stress corrosion cracking (SCC) evaluation. The tests revealed that GBCD control suppressed IGSCC initiation or propagation and that cracks were predominantly propagated along random grain boundaries. It is considered that induced lower- S CSL boundaries result in high resistance to IGSCC.