Effect of Thermal Cycling on Creep Behavior of Powder-Metallurgy-Processed and Hot-Rolled Al and Al-SiC Particulate Composites

Abstract

The tensile creep behavior of powder metallurgy (P/M)-processed and hot-rolled commercially pure Al and Al-5 or Al-10 vol pct SiC particulate composites has been evaluated after subjecting to 0, 2, and 8 thermal cycles between 500°C and 0°C with rapid quenching. The images of microstructures obtained using scanning and transmission electron microscopy as well as changes in the electrical resistivity, Young's modulus, and microhardness have been examined in the samples subjected to thermal cycling, in order to compare the effects of structural damage and strengthening by dislocation generation. The damage is caused by voids formed by vacancy coalescence, and is more severe in pure Al than in Al-SiC p composites, because the particlematrix interfaces in the composites act as effective sinks for vacancies. Creep tests have shown that the application of 2 thermal cycles lowers the creep strain rates in both pure Al and Al-SiC p composites. However, the creep resistance of pure Al gets significantly deteriorated, unlike the mild deterioration in the Al-5 SiC p composite, while the time to rupture for the Al-10 SiC p composite is increased. The dislocation structure and subgrain sizes in the Al and in the matrices of the Al-SiC p composites in the as-rolled condition, after thermal cycling, and after creep tests, have been compared and related to the creep behavior. The dimple sizes of the crept fracture surfaces appear to be dependent on the void density, tertiary component of strain, and time to rupture.

Development of a novel Al–Cu–Ti metallic glass reinforced Al matrix composite consolidated through equal channel angular pressing (ECAP)

“…The similar behavior has been reported for glass particles reinforced Al-based composites [6,33]. As The significant increase in the mechanical strength of the composite compared to the pure aluminum arise from strengthening mechanisms due to the presence of micro sized reinforcement particles, including grain refinement strengthening [34], load transfer effect [34] and enhanced dislocation density induced by the difference in the coefficient of thermal expansion between the matrix and reinforcing particles [35,36]. Grain refinement of the composite matrix increases the strength according to the well-known Hall-Petch equation:…”

Application of powder metallurgy and hot rolling processes for manufacturing aluminum/alumina composite strips

“…Also, the uniformity of the alumina particles has an important effect on the strength of the AMCs [38,45]. However, the hardness of the composites is expected to be higher with increasing the alumina content in the matrix, because of the dislocations generated due to the CTE mismatch between the alumina particles and the aluminum matrix [46,47]. The mean free path for dislocation movement is a function of the inter particle spacing.…”

“…The mean free path for dislocation movement is a function of the inter particle spacing. On the other hand, a high density of dislocations formed through the hot rolling process is expected to give rise to a high back stress, resisting further dislocation motion and causing dislocations to pile-up [6,46,48]. So, dislocations pile-up at metal/ceramic interfaces is caused by alumina particles.…”

Effect of hot rolling temperature and thermal cycling on creep and damage behavior of powder metallurgy processed Al–SiC particulate composite

“…Thermal cycling has been found to cause increase in microhardness near the particle-matrix interfaces of pure Al-TiC and Al-SiC composites, which could be attributed to strain hardening of the matrix by increase in dislocation density [28]. Further studies by Pal et al [29] have shown that subjecting the Al-SiC p composites to 2 or 8 thermal cycles leads to reduction in steady state creep rates along with significant increase in the time to rupture. Improvement in creep resistance has also been achieved by introducing line and point defects in the Al matrix by methods including prestressing [30] and quenching [31].…”