Crystallographic study of grain refinement of Al by Nb addition

Abstract

The grain refinement of Al by the addition of a small amount of peritecticforming solute, Nb, has been studied from the crystallographic point of view. Combining the observations of optical microscopy and scanning electron microscopy with the results of energy-dispersive X-ray spectroscopy and X-ray diffraction, it is confirmed that the particles observed at or near the grain centres of refined Al alloys are pro-peritectic Al 3 Nb particles. The crystallographic matching between the Al 3 Nb particles and Al grains has also been evaluated using an edge-to-edge matching model and further verified using electron backscatter diffraction and transmission electron microscopy. It is found that there are reproducible crystallographic orientation relationships between the Al 3 Nb particles and Al grains, and the experimental results are consistent with the predictions of the edge-to-edge matching model. This implies that the properitectic Al 3 Nb particles are favourable nucleation sites for Al grains from the crystallographic point of view. Furthermore, the analysis of the size distribution of Al 3 Nb particles reveals that the Al 3 Nb particles at the grain centres have relatively large particle size, which also corroborates the high potency of Al 3 Nb according to the free growth model. It is therefore concluded that the significant grain refinement resulting from the addition of Nb is predominantly attributed to the in situ formed Al 3 Nb particles which promote grain refinement via enhanced heterogeneous nucleation.

Optimization of Casting Process Parameters for Synthesis of Al-Nb-B Master Alloy

“…[8][9][10][11] Recent studies have reported that the niobium addition which forms Al 3 Nb particles in the melt is found to be an effective grain refiner of Al-Si alloys. [12][13][14][15] Further, it has been observed that the addition of Nb along with B enhances the grain refinement of Al-Si alloys as compared to the refinement occurring with only Nb or boron additions. This enhanced grain refinement was attributed to the similarities between the Al-Nb-B and Al-Ti-B systems.…”

Novel approach to grain refinement of cast Zn alloys

“…Based on the solidification of antimony, silver and copper alloys, Asato and co-workers firstly defined the conceptual peritectic reaction theory [156]. Then, it was introduced to elucidate the grain refinement of aluminium alloys by Al 3 Ti (Crossley and Mondolfo [145]) and Al 3 Zr/Al 3 Nb (Wang et al [162,163]), respectively. Similarly, Emley [146] also used peritectics to explain the grain refinement of Mg-Zr alloys.…”

“…Then, the convergent beam Kikuchi line diffraction pattern (CBKLDP) technique [216] was introduced to determine the ORs between the nucleant particles and surrounding Zn grains. The CBKLDP technique has been proven to be an accurate and reliable method for ORs' determination [162,163,218,219]. To determine the ORs using CBKLDP technique, six steps should be conducted as follows:…”

“…There will be no CS-zone formed in (d) Table 2. 3 The experimental orientation relationships determined by Wang et al [162][163] …”

“…The E2EM model was first applied to explain the crystallographic features in alloy development and solidphase transformations [109,193,194,203]. Then, it was introduced to predict new grain refiners for cast metals by Zhang [16,19], Qiu [20,75,76], Fu [154,204], Jiang [73], and Wang [162,163], etc.…”