Effect of initial grain sizes on the grain boundary network during grain boundary engineering in Alloy 690
- PDF / 1,710,143 Bytes
- 12 Pages / 584.957 x 782.986 pts Page_size
- 22 Downloads / 242 Views
Shuang Xia,a) Hui li, Bangxin Zhou, and Qin Bai Institute of Materials, Shanghai University, Shanghai 200072, China; and Key Laboratory for Microstructures, Shanghai University, Shanghai 200444, China
Cheng Su and Zhigang Cai Technical Department, Jiuli Hi-Tech Metals Co., Ltd., Huzhou 313008, China (Received 17 October 2012; accepted 1 February 2013)
Grain boundary engineering (GBE) has been carried out in nickel-based Alloy 690 with different initial grain sizes. The microstructure evolution during GBE-processing is characterized using electron backscatter diffraction to study the initial grain size effects on the grain boundary network (GBN). The microstructures of the partially recrystallized samples revealed that the GBE-processing is a strain-recrystallization process, during which each grain-cluster is formed by “multiple twinning” starting from a single recrystallization nucleus. Taking into consideration the coincidence site lattices (CSLs) and +, which is defined as the reciprocal density of coincidence sites, a high proportion of low-+ CSL grain boundaries (GBs) and large grain-clusters are found to be the features of GBE-processed GBN. The initial grain size has a combined effect on the low-+ CSL GBs proportion. A large initial grain size reduces the number of recrystallization nuclei that form, increasing the cluster size, but decreasing twin boundary density. On the other hand, smaller initial grain sizes increase the density of twin boundary after recrystallization, while decreasing grain-cluster size. Neither the grain-cluster size nor the twin boundary density is the sole factor influencing the proportion of low-+ CSL GBs. The ratio of the grain cluster size over the grain size governs the proportion of low-+ CSL GBs.
I. INTRODUCTION
The grain boundary network (GBN) plays a noticeable role in the grain-boundary-related properties in polycrystalline materials. The concept of “grain boundary engineering” (GBE),1,2 means “grain boundary design and control” that aims at improving the grain-boundary-related properties. Coincidence site lattices (CSLs) play an important role in GBE, with the notation + denoting the reciprocal density of coincidence sites; the improvement in grain-boundaryrelated properties are sought to be effected by enhancing the proportion of the so-called low-+ CSL grain boundaries (GBs)3 (+-value # 29). GBE has been successfully applied in many low stacking fault energy (SFE) face centered cubic (FCC) metallic materials, such as nickel-based alloys,4–9 copper alloys,10–13 lead alloys14,15 and stainless steels.16–20 Two types of thermomechanical treatment are reported for GBE-processing: iterative strain annealing4,5,8,10–14 and one-step strain annealing.6,7,9,15–20 Although different processing schedules are applied during GBE-processing, they have the same principal purposesof increasing the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.37 J. Mater. Res., Vol. 28, No. 9, May 14, 2013
http://journals.cambridge.org
Downloaded: 13 Mar 2
Data Loading...
