Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Alloy 825 is widely used for chemical and petrochemical applications due to its good combination of mechanical properties and corrosion resistance. However, intergranular corrosion (IGC) is one of the serious problems for alloy 825 exposed to aggressive environments, which could result in unexpected failures and lead to huge losses. The grain boundary structure, which can partly be described by coincidence site lattice (CSL) model, can influence the grain boundary chemistry and the susceptibility to intergranular corrosion. The field of grain boundary engineering (GBE) has developed a lot over the last two decades since the concept of grain boundary design was proposed. The aim of GBE is to enhance the grain-boundary-related properties of materials by increasing the frequency of low ΣCSL (Σ≤29) grain boundaries (GBs) and tailoring the grain boundary network. It was reported that in some fcc materials with low stacking fault energy, such as Ni-based alloys, lead alloys, austenitic stainless steels and copper alloys, the frequency of low ΣCSL GBs can be greatly increased by using proper thermomechanical processing (TMP), and as a result the grain boundary related properties were greatly enhanced. In this work, GBE is applied to the manufacture of Ni-based alloy 825 tubes by cold drawing using a draw-bench on a factory production line and the subsequent annealing. The effect of thermomechanical processing on the grain boundary character distribution (GBCD) of alloy 825 was studied by means of the EBSD technique and orientation image microcopy (OIM). The results show that the proportion of low ΣCSL grain boundaries increase to more than 75% by the TMP after 5% cold drawing and subsequent annealing at 1050 ℃ for 10 min, and simultaneously the large- size highly-twinned grain- cluster microstructure is formed. The size of the grain- cluster and proportion of low ΣCSL grain boundaries decrease with the increase of pre-strain. The proportion of low ΣCSL grain boundaries decreases with the increase of the mean grain size. The annealing temperatures in the range of 1050~1125 ℃ have no obvious effect on the GBCD of the specimen with 5% cold drawing deformation; while the proportions of low ΣCSL GBs of the sample with 3%, 7% and 10% cold drawing deformation decrease with the increase of annealing temperature.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：采用工厂生产线上的冷拔机对镍基825合金管材进行冷拔加工然后再进行退火，作为晶界工程（GBE）处理。利用EBSD和取向成像显微技术（OIM）研究了不同冷拔变形量和不同退火温度对825合金晶界特征分布（GBCD）的影响。结果表明，合金在冷拔变形5%，1050℃退火10min时，低∑CSL（coincidence site lattice,∑≤29）晶界的比例可提高到75%以上（Palumbo-Aust标准），同时形成大尺寸的“互有∑3n取向关系晶粒的团簇”显微组织。随着再结晶退火前冷拔变形量的增加，晶粒团簇的尺寸减小，同时低∑CSL晶界的比例也下降，并且低∑CSL晶界的比例随晶粒尺寸的增加而下降。当合金经过5%的冷拔变形后，在1050~1125℃的温度范围内退火处理10min时的晶界特征分布无明显变化，退火温度对合金的低∑CSL晶界比例影响较小；当经过3%，7%，10%的冷拔变形后，合金的低∑CSL晶界比例随着退火温度的升高不断下降。
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