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形變及熱處理對825合金管材晶界特征分布的影響
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更新時間：2015-10-12
采用工廠生產(chǎn)線上的冷拔機(jī)對鎳基 825 合金管材進(jìn)行冷拔加工后再退火, 進(jìn)行晶界工程(GBE)處理. 利用 EBSD 和取向成像顯微技術(shù)(OIM)研究了不同冷拔變形量和不同退火溫度對825合金晶界特征分布(GBCD)的影響.
形變及熱處理對825合金管材晶界特征分布的影響EFFECT OF DEFORMATION AND THERMO-MECHANICAL?PROCESSING ON GRAIN BOUNDARY CHARACTER DISTRIBUTION OF?ALLOY 825 TUBES?
采用工廠生產(chǎn)線上的冷拔機(jī)對鎳基 825 合金管材進(jìn)行冷拔加工后再退火, 進(jìn)行晶界工程(GBE)處理. 利用 EBSD 和取向成像顯微技術(shù)(OIM)研究了不同冷拔變形量和不同退火溫度對825合金晶界特征分布(GBCD)的影響. 結(jié)果表明, 合金在冷拔變形5%, 1050 ℃退火 10 min 時, 低Σ值重合位置點陣(∑CSL, coincidence site lattice, ∑≤29)晶界的比例可提高到75%以上(Palumbo-Aust 標(biāo)準(zhǔn)), 同時形成大尺寸的“互有∑3n取向關(guān)系晶粒的團(tuán)簇”顯微組織. 隨著再結(jié)晶退火前冷拔變形量的增加, 晶粒團(tuán)簇的尺寸減小, 同時低∑CSL 晶界的比例也下降, 并且低∑CSL 晶界的比例隨晶粒尺寸的增加而下降. 當(dāng)合金經(jīng)過5%的冷拔變形后, 在1050~1125 ℃的溫度范圍內(nèi)退火處理10 min時的晶界特征分布無明顯變化, 退火溫度對合金的低∑CSL晶界比例影響較小; 當(dāng)經(jīng)過3%, 7%和10%的冷拔變形后, 合金的低∑CSL晶界比例隨著退火溫度的升高不斷下降。
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 thermo-mechanical?processing (TMP), and as a result the grain boundary related properties were greatly enhanced. In this work, GBE?is applied to the manufacturing 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 thermal-mechanical processings 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.?
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