Influence of heat treatments on the tensile properties and thermal expansion behavior of Fe-Ni wire
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摘要: 分別采用X射線衍射、金相顯微鏡、原子力顯微鏡和透射電鏡等組織表征手段以及室溫拉伸和熱膨脹系數測試等性能測試方法,對比研究了高溫退火、低溫時效處理對冷拔Fe-Ni合金絲微觀組織演變、拉伸強度以及熱膨脹系數的影響.研究結果表明:原始絲材強度高,但是室溫熱膨脹系數較大;而950℃退火導致晶粒粗化以及位錯密度降低,雖然室溫熱膨脹系數低,但強度不足.相比之下,500℃較低溫度的時效處理,能獲得最優的強度/熱膨脹系數組合(1189 MPa/0.2×10-6℃-1).對Fe-Ni合金絲相應的強化機制以及熱膨脹系數的影響因素分別進行了討論分析,分析結果表明:細晶強化與位錯強化是該合金絲的主要強化機制,而熱膨脹系數則主要受溶質原子-位錯交互作用影響.揭示出,合適的熱處理工藝選擇對于Fe-Ni合金絲力學性能/熱膨脹性能優化具有重要意義.Abstract: Although Fe-Ni wires have numerous potential applications, the effect of heat treatments on the microstructures and properties of Fe-Ni wires is currently unclear. In this study, different high-temperature annealing and low-temperature aging treatments (i.e., ① annealing at 950℃ for 3 h+quenching, ② annealing at 950℃ for 3 h+quenching+aging at 500℃ for 2 h, and ③ aging at 500℃ for 2 h) were applied to cold-drawn Fe-36.24% Ni alloy wires to comparatively investigate their influences on the microstructural evolution, tensile strength, and thermal expansion coefficient, with the aid of microstructural characterization methods, such as X-ray diffraction, optical microscopy, atomic force microscopy, and transmission electron microscopy, as well as property measurements, such as room-temperature tensile testing and thermal expansion coefficient. The experimental results clearly show that the as-drawn Fe-Ni wire, although having a high tensile strength, exhibits an unfavorable high thermal expansion coefficient. The Fe-Ni wires annealed at 950℃ (wires subjected to ① and ②) have a relatively low thermal expansion coefficient but exhibit insufficient strength. In comparison, the wire aged at 500℃ (wire subjected to ③) shows a high strength (1189 MPa) and a low thermal expansion coefficient (0.2×10-6℃-1) at the same time. The relative strengthening mechanisms and factors affecting the thermal expansion coefficient are discussed and analyzed in terms of the microstructures. Grain boundary strengthening and dislocation hardening are observed to be the dominant strengthening mechanisms of the Fe-Ni wires, and the solute atom-dislocation interaction is mainly responsible for the evolution of the thermal expansion coefficient. The present work clearly demonstrates that suitable heat treatments are important for the optimization of the strength/thermal expansion coefficient of Fe-Ni alloy wires, which will be helpful for material design and technology tailoring of Fe-Ni wires to develop a new alloy with enhanced performance.
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Key words:
- Fe-Ni alloys /
- heat treatments /
- strength /
- thermal expansion coefficient
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參考文獻
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