Chinese Journal of Rare Metals

2026, v.50;No.366(09) 1500-1512

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Research Progress on Alloying, Microstructure, and Mechanical Properties of Ni-Based/Fe-Ni-Based Exhaust Valve Alloy

Lin Hao;Wang Jingzhong;Wang Limin;Zhao Lijia;Wang Zhigang;Zhou Jie;

Abstract：

With the continuous development of internal combustion engines(ICE),exhaust valves face increasingly harsh operational environments,including exposure to higher temperatures,elevated exhaust pressures,and severe thermal corrosion from sulfur compounds.These challenging conditions demand improvements in valve materials,as traditional valve steels are becoming insufficient to meet modern performance requirements.Consequently,alternative materials with enhanced high-temperature strength,corrosion resistance,and mechanical durability have become essential.Nickel(Ni)-based and iron-nickel-based(Fe-Ni-based) alloys have garnered significant attention due to their exceptional resistance to high-temperature oxidation,creep resistance,and corrosion resistance.However,the high cost of nickel has constrained the large-scale application of nickel-based alloys in the production of exhaust valves.In contrast,iron-nickelbased alloys offer a more cost-effective solution while maintaining comparable mechanical properties,making them a promising candidate for the future development of valve alloys.The present study provided a comprehensive review of the research progress in understanding the role of various alloying elements,the microstructure,and the mechanical properties of Ni-based and Fe-Ni-based valve alloys.Special attention was given to the role of key alloying elements,including Ni,chromium(Cr),carbon(C),titanium/aluminum(Ti/Al),and niobium(Nb),in enhancing the performance of these alloys.The effect of heat treatment parameters,such as solution treatment and aging processes,on the grain size,precipitation phases(γ',MC,M_(23)C_6,etc),and overall mechanical properties was also examined.Ni played a critical role in the formation of γ' strengthening phase,which was a key factor in the high-temperature performance of these alloys.Ni could dissolve a wide range of alloying elements and did not undergo allotropic transformation,making it stable across a broad temperature range.As Ni content increased,the allotropic matrix structure became more stable at high temperatures,allowing for improved hightemperature performance.However,the high cost of Ni had led to efforts to develop Fe-Ni-based alloys with reduced Ni content,which still maintained satisfactory mechanical properties.Cr was another essential element in valve alloys,contributing to both corrosion resistance and mechanical strength.Cr formed stable carbides,such as Cr_(23)C_6,which helped pin grain boundaries and improved the high-temperature mechanical properties of the alloy.In addition to forming protective oxide layers that enhanced oxidation resistance,Cr also lowered the stacking fault energy in Ni matrix,thereby stabilizing the matrix structure.C was indispensable in valve alloys as a grain boundary strengthening element.It reacted with various metals(Cr,Ti,Nb,etc) to form high-melting-point carbides such as MC and M_(23)C_6,which contributed to enhanced mechanical strength and thermal stability.As C content decreased,the amount and precipitation temperature of M_(23)C_6 decreased,while MC carbide precipitation was promoted.The formation of carbides could further improve the creep resistance of Ni-based valve alloys,making C content a crucial factor in alloy design.Ti and Al were vital for the formation and stabilization of γ'phase,which was the primary strengthening phase in these alloys.Ti and Al formed coherent precipitates within the matrix that obstructed dislocation motion,thereby improving the alloy's high-temperature strength.Furthermore,adjusting Ti/Al ratio could influence the morphology and distribution of γ' phase,affecting the alloy's long-term stability under high-temperature conditions.Nb served as a potent solid-solution strengthening element and played a significant role in forming γ' phase.Nb increased the anti-phase boundary energy,which enhanced the alloy 's strength and creep resistance.Additionally,Nb could delay the coarsening of γ' phase,thereby extending the alloy' s service life under high-temperature conditions.Nb also promoted the formation of a dual-layer oxide film,which improved the alloy' s high-temperature oxidation resistance.The synergistic effects of Nb with other elements such as Ti and Al required further study to optimize the mechanical properties of Fe-Ni-based valve alloys.Heat treatment was a critical factor influencing the microstructure and mechanical properties of valve alloys.Solution treatment,followed by aging,was commonly used to dissolve intermetallic compounds and remove residual stresses in the alloy matrix.This process led to the precipitation of γ' phase,which significantly enhanced the mechanical properties of the alloy.Controlling heat treatment parameters,such as solution temperature,aging time,and cooling rates,allowed for the fine-tuning of the precipitation behavior of strengthening phases(γ',MC,M_(23)C_6,etc) to achieve the desired balance between strength and ductility.In conclusion,Fe-Ni-based valve alloys were emerging as a promising alternative to traditional Ni-based alloys due to their lower cost and comparable mechanical properties.Continued research on the synergistic effects of alloying elements,as well as the optimization of heat treatment processes,would be crucial for advancing the development of these materials.

Key Words： valve alloy;heat treatment;microstructure;mechanical properties

Abstract:

Keywords:

Foundation: 国家重点研发计划项目（2021YFB3794202）;; 中信-CBMM R&D铌技术合作项目（D148/M）;; 中信合作项目（D197/M2124）资助

Authors: Lin Hao;Wang Jingzhong;Wang Limin;Zhao Lijia;Wang Zhigang;Zhou Jie;

DOI: 10.13373/j.cnki.cjrm.XY24100016

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