工业耐热合金与环境反应的高温氧化图

The development of creep-resistant and Al2O3-forming austenitic stainless steels modified by multi-components allows their applications at higher temperatures in aggressive environments typical of in ultra-supercritical power plants and energy production industries. This proposal involves fundamental analysis and possible modelling for the solid-gas reactions between Al2O3-forming Fe-Ni-Cr-Al alloys modified by adding Si with single oxidant X (O/S/Cl). The important basis to study such complex system is the systematic general treatment for the oxidation of ternary alloys previously developed for the simplest case, assuming ternary ideal solid-solution alloys, forming insoluble oxides and ignoring double oxides. The aim of the study is to extend this theoretical treatment into non-ideal ternary and quaternary systems, considering all types of oxidation modes involving all the alloy components. The critical issues is to construct both thermodynamic phase diagrams and kinetic diagrams (Oxidation Map) of Fe-Ni-Cr/Al alloys reacting with single oxidant X. Thermodynamic diagrams predict the nature of the phases stable under a given oxidant pressure without involving any changes of the alloy composition due to oxidation, while kinetic diagrams present the scaling behavior in dependence of the alloy composition and oxidant pressure. .The thermodynamic diagrams of the quaternary systems involves the four metal components Fe/Ni-Cr-Al under a constant Ni content plus oxidant X with triangular basis to represent the alloys composition plus a third axis perpendicular to the base triangle to report the oxidant pressure, presented using for simplicity a projection of the relevant geometrical parameters on the basic triangle. The thermodynamic features will be examined, to predict the stability of all types of single and double oxides under equilibrium condition. Subsequently, the same procedure can be adopted to present the corresponding kinetic diagrams for the same systems, which predict the regions of stability of scales with all the possible different compositions stable in contact with the alloy as functions of the composition of the alloy as well as of thermodynamic and kinetic parameters involved (diffusion coefficients of the metal components in the alloy, parabolic rate constants for the growth of the various oxides as functions of the oxygen pressure both in the gas phase and at the alloy/scale interface, etc.). The critical contents of Cr and Al needed for the transition from the internal to external oxidation are also determined as functions of the same parameters under both high and low oxidant pressures..Finally, the study includes the use of the oxidation map to examine the combined effect of alloying elements Cr, Si on the selective oxidation of Al, coupled with experimental studies of the corrosion of heat-resistant alloys of practical importance, to provide a better understanding of the complex corrosion behavior of Al2O3-forming austenitic alloys at high temperatures..Key words: Austenitic alloys, Thermodynamics, Kinetics, Oxidation Map, Selective oxidation

现代奥氏体钢经多元改性并控制铝含量使具有超强抗高温蠕变并能生成氧化铝膜，成为服役超超临界电站、能源再生等苛刻环境的候选材料。研究铝、硅改性的奥氏体合金在含氧、硫、氯气氛中的高温反应性，分析与模拟多元Fe-Ni-Cr/Al基合金与单氧化剂X（O/S/Cl）反应的氧化热力学特征和动力学过程，特别考虑这些实际体系可能出现的复合氧化物，建立在不同氧压下四元Fe/Ni-Cr/Al-X、及限定镍的五元Fe-Ni-Cr-Al-X体系的氧化热力学平衡相图和考虑扩散等动力学因素的合金氧化图。预测合金表面的氧化膜的性质、直观地表征复杂体系的腐蚀行为。实验研究不同含铝奥氏体钢的氧化、硫化与氯化、应用其结果验证理论模拟并修正采用的数据。应用合金氧化图研究合金元素Cr、Si对合金发生铝的选择性外氧化的影响、对现代新材料与涂层的设计提供指导。.关键词(不超过5个，用分号分开): 奥氏体合金

经多元改性并控制铝含量的现代耐热材料具有超强抗高温蠕变并能生成氧化铝膜，成为服役超超临界电站、能源再生等苛刻环境的候选材料。本项目旨在研究铝改性的、铁/镍/钴基耐热合金在含氧、硫、碳气氛中的高温反应性，分析与模拟多元Fe/Ni/Co-Cr-Al基合金与单氧化剂（O）和双氧化剂（O-S或O-C）反应的热力学特征和动力学过程。首先，构建了能涵盖各组分的三元合金在不同环境（温度，氧分压）条件下的氧化热力学相图，预测体系在平衡状态可能形成的各种稳定氧化物的性质及其随合金成分和氧化剂分压变化的规律。随后，综合考虑热力学和动力学两方面因素、包括氧化过程中的扩散等动力学因素、计算并建立合金氧化动力学图。基于此类具有普适性的氧化图，可以建立任一实用合金在不同环境中发生腐蚀反应的二元、三元以及四元系理论氧化图，如最有实用意义的Ni/Fe-Cr-Al-O、Cr/Al-O-C等体系。应用此类理论氧化图可以直观地表征复杂的腐蚀动力学过程、更好低理解高温合金腐蚀机制、进而提出促使合金表面形成保护性组元的选择性外氧化膜所需要的临界成分和环境条件。同时，实验研究了一系列具有不同铝和铬含量的Fe/Ni/Co-基三元、四元合金的纯氧化、复合氧化与硫化、以及氧化与碳化的腐蚀行为、并通过建立相应体系和温度下的理论氧化图来诠释这些合金与单一或双重氧化剂反应的热力学特性和动力学过程。特别地，籍合金氧化图可以诠释向合金中添加次活泼元素铬所产生的”第三组元作用”、描述合金发生由铝和铬的内氧化、内硫化或内碳化向形成仅含最活泼组元铝和铬的选择性外氧化转变的临界浓度。为令高温材料的事业，能更恰当、有效地利用“活泼组元的选择性氧化”的效应促使工程材料在尽可能低的铝浓度下在其表面生成连续的、缓慢生长的保护性氧化膜、同时又能较好地规避其可能对材料力学性能的负面影响，为现代新高温材料与涂层的设计提供参考。