Effects of La 2 O 3 Content and Rolling on Microstructure and Mechanical Properties of ODS Molybdenum Alloys
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JMEPEG DOI: 10.1007/s11665-017-2959-1
Effects of La2O3 Content and Rolling on Microstructure and Mechanical Properties of ODS Molybdenum Alloys Jingling Ma, Wuhui Li, Guangxin Wang, Yaqiong Li, Hongbo Guo, Zeliang Zhao, and Wei Li (Submitted June 4, 2017; in revised form August 20, 2017) In order to study the effects of La2O3 content and rolling on microstructure and mechanical properties of Mo-La2O3 alloys, Mo-0.5% (1%) La2O3 alloys were prepared by liquid-solid doping technique, subsequently rolled either by a single-direction rolling or a cross-rolling. As a result, three different materials were prepared for this study. After being annealed at 1800 °C, the single-directionally rolled Mo-1% La2O3 alloy shows the best mechanical properties in terms of strength, hardness, and sagging deformation among the three materials. This is attributed to the observation that the alloy is only recovered with a microstructure of subgrains and dislocations. The single-directionally rolled Mo-0.5% La2O3 exhibits the worst mechanical property among the three materials. In this material, coarse grains, but no subgrains and dislocations, can be observed after annealing, indicating that it is fully recrystallized. For the cross-rolled Mo-1% La2O3 alloy, grains of dispersed sizes, but no dislocations, are visible after annealing, implying that this alloy is partially recrystallized. Accordingly, the mechanical property of this material is in between the other two materials. Thus, the mechanical properties of the three materials can be well understood based on OM, SEM, and TEM results. Overall, the single-directionally rolled Mo-1% La2O3 alloy possesses good mechanical properties and is more suitable for high-temperature applications. Keywords
high-temperature mechanical property, La2O3, microstructure, Mo alloys, rolling
1. Introduction Molybdenum is a widely used high-temperature metal with excellent physical properties, such as high melting point, low thermal-expansion coefficient, high creep resistance, and hightemperature strength. It is thus very useful for many important high-temperature applications (such as critical parts in missiles, turbines, and crucible) (Ref 1-3). However, due to its lower recrystallization temperature, pure Mo is not appropriate for some components used above 1200 °C. It is known that grain boundary (GB) of Mo is weaker because of the segregation of O, N, and other impurity elements at grain boundary (Ref 4, 5). Some measures of purifying grain boundaries or decreasing grain sizes (Ref 6-8) have been taken to reduce the segregation concentration at grain boundaries of purifying GB or decreasing grain sizes. Doping with dispersed phase particle (such as carbide and oxide) (Ref 7, 9) can refine grains of pure Mo because it can accelerate grain nucleation and hinder grain growth. This can result in a significant increase in strength and a large reduction of segregation concentration at grain boundaries. Particularly, dispersed rare-earth oxide particles Jingling Ma, Wuhui Li, Guangxin Wang, and Yaqiong Li,
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