Effect of Heat Treatment on Microstructure and Mechanical Properties of VDM Alloy 780 Premium
Effect of Heat Treatment on Microstructure and Mechanical Properties of VDM Alloy 780 Premium
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热处理对 VDM 780 Premium 合金显微组织和机械性能的影响
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
J. Klöwer
中科院分区：
文献类型：
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作者：
M. Bergner;J. Rösler;B. Gehrmann;J. Klöwer
VDM Alloy 780 Premium是由德国布伦瑞克工业大学和VDM Metals GmbH合作开发的一种新型718型高温合金[1,2]。除了第二相（下文称为δ相）外，它还含有用于强化的γ′相（请注意，晶体结构的测定尚待确定）。它可能不具有与718合金中的δ相相同的DOa结构。与合金718一样，δ相可用于高温下的晶粒细化和晶界强化。与718合金相比，在化学成分上最重要的区别是用约25%的Co代替了铁，高铝含量（约2%）与低钛含量（约0.2%）相结合。首先，这些措施稳定了强化阶段，并允许高达750°C的应用温度。其次，尽管铝含量相对较高，但δ相仍然保留。为了充分利用Alloy 780，必须了解合金两相的析出动力学以及组织和力学性能的同步演变。因此，本文讨论了热处理对相动力学、显微组织演变和力学性能的影响。首先，将证明适当控制热处理参数可以使合金的δ相分布与718合金相同。其次，将介绍维氏硬度测试和蠕变断裂实验，揭示热处理策略和机械性能之间的相互关系。常温下，该合金不含γ″相，但强度达到或超过718合金，蠕变强度远优于718合金。
VDM Alloy 780 Premium is a new 718-type superalloy recently developed in a cooperation between Technical University Braunschweig and VDM Metals GmbH [1, 2]. It contains the γ′-phase for strengthening in addition to a second phase, in the following referred to as δ-phase (Note that determination of the crystal structure is pending. It may not have the same DOa structure as the δ-phase in Alloy 718.). As in Alloy 718, the δ-phase may be used for grain refinement and strengthening of grain boundaries at elevated temperatures. Most important differences in chemical composition compared to Alloy 718 are the essential replacement of Fe by about 25% Co and a higher Al-content (about 2%) in combination with a lower Ti-content (about 0.2%). Firstly, these measures stabilize the strengthening phase and allow for application temperatures of up to 750 °C. Secondly, the δ-phase is preserved despite the relatively high aluminum content. To make best use of Alloy 780, the precipitation kinetics of both phases along with the concurrent evolution of microstructure and mechanical properties must be understood. Consequently, this article deals with the influence of heat treatments on the phase kinetics, microstructure evolution and mechanical properties. Firstly, it will be demonstrated that proper control of the heat treatment parameters allows for a distribution of the δ-phase as in Alloy 718. Secondly, Vickers hardness testing along with creep rupture experiments will be presented, revealing interdependencies between heat treatment strategies and mechanical properties. At ambient temperature, the strength of the new alloy meets or exceeds that of Alloy 718 despite absence of the γ″-phase, while its creep strength is far superior.