Grain-orientation dependent nitriding behaviour of cubic and hexagonal substrates

立方体和六方体基材的晶粒取向相关氮化行为

• 批准号: 343168123
• 负责人: Dr. Maryam Akhlaghi
• 金额: --
• 依托单位: Institut für Werkstoffwissenschaft
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/343168123?language=en
• 关键词: Grain; orientation; dependent; nitriding; behaviour

Previous nitriding investigations performed on polycrystalline austenitic stainless steels and ferritic Fe-based alloys revealed that in the presence of residual macrostresses on the surface of nitrided specimen, the nitriding rate depends on the orientation of surface grains. That is, the surface nitrogen concentration and the nitriding depth decrease upon increasing the angle between the surface normal of the grain and the normal of a {100} plane. This phenomenon can be ascribed to the heterogeneous distribution of residual macrostress developed during nitriding on the differently-oriented surface grains due to the elastically anisotropic nature of cubic substrates. Up to now, this phenomenon is only studied for a limited range of cubic materials with Zener´s anisotropy ratio larger than one. In order to confirm the current idea for the grain-orientation dependence of the nitriding behaviour of polycrystalline alloy, and in order to improve the understanding of this phenomenon, it is desired to broaden the range of materials for which data on orientation-dependent nitriding exist. Therefore, the primary purpose of this research is to investigate the grain-orientation dependent nitriding behavior of a broader range of metallic substrates with different elastic properties or different crystal structures. To do so, controlled gaseous nitriding experiments will be performed on the cubic W-based alloys (W-V and W-Ti) with Zener´s anisotropy ratio equals to one, on the cubic Mo-based alloys (Mo-Cr, Mo-V and Mo-Ti) with Zener´s anisotropy smaller than one and on the hexagonal Co-based alloys (Co-Cr and Co-V). Studying internal nitriding of refractory metal-based substrates (Mo- and W-based alloys) will be carried out at moderate temperature of 900 °C using NH3 gas or a mixture of NH3 and H2. This is the first time that the internal gaseous nitriding of these materials will systematically be studies at moderate nitriding temperatures using NH3-based media. Also, low-temperature nitriding of hexagonal Co-based alloys which may result in development of expanded phases will be performed using temperature range of 350-450°C. Previous low-temperature nitriding experiments revealed only the development of austenitic expanded phases upon nitriding of stainless steels. Thus, in this research the possibility for the formation of hexagonal expanded phase, for the first time, will be investigated.

以往对多晶奥氏体不锈钢和铁素体铁基合金的渗氮研究表明，在渗氮试件表面存在残余宏观应力的情况下，渗氮速度取决于表面晶粒的取向。也就是说，表面氮浓度和渗氮深度随颗粒表面法线与{100}面法线夹角的增大而减小。这种现象可归因于立方体衬底的弹性各向异性导致渗氮过程中在不同取向的表面颗粒上形成的残余宏观应力的不均匀分布。到目前为止，这种现象只在齐纳-S各向异性比大于1的有限范围内的立方材料上被研究过。为了证实当前关于多晶合金渗氮行为与晶向有关的观点，并为了提高对这一现象的理解，希望扩大存在取向相关渗氮数据的材料的范围。因此，本研究的主要目的是研究具有不同弹性性质或不同晶体结构的多种金属基材的晶向氮化行为。为此，将对齐纳-S各向异性比为1的立方钨基合金(W-V和W-Ti)、齐纳-S各向异性小于1的立方钼基合金(Mo-Cr、Mo-V和Mo-Ti)以及六方钴基合金(Co-Cr和Co-V)进行受控气体氮化实验。研究难熔金属基材(钼和钨基合金)的内部氮化将在900℃的中等温度下使用NH3气体或NH3和H2的混合物进行。这是首次利用氨基介质在中等氮化温度下系统地研究这些材料的内部气体氮化。此外，六方钴基合金的低温氮化将在350-450°C的温度范围内进行，这可能会导致扩展相的发展。以前的低温氮化实验表明，不锈钢氮化时只会产生奥氏体扩展相。因此，在这项研究中，将首次探讨形成六方相的可能性。