Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Microelement Hf added in Ni-based powder metallurgy (PM) superalloy can modify microstructure and improve mechanical properties, such as stress-rupture life, creep resistance and crack growth resistance, and also benefit to eliminate notch sensitivity. So systematically studying the effect of microelement Hf on PM superalloy microctructure will help to comprehend its corresponding mechanism. The effects of microelement Hf on the morphologies, chemical compositions and content of g' phase and MC carbide in FGH97 PM Superalloy were investigated by means of SEM and physiochemical phase analysis. The results showed that Hf facilitated the precipitations of g' phase and MC carbide, and changed chemical compositions of g' phase and MC carbide, the effect of Hf on the size and morphology of MC carbide was not obvious, while Hf greatly affected the size and morphology of g' phase and accelerated the splitting of g' phase from one instable cubic g' particle to stable octet of cubes. As Hf affected the lattice misfit of g'/g phase (d), modifying Hf content changed the critical splitting size of g' phase (Dc). The relationship between Dc and Hf content (w(Hf)) was found to be Dc=315.4+640.2w(Hf)-358.2[w(Hf)]2. With Hf content increased, the absolute value of d decreased and Dc increased. Cubic g' particle split into an octet of cubes when g' phase grew up to the critical splitting size.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Hafnium (Hf) is one of the most important microelements in powder metallurgy (P/M) superalloy. Hf modifies the microstructure and drastically improves mechanical properties in P/M superalloy. The effect of Hf in a nickel-based P/M superalloy was systematically studied by means of FEG-SEM, TEM, AES, EDS and physical and chemical phase analysis. Hf mainly distributes at interdendritic region of the solidification powder in form of solid solution, which is helpful to reduce prior particle boundary (PPB). Hf facilitates morphology of γ′ phase to be unstable and enhances the large cubic γ′ phase to split into smaller ones, so the γ′ phase turns into a stable state with a lower energy faster. Hf is mainly distributed in γ′ phase and MC carbides, which changes the distribution of element between the γ′ phase, MC and g solid solution, which is beneficial to eliminate notch sensitivity and improves overall mechanical properties of the alloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：利用FEG-SEM, TEM，AES，EDS分析技术以及物理化学相分析等方法，系统地研究了微量元素Hf在镍基粉末高温合金中的作用。结果表明：元素Hf以固溶态分布在枝晶间γ固溶体内，有助于减少原始粉末颗粒边界组织。元素Hf促进γ′相形态失稳，导致大尺寸立方状γ′相发生分裂，更快地进入γ′相低能稳定的择优形态。元素Hf主要分布在γ′相和MC型碳化物中，改变γ′相和MC型碳化物及γ固溶体相间合金元素的再分配，有利于消除合金的缺口敏感性，改善合金综合力学性能。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：研究了含微量元素Hf(0-0.89%)的FGH97粉末高温合金中拓扑密排μ相的析出动力学、组织形态以及μ相对Hf含量为0.30%的合金盘坯力学性能的影响。结果表明：Hf含量为0.30%和0.89%的合金经750-900℃长期时效后μ相已明显析出，并随着时效温度的升高、时效时间的延长以及Hf添加量的增加，μ相析出量增加和尺寸长大。合金中的μ相主要在晶内以长条片状形态析出。合金盘坯(Hf含量为0.30%)在550-650℃长期时效后没出现μ相，高温拉伸性能和高温持久性能没有降低，组织稳定性良好。750℃长期时效后μ相的析出对合金盘坯的高温拉伸强度无明显影响，但降低拉伸塑性和高温持久寿命，而提高持久塑性约20%。详细讨论了μ相的析出行为、γ固溶体中合金元素的再分配以及合金断裂断口的特征，从理论上解释了μ相对力学性能的影响的脆-韧双重作用的机理，并提出控制和避免μ相大量析出造成性能劣化的措施和方法。
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