GH4169合金中δ相对疲劳性能的影响规律研究

发布时间：2018-01-13 16:15

本文关键词：GH4169合金中δ相对疲劳性能的影响规律研究　出处：《贵州大学》2016年硕士论文　论文类型：学位论文

【摘要】：GH4169合金是一种时效强化型高温合金,由于其良好的强韧性,耐蚀性,焊接性能及抗疲劳性能,在航空航天和石油行业得到广泛的运用。合金中析出相δ相的析出、溶解规律及其热加工行为已得到广泛的研究。外在环境因素、加载条件对GH4169合金疲劳裂纹扩展速率的影响规律也有报道。然而δ相含量对GH4169合金断裂韧性及疲劳裂纹扩展速率的研究却鲜有报道。本文通过定量表征δ相的含量对GH4169合金疲劳裂纹扩展及断裂性能。采用OM、SEM、TEM等技术手段表征GH4169合金显微组织及δ相的体积分数。研究不同的δ相含量和晶粒尺寸对GH4169合金断裂韧性和疲劳裂纹扩展速率的影响机制。本文研究这六种热处理工艺中,δ相含量随着固溶温度的下降及保温时间的延长而增加。随着δ相的增加,材料的强度降低,但是塑性却有所增加。随着晶粒尺寸的增加,材料强度下降,符合霍尔佩奇关系。材料的冲击韧性随着δ相的增加而降低。随着δ相含量的增加,GH4169合金断裂韧度呈现下降的趋势。δ相主要沿晶界分布。由于δ相本身为金属间化合物,且其周围会形成贫Nb元素的微塑性区,对裂纹扩展有吸引作用,从而导致裂纹发生沿晶扩展。晶粒尺寸增大会降低裂纹遇到晶界的概率,在一定的晶粒尺寸范围内增加裂纹的扩展阻力,提高材料的断裂韧度。通过紧凑拉伸试样得到六种工艺状态下GH4169合金的Paris曲线。结果表明,δ相含量的增加会导致Paris曲线的稳定扩展阶段和快速扩展阶段的疲劳裂纹扩展速率增加。稳定扩展阶段裂纹尖端塑性区大于等于晶粒尺寸,分布在晶界上的δ相会加速疲劳裂纹扩展速率。在快速扩展阶段,裂纹尖端塑性区远大于晶粒尺寸,δ相对疲劳裂纹扩展的影响作用更加显著。在低应力强度因子状态下,接近于Paris曲线的初始扩展阶段时,裂纹尖端塑性区小于晶粒尺寸,δ相对疲劳裂纹扩展速率的影响效果降低。在这个阶段,一定的晶粒尺寸条件的,适当的增加晶粒尺寸有助于降低疲劳裂纹扩展速率。
[Abstract]:GH4169 alloy is a kind of aging strengthened superalloy, because of its good strength and toughness, corrosion resistance, welding property and fatigue resistance. It has been widely used in aerospace and petroleum industry. The precipitation, dissolution and hot working behavior of 未 phase in alloy have been widely studied. The effect of loading conditions on the fatigue crack growth rate of GH4169 alloy is also reported. However, the study of 未 phase content on fracture toughness and fatigue crack growth rate of GH4169 alloy is rarely reported. The fatigue crack propagation and fracture properties of GH4169 alloy were quantitatively characterized by the content of 未 phase. OM was used. SEM. TEM and other techniques were used to characterize the microstructure and volume fraction of 未 phase in GH4169 alloy. The effects of 未 phase content and grain size on fracture toughness and fatigue crack propagation rate of GH4169 alloy were studied. Mechanism. In this paper, six kinds of heat treatment processes are studied. The content of 未 phase increases with the decrease of solution temperature and the prolongation of holding time. With the increase of 未 phase, the strength of the material decreases, but the plasticity increases. With the increase of grain size, the strength of the material decreases. The impact toughness of the material decreases with the increase of 未 phase and increases with the increase of 未 phase content. The fracture toughness of GH4169 alloy shows a decreasing trend. 未 phase mainly distributes along grain boundary. Because 未 phase itself is an intermetallic compound, and there is a microplastic zone around it, which is poor in NB element. The increase of grain size will reduce the probability of crack meeting grain boundary and increase the resistance of crack propagation in a certain range of grain size. The Paris curves of GH4169 alloy under six different processing conditions were obtained by compact tensile test. The results showed that the fracture toughness of the alloy was improved. The increase of 未 phase content leads to the increase of fatigue crack growth rate in the stable and fast growth stages of the Paris curve, and the plastic zone at the crack tip is greater than or equal to the grain size in the stable growth stage. The 未 phase distributed on the grain boundary will accelerate the fatigue crack growth rate. At the rapid growth stage, the plastic zone at the crack tip is much larger than the grain size. The effect of 未 on fatigue crack growth is more obvious. At the condition of low stress intensity factor, the plastic zone at crack tip is smaller than grain size when it is close to the initial growth stage of Paris curve. The effect of 未 on fatigue crack growth rate is reduced. At this stage, a proper increase of grain size is helpful to reduce the fatigue crack growth rate under certain grain size conditions.
【学位授予单位】：贵州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG132.3

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