Cu-Be-Co-Ni合金组织性能及时效硬化行为研究
发布时间：2018-08-27 08:01
【摘要】：铍铜合金的使用性能与其显微组织密切相关,尤其是合金中析出物的状态。通过优化析出物的的状态,可以获得性能更佳优异的合金。本文对Cu-Be-Co-Ni合金合金高温压缩变形行为、不同单级和双级时效热处理工艺下的显微组织、相变规律、断裂韧性、疲劳行为以及时效硬化机理进行了系统研究,得到的主要结论如下：Cu-Be-Co-Ni合金高温压缩变形是一个热激活的过程,主要分为加工硬化、动态回复和动态再结晶三个阶段。合金的应力峰值随应变速率的增加而上升,随着变形温度的增加而降低。结合XRD测试与导电率法,对固溶软态及硬态Cu-Be-Co-Ni合金的时效析出动力学规律进行了研究,获得了相应的时效动力学方程。固溶软态合金320℃时效过程中,析出物均匀形核,具有很长的相变孕育期：固溶硬态合金320℃时效过程中,析出物在界面非均匀形核,时效初期就可达到很高的相转变率。通过320℃预时效30 min,随后在280℃时效360 min的断续时效处理,可以显著改善Cu-Be-Co-Ni合金的韧性。与普通峰值时效合金相比,断续时效处理后合金的抗拉强度仅降低了3.3%,而均匀伸长率以及平面应力断裂韧度分别提高了17.1%和23%,断裂过程中裂纹萌生所需能量提高了84%,裂纹扩展所需能量提高了将近2倍。合金中析出物以密集分布的小尺寸颗粒状态存在并且与位错间相互作用机制为位错剪切析出粒子时,合金将具有更高的塑性和断裂韧性。Cu-Be-Co-Ni合金的疲劳裂纹扩展速率与显微组织密切相关,根据裂纹尖端反向塑性区(RPZ)尺寸与合金显微组织参数之间的关系可以很好地解释疲劳裂纹扩展机理。应力场强度因子水平较低时,RPZ尺寸小于晶粒尺寸,疲劳裂纹在晶粒内部及晶界附近局部区域独立扩展,主要受到晶内析出物的影响,合金的疲劳裂纹扩展速率随合金中可变形析出物含量的增加而降低。应力场强度因子水平较高时,RPZ尺寸约为晶粒尺寸的1～2倍,疲劳裂纹沿晶界扩展,晶界的特征成为影响疲劳裂纹扩展速率的主要因素。胞状不连续脱溶产物和母相间连续的相界面将有效地阻碍疲劳裂纹的扩展。通过对不同时效状态下Cu-Be-Co-Ni合金中析出物的特征进行定量研究,建立了合金的屈服强度模型,揭示了合金的析出强化机理。对于仅含有不可变形析出物的普通峰值时效和过时效合金来说,析出强化的贡献来自于Orowan机制。而双级时效和欠时效的合金中同时含有可变形及不可变形析出物,两者的临界转换尺寸为1.5 nm,析出强化效果由位错剪切析出粒子以及Orowan机制共同提供,其中Orowan机制起主要作用。根据Cu-Be-Co-Ni合金单向拉伸及拉伸-压缩变形(Bauschinger)行为,分别研究了合金各向同性强化和随动强化对合金应变硬化的贡献,建立了合金析出物微观特征与宏观应力-应变行为之间的模型。该模型表明合金的抗拉强度和均匀伸长率取决于两个相互矛盾的因素：位错动态回复速率和存储在析出粒子周围的位错密度增长速率,优化合金性能的关键在于平衡这两个相互矛盾的因素。研究结果表明,含有可变形及不可变形混合析出物的合金可达到这两个因素间的良好平衡,从而获得最佳的性能。
[Abstract]:The service properties of beryllium-copper alloys are closely related to their microstructure, especially the state of precipitates in the alloys. By optimizing the state of precipitates, better alloys with better properties can be obtained. Fracture toughness, fatigue behavior and aging hardening mechanism of Cu-Be-Co-Ni alloy are systematically studied. The main conclusions are as follows: high temperature compression deformation of Cu-Be-Co-Ni alloy is a thermal activation process, which is divided into three stages: work hardening, dynamic recovery and dynamic recrystallization. The ageing kinetics of solid solution soft and hard Cu-Be-Co-Ni alloys was studied by XRD and conductivity method, and the corresponding ageing kinetics equations were obtained. The toughness of Cu-Be-Co-Ni alloy can be significantly improved by pre-aging at 320 C for 30 min and then aging at 280 C for 360 min. The tensile strength of Cu-Be-Co-Ni alloy after intermittent aging treatment is stronger than that of normal peak aging alloy. The crack initiation energy is increased by 84% and the crack propagation energy is increased by nearly two times. The precipitates in the alloy exist in densely distributed small size particles and interact with dislocations as dislocations. The fatigue crack growth rate of Cu-Be-Co-Ni alloy is closely related to the microstructure. The mechanism of fatigue crack growth can be well explained by the relationship between the size of RPZ and the microstructure parameters of the alloy. The fatigue crack propagates independently in the grain interior and the local area near the grain boundary. The fatigue crack propagation rate decreases with the increase of the content of deformable precipitates in the alloy. The RPZ size is about 1 of the grain size when the stress field intensity factor is high. Fatigue cracks propagate along grain boundaries, and grain boundaries are the main factors affecting the growth rate of fatigue cracks. The discontinuous cell-like desolvation products and the continuous phase interface between parent phase will effectively inhibit the growth of fatigue cracks. The yield strength model reveals the precipitation strengthening mechanism of the alloy. The contribution of precipitation strengthening to the normal peak aging and over aging alloys with only undeformed precipitates comes from the Orowan mechanism. At 1.5 nm, the precipitation strengthening effect is provided by dislocation shear precipitation particles and Orowan mechanism, in which Orowan mechanism plays a major role. Based on the uniaxial tensile and tensile-compressive deformation (Bauschinger) behavior of Cu-Be-Co-Ni alloy, the contributions of isotropic strengthening and follow-up strengthening to strain hardening of the alloy are studied, and the alloy is established. The model shows that the tensile strength and uniform elongation of the alloy depend on two contradictory factors: the dynamic recovery rate of dislocation and the growth rate of dislocation density stored around the precipitated particles. The results show that the alloy containing deformable and non-deformable mixed precipitates can achieve a good balance between the two factors and obtain the best properties.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG146.11
本文编号：2206623
[Abstract]:The service properties of beryllium-copper alloys are closely related to their microstructure, especially the state of precipitates in the alloys. By optimizing the state of precipitates, better alloys with better properties can be obtained. Fracture toughness, fatigue behavior and aging hardening mechanism of Cu-Be-Co-Ni alloy are systematically studied. The main conclusions are as follows: high temperature compression deformation of Cu-Be-Co-Ni alloy is a thermal activation process, which is divided into three stages: work hardening, dynamic recovery and dynamic recrystallization. The ageing kinetics of solid solution soft and hard Cu-Be-Co-Ni alloys was studied by XRD and conductivity method, and the corresponding ageing kinetics equations were obtained. The toughness of Cu-Be-Co-Ni alloy can be significantly improved by pre-aging at 320 C for 30 min and then aging at 280 C for 360 min. The tensile strength of Cu-Be-Co-Ni alloy after intermittent aging treatment is stronger than that of normal peak aging alloy. The crack initiation energy is increased by 84% and the crack propagation energy is increased by nearly two times. The precipitates in the alloy exist in densely distributed small size particles and interact with dislocations as dislocations. The fatigue crack growth rate of Cu-Be-Co-Ni alloy is closely related to the microstructure. The mechanism of fatigue crack growth can be well explained by the relationship between the size of RPZ and the microstructure parameters of the alloy. The fatigue crack propagates independently in the grain interior and the local area near the grain boundary. The fatigue crack propagation rate decreases with the increase of the content of deformable precipitates in the alloy. The RPZ size is about 1 of the grain size when the stress field intensity factor is high. Fatigue cracks propagate along grain boundaries, and grain boundaries are the main factors affecting the growth rate of fatigue cracks. The discontinuous cell-like desolvation products and the continuous phase interface between parent phase will effectively inhibit the growth of fatigue cracks. The yield strength model reveals the precipitation strengthening mechanism of the alloy. The contribution of precipitation strengthening to the normal peak aging and over aging alloys with only undeformed precipitates comes from the Orowan mechanism. At 1.5 nm, the precipitation strengthening effect is provided by dislocation shear precipitation particles and Orowan mechanism, in which Orowan mechanism plays a major role. Based on the uniaxial tensile and tensile-compressive deformation (Bauschinger) behavior of Cu-Be-Co-Ni alloy, the contributions of isotropic strengthening and follow-up strengthening to strain hardening of the alloy are studied, and the alloy is established. The model shows that the tensile strength and uniform elongation of the alloy depend on two contradictory factors: the dynamic recovery rate of dislocation and the growth rate of dislocation density stored around the precipitated particles. The results show that the alloy containing deformable and non-deformable mixed precipitates can achieve a good balance between the two factors and obtain the best properties.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG146.11
【参考文献】
相关期刊论文 前10条
1 王伟;;铍铜合金的生产和应用前景分析[J];有色金属加工;2014年02期
2 朱兴水;;高等级铍铜合金的应用与发展趋势[J];科技创新导报;2014年04期
3 王松;谢明;王塞北;陈永泰;张吉明;杨有才;;时效态高强高导Cu-Ag-Cr合金的组织与性能[J];稀有金属;2014年02期
4 丁宗业;贾淑果;邓猛;宋克兴;刘平;;Cu-0.36Cr-0.03Zr合金的时效动力学[J];中国有色金属学报;2013年07期
5 Yongbo XU;Daokui XU;Xiaohong SHAO;En-hou HAN;;Guinier-Preston Zone,Quasicrystal and Long-period Stacking Ordered Structure in Mg-based Alloys,A Review[J];Acta Metallurgica Sinica(English Letters);2013年03期
6 熊明华;严红革;苏斌;陈吉华;曾佩兰;吴远志;;亚晶及析出相强化对Al-Zn-Mg-Cu合金性能的影响[J];特种铸造及有色合金;2012年11期
7 王俊峰;贾淑果;陈少华;刘平;宋克兴;刘红勋;;固溶态Cu-Ni-Si合金时效过程的相变动力学[J];中国有色金属学报;2012年10期
8 李斌;刘贵民;丁华东;雍青松;郑晓辉;;弥散强化铜合金的研究现状[J];材料导报;2012年17期
9 何柏林;王斌;;疲劳失效预测的研究现状和发展趋势[J];机械设计与制造;2012年04期
10 ;Microstructure and properties characteristic during interrupted multi-step aging in Al-Cu-Mg-Ag-Zr alloy[J];Rare Metals;2011年04期
，本文编号：2206623
本文链接：https://www.wllwen.com/shoufeilunwen/gckjbs/2206623.html
