【作者】 贾磊；

【导师】 吕振林； 谢辉；

【作者基本信息】 西安理工大学 ， 材料科学与工程， 2009， 硕士

【摘要】 本文采用熔炼法分别制备了Cu-Ni-Si合金的近平衡凝固试样和普通熔铸试样,并对普通熔铸合金进行了450℃等温时效和轧制+等温时效后处理。采用OM结合SEM分析了Cu-Ni-Si合金的显微组织,利用XRD与EDS分析确定了合金的相组成及合金元素的分布状况,通过DTA分析考察了近平衡凝固条件下合金的相变过程及其对应的相变温度,Cu-Ni-Si合金的电导率采用涡流电导仪(ECA)测量。在上述实验结果的基础上,系统研究了Cu-Ni-Si合金的近平衡相变过程和导电机制,为后续高强高导Cu-Ni-Si合金的制备研究提供了理论基础。本文的主要研究工作和所获得的结论如下：1.当Cu含量高于40%时,Cu-Ni-Si合金的近平衡凝固显微组织主要由初生富Cu相α-Cu(Ni,Si)、共晶相α-Cu(Ni,Si)+β1-Ni3Si以及针状组织δ-Ni2Si组成；当Cu含量为40%时,合金的近平衡凝固组织为完全的共晶组织α-Cu(Ni,Si)+β1-Ni3Si。2. Cu-Ni-Si合金的近平衡凝固行为与合金中Cu含量密切相关。Cu含量为40%的合金熔体以共晶方式凝固；Cu含量高于40%的合金熔体以亚共晶方式凝固,即α-Cu(Ni,Si)作为初生相以匀晶反应L1→α-Cu(Ni,Si)方式首先从合金熔体中析出,并伴随着Ni、Si原子向残余液相的扩散；当残余液相接近共晶成分时发生共晶反应L2→α-Cu(Ni,Si)+Ni3Si直至凝固过程结束；最后过饱和固溶体α-Cu(Ni,Si)中的Ni、Si原子通过固态相变以沉淀相δ-Ni2Si的形式析出。3.普通熔铸法得到的四种Cu-Ni-Si合金显微组织均为初生富Cu相α-Cu(Ni,Si)和共晶相β1-Ni3Si+α-Cu(Ni,Si),但β1-Ni3Si的数量与形貌与合金中Cu含量密切相关。随着Cu含量的降低,合金中β1-Ni3Si的数量增加且逐渐由位于α-Cu(Ni,Si)相晶界交叉处的颗粒向位于晶界上的网状结构过渡；合金中共晶区也随之由离异共晶转变为典型的片层状共晶。4.随着等温时效处理的进行,铸态组织中迅速析出δ-Ni2Si相,随后δ-Ni2Si相的数量几乎不再增加直至时效达到2h后又继续增加；Cu含量为95%和90%的两种合金导电率的变化情况与δ-Ni2Si相的析出情况一致,但Cu含量为80%和60%的两种合金导电率几乎不受时效过程的影响。5.经轧制+等温时效处理后,合金组织中β1-Ni3Si相形成的网状结构被不同程度地打破,沿垂直于轧制平面的组织中出现了明显的轧制织构,四种合金的导电率均出现了较为明显的提高。6. Cu-Ni-Si合金的导电行为受固溶原子浓度和β1-Ni3Si相的数量与形貌的影响。对于Cu含量低于80%的合金,β1-Ni3Si相形成的网状结构成为影响其导电率的主要因素。更多还原

【Abstract】 Cu-Ni-Si alloys with different components were prepared by the methods of near-equilibrium solidification and traditional fusion casting, and the latter samples were subsequently undergone isothermal aging treatment at the temperature of 450℃for different times and rolling+isothermal aging treatment, respectively. The microstructures of Cu-Ni-Si alloys were observed by the combination of OM with SEM. The phase composition and the distribution of alloy elements were identified by both XRD and EDS. The phase transformation during the process of near-equilibrium solidification was checked by DTA analysis under an Ar atmosphere.7510 eddy-conductivity apparatus (ECA) was taken to measure the electrical conductivity of Cu-Ni-Si alloys. Based on the above experimental results, the phase transformation process under the condition of near-equilibrium and the electric conduction mechanism of Cu-Ni-Si system alloys were discussed systematically. The main reseach work and conclusions of this paper are presented as follows.1. The microstructure of Cu-Ni-Si alloys with higher than 40% Cu content under near-equilibrium solidification condition is consisted of primary Cu-rich phaseα-Cu(Ni,Si), eutectic phase (β1-Ni3Si+α-Cu(Ni,Si)) and acicularδ-Ni2Si phase, while there is only eutectic phase (β1-Ni3Si+α-Cu(Ni,Si) in the alloys with 40% Cu content.2. When Cu content is higher than 40%, the Cu-rich phaseα-Cu(Ni,Si) firstly formed as primary phase by the reaction L1→α-Cu(Ni,Si) accompanying with Ni and Si atoms diffusing into residual liquid. The eutectic reaction occurred subsequently by L2→α-Cu(Ni,Si)+Ni3Si when the component of the residual liquid came close to the eutectic point. Cu-Ni-Si alloys with higher than 40% Cu content solidified as the mode of hypoeutectic reaction while the alloys with 40% Cu content solidified as eutectic reaction. Finally, after liquid/solid transition had been finished, Ni and Si atoms in Cu-rich phaseα-Cu(Ni,Si) were supersaturated and trended to precipitate as 8-Ni2Si phases by solid-state phase transforming.3. The microstructure of Cu-Ni-Si alloys fabricated by traditional fusion casting is consisted of both Cu-rich phase a-Cu(Ni,Si) and eutectic phase (β1-Ni3Si+a-Cu(Ni,Si)). With the decrease of Cu content, the amount ofβ1-Ni3Si increased and its morphology transformed from the particles on the junction of grain boundary of a-Cu(Ni,Si) phase to the netted texture on the grain boundary. The eutectic zones also became to the typical lamellar eutectic structure from the separated eutectic microstructure.4.δ-Ni2Si phase precipitated rapidly from Cu-Ni-Si alloys fabricated by traditional fusion casting with the progress of isothermal aging treatment, and then did not increase until ageing for more than 2 hours. The electrical conductivity of the alloys with 95% and 90% Cu content increased synchronously with the precipitation ofδ-Ni2Si phase, while that of the alloys with 80% and 60% Cu content wasn’t affected by isothermal aging treatment.5. The netted texture ofβ1-Ni3Si phase was destroyed, and there was rolling texture in the Cu-Ni-Si alloys after rolling+isothermal aging treatment. The electrical conductivity of four researched alloys all increased obviously after rolling+isothermal aging treatment.6. The electrical conductivity of Cu-Ni-Si alloys is controlled by the combined action of both netted texture ofβ1-Ni3Si and solid solution of Ni and Si atoms, and the former is the major factor for the lower conductivity of the alloys with lower than 80% Cu content.更多还原