稀土添加和时效处理对Cu-Ni-Si合金组织与性能的影响

发布时间：2018-12-09 15:41

【摘要】：随着发电机组容量的提高,对发电机组运行的安全性及可靠性提出了更高要求。转子槽楔是发电机组的重要部件之一,Cu-Ni-Si合金是目前应用最广泛的槽楔材料。Cu-Ni-Si是一种时效强化型合金,时效前冷变形、时效温度、时效时间是影响性能的关键因素。稀土和稀土氧化物作为有效的添加剂,可改善合金组织和性能。本文采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM、HREM)、室温拉伸、电导率测量等方法研究Cu-Ni-Si合金时效过程中的显微组织、力学性能和电性能变化;研究稀土和稀土氧化物在合金中的分布和存在形式,以及其对合金组织和性能的影响及作用机理。本研究主要结论如下:1、铸态Cu-Ni-Si合金为典型的树枝晶组织,存在明显的晶内偏析和枝晶偏析。热挤压可消除铸造缺陷,同时由于挤压温度较高合金发生动态回复和再结晶。热挤压后的合金中无明显第二相析出,合金处于过饱和状态。Cu-Ni-Si合金经过60%拉拔变形后,在430℃时效3 h具有最佳的综合性能,显微硬度为265.6 HV,抗拉强度为760 MPa,电导率为40.1%IACS。合金在430℃时效时发生有序化转变,550℃时效时其析出相主要为Ni2Si,已经明显长大。Cu-Ni-Si合金在不同时效温度下的相变动力学方程为:400℃:φ = 1-exp(-0.7561t0.72678);430℃:φ = 1-exp(-0.9094t0.70005);460℃:φ = 1-exp(-1.1868t0.53943),可见时效温度越高,时效进行得越快。2、Cu-Ni-Si合金中添加La后,铸态晶粒明显细化,La从0.05 wt.%增加到0.5 wt.%,铸态晶粒尺寸由2.5 mm减小到1.1 mm。铸态组织中除α-Cu相外,还有LaSi2、LaNi3和LaCu2相。随La量增加,含稀土的第二相逐渐由球状变为长条状或块状,尺寸由3～5 μm增加到10～12μm。Cu-Ni-Si合金中添加0.1 wt.%La时,铸态合金抗拉强度和断后伸长率达到峰值,分别为430 MPa和17.15%。添加La后,析出顺序以及析出相类型发生了变化。La含量0.1 wt.%的合金在430℃时效0.5 h后,析出相主要为Ni3Si,并与基体存在共格关系;时效2 h后,合金中除Ni3Si相外,还生成了 LaNi3、LaSi2及Ni2Si相,其中Ni3Si和Ni2Si相与基体保持共格关系,合金处于峰时效状态。3、Cu-Ni-Si合金中添加稀土氧化物LSMO后可促进等轴晶形成,当LSMO量为0.1 wt.%和0.2 wt.%时,铸锭中心存在大量等轴晶。LSMO在铸态合金中的分布与加入量有关,加入量0.1 wt.%时,LSMO主要聚集在枝晶交界处,加入量0.5wt.%时,LSMO在晶粒和晶界处均有分布。LSMO加入量0.1wt.%时,铸态合金具有最佳的塑性变形能力,与未加LSMO的合金相比,其断后伸长率为22.8%,提高71.4%;抗拉强度为382 MPa,略有下降。对加入LSMO 0.1wt.%的合金进行大变形量冷轧(78%),结果显示轧制样品表面平整,没有出现开裂现象,这表明该合金具有良好的冷变形能力。
[Abstract]:With the increase of generator capacity, higher requirements are put forward for the safety and reliability of generator set operation. Rotor slot wedge is one of the important parts of generator set, Cu-Ni-Si alloy is the most widely used slot wedge material at present. Cu-Ni-Si is a kind of aging strengthening alloy, cold deformation before aging, aging temperature, Aging time is the key factor affecting the performance. As an effective additive, rare earth and rare earth oxides can improve the microstructure and properties of the alloy. In this paper, X-ray diffraction (XRD), scanning electron microscope (SEM), (SEM), transmission electron microscope (TEM,HREM), tensile at room temperature and conductivity measurement were used to study the microstructure of Cu-Ni-Si alloy during aging. Mechanical and electrical properties; The distribution and existence form of rare earth and rare earth oxides in the alloy were studied. The effect of rare earth and rare earth oxide on the microstructure and properties of the alloy and its mechanism of action were also studied. The main conclusions of this study are as follows: 1. The as-cast Cu-Ni-Si alloy is a typical dendritic structure with obvious intragranular segregation and dendritic segregation. Hot extrusion can eliminate casting defects, and dynamic recovery and recrystallization occur due to high extrusion temperature. There was no obvious precipitation of the second phase in the alloy after hot extrusion, and the alloy was supersaturated. After 60% drawing deformation, Cu-Ni-Si alloy had the best comprehensive properties after aging at 430 鈩，

本文编号：2369637