發(fā)布時間：2018-12-09 15:41

【摘要】：隨著發(fā)電機組容量的提高,對發(fā)電機組運行的安全性及可靠性提出了更高要求。轉子槽楔是發(fā)電機組的重要部件之一,Cu-Ni-Si合金是目前應用最廣泛的槽楔材料。Cu-Ni-Si是一種時效強化型合金,時效前冷變形、時效溫度、時效時間是影響性能的關鍵因素。稀土和稀土氧化物作為有效的添加劑,可改善合金組織和性能。本文采用X射線衍射(XRD)、掃描電子顯微鏡(SEM)、透射電子顯微鏡(TEM、HREM)、室溫拉伸、電導率測量等方法研究Cu-Ni-Si合金時效過程中的顯微組織、力學性能和電性能變化;研究稀土和稀土氧化物在合金中的分布和存在形式,以及其對合金組織和性能的影響及作用機理。本研究主要結論如下:1、鑄態(tài)Cu-Ni-Si合金為典型的樹枝晶組織,存在明顯的晶內偏析和枝晶偏析。熱擠壓可消除鑄造缺陷,同時由于擠壓溫度較高合金發(fā)生動態(tài)回復和再結晶。熱擠壓后的合金中無明顯第二相析出,合金處于過飽和狀態(tài)。Cu-Ni-Si合金經過60%拉拔變形后,在430℃時效3 h具有最佳的綜合性能,顯微硬度為265.6 HV,抗拉強度為760 MPa,電導率為40.1%IACS。合金在430℃時效時發(fā)生有序化轉變,550℃時效時其析出相主要為Ni2Si,已經明顯長大。Cu-Ni-Si合金在不同時效溫度下的相變動力學方程為:400℃:φ = 1-exp(-0.7561t0.72678);430℃:φ = 1-exp(-0.9094t0.70005);460℃:φ = 1-exp(-1.1868t0.53943),可見時效溫度越高,時效進行得越快。2、Cu-Ni-Si合金中添加La后,鑄態(tài)晶粒明顯細化,La從0.05 wt.%增加到0.5 wt.%,鑄態(tài)晶粒尺寸由2.5 mm減小到1.1 mm。鑄態(tài)組織中除α-Cu相外,還有LaSi2、LaNi3和LaCu2相。隨La量增加,含稀土的第二相逐漸由球狀變?yōu)殚L條狀或塊狀,尺寸由3～5 μm增加到10～12μm。Cu-Ni-Si合金中添加0.1 wt.%La時,鑄態(tài)合金抗拉強度和斷后伸長率達到峰值,分別為430 MPa和17.15%。添加La后,析出順序以及析出相類型發(fā)生了變化。La含量0.1 wt.%的合金在430℃時效0.5 h后,析出相主要為Ni3Si,并與基體存在共格關系;時效2 h后,合金中除Ni3Si相外,還生成了 LaNi3、LaSi2及Ni2Si相,其中Ni3Si和Ni2Si相與基體保持共格關系,合金處于峰時效狀態(tài)。3、Cu-Ni-Si合金中添加稀土氧化物LSMO后可促進等軸晶形成,當LSMO量為0.1 wt.%和0.2 wt.%時,鑄錠中心存在大量等軸晶。LSMO在鑄態(tài)合金中的分布與加入量有關,加入量0.1 wt.%時,LSMO主要聚集在枝晶交界處,加入量0.5wt.%時,LSMO在晶粒和晶界處均有分布。LSMO加入量0.1wt.%時,鑄態(tài)合金具有最佳的塑性變形能力,與未加LSMO的合金相比,其斷后伸長率為22.8%,提高71.4%;抗拉強度為382 MPa,略有下降。對加入LSMO 0.1wt.%的合金進行大變形量冷軋(78%),結果顯示軋制樣品表面平整,沒有出現(xiàn)開裂現(xiàn)象,這表明該合金具有良好的冷變形能力。
[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，

本文編號：2369637