【作者】 雷前；

【导师】 李周；

【作者基本信息】 中南大学 ， 材料科学与工程， 2014， 博士

【摘要】 摘要：铍青铜虽具有高强度、高弹性、高硬度、高耐磨性和优良的导电性能,并在模具、导电簧片、导电弹性元器件上获得了广泛的应用。但该合金由于含铍这一剧毒元素,在生产过程中严重危害人们的健康。同时铍青铜在高于200℃环境下服役使用时,其强度、弹性急剧降低,应力松弛率甚至高达40%以上,影响器件使用甚至工作失效。因此需要开发出新型的超高强、高导电、高抗应力松弛的无铍环保型导电弹性铜合金。本文采用熔铸法研制了一种超高强、高导电、高抗应力松弛Cu-6.0Ni-1.OSi-0.5Al-0.15Mg-0.1Cr合金,并对该合金的成分设计、形变热处理、加工工艺参数、沉淀相变行为、高温应力松弛行为和海水腐蚀行为进行了系统的研究和分析,得出如下主要结论：(1)合金的铸锭组织呈树枝状结构,基本可以分为枝晶骨架、枝晶间的非平衡凝固第二相粒子和过渡区。枝晶骨架主要为α-Cu相,第二相粒子主要为Ni2Si相、Ni3Si (Ni74Si26)和Ni3Al相。Al、Mg、 Cr元素则均匀地分布在基体中。(2)合金高温压缩变形的真应力-真应变曲线具有动态再结晶特征,可分为加工硬化、回复和动态再结晶三个阶段。绘制的应变量为0.6时的加工图表明合金适宜的热加工温度范围为850℃-900℃。试样在750℃下热压缩变形后,截面形成了立方织构{001}<100>；800℃变形后形成Gauss织构{011}<100>和旋转立方织构{001}<110>；850℃和900℃变形后则形成Copper织构{112}<111>、S织构{123}<634>和Gauss织构{011}<100>。(3)合金合适的形变热处理工艺为：940℃/4h均匀化退火→900℃热轧80%→980℃/4h固溶处理→冷轧50%→450℃C/1h时效处理,获得的性能为：硬度341HV,电导率26.5%IACS,抗拉强度1090MPa,屈服强度940MPa,伸长率3.5%。合金在450℃时效具有很好的抗过时效能力,即使时效20小时后硬度值仍有330.1HV。峰时效态合金在室温、100℃和200℃下加载100小时后的应力松弛率分别为4.05%、6.52%和9.74%。(4)合金过饱和固溶体在450℃时效相变贯序为：过饱和固溶体→L12有序化(Ni3Si)→β-Ni3Si相→β-Ni3Si相+δ-Ni2Si相。在450℃时效5min后即发生沉淀析出,析出相尺寸约为3-4nm；时效15min后,析出相尺寸长大为4-5nm；时效60min后,析出相为β-Ni3Si和δ-Ni2Si相,尺寸为6-8nm；时效480min后,析出相为β-Ni3Si, δ-Ni2Si和δ’-Ni2Si相,尺寸为13-15nm。(5)过饱和固溶体在500℃C时效处理5min后,即出现了Ni3Si相L12有序化,时效处理10min后合金中出现了条带状的不连续胞状析出。550℃时效处理5min后即发生了不连续胞状析出。600℃C时效处理10min后,合金发生了沉淀析出,主要沉淀析出相为8-Ni2Si,时效1h后,δ-Ni2Si分布上出现了存在不同方向的变体。650℃等温时效10min后,合金发生了δ-Ni2Si析出相沉淀析出,粒子呈棒状,尺寸约为100nm,时效30min后析出相尺寸长大到约150nm,时效60min后析出相长大至200nmo。700℃等温时效10min后,合金发生了8-Ni2Si相沉淀析出,粒子尺寸约为100nm。750℃等温时效10min后,合金发生了8-Ni2Si相沉淀析出,析出相粒子呈棒状,尺寸约为150nm。时效30min后,粒子呈圆盘状,尺寸约为250nm。(6)欠时效、峰时效和过时效态三种状态下,合金的静态腐蚀速率分别为0.033226mm/a,0.022975mm/a和0.0019456mm/a,合金的耐蚀能力大小为：过时效>峰时效>欠时效。XPS定量分析结果表明合金样品表面的腐蚀产物主要由Cu2O、CuO和Cu2(OH)3Cl构成。在NaCl溶液的浸泡过程中,铜氧化生成Cu2O,部分Cu2O进一步氧化成为CuO,部分Cu2O、H2O和CuCl结合形成Cu2(OH)3Cl。合金在氯化钠溶液中浸泡后生成了成分为碱式氯化铜Cu2(OH)3Cl和CuCl2·3Cu(OH)2的腐蚀产物,对合金表面具有一定的保护作用。更多还原

【Abstract】 ABSTRACT:Cu-Be alloys with high strength, elasticity, hardness, wear resistance and good electrical conductivity are widely used for manufacturing of dies, die mosaic pieces and elastic components. However, the alloying element beryllium is toxic and it is harmful to humans during the alloy production. Furthermore, the strength and elasticity of Cu-Be alloys decrease drastically as performed at temperature above200℃, and the stress relaxation rate is about40%, which cause materials failure. Therefore, substantial efforts have been made to develop a new Be-free conductive elastic copper alloy.In this paper, an environmental-friendly Cu-6.0Ni-1.0Si-0.5Al-0.15Mg-0.1Cr alloy with ultrahigh strength, good electrical conductivity and excellent anti-stress relaxation resistance was designed and prepared by a medium-frequency induction furnace. The composition design, thermo-mechanical heat treatment, process parameters, precipitation behavior, stress relaxation behavior and corrosion behavior were investigated in detail. Some conclusions were drawn as following.(1) Developed dendrites appeared in the initial casting ingot, including dendrite skeleton, non-equilibrium precipitates and transition zone. The dendrites were rich in Cu, while non-equilibrium precipitates were rich in Ni and Si. The precipitates were Ni2Si, Ni3Si (Ni74Si26) and Ni3Al particles. Elements of Al, Mg and Cr were disturbed in the alloy evenly.(2) The stress-strain curves of alloy deformed at evaluated temperature exhibit dynamic recrystallization feature, and the process could be divided into working hardening, dynamic recovery and dynamic recrystallization. Hot processing map was established on the basis of dynamic material model theories and Prasad instability criterion, indicating that appropriate hot processing temperature range for hot deformation was850-900℃. After hot compression deformed at750℃, Cube texture of{001}<100> was formed on the cross section. Gauss texture of{0115<100> and rotated cubic texture of{001}<110> were formed as deformed at800℃; Copper texture of{112}<111>, S texture of{123}<634> and Gauss texture of{011}<100> were formed as deformed at850℃and900℃.(3) The appropriate thermo-mechanical heat treatment method for designed alloy is that:homogenization treatment at940℃for4h→hot rolling by80% at900℃→solution treatment at980℃for4h→cold rolling by50%→aging treatment at450℃for1h. After above treatments, the alloy could achieve good properties:hardness was341HV, electrical conductivity was26.5%IACS, tensile strength was1090MPa, yield strength was940MPa, and elongation was3.5%. The hardness was330.1HV even as the alloy was aged at450℃for20h, indicating that the alloy have good anti-over aging resistance. After loading at room temperature,100℃and200℃for100h, the stress relaxation rates of peak-aged specimens were4.05%,6.52%and9.74%, respectively.(4) The order of the phase transformation in supersaturated solution solid during ageing at450℃was that:supersaturated solution solid→L12ordering (Ni3Si)→β-Ni3Si→β-Ni3Si+5-Ni2Si. Precipitation occurred as the supersaturated solid solution was aged at450℃for5min, and dimension of precipitates was3-4nm. Dimension of precipitates grew up to4-5nm as aged for15min. Precipitates of (3-Ni3Si and δ-Ni2Si with6-8nm appeared as aged for60min. Precipitates of β-Ni3Si,δ-Ni2Si and δ’-Ni2Si with13-15nm appeared as aged for480min. Precipitates of β-Ni3Si and δ-Ni2Si with100-200nm appeared as aged for24h.(5) L12ordering appeared in the supersaturated solid solution as aged at500℃for5min, and discontinuous precipitation appeared as aged for10min. Discontinuous precipitation appeared as aged at550℃for5min. Continuous precipitation appeared as aged at600℃for10min, and two variants with perpendicular growth direction were observed. Rod shape δ-Ni2Si precipitate with size of100nm appeared as aged at650℃for10min, and size of ones grew up to150nm and200nm as aged for30min and60min, respectively.δ-Ni2Si precipitates with size of100nm appeared as aged at700℃for10min. Rod-shape8-Ni2Si precipitate with size of150nm appeared as aged at750℃for10min, while disk shape ones with size of250nm appeared as aged for30min.(6) The corrosion rates of designed alloy with treatment states of under-aged, peak-aged and over-aged aged were0.033226mm/a,0.022975mm/a and0.0019456mm/a, respectively. The order of anti-corrosion resistance among the three aged treatment states was that: over-aged> peak-aged> under-aged. XPS results showed that the corrosion product layer mainly contained compounds of CuO, CU2O, CuCl and CuCl2. With increasing immersion time, Cu was oxidized to CU2O, partial Cu2O were further oxidized to CuO, and some CU2O was transformed into Cu2(OH)3C1and CuCl2·3Cu(OH)2, which could protect the matrix from corrosion.更多还原