【作者】 苏娟；

【导师】 卫英慧；

【作者基本信息】 太原理工大学 ， 材料学， 2011， 硕士

【摘要】 铜及其合金是工业中应用广泛的金属材料,但是铜合金强度低、耐磨性差,严重限制了其应用。金属材料的表面通过机械研磨处理使表面获得纳米晶是近几年表面强化方法研究的热点之一,这种技术在工业应用上具有非常广阔的应用前景,它将纳米晶体材料的优异性能与传统工程金属材料结合了起来。堆垛层错能(SFE——stacking fault energy)对面心立方金属的变形机制有较大的影响,较低的层错能会抑制位错滑移,而使变形以孪生的形式出现,除了SFE外,高应变速率和低温也会导致孪生塑性变形,Cu的层错能为78mJ/m2,加入合金元素后层错能变化较大。本文对纯铜,Cu-2wt%Ti合金,Cu-10wt%Ni合金进行不同时间的表面机械研磨处理(SMAT),探究不同合金元素的溶入对铜合金层错能的影响,以及层错能的不同对形变机制的影响。还研究了时效Cu-2wt%Ti合金SMAT过程与未时效处理的Cu-2wt%Ti合金形变机制的差异。探究了层错能的降低所引起的强化,提高了材料的耐磨性。利用显微硬度仪测了不同材料纳米化后表面到心部的硬度值,利用OM, XRD, SEM等测试手段对组织进行了表征。对SMAT的Cu-2wt%Ti合金试样进行了时效分析,对纳米化后的纯铜试样进行了退火保温,研究了纳米晶粒的热稳定。结果表明：(1)纯铜表面纳米化后,表层晶粒细化,但没有看到明显的形变孪晶,形变方式主要为位错的滑移。Cu-10wt%Ni合金表面纳米化后,随着纳米化时间的延长,形变孪晶的数目明显增多,孪晶交割程度不明显,其形变方式为开始为位错的滑移,位错发生塞积后,形变以孪生为主,但孪生可以改变位相差,随后又以位错滑移为主。(2)不论是固溶态Cu-2wt%Ti的纳米化试样还是固溶+时效纳米化后的纳米化试样,都可以明显看到其大量的形变孪晶与交叉孪晶,且有分层现象。Ti的溶入大大降低了铜的层错能,所以其形变方式主要为孪生,出现明显分层想象的原因是大晶粒与小晶粒塑性形变机制不同,大晶粒易于发生孪生,而小晶粒更易滑移,所以出现了分层现象。固溶态Cu-2wt%Ti合金时效后会使材料层错能提高,表现在纳米化相同时间,形变孪晶数量降低,交割程度降低。(3)纯铜板材、铜镍合金、铜钛合金经表面纳米化后表面硬度明显高于心部,耐蚀性能都有所下降,耐磨性提高。Cu-10wt%Ni合金的耐磨性高于纯Cu的原因主要是由于溶质原子的溶入造成的固溶强化,而Cu-2wt%Ti合金耐磨性高于纯Cu的原因除了固溶强化外还有就是其层错能的降低,使得层错带变宽,易于产生孪晶,孪晶与宽的层错带都可以阻碍位错的运动。(4)表面纳米化45min、60min后400℃时效,时效温度与Cu-2wt%Ti合金的再结晶温度接近或处于其范围内,所以时效过程与再结晶交叠,样品表面Ti含量偏高有可能是因为表层一定范围内发生了调幅分解。(5)经过纳米化30min、60min的纯铜板材,在450℃退火保温不同的时间,通过XRD衍射分析,表面纳米晶的确有长大趋势,不过仍在纳米级别范围之内。微观应变越大纳米晶的热稳定性越好,大的微观应变可以抑制纳米晶粒的长大。更多还原

【Abstract】 Copper and its alloys are widely used in industry as metal material. However, copper alloys have lower strength, poor wear resistance. So its application is severely limited. The surface of metallic materials can form nanocrystalline by means of surface mechanical attrition treatment (SMAT) and this is one of popular research method about surface strengthening in recent years. The application of this technology in industry has a very broad application prospects. It combines the performance of nanocrystalline materials with traditional construction materials. Stacking fault energy(SFE) has a greater impact on deformation mechanism of face centered cubic metals. Lower stacking fault energy will inhibit dislocation glide and as a result the form of deformation is twin. High strain rate and temperature also can cause Twin plastic deformation beside SFE. The stacking fault energy of Cu is 78mJ/m2, and the stacking fault energy has a great change after adding alloying elements.In this paper, pure copper, Cu-2wt%Ti alloys and Cu-10wt%Ni alloys have been treated with different time of the surface mechanical attrition treatment (SMAT). The impact of different alloying elements dissolved in the copper alloy on stacking fault energy has been researched and the impact of different Stacking fault energy on deformation mechanism has been researched too. The difference between the surface mechanical attrition treatment process of aging Cu-2wt%Ti alloy and deformation mechanism of not aging Cu-2wt%Ti alloy has been studied. And we have researched the harden caused by dropping of stacking fault probability. And material wear resistance is improved. The hardness of different materials after surface nanocrystallization from surface to core has been measured by the microhardness tester. The materials was characterized by OM, XRD, SEM and so on. Cu-2wt%Ti after surface mechanical attrition treatment was analyzed after ageing. the pure copper samples after surface nanocrystallization was annealing and Thermal stability of nanocrystalline was studied.The results show that:(1) the surface grain of pure copper was refined after surface nanocrystallization, but obvious deformation twins was not been found. the main deformation way was dislocation slipping. After surface nanocrystallization, along with the extending of time for surface nanocrystallization, the number of deformation twins increased obviously in Cu-2wt%Ti alloy. The intersecting of deformation twins was not obvious and the main deformation way was dislocation slipping. After dislocation pile-up, the main deformation way was twinning, but twinning can change phase difference and after this the main deformation way was dislocation slipping.(2) Both Cu-2wt%Ti nano-samples in solid solution state and the samples treated by solution and aging, a mass of deformation twin crystal and crossover twin crystal were observed as well as a phenomenon of layering. With the introduction of Ti, Stacking Fault Energy of Cu was brought down, which led to the twinning of crystal. Layering occured because big crystal particles tended to twin but small ones were easy to slip under the different plastic deformation mechanisms of them. Cu-2wt%Ti in the solid solution state possessed higher stacking fault energy afer the aging treatment, which can be certified by nano change at the same time, reduction of deformation twin crystal and drop of intersecting of deformation twins.(3) Pure copper, Cu-10wt%Ni alloys and Cu-2wt%Ti alloys occupied higher hardness in their surface than that in the heart atfer the surface nanocrystallization. Besides, their corrosion resistance is a bit lower than before. In contrast, they all have an increased abrasion performance. The solution strengthening which derived from soluteatoms solutioned in the Cu-10wt%Ni alloys, made the alloys more wear resistant than pure Cu. Other than the solution strengthening, the decreaseing of stacking fault energy in the Cu-2wt%Ti also made its wear resistant higher than pure Cu. As a result the fault strips widened and the twins can form easily and The twins and stacking fault both can block motion of dislocations(4) After the surface nanocrystallization for 45min and 60 min, respectively, the samples of Cu-2wt5Ti alloys went on to be aged in temperature of 400℃which is similar to its recrystallization temperature or within the range of its recrystallization temperature. Therefore, the aging procedure was carried out in the meanwhile of recrystallization and high Ti concentration in the surface was due to the spinodal decomposition, which occurred in the surface layer wihtin a certain range.(5) After the nanorization of pure copper sheet for 30min and 60 min, respectively, at the temperature of 450℃, its surface indeed had a tendency of growth although only in the nanometer level which can be found by XRD. In addition, the bigger microscopic strain made the steel more stable, and also restrained the growth of the nanocrystal in it.更多还原