【作者】 李玉峰；

【导师】 周玉； 欧阳家虎；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 博士

【摘要】 本文采用化学沉淀法制备SrSO4和BaxSr1-xSO4 (0<x<1)固溶体纳米粉体,将其作为固体润滑剂加入到陶瓷材料中,采用热压烧结和放电等离子烧结法分别制备出TZ3Y20A-SrSO4、TZ3Y20A-BaxSr1-xSO4与Al2O3-SrSO4复合材料。利用XRD、SEM、TEM、BET、TG-DSC、Raman光谱、万能力学试验机和高温摩擦磨损试验机等测试手段表征了碱土金属硫酸盐粉体的形貌、结构和热稳定性,分析了具有复杂结晶形态SrSO4粉体的形成机理,系统地研究了硫酸盐和Ag对复合材料的微观组织结构、力学性能和高温摩擦学性能的影响,探讨了不同复合材料在宽温域下的自润滑机理。通过选择合适的工艺参数,利用化学沉淀法可以获得薄片状SrSO4和球形BaxSr1-xSO4 (0<x<1)固溶体纳米粉体。在室温至1300℃范围内碱土金属硫酸盐粉体均具有良好的热稳定性。通过改变反应物溶液中[Sr2+]:[SO42-]的摩尔比可以控制SrSO4纳米粉体的最终结晶形貌。随着反应物溶液中[Sr2+]:[SO42-]摩尔比的增加,SrSO4粉体形貌由针棒状转变为六方形薄片状。这是由于溶液中存在的过量Sr2+离子在SrSO4晶体(020)晶面和(210)晶面上的沉积速度要明显高于(002)晶面,使得不同晶面生长速度存在差异所造成的。以Sr-EDTA配合物为反应物,采用化学沉淀法和酸沉积法分别制备出具有复杂晶体学形态的SrSO4粉体。花生形SrSO4粉体是由许多椭球形的纳米颗粒团聚构成,且具有较大的比表面积和介孔结构,形成机理可以分为形核、生长和团聚三个过程。通过酸沉积法获得的哑铃形SrSO4粉体主要是通过针状纳米SrSO4晶体的定向附着而形成的。采用热压和放电等离子烧结法分别制备出TZ3Y20A和Al2O3陶瓷以及TZ3Y20A-SrSO4、TZ3Y20A-BaxSr1-xSO4、Al2O3-SrSO4等复合材料。随复合材料中SrSO4含量的增加,复合材料的致密度和力学性能随之升高。Ag润滑剂的加入能够显著提高放电等离子烧结TZ3Y20A-SrSO4和Al2O3-SrSO4复合材料的致密度和维氏硬度。放电等离子烧结TZ3Y20A陶瓷的摩擦系数和磨损率随测试温度的升高而增加。Al2O3陶瓷经高温磨损后表面存在由细小磨屑颗粒组成的表面膜,能够降低其高温摩擦系数。TZ3Y20A和Al2O3陶瓷的高温磨损机制为脆性断裂和剥离磨损。SrSO4润滑相的加入能够显著改善陶瓷材料的高温摩擦学性能。在600℃时,放电等离子烧结TZ3Y20A-SrSO4和Al2O3-SrSO4复合材料的平均摩擦系数分别为0.28和0.22,磨损率在10-6至10-5mm3/Nm数量级。加入Ag润滑剂后,Ag与SrSO4的协同润滑作用能够进一步降低复合材料在宽温域下的摩擦系数和磨损率。放电等离子烧结Al2O3-SrSO4-Ag复合材料在室温和760℃时的平均摩擦系数均小于0.2,磨损率在所采用表面轮廓仪的测量精度范围内无法测量到。放电等离子烧结TZ3Y20A-BaxSr1-xSO4 (x=0.25, 0.5, 0.75)复合材料在宽温域下具有良好的摩擦学性能。从室温至760℃范围内不同TZ3Y20A-BaxSr1-xSO4复合材料的平均摩擦系数在0.1~0.3之间,磨损率在10-6至10-5mm3/Nm数量级。BaxSr1-xSO4 (0<x<1)固溶体是一种具有良好性能和应用前景的高温固体润滑剂。放电等离子烧结TZ3Y20A-SrSO4和TZ3Y20A-BaxSr1-xSO4 (x=0.25, 0.5, 0.75)复合材料具有良好的高温循环滑动摩擦学性能。在高温时硫酸盐和Ag润滑剂通过塑性变形和熔融的方式在摩擦表面形成具有低剪切强度的润滑膜,起到降低复合材料摩擦系数和磨损率的作用,使得复合材料在宽温域下内具有良好的自润滑性能。更多还原

【Abstract】 Nanoscale SrSO4 and BaxSr1-xSO4 (0<x<1) solid solution powders were prepared using the chemical precipitation method. TZ3Y20A-SrSO4, TZ3Y20A-BaxSr1-xSO4 and Al2O3-SrSO4 composites were then fabricated by hot-pressing and spark plasma sintering methods, respectively. The structure, morphologies, thermal stabilities and formation mechanisms of alkali-earth metallic sulfate powders and the effects of sulfate and Ag solid lubricants on microstructure, mechanical properties and high temperature tribological properties were investigated by XRD, SEM, TEM, BET, TG-DSC, Raman, universal testing machine and high temperature friction and wear tester. The self-lubricating mechanisms of different ceramic matrix composites over a broad temperature range were studied.The chemical precipitation method was employed to prepare nanoscale tablet-like SrSO4 and ellipsoidal-shaped BaxSr1-xSO4 (0<x<1) solid solution powders. Both nanoscale SrSO4 and BaxSr1-xSO4 (0<x<1) solid solution powders exhibit good thermal stability from ambient temperature to 1300℃. The crystal morphology of nanoscale SrSO4 powders could be controlled by the molar ratio (R) of [Sr2+]:[SO42-] in solution. With increasing R, the morphology of SrSO4 powders varies from a needle-like to a plate-like feature, because excessive Sr2+ cations in solution are more preferentially absorbed on (020) and (210) planes than on (002) plane, which lead to the difference in growth rates of crystal planes.The peanut-type and dumbbell-like SrSO4 particles with complex crystal morphologies were synthesized by precipitation reaction of Sr-EDTA chelating precursors. The peanut-type SrSO4 particles are composed of a large amount of nano-size ellipsoidal subcrystals. The peanut-type SrSO4 particles have a relatively large Brunauer–Emmett–Teller (BET) surface area and contain a large number of mesopores. A three-stage formation mechanism, including nucleation, growth and aggregation, is proposed to account for the formation process of peanut-type SrSO4 particles. The dumbbell-like SrSO4 particles are formed by oriented attachment of nanoscale needle-like SrSO4 subcrystals.TZ3Y20A and Al2O3 ceramics, TZ3Y20A-SrSO4, TZ3Y20A-BaxSr1-xSO4, Al2O3-SrSO4 composites were fabricated by hot-pressing and spark plasma sintering methods, respectively. Relative density and mechanical properties of the composites increase with increasing SrSO4 content. The addition of Ag lubricant improves significantly relative density and Vicker’s hardness of spark-plasma-sintered composites.The friction coefficient and wear rate of TZ3Y20A ceramic increase with increasing testing temperature. At high temperature, a film with very fine grains is formed on worn surfaces of Al2O3 ceramic, which could reduce the friction coefficient of Al2O3 ceramic. Delamination wear and brittle fracture are found to be the dominating wear mechanisms of TZ3Y20A and Al2O3 ceramics at high temperature.The tribological properties of oxide ceramics could be improved with the incorporation of SrSO4 solid lubricant. TZ3Y20A-SrSO4 and Al2O3–SrSO4 composites exhibit low and stable friction coefficients of 0.28 and 0.22 and wear rates in the order of magnitude of 10-6 to 10-5 mm3/Nm at 600℃. With the addition of Ag into both TZ3Y20A-SrSO4 and Al2O3–SrSO4 composites, friction coefficients and wear rates of composites are effectively reduced by the synergistic effects of Ag and SrSO4 solid lubricants over a broad temperature range. At room temperature and 760℃, friction coefficients of Al2O3-SrSO4-Ag composites are less than 0.2 and the wear rates are not measured in the precision range of currently used surface profiler.TZ3Y20A-BaxSr1-xSO4 (x=0.25, 0.5, 0.75) composites have an excellent tribological properties over a broad temperature range, which have friction coefficients of 0.1~0.3 and wear rates in the order of magnitude of 10-6 to 10-5 mm3/Nm. The BaxSr1-xSO4 (0<x<1) solid solutions are novel solid lubricants for sliding wear applications at extreme environments. TZ3Y20A-SrSO4 and TZ3Y20A-BaxSr1-xSO4 (x=0.25, 0.5, 0.75) composites exhibit excellent high temperature cyclic sliding wear properties over a temperature range of room temperature to 700℃.At elevated temperatures, plastic deformation of alkali-earth metallic sulfate and melting of Ag during sliding plays an important role in formation of lubricating films on worn surfaces to reduce friction and wear of the composites.更多还原