氧碳比对MPCVD法同质外延单晶金刚石的影响

以Ib型(100)取向高温高压(HPHT)单晶金刚石为基底、H2-CH4-CO2混合气为反应气源,利用10kW、2.45GHz不锈钢谐振腔式微波等离子体化学气相沉积(MPCVD)装置进行金刚石同质外延生长。通过光学显微镜表征外延生长金刚石的表面形貌;Raman光谱表征金刚石的结晶质量;螺旋测微仪测厚再计算生长速率,着重探讨工艺因素中氧碳比对同质外延金刚石生长速率、表面形貌、金刚石结晶质量的影响。结果表明随着氧碳比的增加,金刚石生长模式由二维形核模式转变为台阶流模式,结晶质量提高,生长速率变慢;在微波功率7.8kW、CH4浓度(与H2的比例)8%、气压18kPa、基底温度1080℃条件下,氧碳比为0.8时,金刚石结晶质量好且生长速率高(达16μm/h)。反应气源中引入合适比例的CO2是获得高的生长速率同时有效改善同质外延单晶金刚石结晶质量的有效方法。     

Effect of rare earth Pr on microstructure and mechanical properties of Al2O3-SiO2（sf）/Al-Si composites

The Al₂O₃-SiO₂(sf) (volume fraction, 20%)/Al-12.6Si metal matrix composites(MMCs) with or without rare earth Pr addition were fabricated by infiltration squeeze method. Effect of Pr addition on microstructures and fractographs of Al-Si MMCs was investigated by SEM and TEM. Tensile properties at room temperature and 200 °C were tested. It is shown that the addition of Pr is favorable to produce uniform microstructures and modify the eutectic Si crystal effectively. Compounds/intermetallics with high content of Pr are formed at the interface between short fiber and matrix. Yield strength(σ_0.2), ultimate tensile strength(σ_b) and fracture elongation of Al-Si MMCs are improved by adding suitable amount of Pr. Compared with those values of Al-Si based MMC at 200 °C, σ_0.2 and σ_b of MMC with 0.29% Pr are increased by 33% and 55%, respectively. The tensile fracture surface of Al-Si MMCs with Pr addition presents ductile fracture features.     

Sr、RE对A356合金组织结构和力学性能的影响

A356合金重熔过程中通过混合添加适量Sr、RE来改善合金的微观组织结构。采用金相分析、X射线衍射分析(XRD)及力学性能测试等试验方法,分析了Sr、RE混合添加对合金的初晶晶胞特征参数、共晶Si相形貌和力学性能的影响。研究发现,A356合金重熔过程中,Sr、RE混合添加能够强化合金的细化效果及共晶Si相的变质效果。Sr、RE的添加,能够大幅度提高合金的综合力学性能,合金抗拉强度由变质前的153MPa提高到变质后的252MPa,伸长率由不足5%提高到超过13%。     

微波等离子体炬法合成金刚石薄膜的研究

现采用微波等离子体炬法合成了金刚石薄膜,并探讨了微波功率变化对对金刚石膜质量的影响。结果表明:随着微波功率的增加,制备的金刚石薄膜结晶性越来越好;通过拉曼分析在微波功率800W,发现在1332cm-1处金刚石峰的相对强度最高,金刚石相纯度最高。     

Synthesis of tetragonal BaTiO3 film on Ti substrate by micro-arc oxidation

BaTiO3 films on Ti substrate were fabricated by alternative current（AC） and direct current（DC） micro arc oxidation （MAO）. Microstructures of films were investigated by means of SEM, XRD and TEM. The results show that the amorphous phase and primitive cubic phase are the main phases in the films prepared by AC MAO. Even after being annealed at 1 200 ℃ for 8 h, only a few tetragonal phases can be observed in films prepared by AC MAO. However, tetragonal BaTiO3 phase can be produced by DC MAO directly. In the films prepared by DC MAO, a mixture of cubic phase and tetragonal phase is formed. After sparking spacious distribution, sparking duration and temperature gradient near sparking sites were taken into account, and a mechanism of synthesis of tetragonal BaTiO3 phase by DC MAO was proposed.     

AZ91D镁合金微弧氧化涂层的干摩擦磨损行为

在硅酸钠电解质体系中,采用电流密度100 A/m2的非对称交流脉冲电源模式处理AZ91镁合金,在其表面获得均匀的陶瓷涂层.采用M2000磨损试验机研究了该涂层合金的干式滑动摩擦磨损行为.采用X射线衍射仪和扫描电镜对陶瓷涂层结构和磨损表面进行观察分析.结果表明:根据载荷大小,涂层处理后AZ91D镁合金的磨损行为明显分为3个阶段,这些阶段同陶瓷层是否磨穿密切相关;微弧氧化涂层AZ91D镁合金的磨损机理主要是磨粒磨损;受表面状况的影响,陶瓷涂层的摩擦因数在 0.20～0.45 间波动;在较高载荷下,涂层被磨穿后,涂层的摩擦因数趋于基体合金的摩擦因数,涂层合金的表面变形能力提高,该阶段质量磨损速率随载荷增加,趋势变得缓慢.     

混合稀土含量对A356铝合金组织结构的影响

采用金相显微镜、SEM、EDS和差示扫描量热法(DSC)等手段研究混合稀土(RE)合金添加量对Ti-B-Sr联合细化变质的A356铝合金显微组织结构的影响。结果表明:当稀土添加量为0.1%～0.3%(质量分数)时,随着稀土含量的增加,初晶晶胞尺寸、硅相尺寸、二次枝晶臂间距减小,硅相圆整度提高(长径比降低);当稀土添加量为0.3%时,初始α(Al)相的平均枝晶胞尺寸为76μm,二次枝晶间距为11.3μm,Si相长径比为2.13;加入0.1%～0.3%的稀土降低了合金的共晶点温度和初晶α(Al)的形核温度,并减小组织熔化过程中共晶反应的放热量。