工艺参数对304不锈钢表面激光熔覆Ni基合金涂层的组织、耐磨性及耐腐蚀性的影响

研究了不同工艺参数对304不锈钢表面激光熔覆Ni基合金后熔覆层微观组织及硬度、耐磨、耐蚀性能的影响,并寻求最佳激光工艺参数,以期获得冶金结合较好,耐磨、耐蚀性能良好的熔覆层。根据组织与性能的综合分析可知,最优激光工艺参数为激光功率2.5kW、扫描速度4mm/s、送粉速率300mg/s。利用优化工艺参数熔覆后的熔覆层宏观形貌平整、光滑,熔覆层宽度为14.36mm,高度为1.612mm,熔池深度为0.248mm,稀释率为13.33,硬度较高,平均显微硬度为646.4HV,并且耐磨损性能较好,磨损量较低。此外,熔覆层的耐腐蚀性能也较好,自腐蚀电位为-286.77mV。在一定的激光工艺参数下,组织从结合区至熔覆层表层依次为平面晶、胞状晶、柱状晶、树枝晶、等轴晶。激光功率、扫描速度、送粉速率不同,熔覆层中组织粗细变化呈现一定的规律性:随着激光功率的增大,组织由细小逐渐变的粗大;随着扫描速度的增大,组织先变细小,然后变粗大;随着送粉速率的增大,组织逐渐变细小。合金的耐磨性与耐蚀性不仅与组织大小有关,而且与组织物相组成密切相关。

屏式过热器异种钢焊接接头失效分析

某电厂前屏过热器管与限位块的异种钢焊接接头在运行期间发生泄露失效,利用电子探针、光学显微镜、显微硬度计及扫描电镜等手段对过热器管、限位块以及接头熔合区进行化学成分、显微组织、显微硬度、断口形貌分析。结果表明：过热器管侧熔合区出现增碳层,熔合区组织为类马氏体,且出现σ相脆化,导致熔合区显微硬度高,脆性大,且熔合区为结构上的应力集中点,在热应力长期作用下导致熔合区起裂;随着锅炉的起停以及管内介质温度、压力的变化使得裂纹进一步向管内扩展,其断口特征呈现似河滩条带;当管道承载能力低于管内介质压强时管道则泄漏失效。

Effect of Extrusion Ratio on the Microstructure and Mechanical Properties in an Al-Cu-Mg-Ag Alloy

In order to examine the effect of extrusion ratio on the microstructure and mechanical behavior in Al-Cu-Mg-Ag alloy, the Al-6.3 Cu-0.48 Mg-0.4 Ag alloy was subjected to extruding with different extrusion ratios of 17, 30 and 67. The results indicate that the grains are refined and the strength is improved effectively with increasing extrusion ratio. However, further investigation shows that the extrusion ratio of 30 is more effective than the lower extrusion ratio（17） and the higher extrusion ratio（67） to refine the grains in the T6-temper alloy. Moreover, the sample with an extrusion ratio of 30 obtains more precipitates and superior mechanical properties after T6 treatment. This study supports the idea that there exists a critical extrusion ratio for grain refinement and improvement of mechanical properties for the T6-temper alloy. Recrystallization and precipitation during T6 treatment were introduced to explain the effects of extrusion ratio on the microstructure and mechanical properties of the Al-Cu-Mg-Ag alloys.

水冷壁管镍基涂层的制备及其特性研究

水冷壁管工作在高温、高压、烟气腐蚀与冲蚀的恶劣环境之中,极易受到严重的高温腐蚀和飞灰的磨损,使管壁减薄甚至导致爆管事故的发生。本文采用激光熔覆的方法制备了Ni60涂层,分析了涂层的显微组织结构,对比测试了涂层和基体的显微硬度、耐磨及耐蚀性能。实验结果表明,激光熔覆涂层的组织均匀,显微结构主要以树枝晶及枝晶间的共晶组织为主。涂层的硬度达到基体的2.5倍;高温下基体的磨损量是涂层的2倍,与此同时Ni基涂层有效的提升了基体的耐蚀性能。