Liu Hongxi

CHARACTERISTIC BEHAVIORS OF PARTICLE PHASES IN NiCrBSi-TiC COMPOSITE COATING BY LASER CLADDING ASSISTED BY MECHANICAL VIBRATION

The good high temperature wear resistance and corrosion behavior of particle reinforced Ni-based alloy composite coating have attracted extensive attention in material science and engineering.It is necessary to analyze the morphologic characteristics and distribution of particles in composite coating.TiC particle reinforced NiCrBSi composite coating on medium carbon steel surface was fabricated by mechanical vibration assisted laser cladding technique.According to the distribution characteristics of hard phase particles in laser cladding molten pool,the growth morphology of TiC particle and endogenous M_(23)C_6 carbide,formation mechanism and its distribution characteristics inγ-Ni solid solution were analyzed by XRD,SEM and EDS.The results showed that most of TiC particles dissolved into the melted Ni-based alloy,but some supersaturated Ti and C atoms were precipitated in the form of TiC particles eutectic during cooling process.The TiC particles lateral growth with heterogeneous nucleation way depended on M_(23)C_6 type carbide substrate.At the same time,some composite carbide core-shell structure with(Ti,Cr,Ni,Fe,Si)C encapsulated TiC were generated in the coating.Under the effect of vibrant force,the bulky branch crystal eutectic structure disappeared in the bottom of laser cladding coating,the TiC particle floatation trend slowed down with the fluid stratosphere which caused by vibratory force and high-pressure gas,and some double and petal shape TiC particle clusters were also formed.The precipitated TiC particle increases with the Cr content in the inter-dendrite reticular(Fe,Ni) solid solution,and the average particle size was increased by more than 25%.The XRD results indicated that the diffraction peak intensity and lattice integrity of the main hard phases were enhanced,the half peak width was broadened and the crystalline grain size become smaller.The mechanical vibration promoted the dispersion of particles in the matrix dendrites and inter-dendrite.

激光铝热还原法制备Al 2 O 3 /Ti-Al基复合涂层

利用Al和TiO 2 之间的放热化学反应, 采用激光原位合成技术在TC4钛合金基体材料表面制备了Al 2 O 3 /Ti-Al金属间化合物基复合涂层。对比分析了激光功率、激光束扫描速度和光斑尺寸变化对激光能量密度变化量的影响程度, 借助X射线衍射仪(XRD)、光学显微镜(OM)、能谱仪(EDS)和显微硬度计分别考察了激光束扫描速度对复合涂层表面宏观形貌、截面显微组织结构和显微硬度的影响。结果显示, 扫描速度的变化对激光能量密度变化量的影响程度最大, 光斑尺寸次之, 激光功率的变化影响最弱。随着激光束扫描速度的增大, 复合涂层表面渐趋粗糙, “鱼鳞纹”状形貌特征趋于明显, 复合涂层与基材结合区厚度减小。激光原位复合涂层主要由k-Al 2 O 3 和α-Al 2 O 3 增强相与α-Ti和α 2 -Ti 3 Al基体相组成。随着激光束扫描速度增大, 复合涂层内k-Al 2 O 3 部分转变为α-Al 2 O 3 , Al 2 O 3 增强相有由枝晶状向纤维状转变的趋势; 复合涂层截面显微硬度自基体至涂层表面过度平缓, 且涂层区显微硬度分布均匀, 明显高于基材平均显微硬度。利用Al和TiO 2 之间的放热化学反应, 采用激光原位合成技术在TC4钛合金基体材料表面制备了Al 2 O 3 /Ti-Al金属间化合物基复合涂层。对比分析了激光功率、激光束扫描速度和光斑尺寸变化对激光能量密度变化量的影响程度, 借助X射线衍射仪(XRD)、光学显微镜(OM)、能谱仪(EDS)和显微硬度计分别考察了激光束扫描速度对复合涂层表面宏观形貌、截面显微组织结构和显微硬度的影响。结果显示, 扫描速度的变化对激光能量密度变化量的影响程度最大, 光斑尺寸次之, 激光功率的变化影响最弱。随着激光束扫描速度的增大, 复合涂层表面渐趋粗糙, “鱼鳞纹”状形貌特征趋于明显, 复合涂层与基材结合区厚度减小。激光原位复合涂层主要由k-Al 2 O 3 和α-Al 2 O 3 增强相与α-Ti和α 2 -Ti 3 Al基体相组成。随着激光束扫描速度增大, 复合涂层内k-Al 2 O 3 部分转变为α-Al 2 O 3 , Al 2 O 3 增强相有由枝晶状向纤维状转变的趋势; 复合涂层截面显微硬度自基体至涂层表面过度平缓, 且涂层区显微硬度分布均匀, 明显高于基材平均显微硬度。