论文部分内容阅读
为研究激光熔覆过程中原位自生TiC的生长机制,使用扫描电子显微镜对TC4+10%Cr3C2混合粉末CO2激光熔覆涂层中原位自生TiC的分布与形态特征进行了观察。结果表明,涂层中TiC主要以枝晶、颗粒丛和平均尺寸在0.5μm左右的密集小颗粒3种形态出现,并表现出了“枝晶(表面附近)→颗粒丛(涂层中部)→密集小颗粒(结合界面附近)”的分布特点。涂层中的枝晶具有块状颗粒线性排列的特征,多呈十字状,二次晶臂间表现出较一致的取向;颗粒丛形貌中不同TiC颗粒间取向杂乱,表现为随机粘结,无明显取向;结合界面附近的密集TiC小颗粒多呈随机分布,表面光滑近球状,无明显的棱角。分析表明,涂层中不同形态的TiC分布主要取决于对应位置的过冷度和冷却速度。大的过冷度能够显著增加形核密度,而过高的冷却速度将导致TiC晶体长大不充分。涂层中原位自生TiC所表现出的上述分布与形态特征为TiC晶体自身的晶体学特点和液固前沿的温度、浓度梯度等因素共同作用的结果。
In order to study the growth mechanism of in-situ TiC during laser cladding, the distribution and morphology of in-situ TiC in TC4 + 10% Cr3C2 mixed powder CO2 laser cladding coating were observed by scanning electron microscopy. The results show that TiC in the coating mainly appears in the form of dendrites, clusters and dense small particles with an average size of about 0.5μm, and exhibits “dendrites (near the surface) → particle clusters (middle of the coating) → dense small particles (bonding interface near) ”distribution characteristics. The dendrite in the coating has the feature of linear arrangement of massive particles, mostly in the form of cross, with more uniform orientation between the secondary crystal arms. The disordered orientation of different TiC particles in the particle cluster morphology shows random bonding, There is no obvious orientation. The dense TiC small particles in the vicinity of the interface are mostly randomly distributed, the surface is smooth and nearly spherical with no obvious edges and corners. The analysis shows that the distribution of TiC in different coatings mainly depends on the degree of subcooling and the cooling rate in the corresponding locations. Large undercooling can significantly increase the nucleation density, while too high a cooling rate will lead to insufficient growth of TiC crystals. The above-mentioned distribution and morphological characteristics exhibited by the in-situ TiC coating are the result of the interaction between the crystallographic characteristics of the TiC crystal and the temperature and concentration gradient of the liquid-solid frontier.