激光功率对锆合金激光熔覆复合涂层成形及微观组织的影响

    Effect of Laser Power on Formation and Microstructure of Composite Coatings on Zirconium Alloy by Laser Cladding

    • 摘要: 以Ni60A+WC粉末为熔覆材料,采用激光熔覆技术在锆合金表面制备了ZrB2+ZrC原位增强复合涂层。研究了激光功率对熔覆层成形、微观组织、增强相及显微硬度的影响规律。结果表明:熔覆层外观成形较好,未发现气孔和裂纹等缺陷,随着激光功率的增大,熔覆层宽度和高度都显著增加。熔覆层增强相主要为细小的α-Zr枝晶、颗粒状及块状的ZrC以及Zr(B,C)2。在未熔的WC颗粒内部生成了ZrB2+ZrC的层状共晶组织,在高温下ZrB2和ZrC两者的生成吉布斯自由能接近,易形成两者的层状共晶组织。随激光功率增大,熔覆层中二次枝晶的生长受到抑制,颗粒状增强相逐渐向块状增强相转变。熔覆层显微硬度随着激光功率的增大而显著升高,激光功率为2.8 kW时,熔覆层的显微硬度值最高(约720 HV0.5)。

       

      Abstract: ZrB2+ZrC in-situ reinforced coating was fabricated by laser cladding Ni60A+WC powder on zirconium alloy.The effect of laser power on the formation, microstructure, reinforcements and microhardness of coating was investigated.The results indicate that good appearance of the coating is obtained and no defects such as pores and cracks are found.As the laser power increases, the width and height of the coating increase significantly. Reinforcements in the coating are mainly composed of fine α-Zr dendrites, granular and block ZrC and Zr (B, C)2. ZrB2+ZrC lamellar eutectic is formed inside the unmolten WC.The similar values of Gibbs free energy for forming both ZrB2 and ZrC at elevated temperature make it easy to form lamellar eutectic. With laser power increasing, the growth of the secondary arm of dendrites is suppressed and the granular reinforcements gradually transforme to block reinforcements.The microhardness of the coating increases significantly as laser power increasing.The highest value of microhardness(about 720 HV0.5)is obtained when the laser power is 2.8 kW.

       

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