采用等离子喷涂和激光重熔复合工艺在TiAl合金表面制备了纳米Al_2O_3-13wt%TiO_2复合陶瓷涂层.为了使重熔后的陶瓷涂层保留一定的纳米结构组织,采用相对较低的激光功率和能量密度进行重熔.用扫描电镜(SEM)和X射线衍射仪(XRD)分析了涂层形貌、微观结构和相组成.结果表明,等离子喷涂纳米陶瓷涂层由纳米颗粒完全熔化区和部分熔化区两部分组成,具有等离子喷涂态的典型层状结构;由于受到激光功率、能量密度、陶瓷材料热物性参数和涂层厚度等因素的综合影响,重熔后陶瓷涂层出现了明显的分层结构特征;依据组织形态的不同,可将其大致分为:重熔区、烧结区和残余等离子喷涂区.重熔区由致密细小的等轴晶组成,并且保留了部分来源于原等离子喷涂部分熔化区的残留纳米粒子.由于等离子喷涂过程中涂层沉积时的快速凝固作用,涂层以亚稳相γ-Al_2O_3为主,经过激光重熔处理后,γ-Al_2O_3又重新转变为稳定相α-Al_2O_3.
Nanostructured Al_2O_3-13wt% TiO_2 composite ceramic coatings were prepared by plasma spraying and laser remelting on TiAl alloy surface. To retain nanopartilces in the plasma-sprayed nanostructured ceramic coating after laser remelting,a lower laser power and energy density were used. The morphology,microstructure and phases of the coating were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the plasma-sprayed nanostructured ceramic coating with a lamellar-like structure as conventional coating consists of fully melted region and partially melted region. The laser remelted coating exhibits obvious layer-like characteristics due to influence of laser power,energy density,thermophysical parameters of ceramics and coating thickness. According to the microstruetural morphology,the remelted ceramic coating can be divided into the remelted zone (with fine equiaxed grains),the sintered zone and remained plasma-sprayed zone. Due to the rapid heating and cooling for laser remelting,some remained nanoparticles are observed in the remelted zone. θ-Al_2O_3 phase and partially α-Al_2O_3 phase are transformed into metastable phase of γ-Al_2O_3 after plasma spraying. While the metastable γ-Al_2O_3 phase in the remelted zone is re-transformed into stable phase of α-Al_2O_3 again after laser remelting.
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