7075铝合金表面HVOF喷涂WC-12Co颗粒的沉积行为

Deposition Behavior of HVOF Sprayed WC-12Co Particles on AA7075

摘要:

在抛光的7075铝基体上采用HVOF（超音速火焰喷涂）沉积了WC-12Co颗粒，用SEM、EDS和纳米压痕硬度仪对沉积物的显微组织、成分和硬度进行了分析。研究了未融颗粒、未完全熔融颗粒和熔融颗粒这3种不同熔融状态下6种颗粒的沉积行为，发现不同类型的颗粒均对基体有冲击，使其发生变形或有一定的撕裂。未熔融颗粒沉积时，高速冲击铝基体使其发生挤压变形，颗粒反弹后，基体遗留挤压坑。除了反弹的未熔融颗粒，未完全熔融颗粒和熔融颗粒的沉积物与原始粉末相比，沉积物的表面形貌和横截面形貌与原始粉末不同，沉积物表面有一定的熔化特征，这是颗粒在HVOF焰流中受热温度较高使其有一定的熔融；高温高速的颗粒冲撞基体后，沉积物横截面更为致密，它们与基体之间存在冶金结合，形成了一个互熔区，表明沉积物撞击基体时温度高于铝的熔点，将铝融化并挤压进颗粒中。颗粒沉积后，在基体表面上形成一层厚度约为5 μm的硬化层，该层的硬度呈梯度变化，近表面处硬度为3420 MPa，是基体（2200 MPa）硬度的1.56倍。硬度的增加源于两个因素：高温高速颗粒的喷丸作用，及颗粒挤压基体塑形变形的加工硬化。

Abstract:

WC-12Co particles were deposited on polished AA7075 (7075 aluminum alloy) substrate by HVOF (high velocity oxy-fuel) spraying. The microstructure, composition and hardness of the deposits were analyzed by SEM, EDS and nanoindentation hardness tester, respectively. The deposition behavior of six types of particles in three different molten states, including non-molten, semi-molten, and molten particles, was investigated. Results show that different types of particles have great impact on the substrate, which makes the AA7075 substrate deform or causes tears. The surface morphology and cross-sectional morphology of the deposits are different from those of the original powder. The surface of the deposits exhibits certain melting characteristics, and the cross-section is relatively dense. The semi-molten particles and molten particles generate some tearing to the substrate, and have a metallurgical bonding with the substrate to form a mutual meting zone. After the deposition of the particles, a hardened layer is formed on substrate surface with a thickness about 5 μm, and there is a certain gradient change in the hardness. The hardness near the surface is 3420 MPa, which is 1.56 times higher than that of the substrate (2200 MPa). The increase in hardness is originated from two factors: the peening effect of particles at high temperature and high speed, and the work hardening caused by particle extruding substrate.