Elucidation of Elemental Steps of Thermal Spraying Accompanied by In-Process Reaction and Structure Control in Composite Coatings

阐明复合涂层中伴随过程反应和结构控制的热喷涂基本步骤

• 批准号: 12450306
• 负责人: TSUNEKAWA Yoshiki
• 金额: $ 9.54万
• 依托单位: Toyota Technological Institute
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450306/
• 关键词: In-process reaction; HVOF spraying; Plasma spraying; Exothermic reaction; Wettability; In-situ composite; Molten droplet temperature; Flight velocity; 生成複合皮膜; 基材予熱

It is known that thermodynamically unstable hard particles such as WC in composite spray materials are ready to decompose to W_2C and tungsten during the thermal spray process. Reactive thermal spraying based on in-process reactions has been recently focused on the fabrication of composite coatings containing nitrides or carbides as a reinforcement. The present study is classified into two main categories:(1) Fundamental aspects of a plasma sprayed cast iron coating on an aluminum alloy substrate, including (i) the effects of preheat substrate temperature on the splat morphology, (ii) the formation of a reaction layer and pores and (iii) the splat microstructure, were investigated in low pressure plasma spraying. With an increasing substrate temperature, the splat morphology changes from a splash-type to a disk and star-shape. Deformed substrate ridges, mainly due to the slight surface melting, are recognized adjacent to the splat periphery at high substrate temperatures. The flattenin … More g ratio of disk splats decreases with substrate temperature because the ridges act as an obstacle for splat expansion. A reaction layer composed of iron, aluminum and oxygen is ready to form at high substrate temperatures, which, along with the deformed ridges, improves the adhesive strength of splats. However, the pores appear at the splat interface at low substrate temperatures, which hinder the formation of a reaction layer. The amount of graphitized carbon increases in cast iron splats with an increase in substrate temperature.(2) reactive HVOF spraying characterized by high flame velocity and low flame temperature was applied to the formation of in situ composite coatings. Granulated particles of SiO_2/Al-Mg were sprayed onto an aluminum substrate to fabricate the composite coatings. Through the reduction of SiO_2 accompanied by an exothermic reaction, the composite coatings are expected to consist of MgAl_2O_4 and Al-Si alloy matrix. However, the sprayed coatings actually consist of MgAl_2O_4, Al-Si and additional Mg_2Si. This is because the formation rate of Mg_2Si is much faster compared with that of MgAl_2O_4, although MgAl_2O_4 is more thermodynamically stable than Mg_2Si. The amount of formed MgAl_2O_4 decreases with an increase in the spraying distance, although it gives a longer in-flight period of droplets. Hence, the in-process reaction such as MgAl_2O_4 formation mainly occurs on a substrate. Less

在热喷涂过程中，复合喷涂材料中的WC等不稳定硬质颗粒容易分解为W_2C和钨。基于过程反应的反应热喷涂技术是近年来研究的热点之一，它主要用于制备以氮化物或碳化物为增强相的复合涂层。本研究分为两大类：（1）在低压等离子喷涂条件下，研究了铝合金基体上等离子喷涂铸铁涂层的基本特征，包括（i）基体预热温度对溅射形貌的影响，（ii）反应层和气孔的形成，以及（iii）溅射组织。随着衬底温度的升高，溅射形貌由溅射型向盘状和星形转变。变形的衬底脊，主要是由于轻微的表面熔化，被认为是在高衬底温度下的飞溅周边附近。The Bouncing ...更多信息 盘飞溅的g比随着衬底温度而降低，因为脊部充当飞溅膨胀的障碍。由铁、铝和氧组成的反应层易于在高衬底温度下形成，其沿着变形的脊提高了溅射物的粘合强度。然而，在低衬底温度下，孔出现在溅射界面处，这阻碍了反应层的形成。随着基体温度的升高，铸铁飞溅物中石墨化碳的量增加。(2)采用具有高火焰速度和低火焰温度特点的反应超音速火焰喷涂技术制备原位复合涂层。将SiO_2/Al-Mg颗粒喷涂到铝基体上制备复合涂层。通过SiO_2的还原和放热反应，复合涂层由MgAl_2O_4和Al-Si合金基体组成。而喷涂层实际上是由MgAl_2O_4、Al-Si和附加的Mg_2Si组成。这是因为Mg_2Si的形成速率比MgAl_2O_4快得多，而MgAl_2O_4的结晶稳定性比Mg_2Si好。随着喷涂距离的增加，MgAl_2O_4的生成量减少，但飞行时间延长。因此，诸如MgAl_2O_4形成的过程中反应主要发生在衬底上。少