TC4合金激光熔覆材料的研究现状

Research Status of TC4 Alloy Laser Cladding Materials

TC4合金属于(α+β)双相合金,具有密度小、比强度高、耐高温、耐腐蚀、无磁、相容性好等优点,被广泛应用于航空航天领域。但是TC4合金硬度低、耐磨性差的缺点在很大程度上限制了其应用与推广,因此对TC4合金进行表面改性具有重要意义。激光熔覆是新型的表面改性技术,由于其具有可加工材料广泛、效率高、熔覆层与基体相容性好、节省材料、环保、无污染等优点,在TC4合金表面改性领域获得了广泛的应用。利用激光熔覆技术对TC4合金进行表面改性始于20世纪80年代,经过近40年的探索,学者们发现影响熔覆层质量与性能的因素有激光熔覆材料、激光工艺参数以及工艺处理条件等。在考察各种因素对熔覆层的影响后发现,激光熔覆材料对熔覆层的质量与性能起到决定性作用。根据材料成分构成可以将熔覆材料分为金属及金属合金粉末、陶瓷粉末、纳米陶瓷粉末、金属-陶瓷复合粉末及其他粉末。其中,金属及其合金具有极高的硬度,但是不耐高温,适合在400~900℃下使用。陶瓷材料具有高硬度、高熔点等特点,在激光熔覆过程中可以作为增强相使用,但是其韧性低,易产生裂纹,而纳米陶瓷材料可有效缓解界面应力集中,减少熔覆层中的裂纹、气孔等缺陷。金属-陶瓷复合材料可以借助激光熔覆技术将金属的强韧性和陶瓷材料的耐磨、耐高温性结合起来,是目前激光熔覆领域的研究热点。其他熔覆材料如稀土及其氧化物粉末、固体润滑剂粉末、包覆型粉末等具有特定的性能,在熔覆粉末中添加少量此类粉末可以显著改善其熔覆层性能。本文概述了近年来学者通过改变熔覆粉末成分来改善TC4合金表面性能的研究成果,对熔覆粉末进行了分类,介绍了各类粉末的优缺点和应用场合,指出了TC4合金表面改性存在的主要问题(开裂问题),分析了裂纹产生的原因并提出了相应的解决方案。

TC4 alloy belongs to(α+β)dual-phase alloy,it is widely used in the field of aerospace because of its advantages such as small density,high specific strength,high temperature resistance,corrosion resistance,non-magnetic and good compatibility.However,the low hardness and poor wear resistance of TC4 alloy limit its application and promotion to a large extent.So it is of great significance to modify the surface of TC4 alloy.Laser cladding technology is a new surface modification technology and it has been widely used in the field of surface modification of TC4 alloy due to its advantages in processable materials,high efficiency,good compatibility between cladding layer and substrate,material saving,environmental protection and pollution-free.Surface modification of TC4 titanium alloy by laser cladding technology began in 1980s.After nearly 40 years of research and exploration,researchers found that the factors affecting the quality and properties of the cladding layer were laser cladding materials,laser processing parameters and processing conditions.After considering the influence of various factors on the cladding layer,it is found that the laser cladding material plays a decisive role in the quality and performance of the cladding layer.According to the composition of materials,cladding materials can be classified into metal and metal alloy powder,ceramic powder,nano-ceramic powder,metal-ceramic composite powder and other powders.Among them,metals and their alloys have very high hardness,but they are not resistant to high temperature,so they are suitable for using at temperatures of 400—900℃.Ceramic materials have high hardness and high melting point.They can be used as reinforcing phase in laser cladding process,but their toughness is low and cracks are easy to occur.Nano-ceramic materials can effectively alleviate the stress concentration at the interface and reduce the cracks and pore defects in the cladding layer.Cermet composites can combine the strength and toughness of metals with the wear resistance and high temperature resistance of ceramics by laser cladding technology,which is a research hotspot in the field of laser cladding at present.Other cladding materials,such as rare earth and its oxide powder,solid lubricant powder and coated powder have specific properties,and the properties of cladding layer can be significantly improved by adding a small amount of such powder into the cladding powder.This paper summarizes the research results of improving the surface properties of TC4 alloy by changing the composition of cladding powder.The classification of cladding powders is introduced.The advantages,disadvantages and application occasions of various powders are introduced.It is pointed out that the main problem of surface modification of TC4 alloy is the cracking of cladding layer.The causes of cracking are analyzed and the corresponding solutions are put forward.