陶瓷型芯型壳激光增材制造研究进展

Research Progress of Ceramic Cores and Shells Prepared by Laser Additive Manufacturing

空心涡轮叶片是燃气轮机热端的关键零部件,其结构十分复杂,制造难度极大。陶瓷型芯型壳是用于涡轮叶片铸造的重要部件,随着燃气轮机的热端工作温度逐渐升高,所需要的叶片结构也更加精细,传统的精密铸造工艺已经无法满足叶片快速升级换代的需求。激光增材制造技术无需模具,可以加速新产品的研发,缩短制造周期,满足个性化需求。目前可用于型芯型壳制造的激光增材制造技术主要有激光选区烧结和立体光刻两大类。主要介绍了这两大类激光增材制造技术在陶瓷型芯型壳制备方面的应用,从材料配方、素坯成形、后处理烧结等多个方面综述了当前国内外的最新研究进展,探讨了两类技术各自的优势、目前存在的问题以及未来发展的趋势。

Significance Gas turbine is the most promising device for power generation and ship power in this century due to its high efficiency and low emission.The hollow turbine blade with a complex structure is the key part of a gas turbine.The working temperature of the turbine blade is very high,which requires high metal quality and elaborate structures of turbine blades.High gas temperature means high working efficiency.With the further increase of industrial demand,the gas temperature of a turbine reaches more than 1700℃.Therefore,the turbine blades with more delicate and complex hollow structures should be fabricated to improve the cooling efficiency.The ceramic cores and shells are important components for casting of superalloy turbine blades due to their high temperature capabilities and chemical inertness.The traditional methods to fabricate ceramic shells and cores are the investment casting method which is time-consuming,high cost,low yield,and not sufficient for the update-requirement of turbine blades.In order to overcome these problems,additive manufacturing(AM)has been gradually developed.The AM technology has been widely used in different fields such as medicine,engineering,and aerospace to fabricate delicate parts without any molds.It can save materials,accelerate the research of new products,and meet customized needs,thus greatly reducing fabrication costs.In the past few decades,dozens of AM technologies have been developed and each of them has its unique application fields.As for the fabrication of ceramic cores and shells,the most suitable laser-based AM technologies are selective laser sintering(SLS)and stereolithography apparatus(SLA).Progress Different from other AM technologies,the most significant advantage of SLS is that it doesn’t need any support during the fabrication process.Large-scale ceramic parts with precise structures can be fabricated by SLS.The preparation of ceramic cores and shells by the SLS process is shown in Fig.3.First,the green bodies of ceramics are first built by the SLS equipment,and then the green bodies are infiltrated with silica sol or other materials which could fill the pores of ceramics to improve the density of green bodies.The organic binder in the green bodies can be removed through thermal decomposition at 600℃and the green bodies are sintered at 1200--1600℃to obtain the densified ceramic cores and shells.SLA has been known for several years as an AM technology to fabricate the polymer-based parts.This technology utilizes liquid photo-curable resin which can be cured under ultraviolet light or laser irradiation.At present,there are two main processes for preparing ceramic cores and shells by the SLA technology(Fig.6).The first process combines SLA and gel-casting.A resin mold is first made by SLA and then the ceramic slurry is injected into the mold cavity to get the green body of ceramic core and shell.In the other process,the ceramic slurry and photo-curable resin are mixed and the ceramic green bodies are directly formed by SLA.Both of ceramic green bodies made by these two technologies have enough density so that the infiltration process is no longer required and the rest of the post-processing process including debinding and sintering are the same as that of SLS.Characteristics of different laser-based AM processes used for ceramic core and shell manufacturing are shown in Table 2.It can be concluded that both of two AM technologies have their own strengths and weaknesses.SLS has an advantage in manufacturing large size ceramic cores and shells,while the parts made by SLA have higher resolution.Conclusions and Prospects In this review,the development of these two AM processes in the fabrication of ceramic cores and shells are introduced in terms of material preparation,green body fabrication,and post-processing.The advantages,weaknesses and future development of both two methods have been discussed.