Study on fine microstructure regulation and properties of laser cladding high strength and toughness iron based coatings

Laser cladding, as a surface strengthening technology with high precision forming and low damage control, can endow parts with higher surface properties. As a low-cost coating system, iron-based coating has been widely used in the field of surface strengthening of various mechanical parts. With the pursuit of high performance and long life of parts, higher requirements are put forward for the design and performance of laser cladding coating materials.

In the article "Study on Fine Structure Regulation and Properties of Laser Cladding High-strength and tough Iron-based Coatings" published in Acta Metallica, the authors' team designed and prepared nano-bainite iron-based coatings, ultra-fine eutectic reinforced iron-based coatings, particle-reinforced martensitic coatings and high-hardness amorphous iron-based coatings in recent years. The research results are introduced in detail from the aspects of design idea, microstructure and mechanical properties of the coating, and the future development direction is prospected.

Cross section topography of cladding layer at different cladding rates

outlook

Laser cladding of iron-based alloy coating has broad application prospects in engineering field because of its advantages of high strength, high hardness, easy metallurgical bonding with steel matrix and low cost. In recent decades, scholars and engineers have also carried out extensive research in the field of laser cladding of iron-based alloys, and achieved certain results.

However, the problems of crack and embrittlement of iron-based laser cladding layer have been the main problems in the popularization and application of laser cladding technology of high strength iron-based alloys. At present, our team is focusing on reducing crack sensitivity of iron-based laser cladding layer, inhibiting intergranular crack initiation and expansion, and improving toughness, from the aspects of cladding alloy system design and fine structure regulation mechanism. The design and development of coating systems with high strength and toughness, such as nano-bainite coating, ultra-fine eutectic reinforced iron base coating, particle reinforced martensitic coating and high hardness amorphous iron base coating are carried out.

According to the results of this study, it can be seen that the idea of multi-type precipitation strengthening and the introduction of plastic/ductile phase on the ferrite/martensitic matrix to prevent crack propagation will help to further improve the strength and toughness limit of laser cladding coating, and obtain a better match between ultra-high strength and excellent toughness and plasticity.

Therefore, the future development of laser cladding iron base coating needs to be combined with high-throughput material calculation and experiments, and continue to carry out research on ultra-high strength and toughness iron base laser cladding alloy from the following aspects: (1) to develop special materials for high strength and toughness cladding based on fine microstructure regulation. The phase structure of the cladding matrix is nano-sized and submicron-sized by adjusting the composition and microstructure, and the order structure of the superfine strengthened phase and toughened phase is obtained.

(2) Carry out theoretical research based on dislocation strengthening and second phase precipitation strengthening. The matrix phase of ductile iron was enhanced by in-situ formation or addition of nano-particle phase, and the laser cladding structure of ductile matrix phase and high-density dislocation entanglement/nano-precipitated phase was uniformly strengthened.

(3) To carry out the research and development of a new type of iron-based laser cladding multi-component alloy. The multi-component amorphous Fe-base alloy can obtain the ultra-high strength Fe-base amorphous and the crystal phase complex structure with certain strength and toughness, which can improve the strength and toughness of the Fe-base alloy coating at the same time, and has certain corrosion resistance. It is necessary to study the coupling strengthening mechanism of different types of precipitated phases and the strengthening and toughening mechanism of the composite structure composed of martensitic/ferrite matrix and plastic phase, accumulate relevant data and experience, and through material calculation and experimental research, it is expected to eventually develop ultra-strong and tough laser cladding iron base alloy system that can meet various service conditions.

Citation information:

Feng Kai, GUO Yan-Bing, FENG Yu-Lei, YAO Cheng-Wu, ZHU Yan-Yan, ZHANG Qun-Li, LI Zhu-Guo. Study on fine microstructure and properties of High strength and toughness iron based coatings by laser cladding [J]. Acta Metalica Sinica, 2022, 58(4): 513-528.

Kai FENG, Yanbing GUO, Yulei FENG, Chengwu YAO, Yanyan ZHU, Qunli ZHANG, Zhuguo LI. Microstructure Controlling and Properties of Laser Cladded High Strength and High Toughness Fe-Based Coatings[J]. Acta Metall Sin, 2022, 58(4): 513-528.

DOI: 10.11900/0412.1961.2021.00549

This article is from the metal circle, the author of Acta Metallica