CLADDING TECHNOLOGY SHANXI CO., LTDEffects of Additives on Microstructure and Performance of Centrifugal SHS Ceramic Composite Steel Pipe
Literature Overview
The research by Zhang Shuguang, Liang Yufeng, Zhang Baoping, Li Jun, Gao Qiufan, and Wang Kezhi, published in the Journal of Chinese Society for Rare Metals in 2002, represents a significant advancement in the understanding of process variables affecting the quality of SHS ceramic-lined steel pipes. This multi-institutional study, involving the Beijing General Research Institute for Nonferrous Metals, China Aluminum Corporation, Shanghai Baoshan Iron and Steel Company, the Fifth Second Research Institute of Ordnance Industry, and the University of Science and Technology Beijing, investigated the systematic effects of various additives on the microstructure, mechanical properties, and bonding characteristics of centrifugal SHS ceramic composite steel pipes. The centrifugal SHS variant introduces rotational motion during the synthesis process, utilizing centrifugal force to enhance powder compaction and promote densification of the ceramic layer.
Core Technical Findings
The authors examined several categories of additives including sintering aids, grain growth inhibitors, and phase modifiers. The centrifugal SHS process operates at rotational speeds typically between 1000 and 3000 revolutions per minute, generating centrifugal accelerations that range from 500 to 2000 g. This centrifugal field serves to compact the powder mixture radially outward against the steel substrate, promoting densification and reducing porosity in the resulting ceramic layer.
| Additive Type | Examples | Effect on Microstructure | Effect on Properties |
|---|---|---|---|
| Sintering aids | CaO, MgO, Na2O | Promote liquid phase formation at lower temperatures | Improved densification, reduced porosity |
| Grain growth inhibitors | ZrO2, TiO2 | Restrict grain coarsening during high-temperature reaction | Improved fracture toughness |
| Phase modifiers | SiO2, Fe2O3 | Alter ceramic phase composition | Modified thermal expansion, improved bonding |
| Combustion promoters | Fe, Mg, Ni | Accelerate combustion wave propagation | More complete reaction, reduced unreacted zones |
The study revealed that the addition of calcium oxide as a sintering aid significantly reduced the porosity of the ceramic layer from approximately 15 percent to less than 5 percent, while maintaining adequate reaction enthalpy. However, excessive amounts of sintering aids led to the formation of glassy phases that reduced the hardness and wear resistance of the ceramic layer. The optimal concentration was determined to be in the range of 3 to 5 weight percent.
Microstructural Characterization
The authors employed optical microscopy, scanning electron microscopy, X-ray diffraction, and Vickers hardness testing to characterize the ceramic layers produced with different additive formulations. The base ceramic without additives consisted primarily of alpha-alumina with a grain size distribution ranging from 10 to 50 micrometers, exhibiting significant porosity and occasional unreacted aluminum particles. The addition of zirconia as a grain growth inhibitor refined the grain structure to a more uniform 5 to 20 micrometer range, improving the Vickers hardness from approximately 1400 HV to 1600 HV.
The interfacial region between the ceramic layer and the steel substrate was found to be complex, consisting of a transition zone with mixed phases including iron aluminide (FeAl, Fe2Al5), iron oxide, and partially reacted ceramic. The thickness of this transition zone varied from 50 to 200 micrometers depending on the additive formulation. The presence of iron aluminide phases was identified as critical for achieving metallurgical bonding, as these phases provide a gradual transition in thermal expansion between the steel and the ceramic.
Performance Testing and Results
The mechanical and tribological performance of the ceramic-lined pipes was evaluated through bond strength testing, Vickers hardness profiling across the cross-section, and dry sliding wear tests against alumina and silicon carbide counterparts. The bond strength, measured by a push-out test method, ranged from 30 to 85 megapascals depending on the additive formulation. The highest bond strength of 85 megapascals was achieved with a formulation containing 3 percent calcium oxide and 2 percent zirconia, which provided an optimal balance between densification and grain refinement.
The wear resistance, expressed as specific wear rate in cubic millimeters per newton meter, improved by a factor of 5 to 8 compared to the bare steel substrate. The wear mechanism transitioned from abrasive wear on bare steel to primarily adhesive wear on the ceramic-lined surface, indicating the effectiveness of the ceramic layer in resisting abrasive media.
Engineering Practice Integration
For engineers considering the application of centrifugal SHS ceramic-lined pipes in industrial service, several practical considerations emerge from this research. The additive formulation must be tailored to the specific service environment; for example, in acidic environments, the addition of zirconia improves chemical stability, while in high-temperature oxidizing environments, the addition of chromium oxide enhances oxidation resistance. The centrifugal process introduces additional equipment requirements and safety considerations, as the high rotational speeds during the exothermic reaction present potential hazards related to pressure buildup and thermal runaway.
Quality control for centrifugal SHS products requires attention to the uniformity of the ceramic layer thickness around the circumference, which is influenced by the alignment of the rotating assembly and the consistency of powder loading. Non-destructive testing methods suitable for this application include eddy current testing for detecting surface and near-surface defects, and acoustic emission testing for monitoring the reaction process in real time.
Study Insights and Outlook
This research represents a mature stage in the development of SHS ceramic composite pipe technology, moving beyond feasibility demonstration to systematic process optimization. The multi-institutional collaboration brings together expertise in powder metallurgy, materials science, and industrial manufacturing, resulting in comprehensive findings that bridge fundamental understanding and practical application. The identification of additive interactions and their effects on both microstructure and performance provides a valuable framework for process development. For the cladding and bimetallic products industry, this work demonstrates that the SHS process can be effectively tailored through materials design to produce ceramic-lined pipes with predictable and controllable properties, opening possibilities for applications in mining, chemical processing, and energy sectors where wear and corrosion resistance are critical requirements.