Multi-Objective Optimization of Process Parameters in Pack Siliconizing on AISI D2 Steel
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ORIGINAL PAPER
Multi-Objective Optimization of Process Parameters in Pack Siliconizing on AISI D2 Steel Mojtaba Najafizadeh 1 & Mehran Ghasempour-Mouziraji 2 Received: 19 June 2020 / Accepted: 23 September 2020 # Springer Nature B.V. 2020
Abstract In this study, the formation of the silicon coating on the AISI D2 steel with the pack siliconizing method has been investigated. To do so, different times (2, 3, 4 h) and temperatures (650, 800, 950 °C) for heat treating, and Si (8, 10 and 12 wt%) with the same percentage of NH4Cl and NaF (0.5 + 0.5 wt%), and balances Al2O3 halide activator were used. For characterization of coating, SEM (thickness, EDX), XRD, and micro-hardness were used. Based on the experimental results, by increasing time, temperature, and silicon percentage, thickness of the coating, and micro-hardness and percentage of the silicon with the EDX are increased. To run optimization, a Central Composite design, CCD, was used to find the best combination of parameters. Eventually, the optimal combination of parameters was introduced then verified. According to optimization, 4 h holing time, 11.744 Si percentage and 950 degree Celsius are the best combination of process parameters. Keywords Multi-objective optimization . Pack cementation technique . Mechanical property
1 Introduction The high strength D-type tool steels are widely used in both machining and forming operations because of their high strength, thermal stability and consequently, enough strength at elevated temperatures [1–4]. In these tools, it has been observed that by increasing the hardness, the wear mechanism shifts from adhesive type to delamination type due to the brittleness of the tools; consequently, cracks appear on the tools during loading [5, 6]. Hard coatings are deposited in order to improve some properties on the tool surface such as hardness and wear resistance as well as corrosion protection without leading any conversion in the material ductility.
* Mehran Ghasempour-Mouziraji [email protected] Mojtaba Najafizadeh [email protected] 1
The State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2
School of Design, Management and Production Technologies, University of Aveiro, Estrada do Cercal, 449, Santiago de Riba-Ul, 3720-509 Oliveira de Azeméis, Portugal
Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) are largely used to deposit various coatings in steel tools. It has been reported that Pack method on AISI D2 has effectively improved all the surface properties [7]. Among the employed CVD processes, Halide Activated Pack Cementation (HAPC) is one of the most widely used for the surface properties improvement in many alloys [8, 9]. During this process and at high temperature, the powders make reaction with the halide activators while forming volatile vapors. At high temperatures, chemical gradients act as a driving force for diffusion from the pack to the substrate and then diffusion in the solid state. Among
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