Microstructural Evolution of AerMet100 Steel Coating on 300M Steel Fabricated by Laser Cladding Technique
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TRODUCTION
ULTRAHIGH-STRENGTH steel (UHSS), with yield strength in excess of 1350 MPa, is often used as load-bearing components such as central spindles, wheel gears, and landing gears due to its high specific strength and good plasticity and toughness.[1] 300M steel is one of the most widely used UHSS because of its low cost, good fracture toughness, and fatigue properties.[2,3] However, usability of 300M steel is constrained by its limited corrosion and stress corrosion cracking resistance in marine environments.[2,4] To address this limitation, high-velocity oxy-fuel (HVOF)-sprayed coatings[5–7] and electrodeposited coatings[7–9] have been used to improve the corrosion resistance of 300M steel. However, electroplating techniques could cause severe environmental pollution and the hydrogen embrittlement of the steel substrate may induce premature, unexpected, and potentially catastrophic failures.[10] In addition, the abrupt change of chemical composition and mechanical properties between coating and
JIAN LIU, JIA LI, XU CHENG, and HUAMING WANG are with National Engineering Laboratory of Additive Manufacturing for Large Metallic Components, School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing, 100191, China. Contact e-mail: [email protected] Manuscript submitted July 28, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
substrate could lead to crack propagation along the interface.[6] AerMet100 steel, originally developed as a replacement to 300M steel in landing gear production for carrier-based aircrafts,[11,12] has shown improvements in terms of resistance to corrosion and hydrogen embrittlement as well as comparably low notch sensitivity and improved fracture toughness.[8,13–15] Thus, AerMet100 steel might be a used as a reliable protective coating that has the potential to improve corrosion resistance while reducing the notch sensitivity of 300M steel. Moreover, compared to traditional coatings, AerMet100 steel has a similar linear expansion coefficient, strength, and plasticity to those of 300M steel, which could be beneficial in reducing the residual stress and cracking tendency during material fabrication and service. Laser cladding, which provides good metallurgical bonds while introducing minimal dilution and reduced distortion of the components, has been widely used in fabricating high-performance coatings and functionally gradient materials.[16–18] And the fine-scaled microstructures, extended solubility, and uniform solute distributions in the cladding layer could enhance the surface properties.[16,19] During laser cladding, the samples are quickly heated to a high temperature followed by immediate cooling, which leads to rapid solidification in the molten pool and complicated solid-state phase transformations in both the cladding layer and the HAZ, introducing complicated microstructural changes that have a huge impact on the mechanical properties of
the material.[20] Lourenc¸o et al.[21] investigated the fatigue properties of laser cladding of AerMet100 powder on th
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