Laser surface alloying of a marine propeller bronze using aluminium powder. Part I: Microstructural analysis and cavitation erosion study

• Published in: Surface & coatings technology Vol. 200; no. 8; pp. 2602 - 2609
• Main Authors: TANG, C. H, CHENG, F. T, MAN, H. C
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier 24.01.2006
• Subjects: Applied sciences; Contact of materials. Friction. Wear; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Other topics in materials science; Physics; Bronze; Cavitation erosion; Mechanical properties; Elasticity; Surface treatments; Copper base alloys; Hardness-to-elasticity ratio; Surface alloying; Hardness; Cavitation; Lasers; Morphology; Wear; Laser surface alloying; Manganese-nickel-aluminium-bronze; Damage morphology; Microstructure; Erosion; Tribology
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2004.12.021

In a previous study laser surface melting (LSM) was employed to improve the cavitation erosion resistance of manganese-nickelaluminium-bronze (MAB. To further enhance the improvement, laser surface alloying (LSA) using fine aluminum powder has been attempted in the present study. By employing appropriate laser processing parameters, a homogeneous alloyed layer of thickness about 1 mm, free of cracks or pores, was obtained. The alloyed layer was composed of a single phase, the bcc beta-phase, with a Knoop microhardness higher than 300 HK. Cavitation erosion test in deionized water of the alloyed layer recorded a 30-fold improvement in the cavitation erosion resistance compared with as-received MAB. The resistance achieved in LSA was more than 3 times that by LSM. The relatively low-cavitation erosion resistance of as-received MAB was attributable to its heterogeneous and multi-phased structure. Surface-alloyed MAB, on the other hand, was characterized by a homogeneous microstructure which was single-phased. Apart from microstructural homogenization, the enhancement in cavitation erosion was also related to the increase in microhardness. Morphological evolution monitored over a period of cavitation erosion test revealed that brittle fracture mode prevailed, with material being chipped away from weak triple junctions and grain boundaries. Such a mode of erosion damage was similar to the case in laser surface-melted MAB, but at a much milder degree, consistent with a higher erosion resistance in the case of LSA. The higher Al content in the LSA samples which resulted in a harder beta phase could be the major reason for the higher resistance. In addition, the relatively larger grains in the Al-alloyed samples resulted in less grain boundaries, which were vulnerable sites for erosion initiation, hence also contributing to higher cavitation erosion resistance compared with the laser-melted samples.